From the collection of the
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San Francisco, California
2007
Bound
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Periodic,! 594816
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This Volume is for
REFERENCE USE ONLY
RADIO BROADCAST
VOLUME XII
NOVEMBER, 1927, to APRIL, 1928
GARDEN CITY NEW YORK
DOUBLEDAY, DORAN & COMPANY, INC.
1928
. -
• : '.
INDEX
("Illustrated Articles. Editorials in Italics)
PAGE
* A AND B Power Units, Testing
xTt (Howard E. Rhodes) 443
*A Power Unit, A New (Ralph Barclay) 350
*Accessories, Some Reliable Radio
Power Supply 293
Action from the Radio Commission 15
Advertising a Service ? Is Direct 16
Advertising? What is the Matter with
Radio 14
*Air Liner, The Eyes of a Future
("Anonymous") 271
*Aircraft Radio? What's the Trouble
With 11
*A. C. "Bandbox," the (John F. Rider) 369
*A. C. Browning-Drake Receiver, An
(Glenn H. Browning) 343
*A. C. Loftin- White Receiver, An (John
F. Rider) 438
*A. C. Push-Pull Amplifier and B Sup-
ply, An (J. E. Coombesp 287
*A. C. Receiver, A Quality Five-Tube
(James Millen) 135
*A. C. Super-Heterodyne, A 45-kc
(Dormand S. Hill) 274
*A. C. Tubes, Electrification Without
(Lewis B. Hagerman) 413
* Amplification— Why? Push-Pull (How-
ard E. Rhodes) 202
*Applications of the Four-Electrode
Tube (Theodore H. Nakken) 109
*Are Programs Going in the Wrong
Direction? (John Wallace) 219
* Aristocrat, The Improved (Arthur H.
Lynch) 46
*Armchair Engineer, The (Keith Hen-
ney) 360
*As the Broadcaster Sees It (Carl
Dreher) 50, 142, 235, 311, 367, 429
*D DEVICE Output, Constant (G.F.
l-> Lampkin) 304
*B Device Shall I Buy? What (Howard
E. Rhodes) 120
""Bandbox," The A. C. (John F. Rider) 369
*Beauty — The Keynote in the New
Radio Receivers . 118
Blue Laws of Radio, The 409
Book Reviews:
Drake's Radio Cyclopedia, by
Harold P. Manly (E. H. F.) 236
Inventions and Patents, Their
Development and Promotion,
by Milton Wright (E. H. F.) 125
Principles of Radio Communi-
cation, by J. H. Morecroft
(Carl Dreher) 394
Story of Radio, The, by Orrin
E. Dunlap (C. D.) 137
Booklets Available, Manufacturers'
62, 153, 244, 320, 392
Broadcasting Conditions, The Com-
mission Improves 278
Broadcasting Conditions, What Readers
Say About 200
Broadcasting Situation ? What Is the
True 346
*Browning-Drake, Electrifying the
(James Millen) 33
*Browning-Drake Receiver, An A. C.
(Glenn H. Browning) 343
PAGE
, Pioneer Picture Broadcast-
ing Station (Edgar H. Felix) . . 362
*C. W. Transmitter, A Short-Wave
Phone and (Kendall Clough) ....... 410
Can the Serious Problem of Radio Patents
Be Settled ? ....................... 198
*"Channel Numbers"? Meters, Kilo-
cycles, or (Ralph H. Langley) ..... 18
*Coils, Matching R. F. (F. J. Fox and
R. F. Shea) ...................... 308
Commission Announces a New Policy,
The ............................. 199
Commission Improves Broadcasting Con-
ditions, The ...................... 278
Commission Retreats, The ............ 408
Commission Suggests Synchronization
Schemes ......................... 199
Commissioner Appointed, New ........ 281
*Concomitants of Good Quality ....... 230
*Constant B-Device Output (G. F.
Lampkin) ........................ 304
*Cooley Picture Receiver, Why I In-
stalled a (Edgar H. Felix) ......... 215
*Cooley "Rayfoto" System Works,
How the (Austin G. Cooley) ........ 23
DESIGNING an R. F. Amplifier
(Sylvan Harris) ............... 376
Direct Advertising a Service ? Is ....... 16
Directory of Manufactured Receivers,
"Radio Broadcast's"
70, 154, 246, 322, 388
*Do You Own a Battery Operated Set?
(Howard E. Rhodes) .............. 30
Does Monopoly Rule the Commission? 346
*DX Listener Finds a Champion, The
(John Wallace) ................... 140
•rpDUCATION, University Offerings
-LL< in Radio (Carl Dreher) ......... 339
*Electrification Without A. C. Tubes
(Lewis B. Hagerman) ............. 413
*Electrifying the Browning-Drake
(James Millen) ................... 33
*Electrifying the " Hi-Q " (F. N. Brock) 436
*Electrifying Your Present Set (Zeh
Bouck) .......................... 416
*Engineer, The Armchair (Keith Hen-
ney ............................. 360
Engineering To-day, Radio ........... 16
*"Equaphase" Circuit, The Freshman
(J. O. Mesa) ..................... 42
*Experimental Screen-Grid Receiver,
An (Charles Thomas) ............. 434
*Eyes of the Future Air Liner, The
("Anonymous") .................. 271
"TT'ACTS About the Fada "Special"
r Receiver (John F. Rider) ........ 128
*Fantasy on Sponsored Programs, A
(John Wallace) ................... 306
First Rayfoto Transmission, The ....... 348
*45 kc. A. C. Super-Heterodyne, A
(Dormand S. Hill) ................ 274
*Four-Electrode Tube, Applications of
the (Theodore H. Nakken) ......... 109
*Four-Tube "Lab" Receiver, The
(Keith Henney) .................. 423
*Four-Tube, Screened-Grid Receiver, A
(McMurdo Silver) ................ 355
Sound
PAGE
Frequency Allocation Outstanding
Achievement of International Confer-
ence ............................. 280
*Freshman "Equa phase" Circuit, The
(J. O. Mesa) ..................... 42
From the Manufacturers ............. 174
46
of Your Radio Receiver,
vJMeasuring the (Keith Henney) . . 123
Growing Political Pressure on the Com-
mission, The ..................... 347
•TJELIUM ATOM, Radio Enlists
11 the (Volney G. Mathison) ...... 195
Here and There ..................... 409
High-Frequency Channels, Limitations
to the Use of ...................... 347
*Hogan, An Interview with J. V. L.
(Edgar H. Felix) .................. 353
*How Radio Developments Have Im-
proved Recording and Reproducing
(Sylvan Harris) ................... 414
*How the Cooley "Rayfoto" System
Works (Austin G. Cooley) ......... 23
*How the "NR-60" Was Engineered
(John F. Rider) .................. 299
How the Radio Beacon Works ......... 108
How tlte Radio Commission Can Set
Radio to Rights ................... 105
*How the "Synchrophase" Seven Was
Developed (John F. Rider) ......... 232
*How to Improve Your Old Receiver
(Edgar H. Felix) .................. 133
"TMPROVED Aristocrat, The (Arthur
1 H. Lynch) ......................
*Improved Shielded Six (John E. Mc-
Clure) ........................... 44
Inside the Radio Industry ............ 281
Interference, Suppressing Radio (A. T.
Lawtpn) ................... 48, 217, 379
""Interview with J. V. L. Hogan, An
(Edgar H. Felix) .................. 353
Is Direct Advertising a Service ? ....... 16
KEY to Recent Radio Articles, A
(E. G. Shalkhauser) .......... 76, 255
Kit Shall I Buy? What 66, 170, 257, 330, 393
*T AB" Receiver, The Four-Tube
-L' (Keith Henney) ............... 423
""Laboratory Information Sheets,
"Radio Broadcast's":
Acoustics .................. 318
A. C. Audio-Frequency Ampli-
fier, An .................. 148
A. C. Tube Data ........... 58
Audio Amplification ......... 316
Audio Amplification, A Prob-
lem in .................... 448
B Power Device Character-
istics ................... 146
B Power Unil Characteristics 448
Characteristic! of Speech .... 446
Circuit Diagram of an A. C.
Audio Amplifier .......... 148
Coil Reactance ............. 58
Comparing the 112, 171, and
210 Type Tuoes .......... 314
cx-312 (uc-112) and cx-371
(ux-171), The ........... 386
594816
25
INDEX— Continued
PAGE
Data on the ux-222 (cx-322) 384
Ear, The 318
Exponential Horn, The 446
Fading 242
Filter Choke Coils 387
Filter Condensers 450
"Gain" 148
Grid Bias 387
How the Plate Circuit Affects
the Grid Circuit 387
Inductive Reactance 58
Loud Speakers 146
Modulated Oscillator, A 316
Obtaining Various Voltages
from a B-Power Unit 60
112, 171, and 219 Tube Curves 314
112-A and 171-A Type Tubes,
The 238
Operating Vacuum Tubes in
Parallel 56
Oscillation Control 150
R. F. vs. A. F. Amplification 448
Regulator Tube, The 386
Resonant Circuits 318
Selectivity and Sensitivity . . . 384
Simple Wavemeter, A 386
Single-Control 150
Solenoid Coil Data 60
Speech 150
Standard and Constant-
Frequency Stations 238
Table for Wavelength-
Frequency Conversion 240
Testing Receivers 316
Three-Tube Roberts Reflex. .. 242
Three-Tube Roberts Reflex,
The 242
Transmission Unit, The 60
Tuning 450
Type 280 and 281 Tubes. The 450
Unit of Capacity, The 56
Wave Traps 240
Wavelength-Frequency Con-
version 240
*Laboratory, "Strays" from the
228, 310, 427
"Langley, Ralph H 225
Limitations to the Use of High-Frequency
Channels 347
"Listeners— Guests or Customers?
(John Wallace) 37
"Listeners' Point of View, The (John
Wallace) 37, 140. 219, 306, 365, 419
Listeners Served by Reallocations,
Rural Radio 279
*Loftin-White Receiver, An A. C.
(John F. Rider) 438
*Loud Speakers 126
*Loud Speakers and Power Equipment
22, 373
*Loud Speakers and Sets, Some New . . 358
"A/TAKE Your Own Radio Picture
1VJ. Receiver (Austin G. Cooley) . . . 114
Manufactured Receivers, "Radio Broad-
cast's Directory of .... 70, 154, 246, 322, 388
Manufacturers' Booklets Available
62, 152, 244, 320, 392
*March of Radio. The
14, 105, 198, 278, 346, 406
*Matching R. F. Coils (F. J. Fox and
R. F. Shea) 308
"Measuring the "Gain" of Your Radio
Receiver (Keith Henney) 123
*Meters, Kilocycles, or "Channel Num-
bers"? (Ralph H. Langley) 18
*Modern Radio Receiver, Refinements
of the (Edgar H. Felix i 26
Monopoly Rule the Radio Commission ?
Does 346
Month in Radio, The 17, 108, 349
*Month's New Phonograph Records,
The 441
'"Motor-Boating," No (H. O. Ward) 433
*XTEW A Power Unit, A (Ralph Bar- 350
1 > clay)
New Commissioner Appointed 281
*New Recordings by Radio Favorites 289
*New "Two-Ten" Power Amplifier, A
(William Morrison) 138
PAGE
News of the Patent Field 16, 108
*No "Motor-Boating" (H. O. Ward) . . 433
*"NR-60" Was Engineered, How the
(John F. Rider) 299
*PlCTAMONIC" Circuit, The R. G.
vJ S. (David Grimes) 39
$100,000 to Improve Broadcasting 107
"Operating Your Rayfoto Picture Re-
ceiver (Austin G. Cooley) 296
*Our Readers Suggest ..."
35, 131, 213, 293, 363, 421
*Output, Constant B-Device (G. F.
Lampkin) 304
*Output Device? Why the (Keith Hen-
ney) 294
* PATENTS:
Can the Serious Problem of
Radio Patents Be Settled? 198
Patent Field, News of the . . . . 16, 108
Prospects for Patent Pooling . . 15
Prospects of a Patent Pool, The 198
*Phonograph Joins the Radio Set, The
- 112, 206
*Phonograph Records, The Month's
New 441
Picture Broadcasting Becomes a Practical
Reality 406
*Picture Broadcasting Station, CJRM,
Pioneer (Edgar H. Felix) 362
*Picture Receiver, Make Your Own
Radio (Austin G. Cooley) 114
*Picture Receiver, Operating Your
Rayfoto (Austin G. Cooley) 296
*Picture Receiver, Why I Installed a
Cooley (Edgar H. Felix) 215
Political Pressure on the Commission,
The Growing 347
Possibilities of Still Picture Broadcasting 406
*Power Devices 127
*Power Equipment, Loud Speakers and 373
*Power Supply Accessories, Some Re-
liable Radio 293
*Po\ver Unit, A New A (Ralph Barclay) 350
*Programs, A Fantasy on Sponsored
(John Wallace) 306
*Programs Going in the Wrong Direc-
tion? Are (John Wallace) 219
*Push-Pull Amplification— Why? (How-
ard E. Rhodes) 202
*Push-Pull Amplifier and B Supply, An
A. C. (J. E. Coombes) 287
* DUALITY Five-Tube A. C. Re-
\,f. ceiver, A (James Millen) 135
*T~). G. S. "Octamonic" Circuit, The
JA. (David Grimes) 39
Radio Beacon Works, How the 108
"Radio Broadcast's" Directory of
Manufactured Receivers
70, 154, 246, 322, 388
"Radio Broadcast's" Laboratory In-
formation Sheets (See Laboratory)
56, 146, 238, 314, 384, 446
Radio Commission, Action from the .... 15
Radio Commission Can Set Radio to
Rights, How the 105
*Radio Education, University Offerings
in (Carl Dreher) 339
Radio Engineering To-day 16
* Radio Enlists the Helium Atom (Vol-
ney G. Mathison) 195
*Radio Favorites, New Recordings by 289
*Radio Folk You Should Know 225, 286, 440
*R. F. Amplifier, Designing an (Sylvan
Harris) 376
*R. F. Coils, Matching (F. J. Fox and
R. F. Shea) 308
Radio Industry, Inside the 281
"Radio Industry" Standards 107
"Radio Interference, Suppressing (A. T.
Lawton) 48, 217, 379
*Radio Picture Receiver, Make Your
Own (Austin G. Cooley) 23
"Radio Receivers for $175 or Less 19
"Radio Receivers Representing a Wide
Price Range 302
PAGE
*Rayfoto Picture Receiver, Operating
Your (Austin G. Cooley) 296
*" Rayfoto" System Works, How the
Cooley (Austin G. Cooley) 23
Rayfolo Transmission, The First 348
*Receivers and Their Chassis, Some
Fine 226
Recent Radio Articles, A Key to (E. G.
Shalkhauser) 76, 255
*Refinements of the Modern Radio Re-
ceiver (Edgar H. Felix) 26
*Roberts, Walter Van B 286
Rural Radio Listeners Served by Real-
locations 279
*QCREENED-GRID Receiver, A
O Four-Tube (McMurdo Silver) . . 35o
*Screened-Grid Tube, The (Keith Hen-
ney) 208
*Screened-Grid Tube, The (The Labora-
tory Staff) 282
*Set Shall I Buy? What (Edgar H.
Felix) 211
"Shielded Six, The Improved (John
E. McClure) 44
Short-Wave Notes 331
"Short-Wave Phone and C. W. Trans-
mitter, A (Kendall Clough) 410
Short-Wave Spectrum, The Shrinking 407
*Some Fine Receivers and Their Chassis 226
"Some New Loud Speakers and Sets 358
"Some Reliable Radio Power-Supply
Accessories 293
South Has Few Stations, Why the 107
Standards, "Radio Industry" 107
""Strays" from the Laboratory 228, 310, 427
"Super-Heterodyne, A 45 kc. A. C.
(Dormand S. HUD 274
"Suppressing Radio Interference (A. T.
Lawton) 48, 217, 379
Synchronization Schemes, The Com-
mission Suggests 199
""Synchrophase" Seven Was De-
veloped, How the (John F. Rider) . . 232
"TECHNICAL Radio Problems for
J- Broadcasters and Others (Carl
Dreher) 311
"Television in Europe (William J. Brit-
tain) 103
"Testing A and B Power Units (Howard
E. Rhodes) 443
Two Stations Cannot Occupy the Same
Ether Space 348
""Two-Ten" Power Amplifier, A New
(William Morrison) 138
"TTNIVERSITY Offerings in Radio
U Education (Carl Dreher) 339
"T 7-ACUUM-TUBE Voltmeter, A
V (The Laboratory Staff) 221
TTT'EAF Transmitters, The New 108
rr "What B Device Shall I Buy?
(Howard E. Rhodes) 120
What Broadcasters Want 107
What Can the Commission Do? 105
"What is a Good Radio? (Keith Hen-
ney) 28
What is the Matter with Radio Advertising 14
"What's the Trouble with Aircraft
Radio? ("Anonymous") 11
What Is the True Broadcasting Situation? 346
What Kit Shall I Buy?
66, 170, 257, 330, 393
What Readers Say About Broadcasting
Conditions 200
"What Set Shall I Buy? (Edgar H.
Felix) 211
What to Tell the Consumer— And Where 107
Who Buys This Year's Radio Sets ? 279
"Why I Installed a Cooley Picture Re-
ceiver (Edgar H. Felix) 215
"Why the Output Device? (Keith Hen-
ney) 294
Why the South Has Few Stations 107
Will the Radio Industry Do It Again ? . 349
INDEX— Continued
AUTHORS
PAGE
Barclay, Ralph 350
Bouck, Zeh 416
Brittain, William J 103
Brock, F. N 436
Browning, Glenn H .... 343
Clough, Kendall . . 410
Cooley, Austin G 23, 114, 296
Coombes, J. E 287
Dreher, Carl
50, 142, 235, 311, 339, 367, 394, 429
Felix, Edgar H.
Fox, F. J
26, 133, 211, 215, 353, 362
308
Grimes, David 39
Hagerman, Lewis B 413
Harris, Sylvan 376, 414
Henney, Keith 28, 123, 208, 294, 360. 423
Hill, Dormand S 274
Lampkin, G. F. . 304
Langley, Ralph H 18
Lawton, A. T 48, 217, 379
Lynch, Arthur H 46
McClure, John E 44
Mathison, Volney G 195
Mesa, J. O 42
Millen, James 33, 135
Morrison, William 138
PAGE
Nakken, Theodore H 109
Rhodes, Howard E . . . . 30, 120, 202, 443
Rider, John F 128, 232, 299, 369, 438
Shalkhauser, E.G.. . . 76, 255
Shea, R. F 308
Silver, McMurdo 355
Smith, Francis Gow 403
Thomas, Charles 434
Wallace, John. . . .37, 140, 219, 306, 365, 419
Ward.H. O 433
PORTRAITS
(*Portraits in "The March of Radio")
*Alexanderson, E. F. W . . 406
*Bellows, Henry A ...
Boult Reber
*Bown, Ralph
*Butman, Carl H . . . .
Buttolph, David
Cason, Bob
Coates, D. R. P
Cooley, Austin G
198
38
346
198
140
... 38
... 362
.114. 215
Damrosch, Walter 289, 420
Dieckmann, Max 104
*Dillon, John F 107
Dole, Frank 307
PAGE
*Fadden, B. J 201
Golden, Ernie . . 207
Goldsmith, Alfred N 346
Hall, Anita DeWitte . . 38
Hall, Bob 306
Hare, Ernest 113
Hogan, J. V. L 353
Jones, Billy 113
Jones, Lester L 440
Langley, Ralph H 225
Lindbergh, Charles A 113
*Marconi, Signora 17
Mengelberg, Willem 289
Morecroft, J. H • 339
Palmer, Lester. . 306
*Pickard, Sam 198
Roberts, Walter Van B 286
Shumsky, Oskar 419
Smith, Francis Gow 402
Sokoloff , Nikolai 289
Theremin, Leon 427
Verbrugghen, Henri 289
Wynn, Eunice 365
Copyright, 1928, by
DOUBLEDAY, DORAN & COMPANY, INC.
K
,
iRefinemerit^in Modern Radio Sets
' • ! ^ ;
A Directory of Manufactured Receivers
How the Cooley Rayifoto Picture Recorder^brks
1 . '. .', •. i \. ' -.
Lets Do AwayWith Meters and Kilocycles
/ ' •;' V 1 ' ' '•
iiMtat's the Matter With Aircraft Radio]/
What is a Good Radio Set? 1
Company
RADIO
TUBES
The Right Tube
in the Right Socket
There are now twenty distinct types of
Cunningham Radio Tubes each expressing
the correct balance in design and specifica-
tion to perform a definite function most
efficiently in your radio. Your dealer will
tell you the correct type your radio is de-
signed to use. Equip throughout with Cun-
ningham Radio Tubes. By so doing you
insure maximum performance in your radio.
Twenty different types —
all in the Orange and Blue carton
E. T. CUNNINGHAM, Inc.
NEW YORK CHICAGO SAN FRANCISCO
RADIO BROADCAST ADVERTISER
ALL
METAL
SHIELDED
TRADE MARK REGISTERED
MAGNIFICENT TONE-SUPER SELECTIVE-POWERFUL DISTANCE GETTER
or Battery Set;
Lhi?k_™.r_^i.7diua^.--s--n-2
rby L
Before 1 bought your"3et I tried out
and heard quite a number of differ-
ent makes nets and I believe I can
truthfully say tliat I never yet have
heard a aet with such wonderful
tone and clearness aa the Miraco. 1
never thought that a Bet could be as
clear and reproduce tones and voices
as the Miraco. Saturday I listened to
a $450.00 set and it can't even coma
near your eet for clearness and vol-
nm*.lhave lore ed some very distant
stations on the Uni tune and although
people won't hardly believe me. the
first week I had KFI Los Angeles OD
two nights in succession on a 30-ft.
temporary inside aerial.— FRANK.
A. OLDENBURG. Milwaukee. Win.
SHARPLY SEPARATES STATIONS
The UniCune brings in stations very
clearly and with a selectivity that is
amazing when you take in consider-
ation the mass of stations on the air
at the name time. I have heard three
and f our station* that wereon almost
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and was able to tune out one after
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ence.-W. L. BItOBACK. San
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EXPERIENCED FAN PRAISES SET
Miraco is the most wonderful radio
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betrody
HAS POWER TO SPARE -
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onderfut
America's bfe, old, reliable Ra-
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Miraco sets "the finest, most
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Unless 30 days' use in your
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Your verdict final. Save or
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ADDRESS
RADIO BROADCAST
NOVEMBER, 1927
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XII, No. 1
Cover Design - ' - From a Design by Harvey Hopkins Dunn
Frontispiece - Proper Radio Equipment on an Airplane 10
What's the Trouble With Aircraft Radio? ».•».» Anonymous 1 1
The March of Radio An Editorial Interpretation 14
What's the Matter With Radio Advertising?
Action from the Federal Radio Commission
Prospects for Patent Pooling
Is Direct Advertising a Service?
Radio Engineering Today
News of the Patent Field
The Month in Radio
Meters, Kilocycles, or "Channel Numbers"? - Ralph H. Langley 18
Radio Receivers for $175 or Less 19
Loud Speakers and Power Equipment - - - 2,2
How the Cooley "Rayfoto" System Works Austin G. Cooley 23
Refinements of the Modern Radio Receiver - - Edgar H. Felix 26
What is a Good Radio? Keith Henney 28
Do You Own a Battery Operated Set? - - Howard E. Rhodes 30
Electrifying the Browning-Drake James Millen 33
Our Readers Suggest. . . . - ' 35
Listeners — Guests or Customers? John Wallace 37
The Listeners' Point of View
The R.G.S. "Octamonic" Circuit - - - - David Crimes 39
The Freshman "Equaphase" Circuit - ••*-*/. O. Mesa 42
The Improved Shielded Six - John E. McClure 44
The Improved Aristocrat Arthur H. Lynch 46
Suppressing Radio Interference A. T. Lawton 48
As the Broadcaster Sees It - - - - CarJ Dreher 50
Putting Freak Broadcasting In Its Place Abstract of Technical Article
Background Noises Auditorium Acoustics
"Radio Broadcast's" Laboratory Data Sheets 56
No. r37 Operating Vacuum Tubes in Parallel No. 141 Obtaining Various Voltages from a
No. 138 The Unit of Capacity B-Power Unit
No. r39 Inductive Reactance No. 143 Solenoid Coil Data
No. 140 Coil Reactance No. 144 The Transmission Unit
No. 141 A. C. Tube Data
Manufacturers' Booklets Available 62
What Kit Shall I Buy? 66
"Radio Broadcast's" Directory of Manufactured Receivers - - - 70
A Key to Recent Radio Articles - - - - E. G. Shal1{hauser 76
AMOT^G OTHER THINGS. . .
"DOR more reasons than one, the New York Radio Show is
1- generally accepted as the event which crystallizes interest
in all things radio. This is written as the show closed and a more
impressive show we have never seen. "Impressive" from the
point of view of the exhibits, certainly, but more impressive be-
cause of the tremendous interest in all things radio demonstrated
by all sorts and conditions of people who thronged Madison
Square Garden. Careful observation of the crowds and their
interest indicated that while the complete sets drew much at-
tention, the home-assembled receivers — built from kits, were
equally interesting. This definite and lively interest in the
home-built sets is especially important in view of the pronounce-
ments of some knowing radio sages who aver that home building
is seriously on the decline.
A CTUAL transmission and reception of "still" pictures by
./V. radio was demonstrated thousands of times during the
week of the show by Austin G. Cooley who set up a complete
Cooley "Rayfoto" transmitter and receiver in a special booth
provided through the courtesy of G. Clayton Irwin, Jr., manager
of the show. The picture converter or transmitter was set up.
connected to a small radio transmitter and through a standard
broadcast receiver, the pictures were received with great
rapidity and success before the very eyes of eager crowds. The
simplicity and speed of the receiver astounded those who saw
the demonstration, and every visitor was eager to know when
he could build the apparatus and how soon pictures would be
sent and where he could get information. Experimental picture
transmissions from various broadcasting stations will be sent
even before you read these words; complete information on
how the system works, how to build and operate it appears
exclusively in this and following issues of RADIO BROADCAST.
And those who wish to receive printed matter describing
details of the system should at once address a letter to the
undersigned who will see that all information is mailed at once.
The impressive success of the Cooley "Rayfoto" demonstration
proves beyond all question that a new era has dawned for the
home experimenter, and to be frank, we are as enthusiastic over
the possibilities opened up as the keenest of experimenters.
A WORD about the authors in this issue: the anonymous
-ti. author of the absorbing leading article is a very well-known
figure in aviation and radio. Ralph Langley, who explains his
scheme for numbering broadcast channels, is executive assistant
to the president, Crosley Radio Corporation. He was until
recently in charge of receiver design for the General Electric
Company. Howard E. Rhodes who describes what's new in
A-power units is one of the able technical staff of this magazine.
James Millen, who is a consulting engineer and a native of
Long Island, will shortly desert these parts and settle in Boston.
TN THE next issue we shall have an important article by T. H.
1 Nakken on the shielded grid tube indicating what such a tube
means to American radio .There will be valuable constructional
articles and a description of the technical features of well known
manufactured receivers — information never published before.
Austin Cooley will tell how to build a Cooley "Rayfoto"
receiver — facts for which many experimenters are waiting.
— WILLIS KINGSLEY WING.
Doubleday, Page & Co.
MAGAZINES
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WORLD'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
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LE PETIT JOURNAL
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Copyright, 1927, in the United States, >fcu>/oundldnd, Great Britain, Canada, and other countries by Doubleday, Page & Company.
TERMS: $4.00 a year; single copies 35 cents.
8
All rights reserved.
RADIO BROADCAST ADVERTISER
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A battery eliminator isn't one of those things you can just look at and say it's good or bad.
Nor can you determine its qualities with a few moments' trial. How then can you be as-
sured of a reliable unit of lasting satisfaction? Over 700,000 satisfied users of light socket
power units wilt tell you to be sure it is Raytheon approved and equipped with the
Raytheon long life rectifying tube.
You can identify a Raytheon type power unit by the green Seal of Approval on the front. Only
unitsthat have been tested and approved can usethissymbolorthe Raytheon gaseous type tube.
Our Technical Service Department will be glad to answer questions or send the latest Radio
Power Bulletin covering in detail any subject on light socket power in which you may be
interested.
RAYTHEON MANUFACTURING CO., Cambridge, Mass.
Type BH
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TypeBA
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. THE HEART OF RELIABLE RADIO POWER
ONE AEROPLANE ON WHICH T 'ROPER <HADIO EQUIPMENT IS USED
fcf HE Dornier-Napier Whale of Captain F. T. Courtney, originally designed for a flight from London to the United States
•*• and return, has a SOO-tvatt Marconi i.c.w. transmitter, using a 200-foot trailing antenna, an eight-tube r.f. amplifier
ahead of a four-tube super-heterodyne, usable on commercial wavelengths, and a Marconi Bellini-Tosi direction finding
antenna. The all-metal construction of the ship introduced special receiving problems which had to be solved. Note in the
lower illustration part of the receiving antenna rising over the motor nascelle. The top photograph shows the radio controls.
A wind-driven generator supplies power for the transmitter and charges special storage batteries. In case of a forced landing,
a 40-foot mast can be erected, and the batteries are made to supply current to the motor generator which runs the main set.
Few airships have been so completely equipped.
NOVEMBER, 1927
RADIO BROADCAST
11
°Whats the TROUBLE with
Jtmiuft RADIO?
rHO is to blame for the fact that
radio communication is not in
general use in flying? Isittheradio
engineer? Or can it be shown that the fault
lies with the airman? Why did not Lind-
bergh and Chamberlin use radio? Who
knows in what different manner the fatal
flight of Nungesser and Coli might have
ended had there been radio equipment
aboard the White Bird? What of the Golden
Eagle and the Miss Doran? Had these
planes been equipped with radio would
they have been lost? Probably not. There
is reason to believe that even though forced
down, so well would they have been fol-
lowed by radio watchers on land that they
might have been quickly found.
Commander Byrd made good use of
radio at times in the flight that ended just
short of Paris. But did he, schooled in the
Navy and certainly aware of the possibili-
ties for its use, make the most of his radio?
One wonders. Why, when approaching the
French coast, was he unable to learn the
kind of weather awaiting him at Paris?
Hegenberger and Maitland were
able to use their radio equipment but
a small part of the time on their flight
to Hawaii. Receiver trouble devel-
oped soon after leaving the Pacific
Coast and it was not until they were
within eight hundred miles of their
goal that they were able to pick up
signals again. The preparations for
their flight were said to have been
most thorough. The radio must
surely have been thoroughly tested
before the take-off, yet it failed
them in time of need. They had
planned to fly the course laid down by the
radio beacon. To do this it was necessary
to make continuous use of the radio re-
ceiver. Fortunately, when it failed, they
were prepared to navigate by better-known
means. Such was the thoroughness of Army
Air Corps methods of preparation.
However, there has been no excuse for
the lack of radio equipment of some sort
on all of the trans-oceanic flights. The dis-
turbance created by the ignition system
which is almost always offered as an argu-
ment against it, is not an absolute bar to
the use of radio. Ignition disturbance has
no effect on the radio transmitter. Even
a receiver could have been used to some
extent in the presence of ignition noise.
This is particularly true for a plane in which
the cabin is located some little distance
from the engine. Furthermore, the receiver
could have been successfully used while
passing over vessels at sea. The ship's trans-
mitter under the circumstances of such
short range would have pushed signals
A 7v[O7^TMOLJS" conceals the identity of an individual who is
cXA excellently qualified to write on the closely related problems of
the airplane and radio. All we can say is that he is an expert who is
well \nown in both fields. The author \nows aviation — not from a
swivel-chair vantage point, but from long flying experience and he
Ifrtows radio from both the practical and distinctly technical angles.
Too few radio men \now anything about the problems that the aviator
has to meet, and too few of the airplane jol\ know radio. Certainly
there is a middle ground on which both may meet and this article is
the first of several which will discuss this interesting jield. The increas-
ing fatality list of those attempting stupid and pointless trans-oceanic
jiights has demonstrated to almost the whole world that long-distance
/lying must be made safer and surer by every means at our command.
And through radio will come much of this essential surety.
— THE EDITOR.
through the ignition disturbance at least
sufficiently to have given information on
weather and course.
RADIO MUST BE USED ON LONG FLIGHTS
IT WOULD be very interesting to know
the reasoning which led to a decision to
leave radio out of the plans for some of
these flights. Undoubtedly the real reasons
will not be given to the public. One strongly
suspects that the lack of ability to handle
radio on the part of the crew aboard each
of these planes had a great deal to do with
the matter. Of course, Lindbergh flew alone
and could have made little use of any kind
of radio equipment for that reason. Cham-
berlin knew little or nothing about radio,
and it is likely that Levine, his passenger,
knew less, inexperienced as he was in such
matters. There is no telling how much Coli
or Nungesser or Captain Hamilton, the
British pilot, knew about the use of radio
equipment.
None of these flights should have been
undertaken without radio equipment,
and a competent radio operator to
handle it. On some of the flights one
of the pilots acted as radio operator.
This did not prove entirely satisfac-
tory. Hegenberger, who flew with
Maitland to Hawaii was fairly fa-
miliar with radio apparatus, but when
his receivers (there were two aboard)
became inoperative, he was unable to
locate the source of trouble. It is
doubtful if his knowledge of radio
was sufficient to have enabled him
to diagnose trouble as a trained radio
operator could have done.
12
RADIO BROADCAST
NOVEMBER, 1927
The desire to carry passengers on these
flights has prevented a good radio operator
being present. Miss Doran in the Pacific
flight, and the Princess Lowenstein-
Waltheim in the Atlantic flight of Captain
Hamilton, and Philip Payne in Old Glory
should have been replaced with radio
operators, and, at least, radio receiving
equipment. The fact that Brock and Schlee
flew successfully to England without radio
is no proof that radio was not needed.
Redfern carried neither companion nor
radio. He should not have been permitted
to leave without both. And his companion
should have been a good radio man.
Thus it is seen that some of these fliers
were unmindful of the value of radio, and
that others were unable to make the most
of equipment which they had chosen to
use.
Who is to blame that the value of radio
has been so vastly underestimated in these
flights? The question
is important. Upon the
correctness of the an-
swer depends in a great
measure the solution of
one of the problems which
at present confronts avia-
tion.
WHY AVIATORS DON'T LIKE
RADIO
"THERE have been
1 many discussions on
this subject between fly-
ing folk and men interested
in radio. These discussions
have usually been of a
character to which the
terms " heated," and some-
times "overheated," could
justly be applied. Gener-
ally, the debates ended
only in disagreement. The
pilot and the engineer have
not been brought to the
same way of thinking. Not
only have they disagreed
as to who is to blame for
the neglect of radio, but the pilot has stren-
uously objected times without number to
the use of radio on his plane.
It is, of course, true that the military
and naval flier has on occasion done much
with the equipment designed for him by
the radio engineer. Very often it was only
because that flier was a member of an
organization, in which obedience to an
order is almost instinctive, that he made
real use of his equipment. Often, it is true,
he was pleased with the results of his effort
and so converts to the cause of radio have
gradually been made. They are, however,
all too few. As for the commercial fliers,
apparently little belief in the need for radio
exists. One never hears of radio being used
on their planes. Not even the Air Mail com-
panies, or our own Post Office department,
have seen fit to equip mail planes with even
a receiver with which to receive information
on the weather. The Air Mail for a time
carried out experiments with radio but no
practical or extensive use has yet been
made of it.
What has the radio engineer to say for
himself in the face of this obvious disdain
on the part of the flier for radio? Were he
a psychologist it might occur to him that
the feeling of the pilots about the matter
might be based on something inherent
in the flying profession, or in the flier's
training. Could he put himself in the place
of the average war-trained flier he would
remember that in the exciting days of the
war the urge to fly was the strongest thing
in his life. It was for that reason that he
joined the Air Service instead of going into
some other branch of the Service. That was
why he worked as he never had worked
before during preliminary training days at
ground school. His eyes were always lifted
to the men in the air. Everything but flying
was subordinated. Nothing appealed to him
either at ground school or at the flying
AT AN EUROPEAN AIRPORT
Elaborate means of radio communication are required by law on passenger air routes
in some European countries. The two radio towers at the Tempelhof, Berlin, airport,
are clearly discernable in this aerial picture
school to which he was later ordered, as
strongly as the airplane and flying. Motors,
navigation, gunnery, photography, radio —
all had to be learned; but he learned them,
for if they were not learned he would not
be taught to fly. But flying was the thing—
devil take the rest. Whom did he worship
the most, his gunnery instructor or his
radio instructor, or any of the other ground
instructors? None of these. He worshipped
the man who taught him how to fly. Usually
his flying instructor was the biggest man
on his horizon. His radio instructor was
usually a non-flier, "Keewee" being the
term contemptuously applied to any ground
officer of the Air Service. Usually this man
made no impression, or a poor one at the
most. He often stood between the cadet
and his flying goal. For all who would fly
must, in addition to many other things,
learn to send and receive radio signals. If
he could not pass the speed test he could
not fly. That was the regulation, and many
a good man was " shot down " by the elusive
da-dit-da before he ever had a chance to
learn to fly, and was accordingly sent away
from flying school. At the advanced flying
school came practice with actual transmit-
ting and receiving of signals while in the air.
This was usually even more boring than
the practice in the code room. Generally,
the radio failed to function. Anyhow, who
wanted to sit in the rear cockpit of a ship
which was being flown by someone else
and fiddle with knobs and dials and try to
pick up the faint signals bravely endeavor-
ing to penetrate the noise and roar of the
motor and the disturbance created by the
ignition system?
Thus was built up all through the fliers'
training, a genuine dislike for radio. As so
many of the present fliers were war-trained,
it is little to be wondered at that radio still
has no appeal for them, and that the aver-
age flier has but little faith in it. A man was
generally judged by his
ability to handle his
"ship." If he was clever
with radio, providing he
was able to fly, he was
forgiven by his fellows.
Experienced fliers are
among the most conserv-
ative of men, strange as
that may seem. Little do
they relish change or inno-
vation. They have been
flying through all kinds
of weather and over all
kinds of country without
the use of radio. Why
change now? Radio is just
another thing to worry
about. It probably won't
work anyway, and the
receivers in the helmet
hurt your ears and you
can't hear your motor.
So poor old radio goes for
consolation to the amateur
who has been such a good
friend all these years. All
of which the radio engi-
neer has probably not realized.
TECHNICAL PROBLEMS IN THE PLANE
IN ADDITION to the obstacles formed
* by the fliers' attitude, there have been
many technical difficulties to overcome.
Chief of these is the interference caused by
the ignition system of the airplane engine.
This has been a most serious obstacle and
has not been completely overcome. It is
true that, by completely shielding the
ignition system, the troublesome noise can
be reduced to a point where very satisfac-
tory reception in an airplane is attained, but
such shielding is difficult to install and even
more difficult to maintain.
How is a motor shielded to reduce this
interference? How does the ignition system
of a motor produce interfering noises in a
radio receiver?
The ignition system consists of a highl-
and low-tension side. The low-tension side
consists of everything from the switches to
NOVEMBER, 1927
WHAT'S THE TROUBLE WITH AIRCRAFT RADIO?
13
the low-voltage side of the magneto in mag-
neto ignition; and everything from the bat-
tery, including switches, generator, meters,
voltage regulator, and distributors in the
battery type of ignition. In the high-tension
side we have everything from the high-
tension side of the magneto in the first type
of ignition, and from the distributors in the
second type, down to the spark plugs. In
these systems every make and break con-
tact, as in voltage-regulator relay or dis-
tributor, produces a disturbance each time
the circuit is opened or closed, which should
be regular and very frequent, otherwise
the pilot has something much more serious
to worry about than the QRM from his
ignition. The spark plug has not been men-
tioned in detail yet. Usually there are two of
these little short-wave transmitters in each
cylinder of the motor. The average air-
plane engine runs at speeds of from 1400
to 1800 revolutions per minute. This means
that in an eight-cylinder, four-stroke-cycle
engine, equipped with but one spark plug
per cylinder, there will be at 1500 r.p.m.,
six thousand sparks per minute, or one
hundred sparks per second. This produces
a noise in a radio receiver which resembles
the noise produced by a stream of shot on
a loose tin roof. Oscillograms of this QRM
indicate that part of the noise is due to
induction, just as the "click" heard in
a receiver when an electric light switch
nearby is opened or closed, is caused by the
change in current. The rest of the noise is
produced by the oscillating spark in the
gap in the spark plug itself. This is a true
electro-magnetic disturbance of a definite
wavelength. Apparently, then, it should be
easy to reduce this interference by means of
a short-wave trap; and so it should, but due
to the difference in the constants of these
small oscillating systems, the use of wave
traps has not proved very satisfactory. Up
to the present time the most satisfactory
method of freeing the receiver of this an-
noying disturbance is by shielding the
whole ignition system.
Completely shielding the ignition system
requires that every wire and electric device
about the whole plane which carries current
be covered with an electric shield. This is
usually a braided copper sleeve, slipped
over the wire, or a metal container for such
devices as regulators, distributors, and
switches. This shield must be connected to
the ground of the plane. The ground of an
airplane consists of all the metallic parts,
such as the motor, brace wires, cables
and fittings. If you have a few inches of
frayed shielding it will cause all the noise to
come right back to the receiver. Shielding
produces a hazard, the danger of which
may be readily realized. If there is faulty
insulation anywhere in the system, the
vital ignition current will jump through to
the ground and out goes part or all of the
ignition, depending upon where the break
occurs, and, it is needless to say, down
comes the plane, to make as safe a landing
as the pilot can. It would appear that the
solution of this problem is to use nothing
but the best of insulation. This is more diffi-
cult than it sounds. When a high-tension
lead is shielded a corona discharge takes
place through the insulation to the
grounded shield. The corona produces a
chemical change in insulation and it no
longer insulates, the engine ceases to
"percolate," and the aviator to "aviate."
Now, the pilot knows all this and his
feeling for radio has increased in warmth,
but not in a direction the radio engineer
would like to see. The old feud still exists.
The pilot says the engineer loads his plane
with hazardous equipment, and the en-
gineer says the pilot is too fussy about what
happens to him.
THE FUTURE — WORK FOR ALL
AND so it stands, until the necessity
for radio communication between the
air and the ground is made apparent to all
concerned with flying. That this necessity
exists there is no doubt in the minds of
many besides the radio engineer, but now
the demand for radio is insufficient to in-
duce very much research on these problems.
Such problems can be and are, of course,
being worked on in laboratpries. However,
there is a definite limit to what can be done
in a laboratory on the ground. The condi-
tions existing in a plane — the vibration,
the noise of wind and motor and ignition,
cannot be adequately reproduced in a
laboratory; nor can engineers conceive of
the conditions except by repeatedly ex-
periencing them in test flights. What I am
driving at is this. There should be a labora-
tory in which the ground and air work is
connected and closely related. The engineer
should be placed in a position not only to
see the problem as the flier sees it, but both
flier and engineer should be encouraged to
work together. Confidence in the ability
and work of the engineer will then come to
the flier. Better radio sets will be built,
and let us hope that they will be built as a
part of the plane and not tacked on — an
afterthought. Airplane designers will make
provisions for these sets and the power re-
quired to operate them. Then, and then
only, will pilots want radio, and make good
use of what they get.
Before passenger carrying air lines are
permitted to operate either in this country
or on trans-oceanic flights, this matter of
radio should be included in the regulations
covering the safety and inspection of the
planes. The Department of Commerce
should make regulations to fit the needs of
the moment. Because commercial aviation
is in its growing stage, the regulations
should be fairly elastic. But before passen-
gers are permitted to risk their lives, regula-
tions regarding suitable radio equipment
and personnel to operate it should be laid
down. These should cover all long flights,
whether over water or land. By long flights
is meant anything over 500 miles.
The radio beacon has had but a very
short test outside of the Air Corps ex-
perimental tests. But it is apparent even
on such short trial that regular flights over
long distances of water should not be
thought of without contemplating the use
of such a beacon. For regular passenger
routes over land, the beacon should be de-
pended upon at least for night flying. How-
ever, the story of this beacon and its possi-
bilities is too long to include here.
As in so many other things, practice and
test are essential to development, and this
is no less true of radio on aircraft. The more
use made of it the more experience gained.
Radio has a very definite and important
place in aviation, and it is only to be re-
gretted that use has not been made of it on
all transatlantic and transpacific flights.
It is likely that the unsuccessful flights
would not have had so tragic an ending,
had radio played the part that it must come
to play in the future of aviation.
WHEN RADIO WAS NO MORE THAN A DREAM
King Edward VII receives a lesson in aeronautics at the hands of Wilbur Wright. Planes of ten years
hence, equipped with powerful radio transmitters and receivers, will probably be as much in advance
of present day design as are the planes of to-day as compared to this fragile looking craft of Wright's
NFVVS AND INI1.HPKKTATIQN OF" ('.IIUUKNT UAhlQ KVKIM I S
What is the Matter With Radio Advertising?
FROM time to time, trade associa-
tions and better business bureaus
formulate codes of ethics for the
guidance of writers of radio advertisements.
These codes aim to curb exaggerated claims
as to long distance reception, quality of
tone and other excesses so freely used in
radio announcements.
The beautifully worded hyperboles, char-
acterizing modern advertising, have re-
ceived such spirited attacks recently, that
we may look forward to saner and more
informative advertising copy. So great is
public interest that a book on this subject,
Your Money's Worth, is threatening to
become a best seller. Radio advertising
receives its share of scathing criticism from
these authors who leave no one unscathed.
Imagination — at least — is lacking when
an entire industry depends upon a few
standardized general appeals to sell its
products to the public. If the advertising is
to be believed, all receiving sets possess
unbelievable selectivity, marvelous sensi-
tiveness and magnificent tone quality, re-
gardless of pjice. Rarely does any enlighten-
ing information appear in a radio advertise-
ment by which a prospective purchaser may
judge the superiority of one receiver over
another. Magical phrases are concocted,
playing upon the ignorance of the non-
technical, to suggest fancied engineering
superiority. The uninitiate must be
guided by such medicine-man hokum
as "utilizing the new intra-paralytic
principle of interference submer-
gence," "delightful tone quality ob-
tained with the mastertonic sliding
trombone transformers," or "securing
magical selectivity by the matched
prismatic quartz inductances."
Aside from such senseless and
meaningless technical appeals, most
radio advertising confines itself to
generalized boasts. The same charge
may be made not only against the
advertising of radio sets, but that of
automobiles, iceless refrigerators, and
any mechanical or electrical product.
The readers of RADIO BROADCAST
frequently demand that some com-
parative technical tests be made to
form a basis of judging the relative
qualities of sets.
We have given considerable
thought to this problem and we
would unhesitatingly publish com-
parative information, could we dis-
cover a method of making compara-
tive tests which would not involve
the human element and which would
be a real test of merit, taking into
consideration all of the factors which con-
tribute to the desirability of a radio re-
ceiver.
Take, for example, the factor of gain in
the radio-frequency amplifier. We may im-
press a standard modulated signal from an
oscillator upon a receiver and measure the
resultant fluctuations in plate current of
the detector circuit, thus giving an evalua-
tion in the over-all gain of the radio-fre-
quency amplifier. We may also obtain a
selectivity curve for each receiver which
gives a fair index to that quality. Further-
more, given an adjustable audio frequency
oscillator, with which to modulate the in-
coming test signal, we can determine with
a fair degree of accuracy the tonal range
and characteristics of the audio frequency
amplifier. These three tests would give an
index to the three major qualities of a re-
ceiving set, namely its sensitiveness, selec-
tivity and fidelity.
Unfortunately, carrying out such tests is
far from simple. Most receivers have a gain
control in the radio-frequency amplifier
system which greatly complicates labora-
tory tests as a means of comparing receiving
sets. Testing a five-tube receiver, the gain
might well be adjusted as high as possible,
so that it would show maximum amplifica-
tion per stage. However, when so adjusted,
it is likelv to show more than normal dis-
>
SENATORE MARCONI TESTING BEAM TRANSMISSION
The inter-continental beam transmitters of the Marconi Com-
pany, now in operation, resulted from a long series of tests. 1 his
illustration shows Senatore Marconi testing a short-wave trans-
mitter from a boat on a lake at Livorno, Italy, in 1916
tortion in its audio-frequency amplifier.
On the other hand, more conservative ad-
justment of the radio frequency gain would
handicap its sensitivity rating, although it
might improve its showing with respect to
tone quality. Five engineers could test a
number of receivers and secure entirely
different results.
If a sufficient number of test conditions
are fixed so that the element of adjustment
would be minimized, some receiving sets
would be unduly handicapped by the test
conditions in one respect or another. Con-
sequently, laboratory comparisons, with
the test methods we now have available,
do not, for the present at least, seem to
offer a means of supplanting generalities in
radio advertising. But we may look forward
to developments in this direction, as our
experience with laboratory measurements
of sets increases.
Another possible method of making ad-
vertising copy more informative is to give
a few outstanding facts regarding a re-
ceiver, such as number of tubes, number of
controls, and other specifications. But the
number of tubes in a receiver is hardly a
guide to its efficiency. There are ten-tube
receivers which give no better results than
other six-tube sets. The writer, for instance,
has a four-tube receiving set with a 210
tube in the output, which he would confi-
dently enter in any contest for sensi-
tiveness, selectivity and tone quality.
But, as a commercial product, it is
practically useless. It takes an ex-
pert to tune the set and the filters,
chokes and by-pass condensers, which
are a part of it, would not fit into two
set cabinets of normal dimensions.
So the listing of specifications is
hardly a panacea for indefiniteness
in radio advertising.
What remains to assist the honest
advertiser in preparing truly inform-
ative copy? If we rule out bunk,
generalities and specifications, of
what may the set manufacturer speak
without being frowned upon? Only
three general points suggest them-
selves— outward appearance, price,
and reputation, the same factors
which the automobile industry has
found successful as selling appeals.
Another possibility is to consider
some one, simple, technical detail
— the thickness of shielding, the
strength and rigidity of the chassis,
or the accuracy with which tuning
circuits are matched — as an indica-
tion of the skill and care displayed
throughout the whole receiver. Such
NOVEMBER,
MORE ABOUT PATENT CONTROVERSY
15
a pojfcy has advantages, being informative,
specific, interesting, and, above all, based
on facts instead of on generalities.
Prestige and reputation are the product
of years of successful manufacture, and,
consequently, production figures and value
of sets sold by a manufacturer are a founda-
tion of fact by which an old established
manufacturer may distinguish himself from
others.
A method, which has been successful in
other fields, is to "sell" the engineer who
designs the product. Certain companies
have engineering and research staffs of
acknowledged competence and reputation,
whose designs are worthy of great public
confidence.
A thorough and detailed study of the
radio receiver and those who build it, on
the part of the advertising copy writer, is
the best preparation for writing advertising
which features facts rather than fancy.
Action from the Radio Commission
THE Federal Radio Commission has
begun suit against station KWKH,
which it charges with the misdeed of
using three times the power permitted by
its license, for forty successive days. As a
result, KWKH is liable to fines aggregating
$20,000 at the rate of $500 a violation.
If the Commission has a good case and wins
out in the courts, it will certainly gain wide
respect. The numerous violations of the
Commission's regulation as to maintenance
of assigned frequencies are likewise subject
to fines of five hundred dollars a day.
Certain stations frequently wander as much
as ten kilocycles from their channels. The
former WSOM, for example, was found at
different times, within eight days, 24.8,
23.9, 12.5 and 1 6. i kc. from its assigned
channel.
The Commission, in a public statement,
threatened to eliminate about twenty-five
of the most flagrant wavelength wobblers
but, as usual, grew softhearted in the end
and gave them additional grace. Hetero-
dyning is far too widespread to make listen-
ing to any but relatively nearby stations
any very great pleasure.
The Commission's claim, however, that
practically all heterodyning is due to fre-
quency wobbling is not entirely founded on
fact. There are altogether too many assign-
ments of stations to the same frequency
whose carrier waves are bound to create
interference. The clearest broadcasting
channels as a matter of fact, are at this
time the higher frequencies between 1250
and i 500 kc. On these frequencies, we find
mostly low-powered stations which do not
interfere with each other.
The numerous hearings held in Washing-
ton, upon demand of some of the 'stations
now assigned to these superior channels,
are based on the fallacious superstition that
the lower frequencies are the most desirable.
At one time, when the lower frequencies
were reserved for the better stations, while
as many as twenty and thirty low- and
medium-powered stations were huddled on
the lower end of the broadcast band, the
ambition to leave the higher frequencies
was justified. Although conditions have
changed, prejudice against the higher fre-
quencies persists.
Mr. May, seeking a lower frequency
for his advertising station, KMA, for exam-
ple, testified before the Commission that
it was a well known fact among radio en-
gineers that the channels below 350 meters
were "practically no good for broadcasting
purposes," although, as an expert brought
out, KDKA, KOA, WBBM, WOK, and numerous
other stations, occupying these allegedly
unsatisfactory frequencies, have built up
nationwide audiences.
The claim that stations do not "get out"
on the very high frequencies is made be-
cause the public is not accustomed to look-
ing for its programs on these channels.
There are too few worthwhile stations
using them. Why not assign a few really
good stations to the higher frequencies, so
as to distribute the public's attention
throughout the broadcast band?
Prospects for Patent Pooling
THE Radio Manufacturers' Associa-
tion is looking into the matter of
patent pooling and seeking to in-
augurate a system of cross-licensing in the
same manner that the automobile industry
accomplished this through the National
Automobile Chamber of Commerce. There
is one great difference, however, in the
radio situation and that lies in the fact that
a single group has already concentrated
most of the patents in its own hands and
consequently no one has much to offer it
for bargaining purposes.
We learn of the formation of a Radio
Protective Association in Chicago with the
object of battling against "radio monop-
oly" which, say the sponsors for the new
organization, "will be taken to Congress,
to the Department of Justice and to the
Courts."
No matter how much outsiders may pro-
test, there is no question about the fact
that the Radio Corporation of America
has in its hands most of the essential pa-
tents to the 'manufacture of the radio
receiver and it is not at the mercy of any
outside group. A patent is an entirely legal
monopoly created by legislation in accord-
ance with provisions in the Constitution
of the United States. Furthermore, the
Radio Corporation is extending licenses to
competing companies on what appears to
be a fair basis. A rather large minimum
royalty guarantee is required of the set
TESTING "BEAM" TRANSMISSION IN 1916
Senatore Marconi's principal assistant in the development of the short- England with Canada, India, Australia and South America, and the
wave "beam" is C. S. Franklin who is here shown on the lake at Livorno, New York-London link will shortly be opened. C. S. Franklin, Senatore
Italy, testing a short-wave receiver with transmissions from the parabolic Marconi's chief research engineer, famed for his work in developing the
reflector shown in the accompanying photograph. (Right) The "beam" "beam" method is shown here operating the beam transmitter with its.
system of short-wave communication has already satisfactorily linked parabolic reflector from the shore of the lake at Livorno
16
RADIO BROADCAST
NOVEMBER, 1927
maker; said to be $100,000 a year, which
effectively throttles the small producer.
Under the patent law, a patent holder has
full rights to deny the issuance of licenses
to anyone he chooses and, therefore, unless
the legal attitude of the patent law is
completely reversed, the R.C.A. is entirely
within its rights.
The object of the patent law is to assure
that inventors are encouraged and properly
rewarded. Times have changed and inven-
tion is much less a product of individual
genius than it is the marshalling of many
minds, research facilities and laboratory
experience. The reward, instead of going
to individual inventors and their backers,
now goes to large corporations which make
it possible for the complex invention of this
day to be made.
The major purpose of the patent is thus
fulfilled, both under modern conditions
and under those which obtained in
the past. We may add a new inter-
pretation in that the patent mo-
nopoly shall not be used in restraint
of competition and ' compel patent
holders to extend licenses to all those
willing to pay just license fees. This
plan is followed in Canada. But such
a course in this country would be a
new situation, a reversal of prece-
dents. It would require new legisla-
tion. A possible and, indeed, probable
solution of the present radio situation
is that the Radio Corporation will
extend licenses to smaller concerns on
a smaller minimum guarantee, but
upon a higher percentage of royalties
than it extends to those guaranteeing
$100,000 a year.
The radio industry is suffering from
the existence of too many incompe-
tent small manufacturers which are
bound, in time, to be eliminated by
natural economic processes. Hasten-
ing their passing by patent pressure
is a painful but effective method
which, however, reacts unfavorably
against those exerting it. But, what-
ever the considerations animating
the policy, the legality of the R. C. A.'s
present patent course does not appear to
be open to question.
Is Direct Advertising a Service?
A NUMBER of the direct advertising
stations have appeared before the
Commission, claiming great losses
of audience and service range because of
their high frequency assignments. Mr.
May, speaking for KMA, recently spent
three and a half hours on the stand, a
record for a single witness before the Com-
mission to date, to prove himself the most
popular announcer in the United States
and his station the greatest service to hu-
manity of any station in the corn belt.
450,000 people wrote him during the first
seven months of the year, a larger number
than practically any but one or two key
chain stations can claim.
On the other hand, every questionnaire,
not specially circulated by the stations
themselves or by farm papers, indicate the
wholehearted public condemnation of di-
rect advertising by radio. RADIO BROAD-
CAST'S questionnaire, in which 10,886 ex-
pressions of approval and disapproval were
made, found KFNF the most unpopular
broadcasting station in the country, 18.8
per cent, of the audience demanding its
removal. Considering the fact that those
who answered this questionnaire were dis-
tributed all over the United States, this
seems to represent about 100 per cent, of
the listeners within the annoyance range of
this station. WJAZ won the disapproval of
1 5 per cent, of the listeners, most of this
vote being a spite vote because WJAZ upset
the Radio Act of 1912, rather than because
of present day program unpopularity; while
KMA came out third with condemnation
from 13 per cent, of those answering.
SIGNORA MARCONI
The illustration shows the wife of the noted Italian with the
radio receiver fitted up for her use in their palace in Rome.
Signora Marconi was formerly the Countess Maria Cristina
Bezzi Scali
However, 450,000 people do not write
a station for nothing. There is no question
but that there is a field for the local broad-
casting station in the serviceof the small local
merchant. The public, however, resents be-
ing sold harness, glue, tires, and laundry ser-
vice in the guise of entertainment. The mail
order buyer in the rural district is about the
only group which responds. Evidently, in
spite of the harsh dislike which we have of
the direct advertising stations, we must con-
fess that they have an audience and, as such,
deserve consideration, but only in propor-
tion to the importance of that audience.
Radio Engineering To-day
ALPH H. LANGLEY of the Crosley
Company writes us at some length
in comment on D. A. Johnson's
criticism of radio engineers, which we
headed, some months ago, "There Are no
Radio Engineers." Mr. Langley points out
R
the excellent progress made in building up
technical knowledge through the work of
the Institute of Radio Engineers and de-
scribes what is being done in the way of
standardizing symbols and terms and
measurements. Mr. Langley says:
No branch of engineering can become an exact
science, until its methods of measurement have
been developed and standardized. But the pro-
gress which radio science has made in this
respect during the past three years is remark-
able and gratifying. It is now possible to pre-
dict with reasonable accuracy the field strength
which will be delivered at any receiving point
by any transmitter. The characteristics of the
transmitted wave are accurately measurable.
The field strength necessary to produce a
given output voltage on any receiver can be
determined from the measured characteristics
of the receiver and of the antenna. The ability
of the receiver to exclude undesired signals
and its acoustic performance, as well as that of
the loud speaker, are. also subject to pre-
cise measurement. Transmitters have been
metered and their characteristics known
for many years. Thus every part of the
broadcast mechanism has yielded to pre-
cise determination.
As a mushroom and a boom in-
dustry, radio was certainly unscien-
tific. But progress has been made.
An inspection of the twenty leading
manufacturers' plants would quickly
convince Mr. Johnson that the design
and manufacture of the radio product
is a precision task of the highest order,
performed to the most rigid standards.
News of the Patent Field
A RECENT licensee under Radio Cor-
poration patents, and probably the
most important from the standpoint of
royalties to be paid, is the Atwater Kent
Manufacturing Company. This brings the
total number of licensees to twenty-three,
including some of the principal manu-
facturers of the industry. Within the pale
are a number of companies who must
produce considerably more sets and
do a much larger share of the total radio
business this year than last if they are
to earn their royalty guarantee. On the other
hand, there are still one or two large manufactur-
ers outside the pale who have not yet indicated
any intention or desire to obtain a license. No one
knows yet just what their course will be. One
possibility is an attempt to build receiving sets
completely evading infringement of Radio Cor-
poration patents. There are engineers who con-
tend that this is not impossible, although really
more than this result must be achieved. The sets
must not only avoid patent difficulties, but must
be as inexpensive to manufacture and as efficient
so far as results are concerned as receiving sets
made under Radio Corporation licenses. That
is no small problem, f t f Heins and Bolet ac-
cepted a consent decree in a case brought by the
Westinghouse Company under Armstrong,
Fessenden and Vreeland patents, f I f The de-
cree against the Claremont Machine Company,
secured by the C. F. Mueller Company, for a
machine for folding noodles was sustained, Ml
A decision rendered in the U. S. Circuit Court al
Philadelphia upheld the Lektophone patent
1,271,529, declaring that Lumiere's invention
does not anticipate Hopkins and that the de-
NOVEMBER, 1927
BRIEF RADIO NEWS AND COMMENT
17
fendants' device, employing a flexible rubber
liaison member, held in place by a rigid frame
ind covered by an ornamental hood, is an in-
fringing device. I M The following sets are now
licensed under R. C. A. patents: Zenith, Splitdorf,
Stromberg-Carlson,Bosch,Crosley,All-American,
Freed-Eisemann, Howard, King, Fada, Federal,
Murdock, Freshman, Amrad, Steinite, Gilfillan,
Day-Fan, Bremer-Tully, Atwater Kent, Federal-
Brandes, A. H. Grebe, Pfansteihl and United
States Electric (Apex, Case, Slagle, Workrite,
and Sentinel).
The Month In Radio
THE evolution of marine radio communica-
tion was recently described by T. M.
Stevens, General Superintendent of the
Marine Department of the R. C. A. Broadcast-
ing considerably hastened the adoption of a
continuous wave transmission on a new series of
channels, greatly mitigating interference with
broadcasting. In 1922, there were twelve spark
stations, using principally the waves of 450 and
600 meters, along the coast from Cape May to
Bar Harbor. Both on account of congestion and
because of the protests of broadcast listeners,
seven of these twenty spark stations are now
closed down and the remainder have been re-
placed by more efficient vacuum tube transmit-
ters. Three hundred ship spark transmitters have
also been converted into modified tube transmit-
ters so that they no longer interfere with broad-
casting programs.
A few small independent companies are still
compelled to use spark transmitters, while many
foreign ships with spark transmitters are still
working in a manner to interfere with broadcast
listening. It is understood that the independent
radio companies, operating spark stations, are
experiencing difficulty in obtaining properly
licensed vacuum tube transmitting equipment.
The foreign ship interference will probably be
tackled by the International Conference at
Washington. Under the circumstances, spark in-
terference with radio programs is likely to be a
thing of the past within two or three years, and,
possibly sixty to eighty per cent, of the inter-
ference is already eliminated. ? f f Things have
changed for ship operators since the writer
pounded the key some twelve years ago. In those
days, the emolument was sixteen dollars a month
and now it averages a hundred. Considering that
the work is generally pleasant and practically
all expenses are paid, the radio operator's lot is
one to be envied, when compared with that of
the clerk with his dull routine and the artisan
with his arduous and confining tasks. The radio
operator's principal complaint, as we have
gathered from interviewing a few, is that once
senior operator on a desirable ship, contact with
superiors is so limited that the opportunities for
advancement are practically nil. Nevertheless,
most of the executives of commercial radio com-
panies were once "brass pounders." There is no
employment more romantic, responsible and
broadening than that of radio operating for the
young enthusiast, seeking a career of adventure
and promise. Iff The listeners of KFWO, an
efficient little 25O-watter at Avalon, owned by
Lawrence Mott of short-wave fame, have been
receiving play-by-play reports of the games
played in Chicago by the Cubs. Why this station
should go so far afield to present its listeners with
this feature is explained by the fact that Mr.
William Wrigley, Jr., is so interested in the doings
of the Cubs that, while he summered at Catalina.
play-by-play reports were sent him by telegraph.
Mr. Mott suggested to Mr. Wrigley that these
play-by-play reports be diverted to KFWO and
then broadcast. Colonel Green has a rival! f f I
The Egyptian government plans to erect a
broadcasting station. There are already three
thousand sets in operation which, to receive the
principal European programs, must be highly
sensitive. Eighty-five per cent, of the population
of Egypt lives within 150 miles of Cairo and
hence a single station can greatly stimulate a
market which American manufacturers may do
their share in supplying, f f f Any listeners, hear-
ing broadcasting station SOL, have been victims
of a slight error which is excusable, due to the
distance involved. They are doubtless hearing
station XOL, operated by the Tientsin Govern-
ment in China. Its power is 500 watts and it
uses a wavelength of 480 meters. A special license
is required from the Chinese government to act
as an importer of radio sets and one American
Company has taken advantage of this privilege
by conforming with the regulation, f ( t A beam
station, another link in the Marconi worldwide
service, has recently been opened for commercial
use at Johannesburg, South Africa, f ? ? WLW,
using its short wavelength, supplied an Austral-
asian program recently, enjoyed by listeners of
2 FC, Sydney, Australia, and I YZ, Auckland,
New Zealand. America is the largest exporter
of broadcasting programs in the world, f f If
The interference problems of Australia are caus-
ing distressing controversy. A new 1 5-kw. broad-
caster is to open at Wellington on 420 meters.
What worries the Australians is if Sydney on 440
and Adelaide on 400 meters will not suffer serious
interference. Cautious fellows these Australians!
fit JOAK, Tokio, already frequently heard on
the Pacific Coast on its thousand watts, is to go
on 40,000 watts, which should certainly bring
it within range of a good part of the United
States during early morning, midwinter hours.
It won't be long now before a few American
broadcasters will have to close down because of
foreign interference. Iff There are 206,334
listeners in Australia, duly licensed and paying
license fees, f f ? The British Broadcasting
Corporation issued a statement recently that it
had discovered the advantages of rating stations
in terms of kilocycles rather than meters. The
advantages of the kilocycle rating have become
obvious to the American listener and have been
used in this magazine since August, 1925. In
talking to the members of the Federal Radio
Commission, we have been pleased to notice
that, though at the first the word "wavelength"
was rather frequently in the conversation, it
did not take long for the Commission to adopt
"frequency" as the only practical term to desig-
nate the radiation of a broadcasting station.
WHO REPRESENTS THE LISTENER?
OUR editorial some months ago, entitled
"Where Are the Listeners' Organizations?"
has brought forward a good deal of correspond-
ence from ambitious would-be executive secre-
taries, disillusioned leaders who have attempted
to form local organizations and readers request-
ing RADIO BROADCAST to sponsor such an organ-
ization. A number have expressed the opinion
that listener organizations would be more of a
nuisance than an aid to broadcasting. W. W.
Waltz, for example, writes that, although in his
area wjz, WEAF, WGY and KDKA are the obvious
program leaders, there is a certain advertising
station which any Philadelphia listener will re-
cognize, "whose sole idea is to sell every ampere
that can be forced off of their antenna. There is
no use in trying to describe the junk they broad-
cast. Everything from near-dirty stories to
grand opera selections by the most horrible or-
chestras in existence. One complaint after an-
other has been made, officially and otherwise, in
regard to the manner of operation of this station.
Their equipment is modern, but it is adjusted
to give a wave like a spark set. And believe it or
not — is the most popular station in the city!"
The conclusion to be drawn is that no organiza-
tion can be truly representative of listener tastes.
HOW LONG, OH LORD, HOW LONG?
WE TAKE a special delight in reminding the
authors of publicity statements boasting
of revolutionary inventions, of the prior discov-
ery and origin of these same inventions, in the
hope that more care and conservatism may be
displayed, as time goes on, by the publicity ro-
mance writers. We note that Mr. C. Francis
Jenkins, who has spent many years in research in
telephotography, announces the development of
radio guiding channels to keep aviators on a
definite course and of a receiving set giving visual
indication of deviation from the guiding course.
The former has already been widely used exper-
imentally, especially by the Navy Department,
and is a well known invention. The visual indica-
tor is not so widely used, although its develop-
ment in direction-finding apparatus was recorded
in these columns several months ago. About
twenty-five ships on the Great Lakes are already
equipped with the visual direction indicator.
FADING TESTS AT MELBOURNE, AUSTRALIA
Station 3 LO at Melbourne has made a gift to the University of Melbourne for research on the causes
of radio fading. R. O. Cherry, working under Professor Laby of the University, is here seen calibrating
the portable receiver for measuring signal intensities. The set is carried in an automobile
METERS, KILOCYCLES, OR "CHANNEL NUMBERS"?
By RALPH H. LANQLEY
Croslty Radio Corporation
ONE of the most practical and interesting sug-
gestions tending to simplification of radio
as far as the non-technical user of radio re-
ceivers is concerned is that of Mr. Langley, which
be so interestingly discusses in this article. The
use of radio receivers will become more and
more widespread as the receiver becomes more
simple to operate. Great strides in this direction
have been made, what with single-control operation
and direct light-socket powering of sets. But still,
thousands of listeners who don't even know the
difference between alternating and direct cur-
rent, try to solve the dual mysteries of wavelengths
and kilocycles which confront them in their local
newspaper radio programs and on the dials of their
receiving sets. Mr. Langley rightly asks, why should
they bother with this wavelength-kilocycle terminol-
ogy? Frequency calculations in kilocycles — or
meters if you belong to that school — are important
and necessary for the engineer and the technician,
but the listener has no earthly concern for them.
A committee of the National Electrical Manu-
facturers' Association has been appointed to con-
sider Mr. Langley' s suggestion and to take appro-
priate action. That committee consists of R. H.
Langley, chairman; L. W. Chubb, George Lewis,
M. C. Rypinski, J. M. Skinner, R. H. Manson,
and A. E. Waller. — THE EDITOR.
^ERHAPS there is no such thing as "the aver-
age broadcast listener." But millions of them
come pretty close to the average, and I wonder
just what they think when they hear the announcer
say that he is broadcasting "on a frequency of twelve
hundred and sixty kilocycles." In all but a very few
cases, I venture to say that their thoughts have
nothing to do with the meaning of these words. Last
year it was a "wavelength of two hundred and
ninety one and one tenth meters" and that was even
worse. Why so many numbers and so many strange
words?
Wavelength in meters, and frequency in kilocycles;
related to each other by some mathematical law, and
yet not related to anything the man in the street has
ever heard of. Even the radio engineer must resort
to a tabulation or a slide rule to translate one into
the other, and yet each and every broadcast listener
is expected to use them when he wants to hear his
favorite stations. The newspapers print them, and
you are expected to know, or somehow to find out,
where they all come on the dials of your receiver.
The change from "wavelength" to "frequency"
was, of course, a very logical one. It can easily be
demonstrated that the current in your receiver or
in the distant transmitter has a frequency. The wave
out in space is the thing that has a wavelength (as
well as a frequency). Primarily we are not interested
in the wavelength out in space — but the currents in
the receiver — which the listener can hear. Then
again, the wavelength listings were irregular and had
to be given with at least four figures and a decimal
point. The frequencies are given in three or four
figures, and the last one is always a zero, because
the frequencies are spaced in multiples of ten. But
they start at 550 and stop at 1500, and the system
is still far from being simple for Mr. Average
understand.
Some manufacturers have tried to put these strange numbers
on the dial of the receiver when it was built. Then if you knew
and could remember the wavelength or the frequency of the
zoo
Listener to
station you wanted to get, you could
set the receiver to that point, and there
was the station. There were a lot of me-
chanical difficulties in doing this, but
more than anything else, it was the com-
plexity of the numbers themselves that
kept the conventional "zero to one hun-
dred" dial on the sets. Here, of course, is
another set of numbers, that must be read
from a dial and related to the wavelength or
the frequency or the call letters of the sta-
tions. It is no secret that the average lis-
tener does not know to whom he is listening,
or how to find a particular station, except
in the case of a very few that are near to
him. The others are too hard to find, and
many that he could hear and hear well, he
does not bother with.
It would be possible to record the loca-
tions of our homes and places of business
by their latitude and longitude. Your home
address, for example might be given as
"north 43° 28' 37.42", east 76° 18' 58. 1 3"."
That would be just about as easy and just
about as logical and just about as technic-
ally correct as wavelength in meters or
frequency in kilocycles for a broadcasting
But our houses and our offices are con-
veniently numbered and so are our telephones. Why
not, then, use plain simple numbers for the broad-
cast frequencies and wavelengths?
"This is station XYZ on Channel 16." When you
want station XYZ again, you will turn to the number
1 6 on the dial. There will be numbers on the dial
running from I to 96, representing the 96 broadcast
channels. You will soon remember the fact that your
favorite stations are at 16, 23, 38, 67, and 84. If
you notice in the paper that station PQR, on channel
53, is giving an unusually good program, there will
be no difficulty about finding it. And the numbers
will be the same on all receivers. When you trade in
the old set, or when you go over to John's house,
you will not be at a loss to know where to find the
stations.
A DIAL WITH NINETY-SIX NUMBERS
IT WILL be more desirable, of course, to arrange
a dial with these simple numbers, than it is to
make one that reads in frequencies from 550 to 1 500,
or in wavelengths from 199.9 to 545.1 with tenths
on every one of the 96 of them. And there will not
be any unnecessary "meters" or "kilocycles" tied
to them. They will just be plain numbers like the
one on your front door. You can have a table showing
the wavelengths and frequencies corresponding to
the channel numbers if you want it; the newspapers
and the magazines will print them. But the average
listener will not want any such list; he will have no
use for it.
Some day the range of frequencies allotted to
broadcasting may be increased. When this is done,
it is almost certain to be in the direction of the
short waves. Then our series of 96 numbers will
have to be continued, from 96 up. By starting the number series
at the long-wave or low-frequency end, we shall leave room
for expansion into the short waves, and we shall also have the
smaller numbers for those channels now assigned to the larger
and more widely known stations.
1500
L
'ECEIVERS L $175 or less
<J
AVERAGE CITIZEN
¥T IS an erroneous impression that to possess a modern radio receiver combining
*• both artistic merit and fidelity of reproduction one must spend an inordinate
amount of money. The fact is that set makers have produced electrically good re-
ceivers and housed them in cabinets that will grace any home—and all at a genuinely
moderate price. This and the following pages show attractive moderate-priced re-
ceivers ranging in cost from $175 to less than $100. The inspiration for the Bosch 76
receiver shown above is Gothic and it is evident how effectively it may be combined
with the furnishings of many a living room. This six-tube RFL circuit receiver uses
either a loop or antenna and has an interesting volume control and vernier tuning
adjustment. Its price is $175
20
NOVEMBER, 1927
THE "MILAN"
A cone loud speaker is supplied with
this Apex receiver, the price for chassis,
cabinet, and loud speaker, being only
$135.00. The circuit comprises six
tubes, the audio amplifier employing
impedance coupling, which is respon-
sible for excellent quality of reproduc-
tion. The set is fully shielded and a
single dial controls the tuning
BELOW
The Kennedy " Co-
ronet." priced at
$125.00. Seven
tubes, including
four matched r. f.
stages, are used
FOR LESS THAN $100
The Workrite 17 has an all-metal chassis,
shielded r. f. coils, single-control illuminated
drum dial, and a combination switch and
volume control. Price $95.00
BY AUDIOLA, CHICAGO
A six-tube console receiver for
$110.00. There are three r. f.
slates, and tuning is accom-
plished by means of a single
knob
WHAT $70.00 WILL BUY
A table model of the Fresh-
man "Equaphase." As de-
scribed elsewhere in this is-
sue of RADIO BROADCAST,
the "Equaphase" principle
makes possible the elimi-
nation of the cause of os-
cillation
THE "IROQUOIS" CON-
SOLE
This attractive six-tube,
one-dial recei ver, by Mo-
hawk of Chicago, retails for
$130.00. less accessories,
for battery operation. For
electrical operation the re-
ceiver may be obtained at
an additional cost of
$110.00, in which case it
is complete with accessories
AN EXAMPLE OF COMPACTNESS
Here is a six-tube receiver by Stewart-Warner which
is offered at $80.00. There are three r. f. stages, one
of which is untuned. A single dial controls tuning,
but there is an auxiliary one for bringing the an-
tenna circuit into exact resonance, and also a vol-
ume control
NOVEMBER, 1927
21
OF THE NEUTRODYNE FAMILY
For $100.00 it is now possible to obtain
a single-control neutrodyne receiver.
The Freed- Eisema tin 1SR-9 is such a
receiver and, in addition to the single-
control feature, it is completely shielded
and has a pilot light on the front panel.
Equal amplification throughout the
broadcasting frequency spectrum is
claimed by the manufacturers
BELOW
The "Warwick," at $138.00, is
one of the offerings of Amrad
for the 1927-28 season. It is a
single-control neutrodyne, com-
pletely shielded, and may be
used with either loop or antenna
BY SPLITDORF
This is a receiver for the man who still
believes in two-dial tuning. There are
six tubes in all, three of these being
r. f. stages. It is wired for use of a
power tube in the last audio stage. The
price is $75.00. The elliptical cone
shown is priced at $35.00
MCMILLAN'S "RIDGEWAY"
Yet another shielded six-tube,
single-control receiver, this one
being priced at $110.00. A long air
column and deep-toned horn are
included. There is ample space for
batteries or power equipment
ZENITH MODEL 12
Single control is again manifest in this
six lube receiver, four variable con-
densers bcinj,' manipulated by :i simple
movement of the illuminated dial. The
chassis is of metal, and the receiver is
completely shielded. The cabinet is of
mahogany. Price $100.00
What Receiver Shall I Buy?
rPHE moderate-priced receivers exhibited at radio
-^ shows throughout the country this Fall are at-
tracting widespread attention because the offerings in
this class more than those in any other price range
present greater values than ever before. Radio is now
old enough so that those who bought radio sets two and
three years ago are now thinking about replacing the
old outfit with a more modern and satisfactory one.
These pages show a few of these decidedly interesting
receivers which can be had at a moderate price and
which at the same time guarantee excellent electrical
performance. These receivers are simple to control, more
than ordinarily compact, and what is of growing im-
portance, are handsome. There are table receivers for
those who have but little space for a set, and more pre-
tentious console sets for those who want both a radio
receiver and an attractive piece of furniture. Practically
all the console models in the medium-price range not
only provide space for a loud speaker but also have
convenient compartments for A and B socket power
units and the convenient relay switch which, through
the on-off switch on the receiver panel, controls both A
and B units. Many buyers are interested in the console
set with these compartments because they can at any
time purchase A and B units for their set and, in effect,
completely "socket-power" it.
22
LOUD SPEAKERS AND POWER EQUIPMENT
NOVEMBER, 1927
A ROLA CONE
Here is a table model of the well-known
Rola cone loud speaker, retailing at
$28.50. This unit is equipped with a
low-pass electrical filter lor the elimi-
nation of tub?, distortion. The heavy
turned-wood disk serves as an acous-
tical battle surface.
FOR A AND B CURRENT
This Philco power unit will pro-
vide 180 volts at 60 mils., and there-
fore is adequate for a receiver em-
ploying six or more tubes, with a
power tube in the output stage.
The unit, costing $79.50, is sup-
plied in an attractive metal rase.
A built-in trickle charter keeps the
A battery in good condition
A CONSOLE LOUD
SPEAKER
The exponential horn type
of loud speaker, of which
this is an example, is be-
coming increasingly popu-
lar, due to its excellent
reprodm ing qualities. The
one here is by Temple,
Chicago, anil lists at $65.00
THE "UNIPOWER
A trickle charger and storage
battery are. combined in this
useful device by Gould. It
may be obtained in either a
four- or six-volt output form
AN
INEXPENSIVE
CHARGER
A six-volt storage battery may
be quickly charged with this
device, a product of the Valley
Electric Company. St. Louis.
The charging rat* is 6 ami>eres
and the price, $19.50
FOR A AND B CURRENT
Another device which is capable of
run vert ing your a. c. house current
into suitable power for your receiver
by Kxide. The B output is 180 volts
maximum, while the A supply is six
volts. A trickle charger keeps (he A
battery well charged. The approximate
cost of operating this device is one cent
an hour
AN EXPERIMENTAL SET-UP
This photograph, taken about four years ago in RADIO BROADCAST Laboratory, shows some
of the early photograph transmission and reception apparatus designed by the author
RADIO BROADCAST Photograph
How the Cooley aRayfoto
THE articles announcing a system of radio
picture reception appearing in the Septem-
ber and October issues of RADIO BROAD-
CAST have attracted widespread attention among
radio experimenters. Even without specific data
as to the actual operation of the Cooley " Ray-
foto" system, experimenters have been fairly
besieging the writer since the appearance of these
articles and the demonstration of the " Rayfoto"
transmitter and receiver at the New York Radio
Show.
All the obstacles to making this new field
available to the experimenter are being removed,
one by one. Engineers are busy designing com-
ponents and manufacturers are busy getting into
production to meet the demand. And, for the
broadcasters, an important method of supplying
broadcasting stations with "picture" programs
has been evolved. In this article we shall sketch
briefly just how the Cooley "Rayfoto" system
functions, what each part does, and what its
purpose is. These technical details will give the ex-
perimenter a clear picture of what the difficulties
are and what technical knowledge is needed for
him to assemble and operate the apparatus. The
Cooley "Rayfoto" recorder is no more difficult
to build than a five-tube receiver.
THE SYSTEM IN BRIEF
IN A few words, the cycle of transmitting and
receiving a "Rayfoto" picture is as follows:
The subject, any ordinary positive or negative
print, is placed on the drum of the transmitter
or converter which revolves and feeds it along a
By AUSTIN G. COOLEY
shaft before an optical system, which, in turn, fo-
cuses the reflected light on to a photo-electric cell.
The amplified currents from this cell are
8oo-cycle audio-frequency currents varying in
amplitude in accordance with the subject.
These currents control the radio transmitter
output and the signals are received on a con-
ventional broadcast receiver. They are then fed
into the "Rayfoto" printer which produces a
corona discharge in accordance with the strength
of the received signal. The corona discharge
All you need for picture reception is a
standard receiver, an oscillator, a
stop-start motor mechanism, photographic
paper, and enthusiasm. The important
part of the receiving mechanism is the
motor mechanism. Wiib oscillators and
receivers we are all familiar. The motor
mechanism and all other necessary
components duly approved and labelled
with the Cooley Rayfoto label will soon
be on the market. Those eager to be the
first in their communities to receive pic-
tures by radio may send their names and
addresses to RADIO BROADCAST and
these will be sent to the manufacturers
making the parts. The total cost will
not be more than $100. — THE EDITOR
takes place at the point of a corona needle which
feeds along a revolving drum as the needle traces
over a photographic paper wrapped around the
drum. At the end of each revolution of the drum
the received signals are diverted from the
printer unit to a relay which is actuated when a
synchronizing signal is received at the beginning
of the revolution of the convertor drum. This
relay in turn operates the trip magnet which re-
leases the recorder drum so it may start off at the
same time as the convertor drum. After the
needle has fed along the entire length of the
paper, the latter is removed from the drum,
developed, washed, fixed, and washed again.
The result is a picture of a prize fighter who has
been knocked out a few minutes before; or a
picture of a railroad wreck just occurred; or
maybe a picture of some sweet young thing
who may have won a bathing beauty contest in
the afternoon.
Phototelegraphy is not complicated and in-
volves nothing that is really new in physical
science, but many of the "kinks" involved must
be well understood if good initial success is to be
expected. Most of the difficulties ordinarily in-
volved in picture reception work will be pre-
vented because manufacturers will supply equip-
ment especially designed for the purpose and
if the experimenter understands the principles
of the system and can handle amplifier and oscil-
lator circuits, he should have no difficulty in
setting up his "Rayfoto" recorder and having
good picture reception right from the beginning.
All systems of phototelegraphy have one
24
RADIO BROADCAST
NOVEMBER, 1927
limitation in common: They can transmit only
one shade and one unit area of the picture at a
given instant and therefore transmission must be
accomplished by dividing up the subject to be
transmitted into thousands of small areas.
The " Rayfoto" and many other systems trans-
mit the signals for each unit area in rapid suc-
cession and the resultant signal varies in ampli-
tude in accordance with the shading of the pic-
ture. The speed at which the impulses are trans-
mitted depends largely upon the ability of the
receiving apparatus to reproduce rapidly the
electrical impulses on the recording medium.
The corona method of printing used by the
Cooley "Rayfoto" system is capable of printing
faster than any other system the author knows
of, but for simplicity and low first cost we are
using a signal frequency of about 800 cycles per
second, which does not permit printing as rapidly
as is possible with the system when higher fre-
quencies are used. The possibility of operation at
higher frequencies has been taken into consider-
ation in designing the present equipment so that
the speed of transmission can gradually be in-
creased without necessitating any radical changes
in equipment.
As explained in the October issue of RADIO
BROADCAST, the picture or subject to be trans-
mitted is placed, at the transmitting station,
upon the drum of the picture transmitter, which
we will hereafter call the "convenor." A small
spot of the picture is illuminated and the re-
flected light from this spot actuates a photo-
electric cell, the signals from which control the
radio transmitter after the photo-electric cell
currents have been sufficiently amplified. Each
time the drum is revolved, the spot of light
traverses a different path an eightieth of an inch
wide across the picture. The line is broken up
into 480 sections by the optical system so that
480 electrical impulses are transmitted every
revolution of the drum and each impulse cor-
responds in intensity to the reflected light from
a small area of the picture. The result is that
480 electrical impulses are transmitted for each
revolution of the drum, or about 800 per second
when the drum is making one hundred revolu-
tions per minute. Running at this speed the drum
feeds along the shaft 1, Fig. i, at the rate of
one and a quarter inches per minute. The drum
is two inches in diameter and about five inches
long. This will give us an operating speed of four
minutes for a five-by-six-inch picture.
The beginning of each revolution is marked
by an impulse made up of twenty strong 800-
cycle signals in succession. This impulse is used
at the receiver to start the recording drum off at
exactly the same time as the transmitter drum,
for it is necessary that the two drums start off
together. To accomplish synchronism in this
way, known as the "stop-start" method, the
recording drum must start a revolution at the
same instant as the transmitter drum. It is neces-
sary that the recorder drum run slightly faster
than the converter drum, then stop at the end
of the revolution for an instant until the con-
verter drum completes its revolution. A trip
magnet operated by the strong synchronizing
impulse releases the recording drum at the
proper time.
This trip magnet is operated through a relay
which is connected to the rest of the system only
after the revolution of the recording drum has
been completed. Between the time the recorder
drum stops and the time the synchronizing im-
pulse is received, there must be no strong signals
received, so we paste a strip of white paper at
the end of the picture being transmitted so the
signals will be weak while the recorder drum is
stopped. Should a crash of static or some other
disturbance be received during this waiting
period, or "recorder lap," as it is called, the re-
corder drum will be released in advance of the
synchronizing signal. By making the recorder
lap very small, the danger of such a " static slip "
will be reduced proportionately. The wider the
white strip on the picture being transmitted, the
greater will be the chances of a good start after
a static slip so that the only marring effect will
be one line slightly out of place.
RADIO BROADCAST Photograph
SOME EARLY "RAYFOTO" EQUIPMENT IN RADIO BROADCAST LABORATORY
The apparatus on the right of this picture is a Cooley photograph transmitter and in the center is an
amplifier and "corona" apparatus. The picture receiver at the left has been redesigned in many ways
to make its operation as simple as possible. This apparatus was photographed four years ago
We will consider here a few of the principles
involved that affect the characteristics of the
received picture. In picture work, we wish to
reproduce at the recorder shades of light and
dark corresponding exactly to those of the
transmitted subject. The light reflected from the
subject varies the current through the photo-
electric cell in a ratio almost directly with the
intensity of the light, and this current, after
amplification, is made to control the power input
to the radio transmitter modulator which there-
fore varies directly proportionately to the re-
flected light, due to the characteristics of the
Heising modulator.
The final modulated radio signal sent out
over the air will vary as the square root of
the reflected light. The received signal is am-
plified lineally in the radio-frequency stages
of the receiver. The detector output varies as the
input squared, however, and therefore the cur-
rent in the plate circuit of the detector will be
directly proportional to the reflected light. The
signal then can be amplified in the audio ampli-
fier and delivered to the " Rayfoto" printer with
an intensity directly proportional to the reflected
light at the transmitter.
Limited by the data available at the present
time, this is as far as we can go with the signal
and know definitely what we are doing in the
way of maintaining the proper signal ratio
through the various circuits. We have no exact
data on the relation of the input to output of the
Cooley " Rayfoto" printer. Also we do not know
the relation of the power delivered by the
" Rayfoto" printer to the effect it has on the re-
ceiving paper. This factor is quite flexible and
can be controlled considerably by the selection
of the printing paper and its time of develop-
ment in the photographic solutions. The printing
paper we recommend today probably will not
be the paper you will be using next year. It is
therefore necessary to have some control over
the system so we may match our amplification
characteristics to conform with those of the re-
cording paper we may choose to use. For ex-
ample, if the received picture does not show
sufficient contrast in the lighter shades but too
much in the darker shades, we must adjust our
amplification characteristics to correct for this.
One way it can be done is to reduce the filament
voltage on one of the amplifier tubes so that the
strong signals are cut off somewhat by running
over the top knee of the characteristic curve
while the signals of lower value are on the straight
portion of the curve. Additional correction may
be obtained by reducing the time of development
in the photographic solution.
The most convenient place for signal charac-
teristic control is in the detector circuit, because
of its "squared" characteristic. This character-
istic may be varied considerably by proper pro-
portioning of the grid condenser and grid leak.
If the grid leak can be brought down to a very
low resistance, say 500 ohms, and the plate
voltage made adjustable over a range of from 4
to 40 volts, additional control of considerable
value will be gained. Instead of varying the plate
voltage, a variable grid battery may be used.
EFFICIENT AUDIO STAGES NECESSARY
A GOOD picture must not only represent exact
shadings of the subject but it must also
show up most of the small details of the original.
A poor audio amplifier system will blur up the
details in black shades and will not permit any
of the details in the light shades to appear. The
amplifier must not oscillate at any audio or
super-audio frequency or even tend to oscillate.
Oscillations in audio amplifiers most generally
occur because of feed-back through the B bat-
teries from one stage to another and can be pre-
NOVEMBER, 1927
HOW THE COOLEY "RAYFOTO" SYSTEM WORKS
25
vented by the use of low-resistance batteries, a
very large condenser across batteries of moder-
ately high resistance, or by the use of inde-
pendent batteries for the audio amplifier. The
first pictures transmitted will contain sufficient
contrast so that imperfect amplifying charac-
teristics will not appear very noticeable. Never-
theless, the progressive experimenter should try
to keep one step ahead of the game.
The plate current drain on the B batteries due
to the Cooley "Rayfoto" printer will be about
10 or 15 milliamperes, so that the total current
drain of the printer and an ordinary five-tube
receiver will be in the neighborhood of 45 mil-
liamperes. However, this additional drain of
15 milliamperes will only be present when the
printer is being used and, since it will not be
operated for long periods at a time, an ordi-
nary set of B batteries should be good for
many months of service. A total voltage of
about 200 volts is required.
Naturally an amplifier that can be operated
without oscillating is much more efficient than
one that tends to oscillate and which therefore
requires the introduction of some loss to prevent
oscillations. In many cases, however, it is more
convenient to use an amplifier we already have
and which can be "doctored" up a little to make
it serviceable for " Rayfoto" work. A resistance
across the secondary of one or more of the trans-
formers will prevent the amplifier from oscillat-
ing. The required resistance may vary between
100,000 ohms and 2 megohms.
Many broadcast receivers have sufficient am-
plification in their own system so that additional
audio amplification is not necessary. You may
test out your receiver in the following manner
to determine whether any additional amplifica-
tion is required to operate the recorder: Place a
milliammeter in the plate circuit of the last
amplifier stage; cut the current down to 0.2
milliamperes by increasing the C battery poten-
tial; short-circuit the loud speaker terminals;
then tune-in a local broadcasting station. If the
milliammeter jumps up over 15 milliamperes, no
additional amplifier stage is needed. Even if it
only goes to ten mils, it will not be necessary to
use the added stage but this amount of current
will allow only a very small margin of safety.
If an added stage of amplification is required, a
special transformer should be used, one that is
capable of operating without saturation and
which will not produce oscillations in the audio
system. Special transformers for this work will
soon be available.
The Cooley "Rayfoto" printer is the device
for producing the corona discharge that affects
the photographic recording paper. It converts
the received audio-signal into a fluctuating source
of light corresponding to the transmitted signal.
This unit consists of a modulated oscillator feed-
ing a corona coil. The corona discharges are
secured from the high-voltage side of the corona
coil secondary winding.
Readers may wish to have some explanation
of the nature of the corona we refer to here.
Visually, the corona discharge at the needle point
riding on the paper is a small spray of blue sparks
similar in appearance to those produced by a
violet-ray machine. This discharge occurs when
a difference of potential of 13,000 to 26,000 volts
per centimeter (which, incidentally, won't hurt
you) exist around the needle point. This potential
is produced by the radio-frequency amplifying
transformer, known as the corona coil. The pri-
mary of this coil is part of a vacuum-tube oscilla-
tor operating at a frequency of 333 kc. (about 900
meters). The plate circuit is supplied by the sig-
nals from the radio receiver. After being amplified
to supply enough power to the modulation trans-
former, these signals are strong enough to produce
a strong corona discharge when strong signals are
received. For the sake of efficiency and shading,
about one hundred volts of direct current is sup-
plied, in series with the modulation transformer
to the plate of the oscillator. This boosting
voltage must not be sufficient to produce a corona
that will print when weak signals are coming
through.
The oscillator of the "Rayfoto" printer radi-
ates for some distance if the frequency is high,
and to prevent such interference we have chosen
the reasonably low frequency of about 333 kc.
We do not recommend an oscillator frequency
corresponding to more than this unless careful
shielding is used.
The "Rayfoto" recorder is the mechanical
unit of the system which consists of the re-
ceiving drum driven by a motor and controlled
with a "stop-start" system of synchronizing.
A screw feed arrangement feeds the corona needle
along the drum as it revolves so that the needle
moves along at approximately the same speed
that the converter drum as the transmitter
moves along its shaft.
The "stop-start" mechanism consists of a
slip clutch between the motor drive and the
drum, and a trip magnet arrangement that stops
the drum at the end of each revolution until the
synchroi. izing impulse is received. This impulse
trips the armature of the magnet which operates
through a relay. By this system, the transmitter
and receiver are synchronized about twice a
second, thereby eliminating much delicate and
expensive synchronizing apparatus.
The recorder drum is the same size as the one
at the transmitter but since the recorder has a
slight "lead," that is, runs slightly faster than
the converter drum, the received picture will
be stretched out a small amount, depending
upon the amount of lead. To compensate this,
the gears between the drum and screw feed
shaft will be of such a ratio that the needle will
feed along a little faster than the transmitter
drum so that the proper proportions are restored.
As a result the received picture will be slightly
larger than the one transmitted.
It is desired to keep the lead as small as possi-
ble so as to prevent excessive stretching of the
picture. Also, if the lead is too much, the trip
magnet may be tripped from a subject signal
instead of the synchronizing signal. If the lead is
too small, the synchronizing signal may be re-
ceived before the recorder drum has finished
its revolution and has switched the relay in the
circuit. Consequently the relay will be operated
by the next strong subject signal.
Complete constructional data for a Cooley
Spot Of lighten picture "Rayfoto" receiver which may easily be made
at home is scheduled for next month's RADIO
BROADCAST.
Lens to focus _- •
lighten picture
Glass prism to change
direction of light _
Photo-electric cell -
Output signals from cell consist of audio-
freqency currents of varying amplitude.
Frequency is determined by speed of disk,"
and amplitude by shading of picture
To amplifier and radio transmitter
Light is broken up by passing through
holes in revolving disk. Frequency
determined by speed of disk
Picture being transmitted
"Converter" drum moves^downward
along threaded shaft y8o every revolution
-- Holes in disk interrupt
light from lamp L
Motor drives disk and drum
A PICTURE DIAGRAM OF THE COOLEY TRANSMITTER
This drawing shows graphically how the Cooley picture transmitter produces electrical sig-
nals varying in strength in accordance with the shading of the picture being transmitted
IN Stromberg- Carlson
receivers, a manufactur-
ing refinement, not evi-
dent to the casual ob-
server, is found in the
cord connecting the set
to the light socket. It is
made with unusual care
THE MODERN RADIO RECEIVER
By EDQAR H. FELIX
THE modern manufactured receiver has
become a precision product, built under
most exacting conditions prescribed by
skilled engineering departments. It is no longer
a heterogeneous combination of parts, wired to-
gether in conformation to circuits supposedly
possessed of magical qualities. Performance is
the product of a thousand and one engineering
decisions carried out with a care so far above and
beyond that which the average buyer can ap-
preciate that engineering refinements are no
longer considered suitable as selling arguments
by which to sway the buyer's preferences.
Where should the by-pass condenser across
the filament leads be placed? Is the improved
performance attained by placing it directly
underneath the tube sockets sufficient to warrant
a special moulding? Does a one per cent, differ-
ence in moisture content of the insulating paper
of fixed condensers reduce losses sufficiently to
justify an additional cost of twelve cents per
receiver and does that involve an increasing
percentage of condenser breakdowns? Should
three more turns be used on the radio-frequency
transformer primary to get slightly improved
quality or does that involve a sacrifice in selec-
tivity too great to be permitted under present
broadcasting conditions? Should the audio-fre-
quency system be designed to cut off at 5500
cycles or at 4800, in the first case giving slightly
improved reproduction; in the other, slightly
reducing the effect of certain types of interference
noises?
It is such highly technical questions as these,
clouded in a veil of mystery to all but the ex-
perienced radio engineer, that makes one radio
set better than another. The placing of a socket
half an inch one way or another may make an
imperceptible difference in performance, but it is
the multiplication of such details, carefully de-
termined after engineering study, that assures
the buyer of his money's worth.
In a sense, we have come to a parting of the
ways between the factors that make real radio
performance and those which make up the buy-
er's mind between one radio set and another.
There is a premium on the little, superficial
improvements which the buyer can appreciate
because they are the only practical ways of ex-
pressing engineering ingenuity to the ultimate
consumer.
ONE REFINEMF.NT OF FADA
'"THE Fada receivers of this year, for example,
•1 employ a new simplified power switch and
volume control, an obvious convenience which
any prospective purchaser will appreciate. One
control takes the place of two. Hidden in
the beautiful cabinet, is a chassis made of A
inch pressed automobile body steel. It is sup-
ported on a three-point suspension with absolute
rigidity so that the parts mounted in it cannot
get out of alignment. The accurate matching of
variable condensers contributes not only to se-
lectivity but to quality of reproduction. In past
years, an accuracy of one per cent, in capacity
throughout the tuning range has been considered
satisfactory. The Fada condensers are matched
to an accuracy of j of i per cent, and the same
standard is applied to the tuning inductances
coupled with them. These are a few of the hidden
values which make for good performance.
The shaft on which the tuning drums and var-
iable condensers are mounted is one-half-inch
flash copper plated piston rod steel and is gauged
to a tolerance of .0005 of an inch! The day of the
curtain rod condenser support is over. The pis-
tons in your automobile are gauged to no closer
tolerance.
Advertisements shout uniformly about the
most selective receiver with the best tone quality,
but give the discriminating buyer no real facts
to help him appreciate the performance of a
receiver. Generalities may sell the uninformed
and help to create name familiarity, but sterling
worth, built in by ingenious engineering and
painstaking manufacture, is hardly ever con-
veyed to the reader of advertising.
GOOD THINGS YOU DON'T SEE
ANOTHER instance of superficial selling
points which make an obvious appeal to
the uninformed buyer and the equally important
hidden refinements which contribute even more
significantly to good performance is found in
the Freed-Eisemann receiver. Several models are
equipped with a voltmeter so that the set owner
can readily check the A, B, and C voltage applied
to every tube of his receiver. Since accurate
voltage supply is of vital importance in the per-
formance of the receiver, the selling value of that
feature is obvious. But how many buyers know
of the two special bonding clips which ground
the shielding of the detector stage in order to
dissipate more readily the radio-frequency cur-
rents generated in that shield? It is a minor point,
but an expression of the engineering care which
makes the modern radio receiver.
Recently, the writer visited the Stromberg-
Carlson factory at Rochester, New York. A com-
plete understanding of the refinement which is
concealed in the cabinet of the Stromberg-Carl-
son receiver hardly ever penetrates beyond the
monument to engineering skill and idealistic
NOVEMBER, 1927 REFINEMENTS OF THE MODERN RADIO RECEIVER
27
production standards which that new factory
actually is. One could write a thousand words on
how the cord by which you tap the a. c. power
line is made! Only a detail, but it assures unfail-
ing service for a period of years. It means no
frayed cord and no breakdowns, an advantage
which passes practically unnoticed in the atten-
tion of almost every buyer of that receiver. But
to give him that advantage, special engineering
standards have been set for every item of ma-
terial used in the flexible cord. The fine copper
wires which, woven together, make an everlasting
cable, are ten times as strong as ordinary wire.
Special flexible conductor, which does not break
if sharply bent, is employed. The individual
strands are so fine that they cut the finger like
a razor blade. Covering these wires are insulating
materials adding a factor of safety far above
and beyond that considered necessary. And
finally, selected cotton is woven over the insulat-
ing material, giving a mechanical strength so
that the copper wire itself is relieved of most of
its load. Last, but not least, comes an outer cov-
ering of silk so woven that there will be no un-
twisting of the cable and it will hold its lustre
for a period of years. Outwardly, there is but
little to distinguish this little engineering master-
piece from an ordinary power con-
necting cord which will fray, untwist,
and break in the course of time, par-
ticularly if it must be pulled out each
time the vacuum cleaner is used.
Probably not one salesman in ten
thousand selling the Stromberg-
Carlson receiver ever considers this
refinement — one of a thousand which
conscientious engineering has built
into that product.
SOMETHING ABOUT CONDENSERS
ONE feature which every radio
enthusiast appreciates is the
advantage of straight frequency-line
tuning condensers over the straight
capacity-line type. The desirability
of even spacing of stations over
the tuning dial throughout the
broadcast range is obvious. But,
with the almost universal tendency
toward multiple condensers, needed
to obtain single control, the neces-
sity for straight frequency-line condensers has
caused many an engineer gray hairs. It is very
difficult to secure uniformity in quantity
with condensers having the peculiarly shaped
plates necessary in straight frequency-line tuning.
With straight capacity-line used in connection
with matched inductances, uniformity is easily
attained and tuning circuits readily matched.
All that need be done to match the stages is to
adjust the condensers at any point on the wave-
length scale, after the receiver is assembled.
Once that is done, absolute accuracy is likely to
obtain at all dial settings. But straight capacity-
line condensers mean that, at the short wave-
length end of the dial, stations are hopelessly
crowded, while, at the upper end, they are widely
and wastefully separated.
A fine example of engineering refinement in
meeting this problem is embodied in the Federal
receiver. Condensers with square plates, sliding
in rigid grooves, assure absolute uniformity of
capacity variations and attain a standard of
accuracy almost impossible to secure with con-
densers having specially formed plates to secure
the straight frequency-line effect. But the buyer
of a Federal does not sacrifice the advantages of
straight frequency-line tuning by the use of these
condensers. An ingenious and well designed gang
tuning control mechanism gives him all the
advantages of straight frequency-line tuning
The mechanism is a masterpiece of mechanical
design.
Another example of true engineering beauty
is embodied in the antenna tuning compensator
which is a part of the mechanism. With multiple
tuned circuits, the designer has the choice of
several ways to compensate any variations in
antenna capacity. He may use a broadly tuned
antenna or input stage which gives but little or
no amplification. Such a stage contributes its
share of tube noise and accentuates nearby sta-
tion interference. Or else he may employ a
sharply tuned stage which has a separately
adjusted compensating condenser. Of course,
the most efficient and satisfactory method to the
user is an antenna stage which tunes sharply and
contributes its share of amplification. Those
having receivers with a vernier antenna com-
pensating condenser have noticed that, although
they have a main tuning dial which gives the set
the appearance of one control, they must actually
adjust two dials — the main tuning control and
the compensator — to tune-in a station properly.
With the Federal receiver, the compensator is
geared with the main tuning adjustment and
automatically keeps the antenna circuit in step
with all the rest throughout the tuning range.
THE R.F. OSCILLATOR USED BY BOSCH TO MATCH COILS
The author would not be surprised to discover
that the electrical law determining the correct
compensating adjustment needed for all types
of antenna systems and working out the mechan-
ical arrangement which assures adherence to
that law was a bigger engineering job than
designing the entire radio set marketed in 1924.
All this engineering precision applied in design
may be nullified by carelessness in production.
The electrical and mechanical measurements
made in the modern radio plant are of an order
of precision unrivaled in any field of quantity
production. Atwater Kent, for example, makes
1 59 precise tests, each requiring engineering
knowledge to perform, in producing a single
receiver. Some of these tests entail mechanical
precision measurements; others electrical meas-
urement of currents of mere millionths of an
ampere. But every test contributes to the pur-
chaser's assurance of reliable radio service.
MATCHING INDUCTANCES IN QUANTITY
HOW one manufacturer applies engineering
precision to production is best expressed in
the words of William F. Cotter, radio engineer
for the American Bosch Magneto Corporation:
"The subject of sorting and matching of in-
ductance coils is one to which we have given
considerable thought. Its importance is recog-
nized by every manufacturer. With one test
fixture capable of handling the job, it would be
comparatively easy to install a check of the
manufactured product and be assured of a high
degree of accuracy. However, when two or more
test fixtures are required to handle the volume
of coils manufactured, and where it is desired to
check these coils at radio frequency, a more
serious problem presents itself.
" We have employed several methods over the
last three years The one I describe, however,
represents our latest development and is the re-
sult of all our past experience.
"A radio-frequency oscillator is built up
around the standard 2O1-A tube. Incorporated
in the tuned circuit of the oscillator at nearly
ground potential is a resistance of approximately
10 ohms. Across this resistance is shunted in
series the coil to be tested and a variable con-
denser with its separate vernier condenser.
When this series circuit is brought to resonance,
the total resistance of the shunt circuit comes
down somewhat in the neighborhood of the
lo-ohm resistance, and one-half of the oscillation
current is diverted to the series tuned circuit.
Included in this tuned circuit is, of course, the
usual thermo-galvanometer.
" By means of a properly chosen vernier con-
denser, the coils coming through can
be checked for accuracy and sorted
in as many divisions as experience
shows necessary. However, while
this is suitable for one test fixture,
the problem of keeping two or three
fixtures oscillating at the same fre-
quency presented itself. Naturally,
if the frequency of the individual
oscillators varies, say 10 per cent ,
it is quite impossible to group
coils together just by dial readings.
"We have solved this problem by
building a crystal oscillator as one
of the test fixtures. Other oscillators
of ordinary type are built and each
is equipped with a vacuum-tube de-
tector. The oscillators are placed so
that it is possible to couple in some
of the energy from the crystal oscil-
lator. By means of a headset, the
operator adjusts his oscillator to zero
beat with the crystal oscillator. Usu-
ally, it is not necessary to check
this setting more than two or three times a day.
By this method, coils may be checked and sorted
with an accuracy of a few tenths of one per cent."
That is engineering refinement. It is the
kind of "detail" which makes the 1927 radio
receiver a precision product.
The broadest appeal to the radio buyer, and
one to which most people respond, by and large,
is the outward beauty of the product and the
name reputation of the manufacturer. Faced, as
a prospective buyer is, with numerous products
attractive from these standpoints, he is easily
swayed from one brand to another by superficial
selling points. The more discriminating and in-
telligent buyer — and in the radio field, because
of the host of persons who have a smattering of
technical knowledge, this class is predominant
and influential — looks to the hidden qualities,
the expression of engineering ingenuity and
manufacturing skill, as well as the performance
qualities, in deciding between one receiver and
another. The glittering generalities which have
characterized successful advertising and have
successfully built up huge quantity production,
are at last beginning to suffer a reaction. There
are too many "best" automobiles and too many
"finest" radio sets. But facts, the refinements,
the details, presented to those who can under-
stand them, are indisputable evidence of inherent
quality.
A RADIO receiver, as any engineer will
tell you, is a complicated and highly
organized machine, designed to perform
several functions none of which is independent
of the others. It is because of these intercon-
nected functions that the engineer will wish he
were in Europe if you ask him:
"What is the best radio?"
An automobile, on the contrary, is compara-
tively simple. It has but one function to perform,
it must take energy in some inert form, say un-
confined gasoline, and convert it into some other
dynamic form which is useful in carrying some-
one somewhere.
To answer a question regarding the best auto-
mobile, then, is simpler, especially since the auto-
mobile industry has been established long enough
for the most expensive car to be usually the best.
Unfortunately, radio has not even this truth to
go on, for, all things considered, the most expen-
sive radio does not always pan out to be the best.
A radio must do three things, and therefore
there are three problems of design. They deal
with:
1. SENSITIVITY. The receiver must be sen-
sitive enough to pick up the signals one wants
and amplify them sufficiently to give good
loud speaker volume.
2. SELECTIVITY. The receiver must accept
signals from the one station the owner wants
and reject all others.
3. FIDELITY. The loud speaker signals must
be a faithful reproduction of the original in
tone and in relative volume.
Thus a perfectly selective and sensitive re-
ceiver would pick up any station operating at
any distance on any frequency, and would turn
a deaf ear to all others, no matter how near the
given station in frequency or distance, or how
great their power. If the receiver has 100 per
cent, fidelity of reproduction, signals as loud as
the original would come from the loud speaker,
and with all tones exactly as they originate in
the studio.
Needless to state, there is no such receiver.
There are several reasons for this. As men-
tioned above, these varied functions of a receiver
depend upon each other, and not always to the
same degree. For example, an infinitely selective
receiver would be in the present state of the art,
highly unsatisfactory from the standpoint of
fidelity. Advertising writers to the contrary, one
cannot have something for nothing, even in radio.
There are those, however, who desire to know
which of two receivers is the better, and among
these are the reputable manufacturers them-
selves. It is for this reason that set testing meth-
ods have changed.
Not so long ago, when a receiver had been put
together and wired someone took it to a test
bench where it was hooked to batteries and an
antenna. If signals came out of a horn somewhere
the set worked. It was sent to the dealer at once.
This was an obvious test.
The obvious, as we all know, is not always the
best. In the case of good radio receivers, this
older, obvious test has given way to more scien-
tific tests which do not depend upon a smoke
covered antenna or the often tired ears of a
test man, but upon tireless and unemotional in-
struments.
In spite of the fact that these tests have been
practised — sporadically, we suspect — in the bet-
ter known laboratories, it has been only within
the last half year that descriptions of them began
to appear in the technical literature. So new is the
industry that standard tests have not been de-
veloped, nor have engineers even agreed among
themselves regarding even the nature of these
tests. Probably while this is being read, com-
mittees of the various radio organizations and
By KEITH HENNEY
Director of the Laboratory
radio engineering societies will be weighing con-
ditions of test and endeavoring to set definitions
of the perfect receiver, definitions that everyone
will recognize.
WHAT HAPPENS INSIDE THE BOX?
NOW, before trying to find how much of any-
thing a receiver does, it is well to get an idea
of what happens inside the box, to discover if
possible what should happen and how much.
Then we shall have some idea of what to look for
and what the relative order of magnitude will be.
For example, harking back to the automobile,
almost everyone knows that an automobile has a
carburetor. Some people know what it is for; the
writer does not. There is also a clutch and some
other apparatus which everyone who is about
to buy or run or design or fix a car should
know all about. He should know what these
various pieces of equipment are for, what hap-
pens if you leave some of them at home, and
when the car runs properly, what the magnitudes
of the various operations are. The quantity of
gas and oil per mile, or hour, revolutions per
minute, miles per hour, ability to climb hills,
"pick-up," etc., are all terms that have both
definition and dimensions.
A radio receiver also has several pieces of com-
ponent apparatus. Each has a different function,
and in each piece of apparatus something
happens when the set is operating properly.
What we must know first is what is each part for,
how it does its work, and then how much should
a good unit do? This will enable us to define a
perfect receiver, and if we have laboratory equip-
ment and patience, or if the manufacturers will
supply us with the proper data, we shall be able
to decide just where in the scale of goodness our
particular receiver stands.
The inner works of the receiver, except super-
heterodynes, consist of three parts: a set of tubes
which serve as radio-frequency amplifiers, boost-
ing in magnitude the incoming signals without
change in form and very sharply tuned; a de-
tector more broadly tuned which changes the
signals into an audible form; and third, audio
amplifiers which bring the detector signals to
loud speaker volume. The last are not tuned at
all, or at least very broadly.
The radio frequency amplifiers are intimately
connected with the transmitting station. The
receiving antenna or loop is situated in a reser-
voir of energy, part made by man, part by nature;
part useful, part disturbing. A fair share of this
energy is created by broadcasting stations which
pour their output into what scientists call the
"ether" and what the layman calls the "air."
The energy one wishes to receive speeds from
the broadcasting station with the velocity of
light, so fast that it may be heard from the loud
speaker before it is heard in the rear of an audi-
torium in which the broadcasting may occur.
This is because sound travels through air at
I loo feet a second and radio waves through the
ether at 186,000 miles a second.
The receiving antenna is almost as intimately
connected with the transmitter as if a wire joined
them metallically, although less efficiently to be
sure. What comes out of the transmitter sets up a
voltage across the receiving antenna. Naturally,
the stronger the transmitter, the nearer to the
receiver, or the higher the receiving antenna the
greater is the received voltage.
Here is where we start on our measuring ex-
pedition. How can we measure the relative
strength of a transmitter at a given locality?
HOW RECEIVED ENERGY IS MEASURED
IN THEORY the problem is about as follows.
The actual voltage across a given antenna is
measured by the substitution method. That is,
a given deflection on a meter is secured from the
distant station. Then a voltage which can be
read on another meter is substituted for the
distant transmitter and when the proper deflec-
tion is secured the voltages are equal. The process
may be changed as follows. The given deflection
is secured. Then a much greater voltage, which
NOVEMBER, 1927
4 6 8 10
RADIATED POWER
CONDITIONS UNDER WHICH SETS WORK
Estimates agree that a radio set must have de-
livered to its antenna a signal strength of be-
tween one and ten millivolts per meter for
"good" service. This means that the received
•signal will then be strong enough to over-ride
ordinary static and local electrical disturbances.
This curve shows the increase in power neces-
sary at the broadcasting station to increase the
range at which a field strength of ten millivolts
per meter is delivered. Curve A shows the power
required to lay down this field strength without
any absorption of the wave; Curve B shows the
unit power needed to lay down an equivalent
field strength with all sources of absorption in-
cluded. Note that at a distance of about 20 miles
from the station, only about 1.1 units power is
required for ten millivolts while, with absorp-
tion, ten units are required to produce the
equivalent signal
can be easily measured, is cut down in known
steps until the same deflection is noted. In this
manner the field strength of a given station may
be definitely measured.
Since the field strength at a given receiver
varies with the antenna height, the usual basis
. of comparison is field strength per meter height.
It is merely the actual voltage measured divided
by the effective height of the receiving antenna.
This is expressed in millivolts per meter and is a
factor which is a measure of the effectiveness of a
given transmitter at a given locality at a given
time of day.
A given number of millivolts per meter will
produce a certain loud speaker response with a
given receiver. The more sensitive the receiver
the greater loud speaker signal will be secured
from a given field strength, or conversely, a given
WHAT IS A GOOD RADIO?
signal may be produced by a weaker field
strength the more sensitive the receiver.
What, then, may be considered a good signal?
Here we are talking dimensions or magnitude.
What we want to know is the field strength that
will override static and other interference to
produce a good lusty loud speaker signal, one
that will be good, day or night, rain or shine.
The following table is taken from Dr. Alfred
N. Goldsmith's paper in the /. R. E. Proceeding
for October 1926 and shows what may be ex-
pected from various field strengths.
NATURE OF
SIGNAL FIELD STRENGTH SERVICE
o.i millivolt per meter poor service
, 0 " fair service
I0 0 « " " very good service
I00 0 •• " " excellent service
looo'o " extremely strong
So far so good. Let us see how powerful a sta-
tion must be to deliver such a field strength over
a certain distance. Again quoting from Doctor
Goldsmith's paper we have the following data.
ANTENNA POWER SERVICE RANGE
5 watts ' mile
50 " 3 ™les
500 I0 ",
5000 " 3°
50,000 loo
There seems to be some regular progression
here between the power and the range of station
—in fact a law exists stating that the range of the
station varies with the square of the power of
the station. That is, to double the range we must
quadruple the power. To increase the service
range three times we actually increase the power
the square of three or approximately ten times.
Now quoting Lloyd Espenschied in the Bell
Svstem Technical Journal (January 1927), we find:
' Fields between 5 and 10 millivolts per meter
represent a very desirable operating level, one
which is ordinarily free from interference and
which may be expected to give reliable year-
round reception, except for occasional interfer-
ence from nearby thunder storms.
From o. 10 to i millivolt per meter, the results
50
100 150
DISTANCE.MILES
29
may be said to run from good to fair and even
poor at times.
Below o.i millivolt per meter, reception be-
comes distinctly unreliable and is generally poor
in summer.
Fields as low as o. i millivolt per meter appear
to be practically out of the picture as far as re-
liable, high quality entertainment is concerned.
WHAT POWER DO STATIONS DELIVER?
FROM a given station the field strength falls
off according to an inverse law, that is, if we
double the distance we shall halve the field
strength: "a 5 kw. station may be expected to
deliver a field of 10 millivolts from 10 to 20
miles away and a i.o millivolt field not more
than 50 miles away."
In a Bureau of Standards paper, "General H
port on Progress of Radio Measurements,"(April,
1924) the following data were published. When
WEAF was transmitting with 3 kw., its field
strength at 10 miles was 32 millivolts per meter.
When KDKA has a nominal power of 10 kw. its
field at 10 miles was 43 millivolts.
All of these statements may be expressed
graphically and the curves on these pages contain
much meat for thought. What everyone wants is
good lusty signals from a high quality station,
day and night, without resorting to regenerative
receivers to boost the volume at the cost of fidel-
ity, without being forced to listen to nearby poor
quality stations riding in on an adjacent chan-
nel, or without having his program more
than liberally punctuated with static or ex-
traneous noises. It is up to broadcasting stations
to produce a field strength that will insure
programs and transmission of this desirable
quality. It is up to design engineers to produce
receivers that will serve their owners with loud
speaker signals from the field strengths laid
down by high quality stations. Mathematics
alone is not infallible; some experiment and la-
boratory work must go with it to make certain
all the factors have been considered.
Subsequent articles will deal with methods by
which engineers check up on the soundness of
their design; methods by which sensitivity,
selectivity, and fidelity may be measured.
10.0
ST
MTON WE^
F
(610 Kc.)
(Bell System Technical Journal)
en
1
[
Jan. 1927
.LI-VOLTS PE
c
\
RENGTH IN Ml
p
V
"•*».
Ift
HOW FIELD STRENGTH DECREASES
This curve, from the Bell System Technical
Journal graphically shows how the field strength
of WEAF falls off with distance from the station.
Any receiver, to be subject to tests which indi-
(
»me time
A RADIO "MA?" OF WEAF's SIGNALS
when WEAF was transmitting from Walker Street, New York this
York W£AF s wer£ yery famt indeed A
Mtmd not successfully "pull in" this station. The answer ,s greater
Poland locatL of broadcastmg stations away from areas of great absorpt.on
Do You
a Battery-operated Set?
Many Fine Types of A-Power Supply Units Are Nou> Available to Convert
Your Battery -Operated Set to One Which Requires Almost No Attention
By HOWARD E. RHODES
NOT so long ago, the only way to heat the
filaments of your tubes was to use a
battery. And practically everyone who
had a radio set had a storage battery; few indeed,
even in the olden days, used dry cells to light
their tube filaments unless that was a necessity.
Then the storage battery passed through a cycle
of development. The crude battery which radio
borrowed from the automobile industry was
dressed up. The case became polished wood or
even glass and special precautions were taken
by the makers to keep the acid electrolyte where
it should be, for this battery was not to
be housed in the interior regions of a mo-
tor car but in the parlor of high society.
And now, to compete with the steady
old battery come socket A-power units.
What are they? How much do they cost?
How many tubes will they supply? Do
they need regular attention? Can a socket
A-power unit be installed and be de-
pended upon to light the filaments of the
tubes "when, as, and if wanted"? These
and goodness knows how many other
questions are being asked by technical
and non-technical radio folk these days
as the offerings of 1927 are more and
more widely announced.
The owner of a good radio set of some
years back realizes that the tempting
new 1927 models, operated directly from
the light socket, probably are as superior
to his outfit in convenience and perform-
ance as Whiskery is to Dobbin. But for
one reason or another our loyal owner
decides to keep his receiver. Can't he buy
gadgets to turn his set into a light-socket
outfit? Why not, for there are plenty of
good B socket-power units and a goodly
number of A socket-power units adver-
tised? Well, so he can. He can buy a re-
liable A socket-power unit, a good B
socket-power unit, a relay switch, and
there you are — complete light-socket
operation! He has achieved convenience
which he seems to be pursuing strenu-
ously. The economics of the change
is another matter. Of the convenience
and reliability there is no question.
Take the case of a set owner who bought a re-
ceiver a year ago. He may not be quite ready to
buy a new outfit, but complete light-socket opera-
tion tempts him. His receiver must be operated by
these A and B power units without any sacrifice
in tone quality or volume. If the power units can-
not accomplish this — and for a reasonable length
of time, without renewal of parts — they are not
worth purchasing. There are, fortunately, many
A-power units capable of giving as satisfactory
reception as can be obtained from the un-
adorned storage battery.
The storage battery as a source of filament
power is in many ways an almost ideal device.
The current it supplies is perfectly steady. Its
voltage is practically constant during a greater
part of its discharge, and the slight decrease in
voltage that does take place as the battery be-
THE BALKITE A-POWER SUPPLY
This device will supply filament current to receivers having up to
eight tubes and it requires practically no attention. Inside the case
is a transformer and electrolytic rectifier and an electrolytic con-
denser. The list price is $32.50
comes discharged does not affect the operation
of the receiveradversely because tubes of present-
day design will operate satisfactorily at slightly
lower than rated filament voltage. Automatic
A-power units have been developed because the
public demands convenience. The necessity of
TABLE I
MAX. NUMBER
POWER
NAME OF UNIT
PRICE
TYPE OF
RECTIFIER
OF i AMP.
TUBES UNIT
CAN SUPPLY
INPUT
FROM
LINE
CONTAINER
Lx W x H
Abox
$32.50
Electrolytic
8
Balkite A
32.50
Electrolytic
8
100
111x613 x8)8
Electron Electric A
Regular
45.00
Tube
7
—
12} x 71x9
Giant
49.50
Tube
12
32
Marco A Socket Power No. 500
60.00
Tube
10
47
Illx7}x9
Sterling A Supply
42.50
Tube
8
7 x 11 x8
Valley Socket A
39.50
Tube
12
36
9} x5} x 11
White A Socket Power
43.50
Tube
9
39
111 x7x6j
charging A batteries is a serious annoyance to
many radio users.
TWO GENERAL TYPES OF A UNITS
THE radio set can be operated from the light
socket by the use of A and B power units, or
by designing the receiver to operate with special
a.c. tubes, receiving their filament current from
the power mains. The purchaser of a new set
finds his problem largely solved, for the makers
of light-socket sets have engineered their sets
beforehand. It is to the owner of a battery-
operated set that thisarticleis addressed.
A power units fall into two classes:
(a) units using a rectifier and filter sys-
tem connected through a transformer
to the a.c. line. (See Table I).
(b) units using a special storage battery
in conjunction with a trickle charger.
(See Table II).
The various A-power units listed in Ta-
ble I are all essentially similar in design
but they differ in minor ways that are
of interest. All A-power units in Table 1
must contain ( i ) a step-down transformer
(to lower the voltage of the line to the
proper value required by the rectifier
unit); (2) a rectifying unit (to change
the reduced a.c. to a sort of d.c.); and
(3) a filter system (to smooth out the
product of the transformer-rectifier
circuit). The filter must eliminate the
"hum" which is always present in
unfiltered, rectified a.c.
Enormous capacity in the filter con-
denser is necessary to remove this
troublesome hum. With electrolytic con-
densers a capacity of 30,000 mfd. can be
attained in a reasonable space and at
reasonable cost, and such a large ca-
pacity as this is necessary for adequate
filtration. The electrolytic condensers are
shipped dry and when they are put into
service, distilled water is gradually
added to the condenser container. The
contained chemical, which in some
cases is potassium hydroxide, dissolves
in the water. When it completely dis-
solves, the unit is ready for use.
These electrolytic condensers require practi-
cally no upkeep. Every six months or so a small
amount of distilled water must be added. If the
user is absent minded and lets the water get too
low, the unit is not damaged, but indicates its
need of attention by causing the unit to produce
an audible hum which is heard in the loud
speaker. If, "by a set of curious chances," too
much water is put into the condenser unit, it
will fail to function properly. Excess liquid can
and must be removed with a syringe. When the
water is first put into the condenser can some
heat will be generated for a short time.
The Balkite and Abox units both use the form
of electrolytic condenser discussed above. An
interesting feature of each of these two outfits is
that the chemical rectifier electrode is immersed
in the same electrolyte used for the condenser.
The outer plates of the condenser act as the
second electrode of the electrolytic rectifier. This
NOVEMBER, 1927
DO YOU OWN A BATTERY-OPERATED SET?
31
ingenious scheme achieves very compact con-
struction. Both these units are supplied with
external taps which insert resistance in the
secondary circuit to control the output voltage.
It is always advisable to use the lowest resistance
tap that gives satisfactory results. In the Abox
unit, there is a film of oil on top of the electro-
lyte which prevents excessive evaporation of the
fluid. Both units require the addition of a small
amount of water every six months but do not
require any other attention.
Another interesting A-power unit uses the
Raytheon "A" cartridge — a new type of dry
rectifier. Units of this type are made by Electron,
Marco, Valley, and Sterling. Some of these use
one Raytheon cartridge, others two. The Marco
product, for example, boasts two cartridge recti-
fiers. A rheostat in the primary circuit allows
regulation for different loads. A meter on the
front of the panel simplifies proper ad-
justment. Inside the box is a relay with
silver contacts — to avoid sticking — so
that the power unit can be controlled
by the filament switch in the receiver.
Either one or two Raytheon "A"
cartridges may be used in the Valley
A-power unit, depending on the num-
ber of tubes in the receiver to be sup-
plied. Full-wave rectification obtains
with the use of two cartridges. Valley
suggests using the full complement of
two cartridges for receivers with seven
or more tubes. A single cartridge will
suffice for more modest receivers. This
Valley device also uses an electrolytic
condenser to smooth the output of the
cartridge rectifiers. Since it is shipped
without liquid, the dry chemical may
rattle in the condenser can and excite
some curiosity on the part of the pur-
chaser. The addition of water, accord-
ing to directions, makes all things as
they should be. Between the rectifier
and filter system is the control rheostat
which provides sufficient regulation for
various loads imposed by the receiver.
The A-power unit from Sterling uses a
single Raytheon cartridge, is equipped
with ar Automatic filament circuit re-
lay, a control rheostat, and a meter to
facilitate the correct voltage adjust-
ment.
The White unit among those listed
in Table 1 is the only one on which
we have information which uses a
Tungar or Rectigon tube as a recti-
fier. The transformer in this device delivers about
8 volts to the plate and about 2 volts to the fila-
ment of the rectifier tube. The rectifier tube has
a rating of 2 amperes, which, according to its
manufacturers, is conservative; the unit, when
operating under normal loads, should therefore
have a long life. The filter circuit in this device,
besides the usual electrolytic condenser, contains
a 4-henry choke to assure complete elimination
of hum. A calibrated rheostat to control the
output is connected between the tube and filter
system and the meter scale on the front panel
enables the user to adjust the unit accurately
and with ease. A six-foot cord with a pendant
switch is supplied to control the a.c. input.
YOU WON'T RECOGNIZE THE STORAGE BATTERY
A LL the units listed in Table I are grouped
** there because they provide a source of A
supply by utilizing a rectifier and filter system,
while those of Table II combine a storage
battery and trickle charger. There are many
radio users who are convinced that the ideal
A-socket power unit is one that is innocent of
liquid of any sort. An unfortunate experience
with the old storage battery may have instilled
this dislike of an A-supply involving liquids.
But as radio has developed and the inevitable
and fortunate process of refinement has occurred,
ingenious ways have been found to mould the
storage battery into a highly desirable product
indeed. Another(school of manufacturing thought
therefore has worked along these lines. They
have taken the storage battery, designed it
exactly to fit modern radio needs, and in the
process have succeeded in producing a unit
which has none of the disadvantages always
quoted against it. Since any of the two distinct
types of socket-power A units listed in Tables
I and 1 1 supply satisfactory A potential to the re-
ceiver, and differ largely in the electrical means
used to produce the direct current for the tube fila-
ments, whether one chooses one type or the other
is entirely a matter of personal preference.
THE VESTA GLASS ENCASED A-POWER UNIT
This is a combination storage battery and trickle charger combined
with a relay so that its operation is entirely automatic. A distinctive
feature is that the entire unit is enclosed in a moulded glass case so
that all the parts are visible. The list price is $47.50
Storage battery makers, since radio became
popular, have sought to reduce the routine at-
tention demanded by the storage battery. To-
day's battery requires only the occasional ad-
dition of distilled water. Keeping the battery
"up" is automatically accomplished by a trickle
charger. By a study of the demands on storage
batteries used by a wide variety of radio owners,
sufficient data have been collected to accomplish a
storage battery-trickle charger combination which
needs only slight attention.
The principles of operation of this type of de-
vice have not been changed, but this year many
important improvements have been made which
insure satisfactory service and almost entire
freedom from user attention. Unusually thick
plates, especially designed vent caps, built-in
"state of charge" indicators, conveniently lo-
cated controls to vary the charging rate, and
special cell construction to insure long life in
trickle-charging service — all contribute to make
the combination trickle charger and storage
battery a convenient and satisfactory A socket-
power unit.
Let us discuss some of the points of interest in
these devices. The Acme A-power unit, type
APU-6, is designed to supply 8 to 10 tubes. The
battery unit can be charged at two rates: 5 and
ij amperes. This wise provision permits adjust-
ment of the unit to take care of the demands of a
receiver with many tubes, or the lesser
current requirements of a set with
fewer tubes.
The Westinghouse"Autopower" has
much to commend it. Our friends in
East Pittsburgh have combined in a
compact unit both a storage battery
and an efficient trickle charging de-
vice, the latter developed during the
last year. This rectifier, which is the
heart of the charger, is interesting
enough to merit a slight digression
Several years ago, it was found possi-
ble to make a solid body of matter
conduct electricity more freely in one
direction than in the opposite one. This
was the origin of Rectox, the trade
name of the rectifier used in the "Auto-
power" and some units by other mak-
ers, operating under Westinghouse
licenses. The first materials to show
this property offered three times as
much resistance to the passage of elec-
tric current in one direction as in the
other. The present Rectox units, de-
veloped after considerable research,
have increased this resistance ratio of
3 to i to as high as 20,000 to I in the
final units. The life of this rectifier unit
is said to be indefinite.
A special clip on the front of the
"Autopower" makes it possible to ob-
tain three different rates of trickle
charging. In addition, a "booster" rate
can be used to revivify the battery
if the receiver has been used for an
excessive length of time. (One thinks
of the nj- hour continuous Lindbergh broad-
cast of last June!) The unit contains a relay,
which, when the set is turned on, automat-
ically disconnects the a.c. from the trickle
charger and connects it instead to two leads
terminating in a plug on the side of the "Auto-
power" unit into which the connecting cord of a
B-power unit is connected. When the radio re-
ceiver is turned off, the relay automatically closes
the trickle-charger circuit and the battery begins
to charge. At the same time, the relay opens the
TABLE II
NAME OF UNIT
WATTS
INPUT
PRICE
MAX. NUMBER
OF TUBES UNIT
CAN SUPPLY
TYPE RECTIFIER
USED IN
CHARGER
SIZE
Lx WxH
Acme A power
_
$35.00
10
Tube
Ilix7x9i
Autopower
Basco A power
22
35
35.00
40.00
10
12
Copper oxide
Tube
11 x6f x9}
125 x 5J x 10
Compo
26
42.50
8
Tube
105 x5j x8}
Exide Radio Power
17
31.90
10
Tube
11 x5,"n x9
Philco A Socket Power (603)
32.50
6
Electrolytic
12! x 9$ x7j
Unipower — AC-6-K
24
39.50
10
Electrolytic
!Hx7&xlO
Universal
—
32.50
8
Dry disk
8ft x 8 x 7J
Vesta A Power
—
37.50
—
Dry rectifier or
9J x 7J x 9j
electrolytic
Greene-Brown
29
30.00
10
Tube
8f x 31 x 10i
32
RADIO BROADCAST
NOVEMBER, 1927
circuit to the B-power unit so that this unit is
automatically disconnected. The "Autopower"
requires no attention except the occasional ad-
dition of distilled water to the battery.
WHAT THE UNITS CONTAIN
THE Basco A-power unit contains in a single
case the storage battery, the rectifier, an
automatic relay (similar to the type just de-
scribed above), an emergency switch, trans-
former, fuses, and a terminal board. The battery
is an all-glass Exide unit with a capacity of 45
ampere hours. It is equipped with colored in-
dicator balls to show the condition of charge.
A thin film of oil on the surface of the electrolyte
prevents undue evaporation and also prevents
spraying and corroding of battery terminals.
This battery has a large water space and the
ordinary user will not have to add distilled water
oftener than every half year. The Basco A unit
is connected to the receiver just as if it were an
ordinary battery and when the receiver is turned
on, the current from the battery flows to the
tubes and at the same time passes through an
automatic relay which closes a circuit and makes
1 10 volts (for your B-power unit) available at a
plug on the side. When you are through using
the set, turn off the switch. The relay automati-
cally opens the B-power unit circuit and puts the
battery on charge. A Raytheon "A" rectifier is us-
ed as the charging rectifier. This rectifier has the
advantage that its rate of charge automatically
decreases as the battery becomes charged. Danger
of overcharging is decreased. The "emergency"
switch mentioned above is used to recondition the
battery after it has stood idleforsome time. Turn-
ing this switch recharges the battery at a high
rate and inconvenience is reduced to a minimum.
A 35-ampere hour battery in a composition jar
with a special cellulose moisture-proof pad on
top of the plates and a paste electrolyte are
features of the Compo A-unit. An eye-dropper
full of distilled water in each cell about every four
months is all the attention the unit requires.
Three rates of trickle charging are available:
0.2, 0.4, and 0.6 amperes.
The Exide model jA 6-voIt A-power unit is
designed to supply constant voltage direct cur-
rent for the operation of the filaments of the
tubes in any standard radio set. It comprises a
storage battery and trickle charger with three
taps, each affording a different charging rate.
This rate depends, of course, on the number of
tubes in the receiver and the number of hours the
set is used. The battery is a standard Exide unit
of excellent design and construction and con-
tains ample space for excess electrolyte over the
tops of the plates, thus making necessary the
addition of distilled water only once or twice a
year. The makers recommend it be used with the
Exide master control switch which contains an
extra plug for the a.c. supply for a B-power unit.
The unit has a visible charge indicator consisting
of two small colored balls so that the condition of
the battery can be told at a glance. The entire
unit is contained in a nicely finished sheet steel
enameled case, fitted with two carrying handles.
The Philco A socket-power unit also affords a
dependable source of filament potential. Philco
has refined this unit in many ways during the
last year to make it entirely fool-proof and eco-
nomical in operation. The model 603 A power unit,
listed in Table II, consists of a high-efficiency
transformer and rectifier with a battery espe-
cially designed for trickle charging service. The
battery has unusually thick plates and separators.
Spray-proof construction, preventing the leakage
of electrolyte from the battery, and the built-in
state-of-charge indicator, are two important im-
provements. These heavy plates and separators
insure long life and freedom from the danger of
internal short-circuit. Without the built-in
Philco indicator there would be no simple means
of determining the condition of the battery ex-
cept through the use of a hydrometer and when
it is used there is always the possibility that some
acid will be spilled, incurring the righteous wrath
of the housewife. Special vent-caps have been
A PHILCO UNIT
This Philco unit incorporates several interesting features among which are a visible indicator of the
•state of charge of the battery and special vent caps on the battery which absolutely prevent any
.acid from leaking out of the battery. These vent caps do not have to be removed in order to add
water to the battery
incorporated in the Philco units which make
possible the addition of water to the battery
without removing them. And water need not be
added to these cells oftener than twice a year.
Water will flow down these vent-caps, but it is
impossible for any of the enclosed acid to leak
out. In normal operation the vent-caps need
never be removed. Philco units employ an
"economizer" which permits the user to adjust
the charging rate to the lowest current consump-
tion which will, at the same time, keep the bat-
tery properly charged as shown by the visual
indicators. By using the lowest possible rate,
gassing of the electrolyte is prevented, and this re-
duces the frequency with which water need be
added. Three charging rates are available with a
"booster" rate for emergency use. The batteries
are in a glass container. Philco units can be had
for operation on 25- 30- 40- 50- or 60- cycle a.c.
Type A6o3 is designed to supply up to six tubes
and type A-36 is designed to supply up to ten
tubes. The latter type contains a dry trickle
charger which provides three rates: 0.25, 0.5.
0.26 amperes and a i.o-ampere rate for booster
service.
The Unipower type Ac-6K provides, accord-
ing to its makers, three unique features. First, a
"Kathanode" cell construction which insures
long battery life; secondly, an automatic cut-off
in the rectifier cell which suspends charging
if the user fails to add water when necessary, and
third, five charging rates with a high rate of ij
amperes — meeting the requirements of all grades
of receivers.
In the " Kathanode" design, porous glass wool
mats are fitted against the positive plates to
prevent the shedding of active material which
frequently occurs if the battery is overcharged.
The glass mats, by capillary action, draw fresh
acid to the plates, increasing efficiency. The Uni-
power, cased in rubber, contains three " Katha-
node" constructed battery cells, a rectifier cell,
a transformer, as well as the essential switches,
terminals, and connections. All these cells are
watered at once and the rectifier is designed so
that when the level of electrolyte exposes the
tops of the cell plates, the charging current is
automatically cut off until water is added. The
makers feel this safeguard is essential to the
proper operation of the battery. On the front of
the unit, a dial regulates the charging rate, which
ranges from 0.25 to 1.5 amperes in five steps.
A Rectox dry disk rectifier is used in the Uni-
versal A-power unit. The 36-ampere-hour battery
is assembled in a three-compartment glass jar
with mounted hard rubber covers. This A-power
unit has a visible state-of-charge indicator, and
the whole device is supplied in a steel container.
One of the first battery-trickle charger com-
binations received in the Laboratory in which
glass was the container was the handsome Vesta
A-power unit. Vesta now makes two A-power
units, one containing an electrolytic trickle
charger and the other a dry trickle charger. A
visible charge indicator shows the state of the bat-
tery; when the three colored balls float at the top
of a small compartment, the battery is fully
charged and as the charge decreases, one ball
after another gradually sinks to the bottom of
the compartment. The Vesta unit has a socket
into which the a.c. plug for the B socket-power
unit may be plugged.
So the A-power devices of 1927 look and per-
form very differently from the indiscriminate
units with which the radio user of some years
ago was content. If a variety of A-power devices
are offered the purchaser and he does not know
what type to use, he should ask his local dealer to
install them in his home so he can easily choose
the one which best fits his own needs and his
local conditions.
Rtl
C2
R4
R7
L3
C1
R 12 I I I Z RADIO BROADCAST Photograph
(UNDER COIL)
A NEW BROWNING-DRAKE RECEIVER
The new Browning-Drake receiver shown above is to be described constructionally next month. It has been designed for complete
a.c. operation although batteries may be used if desired. This first article discusses the various a.c. tubes suitable for the purpose
A Discussion of the New A. C. Tubes and How They May
Be Incorporated in a New Design Browning-Drake Receiver
WITH the availability of really good a.c.
tubes, another and important step
toward the ideal radio set is made.
With the a.c. tube, no storage battery or A-power
unit is required. All that is necessary is merely
a compact little transformer for decreasing the
line voltage to a suitable operating value. As
far as actual performance is concerned, the new
a.c. tubes are essentially the same as the well-
known 20I-A or JOI-A type tubes. The person
with a set equipped with standard tubes will
not improve the performance of his set by chang-
ing it over for a.c. tube operation. If his storage
battery, charger, and tubes are in good condi-
tion, there is nothing to be gained by such a
change. If, however, the batteries have about
run their useful life, or if the charger has died of
old age, the new tubes offer a number of worth-
while attractions to the home constructor. First,
they open new fields for experiment; second,
they enable him to build a completely lamp-
socket operated receiver for less money than a
battery operated receiver with its associated
storage battery and charger, and at the same time
there results a receiver somewhat simpler to
maintain.
Once a few of the little tricks of the use of a.c.
tubes are acquired one will have no difficulty in
constructing any of the popular circuits for a.c.
operation or in replacing old tubes in any
standard receiver with new a.c. tubes. Perhaps
the best way of acquiring this knowledge is to
carefully follow the details in connection with
By JAMES MILLEN
the construction of some popular circuit for use
with the new tubes. With this in mind, we have
selected the Browning-Drake as one of the most
popular receivers which has been described in
past issues of RADIO BROADCAST, and have re-
designed it not only for complete a.c. operation,
but also to incorporate the latest ideas on layout,
audioarsplification, and other slight modifications
of the original Browning-Drake circuit. Further-
more, the set has been so designed that it may, if
desired, be wired for battery operation where the
constructor is not so fortunately situated as to
have a.c. on tap. The photograph gives an
idea of how the completed receiver looks. Com-
plete construction data on this set will be given
in the next article. In this article we will consider
some of the general problems involved in the
use of a.c. tubes. First of all let us consider the
different a.c. tubes available for all but the last
audio stage. The last audio, or power tube, be
it of the 112, 171, or 210 variety, may be oper-
ated on raw a.c. just as well as on batteries. No
special a.c. tube is required, therefore, in the
last audio stage.
It will be seen from the table on the next page
that the a.c. tubes may be divided into two gen-
eral types, i. e., those using a low-voltage high-
current filament, and those having a separate
heater element. The heater type tubes are better
suited as detectors than the filament type, but
either type are about equally well suited as radio
and audio amplifiers. Since the heater tubes are,
in general, more expensive and have shorter lives,
it is advisable to restrict their use to the detector
socket.
The different filament heating transformers
available are mostly designed for direct opera-
tion with the RCA-Cunningham tubes without
the use of rheostats or other resistors. The volt-
age taps on some of the transformers available
at present are:
MANUFACTURER
Amertran
Dongan
General Radio
Modern
National
Silver-Marshall
Thordarson
TAPS (IN VOLTS)
.5,2.5. 5-0
.5. 2.5, 5.0
.5, 5-o, 7-5
.5,2.5, 5.0
.5, 2.5, 5.0
.5,2.5, 5-o
•5, 2.5, 5.0
2,
When a.c. tubes of other manufacturers are
used with transformers having the proper taps
for the RCA-Cunningham tubes, special rheo-
stats made by General Radio and Carter should
be used in the low-voltage transformer leads.
When tubes of the Armour-Van Home type are
used throughout, then two short lengths of re-
sistance wire with a total resistance of about o. I
ohms should be inserted in the leads to the
detector and audio amplifier tubes so that they
operate at a slightly lower voltage than the radio-
frequency amplifier tube. Several manufacturers
make special resistors for just this use.
Where the Kellogg tube is used only as a de-
tector, the 2.5-volt filament transformer winding
34
will be found just right. Where Kellogg tubes are
used throughout, then the 1.5- and 2.5-volt wind-
ings should be connected in series (that is, so
that their voltages add rather than subtract)
to give 4 volts which may be dropped down to the
desired 3 volts with a suitable rheostat or fixed
resistor. The filament voltages required by any
of the tubes are far from critical and the tubes
will be found to perform excellently with voltages
considerably below the rated values. Operating
the detector at a lower voltage often results in
almost complete elimination of any hum. If
the heater voltage of a uv-22y detector is exces-
sive, the set will cease to regenerate, and, in fact,
practically stop operating. Generally, about 2.2.
volts seems to work best with the 22y's when used
as detectors and a six-inch length of wire from
an old-ten ohm rheostat, in series with one of
the 2.5-volt transformer leads, will give this lower
voltage.
The 1.5- and z.j-volt transformer windings
should not be center-tapped as potentiometers
located close to the tube sockets are necessary for
the best results. The 5-volt winding for the
171 or the 7. 5-volt winding for the 210, however,
may just as well have a center tap and thus
eliminate the need for one potentiometer. The
detector and the power-tube filament circuits
should be wired with No. 18 equivalent rubber
covered twisted wire. The proper size wire for the
radio and first audio stages, containing high-
current tubes, may be determined by estimating
the total current drawn by these tubes from the
table of characteristics and then selecting a wire
that will carry such a current from the table
below. In the case of the Browning-Drake re-
ceiver using RCA tubes, No. 18 may be used,
but if the Van Horne-Armour type tubes are
used, then No. 16 will be necessary. The follow-
ing table gives the current-carrying capacity of
rubber covered copper wire:
WIRE SIZE
14
16
18
20
CURRENT
1 1 amperes
6
3
I.J
THE R. F. AMPLIFIER
CITHER the heater or the filament type of
•^ tube will work well in the radio stages, but
because of its longer life, lower cost, and simpler
connections, the filament type is generally to be
preferred. There is, however, one real advantage
that the heater types have over the filament
types when used with some cir-
cuits, and that is lower inter-
electrode capacity, which often
facilitates neutralization. The fila-
ment type a.c. tube may be
employed in the r.f. stage of a
Browning-Drake receiver with
materially improved results over
those obtained with the customary
199 type tube.
While frequently no negative
grid bias is employed on the r.f.
tubes in a battery operated re-
ceiver, the use of this bias is es-
sential with the a.c. filament type
tube. This biasing voltage may
be obtained from a C battery or
RADIO BROADCAST
by utilizing the voltage drop across a suitable
resistor which can also provide the bias for the
first and second audio-frequency stages.
The optimum r.f. tube plate voltage for mini-
mum hum does not seem to be at all critical and
the 6-5-volt tap on the average B supply unit
gives as good results as any, with less tendency
for the radio-frequency stage to oscillate than
when the go-volt terminal is used. The C bias
on the r.f. tube should be a little more negative,
for a given plate voltage, than on the a.f. stages.
The use of a somewhat lower plate voltage on
the r.f. tube than on the a.f. tubes permits the
use of the same C voltage on both the audio-
and radio-frequency tubes.
The use of a.c. tubes and a B power unit make
two of the forms of volume controls considered
more or less standard with battery operated
receivers — the r.f. filament rheostat and the
variable series resistor in the r.f. plate circuit —
unsuited for the electric receiver. There are,
however, at least two other systems of volume
control which will give satisfactory results. One
is a variable antenna coupling coil, and the other
is a variable resistor across the primary of the
r.f. transformer. By this means it is possible to
control the volume by varying the r.f. input to
the detector circuit.
A potentiometer across the filament circuits
of both the radio and first audio stages must be
employed. As the voltage is low, this unit may
be a 30-ohm rheostat with a third connection
made to the "open" end of the winding. As this
potentiometer may, from time to time, require a
minute change of adjustment, it is well to locate
it in some convenient place on the sub-panel.
The potentiometer should not in general be
mounted on the front of the panel, as for best
results it must be hung directly across the fila-
ment leads at about an equal electrical distance
from all the tubes. The adjustment of this poten-
tiometer is quite critical, and a very slightly
different setting is frequently required at night
than during the day in order almost completely
to eliminate all the hum — and the hum can cer-
tainly be reduced to a very low order if the re-
ceiver is carefully constructed and adjusted.
A. C. TUBES IN THE AUDIO AMPLIFIER
NOVEMBER, 1927
of the ux-226 (cv-^2(>) tubes with 90 volts on
the plate, the grid bias should be adjusted until
the drop across its terminals, as measured with a
high-resistance voltmeter, is about 6 volts. In
the case of the Browning-Drake receiver to be
described in detail next month, a fixed 5OO-ohm
wire-wound resistor is used to obtain C bias and
this value of resistance is just right. Any of the
several different forms of audio amplification may
be employed with excellent results.
Where the grid bias for several stages is ob-
tained by taking the voltage drop across one re-
sistor, as in this case, then the use of a "grid
return filter" in each stage is recommended and
such filters have been used in the a.c. Browning-
Drake receiver. These filters merely consist of a
o. i-megohm resistance and a i-mfd. condenser
connected so as to prevent any of the audio-
frequency currents from flowing through the
grid bias resistance. In the last or power stage,
the 171 is recommended as the tube best suited
for home use. A 2ooo-ohm wire-wound resistor
will automatically provide the proper grid bias
for this tube regardless of the plate voltage,
within reasonable limits. A loud speaker pro-
tective device to eliminate the direct current
from the loud speaker windings should be em-
ployed.
THE DETECTOR
\ A /HILE either form of a.c. tube may be used
* 'as a detector, the uv-22y type of heater
type tube has several advantages over the fila-
ment type. First, the a.c. hum can be, for all
practical purposes, entirely eliminated. The
hum from a filament type a.c. tube is not what
could in any way be termed objectionable, yet,
it is there. The heater tube may be used with
either a grid-leak condenser arrangement or with
C bias, whereas, the 226 type of tube, while it
will function quitewell witha grid-leak condenser,
is better suited for plate rectification. Plate recti-
fication, however, is not as sensitive as the grid-
leak condenser arrangement and its use in con-
nection with an all a.c. operated receiver also
leads to other complications. The Kellogg a.c.
tube may be used as a detector with excellent
results.
In using the heater type tube as a detector,
AS THERE is nothing to be gained by the either a negative or a positive bias of about 40
* * ncp r\f fhp mnrp pvnpticivp hpatpr t\/np tiihp \;r\ltc nr art Qhriiil/i HP 'irMiltp/l tn tVin hpitur n!p_
use of the more expensive heater type tube
in the first audio stages, the filament type is to
be recommended. As already mentioned, the one
potentiometer and grid bias resistor serves
both the radio and the audio stages. In the case
A. C. TUBES
Heater Type
NAME
Ef
If
Ip
RP
Mu
Gm
Ep
E* 1
0-327
2-5
•75
4.2
8600
7-8
905
90
-45
UY-227
2-5
.65
3-5
10350
8.7
860
90
-4-5
McCullough
3.0
.0
4.2
9400
8.6
870
90
-45
Sovereign
3.0
• 5
4.6
9100
8.5
935
90
-4-5 1
Marathon
5-5
.0
4.2
9500
7-3
775
90
-4-5 !
Arcturus
15.0
0-35
3 '
12150
10.5
870
90
-4-5 I
Magnatron
2-5
1.50
4.6
8700
9-3
1070
90
-4-5 i
Filament Type
cx-326
•5
1.05
4.6
9000
8.5
935
90
-4-5 i
UX-226
• 5
1.05
4-4
9150
8.7
950
90
-4-5 1
Armor
.0
2.4
3.8
I I2OO
7.8
690
90
-4-5 i
Van Home
.0
2.0
44
9000
9.0
IOOO
90
-4-5
CeCo
5
1.05
2.8
14200
9.2
730
90
-4-5
Magnatron
-5
1.05
4.0
10800
8.8
830
90
-4-5
Ef = Filament Volts lp = Plate Current
EP = Plate Volts Rp = Plate Resistance
EK = Grid Volts Mu = Amplification Factor
If = Filament Current Gm = Mutual Conductance
volts or so should be applied to the heater ele-
ment by means of a potentiometer. In some in-
stances a positive bias seems best and in others,
a negative, and either of these biases are readily
obtainable from the 4O-volt tap supplying C bias
to the power tube or the plus
45-volt tap for the detector. The
adjustment of this bias voltage
is not at all critical, and once
set, will require no further atten-
tion. In fact, a fixed resistor with
center tap, such as the type 438
General Radio, will serve the pur-
pose excellently. This resistor is so
designed as to mount directly on
the terminals of the detector tube
socket.
In a second article which will
appear next month, constructional
details and adjustment sugges-
tions on the a.c. Browning-Drake
receiver will be given.
» »
Our Readers Suggest
9 9
C'p'HESE two pages' are reserved for the many in-
-I teresting contributions from our readers, some of
whom may have run across many ingenious , ideas in
the operation of broadcast receivers and accessories.
These pages will appear regularly in RADIO BROAD-
CAST and all contributions accepted will be paid /co-
at our regular rates. In addition, each month, a prize
of }io will be paid for the best contribution published.
Contributions are especially desired about changes
and simple adaptations dealing with ready-made re-
ceiving sets and accessories. Those who have made
their own receivers are, in a sense, experts, and are
usually well aware of the possible improvements in
the use of their own equipment. Each contribution will
be published as the writer prepares it, telling how he
solved his problem, to which will be added some com-
ments from the staff. Address ail contributions to The
Complete Set Editor, RADIO BROADCAST, Garden
City, New Torf(. — THE EDITOR.
Rewiring an Atwater Kent Receiver
for A. C. Tubes
THERE seems little doubt in the minds of en-
gineers that the alternating-current tube will
eventually find a place in the majority of radio
receivers. It is in anticipation of this eventuality
that RADIO BROADCAST has already devoted
considerable space to the problems of A battery
elimination and the characteristics of a. c. tubes.
We are interested in the following description of
how a reader, Henry March, of New York, altered
a popular type of receiver for a. c. operation,
necessitating few and simple circuit changes. He
writes:
"It has been my pleasure to discover that the
Atwater Kent Model 35 receiver can be easily
adapted to a. c. operation through the use of a. c.
tubes. I presume that the same simplicity of con-
version holds true for many other receivers — a
fact that may interest your readers.
"I rewired my receiver for Arcturus tubes (type
28 amplifier, type 26 detector, and type 30 power
tube), choosing these tubes because of the fact
that they plug into the four-prong socket which
is standard equipment on practically all receivers
wired for storage battery tubes. Thus no addi-
tional filament wiring or special sockets are
required — greatly simplifying the necessary
changes, which are illustrated clearly in the ac-
companying diagrams. Fig. i shows the original
wiring in the receiver. The parts of the circuit to
be changed have been drawn in heavy lines.
Fig. 2 shows the circuit with the changes made.
"All grounds have been eliminated from the fila-
ment circuit. The lower terminals of all r. f. and
a. f. secondaries, excepting that of the power
tube, have been grounded. The detector grid re-
turn to the potentiometer has been eliminated,
and the return is now effected through a 4.5-10
Q.o-volt C battery, positive to the grid. Detector
C minus is connected to the B minus post. The
plus terminal of the main C battery also con-
nects to B minus. Minus 1.5 C battery is
STAFF COMMENT
AS OUR contributor suggests, a. c. tubes of
this type (the characteristics of the Arc-
turus tubes are given on page 34) may be used
in many receivers after relatively simple changes
have been made. However, the operation of alter-
nating-current tubes is essentially a complicated
proposition, and it is recommended that readers
secure specific information on the changes re-
quired in their particular receivers before pro-
ceeding with the alteration. This information can
generally be secured from the manufacturers of
the tubes selected, and from the technical de-
partment of this magazine.
However, a few generalities may be laid down
Ant.
Gnd
C-1.5
B+ 67Sj C-22H. B+ 180
FIG. 2
grounded (supplying the r.f. tubes), while 22.5
minus runs to the power tube in the usual manner.
A Centralab modulator is connected across the
secondary of the first audio transformer as a
volume control.
"The a. c. filaments are operated from an Ives
step-down 'toy' transformer (type 204) at the
14.5 volt tap. All plate voltages remain the same
as in the d.c. set, excepting that 180 volts is
applied to the output power tube, increasing the
possible undistorted power output of the re-
ceiver."
Ant.
Gnd.
FIG. I
for the adaptation of d. c. receivers to a. c. opera-
tion. Much of this is covered diagramatically in
the accompanying circuits.
All grounds must be eliminated from the fila-
ment circuit. Ground all secondaries (filament
side) having the same negative bias. A bias of
minus 1.5 to 3 volts is generally applied to all r. f.
grids.
Run the two filament wires as close together as
possible, lacing or twisting them when conve-
nient. Be sure that all plus filament posts are
connected together. Connect minus B to what
previously were the positive posts. Connect the
r. f. and the a. f. C plus and the detector C
minus to B minus.
Eliminate all filament rheostats and potenti-
ometer r. f. controls. It is not practicable to use
these forms of volume and sensitivity control
with a. c. tubes. With the potentiometer device,
sensitivity is governed by varying the bias on
the r. f. tubes which, with a. c. tubes, would in-
troduce hum at certain adjustments. A 250,000-
ohm variable resistor connected across the r.f.
secondary preceding the detector tube is a pre-
ferred volume control.
Receivers wired for four-prong base a. c. tubes
can be used with d. c. tubes at any time, merely
by substituting an A battery for the transformer.
No other changes are necessary for d.c. opera-
tion of such a receiver.
36
0 + 90V.
1
S
Minus lead inside
0 + 45V.
'i
of Eliminator
D
'U.
| 1000 Q
1.0 mfdT"
* -o c
(40V. at 40m A.)
FIG. 3
C Bias from a Mayolian Socket
Power Unit
B -SOCKET power units in the future will
undoubtedly incorporate extra resistors
making it possible to secure C bias for at least
the power tube. It is not difficult to incorporate
this feature in the average power unit along
the lines described by a contributing reader.
James J. Corrigan, of Des Moines, Iowa:
"I have a Mayolian B power unit, the utility
of which I have doubled by adding an extra re-
sistance and bypass condenser. The drop across
the resistance supplies the C voltage to my power
tube.
"The lead to the negative binding post is
broken at 'X' inside the case (Fig. 3). A 1000-
ohm, two-watt resistor is connected in the break
and by passed witha i.o-mfd. condenser. The post
marked B minus connects as usual to the receiver,
while the C bias voltage is tapped in the elimina-
tor side of the resistor. A forty-volt C battery
is supplanted by this means.
STAFF COMMENT
T'HIS is a simple and practical method of C
battery elimination, readily applicable to all
eliminators giving voltages, under load, in excess
of 180. The C voltage is necessarily subtracted
from the B voltage, and the compromise is some-
times undesirable. If your eliminator has a no-
load potential of about 250 volts, C elimination
is quite worth while. Many B-socket power units
fill the bill. Among them are: Kodel, Burns,
Greene-Browne, Kellogg, and General Radio.
However, the use of a fixed resistor is not
recommended as it is almost impossible to secure
the right bias. It is suggested that a variable
resistor, connected as shown in Fig. 4, be used
instead. Amsco Products manufacture a zero to
2ooo-ohm variable resistor known as a Duostat,
made especially for this purpose. It is equipped
with two variable arms, making it possible to
secure two C bias potentials, one for the power
tube and one for the other a. f. tubes Each arm
of the Duostat must be bypassed with a i.o-
mfd. condenser. Other variable 2OOO-ohm C bias
resistors are made by Carter and
Electrad.
A rough adjustment of the bias
potentials can be made by ear.
However, a much more scientific
RADIO BROADCAST
job can be done with the aid of a small milli-
anipere meter, reading up to 25 milliamperes.
This should be placed in the plate circuit of the
tube on which the bias is being adjusted. The
variable arm is moved until, on a loud signal, the
needle is motionless, or practically so. Any
movement of the needle is an indication of dis-
tortion. If the needle kicks up, turn down the
resistance (lowering the C bias); if the needle
kicks down, increase the resistance.
This careful adjustment is generally made only
on the output tube. The meter is connected in
series with the loud speaker, or the primary wind-
ing of the output device if such is used. As the
power handled in the preceding tubes is generally
small, a rough adjustment by ear is adequate.
Getting High Notes from the
Resistance-Coupled Set
1HAVE a Ferguson Model 12 receiver, in which
were incorporated three stages of resistance-
coupled amplification. I operated this set in con-
junction with a Western Electric 540 AW cone
loud speaker. While the tone quality of this com-
bination was distinctly superior to that of the
average set, there was, at times, a disconcerting
rumble on low notes, which quite counteracted
my pleasure in the unusual reproduction of these
-0 + 180V.
0+ 90V.
0+45V.
O- B
0-J2T
0-X
FIG. 4
low frequencies. There seemed to be a resonance
point in the output system in the neighborhood
of fifty cycles. A friend of mine has an impedance-
coupled set, which, while quite free from the
particular disturbance I mention, is distinctly
partial to higher notes. It occurred to me that a
compromise between resistance and impedance
coupling might be ideal in my particular case.
Upon the advice of an experienced fan, 1
removed the coupling resistor from the second
audio stage, and ran two wires from the prongs
to the primary of an old audio-frequency trans-
former. 1 left the grid leak exactly the same as
when resistance coupling was used (See Fig. 5).
The result is most gratifying. There is no
UX201-AorCX301-A UX201-Aor
I UX240or,CX340 n CX301-A'.
Choke
Coil
UX 171 or
CX371
NOVEMBER, 1927
longer any rumble on the troublesome notes, and
it seems to me that the speaking voice is cleared
up a bit ... it is more natural. Also there is a
slight improvement on the higher notes such as
are occasionally reached by sopranos and violins.
A certain vague sense of muffled sound has alto-
gether disappeared.
STAFF COMMENT
THE experimenter writing the above experi-
ence, Frank Wendell, of Los Angeles, has
accomplished what is being done nightly in the
large broadcasting stations, where the process of
balancing the scale of frequencies is known as
"equalization." With outside or "nemo"
pickups, transmitted over landline to the broad-
casting station, certain frequencies are trans-
mitted with less fidelity than others, and the
boosting up of the delinquent tones is accom-
plished in much the same manner as our corres-
pondent brought up his high notes.
The average cone loud speaker in comparison
with the average horn, is much better on the
low notes. The same holds true of the resistance-
coupled amplifier as compared with other am-
plifying systems; but this type of amplifier also
has a distinct cut-off on high frequencies. The
combination, therefore, is one that favors the low
frequencies — often to such an extent that there
exists the low-frequency rattle referred to.
In the case under consideration, the high notes
have been boosted by substituting a reactance
in place of the resistance. It is probable that the
response curve of the reproducing system has
been leveled out a bit. That is, all frequencies
reach the ear with a closer approach to their
relative amplitudes or volumes.
Taking out a coupling resistor and substituting
a comparatively low inductance choke coil will
always increase the amplification of the higher
notes more than it increases the amplification of
the low notes. The lower the inductance of the
choke coil, the more will be the difference. There
is no reason why the average broadcast fan
should not improve reception by "equalizing"
his receiver in this manner. A resistance-coupled
amplifier (in any receiver) most easily lends itself
to changes of this nature.
VARYING THE AMOUNT OF EQUALIZATION
AN ORDINARY amplifying transformer is
probably the most readily available form
of inductance or choke coil. The primary, in the
case of the average transformer which may be
on hand, should be used.
The high notes will be brought up most if only
the primary of the transformer is used. There will
be less difference from straight resistance coup-
ling if the secondary is used. Different degrees
of equalization will be obtained if the primary
and secondary are connected in series, with, first,
the grid and plate posts strapped (using the B
and F posts as terminals) and, secondly, with
the grid and B posts strapped.
The grid leak of the tube out-
putting to the choke coil is not
touched but the bias applied
through the leak should be increased
by about 4.5 volts.
Connect speaker
to set through
—o output device
- A «• -B +C -9 -40 +180
FIG. 5
The Listener's Point of View
LISTENERS— GUESTS OR CUSTOMERS
A
SIR:
I READER at Long Beach, California,
addressed us not long ago as follows:
May I be permitted to call to your attention
the excellent and timely article appearing on
page 1 5 of Radio News for July, 1927, entitled
"The Fly in the Ointment," by one Nellie
Barnard Parker?
A great many listeners hereabouts were struck
by the miserably poor taste displayed by the
writers of the "can't-the-announcer-be-choked"
and the "sprayed-with-petroleum" telegrams
to which the writer refers; and one of us, at least,
was equally impressed by the sportsmanship dis-
played by the announcer in reading such tele-
grams to us at all. 1 think that you will agree with
the author of the article in question that '. . .
when a company has spent thousands of dollars
to broadcast a program, it has bought the right
to let you know who your host is and what it
has to sell.'
I, for one, would like to see a similar stand
taken by RADIO BROADCAST; and I believe that
such a stand, in your columns, would more nearly
present the average "Listener's Point of View"
than does much that now appears there.
G. I. RHODES.
Here, indeed, was an invitation for your de-
partment editor to adopt a policy — and if there
is anything an editor, of any variety, keeps an
eagle eye out for, it is "policies." Policies are
what enable him to get his stuff written. So we
swam into the article, a most entertaining one.
The specific fly in the ointment complained
of was an incident in connection with the broad-
casting of opera by KFI and KPO last season, as
the indirect advertising donation of a certain
petroleum corporation.
The opera broadcast was unquestionably one
of the outstanding musical treats af-
forded West Coast listeners that sea-
son. In the intervals between the acts
the announcer read a number of
telegrams of commendation and ex-
plained, with some precision, just who
was financing the broadcast. "And
then," says the author of the article
referred to, "right out of the sky,
came the fly in the ointment! A man
wired in: 'We are enjoying the pro-
gram but can't the announcer be
choked off and let us have opera with-
out telegrams and advertising?" And
pretty soon another 'guest' wired his
objections against being 'sprayed
with petroleum' while he listened.
Clever, yes, but it struck one listener
at least that when a company has
spent thousands of dollars to broad-
cast a program, it has bought the
right to let you know who your host
is and what it has to sell."
That was the case in question. We
are ha»rdly fitted to pass on its merits
since we didn't hear the broadcast.
It is quite possible that the number
of telegrams read and the amount
of advertising dished out were en-
tirely within the bounds of reason.
In fact this seems probable if there
were but two unfavorable com-
ments on it. As the writer points
out with some show of logic, the
By John Wallace
reading of a telegram of commendation sug-
gests the sending of them to other listeners,
and if a large number is received "they are per-
manently bound and the next time there seems a
possibility of interesting some firm in paying
the fiddler for an expensive program, this bulky
volume is brought forth." Thus the telegram
reading may in some cases react finally to the
listeners' benefit.
But departing from this particular instance
wherein the adverse criticism may not have been
entirely warranted, the writer goes on to general-
ize and takes the stand that adverse and de-
structive criticism of a better-than-average
program is never justifiable. This, it seems to us,
is stretching the point to absurdity. She says:
You are free to steer your airship where you
please, casting out your line knowing that there
are just as good tunes on the air as ever were
caught. Such being the case, why send in thought-
less messages to mar the perfect pleasure of your
host? Let him sing his little solo without having
the anvil chorus crab the act!
It is only fair to say that those who criticise
the big programs are in the minority, but there
are just enough of them to destroy that fine
edge of joy and what-a-good-boy-am-I feeling the
sponsors and operators have.
Every graduate operator of a radio is a super-
critic of the air. Like an insect of the ether, the
true radio bug goes sniffing through the air with
his little feeler; when he "contacts" with some-
thing he likes, he settles upon it with a pleasant
little hum. But if it pleases him not, he is liable
to plant a sting, if he is that kind of a bug.
How much nicer it would be if he would remem-
ber that the sponsors and announcers are just
big boys trying to get along! They are not inocu-
lated against praise. It takes on them beautifully
and they break out with brighter and better
THE SANKA AFTER DINNER COFFEE HOUR AT WEAF
Heard over this station on Tuesday evenings at 7:30. They should re-
ceive some kind of reward for getting the maximum number of words
into the title. Anyhow, here are the performers
programs. They invite and welcome constructive
criticism and helpful suggestions, but mere
"razzing" and discourtesy never fanned a gener-
ous impulse into flame. Just be human, kindly
and courteous, remembering that the announcer,
like the fiddler, is doing the best he can.
And don't be the fly in the ointment!
We quote this writer at such length because
hers is a point of view that is all too widely
held, namely: that the purveyor of radio pro-
grams is your host and that all the rules for
polite drawing room conduct should operate
in your attitude toward him.
When a man invites you to his home for dinner
he does so as a private individual, and however
burnt the potatoes may be, it is not common
politeness for you to throw them at him. But if
the same man sets up 'a restaurant and you
happen in there to eat, you are perfectly justi-
fied in calling him all sorts of names if his chef
has too highly seasoned the lobster tbermidor.
He has removed himself from the role of private
individual and become a purveyor to the public.
He has become, to use the word loosely, an artist,
and by universal assent any and all of the prod-
ucts of the artist are open to criticism and he
may not protest. By his very act of setting him-
self up as an artist he tacitly agrees to submit to
any opprobriums that the citizenry feels inclined
to hurl at him. This is true of every sort of artist
— chef, singer, movie producer, poet, electric re-
frigerator manufacturer, sculptor, street cleaner,
painter or sponsor of broadcast programs.
If a man wants to buy himself a box of paints
and surreptitiously records on canvas his im-
pression of the cherry tree in the back yard or
sunset on the drainage canal no one has a right
to comment on the way he does it. It is entirely
his own affair as long as he keeps it
his own affair by contenting himself
with hanging the finished works on
his own wall. But if he starts sending
his pictures to the exhibition galleries
he, by that gesture, professes himself
to be an artist, and his work to be
art; and he automatically becomes
perfectly legitimate meat for anyone
to pounce upon who cares to.
If what he exhibits as art is inex-
cusably bad, the good name of Art
is threatened. And since Art is not
his own private possession but is held
by common consent to be in the cus-
tody of the great unwashed public,
it is incumbent upon that public to
weed out with vituperatives anything
that threatens to cast a smirch upon
it. The commentary that the public
makes is known as Criticism. Criti-
cism may be of many kinds, favorable
or unfavorable, constructive or de-
structive, gentle or splenetic, com-
petent or incompetent. The writer of
the article discussed, and those of
the same misguided frame of mind,
would object to any criticism that
does not fall into the category of
favorable or constructive. This is ob-
viously silly and results from a com-
plete misconstruction of the function
of criticism. Gentle-spirited senti-
mentalists get all hot and bothered
38
RADIO BROADCAST
NOVEMBER, 1927
and are filled with great sympathetic aches when
some public performer gets it in the neck from
a sharp tongued critic. They decry the critic as
mean and lacking in human qualities. But in the
case of a genuine artist their sympathy is wasted.
A true artist doesn't mind adverse criticism —
much; he is his own best judge of whether his
work is good or bad. On the contrary he is
rather stimulated by it. Splenetic or strongly
biased criticism may be far more effective in
egging him on to do better work than soporific
boquets. The only criticism to which he is likely
to object is the incompetent kind — and of this
there is, of course, plenty.
The two critics of the KFI-KPO opera broad-
cast may have been incompetent; they may not
have been aware of all the facts, viz.: that a cer-
tain amount of advertising was necessary if the
broadcast was to pay for itself. As we have said,
we did not hear the program and do not know
whether this reading of telegrams was carried
to excess or not. But not all criticism of radio
programs by minority calamity howlers is in-
competent. A great deal of it is very much to
the point (including, of course, all our own sage
pronunciamentos.)
The fact that a majority of the listeners are
perfectly satisfied with the way any given radio
program is presented does not mean that any
criticism on the part of a few of the minority
is worthless. The oft-repeated phrase about
giving the public what it wants is, at best, just a
phrase. True, some effort is made in this direc-
tion, but the public is not at all sure what it does
want, seldom expresses itself on the subject, and
finally, finds it the course of least resistance to
take what it gets.
The masses continue to be satisfied with what
they are getting until something better comes
along. Then they accept the improvement with
the same placid satisfaction — perhaps wonder
why they were so easily pleased with the old —
but make not the slightest effort to secure further
betterment. It is up to the minority kickers and
mud slingers to secure for them these improve-
ments.
Your average radio listener was perfectly
satisfied with broadcasting as it existed in 1923.
His unimaginative and uncritical mind could
conceive of nothing better. He was getting pro-
grams made up largely of cheap jazz and cheaper
talks. To live up to their views, the advocates
of " throw-away-your-hammer-and-get-a-horn "
would have to argue that things should have been
left for him just as they were. He was satisfied;
his cup of joy was full ; why attempt to overfill it?
BOB CASON AND REBER BOULT
Artists at station WLAC, pianist and baritone
respectively. They call themselves the "Thrift
Twins" for some reason not apparent in the
photograph
But what has happened since then? Programs
have improved and his taste has improved with
them. He has thrown away the cup and has
graduated to the mug, which also is filled to the
brim. Having a mug, will he now demand a
schooner? He will not.
The conclusion that we have been laboring,
somewhat heavily, to reach, is that it is to the
mud slingers and knockers, the minority critics —
or "Flies In the Ointment" — that most of the
credit is due for the rapid strides that radio has
made. Back in radio's dark ages at least fifty
per cent, of every station's time was devoted to
unendurable tin pan jazz. The passive listeners
stood for it. The knockers objected. It was elimin-
ated and the passive listeners found themselves
with fifty per cent, more entertainment for their
money and all through no effort of their own.
Radio has grown up considerably but it still
has a few bad habits hanging over from its in-
fancy. It is up to the knockers to knock these
out. If radio is to be a Bigger and Better man
than it was a boy it is up to the knockers to
pummel it into this new shape. The soft soapers
and dispensers of ointment can do no more for
it than to make it a self satisfied mollycoddle.
Let there be more flies in the ointment!
The British Broadcasting Company
Gets Razzed
*
WE ARE unable to give any very valu-
able dissertation on broadcasting con-
ditions in England, at this distance.
But from what we read there seem to be con-
tinual rumblings in the tight little isle, and most
of them to the effect that the British Broadcast-
ing Company is too highbrow. We have just re-
ceived a copy of a thirty-eight page pamphlet
by one Corbett-Smith flaying the administration
of the B.B.C. A decidedly long-winded affair, it
gets down to points occasionally:
When one sets out to give a radio entertain-
ment, whether music, poetry, drama, speech,
"variety," or anything else, one visualizes (or
should visualize) not the few who are already
educated in some measure to appreciate the best
in these various forms of art, but the vast many
of our people to whom beauty has hitherto been
a closed book — the great mass of our folk who
have never heard good music or noble poetry or
any of our incomparable English literature — and
so who pretend impatiently to disdain these nice-
ties of civilization, as they would call them. . . .
Every single radio program should be so built aiitl
presented as to form a perfect fusion of art, educa-
tion and popular entertainment.
The type of mind which is usually associated
with scholastic education is hopelessly out of
place in radio work. And there is another cause
of the B. B. C.'s failure. It is the born showman
of a very special quality that is needed. The man
with the widest possible range of interests, with
"an accute sense of the inter-relationship of every
kind of activity." Radio entertainment demands
not the depth of the scholar but the breadth of
the sensitive man of the world.
Showmanship, in varying degree, is needed for
every single feature of radio entertainment.
The "superior person" may sometimes scoff;
but that person does not interest us. We have
to compel and to rivet attention. We need, also,
strong and vivid personality. The personality of
the leader of men, not of a cold-blooded corpora-
tion. And we need absolute sincerity, both of
purpose and utterance.
Now the B. B. C. have not begun to appreciate
anything of this. Instead of making a Charles
Dickens their director of programs they have
put in a Matthew Arnold, the apostle of culture.
Dickens enjoyed everybody and everything, even
Fagin and Mr. Murdstone. That was the secret
of his art and of his success. The B. B. C. seem
to enjoy nothing, not even themselves.
It is necessary to emphasize this total lack of
sympathy with the people at large, because it
strikes at the root of the matter. The B. B. C.
are forever vaunting the intensely democratic
character of their service when, in fact, it is about
the most aristocratic business in the country.
The House of Lords is an assembly of plebs
beside it.
Wherein, if Mr. Corbett-Smith's words are to
be taken as true — and he certainly sounds con-
vincing— we see that a government-controlled
monopoly is not one of the best ways of providing
satisfactory radio programs. The point that the
writer pounds in throughout the length of his
diatribe is one which, we think, is well worth
making, namely: that radio's principal service is,
after all, for the masses. The so-called intellectual
class is not interested in radio at all. Its members
do not own receiving sets nor would they listen
to one if it were given them. This is not due
merely to snobbishness; their time is otherwise
occupied, and of other means of entertainment
they have more at their hand than they can
make use of.
But we in the United States have no reason to
fear such a state of affairs as Mr. Corbett-Smith
complains of. Radio stations in this country are
operated essentially for the masses. This is the
natural result of a competitive system which de-
pends for its reimbursement on advertising, di-
rect or indirect. A maximum number of listeners
must be the aim of every station which is not
endowed or privately financed. In fact, here, a
condition exactly the opposite of that alleged to
exist in England is likely to obtain. A majority
of stations, in their devotion to the masses,
quite neglect the upper fringe of listeners. This
is not true of the two score or so better stations.
Careful and intelligent planning has enabled
them to present programs appealing to the widest
possible range of tastes. Their procedure is, first,
to arrange a program that definitely appeals to
the great mass of listeners, and secondly, to
further manipulate it so as to effect a compromise
with the upper crust of listeners.
We, from viewing the subject too closely, are
likely to forget how exceedingly well this has been
done. Take, as an example, the Atwater Kent
Hour. A straight appeal to the masses is made
in the making up of these programs. While the
selections are limited to the classics and to the
opera, it is almost exclusively the sure-fire hits
and tried and true tunes that finally find their
way on to the program. But while the highbrow
may think some of the tunes are banal and over-
worked, they've got him on another score: he
cannot afford to ignore the importance and artis-
try of the performers Atwater Kent employs to
put them over.
ANITA DEWITTE HALL OF KO1L
She is the versatile program director, organist,
pianist, and "Mother Hubbard" of the staff
The R. G. S. "Octamonic" Circuit
How Laboratory Discoveries Were Moulded to Produce the Commercial
Design of a Sensitive and Selective Set— Details of a Striking 1928 Development
THE first article in thisseries(RADio BROAD-
CAST for October) described the concep-
tion and theory of the fundamental
"Octamonic" principle, which obtains a high
degree of selectivity by a function of the vacuum
tube rather than by any special circuit contrap-
tions. It was shown that the super-selectivity
did not impair the tone quality as is the experi-
ence in tuned radio-frequency circuits. The high
frequency of the second harmonic current per-
mits a very sharp resonance curve without un-
duly compromising the side band amplification
which is absolutely necessary for the proper
reproduction of the high-frequency audio tones.
Other points of invention were also discussed,
but it is a long road from invention to commer-
cial design. It is one thing to build a laboratory
model which proves the principle of an idea and
quite another thing to plan the construction of
a radio receiver which will meet all of the com-
mercial conditions encountered in the field with-
out a great many operating controls.
The purpose of this article is to reveal the de-
sign and constructional information which have
been found necessary. These data have been ac-
quired only after a great amount of original
investigations, for there appeared to be little or
no information available on the subject of second
harmonic generation, tuning, amplification, and
detection. The subjects will be discussed in the
order in which they occur in our laboratory note-
book. While the order may appear to be unusual,
the facts were accumulated in just that sequence.
The first study was confined to the harmonic
generating tube. The proper operation of this
tube insures the success of the entire receiver.
The first article showed a C potential bias on the
grid of the harmonic generator — this bias causing
the tube to operate on the lower knee of the grid
voltage-plate current characteristics. This point
of the characteristic gives the greatest amount
of second harmonic energy as the unequal am-
plification between the two halves of the carrier
wave is greatest at this point. However, with the
standard commercial types of vacuum tubes
operating on standard units of B potential such
as 22 volts, 45 volts, or 90 volts, the amounts of
negative C bias required for harmonic generation
do not correspond with the commercial units of
C potential available with the standard C bat-
tery. For instance, the maximum amount of
second harmonic energy appeared to be gener-
ated by a standard CX-JOI-A tube operating on
45 volts plate potential with about 2 volts minus
grid potential. Such a C bias cannot be obtained
conveniently from dry batteries.
Of course, the easiest way to obtain a 2-volt
negative bias on the grid of the harmonic generat-
ing tube is to utilize the principle of an IR drop.
By running the filament return of the tube
through a fixed 6-ohm resistance, a 2-volt drop
may be obtained and if this fixed resistance is
placed on the negative filament lead a negative
2-volt bias is available for the grid. Fortunately
the operation of the second harmonic tube was
not affected by running its filament on 4 volts,
the remaining A battery potential available for
the filament after 2 volts had been extracted
by the fixed resistance for the grid bias. In fact,
By DAVID GRIMES
it was found that the filament of the harmonic
tube could be run much lower than this without
in any way impairing its second harmonic
generating properties. This is explained graphic-
ally by Fig. i which shows the grid voltage-plate
current characteristic of a vacuum tube which
is operated at various filament voltages. The
various filament temperatures materially affect
the upper portions of the characteristic but have
FIG.
little or no effect on the lower knee of the curve.
The filament voltages only affect the saturation
point of the tube.
In the vernacular, this is a fortunate "break"
in design work as it affords a very simple arrange-
ment for the harmonic generator which is very
stable in its performance and exceedingly inex-
pensive. As a matter of fact, a series of tests
shows that the filament voltage of the tube
could be cut down as low as 25 volts before the
second harmonic currents were affected, and the
C bias could vary from i \ to 2 volts. This more
than covers the variation in A battery potential
during the period between full charge and dis-
charge of the A battery. The 45 volt B battery
on the harmonic generator was also found to
be a non-critical factor. Fairly large amounts of
second harmonic currents were generated by this
tube when the voltage had dropped as low as 34
volts or was raised as high as 50 volts.
PROBLEMS IN THE HARMONIC GENERATOR
EXCESSIVE B potentials on the harmonic
generator created an unusual and peculiar
difficulty. There existed a tendency toward
oscillation on the short wavelengths of the input
tuning condenser to this harmonic generator
when the plate voltage was boosted too high.
The source of this oscillation is not obvious and
evaded detection for some little time. One is ac-
customed to expect oscillation in a tube only
when there is a deliberate external feed back
circuit or through the internal electrode capaci-
ties only when the plate circuit is tuned to the
same frequency as the grid circuit — such as oc-
curs in a tuned radio-frequency system. As seen
in Fig. 2, the plate circuit of the harmonic genera-
tor is tuned an octave higher in frequency than
the grid circuit and under these conditions the
well known ordinary oscillation cannot occur.
As a matter of fact the primary of the second
harmonic transformer possesses considerable
effective inductance as the result of the tuning
to the higher octave. The number of turns in
the harmonic transformer primary alone is in-
sufficient to cause oscillation in the harmonic
tube unless the secondary is tuned to the higher
octave. When this is done, there is an increase in
effective inductance over and above the actual
inductance which causes the oscillatory difficul-
ties mentioned, with excessive plate voltages on
the harmonic tube.
The remedy for the difficulty outlined above
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40
lies in reducing the number of primary turns in
the harmonic transformer to such a point that
the effective inductance at the highest com-
mercial voltage will not produce the oscillation
described at the short broadcast wavelengths.
Fig. 3 shows the design details of the tuned
harmonic transformer used for connecting the
output of the harmonic generator to the input of
the detector tube. It will be noted that the
secondary of this transformer has been made
unusually small — much smaller than would be
expected for merely tuning the double frequency
involved. Commercial considerations have con-
trolled the design of this transformer as well.
The general tendency in the modern design of
the radio receiver is to combine as many of
the tuning condensers as possible on one shaft —
exercising the proper care in the balancing of
the condensers and coils so that they will tune
alike for all the broadcast wavelengths. In the
R. G. S. "Octamonic" design, it seemed desir-
able to combine the tuning condenser on the
secondary of the harmonic transformer with the
tuning condenser on the input to the harmonic
generator. The problem is not as simple as the
combining of condensers controlling similar
circuits. The harmonic condenser must always
tune to half the wavelength of the fundamental
tuning condenser in the input of the harmonic
generator. Furthermore, another limitation is
imposed because all available gang condensers
have been designed for tuned radio-frequency
circuits and have therefore equal capacity in all
the individual members of the gang.
This means that the second harmonic trans-
former must be so designed that a standard
o.ooo35-mfd. tuning condenser must tune the
half wavelength band from 100 to 275 meters at
exactly the same settings on the dial as a similar
condenser tunes the fundamental coil for the
respective corresponding fundamental wave be-
tween the 200 and 550 meter broadcast band.
A consideration tuning formula shows that this
can easily be accomplished if the inductance
of the secondary of the harmonic transformer is
made exactly equal to j of the inductance of the
fundamental tuned secondary on the input to
the harmonic generator tube.
SOURCES OF SELECTIVITY
ANOTHER fortunate "break" aids in the
ganging of these two condensers, as one of
them is extremely sharp in tuning while the other
is relatively broad. The real selectivity of the
receiver is obtained by the tuning condenser on
the input to the harmonic generator as the
harmonic currents generated in this tube are
proportional to the square of the resonant input
carrier voltages resulting from this tuning con-
denser. The tuning condenser across the second-
ary of the harmonic transformer is no sharper
than the ordinary tuning circuit on the input to
a detector tube. Slight variations are therefore
permissible in the coils and condensers without
jeopardizing the performance of the receiver.
®
RADIO BROADCAST
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--„ 41 threads
Coil D rf-.li wo""d with
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TYPICAL ASSEMBLY OF COILS
FIG. 3
The two gang condensers may have the same
grounded rotor shaft as there is no need for any
special insulating between these circuits. It is
true that there are different grid biases on the
two tubes to be tuned, but the positive bias on
the grid of the detector tube may be supplied
by the grid leak connecting from the plus fila-
ment of the detector tube directly to the grid,
while the negative C bias on the harmonic gen-
erator is supplied through the common rotor and
the secondary of the fundamental transformer
in the grid circuit of the harmonic generator.
The blocking condenser in the grid circuit of
the detector effectively separates the positive
potential on the grid of the detector and the
negative C bias which exists in the rest of the
harmonic secondary by virtue of the common
grounded rotor shaft. As the negative potential
is obtained by a resistance drop, as previously
described, it is obvious that both the high-fre-
quency currents in the detector grid circuit and
the broadcast frequency currents in the harmonic
grid circuit must return to their respective fila-
ments through this resistance. Feed-back diffi-
culties and oscillation would absolutely occur at
this point in a tuned radio-frequency system,
but no difficulties are encountered in the R. G. S.
"Octamonic" because these two carrier currents
are of different frequency and cannot, therefore,
interfere with one another.
One thing should be made very clear at this
point of the discussion. There is a fundamental
difference between detection as such, and the
generation of second harmonics. As discussed in
the first article of the series the operation of a
tube on the knee of its characteristic curve
will produce not only second harmonic but
® /,
Time
HARMONICfGENERATOR STAGE
'Decrease due
to rectification
DETECTOHj STAGE
FIG. 4
NOVEMBER, 1927
audio currents as well. In this circuit the tube
is acting not only as a harmonic generator
but, incidentally, as a detector. No method is
known at present for the efficient generation of
second harmonics without the incidental detector
action occurring simultaneously. However, in the
detector stage, two possibilities are present.
Either the grid leak system of detection or the
C battery system of detection may be used.
The grid leak system is slightly more sensitive
on very weak signals while the C battery system
will deliver more audio energy on local reception
without distortion. A study of these two types
reveals some interesting facts. There is present,
along with the detector action, some incidental
generation of second harmonics, when the C
battery detector is employed. This would be
expected from the considerations already dis-
cussed in connection with the harmonic genera-
tor. However, second harmonic currents are
almost wholly absent in a detector tube employ-
ing the grid leak system. This means, that
detector action cannot be confused with harmonic
generation. They may or may not occur simul-
taneously. The grid leak detector simply cannot
be used in the generator stage for the creation
of second harmonics. The harmonic generator is
not a detector.
WHAT TYPE OF DETECTOR CIRCUIT?
IT NOW remains to determine which type of
circuit should be used in the detector stage.
Both the C battery and grid leak circuits were
subjected to an extensive series of tests. The grid
leak system was found to be much more satis-
factory and much more stable. The tone quality
was not impaired by the grid leak system and the
distortion which occurred on local reception
when using the C battery system, entirely dis-
appeared when the grid leak system was sub-
stituted. The results were so consistently con-
trary to those anticipated that considerable data
was gathered in an effort to explain the cause.
Fig. 4 shows graphically just what occurred and
why it is desirable to employ the grid leak system
in the bona fide detector. It will be noted that the
incidental detection occurring in the plate cir-
cuit of the harmonic generator is represented by
an increase in the plate current — the increase
being proportional to the modulation on the
incoming carrier waves. Quite the reverse takes
place in the detector circuit. Here the plate cur-
rent decreases upon detection due to the choking
action of the grid leak and condenser in the grid
circuit. The decrease in plate current is propor-
tional to the modulation on the incoming carrier
waves. The rectified or audio currents existing
in the plate of the harmonic generator are not
utilized but, in turn, flow through the B battery
circuit. The detected or audio currents in the
plate circuit of the detector go through the
primary of the first audio transformer and then
flow through the B battery circuit. With these
two audio currents opposing each other in the
B battery at all times there is no audio voltage
drop occurring therein. If a C-battery detector
were employed the two audio currents would in-
crease and decrease simultaneously, causing
excessive audio voltage drops in the common B
battery.
As brought out in the previous article, the
R. G. S. "Octamonic" receiver obtains its
super-selectivity through the sacrifice of some
of the radio-frequency energy. But as radio-
frequency energy is very easily obtained by any
number of r.f. amplifying circuits and selectivity
is not so easily obtained, the sacrifice is well worth
while. However, some form of r.f. amplification
must be placed ahead of the "selectivity" circuits
just discussed. Various r.f. arrangements have
been investigated and the one shown in Fig. 5 is
NOVEMBER, 1927
THE R. G. S. "OCTAMONIC" CIRCUIT
41
recommended. This shows one stage
of radio-frequency amplification
only as one stage has been found to
be more than ample for operating
the harmonic generator on even the
most distant stations. The antenna
is very closely coupled to a tuning
circuit which serves mainly to bring
the antenna circuit to resonance at
the frequency desired. The carrier
wave is then amplified and applied
to the harmonic generator through
a special equalizing coupling circuit
which is designed to pass all of the
broadcast frequencies with approx-
imately undiminished amplitude on
to the harmonic generator. The
theory of the operation of this un-
usual coupling is rather simple. The
total winding consists of 21 turns
which is the proper primary for the
longest wavelength of 550 meters.
Then a tap is taken off at 7 turns
which is approximately the proper
primary for the shortest wavelength of 200 me-
ters. A o.ooo25-mfd. fixed condenser is connected
between the tap and the filament of this amplify-
ing or coupling tube. A variable non-inductive
25O-ohm equalizing resistance is placed in series
with the total winding. The short waves pass
readily through the fixed condenser to the fila-
ment while the longer waves tend to pass more
and more through the entire winding because of
the increasing reactance of the fixed condenser
to the lower frequencies of the longer waves.
This first amplifying tube has been designated
a coupling tube since its main function is purely
a coupling and amplifying action rather than
any aid to the tuning. The coupling to the an-
tenna is made as close as possible so as to derive
the maximum amount of energy therefrom
throughout the broadcast band. Such close
coupling makes the tuning very broad and non-
critical — the real super-selectivity of the receiver
being created by the tuning condenser on the
input to the harmonic generator. In actual opera-
tion, this antenna condenser appears to be
sharper in its tuning than it really is because,
after all, it has an indirect effect, though broad,
on the amount of energy being transformed into
second harmonic currents by the generating
tube. This action gives it an apparent sharpness
greater than that which is really occurring in
the antenna circuit.
CURIOUS MODULATION EFFECTS
ONE very important factor in the design of
the coupling tube circuit is modulation.
Great care must be exercised in the design of this
circuit to avoid any possibility of rectification
action even on the louder signals. Otherwise,
the extreme selectivity of the harmonic generator
will be somewhat modified by a cross-talk or
FIG. 5
modulating action between a near-by high-
powered local station and a distant station
operating on an adjacent carrier channel. The
action is as follows: The receiver in New York
City is tuned to a weak station such as woo in
Philadelphia operating on 508 meters. It is
found that several dial degrees of silence are
obtained between this Philadelphia station and
WEAF, New York City, operating on 492 meters.
However, WEAF is coming in with considerable
field strength impressing considerable 492 meter
energy on the grid of the coupling tube along
with the energy from the Philadelphia station.
If any rectification occurs on the strong signals
from WEAF, audio currents will be set up in the
plate circuit of this radio coupling tube which
correspond to the program being sent out by
WEAF. It must be remembered here that the first
circuit is broad — its function being amplification
"^High External
Resistance
0
GRID VOLTS
FIG. 6
and not tuning. As a result, more
WEAF energy may be present than
the energy coming from Philadelphia
even though the antenna tuning con-
denser has been set in favor of the
Philadelphia station.
Now, the audio currents occurring
in the plate circuit of the coupling
tube as a result of the rectification
of the WEAF carrier wave, will cause
a plate voltage variation in this tube
which corresponds to the program
on the carrier wave of WEAF. This
action will, in turn, affect and vary
the amplification of any other carrier
wave coming through the tube at the
time, such as the Philadelphia sta-
tion which is desired. The audio
modulation or WEAF'S program will
then impress itself on the carrier
wave of the Philadelphia station in
the same manner that the original
audio currents at the studio of
WEAF impressed themselves on the
original carrier wave being sent out from WEAF
on 492 meters. The result is that, while several
dial degrees of silence are obtained between
WEAF and woo, as soon as the Philadelphia
station is tuned-in, the program from WEAF is
found also to exist thereon in the form of cross-
talk or cross-modulation.
The remedy is to operate the coupling tube
on the straightest portion of the grid-voltage
plate-current characteristic curve. For the
standard cx-3oi-A tube, this requires 90 volts
on the plate and 42 volts negative bias on the
grid. This point is very essential. In addition, it
is desirable to have the maximum of coupling
to the harmonic generating tube, not only from
the standpoint of energy transfer, but also for
the purpose of obtaining a fairly high effective
resistance in the plate circuit of the coupling
tube at the particular frequency for which the
input to the harmonic generating tube is tuned.
It is a well known fact that the resistance of a
primary winding increases considerably at the
resonant frequency of the secondary. At the
same time the reactance passes through zero, of
course. The closer the coupling the greater is
the effective resistance of the plate circuit and
resistance in the plate circuit tends to flatten
out the characteristic curve of the coupling tube.
This is shown in Fig. 6. This flattening of the
characteristic curve still further reduces any
tendency toward rectification in the coupling
tube.
A detailed discussion on the audio ampli-
fier as well as a full explanation of the theory and
operation of the harmonic wave-trap shown in
the antenna circuit will be taken up in the next
article of the series. The next article will also
describe in further detail the best wiring arrange-
ments.
The
Better Control of Oscillation Is a Feature of This New Receiver—
The Story of Some of the Difficulties Surmounted in Its Design
ANY radio engineer can make a single re-
/-\ ceiver work in the laboratory but when a
••• ^- factory turns out five hundred a day,
each of which must be thoroughly tested, the
problem becomes somewhat more complex. It
becomes one not only of manufacturing small
mechanical parts to a high degree of precision and
of simplified assembly so that mistakes are diffi-
cult to make, but one of following a circuit that
is electrically sound and as foolproof as possible.
Circuits that are highly sensitive are often
highly critical in their adjustment, necessitating
that they pass through the hands of a well
trained tester before they can be released. What
every set manufacturer wants is a receiver de-
sign such that manufacturing costs and assembly
problems are reduced to the bone, that testing
methods are neither complicated nor expensive in
point of time, and that adjustments are few.
Simplicity of design is not the controlling factor,
for the simplest circuit must embody the same
trouble producing elements as the most complex.
For example, every engineer knows that induc-
tance in the plate circuit of a radio-frequency
amplifier is necessary to transfer energy from one
circuit to the following tube; but he knows too
well that including this inductance tends to
make the previous tube oscillate. One method of
preventing oscillation is to feed back to the input
circuit some of the energy that appears in the
output circuit in such magnitude and phase that
the tube is no longer unstable. Owing to the
fact that unity coupling is necessary to obtain
complete prevention of oscillation (neutraliza-
tion) at all frequencies, it is impossible to neu-
tralize the amplifier over more than a narrow
band at one time. Often the circuits are balanced
at the shortest wavelengths, for the tendency to
oscillate is greatest there; but this is apt to result
in poor transfer of energy on the longer waves.
If it were possible to neutralize a receiver com-
pletely throughout its tuning range and to in-
clude sufficient primary inductance with close
enough coupling to the secondary to produce
proper amplification on the longer waves, the
design engineer's problem would be simple. Un-
fortunately, in spite of the neutralization process,
it is often impossible to utilize the utmost desira-
ble amount of primary inductance and coupling,
and the longer waves suffer.
A method that has been used to maintain the
circuits in a two-or three-stage radio-frequency
amplifier free from oscillations is that of including
By J. O. MESA
resistances in the grid circuits of the amplifying
tubes. It was found in the Freshman laboratories
that, with sufficiently large primary coils, the
resistances became rather large, of the order of
500 ohms. This method of "holding down" an
amplifier is shown in Fig. I, and in Fig. 2 is the
equivalent circuit.
Mathematics will show that for every resist-
ance, another, smaller in actual value, can be sub-
stituted, as in Fig. 2, in the tuned circuit itself
to accomplish the same end, namely, cessation of
troublesome oscillations. In fact, when such ex-
ternal resistances are used, the selectivity of the
circuit suffers, and at the same time the ampli-
fication falls off, showing conclusively that this
external resistance has in effect added considera-
ble damping to the tuned circuit itself.
There is a very serious objection to the use of
FIG. I
FIG. 2
FIG. 3.
resistances as in Fig. i. Under the usual condi-
tions obtaining in a high-amplification circuit,
the value of the stabilizing resistance is somewhat
critical. If the correct value is exceeded, the over-
all voltage gain of the radio-frequency amplifier
is considerably reduced, while if the resistance is
too small, the circuit oscillates violently. Further-
more, any slight variations in the component
parts which make up the radio-frequency ampli-
fier change the value of resistances needed for
best operation.
The solution, naturally, lies in very close
manufacturing limits on the values of inductance,
capacity, and resistance, and for some time re-
ceivers employing the resistance arrangement of
Fig. I were built in the Freshman plant. In spite
of the fact that the resistances were held accurate
to within plus or minus i .25 per cent., difficulty
occurred from oscillation or poor selectivity and
lack of amplification too frequently for comfort.
It became necessary to develop another stabliz-
ing system.
The new method of overcoming oscillations
without the disadvantages previously mentioned
was found by Mr. W. L. Dunn, Jr., and was
developed by the engineers of the Freshman
laboratory. This method is based on a principle
which has been used for a long time in telephone
equalizing circuits, and has been discussed
mathematically by K. S. Johnson in his Trans-
mission Circuits for Telephonic Communication
and by Morecroft on page 92 of the new edition
of his well known Principles of Radio Communi-
cation.
The circuit which has been utilized is shown in
Fig. 3, and it may be seen to consist of a coil and
condenser in parallel with a resistance in each
branch of the parallel circuit. If the resistances
in the two paths are equal to each other and
equal to the square root of the inductance divided
by the capacity, or:
RL = Re = i/L/C
the impedance of the circuit looked at from the
standpoint of the previous tube is a pure re-
sistance at all frequencies.
Therefore, the plate circuit of the previous
amplifier has no inductive reactance in it and
so the tube cannot oscillate, provided the
values of inductance, capacity, and resistance are
properly adjusted.
Limiting the magnetic feed back in the circuit
by using small diameter coils and placing them
at right angles to each other, and by using proper
bypass condensers across impedances which are
common to more than one stage, naturally aid
in keeping the amplifier performing its required
tasks.
I he method of applying this interesting case
of parallel resonance is shown in Fig. 4. Owing
to the fact that some resistance is reflected into
the circuit when a secondary coil is coupled to it
and is tuned to resonance, the actual values of
resistance used are different, 380 ohms being
used in the condenser, or plate branch, and 350
ohms in the inductance branch. The capacity
used is about 100 micro-microfarads and is of the
fixed-variable type, that is, a fixed condenser
having attached to it a small variable capacity
which may be adjusted in the factory so that
the receiver does not oscillate.
When it is realized that closer coupling and
greater primary inductance may be used when
such a circuit is employed, the gain over the
grid resistance method of stabilization is evident.
Nearly double the coefficient of coupling may be
used between primary and secondary in this new
system.
THE RECEIVER
TH E schematic diagram of a battery operated
receiver using this principle is shown in Fig.
5. This receiver is now being manufactured with
large quantity production methods. It has
been found that it is not subject to the difficulties
encountered in the case of the grid resistances
method of preventing oscillation. The condenser
in the plate circuit of the radio-frequency tubes
consists of curved spring plates with mica di-
electric which can be flattened by means of a
screw which is accessible to the inside of the
cabinet. This condenser is adjusted at the factory
JJy
H==s^
= c
:oo
mmf.
ti
380u
— ^\A^
1
FIG. 4.
NOVEMBER, 1927
THE "EQUAPHASE"
UX-201-A
UX.201.A
UX-200-A
UX201-A
Ant. 1 Ant 2
C-40
A- A* B»45
Rnd.
B«90
B-l£0
FIG. 3
so that the amplifier does not oscillate and does
not require readjustment thereafter so long as
tubes having the same plate impedance are
used in the radio-frequency amplifier. When a.c.
tubes are used a smaller capacity is needed owing
to the high low impedance of these tubes com-
pared with the average d.c. tube.
The radio-frequency transformers have sec-
ondaries which are wound on a small bakelite
tubing and have individual turns
slightly spaced. It has been found that
this type of winding can be controlled
so that the inductance of the coil
may be held to within about 0.5 per
cent, of accuracy when manufactured
in large quantities. The primary of the
radio-frequency transformer is a spiral
wound on a wooden form, and is placed
at the ground end of the secondary,
thus having the advantage of a com-
paratively large coupling and at the
same time small capacity between the
primary and secondary.
The audio transformers are
mounted on the tube shelf and have a
4 to i turn ratio. The secondary wind-
ings are of the split or balanced type
which have very low distributed capacity and
very low capacity between windings, with the
result that a quite uniform amplification is ob-
tained between 100 and 5000 cycles per second.
The radio-frequency inductances and audio-
frequency transformers as well as all the other
apparatus which is not accessible to the controls
on the front panel, are mounted on a spring sus-
pended metal shelf. This shelf carries the tubes
and is provided with rubber dampers so that
there is no microphonic feed back.
R.C.A.
AiC.Tube
UX226
The variable condensers used are selected so
that their capacities are equal to within 0.25 per
cent, at two points. Since the plates are of heavy
construction and have rather wide_ spacing, the
capacities of the condensers in any receiver are
practically identical throughout their entire
range. The arrangement of the front panel of
the "Fquaphase" may be seen in the photograph
of this receiver which appears on page twenty.
AUDIO FREQUENCY CHARACTERISTIC
Device Tested : Transformer ES 2774
Circuit Data : EA 5.0, EB 90, Ec 4.5
16
FREQUENCY CYCLES PER SECOND
Scale .95"per Octave
INTERESTING CURVES
Showing the characteristics of the audio
transformers used in the "Equaphase"
The volume control of the battery operated re-
ceivers is obtained by means of a rheostat in
series with the filaments of the radio-frequency
tubes. This method has been used for several
years on Freshman Masterpiece receivers and
has left nothing to be desired.
As mentioned before, a slight modification of
43
the constants of the elements used in the plate
circuit of the radio-frequency amplifiers is neces-
sary toadapt the circuit to the use of thealternat-
ing current tubes of the ux-226 (cx-}26) type.
Since the circuit does not oscillate and has high
amplification throughout the broadcast range,
the volume control can be obtained by means of
a potentiometer across the secondary of the
first audio-frequency transformer. This potentio-
meter has the so-called logarithmic scale, that is,
its resistance varies so that equal angular incre-
ments on the control produce equal increments
of volume. A schematic diagram of the house
current operated "Equaphase" receiver and its
power supply is shown in Fig. 6. The plate supply
is of the conventional type using a ux-28o full-
wave rectifier tube and having a two-section
filter. Various plate voltages are obtained from
taps on a resistor connected across the output of
the filter. The grid bias for the various tubes is
obtained from the drop across the resistance in
the plate circuit of the tubes.
Two independent tests are made on the sensi-
tivity of each receiver before it is packed. These
tests are made by two men who chyk each
other's work without either knowing the other's.
Around the laboratory is fed a continuous 1000-
cycle tone of a certain amplitude which is main-
tained constant. This is available at
each test bench, and is used to modu-
late a small radio-frequency oscillator.
A very small part of this energy is
picked up on a dummy antenna
whence it goes through the receiver
just as a radio signal would. The test
man listens to it comparing it with
the standard input looo-cycle tone by
means of an attenuation box which is
placed in the receiver output. In this
way he reads the relative amplifica-
tion of the receivers, and after fixing
a certain standard he can reject any
which fall below the required limit.
Phonograph music is also fed around
the test benches so that the test man
can listen to music as well as his
standard looo-cycle signal.
Any slight error in a component part is dis-
covered in this way before the receiver leaves
the factory, in which case it can be sent back to
the repair bench for final adjustment.
It can easily be appreciated that this method
of preventing oscillation is one which does not
affect the selectivity of the receiver once it is
properly adjusted. The selectivity of the " Equa-
phase" is quite satisfactory enough for con-
gested districts.
FIG. 6
By JOHN E. McCLURE
"TTT IS seldom that a radio receiver design, or
I kit, outlives a single season's popularity, and
when the exception comes along, it gives
assurance that it must be an unusually fine set.
Such is the "Shielded Six." During this last
year certain refinements of design have been
developed, and the new improved model is now
ready for the 1927-28 season.
Mechanically, the design of the receiver is one
of the prettiest of kit jobs, and the "Shielded
Six" looks more like a carefully worked-out
assembly for quantity production in a modern
factory than a kit receiver. The whole set builds
up progressively on a die-formed and pierced
steel chassis, which is a radical departure from
the often makeshift packing-case baseboards to
which the home constructor is accustomed. The
panel also is of metal, bronze, attractively decor-
ated in the fashion of the new expensive factory-
built sets, being utilized for this purpose.
Electrically, the circuit design involves three
stages of tuned radio-frequency amplification
with controlled regeneration, a grid-biased detec-
tor tube, and two stages of transformer-coupled
audio-frequency amplification. In these respects
the improved model is very like the original, and
the only really startling improvements found in
the set are circuit changes resulting in greatly
increased selectivity, and the addition of vernier
tuning dials found necessary because of the
greatly increased sharpness of tuning.
The antenna stage, or first radio-frequency
amplifier, is left unshielded in the new model to
increase the coil pick-up to a point where the
receiver may be operated in apartment houses
with no antenna at all, and yet give adequate
loud speaker volume on powerful local stations.
If the second, third, or fourth coils were un-
shielded, selectivity would be affected, for
energy pick-up on these coils would affect the
selective tuning action of the tuned circuits.
Shielding not only prevents pick-up of external
interference, but possibly more important, en-
tirely prevents extraneous interstage coupling.
Losses in the r.f. circuits have been reduced
to a minimum through the use of quite low
resistance inductances, wound on threaded ribs
of bakelite coil forms in such a fashion that they
are practically air-supported. These inductances
are tuned by means of newly designed, very
rugged, condensers providing a semi-straight-
frequency, straight-wavelength tuning curve
which gives most satisfactory spacing of stations
over the tuning dial scales. The set may be
adapted for loop reception without a single change
except to pull out the antenna coil and clip on
two loop leads to coil socket posts 3 and 6.
The new set seems amply selective for present
broadcasting conditions, for, in Chicago, it will
cut through a mass of thirty local stations and
bring in out-of-town stations.
While four tuned circuits are employed, only
two tuning controls are used, this being made
possible through extremely accurate matching
of condensers and coils. All coils for a set are
matched to within a quarter of one per cent, and
the condensers are all checked and held within
one per cent, of each other. Since the tuning of
the three right-hand circuits is substantially
identical, a mechanical link serves to turn all
three condensers as the right-hand dial is turned.
The antenna stage condenser is tuned separately.
The audio-frequency amplifier has a highly
desirable characteristic in that it amplifies prac-
tically uniformly all frequencies between 30 and
5000 cycles, above which frequency there is prac-
tically no amplification. The highest funda-
mental note of any musical instrument is 4192
cycles and the jooo-cycle upper limit allows
plenty of leeway for the handling of the highest
fundamental frequency in music, and it has been
proved that frequencies above 5000 cycles do not
contribute, in any measure, to fidelity of repro-
duction. Thus the interference caused by heter-
odyne squeals developed between transmitting
stations, by atmospheric noise and by the tube
and battery noises, all of which are generally
above 5000 cycles, are almost entirely absent.
A group of people listening to the improved
"Shielded Six" receiver operating in conjunction
with a good cone loud speaker and receiving an
organ program, will actually feel the vibration
of the room in which the receiver is located, as
O-CAmp.
0-CDet
THE CIRCUIT DIAGRAM OF THE IMPROVED SHIELDED SIX RECEIVER
THE IMPROVED "SHIELDED SIX"
45
The parts needed for the Improved Model are
listed below. They total exactly $95.00. While
this price may seem a bit high in that fifty-
dollar six-tube sets, completely constructed, are
available, it must be remembered that the
"Shielded Six" has been designed with unusual
care and that all the parts have been very care-
fully matched to insure satisfactory operation.
PREPARATORY TO PLACING THE STAGE SHIELDS IN POSITION
The arrangement of the Silver-Marshall triple link motion is distinctly shown in this pho-
tograph. The transformers are, from left to right, output, second audio, and first audio
they would were they in the original building in
which the organ itself was located.
A. C. OPERATION
AC. OPERATION is so ridiculously simple
• with the "Shielded Six" as to require little
description and if Sovereign or equivalent heater
tubes are used, lighted from a filament trans-
former, only minor changes need be made in the
wiring. The standard Sovereign tubes have the
heater leads coming out on top and all tubes
should have their heater elements connected in
parallel and to the 2j-volt
winding of a filament heating
transformer. It is also well to
ground one side of this wind-
ing. The F — terminal of each
tube socket should be con-
nected to the receiver chassis
while the F+ terminal of each
tube socket should be ignored.
The 2oo-ohm potentiometer
should be eliminated and in
its place a Carter 6ooo-ohm
potentiometer used (the two
center shields will have to
have their corners clipped
away to accommodate the
new 6ooo-ohm potentiome-
ter). Terminals 6 of the three
left-hand r.f. transformers,
which previously connected
to the center arm of the poten-
tiometer, should ground to the
chassis. Theo.j-mfd. potenti-
ometer bypass condenser is
eliminated. The new potenti-
ometer should be connected
with one end to the chassis,
the other end to the +90
binding post, and the arm
connecting to one end of the
8-90 bypass condenser and to
terminals 5 of the three right-
hand r.f. transformers. Five
Sovereign a.c. tubes are used,
with a cx-371 (ux-i7i) type
tube in the last audio stage.
The two filament leads from
this latter power tube socket
are run directly to the 5-volt
terminals of the filament
transformer. The center tap of
a Frost FT 64 resistance shunting the power tube
filament connects through a 2ooo-ohm Carter
fixed resistance to the chassis of the receiver or
ground. A regular B supply, such as the Silver-
Marshall 652A (which will also supply A poten-
tial to the tubes) will then furnish B potential to
the entire receiver, and A, B, and C potential to
the second audio stage, while a 43-volt C battery
will have to be used for the detector and the first
audio stage (terminal 4 of the first audio trans-
former should connect to the C — Del. binding
post of the receiver).
3 — S-M 63 1 Stage Shields .
2 — S-M ji6A Matched Condensers
2 — S-M 3166 Matched Condensers
4 — S-M 515 Coil Sockets ....
3— S-M i i8A Matched Coils . . .
I — S-M i i6A Coil, Matched with Above
6 — S-M 511 Tube Sockets ....
2 — S-M 220 Audio Transformers .
i — S-M 221 Output Transformer .
i — S-M 632 Triple Link Motion .
i — Polymet o.2j-Meg. Grid Leak .
i — Polymet Resistor Mounting
i — Carter o.oo2-Mfd. Condenser .
3 — Carter 105 or Polymet Condensers,
0.5 Mfd
i— Carter M-2oo Potentiometer (200
Ohms)
2 — Carter No. 10 Tip Jacks
i — Carter H-J Resistor
2 — Marco Walnut Vernier Dials .
i — 636 Terminal Strip, ij x 1 1 inches .
i — Crowe 633 Drilled and Engraved
Metal Panel, Size 7x21 Inches .
i — Crowe 634 Steel Chassis, Size 12 x
igj x ij Inches
i — Carter No. 12 Antenna Switch
i — Carter "Imp" Battery Switch .
i — Coil Kellogg Fabricated Hook-up
Wire, Screws, Nuts, Lugs, and
Complete Building Instructions .
Total
$ 6.00
9.00
9.00
4.00
7.50
2.50
3.00
16.00
7.50
2.50
•25
.50
.50
2.70
•75
.20
•25
5.00
2.OO
8.50
6.00
.60
•50
•25
$95.00
THERE IS AN ADVANTAGE IN LEAVING ONE
The antenna tuning stage, the only one of the four tuned stages not
tion. By so doing, the coil pick-up is increased to a point where the
with no antenna at all, and adequate volume obtained on the loud
TUNED STAGE UNSHIELDED
shielded, has purposely been left in this condi-
receiver may be operated in apartment houses
speaker when receiving powerful local stations
ristocrat
RADIO BROADCAST Photograph
A SUITABLE LAYOUT THAT MAKES FOR SIMPLICITY OF CONSTRUCTION
There are many possible variations of design for the new "Aristocrat," the layout here, in fact, not being exactly similar to that described in the text. The
"deck," for example, is mounted away from the front panel in the model described, and one variable rheostat takes the place of the two ballasts shown in the
photograph. New Eby sockets have been substituted for the older pattern ones shown, and binding posts are used for Antenna, Ground, and Loud Speaker
By ARTHUR H. LYNCH
EXACTLY two years ago RADIO BROAD-
CAST first described the "Aristocrat"
receiver. This receiver became unusually
popular and many interesting letters were re-
ceived telling of the good results that were ob-
tained. It was a five-tube affair consisting of a
stage of tuned radio frequency followed by a
regenerative detector, and the audio circuit com-
prised a three-stage resistance-coupled amplifier.
Correspondence is still received from many
readers regarding the receiver and evidently
many "Aristocrats" are still giving good service.
We do not intend in this article to describe a
radically new "Aristocrat" receiver. The original
circuit was carefully thought out and even
though two years have elapsed since it was first
described there are only minor ways in which it
can be improved. An "Aristocrat" receiver care-
fully constructed in accordance with the original
description would be found selective, sensitive,
and capable of giving good quality reproduction
in the majority of cases; there are, however, a few
rearrangements that might be made in the
mechanical design which will make the construc-
tion of this receiver simpler and better looking.
Before going into the details concerning these
suggested changes, a very brief description of
the circuit in its revised form, with special ref-
erence to the ways in which it differs from the
original, will be given. The circuit diagram
of the new " Aristocrat" is given in Fig. I.
An important difference between the new
and the old set is immediately evident to
those who are familiar with the original
circuit, i. e., that the antenna stage now
uses a variocoupler instead of a tapped
coil. Antenna tuning in the original re-
ceiver was accomplished by means of
the taps on the primary of the antenna
coil and by proper use of this adjustment
it was possible to obtain high efficiency
from the receiver with various lengths of an-
tennas. The new antenna coil of the "Aristo-
crat" contains a secondary with primary inside
it, variable coupling between the two coils ac-
complishing the same results as did the taps in
the original coil; with the new arrangement the
.^adjustment can be made more readily and more
accurately. The variable antenna coil is a dis-
tinct improvement and should be incorporated
in the new "Aristocrat" receiver and might also
be used to advantage in receivers constructed
according to the original circuit.
The detector stage df the new "Aristocrat"
remains the same as the original circuit. The
audio amplifier is arranged so that somewhat
greater voltage is placed on the plate circuits of
the first two stages than was originally used.
The new high-mu tubes should be operated with
at least 135 volts on their plates.
Simplicity of construction is the keynote of the
new receiver. The improvements that have been
made in the constructional features of the
"Aristocrat" are, first, the use of a metal panel
of special design and, secondly, a new and unique
type of sub-panel construction. The special
metal panel is designed to accommodate two
variable condensers of the single-hole mounting
type and the panel is also made for use with il-
luminated dials. There are three additional holes
PLATE
VOLTAGE
NEGATIVE C BATTERY VOLTAGE REQUIRED
Power
Semi-power
Audio
Radio
45
00
135
180
16.5
27
40.5
6.0
9.0
12.0
'•5
3.0
o
3
in the panel, the one at the left being for the
antenna rotor control, the center one for the
rheostat knob, and another hole at the right is
for the regeneration control. This panel and dial
combination can be used in constructing any
number of circuit combinations where there are
only two tuning controls and its use in the
"Aristocrat" is a good example of its utility.
The panel measures seven by eighteen inches and
is a product of the Wireless Radio Company,
of Brooklyn, New York.
The new special sub-panel, or "deck" as it is
called, has five Eby DeLuxe sockets mounted on
it and audio amplifying equipment for a five-tube
receiver. It is made of Westinghouse Micarta,
and is built to accommodate ten binding posts.
In the model illustrated the six-wire cable obvi-
ates the use of six of these binding posts, connec-
tion for the batteries being made directly to the
wiring of the receiver by means of this six-wire
cable. The audio amplifier is a three-stage re-
sistance-coupled affair and both the resistances
and condensers are held in place on the "deck"
by clips so that constructors may use any values
which they may prefer. The person who wishes
to experiment can procure additional values of
resistance and condensers than those which
come with the deck and substitute them when
desired.
There are available many different an-
tenna couplers and three-circuit tuners that
may be used in the "Aristocrat." In the par-
ticular receiver illustrated in the photo-
graphs accompanying this article, Sickles
"Aristocrat" coils have been used in con-
junction with Cogswell condensers. The
Cogswell antenna tuning condenser has
been made in a very ingenious fashion. Its
stator plates form one side of the neutraliz-
ing condenser, while the other plate of the
latter is mounted on a pair of hinges and is
NOVEMBER, 1927
adjusted by turning a small screw which pushes
against an eccentric cam. It is all very small,
very simple, convenient, and very effective, as
well as being cheap. At the end of this article
there is given a list of those parts used in the
model that is illustrated, and the photographs
and the circuit diagram should enable experi-
enced constructors to build the receiver with little
difficulty.
NEW TUBES
IT IS possible to procure an improvement in
results from either an old or new "Aristocrat"
by making proper use of the several new types of
tubes that have become available since the
"Aristocrat" first made its bow. A special de-
tector tube, for example, may be used in the re-
ceiver instead of a 201 -A type and it will increase
the sensitivity and volume very considerably.
In this case the detector grid return should go to
negative A instead of to positive as indicated in
Fig. i, unless a special Ceco type H detector
tube is used, when no change is necessary. Ceco
type G high-mu tubes should be used in the
first and second stages of the audio amplifier.
High-mu tubes of other manufacturers should
not be used unless the condenser and resistor
values are changed to comply with the specifica-
tions of the individual makers. The output tube
should be of the semi-power type with proper C
and B voltages. Ceco makes special radio-
frequency amplifier tubes which will give slightly
increased gain in the r. f. stage. They are known
as the type K tubes. These new tubes, without
regard to any other improvements that might
be made, will give greater distance, sharper tun-
ing, and more volume than can be obtained when
ordinary tubes are used.
In the table accompanying this article there
are given data on the C and B voltages that
should be used on the various tubes. The column
headed "Power" gives the voltages when a ux-
171, cx-371, or Ceco ]-ji, is used in the output
stage. The column head "Semi-Power" gives the
required voltages when a ux-na, cx-ii2, or
Ceco type F is used in the output. The voltages
given under the column headed "Audio" refer
to the high-mu tubes in the audio amplifier. The
values given under the column headed "Radio"
apply to either ZOI-A'S or special radio-frequency
THE IMPROVED ARISTOCRAT
47
THE LYNCH "DECK
Its utilization considerably simplifies receiver construction.
The list of parts below tells just what the "deck" comprises
amplifier tubes. If a 171, 371,0^-71 power tube
is used in the output of the receiver, an output
filter or output transformer should be used in the
plate circuit of the tube to protect the windings
of the loud speaker from the high plate current.
As shown, the circuit is wired for a 1 12 or Ceco F
type tube. C bias for the first two audio tubes is
obtained by inserting a battery in the common
grid lead at the point marked "X," the positive
terminal of the grid battery connecting to nega-
tive A.
The results obtainable from the improved
"Aristocrat" receiver do not suffer at all in
comparison with the original set, while the total
cost of building the receiver has been materially
reduced. The automobile business is not the
only one in which the honest claim that produc-
tion methods enable you to purchase a better
product for a lower price. In the case of the
improved "Aristocrat," production methods
have been applied to radio.
Li, L;— -Sickles "Aristocrat" Coils . 5 4-5°
Ci — Cogswell Variable Condenser,
Type A, 0.00035 Mfd. . . . 2.25
Cj — Cogswell Variable Condenser,
Type B, 0.00035 Mfd., Neu-
tralizing Condenser (Cs) At-
tached
C3, C«— Sangamo 0.004 Mfd. Fixed
Condensers
Four Eby Binding Posts .
Six-Wire Cable . . . . •
Wireless Radio Company's
Panel, 7 x 18 Inches, with
Mounting Brackets, Illum-
inated Dials, and Filament
Rheostat (Ri)
Two Kurz-Kasch Knobs .
Lynch Deck, Including the
Following Parts, Mounted and
Ready for Wiring:
Westinghouse Micarta Panel
Seven Resistor-Condenser
Mounts
R2, R3, RI— o.i-Meg. Metallized
Resistors
R5, R6, RT— o.5-Meg. Metal-
lized Resistors
R — 2-Meg. Metallized Resistor
C7, Cs, Ci — o.oo6-Mfd. Tubular
Condensers
Ce — o.ooo25-Mfd. Tubular
Condenser
Five Eby DeLuxe Sockets
Total
2-75
1.20
.60
.60
4.50
.50
12.50
f , Inside Terminals of Secondaries ,
A C5
THE CIRCUIT DIAGRAM OF THE "ARISTOCRAT" RECEIVER
uppressin
Interference from Motion Picture Theatres, Telephone Exchanges, Arc
Lamps, Incandescent Street Lamps, Flour Mills, Factory Belts, Electric Warm-
ing Pads, Precipitators, Etc., Is Discussed, and Remedies Are Suggested
By A, T. LAWTON
A THOUGH this article is really the second
of a series, the first of which appeared
in the September RADIO BROADCAST, it
is nevertheless complete in itself, and the
reader who is suffering from interference of
any of the forms outlined here will profit con-
siderably from a study of this paper. The data
presented here result from a two-and-a-half-year
study conducted by the author in more than 132
cities. The forms of interference covered in the
September article were those due to oil-burning
furnaces, perhaps the most common source of
man-made static, X-ray equipment, and dental
motors. The first kind of interference to be con-
sidered here is that originating at motion picture
theatres.
MOTION PICTURE THEATRES
THE radius of interference from this source is
ordinarily about 200 yards, occasionally
greater, depending on exterior wiring. In the
great majority of cases the direct-current genera-
tor is responsible for the trouble. Contrary to
popular belief, the arc lamps themselves cause
practically no interference; in fact, there is often
less disturbance with the arcs lighted than before
they are "struck," j. e.,
with the generator run- Motor
ning unloaded. The dif-
ference in certain cases
is decided, absorption of
the interference occur-
ring as soon as the arcs
are put on.
Fig. i shows a method
used to eliminate this
interference with success
in actual practice. Five-
ampere fuses are used.
If the commutator is
badly worn, it should
be turned down in a
lathe, and we might re-
mark here that the quality of the carbon brushes
used have a noticeable effect on the intensity of
commutation interference.
Squirrel cage induction motors are in common
use for driving these generators and, ordinarily,
give no trouble unless some defect is present.
TELEPHONE EXCHANGES
[T IS probable that in most cities interference
' from this source has been cleared up. The
larger operating companies have been active in
this regard, but in smaller towns and rural com-
munities much trouble exists. On the larger type
motor ringers, high-tone and low-tone (sometimes
referred to as trouble tone and howler) circuits
are mainly responsible. Complete elimination is
secured by inserting a choke coil in each of the
two brush leads, close up to the machine. De-
tails of the coil required are shown in Fig. 2.
Complications arise if connection is made at a
distance of more than four inches from the
brushes — incomplete elimination resulting.
The greatest offenders in the category of tele-
phone ringing apparatus are pole changers and
frequency converters. These constitute standard
equipment in thousands of small exchanges;
in some larger exchanges they are operated only
after 10 p. M. when the rush hours have passed.
The interference is of a rapid clicking nature and
may carry half a mile or more, depending on
the proximity and layout of the city distribution
and telephone wiring.
For pole changers, definite and conclusive re-
, 2-mfd. Condensers
A.C. Supply
A-*" B-%" C-V D-254" E-%"
Hardwood Bobbin, approx. 300
turns No.22 (about 125 ft.)
FIG. 2
Constructional details for the choke coils recom-
mended for elimination of interference originating
in telephone exchanges
FIG. I
suits are obtained by inserting the coils described
in Fig. 2 in the ringing leads and at least 95 per
cent, of the trouble disappears. Up to the present
we know of only one instance where this method
failed — and peculiarly enough, a simpler method
cleared up the trouble. A single one-half micro-
farad condenser bridged across the contacts gave
loo per cent, elimination.
Frequency converters are a different proposi-
tion, operating off a. c. instead of d. c. as in the
case of pole changers. The surge trap applicable
to pole changers gives only 50 or 60 per cent,
reduction.
A special surge trap is made up for this source
by companies manufacturing the frequency con-
verter, and it will be found more economical in
the long run to purchase this complete rather
than endeavor to make it up locally. For all
practical purposes, complete elimination is ob-
tained through the installation of the special
surge trap.
Automatic telephones, now coming into such
general use, contribute their little quota of dis-
turbance. Usually they affect radio receivers
only in the same residence where the dialing
operation is being carried out, although several
cases are on record where radio sets of next-door
neighbors were also affected.
A single condenser of one microfarad capacity
placed across the dialing circuit will cut out the
clicking noise and does not appear to have any
detrimental effect on the speech transmission
or proper functioning of the line. However, per-
mission of the telephone company should be ob-
tained before making any attachments.
ARC LAMPS
C TRANCE as it may seem, flickering arc
«-5 lamps cause practically no radio interference.
If the arc is jumping violently, however, then
clicks are recorded on radio receivers in the
vicinity; a short distance away interference is
not material. This doesn't mean that arc lamps
cause no disturbance. On the contrary, during a
recent investigation one arc lamp practically
killed radio reception for eleven city blocks along
one street. It was burning perfectly steadily and
showed no sign whatever of defect.
The characteristics were slow clicking in dry
weather, fast clicking in moist atmosphere, and
rapid clicking during rainy weather. On a five-
tube set with loud speaker, the noise was violent,
resembling very much the operating of a pneu-
matic hammer. The source of trouble here was a
minutefissure in the composition head ring which,
filling up with moisture, caused a high-resistance
short across the 4Ooo-volt lines. Evidently the
spark dried up the moisture at each crossover,
and time was required for the path to reform,
otherwise we should have gotten steady buzzing
here.
During all the days this case was under obser-
vation not once did it come on coincident with
the lighting of the arcs, but always twenty
minutes or twenty-five minutes afterward. It
took time to develop, possibly a slight heating
and consequent expansion of the parts being
involved.
If arc lamp interference comes on directly the
lamps are lighted the source is very likely to be
line trouble, such as wires scraping on iron
bracket arms, loose splices, etc.
In many localities where it is prevalent arc
lamp circuit interference starts up before the
lamps are lighted, perhaps twenty-five or thirty
minutes previous to lighting, and it is quite
regular every evening.
This is caused by the rectifying tubes in the
power house or sub-station. These tubes are
"warmed up" for service prior to the line being
switched in; the operation takes twenty-five
minutes or so, and radio-frequency surges pass
out on the line despite the open switch, so even
before the lamps are actually lighted interference
starts. Intensity of the interference is increased
when the lights come on and continues all night,
until the daylight shut-down. Generally speak-
ing, new rectifying tubes do not give trouble, nor
older ones, paralleled. Overloaded tubes, how-
SUPPRESSING RADIO INTERFERENCE
49
ever, or those which have become hard through
long usage, are liable to set up interfering
surges that will travel long distances over the
system.
The obvious thing to do with a defective lamp
is to have it repaired; the same thing applies to
line defects. Rectifying tube disturbance, by
far the worst trouble because of its continuous
nature and wide range, can be cleared up by
putting a choke coil as described in Fig. 3, in
each outgoing d. c. feeder.
Two hundred turns of No. 16 d. c. c. wire are
required on a wooden cylinder 35 inches diameter
and about 12 inches long. Longitudinal slots are
cut in the cylinder for insertion of fibre strips
which keep the wire off the wood and provide
adequate heat radiation facilities. This is for
4-ampere arcs; for 6-ampere arcs it may be as
well to use No. 14 wire.
It seems that in certain instances of this na-
ture, seventy-turn chokes were large enough to
give satisfactory elimination; in the particular
case in mind they were ineffective.
INCANDESCENT STREET LAMPS
IT MAY come as a little surprise when we say
that, given any city where the street lighting
system consists of, say two thousand series arcs
and two thousand series incandescent lamps, on
various circuits, more radio interference will be
caused by the incandescent lamp circuits than
by the arc system.
This is due to less careful installation in the
case of the incandescent system — not because
of any inherent defect. The condition is general.
Of one hundred cases of radio interference due
to faults on series incandescent lighting systems:
42 were caused by down-lead wires scrap-
ing on the iron brackets.
1 5 by loose connections of the wires at the
lamps.
10 by internal defects in the lamp fixture
proper.
10 by partial shorting of the wires in conduit
prior to connection at the lamp.
9 by poor line splices.
5 by leakage or spitting at the disc fuses in
the lamp head.
5 by lamps loose in their sockets.
4 by defective mercury or other type auto-
matic time switches.
It may be remarked here that sources on a
series lighting system giving rise to radio inter-
ference are most difficult to locate. What occurs
at a defective lamp seems to be duplicated in
many lamps either side of the faulty one; in-
tensity values of the interference are misleading
and very careful observation is required.
FLOUR MILLS
JN PRACTICALLY every Hour mill the chlorine
* process of bleaching has been superseded by
the electrical method. This consists of a twenty-
thousand volt spark oscillating directly in the
path of a blast of air, the latter becoming ozonat-
ed, passes on to the grain in process of crushing.
Direct radiation is confined to a few hundred
feet. The source, however, is a vigorous one and
distribution wiring carries the disturbance to
great distances; it is capable of mutilating radio
reception practically all over the average small
town.
Methods of elimination are simple and definite.
One hundred-and-fifty turn choke coils wound
on three or three and a half inch tubing will
kill at least 85 per cent, of the noise and will not
interfere in the least with normal operation.
Operating current here is 12 to 15 amperes;
if the coils are not banked, No. 10 wire will be
suitable. To conform to Electrical Inspections
requirements, enclosure of the coils in a standard
outlet box is recommended, the knockout holes
of which have been opened and covered with
fine wire gauze. This latter affords good ventila-
tion while preventing grain dust accumulating
on the coils.
Self-contained bleachers of the arc type cause
no trouble. They are, however, being rapidly
displaced by the more efficient spark type.
FACTORY BELTS
HIGH-SPEED belts are a fruitful source of
radio interference, especially noticeable in
cold, dry weather. Friction between the pulleys
and belting causes a static charge to form on the
belt and this, after rising to a high potential,
will spark to nearby metal objects, setting up a
"crackling" noise in the receiver.
As most heavy rotary machines are well con-
nected to ground one would imagine that this
static charge would filter away gradually, and
fail to build up to any material potential. The
fact is, and it can be demonstrated, that the film
of oil in the machine bearings is sufficient to
insulate the rotating parts from ground.
A "static collector" is used to get rid of this
trouble. It consists of a wiping contact of springy
FIG. 3
metal, at all times resting on the belt in motion
and permanently connected to earth.
A metal laced belt can set up quite a loud click-
ing interference. Every time the metal lacing
passes over an iron pulley the click is heard.
No such effect is noted, of course, where wooden
pulleys are used, but in the cases cleared up we
simply removed the metal lacing and substituted
rawhide.
ELECTRIC WARMING PADS
WHETHER interference from this source
is to be regarded as serious or not depends
on how far away you live from the offending pad.
The radius is about two dwellings either side
of the one in which the pad is being used, assum-
ing that the houses are close together.
Little thermostats inside the pad automati-
cally break the supply current when the pad
becomes sufficiently heated and switch it on
again when the elements cool sufficiently. This
alternate opening and closing of the no-volt
supply line sets up clicks which are extremely
annoying to broadcast listeners in the immediate
vicinity.
Intensity of the trouble varies with the make
of pad and also with length of service. It seems
that corroded or burned contacts are responsible
for most of the trouble and before going to the
expense of purchasing condensers, etc., it is usual
to open the warming pad and readjust the ther-
mostat contacts after cleaning them up properly.
A different problem is presented in the case of
hospitals. Take a literal, specific example: Two
hundred patients, two hundred pairs of tele-
phones (no loud speaker allowed) and, incident-
ally, two hundred warming pads (one for each
cot), Were in use. Every time a patient gets rest-
less and kicks out his feet he jars the pad thermo-
stats and treats the other hundred and ninety-
nine to a series of sharp clicks usually resulting
in reciprocation.
Substitution of quiet types for the noisy ones
and condenser absorption would seem to be the
best recommendation.
PRECIPITATORS
THIS apparatus is used in the treatment of
various ores as well as for the purpose of
smoke and dust precipitation. Its radio interfer-
ence can be heard ten miles; at five miles it hurts
reception and in the vicinity of the plant, normal
reception is impossible.
As in the case of the
notorious oil-burning
furnace, methods of
elimination which clear
up the trouble in one
installation fail to give
the desired results when
applied to another
plant.
Several cases have
been cleared up ucing
high-frequency chokes,
i.e., placed in th^ high-
tension circuit. The coils consist of 500 turns of
No. i$ or No. 20 bare or covered wire on a tube
three and one half inches in diameter. Individual
turns should be spaced about one eighth inch
apart except at the ends, where one-quarter inch
spacing is recommended.
Fig. 4 shows an arrangement which has given
satisfactory results. It may be necessary in other
cases to split this 500 turn choke, i.e., putting
250 turns near the rectifier and 250 near the
treater.
In the types where the high-tension energy
for the rectifier is obtained through transformer
action direct from a transmission line, inter-
ference is naturally heavie than that experienced
from the more or less self-contained motor gen-
erator type although the actual energy in the
former is less than in the case of the latter.
Average energy values will be about 70 milli-
amps. at 30,000 volts and 80 milliamps. at 50,000
volts, respectively.
Considerable experimental work has been
carried out by different precipitation plants in
this connection and while special treatment was
found necessary in several instances practically
all cases investigated have been cleared up.
Rectifier
Supply
•- Chokes ..-
- -Treater
G W
FIG. 4
AS IHh
MDCASIKR .
KY C:AKI OKFHFR
Drawing by Frantyyn F. Stratford
Putting Freak Broadcasting in Its Place
IN ALL human affairs the tendency is toward
quiescence and boredom. Among vigorous
peoples this drift toward monotony is resisted
by a constant seeking for innovations. Now and
then some fruitful bit of originality rewards the
quest. In the main, however, the innovations
are failures. They have no deep roots in human
desires or interests, and, after the first glance,
they amuse the normal spectator even less than
the old shows he is weary of. The spirit is praise-
worthy, but the results are dreadful, especially
in the arts. Consider the poets, for example.
Here and there one of them, distressed by his
inability to convince the world that he is another
Shelley, decides to be entirely original by print-
ing a magazine of verse with a fake Nujol ad-
vertisement on the cover, no capital letters, and
half the words upsidedown. His originality is
hard on the compositors. To be original, in the
sense of doing something that is not commonly
done, is very easy. To that degree you can be
an exponent of novelty, by entering the nearest
drug store and ordering a pineapple soda with
chocolate cream. But to be fruitfully original
requires more than twenty cents.
We are similarly beset in the art of broadcast
entertainment. The innovations are many, but
most of them are of the twenty-cent variety.
1 do not intend to itemize all the varieties of freak
broadcasting; it would be impossible, and, be-
sides, a certain portion of this department is
consecrated to sensible subjects. A few samples
will suffice.
The broadcasting of alleged disembodied
spirits seems to me to fall into the category of
futilities politely hinted at above. I have no
animus against the spirits as such. It is true that
I have never seen one, and, since studying psy-
chopathology, have doubted their existence.
Nevertheless, as 1 have not seen everything in
the universe, and don't expect to, I acknowledge
that such things as ghosts may exist. But why
broadcast them? If a
ghost wants to see me,
let him or her call on
me at my office, or in
the dark reaches of the
night. But as a broad-
cast listener, I like to
be entertained. As a
broadcast listener, I
also object to the im-
putation that 1 am a
total ass. No doubt 1
am an ass in some re-
spects, but not to the
extent that I can be
kidded, on hearing the
tinkling of glass, a noise
like a $6 saxophone,
and some mumbling
through my loud
speaker, into believing
that authentic goblins
are disporting them-
selves in the studio of
the puissant broad-
caster who is striving to
instruct me. And, when
a committee of spiritualist investigators assure
me that everything is aboveboard, I guffaw
openly at their discourse. Who are they to tell
me so? What do they know about the tricks of
broadcast transmission?
The method used in broadcasting the shades
is to turn on the microphone and, with the studio
doors locked and no one in the room, to listen
for mysterious sounds on the station carrier,
which is assumed to be quiet. The investigating
committee watches the studio doors and snoops
around otherwise at their discretion. But can
they assert with any semblance of plausibility
that they know all the sources of input to the
speech amplifiers of the transmitter? Nothing
could be simpler than to rig up an additional
microphone somewhere in the building and,
paralleling it with the transmitter in the empty
studio, to broadcast any sounds one cares to.
Not even that is necessary. One of the operators
can tap a tube in the speech amplifier and make
noises which will seem inexplicable to the ghost-
chasers. The business of spiritualistic investiga-
tion is at best full of complications, and to
complicate it further by adding the technical in-
tricacies of a broadcast transmitter is beyond all
sense. Whether there is fraud or not — and cer-
tainly in connection with struggling stations
avidly bent on cadging every possible square
inch of newspaper space the possibility of decep-
tion is not remote — the pretence of scientific
investigation under such conditions is simply
silly. The broadcast listeners may not be New-
tons, Goethes, and Mommsens, but they are not
voodoo worshippers either. The studio manager
who first conceived the idea of broadcasting
spirits may have been original, but he omitted
to mix a few brains with his originality.
Even more infantile is the menagerie broad-
casting stunt. The only justification I can see
for it is in connection with a children's hour.
The noises made by sea lions and rhinoceroses
are neither agreeable nor intellectual, and, being
full of steep wave fronts and tones outside the
band of transmittable frequencies, they don't
get over anyway. If a man roared into the trans-
mitter it would sound as much like a lion when
it got through the loud speakers as if a lion did
the roaring.
As one listener, 1 ask to be spared such buf-
fooneries. I respect the urge for originality, but
it must take a more convincing shape than in
such procedures, which have no other use than
to get some station's publicity matter a transient
hearing. If there is nothing interesting left to say,
and nothing beautiful left to play, my counsel is
to shut down the transmitter and economize
on electricity at the rate of three cents per kilo-
watt hour.
Background Noises
M
R. A. S. DANA of Seymour, Connecti-
cut, writes us as follows:
'LET THE GHOST CALL AT MY OFFICE
The better grade of broadcasters have made
such improvement in their quality that there is
but one factor which could be improved in so
far as my ability to judge quality goes.
Is it not possible for them to reduce or elimin-
ate the noise background which accompanies
the transmission? In other words, cannot the
equipment be improved so that it is not possible
to tell when a station is on the air unless speech
or music enters the microphone? According to
present standards, it is easy to locate and tune-in
a station when they are not broadcasting simply
by the racket which occurs when the station is in
tune.
Mr. Dana seems to think that the noise in
question is all generated at the transmitter.
Actually there are three possible sources. In
some cases all are in evidence, and in others none.
Background noise may have its inception
right at the microphone. The transmitter itself
has a degree of inter-
nal hiss caused by cur-
rent passing through
the carbon in the
case of a microphone,
and by tube irregu-
larities in the first
stages of the ampli-
fier associated with a
condenser transmitter.
But if the microphone
is well designed and
the carbon of high
quality, and not too
old, the sensitivity
to external sounds
is so great that the
hiss is seldom audible.
In the case of speech
input some slight hiss
is usually observable,
and occasionally
during pianissimo
passages of musical
performances, but
with proper micro-
ohone care the internal
NOVEMBER, 1927
Q
3
FIG. I
noise level is negligible. If the tubes in the asso-
ciated amplifier of a condenser transmitter are
carefully picked this instrument is practically
noiseless with normal inputs. Of course any type
of transmitter will pick up room noises, and
broadcasters cannot always secure their material
in perfectly quiet places. But in general we may
say that most well regulated stations transmit
practically noise-free modulation. By that I
mean that at a distance of a few feet from the
monitoring cone in the station, which is assumed
to emit a loud signal during modulation, no
sound is audible in the intervals. Of course, by
placing one's ear on the cone one can hear plenty
of rustle, but that is going out of one's way.
It is like saying that the alarm clock in my house,
which I can hear ticking 33 feet away if I listen
hard enough, is causing a disturbance which
should be eliminated.
But after leaving the transmitting antenna,
the modulated wave must run the gauntlet of
electromagnetic disturbances in the medium
between transmitter and receiver. The metaphor
1 have used here may be an unfortunate one, if
it confirms the popular supposition that the car-
rier, in some mysterious way, picks up noises on
its journey through space. People jump to this
conclusion because they find, in tuning their
receivers, with the sensitivity control well down,
that they hear nothing over a certain section of
the broadcast frequency range, and then, run-
ning across a blank carrier, they get a more or
less audible background. The actual sequence
here is more along the following lines, however:
The receiver has been picking up slight disturb-
ances— static, distant violet-ray machines, trans-
mission lines, bells, and the like, right along, but
at a level below audibility, when the receiver
sensitivity is low. But the carrier coming in in-
creases the receiver sensitivity through its hetero-
dyne amplification, hence the noises come up
when the receiver is tuned to a carrier. Of course
neighborhoods vary in the relative strength of
external disturbances, and anywhere there is a
variation with time; normally the atmosphere
may be quiet, but when there is local lightning
plenty of crashes and rumbles will be picked up
by all receivers. However, Mr. Dana's question
probably does not include these relatively rare
periods of acute disturbance.
Finally we must take into account the internal
noises of the receiver itself. There is a tendency
for slight gaseous irregularities in the radio
frequency tubes to be amplified through each
successive stage until quite a noticeable rustle
results in the loud speaker. But if the tubes are
properly exhausted there should be no trouble
from this source. I have an eight-tube receiver,
and, in testing it as 1 write with the sensitivity
control all the way up and the loop removed to
eliminate r.f. input, I am unable to hear any
CARRIER FREQUENCIES ON TELEPHONE LINES
sound whatsoever. With the loop in position I ^
can hear the elevator motors in nearby apart-
ments and a medley of undifferentiated noises,
but then in practice 1 should never think of using " ^
the receiver in this state of excessive sensitivity.
The receiver may also develop internal noises
through regeneration at radio or audio frequency,
or through an impure plate or filament supply.
When at a low level, many such sources of dis-
turbance manifest themselves as rustling or
murmuring sounds which may be ascribed to the
broadcast transmitter.
The increase of transmitting power has un-
doubtedly reduced background noise in radio
reception, by permitting the use of less stages of
amplification and lower sensitivity at the re-
ceiver, for the same signal volume. But the factor
of modulation depth comes into the problem
forcefully. A weakly modulated carrier simply
amplifies static and interference at the expense
of its intelligence-bearing side bands. Deep
modulation is highly desirable on this account,
and limitations on adequate modulation — which
means 80-90 per cent, peaks, are as bad as inade-
quate field strength. Of course the best thing is
to get rid of the carrier altogether, but that is a
technical step feasible, at this stage, only in
radio circuits professionally operated at both
ends.
51
Circuit Efficiency
FREQUENCY
FREQUENCY
Output Currents
Abstract of Technical Article. VII
Making the Most of the Line — A Statement
Referring to the Utilisation of Frequency Bands
in Communication Engineering, by Dr. Frank
B. Jewett. Presented before Philadelphia
Section of the A. I. E. E. on October 17,
1923. Reprinted May, 1924 by Bell Telephone
Laboratories, Inc.
(Continued from October RADIO BROADCAST)
IN A carrier-current telegraph system free of
capacity and inductance, a series of dashes
made at the transmitting key will be repro-
duced accurately as oscillations of the carrier
frequency within a rectangular envelope, as
.--Band Filter
_i__-- Resonant Circuit
U f
S
^
o
FREQUENCY
FIG. 3
shown in Fig. i-A. If, now, inductance and cap-
acity be inserted into the circuit so that it be-
comes resonant to the carrier frequency, the
same keying action will produce, at the receiving
end, a trace like that of Fig. i-B. The circuit
now has a certain "stiffness," so that it takes
some time for it to reach the full amplitude of
oscillation at the carrier frequency, and again,
<M/-pJUb-nJ!a/-r\flll/-° S I
LOW PASS FILTER
HI I II I II I lh-»
HIGH PASS FILTER
FREQUENCY
FREQUENCY
A
BAND PASS FILTER
FREQUENCY
FIG. 4
FREQUENCY
FIG. 2
after the key has been opened, the oscillations
continue in a decaying wave train like that of
the old spark transmitters. The faster the rate of
signalling, the more serious the distortion; if,
for example, dots and dashes are made too
rapidly, the amplitude will never drop to zero at
all, as shown in Fig. i-C, although complete
breaks are made at the key. The reason for this
appears in Fig. 2. The top curve (A,) is a typical
resonance peak, showing how the circuit effi-
ciency, by virtue of the tuning effect, varies with
frequency. This property, as we saw in the first
instalment of this abstract, is a valuable means
of frequency discrimination. But the effect also
involves changing the amplitude of the various
components shown in the input currents of Fig.
2-B to the output currents of Fig. 2-C. As we
saw in the earlier ciscussion, 2-B includes the
components of a square-topped wave. The
suppression of the higher harmonics and the
exaggeration of the carrier frequency have de-
stroyed the rectangular wave shape. We could
get it back by sacrificing selectivity — by broaden-
ing the circuit — but then we sacrifice also the
power of discrimination on which we must de-
pend if we are to make the most of the line.
Obviously what is needed is a form of frequency
discrimination which will pass a certain band of
frequencies with substantially equal efficiency,
and cut off sharply frequencies outside of this
band. Reactive networks known as "filters"
have been devised by telephone engineers to
give this effect. Fig. 3 shows the difference in
transmission characteristics between a resonant
circuit and a filter designed to pass a band of
frequencies in the same neighborhood. Fig. 4
illustrates the principal types of filters and their
respective properties. Such circuits are of the
utmost importance, not only in the practical
communication arts, but also in investigations
of the nature of speech and music. (Cf. Jones:
"The Nature of Language," abstracted in April,
1927, RADIO BROADCAST.)
Besides the property of selective frequency
transmission, the characteristic impedance of
such networks is of importance. Fig. 5 illustrates
two types of band filter with substantially simi-
lar elements, but designed for different connec-
tions. A is feasible for parallel connections, the
impedance being very high for all frequencies
save the band the network is designed to pass.
But when the terminating elements are as
shown in B the impedance to frequencies other
than those in the transmitted region is low, so
that such filters may only be connected in series.
By the use of networks suitably designed and
connected a number of carrier frequencies may
be delivered to a line without mutual absorption,
52
RADIO BROADCAST
NOVEMBER, 1927
and then separated for individual demodulation
at the receiving end of the line.
By the methods described above the multiplex-
ing of lines is accomplished. As an example,
Jewett gives the schematic circuits for the multi-
plication of telephone channels over an open wire
toll line.
Up to about 100 cycles per second the line is
available for d.c. telegraph purposes. Above this
point comes the d.c. telephone band with its
300-2800 cycle range, approximately. From
3000 cycles up to about 35,000 may be used for
carrier-current telephone channels. It is custom-
ary in most cases to use the frequencies below
20,000 cycles for transmission from east to west,
and those above this figure for transmission from
west to east. The attenuation suffered by cur-
rents in the upper range is naturally greater and
correspondingly higher amplification is required
for equal received energy. A band about 2500
cycles wide must be allowed for each carrier
channel, and a space of 1000 cycles is required
for separation between channels with band filters
Normal Line -»._
Trunk Line
Receiving Channels
WEST TERMINAL
FIG. 6
possessing the usual discrimination characteris-
tics.
Fig. 6 shows one terminal of a carrier tele-
phone system. At this end we shall follow out the
steps involved in multiplex transmission. As the
line is also used ford.c. telegraphy and telephony,
a low-pass filter is inserted in the metallic circuit
to prevent the carrier frequencies from reaching
subscribers through the toll board. Likewise in
the carrier line, a two-way high pass filter pre-
vents the currents below 3000 cycles from being
absorbed in the carrier apparatus. Three pairs
are shown leading from the toll board to the
carrier equipment. In the case of the channel
which is shown in heavy lines, the voice currents
pass first through a low frequency circuit which
permits the passage of current between the nor-
mal line and either the transmitting or re-
ceiving side of the carrier equipment, but which
blocks currents between these two halves in a
FOR PARALLEL CONNECTION
J_
JU
10'-
10' -
pWir» Communication
JMM
nnptaie Musical Scale.
64 Fc™
256FcMMid
Vf-
...
«PL:
T'WlWtOTt 1. — - i •
— 1024 FC I Pi
40% FC"
16384 Fc*1
IflP-
10'-
Commercial
&'oKkKtmg >• Radio Communication
"^JLES OCTAVES
10'-
Amateuf
SfMtill S*rv««
\t.
If.
Shorter Hertzian Waves
10:'-
Itf1-
10-
10:i-
Infra Red
io;<-
I '.}**« ?(«?."« J!1;?"* E»»i>. «n»5BhM
10!''-
iir-
.
-.- = .-.- - J -,_..». . _ — ««vB*JS7 V'SiDie SpeCUTJm
Uftra-Violet
iv--
Very Soft X Rays
VS--
_
X-Rays
10"-
....
Gamrr^Rays
irr-
....
FIG. 8
FOR SERIES CONNECTION
FIG. 5
vertical line. The importance of this feature will
appear later on. When the subscriber on this end
talks the voice currents generated in his desk
set modulate the output of one of the carrier
oscillators, and, passing through a band filter,
which selects one of the side bands, merge with
other side bands and go to the trunk line. First,
however, it will be noted that they pass through
a low-pass filter, designed to transmit the east-
bound group of frequencies below 20,000 cycles.
This filter prevents the transmitting carrier
circuits from absorbing incoming energy in-
tended for the receiving channels.
At the other terminal of the line, sketched in
Fig. 7, the receiving process may be traced.
Again the common line is connected to a low-
pass and a high-pass filter. At this crossroads
the low-pass filter selects currents associated
with d. c. telegraphy and telephony and admits
them to the composite set. The high pass filter
selects the carrier side bands coming in from the
west terminal and conducts them to the group-
ing filters, where the incoming currents are led
to the receiving modulators. Again a band filter
selects the appropriate side band for each branch.
The demodulated currents pass to their respec-
tive jacks on the toll operators' board, through
the low frequency balancing circuits. If it were
not for these circuits obviously the received
voice currents would be sent back through the
transmitting carrier equipment, instead of being
confined to the subscriber at the east terminal.
Jewett sums up the process physically as
follows:
We have . . . followed through, from one toll
board to the other, a particular signal and have
seen how it is moved about on the frequency scale
to a position which identifies it from other similar
signals, how it is associated with such signals on a
common line, transmitted to the distant terminal,
isolated at the receiving end from these other
signals and finally restored to its original position
upon the frequency scale.
When a circuit is to be multiplexed for tele-
graph the range between
3000 and 10,000 cycles is
normally devoted to this
purpose. The directional
dividinglineisthen usually
at 6000 cycles, frequen-
cies below this point being
used for transmission from
west to east and frequen-
cies above 6000 for trans-
mission from east to west.
Various combinations of
carrier telephone and tele-
graph are possible. One
layout shown in Jewett's
paper comprises the fol-
lowing facilities: 2 full
duplex normal telegraph
channels; i normal tele-
phone channel; 10 full
duplex carrier telegraph
channels; 3 carrier telephone channels. This
amounts to a total capacity of 24 one-way
telegraph messages and 7 one-way telephone
messages for one pair of wires.
Carrier channels, employing currents of rela-
tively high frequency, are subject to correspon-
ingly greater attenuation and must sometimes
be provided with repeaters at points where low
frequency channels do not require amplification.
At such a repeater station the low frequency
currents are carried around the carrier repeaters
by means of two low pass filters and a wire cir-
cuit. By means of group filters the telegraph
channels are separated from the telephone chan-
nels, and finally each individual frequency is
led by a band filter to the repeater designed for it.
Jewett ends his paper by a brief discussion of
the multiplexing of radio circuits. He points out
that at the high frequencies employed in radio
transmission the range covered by a simple
resonant circuit is usually sufficient to include a
band wide enough for good telephonic quality,
so that filters, with their rectangular characteris-
tics, are not required.
Trunk Line
Receiving Channels
EAST TERMINAL
FIG. 7
A spectrum chart of electromagnetic waves,
with frequency plotted on a logarithmic scale,
taking in everything from the commercial d. c.
telegraph to the gamma rays of radium, is also
supplied, and is reproduced here as a matter of
general interest (Fig. 8).
Auditorium Acoustics
THE Celotex Company of 645 North Michi-
gan Avenue, Chicago, have issued a good-
sized booklet describing their patented
sound absorbing material, Acousti-Celotex,
which, among other applications, has found use
in various broadcasting studios in this country.
About eight pages of the pamphlet are devoted
to a fairly technical discussion of "Analyzing the
Acoustics of Auditoriums," the subject matter
covered being the same as that of our article on
"Studio Design" in the June, 1927, issue of
RADIO BROADCAST. The former article, being
considerably longer, goes into more detail and
takes up special problems, such as the effect of
stage openings and balconies in auditoriums,
factors influencing distribution of sound, etc.
Naturally Acousti-Celotex is the absorbing ma-
terial used in the examples, but the discussion is
commendably general and only a small portion
of the space in this section is devoted to adver-
tising the manufacturer's product. The pamphlet
should prove of interest to many broadcasters
and acoustic engineers.
A word about commercial aspects in such mat-
ters. This department does not recommend
specific products to its readers, but neither does
it labor under any phobia as regards commercial
publications. It is glad to receive them, and,
when the material appears interesting and useful
to technical broadcasters, in the personal judg-
ment of the one who happens to be writing these
papers, they will be mentioned at suitable times
RADIO BROADCAST ADVERTISER
53
ALUMINUM
AT THE RADIO SHOWS
T
year's Radio Shows
demonstrate that Aluminum
has been adopted for shielding
by more of the leading manu-
facturers and Radio Engineers
than ever before.
The RGS "Octa-Monic" is an
outstanding example of the use
of Aluminum in prominent
sets. The specifications call
for Aluminum Box Shields
>
to insure amplification, tone
quality, sensitivity and selec-
tivity.
The standard "knock-down"
ALUMINUM BOX SHIELDS—
5"x9"x6" — are adaptable to
many hook-ups.
Write for new booklet, "Alu-
minum for Radio," telling of
the advantages of Alumi-
num in Radio apparatus.
ALUMINUM COMPANY OF AMERICA
2464 Oliver Building, Pittsburgh, Pa.
Offices in 18 Principal American Cities
ALUMINUM IN EVERY COMMERCIAL FORM
54
RADIO BROADCAST ADVERTISER
Not Regenerative! Not Tuned
A. C. Tube Models
R. G. S. "Octa-Monic"
A-C Tube Kit
including instructions and blue-prints; all
necessary apparatus, ready to build,
$119.60
•
R. G. S. "Octa-Monic"
A-C Tube Chassis
Completely assembled according to latest
laboratory methods, (carefully tested and
selected heavy duty urire, lamp socket
connections, cable, Power (A-C) Trans-
former, etc., etc.,) with instructions and
blue-prints for installation, ready to plug
in your lamp socket and operate, $129.60
R. G. S. "Octa-Monic"
A-C Tube Receiver
housed in an attractive, partitioned, toal-
nut table cabinet, $149.60
NOTE: All models of the R. G.S.
"Octa-Monic" have been adapt-
ed to the Cunningham A-C and
Power Tubes (Four (4) CX 326, one
(/) C 327, and one (1) CX 371.)
The "B" Battery Eliminator and
the Cunningham Tubes are not
included in the following prices.
This eliminates an unnecessary
expenditure on your part be-
cause the A-C Tube models of
the R. G. S. "Octa-Monic" have
been designed to operate satis-
factorily with any good "B"
Eliminator. It is recommended
if your "B" Eliminator has no
"C" battery tap, that you use
the regular 40 volts of C battery.
Price Notice
Above prices do not include Cunningham
A-C and Power Tubes nor the "B" Bat-
tery Eliminator. All A-C models mill
operate on any good eliminator. This,
there/ore permits the use of your own "B"
Battery Eliminator, thereby representing
a very distinct saving to you.
The fundamentally new R. G. S. "Octa-Monic" Receiver developed by David
Grimes is one of the four great radio developments of the past 10 years. The
R. G. S. "Octa-Monic" principles are fully as important and represent as basic
a contribution to the Radio Art as did any of the discoveries of DeForest, Arm-
strong, Alexanderson, etc., etc.
These new and revolutionary principles of tuning, or the radio frequency end
of the R. G.S. "Octa-Monic," produce results not only superior but, these
principles of tuning place this Receiver far in advance of any receiver developed
to date. The R. G. S. "Octa-Monic" is fundamental and is as radically new as
was the Super-Heterodyne.
These highly efficient principles employed in the new R. G. S. "Octa-Monic"
cover not only the tuning or radio frequency end of this receiver but they cover
the amplification end as well. The R. G. S. "Octa-Monic" amplifier (Power
tube in the last stage,) gives, unquestionably, as perfect reproduction as it is
possible to buy, regardless of cost.
The^R. G. S. "Octa-Monic" comes to you more heavily endorsed by able au-
thorities than any other receiver ever presented to the Radio Public. The editor
of one of the most important radio publications in America said that it was the
only receiver he had ever seen in his career as an editor to which the terms "new
and revolutionary" could be applied in good faith.
Selectivity superior to the super-heterodyne without cutting side bands. Selectivity enough to
eliminate the heterodyne squeals of local stations, operating on a higher octave; selectivity that is
equal over the whole dial without being at all critical at any point; selectivity enough to separate
with ease the local jumble of Metropolitan (New York City, Chicago, San Francisco, etc.) stations;
selectivity enough to give five (5) degrees of silence between stations WEAF and WNYC in a lo-
cation 200 yards away from WNYC.
Selectivity positive enough to make use of vernier control unnecessary.
Sensitivity or Distance-Getting Ability. Can work right down to static level. This in-
sures trans-continental or trans-oceanic reception on favorable occasions.
Volume sufficient to fill a hall that will seat 3500.
Tonal Quality that is as nearly perfect as development in the Radio Art will permit-.
Straight Line Audio Amplification.
Stability Margin of 800 ohms. The average receiver has a stability margin of from 6 to
20 ohms. This high stability margin of the R. G. S. "Octa-Monic" eliminates any possibilities of
howling from poor batteries or "motor-boating" from eliminators. Batteries registering as low as
10 volts will deliver a clear tone, free from howling, in this receiver.
Straight Line Radio Amplification insuring reception at all broadcast wavelengths.
Straight Line Volume Control that makes distorting of tone impossible.
DEALERS: Write for Complete Merchandizing Proposals
BUILT FOR MODERN
BROADCAST CONDITIONS
RADIO BROADCAST ADVERTISER
jt(j(yn&
Automatic Wavetrap for prevention of heterodyning and whistling resulting from stations
operating on one-half wave-length or on first octave beat.
Automatic Filament Control.
Employs 135 Volts or 180 Volts. Draws 22 mils.
Each R. G. S. "Octa-Monic" is carefully tested with scientific apparatus and under actual broad-
casting conditions before it leaves the laboratories; while every piece of apparatus is just as thor-
oughly tested before it is built into this receiver.
The R. G. S. "Octa-Monic" is a closely co-ordinated Receiver built of quality apparatus. Careful
tests are the basis for the choice of each piece of apparatus, tests that not only determine the merits
of each individual part, but more importantly its relation to the whole receiver.
Standard Cunningham tubes (5 CXjoi-A's and i CXjyi, Power tube in last stage) and Western
Electric Cone are recommended for best results.
The R. G. S. "Octa-Monic" is highly attractive in appearance. It is built on five-ply, specially
shellaced sub-panel (20" x 9") to which is mounted a beautiful walnut finished, standard size
panel (7" x 21") that will fit any good cabinet or fine console 7" x ai". The panel and drum
escutcheons are trimmed in dull bronze.
You will find your R. G. S. "Octa-Monic" mighty easy to operate.
There are but two drums with vernier adjustments and two control knobs, one of which is an or-
dinary volume control and filament switch, the nearest approach to tuning efficiency, possible.
Stations actually "click" or "tumble-in" as you slowly revolve your drums.
The customary need of wooden screw-drivers or involved balancing devices is entirely removed
in the R. G. S. "Octa-Monic." Major or minor adjustments are unnecessary . The R. G. S. "Octa-
Monic" is free from ordinary service. Tuning condensers are the only moving parts, and as a conse-
quence, there are no fussy mechanisms, either mechanical or electrical, to get out of order.
The R. G. S. "Octa-Monic" operates satisfactorily on either a good "B" battery eliminator or
batteries without "motor-boating" or howling.
Orders cannot be accepted for individual pieces of apparatus or blueprints.
The R. G. S. "Four" employing the Inverse Duplex System (i) R. G. S. "Four" Kit, all parts, com-
plete instructions, $74.40. (2) Chassis, assembled according to latest laboratory methods, $84.40.
All prices slightly higher west of Denver. Canadian and Export prices on request.
Go to your dealer to-day and insist on a demonstration. If he hasn't stocked the R. G. S. "Octa-
Monic" yet, tear off and mail to us the attached coupon with the required information. Every effort
will be made to arrange a demonstration for you.
Arrange for that demonstration now because you have a real radio thrill waiting for you. In the
R. G. S. "Octa-Monic" you will hear radio at its best. And when you hear the R. G. S. "Octa-
Monic" you will know why it is: "The Synonym of Performance."
All models of the R. G. S. "Octa-Monic" and the R. G. S. "Four" are fully protected by
Grimes Patents issued and pending.
'Trade Marl{ Registered.
DEALERS: Write for Complete Merchandizing Proposals
R-G-S Manfg. Co., Inc.
Staten Island
New York
Battery or "B" Elim-
inator Models
R. G. S. "Octa-Monic" Kit
of parts including all required apparatus,
complete instructions and blue-prints,
ready to build, $84.60.
R. G. S. "Octa-Monic" Chassis
complete!} assembled according to latest
laboratory methods, (closely co-ordinated
and specially designed apparatus, eight
foot Da Hery cable, etc., etc.) with com-
plete operational instructions, ready to
operate, $89.60.
R. G. S. "Octa-Monic" Receiver
housed in an attractive, u>ell-designed,uial-
nut table cabinet, $104.60
R. G. S. "Octa-Monic"
Tuning Kit
including all necessary apparatus and com-
plete blue-prints and instructions, $63.60
R. G. S. "Octa-Monic"
Tuning Chassis
completely assembled according to latest
laboratory methods ttuth complete instruc-
tions and ready to unre to your favorite
amplifier, $66.60
Price Note
The apparatus required to build the rod-
ically new and fundamental R. G. S.
Octa-Monic actually lists at oner SIOO.QO.
R. G. S. MANFG. CO., Inc.
Staten Island, New York
Gentlemen:
Please arrange with my dealer, whose address I have printed
below, for a demonstration of the new and'revolutionary R. G. S.
"Octa-Monic". I am much interested in this receiver but this
request for a demonstration and literature, you understand, en-
tails no obligation on my part.
My Name
Street
City or State
My Dealer's Name
His Address
BUILT FOR MODERN
BROADCAST CONDITIONS
56
RADIO BROADCAST ADVERTISER
Kept
Cool—
Li\e the Best
Airplane Motors
TRUVOLT
An All'Wire Variable
Voltage Control
Here is the finest voltage con'
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your power devices! Its spec-
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keeps it cool like an air-cooled
engine. This prevents dete-
rioration and assures permanent
accuracy with long life.
Resistance made entirely of
nichrome wire with very low
temperature coefficient and ex-
posed directly to air — -heat not
held in by enamel coverings as
in other resistances. Permits
potentiometer control and
gives positive metallic contact
at all times with 30 exact read-
ings of resistance.
Type
T-5
T-io
T'20
T-50
T'loo
T'200
1-250
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Ohms
Resistance
O to 500
O to I.OOO
O to 2.OOO
o to 5,000
O to IO,OOO
O to 2O,OOO
o to 25,000
o to 50,000
Milliamperes
Current
224
158
112
71
50
35
32
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Eight stock types with resist-
ances up to 50,000 ohms. All
rated at 25 watts.
List $3.50 each
Also full line of fixed wire
resistances.
Write for free circular
"This Is An
Eliminator Year"
Dept. 14A
175 Varick Street
New York
ELECT RAD
The Radio Broadcast
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. An index appears twice a year dealing with the sheets
published during that year. The first index appeared on sheets Nos. 47 and 48, in No-
vember, 1926. In July, an index to all sheets appearing since that time was printed.
The June, October, November, and December, 1926, issues are out of print. A com-
plete set of Sheets, Nos. I to 88, can be secured from the Circulation Department,
Doubleday, Page & Company, Garden City, New York, for Ji.oo. Some readers have
asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any such errors do appear, a new Laboratory Sheet with the old
number will appear.
— THE EDITOR.
No. 137 RADIO BROADCAST Laboratory Information Sheet November, 192?
Operating Vacuum Tubes in Parallel
METHODS AND RESULTS
TT IS sometimes desirable to operate several tubes
-1 in parallel in order to obtain a greater power
output, and it is of interest to know how efficiently
this may be done.
If two tubes are to be used in parallel in the
output of an audio amplifier the two sockets are
wired so that the grid of one tube connects to the
grid of the other tube and the two plates connect
together. The two filaments are also connected
together. The result is that from these two tubes
we will have only four leads— one from the grids,
another from the plates, and two others from the
filaments.
The amplification constant of the combination
will be equal to the constant of a single tube, pro-
vided both of the tubes have the same constant. If
one of the tubes had a low amplification constant
and the other a high constant the resultant amplifi-
cation constant of the two would be equal to the
arithmetic mean. If the amplification constant of
one tube is six and the other four, the resultant
amplification constant will be five.
The resultant plate impedance will be equal to
one half the impedance of a single tube, and if unlike
tubes are used, the total impedance can be calcu-
lated by the simple laws governing resistances in
parallel. The combined impedance can be stated as
follows:
Imped, of one tube X Imped, of other tube
Imped, of one tube + Imped, of other tube
The greatest power output is obtained when the
two tubes have identical plate impedances and
amplification constants. Fortunately, however, a
very large fraction of the total power of the two
tubes can be obtained even if they differ consider-
ably.
To illustrate, two tubes might be connected in
parallel, the amplification constants of which are
in a ratio of 2 to 1, and the plate impedances of
which are equal, and from the combination we could
obtain 90 per cent, as much power as could be ob-
tained if the tubes were operated in separate cir-
cuits. If, with equal amplification constants, the
plate impedances are in a ratio of 2 to 1, the total
power will be about 90 per cent, of the maximum
possible value. It is evident, therefore, that the
total power will not be decreased by any great
amount even if tubes quite widely differing in
characteristics are used. From two perfectly
matched tubes, feeding into a load resistance
equal to their combined plate impedance, we can
obtain twice as much power as can be obtained from
a single tube feeding into a load resistance equal to
its plate impedance.
No. 138 RADIO BROADCAST Laboratory Information Sheet November, 1927
The Unit of Capacity
CALCULATION AND FORMULAS where C = capacity of condenser in microfarads
K = dielectric constant
'T'HE capacity of a condenser is stated in terms of A = total area of dielectric between
1 the quantity of electricity it will hold per volt. plates in square inches
When a condenser stores a specific quantity of elec- d = thickness of dielectric in inches
tricity known as a coulomb and there is an elec- Example:
trical pressure of one volt across its terminals then What is the capacity in microfarads of a con-
the capacity of the condenser is one "farad." A denser having 2000 plates? The dielectric consists
condenser must be very large to have a capacity of of paraffined paper 0.002 inch thick. The part of
Vaseline Ebonite Glass Mica ^a*" Porcelain
Oiiart? Rpsin shpllar Castor Olive Petroleum
Quartz h leilac Qi, QJ, oa
2.0 3.0 7.0 6.0 2.5 4.0
4.5 2.5 3.5 5.0 3.0 2.0
a farad and therefore a millionth part of a farad
has been adopted as the practical unit and it is
called the "microfarad," meaning one-millionth of
a farad. Capacities smaller than one microfarad can
be expressed in micro-microfarads, corresponding to
a millionth of a microfarad.
The capacity of a condenser may be computed
from the general equation -.
_ 2250 AK
each sheet of dielectric actually between the plates
has an area of 6.3" x 8".
From the table in this sheet it will be seen that the
constant of the dielectric is 2.5.
The total area, A. of the dielectric is: —
A = 6.3 x 8 x 2000
= 100.000 square inches, approximately
Therefore
_ 2250 x 100,000 X 2.5
10'» x 0.002
= 28.1 microfarads
10'°d
RADIO BROADCAST ADVERTISER
57
. . . Modern
Radio is better \vith Battery Power
NOT because they are new
in themselves, but because
they make possible modern
perfection of radio recep-
tion, batteries are the mod-
ern source of radio power.
Today's radio sets were
produced not merely to
make something new, but
to give you new enjoyment.
That they will do. New plea-
sures await you; more espe-
cially if you use Battery
Power. Never were receiv-
ers so sensitive, loud-speak-
ers so faithful; never has
the need been so imperative
for pure DC, Direct Current,
that batteries provide. You
must operate your set with
current that is smooth,
uniform, steady. Only such
current is noiseless, free
from disturbing sounds and
false tonal effects. And
only from batteries can such
current be had.
So batteries are needful
if you would bring to your
home the best that radio
has to offer. Choose the
Eveready Layerbilt "B"
Battery No. 486, modern in
construction, developed
exclusively by Eveready to
bring new life and vigor to
an old principle — actually
the best and longest-lasting
Eveready Battery ever built.
It gives you Battery Power
Here if the Ereready
Laytrbilt"B" Battery No.
486, Eveready's longest-
lasting provider of Bat'
tary Power.
for such a long time that
you will find the cost and
effort of infrequent replace-
ment small indeed beside
the modern perfection of
reception that Battery
Power makes possible.
NATIONAL CARBON CO., INC.
New York |MBllal San Francisco
Unit of Union Carbide and Carbon Corporation
Tuesday night is Eveready Hour Night
— 9 P. M., Eastern Standard Time
WEAF-AW York WOC-DotiMiporl
WJAR— Providence WCCO— { ^"nneaP°"*
WEEI— Boston \ Si. Paul
WFI-Philadrlphia KSD-S«. Louis
WGR-Ouffalo WDAF-Kon.a. City
WC\f.-Pittsburfh WRG-R'ashington
WSAI-CmcinnalJ WGV—Sefieneclady
WTAM-Cfftic/ond WHAS-ioui»»(H«
WWJ-Delroit WSB— Atlanta
WGfi-Chicago WSM-ffashville
WVtC-Memphis
Pacific Coast Stations —
9 P. M., Pacific Standard Time
KPO— KGO— .San Francisco KFJ— Los Angelfs
KFOA-KOMO-SeaHjo KCW-Porf/onrf
Radio Batteries
\rthey last longer
The
air
i s
full of things you shouldn't
miss
58
RADIO BROADCAST ADVERTISER
CME
^Celatsite
lattery Cable
A rayon-covered cable of 5,
6, 7, 8 or 9 vari-colored
Flexible Celatsite wires for
connecting batteries or
eliminator to set. Plainly
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Stranded Enameled
Antenna
Best outdoor an-
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Loop Antenna Wire
Sixty strands of No. 38 bare
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Green or brown silk covering; best
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Flexible Celatsite
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A cable of fine, tinned
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in cartonm colored to match content*.
Acme
Celatsite Wire
Tinned copper bus bar hook-
up wire with non-inflam-
< mable Celatsite insulation, in
I 9 beautiful colors. Strips
easily, solders readily, won't
crack at bends. Sizes 14, 16,
18, 19; 30 inch lengths.
Spaghetti Tubing
Oil, moisture, acid proof; highly
dielectric — used by leading engi-
neers. Nine colors, for wire sizes 12
to 18; 30 inch lengths. (We also
make tinned bus bar, round and
square, in 2 and 2}£ ft. lengths.)
Send for folder
THE ACME WIRE CO., Dept. B
New Haven, Conn.
ACM
IRE
MAKES BETTER RADIO.1
No. 139
RADIO BROADCAST Laboratory Information Sheet November, 1927
Inductive Reactance
HOW IT IS CALCULATED
TF AN inductance coil is connected in series with an
*• a. c. ammeter to a source of alternating current,
a certain amount of current will flow in. the circuit,
depending upon the size of the coil and the fre-
quency of the current. If the voltage of the source is
divided by the current, the quotient will be the
"reactance" of the coil in ohms. For example, if
the frequency of the current being supplied by the
source of potential was 60 cycles and the voltage was
110 volts and the coil had an inductance of 1.0
henry, we would find that 0.292 amperes of current
would flow through the circuit. Then 110 volts
divided by 0.292 gives 377, which is the reactance in
ohms at 60 cycles of a coil with an inductance of
1 .0 henry. The reactance of a coil depends upon its
inductance and upon the frequency of the current.
It can be calculated by means of the following
formula :
Reactance = 6.28 FL
where F = the frequency of the current in cycles
per second, and L = the inductance of the coil in
henries.
In many calculations it is necessary to know the
reactance of some particular coil at some frequency
and for this reason on Laboratory Sheet No. 140 is
given a table of reactance for inductance coils be-
tween 0.01 and 100 henries at frequencies from 60
to 100,000 cycles. From the formula given herewith
it is evident that the reactance of a coil is directly
proportional to the inductance of the coil and also
directly proportional to the frequency. Doubling the
size of the coil gives twice the reactance and twice
the reactance is also obtained if the frequency is
doubled. If these two factors are remembered it is a
simple matter to calculate mentally the reactance
of any coil not given in the table on Laboratory
Sheet No. 140. For example a 10-henry coil has one
third the reactance of a 30-henry coil at, say, 100
cycles. Since the reactance of a 10-henry coil at
100 cycles is 6280 ohms, it follows that the reactance
of a 30-henry coil at the same frequency must be
18,840 ohms.
No. 140 RADIO BROADCAST Laboratory Information Sheet November, 1927
Coil Reactance
COIL INDUCTANCE
IN HENRIES
REACTANCE IN OHMS AT VARIOUS FREQUENCIES
60
100
250
500
1000
10,000
100.000
0.01
3.77
6.28
15.7
31.4
62.8
628
6,280
0.05
18.8
31.4
78.5
157
314
3,140
31,400
0.1
37.7
62.8
157
314
628
6,280
62,800
0.5
188.5
314
785
1,570
3,140
31,400
314,000
1.0
377
628
1,570
3,140
6,280
62,800
628,000
2.0
754
1,256
3,140
6,280
12,560
125,600
1,256,000
5.0
,885
3,140
7,850
15,700
31,400
314,000
3,140,000
10.0
3,770
6,280
15,700
31.400
62,800
628,000
6,280,000
20.0
7,540
12,360
31,400
62,800
123,600
1 ,236,000
12,360,000
30.0
11,310
18,840
47,200
94,200
188,400
1,884,000
18,840.000
40.0
15,080
24,720
61.800
123,600
247,200
2,472,000
24,720.000
50.0
18,850
31,400
78,500
157,000
314,000
3,140,000
31,400,000
100.0
37,700
62,800
157,000
314,000
628,000
6,280,000
62,800,000
This table shows how the reactance of various inductance coils varies with different frequencies. Labor-
atory Sheet No. 139 explains what inductive reactance is and upon what it depends.
No. 141 RADIO BROADCAST Laboratory
Information Sheet November, 1927
A. C. Tube
Data
"HEATER" AND FILAMENT TYPES
that heavv wire be used. Determine the total cur-
rent required by all the tubes and table No. 1 below
(~)N THIS Laboratory Sheet are given data on will tell you what size of wire to use.
W the new a. c. tubes, type
UY-227 (c-327
and
TABLE No. 1
type ux-226 (cx-326). The fo
rmer tube is <
>f the
Size
Current
heater type whereas the latter is of the a. c. filament
type. The heater tube requires a special five-prong
socket whereas the type 26 may be used with any
(B & S Gauge)
12 • 20
14 11
amperes
amperes
standard socket. The filament
voltage and current
16 6
amperes
of the type 27 are 2.5 volts a
id 1.75 amper
es re-
18 3
amperes
spectively. The type 26 requires a filament voltage
of 1 .5 volts and the filament current is 1 .05 amperes.
20 1
5 amperes
The filament current of these tubes is quite large, Table No. 2 on this sheet gives the characteristics
especially so in a multi-tube receiver, and for this of these tubes under various conditions of plate and
reason it is essential in wiring
the filament
leads grid voltage.
TABLE No.
2
UNDISTORTED
TYPE
OF TUBE
PLATE
VOLTAGE
NEGATIVE
GRID
VOLTAGE
PLATE
CURRENT
PLATE
IMPEDANCE
MUTUAL
CONDUCTANCE
POWER
OUTPUT IN
WATTS
UY-227
90
5
3
11,300
725
0.020
&
135
9
5
10,000
820
0.055
c-327
180
13.5
6
9,400
870
0.140
ux-226
90
6
3.7
9,400
875
0.020
&
135
9
6
7,400
1100
0.070
cx-326
180
13.5
7.5
7,000
1170
0.160
RADIO BROADCAST ADVERTISER
59
Dalkite has pioneered—
but not at public expense
Tit
" A" Contains no bat-
/\ fcry.Thesameas
Balkice "AB "but for the "A" circuit only.
Not a battery and charger but a perfected
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Ballrite "B" 9™ °/?* ltmgest
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radio. The accepted tried and proved light
socket "B" power supply. The first Balkite
"B," after 5 years, is still rendering satis-
factory service. Over3oo,oooinuse. Three
models: "B"-W, 67-90 volts, $22.50;
"B"-i35,* 135 volts, #32.50; "B"-i8o,
180 volts, $39.50. Balkite now costs no
more than the ordinary "B" eliminator.
Balkite Chargers
Standard for "A" batteries. Noiseless. Can
be used during reception. Prices drastically
reduced. Model "J,"* rates 2. 5 and .5 am-
peres, for both rapid and trickle charging,
$17.50. Model "N"* Trickle Charger,
rate .5 and .8 amperes, $9.50. Model "K"
Trickle Charger, $7.50.
* Special models for 25-40 cycles at
slightly higher prices
Prices are higher West of the
Rockies and in Canada
n
in
alone remains in its original form; all
others have either been radically re-,
vised in principle or completely with-
power have been made
I D // • oecause the hrst Balkite "J3," pur-
Oy £>alk.ite Firstnoiselessbat- chased 5 years ago, is still in use and
tery charging. Then successful light wil1 be for Xears to come,
socket "B" power. Then trickle charg- Because to your radio dealer Bal-
in
al
And today, most important of kite is a synonym for quality.
Balkite "AB," a complete unit
containing no battery in any form,
supplying both "A" and "B" power
directly from the light socket, oper-
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This pioneering has been impor-
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made Balkite one of the best known
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Because with
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in the field Bal-
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of long life and
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Because of
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socket "B"
power supplies
put on the mar-
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Balkite " AB
Contains no battery.
A complete unit, replacing both "A" and "B" batteries
and supplying radio current directly from the light
socket. Containsnobatteryinanyform. Operatesonly
while the set is in use. Two models: "AB" 6-135, '135
volts"B"current,$59.5o;"AB"6-i8o,i8ovolts,$67.5O.
Because the electrolytic rectification
developed and used by Balkite is so
reliable that today it is standard on
the signal systems of most American
as well as European and Oriental
railroads.
Because Balkite is permanent
equipment. Balkite has pioneered —
but not at the expense of the public.
Today, whatever type of set you
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out), whatever
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Your dealer
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the Balkite equip-
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FANSTEEL PRODUCTS COMPANY, INC., NORTH CHICAGO, ILLINOIS
Licensees for Germany:
Siemens K Halske, A. G. Wernerwerk M
Siemensscadc, Berlin
Sole Licensees in the United Kingdom:
Messrs. Radio Accessories Ltd., 9-13 Hythe Rd.
Willesden, London, N. W. 10
r"" M-EEL
Balkite
Tower Units
60
RADIO BROADCAST ADVERTISER
K4RA5
Parts Make the 2 Dial Karas
Equamatic the World's Best
5-Tube Receiver
"V"OU have r^ad and
•*• heard much about
the new 2-Dial Karas
Kqiiamatic— the -VTube
Receiver that is the talk
of its perfect neutrali-
zation and its Cinn-
pletely balanced opera-
tion. The results you
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Ul
Phenomenal, and tlie 2-
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ei-ett more than you ex-
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Farts insures this. These
parts are essential to the
perfect operation of the
-'-Dial Kquamatic, for
the receiver is built
md them. Some of
The NEW Karas Output
Filter, Price #8.00
The NEW Karas Type 28 "'«« fain°119 £art8 arfl.
Audio Transformer Jn°dwJ ^ut.0^ «,
Price, {(8.00 all the necrssary Karaa
I'arts elsewhere in this
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A Marvelous Purity of Tone
'T'HE 2-Dial Karas
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Tjpe 28 I impregnated
Audio Transformers —
the new Karas Trans-
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steel-clad rases. The new
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aids in building up a
clear, sweet tone for the
2-Dial Fquamatic. This
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Its extremely efficient
operation to the use of
the new Karas S- F. I,.
Variable Condensers,
and Karas Micrometrlc
Dials aid in giving the
•et 1-1000 of an Inch
tuning. The heart of the
Equamatic of course is
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ductance Coils, with their variable primaries and ad-
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tween these two coils to be automatically and continuously
maintained at every wave length setting of the dials.
Easy to Build this Receiver
YOU can easily build
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ceiver In a short time by
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for huildlne. The Karas
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3 Karas Equamatic Coils,
ea,-h $4; 2 Karaa Mfcro-
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KARAS ELECTRIC CO.
4033-K No. Rockwell St., CHICAGO, ILL.
Have You Heard the Knickerbocker 4--
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nn7
.00037 mfd.
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_ — _ — _ _ _ . Coupon ~~ — — ^ — — —
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4O33-K North Rockwell St.. Chicago. III.
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No, 142 RADIO BROADCAST Laboratory Information Sheet November, 1927
Obtaining Various Voltages from a B-Power Unit
VALUES AND CURRENT-CARRYING CAPACITY the total drain from the 90-volt tap is 10 milliam-
IT IS comparatively simple to calculate the resis- peres. Then the total current flowing through Ri
tance values required in the output circuit of a will be equal to 10 plus 1 plus 3, or 14 milliamperes.
B-power unit in order to obtain any specific vol- If the maximum voltage available from the power
tages. This Laboratory Sheet will explain how to unit is 180 and the voltage at terminal No. 2 is to
calculate the values of these resistances. be 90, it follows that the voltage drop across Ri
Consider the fundamental output circuit of a must be 90. Ninety volts divided by 0.014 amperes
B-power unit as illustrated in the sketch. The dia- gives 6400 ohms as the value of Ri.
gram of the rectifier and filter has been omitted *^_ _.. -
since they play no important part in the calculation
of resistance values. Suppose tap No. 1 is to be 45
volts and is to be used to operate a detector tube.
We will assume that the loss current through Rs is 3
milliamperes, or 0.003 amperes. This is an average
figure for the loss current and can generally be used
in this type of calculation. If the voltage at tap
No. 1 is to be 45, then the voltage drop across re-
sistance Rs must be 45. The resistance of Rs will
be equal to the voltage across it divided by the
current through it or, in this case, 45 divided by
0.003, which gives 15,000 ohms as the value of R3.
The voltage at tap No. 2 is to be 90. Since the volt-
age drop across R-> is 45, it follows that the voltage
drop across Ra will also be 45 in order to make the
total voltage between the negative B and tap No. 2
equal to 90. The current (lowing through the resis-
tance Ra will be equal to the loss current at 3 milli-
amperes plus the current drawn by the detector
tube, which is 1 milliampere. Therefore the value
of resistance R2 will be equal to the voltage across
it, 45, divided by the current through it, which is
0.003 plus 0.001, or a total of 0.004 amperes. This
gives a value of 11,250 ohms for R2. Suppose that
Dm
ter
1
o
1
Rj
** 2
I*
B-
Resistance units for B power units are usually
rated in watts and it is essential that the resistances
used be capable of carrying the necessary load
without overheating. The load in watts being han-
dled by a resistance can be determined by multiply-
ing the resistance in ohms by the square of the
current in amperes. In this particular example:
Watts through Rj = 15000 X 0.003'
= 0.135 watts
Watts through R2 = 11250 X 0.004'
= 0.18 watts
Watts through Ri = 6400 X 0.0142
= 1.25 watts
No. 143 RADIO BROADCAST Laboratory Information Sheet November, 1927
Solenoid Coil Data
UNITS FOR THE BROADCAST BAND mfd. variable condensers. The wavelength range of
the coil will be approximately 200 to 550 meters.
THIS Laboratory Sheet gives the data necessary The coils may be wound on hard rubber or bakelite
to wind the secondaries of solenoid type coils tubing, or some type of self-supported winding may
for use with 0.0005-mfd., 0.00035-mfd., or 0.00025- be used.
DIAMETER OF
TUBE IN INCHES
SIZE OF WIRE
NUMBER OF TURNS OF D.C.C. WIRE REWIRED WITH VARIOUS
SIZES OF TUNING CONDENSERS
0.0005 mfd.
0.00035 mfd.
0.00025 mfd.
31
28
26
24
22
20
28
31
34
38
42
38
42
46
50
55
50
54
58
64
72
3
28
26
24
22
20
35
39
43
47
51
48
52
56
61
67
62
67
73
81
88
21
28
26
24
22
20
42
45
48
51
53
54
58
63
70
78
63
73
80
90
98
144 RADIO BROADCAST Laboratory Information Sheet November, 1927
The Transmission Unit
CORRECTION OF LABORATORY SHEET NO. 114
TWO errors occurred in LABORATORY SHEET No.
114 published in the August, 1927, RADIO
BROADCAST. In the last line in the first column, the
word "natural" should be changed to read "com-
mon," and in the first line in the second column, the
same change should be made.
The chart on this sheet makes it possible to deter-
mine easily the number of telephone transmission
units if the current or voltage ratio is known. For
example, from the curve it is evident that if two
voltages or two currents are in a ratio of 5, then the
TU difference between them is 14. If we are dealing
with powers rather than currents or voltages, it is
merely necessary to divide the number of TU ob-
tained from the curve by 2 in order to determine
the TU difference of any two powers. For example,
two powers in the ratio of 8 to 1 have a TU differ-
ence of 9. To determine this value we look up the
number of TU corresponding to a ratio of 8 which
gives 18 and then divide by 2.
To illustrate the use of the curve we might take
an audio amplifier requiring a tenth of a volt input
to produce three volts at the output. If we wanted
to know the overall gain in TU we would divide
three by 0.1 , which gives 30. This ratio on the curve
corresponds to a 29.5 TU voltage gain.
^*
f
i
/
/
/
/
/
/
/
/
J'
/
/
/
/
/
/
/
/
/
\
2 3456
i 10 20 30 40 60 8010
CURRENT OR VOLTAGE RATIO
RADIO BROADCAST ADVERTISER
61
£>*
Announcing
A. C. TUBES
Alternating Current
The new M-26 and N-27 tubes are tubes using raw
A. C. on the Filament or Heater and can be used in
any set specifying these types. The M-26 is used in
the radio and audio frequency stages and has
a standard base. The N-27, of the separate
heater type is used as a detector or
amplifier and has a five prong
base. These tubes will give su-
perior results and maximum use-
ful life in any set designed to use
A. C. tubes of this type.
RADIO
\TUBESr
Write for particulars
C. E. MFG. CO., Inc.
Providence, R. I. U. S. A.
Largest Plant in the World Making Radio Tubes Eiclvsively
Heater
Volt*
t ,5
@@
"^•fo'-Eve,
RADIO
TUBES
CeCo announces a complete kit of tutas for the "Im-
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from your dealer and be sure you are right.
1 Type K, R. K. Amp. -
1 " H, Spl. Detector -
2 " G, HiMu Amp. -
1 " F, Semi Power -
Price »3.00
" 2.50
" 8.00
" 4.30
Total for kit *H.50
;>„,.
Special Radio Frequency types. Demand CeCo.
62
RADIO BROADCAST ADVERTISER
• • • • • • • • • • • • • •
• • • • • • • • • • • • •
Bradky0hm-E
PERFECT Vi
LE RESISTOR
The graphite disc principle,
utilized in the construction
of Bradleyohm-E assures
noiseless, stepless regulation
of plate voltage when used
in B' Eliminator hookups.
By turning the bakelite knob,
the plate voltage output of
the B'Eliminator can be ad'
justed, without steps or
jumps, to the precise value
for maximum volume. That
is why prominent B'Elimi'
nator manufacturers have
adopted Bradleyohm'E.
Ask your dealer for Brad'
leyohm'E in the distinctive
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firadkpunit-A
PERFECT FIXED RESISTOR
This is a solid, molded fixed
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out disturbing its rating.
For resistance'coupling,
grid leaks, and other appli'
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Bradleyunit'A in any de'
sired rating.
ELECTRIC CONTROLLING APPARATUS
278GreenfieIdAve. (gD\ Milwaukee, Wit.
JVWAW.W.W.
Manufacturers* Booklets
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
may obtain any of the booklets listed below by us-
** ing tbe coupon printed on page 64. Order by number only,
1. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS — A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
4. RESISTANCE-COUPLED AMPLIFIERS — A general dis-
cussion of resistance coupling with curves and circuit dia-
grams. COLE RADIO MANUFACTURING COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
6. B-ELIMINATOR CONSTRUCTION — Constructional data
on how to build. AMERICAN ELECTRIC COMPANY.
7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-
TION— Circuit diagrams and discussion. ALL-AMERICAN
RADIO CORPORATION.
8. RESISTANCE UNITS — A data sheet of resistance units
and their application. WARD-LEONARD ELECTRIC COMPANY.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
1 1. RESISTANCE COUPLING — Resistors and their ap-
B'ication to audio amplification, with circuit diagrams.
EjuR PRODUCTS COMPANY.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
1 5. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE CONDENSERS — A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their applica'ion to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
17. BAKELITE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
19. POWER SUPPLY — A discussion on power supply with
particular reference to lamp-socket operation. Theory
and constructional data for building power supply devices.
ACME APPARATUS COMPANY.
20. AUDIO AMPLIFICATION — A booklet containing data
on audio amplification together with hints for the construc-
tor. ALL AMERICAN RADIO CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SH9RT-WAVE WAVE-
METER— Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
positions in the circuit where audio-frequency chokes may
be used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio-frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED.
51. SHORT-WAVE RECEIVER — Constructional data on a
receiver which, by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY — A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL, INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA — Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. RESISTANCE COUPLING^— A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION.
60. RESISTORS — A pamphlet giving some technical data
on resistors which are capable of dissipating considerable
energy; also data on the ordinary resistors used in resistance-
coupled amplification. THE CRESCENT RADIO SUPPLY
COMPANY.
62. RADIO-FREQUENCY AMPLIFICATION — Constructional
details of a five-tube receiver using a special design of radio-
frequency transformer. CAMFIELD RADIO MFG. COMPANY.
63. FIVE-TUBE RECEIVER — Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
64. AMPLIFICATION WITHOUT DISTORTION — Data and
curves illustrating the use of various methods of amplifica-
tion. ACME APPARATUS COMPANY.
66. SUPER-HETERODYNE — Constructional details of a
seven-tube set. G. C. EVANS COMPANY.
70. IMPROVING THE AUDIO AMPLIFIER — Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used.
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM — A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY,
80. FIVE-TUBE RECEIVER — Data are given for the con-
struction of a five-tube tuned radio-frequency receiver.
Complete instructions, list of parts, circuit diagram, and
template are given. ALL-AMERICAN RADIO CORPORATION.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
82. SIX-TUBE RECEIVER — A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams,
and templates for the construction and assembly of socket
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Panel layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequency
transformers of special design. KARAS ELECTRIC COMPANY.
85. FILTER — Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A socket
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimental
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blue print and necessary
data, for building an eight-tube receiver. THE GEORGE W.
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER — Data and blue prints
are given on the construction of a short-wave transmitter,
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES.
90. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification are
given. ALDEN MANUFACTURING COMPANY.
93. B-SOCKET POWER — A booklet giving constructional
details of a socket-power device using either the BH or 3 1 3
type rectifier. NATIONAL COMPANY, INCORPORATED.
94. POWER AMPLIFIER — Constructional data and wiring
diagrams of a power amplifier combined with a B-supply
unit are given. NATIONAL COMPANY, INCORPORATED.
ipo. A, B, AND C SOCKET-POWER SUPPLY — A booklet
giving data on the construction and operation of a socket-
power supply using the new high-current rectifier tube.
THE Q. R. S. Music COMPANY.
101. USING CHOKES — A folder with circuit diagrams of
the more popular circuits showing where choke coils may
be placed to produce better results. SAMSON ELECTRIC
COMPANY.
ACCESSORIES
22. A PRIMER OF ELECTRICITY — Fundamentals of
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
25. ELECTROLYTIC RECTIFIER — Technical data on a new
type of rectifier with operating curves. KODEL RADIO
CORPORATION.
26. DRY CELLS FOR TRANSMITTERS — Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS— Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE — Battery life curves with general
curves on tube characteristics. BURGESS BATTERY COM-
PANY.
29. How TO MAKE YOUR SET WORK BETTER — A non-
technical discussion of general radio subjects with hints on
how reception may be bettered by using the right tubes.
UNITED RADIO AND ELECTRIC CORPORATION.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
31. FUNCTIONS OF THE LOUD SPEAKER — A short, non-
technical general article on loud speakers. AMPLION COR-
PORATION OF AMERICA.
32. METERS FOR RADIO — A catalogue of meters used in
radio, with connecting diagrams. BURTON-ROGERS COM-
PANY.
33. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
34. COST OF B BATTERIES — An interesting discussion
of the relative merits of various sources of B supply, HART-
FORD BATTERY MANUFACTURING COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. CHOOSING THE RIGHT RADIO BATTERY — Advice on
what dry cell battery to use; their application to radio,
with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR — Information on the care of
vacuum tubes, with notes on how and when they should be
reactivated. THE STERLING MANUFACTURING COMPANY.
54. ARRESTERS — Mechanical details and principles of the
vacuum type of arrester. NATIONAL ELECTRIC SPECIALTY
COMPANY.
55. CAPACITY CONNECTOR — Description of a new device
for connecting up the various parts of a receiving set, and
at the same time providing bypass condensers between the
leads. KuR7-KASCH COMPANY.
'Continued on pagt 64}
RADIO BROADCAST ADVERTISER
63
f^ Celestuu^tradivanus
^me Advanced Hi-Q*Six
BOTH CUSTOM-BUILT!
The Hi-Q_ Six — the newest advance in radio — /our completely
isolated tuned stages — Automatic Variable Coupling — symphonic
amplification. A non-oscillating, super-sensitive receiver that as-
sures maximum and uniform ampli/ication on all u;ave lengths
and establishes a totally new standard of tonal qualify.
S y°SUST as Antonio Stradivari gave the
I 5 priceless Custom'built violin to mu'
L!o.oS sicians of his day, so does Hammarlund-
Roberts offer music lovers of our day the
Custom-built Radio.
The advanced "Hi-QSix" — designed by ten
of America's leading manufacturers — made
with America's finest parts — incorporating
every modern constructional feature — and
built under your own eyes from plans so com.'
plete, so exacting and so clear cut that the
only outcome can be absolute radio perfection.
In addition to its unprecedented perform'
ance, the Hi'Q Six offers equally unprecedented
economy, for by building it yourself you can
save at least $100.00 over the cost of finest
factory 'assembled sets. Complete parts in'
eluding Foundation Unit chassis, panels, with
all wire and special hardware cost only $95.80.
The Hi'Q Instruction Book tells the com-
plete story with text, charts, diagrams and
photos. Anyone can follow it and build this
wonderful instrument. Get a copy from your
dealer or write us direct. Price is 25 cents.
J^&mmarlund
R.OQ ELR.TS
Hi Q* SIX
HAMMARLUND-ROBERTS, INC.
1182 Broadway Dept. A New York City
(Associate ^Manufacturers
64
RADIO BROADCAST ADVERTISER
NEW!
the
Two Tube
Official
BROWNING-
DRAKE
Kit Set
This new assembly, the two tube
Official Browning-Drake has been
designed to be used with any good
audio transformer system now on the
market, such as Amertran, Thordar-
son, etc. The combination gives re-
markable tone quality and great vol-
ume. This two tube assembly uses
only the detector and R. F. tubes.
Special type T foundation unit
makes construction easy. The Offi-
cial Browning-Drake Kit is used.
Other Browning-Drake Corporation
products incorporated in the assem-
bly are the cartridge resistance and
the neutralizer.
If your dealer does not carry all of
the specified parts, send us his name
and your requirements will be met
immediately.
DEALERS:— There is profit and
satisfaction in handling popular
products. Write or wire TOD A Y
about the Browning-Drake line
of parts and the Browning-Drake
line of factory-built receivers.
LOOK FOR THIS
TRADE MARK
BROWNING-DRAKE CORP.
Cambridge :: Massachusetts
BROWNING
DRAKE
69. VACUUM TUBES — A booklet giving the characteris-
tics of the various tube types with a short description of
where they may be used in the circuit. RADIO CORPORA-
TION OF AMERICA.
77. TUBES — A booklet for the beginner who is interested
in vacuum tubes. A non-technical consideration of the
various elements in the tube as well as their position in the
receiver. CLEARTRON VACUUM TUBE COMPANY.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
91. VACUUM TUBES — A booklet giving the characteristics
and uses of various types of tubes. This booklet may be
obtained in English, "Spanish, or Portuguese. DEFOREST
RADIO COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS — A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new ^oo-milliampere rectifier tube. CARTER RADIO
COMPANY.
97. HIGH-RESISTANCE VOLTMETERS — A folder giving in-
formation on how to use a high-resistance voltmeter,
special consideration being given the voltage measurement
of socket-power devices. WESTINGHOUSE ELECTRIC &
MANUFACTURING COMPANY.
102. RADIO POWER BULLETINS — Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
103. A. C. TUBES — The design and operating character-
istics of a new a. c. .tube. Five circuit diagrams show how
to convert well-known circuits. SOVEREIGN ELECTRIC Jv
MANUFACTURING COMPANY.
MISCELLANEOUS
38.
LOG SHEET — A list of broadcasting stations with
columns for marking down dial settings. U. S. L. RADIO,
adcasting station
ettings. U. S. L.
INCORPORATED.
41. BABY RADIO -TRANSMITTER OF PXH-QEK — Descrip-
tion and circuit diagrams of dry-cell operated transmitter.
BURGESS BATTERY COMPANY.
42. ARCTIC RADIO EQUIPMENT — Description and circuit
details of short-wave receiver and transmitter used in
Arctic exploration. BURGESS BATTERY COMPANY.
43. SHORT-WAVE RECEIVER OF gxn-gEK — Complete
directions for assembly and operation of the receiver.
BURGESS BATTERY COMPANY.
58. How TO SELECT A RECEIVER — A commonsense
booklet describing what a radio set is, and what you should
expect from it, in language that any one can understand.
DAY-FAN ELECTRIC COMPANY.
67. WEATHER FOR RADIO — A very interesting booklet
on the relationship between weather and radio reception,
with maps and data on forecasting the probable results
TAYLOR INSTRUMENT COMPANIES.
73. RADIO SIMPLIFIED — A non-technical booklet giving
pertinent data on various radio subjects. Of especial in-
terest to the beginner and set owner. CROSLEY RADIO COR-
PORATION.
74. THE EXPERIMENTER — A monthly publication which
gives technical facts, valuable tables, and pertinent informa-
tion on various radio subjects. Interesting to the experi-
menter and to the technical radio man. GENERAL RADIO
COMPANY.
75. FOR THE LISTENER — General suggestions for the
selecting, and the care of radio receivers. VALLEY ELECTRIC
COMPANY.
76. RADIO INSTRUMENTS — A description of various
meters used in radio and electrical circuits together with a
short discussion of their uses. JEWELL ELECTRICAL IN-
STRUMENT COMPANY.
78. ELECTRICAL TROUBLES — A pamphlet describing
the use of electrical testing instruments in automotive work
combined with a description of the cadmium test for stor-
age batteries. Of interest to the owner of storage batteries.
BURTON ROGERS COMPANY.
95. RESISTANCE DATA — Successive bulletins regarding
the use of resistors in various parts of the radio circuit.
INTERNATIONAL RESISTANCE COMPANY.
06. VACUUM TUBE TESTING — A booklet giving pertinent
data on how to test vacuum tubes with special reference to
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT
COMPANY.
98. COPPER SHIELDING — A booklet giving information
on the use of shielding in radio receivers, with notes and
diagrams showing how it may be applied practically. Of
special interest to the home constructor. THE COPPER AND
BRASS RESEARCH ASSOCIATION
09. RADIO CONVENIENCE OUTLETS — A folder giving
diagrams and specifications for installing loud speakers in
various locations at some distance from the receiving set.
YAXLEY MANUFACTURING COMPANY.
USE THIS BOOKLET COUPON
1 RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, N. Y.
Please send me (at no expense) the following book-
1 lets indicated by numbers in the published list above:
Name.
Address.
(Name)
(Street}
(City} (State)
ORDER BY NUMBER ONI Y
1 This coupon must accompany every request. RB 1 1-27
The final improvement
to be made in your set,
install —
MODERN
Type M Transformers
Regardless of how perfectly your set may
be working, there is still finer reception in
store for you. The performance of Modern
Type M Transformers represents such an
advance in audio amplification that they
represent a new standard by which trans-
formers may be judged. They combine
high inductance, large core and wire sizes
and perfectly proportioned windings. Im-
pedances have been carefully matched to
the units with which they must work.
The result is an almost flat performance
curve with full response at 30 cycles and
all harmonics and over amplified high
notes fully eliminated.
Satisfactory performance of Type M
Transformers is guaranteed. Prices 1st
and 2nd stage, $8.50 each; Output $8.00;
Push-Pull, $10.00 each.
Mail coupon below for blue-
print folder showing Type M
audio amplifying circuits
MODERN
"B" Compact
A Raytheon "B" power unit that has been
proven dependable and is guaranteed.
Price $26.50 without tube. Sent by mail,
postpaid, if your dealer cannot supply you.
The Modern Electric Mfg. Co.
Toledo, Ohio
The Modern F.lectric Mfg. Co.
Toledo, Ohio
Please send prints of Typ. M audio circuits. I en-
close 2c stamp.
Name
Address
City
R.B.-n
RADIO BROADCAST ADVERTISER
FILTER
~s ..
^®
/X=
/K4 7-/0A/A L.
r a
»~*S ,67..
K3
\!S
AN ENTIRELY NEW AND UNIQUE
HEAVY-DUTY BETTER-E
Supplies
Detector voltages, 11 to 45, adjustable;
R. F. voltages from 50 to 75;
A. F. voltages from 90 to 135;
Power tube voltage 180 fixed.
An Exclusive Feature
Tubes and by-pass condensers are pro-
tected against excessive and harmful
voltages.
Designed for lasting service with
liberal factors of safety.
A Strictly Heavy-Duty
Power Unit
Output rating is 70 mils at 180 volts.
Uses R. C. A. UX-280 or Cunningham
CX-380 Rectron.
Licensed under patents of Radio
Corporation of America and Associ-
ated Companies.
For 105-115 Volts, 50-60 cycles A. C.
List price with cord, switch and plug,
$40. Rectifier tube $5.
Write National Co., Inc., W. A. Ready.
Pres. Maiden, Mass, for new Bulletin B-124
I « '« a
'Is I" »i
•
m — <•> i"»»™i
Type 7180
A "B" That's Built for Service
.9«« our Exhibit, Booth No. *, Chicago SAow, Oc«. 10th-l6th
NATIONAL TUNING UNITS _ THE HEAVENLY TWINS
More National Tuning Units have been used by set builders than all other similar components combined.
o.-_j-.j .:_,. . ion Afpnnd By Tho OFFICIAL Desigio
BROWNING & DRAKE
Standard sincej 1923
66
RADIO BROADCAST ADVERTISER
New AERO Circuit
Worth Investigating
The Improved Aero-Dyne 6 and the Aer
and Aero 4 are destined to be immens
popular this season!
o 7
sely
AERO Universal Tuned Radio Frequency Kit
Especially designed for the Improved Aero-
Dyne 6. Kit consists of 4 twice-matched
units. Adaptable to 201-A, 199, 112, and the
new 240 and A. C. tubes. Tuning range be-
low 200 to above 550 meters.
This kit will make any circuit better in
selectivity, tone and range. Will eliminate
losses and give the greatest receiving effi-
ciency.
Code No. U- 16 (for .0005 Cond.) . ..$15.00
Code No. U-163 (for .00035 Cond.)... 15.00
AERO Seven Tuned Radio Frequency Kit
Especially designed for the Aero 7. Kit con-
sists of 3 twice-matched units. Coils are
wound on Bakelite skeleton forms, assuring
a 95% air di-electric. Tuning range from
below 200 to above 550 meters. Adaptable
to 201-A, 199, 112, and the new 240 and
A. C. tubes.
Code No. U- 12 (for .0005 Cond.) .. .$12.00
Code No. U-123 (for .00035 Cond.)... 12.00
AERO Four Kit
An exceptionally efficient kit for use in the
Aero 4 and other similar circuits. Consists
of one Aero Universal Radio Frequency
Transformer and one Aero Universal 3-
Circuit Tuner. Uses 201-A, 112, 199 and new
A. C. tubes.
Code No. U.- 95 (for .0005 Cond.) $8.00
Code No. U-953 (for .00035 Cond.) 8.00
NOTE — All AERO Universal Kit's for use in
tuned radio frequency circuits have packed
in each coil with a fixed prim iry a twice
matched calibration slip showing reading
of each fixed primary coil at 250 meters and
at 500 meters; all having an accurate and
similar calibration.
A NEW SERVICE
We have arranged to furnish the home set
builder with complete Foundation Units for
the above named Circuits and for the Chi-
cago Daily News 4-Tube Receiver, drilled
and engraved on Westinghouse Micarta.
Detailed blueprints and wiring diagram for
each circuit included in foundation units
free. Write for information and prices.
You should be able to get any of the above
Aero Coils and parts from your dealer. If
he should be out of stock order direct
from the factory.
AERO PRODUCTS, Inc.
1772 Wilson Ave. Dept. 109 Chicago, 111.
What Kit Shall I Buy?
E list of kits herewith is printed as an exlen-
sion of the scope of the Service Department of
RADIO BROADCAST. // is our purpose to list here
the technical data about kits on which information
is available. In some cases, the kit can he pur-
chased from your dealer complete; in others, the
descriptive booklet is supplied for a small charge
and the parts can be purchased as the buyer likes.
The Service Department will not undertake to
handle cash remittances for parts, but when the
coupon on page 68 is filled out, all the informa-
tion requested will be forwarded.
20 1. SC FOUR-TUBE RECEIVER — Single control. One
stage of tuned radio frequency, regenerative detector,
and two stages of transformer -coup led audio amplification.
Regeneration control is accomplished by means of a variable
resistor across the tickler coil. Standard parts; cost approxi-
mately ^58.85.
202. SC-11 FIVE-TUBE RECEIVER—TWO stages of tuned
radio frequency, detector, and two stages of trans-
former-coupled audio. Two tuning controls. Volume control
consists of potentiometer grid bias on r.f. tubes. Standard
parts cost approximately $60.35.
203. "HI-Q" KIT — A five-tube tuned radio-frequency set
having two radio stages, a detector, and two transformer-
coupled audio stages. A special method of coupling in the
i.f. stages tends to make the amplification more nearly equal
over the entire band. Price $63. 05 without cabinet.
204. R. G. S. KIT — A four-tube inverse reflex circuit,
having the equivalent of two tuned radio-frequency stages,
detector, and three audio stages. Two controls. Price $69. 70
without cabinet.
205. PIERCE AIRO KIT — A six-tube single-dial receiver;
two stages of radio-frequency amplification, detector, and
three stages of resistance -coup led audio. Volume control
accomplished by variation of filament brilliancy of r.f.
tubes or by adjusting compensating condensers. Complete
chassis assembled but not wired costs $42.50.
206. H & H-T. R. F. ASSEMBLY — A tive-tube set; three
tuning dials, two steps of radio frequency, detector, and 2
transformer-coupled audio stages. Complete except for base-
board, panel, screws, wires, and accessories. Price $30.00.
207. PREMIER FIVE-TUBE ENSEMBLE — Two stages of
tuned radio frequency, detector, and two steps of trans-
former-coupled audio. Three dials. Parts assembled but
not wired. Price complete, except for cabinet, $35.00.
208. "QUADRAFORMER VI" — A six-tube set with two tun-
ing controls. Two stages of tuned radio frequency using
specially designed shielded coils, a detector, one stage of
transformer-coupled audio, and two stages of resistance-
coupled audio. Gain control by means of tapped primaries
on the r.f. transformers. Essential kit consists of three
shielded double-range "Quadraformer" coils, a selectivity
control, and an "Ampitrol," price $17. 50. Complete parts
$70.15.
209. GEN-RAL FIVE-TUBE SET — Two stages of tuned
radio frequency, detector, and two transformer-coupled
audio stages. Volume is controlled by a resistor in the plate
circuit of the r.f. tubes. Uses a special r.f. coil ("Duo-
Former") with figure eight winding. Parts mounted but
not wired, price $37.50.
210. BREMER-TULLY POWER-SIX — A six-tube, dual-
control set; three stages of neutralized tuned radio frequency,
detector, and two transformer-coupled audio stages. Re-
sistances in the grid circuit together with a phase shifting
arrangement are used to prevent oscillation. Volume control
accomplished by variation of B potential on r.f. tube.
Essential kit consists of four r.f. transformers, two dual
condensers, three small condensers, three choke coils, one
5oo,ooo-ohm resistor, three i ^oo-ohm resistors, and a set
of color charts and diagrams. Price $41.50.
212. INFRADYNE AMPLIFIER — A three-tube intermediate-
frequency amplifier for the super-heterodyne and other
special receivers, tuned to 3400 kc. (86 meters). Price $25.00.
213. RADIO BROADCAST "LAB" RECEIVER — A four-tube
dual-control receiver with one stage of Rice neutralized
tuned-radio frequency, regenerative detector (capacity
controlled), and two stages of transformer-coupled audio.
Approximate price, $78.15.
214. LC-27 — A five-tube set with two stages of tuned-
radio frequency, a detector, and two stages of transformer-
coupled audio. Special coils and special means of neutralizing
are emp oyed. Output device. Price $85. 20 without cabinet.
215. LOFTIN-WHITE— A five-tube set with two stages of
radio freouency, especially designed to give equal amplifica-
tion at all frequencies, a detector, and two stages of trans-
former-coupled audio. Two controls. Output device. Price
$85.10.
216. K.H.-27 — A six-tube receiver with two stages of
neutralized tuned radio frequency, a detector, three stages
of choke-coupled audio, and an output device. Two controls.
Price $86.00 w thout cabinet.
217. AERO SHORT-WAVE KIT— Three plug-in coils de-
signed to operate with a regenerative detector circuit and
having a frequen y range of from ig.QQOto 2306 kc. (15 to 130
meters). Coils and plug only, price $12. 50.
218. DiAMOND-OF-THE-AiR — A five-tube set having one
stage of tuned-radio frequency, a regenerative detector.
one stage of transformer-coupled audio, and two stages of
resistance-coupled audio. Volume control through regenera-
tion, Two tuning dials.
210. NORDEN-HAUCK SUPER 10 — Ten tubes; five stages of
tuned radio frequency, detector, and four stages of choke-
and transformer-coupled audio frequency. Two controls.
Price $291.40.
220. BROWNING-DRAKE — Five tubes; one stage tuned
radio frequency (Rice neutralization), regenerative detector
(tickler control), three stages of audio (special combination
of resistance- and impedance-coupled audio). Two controls.
Use an Aerial Kit
lo qet Matched Parts
Every part of your aerial
installation should be of uni-
formly high quality, because
one poor unit wUl affect
the entire job.
For complete satisfaction
year in and year out, buy
a Belden Aerial Kit with
Beldenamel Aerial Wire
and the well-known Belden
Lightning Arrester. Don't
take a chance with a poor
antenna system. Ask your
dealer for a Belden Aerial kit.
Belden Manufacturing Co.
X51X-A S. Western Ave., Chicago
BcMm
Aerial Kit
RADIO BROADCAST ADVERTISER
67
Your "B" Battery Eliminator
will give you better service with
•R-
(Trade Mark Registered)
Gaseous
Rectifier Tubes
ARE BETTER
6O Milliamperes - $4.5O
85 Milliamperes - 4.5O
4OO Milliamperes - 7.OO
Ask for Catalog of full line of Standard Tubes.
Guaranteed
The standing of the Q-R-S Company, manu-
facturers of quality merchandise for over a
quarter of a century, establishes your saiety.
Orders placed by the leading Eliminator Man-
ufacturers for this season's delivery, approxi-
mating Four Million Dollars' worth of Q-R-S
Rectifier Tubes, establishes the approval of
Radio Engineers. Ask any good dealer.
THE Q £:S COMPANY
Manufacturers
Executive Offices: 3O6 S. Wabash Ave., Chicago
Factories: Chicago— New York— San Francisco— Toronto, Canada— Sydney, Australia— Utrecht, Holland
Established 1900. References— Dun, Bradttreet, or any bank anywhere
68
RADIO BROADCAST ADVERTISER
Radio • Is • BETTER • With • Dry • Battery • Power
Lou can candle
an e-but not
a battery
IHERE isn't much difference
in the size or shape of batteries.
And you can't tell how good
they are before you use them.
(( If you could, one element
alone would win your prefer-
ence for Burgess. That element
is Chrome. ((Chrome is the pre-
servative that maintains an
abundance of unfailing energy
in Burgess Batteries— long after
mostdry cells ceasetofunction.
The black and white stripes
are individual marks for iden-
tifying Burgess Chrome Batter-
ies. Buy them for long lasting,
dependable performance!
— the preserving element
«sed in leather, metals,
paints and other materials
subject to wear, is also used in Burgess Bat-
teries. It gives them unusual staying power.
Burgess Chrome Batteries are patented.
ny '•Rjidio Engineer
BURGESS BATTERY COMPANY
GmeralSales Office: CHICAGO
Canadian Factories and Offices:
Niagara Falls and Winnipeg
URGESS
FLASHLIGHT & RADIO
BATTERIES
WHAT KIT SHALL I BUY? (Continued)
221. LR4 ULTRADYNE — Nine-tube super-heterodyne; one
stage of tuned radio frequency, one modulator, one oscillator,
three intermediate-frequency stages, detector, and two
transformer-coupled audio stages.
222. GREIFF MULTIPLEX — Four tubes (equivalent to six
tubes); one stage of tuned radio frequency, one stage of
transformer-coupled radio frequency, crystal detector, two
stages of transformer-coupled audio, and one stage of
impedance-coupled audio. Two controls. Price complete
parts, $50.00.
223. PHONOGRAPH AMPLIFIER — A five-tube amplifier de-
vice having an oscillator, a dectector, one stage of trans-
former-coupled audio, and two stages of impedance-coupled
audio. The phonograph signal is made to modulate the
oscillator in much the same manner as an incoming signal
from an antenna.
224. BROWNING-DRAKE — Five tubes; one stage tuned
radio frequency (with special neutralization system), re-
generative detector (tickler control), three stages of audio
(special combination of resistance- and impedance-coup ed
audio). Two controls.
225. AERO Shoit-Wave Transmitting Kit consists of inter-
changeable coils to be used in tuned-plate tuned grid circuit.
Kits of coils, two choke coils, and mountings, can be secured
for 20-40 meter band, 40-80 meter band, or 90-180 meter
band for $12.00
USE THIS COUPON FOR KITS
| RADIO BROADCAST SERVICE DEPARTMENT
1 Garden City, New York.
| Please send me information about the following kits in-
| dicated by number:
Name.
Address .
(Number)
(Street)
(City) (State)
ORDER BY NUMBER ONLY. This coupon must
accompany each order.
RB 11-27
Thumb Nail Reviews
WLS — A skit having to do with various and
droll adventures around the lion's cage in a circus
and centering about one J. Walter Sapp. The
mechanically simulated lions' roars were per-
fectly swell. As for the spoken lines, they were
not at all bad, but suffered from high-schoolish
and unconvincing delivery — a frequent enough
radio play complaint.
WOR — The Kapellmeister String Quartet, ex-
cellent interpreters of chamber music, playing on
this occasion the Schubert Quartet in D minor.
WBBM — The station's own string trio perform-
ing its routine tasks with great gusto and a
splendid attack.
WJZ — The Arion Male Chorus singing "Sleep
Kentucky Babe" in mellow fashion and introduc-
ing some tricky guitar effects against a back-
ground of humming.
JOHN WALLACE.
USE THIS COUPON FOR COMPLETE SETS
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, New York.
Please send me information about the following manu-
factured receivers ndicated bv number:
Name
Address . .
(Number)
(Street}
(City) (State)
ORDER BY NUMBER ONLY
This coupon must accompany each order. RB 1 1-27
The Newest ABC Power
Supply Unit
used with RCA 226 and 227 A C tubes
and the Raytheon BH tube
No. 5552
$20.00
List
This latest development of the Dongan
laboratories combines in one small,
compact case the essential transfor-
mers and chokes designed for use with
R. C. A. 226 and 227 A. C. Filament
Tubes (also UXi7i power amplifier
tube) and the Raytheon BH Rectifier
Tube. Complete power supply is se-
cured, eliminating the need of batter-
ies and charger. R. C. A. 226 and
227 A. C. tubes also take the place of
standard 201 A tubes.
For complete information write to
Dongan laboratories. If your dealer
cannot supply you send check or
money order direct.
DONGAN ELECTRIC MFG. CO.
2991-3001 Franklin St., Detroit, Michigan
Eternal Life
We cannot guarantee eternal life, but we
do guarantee the AEROVOX FILTER
CONDENSER when properly used to out-
last all the«(her equipment used in
conjunction with it.
WHY???
Because —
each section of a block is
individually sealed and impregnated
against moisture absorption.
the safety factor used in
manufacture, testing and rating will per-
mit indefinite continuous operation at the
rated working voltage without injury.
For all eliminators
"'Buill <Btlttr"
70 Wuhington St.. Brooklyn, N. Y.
RADIO BROADCAST ADVERTISER
Ktrliunrf I-.*.
Hut l.:7.Sil:,- of
Typ. GSX.280
FullWavef ' "
Pric. $5.50
es—
Best reception
New broadcast /ievelop-
ments make it necessary to
have the latest types of tubes
for fullest enjoyment of your
receiving set.
Bring it up to date with a
complete installation of the
new Gold Seal radio tubes —
specially developed for mod-
ern reception. You will be
delighted with the improve-
ment.
You can make the changes
yourself — no trouble. Our
new booklet tells you all
about it. Send today for your
copy — it is free. Use coupon
below.
All Standard Types
~!
., Inc. I
| Gold Seal Electrical Co
I ISO Park Ave., New York
Send me copy of the new booklet.
I
I Name
I Address I
K.B.11.37 I
Gold Seat
Radio Tubes •
When Static Ruins Good
Programs -Switch^
Over to
Dubilier
LIGHT-SOCKET AERIAL
Just connect this neat little device to
your set, plug into the nearest light-
socket — and listen to the difference!
It takes only one program to convince
you that crazy poles, loose wires, lead-
ins, etc., are not only unnecessary, but
downright inefficient when compared
to the Dubilier Light Socket Aerial.
Works perfectly on AC or DC, totally
eliminates the lightning hazard and uses absolutely no current.
Sold at all good radio stores on a 5-day money-back basis. Price $ 1 .50.
Used in the Power-Units
You Consider Best
Dubilier Condenser Blocks are the choice of
manufacturers whose battery eliminators are
known for reliability and long life. In building
your own unit remember that the condenser
blocksarethemostexpensiveand important ele-
ments in the circuit. Make sure that yours will
stand heavy loads and long hours of service by
insisting on Dubilier. Diagrams upon request.
Dubilier Micadon
The Standard Fixed Condenser of Radio in
a new case of moulded Bakelite. shaped to
meet the newest type of receiver construc-
tion. Terminals adapted to either screwed
or soldered connections. All standard ca-
pacities. Priced from 45c to $ 1 .50.
Dubilier Metaleak
Accurate resistance ratings and extremely
quiet performance make these tubular grid
leak* popular with amateurs who build with
great care. They are small, but highly im-
portant items in the construction of any type
of receiver. All .tandard resistance— prices
— 75c and 50c.
DUBILIER CONDENSER CORP., 4377 Bronx Blvd., New York
Dubilier
CONDENSERS
70
RADIO BROADCAST ADVERTISER
"RADIO BROADCASTS" DIRECTORY OF
MANUFACTURED RECEIVERS
•I A coupon will be found on page 68. All readers who desire additional
information on the receivers listed below need only insert the proper num-
bers in the coupon, mail it to the Service Department of RADIO BROADCAST,
and full details will be sent. New sets are listed in this space each month.
KEY TO TUBE ABBREVIATIONS
99— 60-mA. filament (dry cell)
01-A — Storage battery 0.25 amps, filament
12 — Power tube (Storage battery)
71 — Power tube (Storage battery)
16-B — Half-wave rectifier tube
80 — Full-wave, high current rectifier
81 — Half-wave, high current rectifier
Hmu — High-Mu tube for resistance-coupled audio
20 — Power tube (dry cell)
10 — Power Tube (Storage battery)
00-A — Special detector
13 — Full-wave rectifier tube
26 — Low-voltage high-current a. c. tube
27— Heater type a. c. tube
DIRECT CURRENT RECEIVERS
NO. 424. COLONIAL 26
Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One to
three dials. Volume control: antenna switch and poten-
tiometer across first audio. Watts required: 120. Con-
sole size: 34 x 38 x 18 inches. Headphone connections.
The filaments are connected in a scries parallel arrange-
ment. Price $250 including power unit.
NO. 425. SUPERPOWER
Five tubes: All 01-A tubes. Multiplex circuit. Two
dials. Volume control: resistance in r. f. plate. Watts
required: 30. Antenna: loop or outside. Cabinet sizes:
table, 27 x 10 x 9 inches: console, 28 x 50 x 21. Prices:
table, $135 including power unit: console, $390 includ-
ing power unit and loud speaker.
A. C. OPERATED RECEIVERS
NO. 508. ALL-AMERICAN 77, 88, AND 99
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Rice neutralized t. r. f. Single drum
tuning. Volume control: potentiometer in r. f. plate.
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,
25 x 38 x 18 inches; No. 99 console, 27i x 43 x 20 inches.
Shielded. Output device. The filaments are supplied
by means of three small transformers. The plate supply
employs a gas-filled rectifier tube. Voltmeter in a. c.
supply line. Prices: No. 77, $150, including power unit;
No. 88, $210 including power unit; No. 99, $285 in-
cluding power unit and loud speaker.
NO. 509. ALL-AMERICAN "DUET"; "SEXTET"
Six tubes; 2 t. r. f. (99), detector (99), 3 transformer
audio (99 and 12). Rice neutralized t.r.f. Two dials.
Volume control: resistance in r.f. plate. Cabinet sizes:
"Duet," 23x56x165 inches; "Sextet," 22} x 13} x 15}
inches. Shielded. Output device. The 99 filaments are
connected in series and supplied with rectified a.c.,
while 12 is supplied with raw a.c. The plate and fila-
ment supply uses gaseous rectifier tubes. Milliammeter
on power unit. Prices: "Duet," $160 including power
unit; "Sextet," $220 including power unit and loud
speaker.
NO. 511. ALL-AMERICAN 80, 90, AND 115
Five tubes; 2 t.r.f. (99), detector (99), 2 transformer
audio (99 and 12). Rice neutralized t.r.f. Two dials.
Volume control: resistance in r.f. plate. Cabinet sizes:
No. 80, 23i x 12} x 15 inches; No. 90, 37} x 12 x 12}
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi-
vidually shielded. Output device. See No. 509 for
power supply. Prices: No. 80, $135 including power
unit; No. 90, $145 including power unit and compart-
ment; No. 115, $170 including power unit, compart-
ment, and loud speaker.
NO. 510. ALL-AMERICAN 7
Seven tubes; 3 t.r.f. (26), 1 untuned r.f. (26), detector
(27), 2 transformer audio (26 and 71). Rice neutralized
t.r.f. One drum. Volume control: resistance in r.f.
plate. Cabinet sizes: "Sovereign" console, 30} x 60J
x 19 inches; "Lorraine" Hiboy, 25} x 53 5 x 17} inches;
"Forte" cabinet, 25} x 13} x 17} inches. For filament
and plate supply: See No. 508. Prices: "Sovereign"
$460; "Lorraine" $360; "Forte" $270. All prices include
power unit. First two include loud speaker.
NO. 401. AMRAD AC9
Six tubes; 3 t.r.f. (99), detector (99), 2 transformer
(99 and 12). Neutrodyne. Two dials. Volume control:
resistance across 1st audio. Watts consumed: 50. Cabi-
net size: 27 x 9 x 11| inches. The 99 filaments are con-
nected in series and supplied with rectified a.c., while
the 12 is run on raw a.c. The power unit, requiring two
16-B rectifiers, is separate and supplies A, B, and C
current. Price $142 including power unit.
NO. 402. AMRAD ACS
Five tubes. Same as No. 401 except one less r.f.
stage. Price $125 including power unit.
NO. 536. SOUTH BEND
Six tubes. One control. Sub-panel shielding. Binding
Posts. Antenna: outdoor. Prices: table, $130, Baby
Grand console, $195.
NO. 537. WALBERT 26
Six tubes; five Kellogg a.c. tubes and one 71. Two
controls. Volume control: variable plate resistance.
Isofarad circuit. Output device. Battery cable. Semi-
slm-kh-d. Antenna: 50 to 75 feet. Cabinet size: 10} x
29j x 16; inches. Prices: $215; with lubes, $250.
NO. 484. BOSWORTH, B5
Five tubes; 2 t.r.f. (26), detector (99), 2 transformer
audio (special a.c. tubes). T.r.f. circuit. Two dials.
Volume control: potentiometer. Cabinet size: 23 x 7
x 8 inches. Output device included. Price $175.
NO. 406. CLEARTONE 110
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All tubes a. c. heater type. One or two dials. Volume
control: resistance in r. f. plate. Watts consumed: 40.
Cabinet size: varies. The plate supply is built in the
receiver and requires one rectifier tube. Filament sup-
ply through step down transformers. Prices range from
$1 75 to $375 which includes 5 a.c. tubes and one rectifier
tube.
NO. 407. COLONIAL 25
Six tubes; 2 t. r. f. (01-A), detector (99), 2 resistance
audio (99). 1 transformer audio (10). Balanced t.r.f.
circuit. One or three dials. Volume control: Antenna
switch and potentiometer on 1st audio. Watts con-
sumed: 100. Console size: 34 x 38 x 18 inches. Output
device. All tube filaments are operated on a. c. except
the detector which is supplied with rectified a.c. from
the plate supply. The rectifier employs two 16-B tubes.
Price $250 including built-in plate and filament supply.
NO. 507. CROSLEY 602 BANDBOX
Six tubes; 3 t.r.f. (26), detector (27), 2 transformer
audio (26 and 71). Neutrodyne circuit. One dial.
Cabinet size: 17} x 5J x 78 inches. The heaters for the
a.c. tubes and the 71 filament are supplied by windings in
B unit transformers available to operate either on 25 or
60 cycles. The plate current is supplied by means of
rectifier tube. Price $65 for set alone, power unit $60.
NO. 408. DAY-FAN "DE LUXE"
Six tubes; 3 t.r.f., detector, 2 transformer audio. AU
01-A tubes. One dial. Volume control: potentiometer
across r.f. tubes. Watts consumed: 300. Console size:
30 x 40 x 20 inches. The filaments are connected in
series and supplied with d.c. from a motor-generator
set which also supplies B and C current. Output de-
vice. Price $350 including pow'er unit.
NO. 409. DAYCRAFT 5
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All a. c. heater tubes. Rellexed t.r.f. One dial. Volume
control: potentiometers in r.f. plate and 1st audio.
Watts consumed: 135. Console size: 34 x 36 x 14 inches.
Output device. The heaters are supplied by means of
a small transformer. A built-in rectifier supplies B
and C voltages. Price $170, less tubes. The following
have one more r.f. stage and are not reflexed: Day-
craft 6, $195; Dayrole 6, $235; Dayfan 6, $110. All
prices less tubes.
NO. 469. FREED-E1SEMANN NR11
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Volume control: potentiometer. Watts consumed: 150.
Cabinet size: 19J x 10 x 10} inches. Shielded. Output
device. A special power, unit is included employing a
rectifier tube. Price $225 including NR-411 power unit.
NO. 487. FRESHMAN 7F-AC
Six tubes; 3 t.r.f. (26), detector (27), 2 transformer
audio (26 and 71). Equaphase circuit. One dial. Volume
control: potentiometer across 1st audio. Console size:
24}x41}xl5 inches. Output device. The filaments and
heaters and B supply are all supplied by one power unit.
The plate supply requires one 80 rectifier tube. Price
$175 to $350, complete.
NO. 421. SOVEREIGN 238
Seven tubes of the a.c. heater type. Balanced t.r.f.
Two dials. Volume control: resistance across 2nd audio.
Watts consumed: 45. Console size: 37 x 52 x 15 inches.
The heaters are supplied by a small a. c. transformer,
while the plate is supplied by means of rectified a.c
using a gaseous type rectifier. Price $325, including
power unit and tubes.
NO. 517. KELLOGG 510, 511, AND 512
Seven tubes; 4 t.r.f., detector, 2 transformer audio.
All Kellogg a.c. tubes. One control and special zone
switch. Balanced. Volume control: special. Output de-
vice. Shielded. Cable connection between power supply
unit and receiver. Antenna: 25 to 100 feet. Panel 7i2
x 27} inches. Prices: Model 510 and 512, consoles, $495
complete. Model 511, consolette, $365 without loud
speaker.
NO. 496. SLEEPER ELECTRIC
Five tubes; four 99 tubes and one 71. Two controls.
Volume control: rheostat on r.f. Neutralized. Cable.
Output device. Power supply uses two 16-B tubes.
Antenna: 100 feet. Prices: Type 64, table, $160: Type
65, table, with built-in loud speaker, $175; Type 66,
table, $175; Type 67, console, $235; Type 78, console,
$265.
NO. 538. NEUTROWOUND, MASTER ALLECTRIC
Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and two 71 in push-pull amplifier). The 01-A
tubes are in series, and are supplied from a 400-mA.
rectifier. Two drum controls. Volume control: variable
plate resistance. Output device. Shielded. Antenna:
50 to 100 feet. Price: $360
NO. 413. MARTI
Six tubes: 2 t.r.f., detector, 3 resistance audio. All
tubes a.c. heater type. Two dials. Volume control:
resistance in r.f. plate. Watts consumed: 38. Panel size
7 x 21 inches. The built-in plate supply employs one
16-B rectifier. The filaments are supplied by a small
transformer. Prices: table, $235 including tubes and
rectifier; console, $275 including tubes and rectifier;
console, $325 including tubes, rectifier, and loud speaker.
NO. 417 RADIOLA 28
Eight tubes; five type 99 and one type 20. Drum
control. Super-heterodyne circuit. C-battery connec-
tions. Battery cable. Headphone connection. Antenna:
loop. Set may be operated from batteries or from the
power mains when used in conjunction with the model
104 loud speaker. Prices: $260 with tubes, battery
operation; $570 with model 104 loud speaker, a. c.
operation.
NO. 540 RADIOLA 30-A
Receiver characteristics same as No. 417 except that
type 71 power tube is used. This model is designed to
operate on either a. c. or d. c. from the power mains.
The combination rectifier — power — amplifier unit uses
two type 81 tubes. Model 100-A loud speaker is con-
tained in lower part of cabinet. Either a short indoor
or long outside antenna may be used. Cabinet size:
42'/2 x 29 x 17% inches. Price: $495.
NO. 541 RADIOLA 32
This model combines receiver No. 417 with the model
104 loud speaker. The power unit uses two type 81
tubes and a type 10 power amplifier. Loop is completely
NO. 539 RADIOLA 17
Six tubes; 3 t. r. f. (26), detector t27). 2 transformer
audio (26 and 27). One control. Illuminated dial.
Built-in power supply using type 80 rectifier. Antenna:
100 feet. Cabinet size: 25!r;, x 7'/8 x 8'/i. Price: $130
without accessories.
NO. 545. NEUTROWOUND, SUPER ALLECTRIC
Five tubes; 2 t.r.f. (99), detector (99), 2 audio (99
and 71). The 99 tubes are in series and are supplied from
an 85-mA. rectifier. Two drum controls. Volume con-
trol: variable plate resistance. Output device. Antenna:
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:
$150.
NO. 490. MOHAWK
Six tubes; 2 t.r.f., detector, 2 transformer audio. All
tubes a.c heater type except 71 in last stage. One di?l
Volume control: rheostat on r.f. Watts consumed: 40
Panel size: 12} x 8J inches. Output device. The heaters
for the a.c tubes and the 71 filament are supplied by
small transformers. The plate supply is of the built-in
type using a rectifier tube. Prices range from $65 to
S245
NO. 522. CASE, 62 B AND 62 C
McCullough a.c. tubes. Drum control. Volume con-
trol; variable high resistance in audio system. C-battery
connections. Semi-shielded. Cable. Antenna: 100 feet
Panel size: 7 x 21 inches. Prices: Model 62 B, complete
\vith a.c. equipment, $185; Model 62 C, complete with
a.c. equipment, $235.
NO. 523. CASE, 92 A AND 92 C
McCullough a.c. tubes. Drum control. Inductive
volume control. Technidyne circuit. Shielded. Cable.
C-battery connections. Model 92 C contains output
device. Loop operated. Prices: Model 92 A, table, $350;
Model 92 C, console, $475.
BATTERY OPERATED RECEIVERS
NO. 542. PFANSTIEHL JUNIOR SIX
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio.
Pfanstiehl circuit. Volume control : variable resistance in
r.f. plate circuit. One dial. Shielded. Battery cable. C-
battery connections. Etched bronze panel. Antenna: out-
door. Cabinet size: 9 x 20 x 8 inches. Price: $80, without
accessories.
NO. 512. ALL-AMERICAN 44, 45, AND 66
Six tubes; 3 t.r.f. (01-A. detector) 01 -A, 2 transformer
audio (01-A and 71). Rice neutralized t.r.f. Drum
control. Volume control: rheostat in r.f. Cabinet sizes:
No. 44. 21 x 10 x 8 inches; No. 55. 25 x 38 x 18 inches;
No. 66, 27} x 43 x 20 inches. C-battery connections.
Battery cable. Antenna: 75 to 125 feet. Prices: No. 44,
$70: No. 55, $125 including loud speaker; No. 66, $200
including loud speaker.
NO. 428. AMERICAN C6
Five tubes; 2 t.r.f. detector, 2 transformer audio.
All 01-A tubes. Semi balanced t.r.f. Three dials. Plate
current 15 mA. Volume control: potentiometer. Cabinet
sizes: table, 20 x 8} x 10 inches; console, 36 x 10 x 17
inches. Partially shielded. Battery cable. C-battery
connections. Antenna: 125 feet. Prices: table, $30;
console, $65 including loud speaker.
RADIO BROADCAST ADVERTISER
71
8 Tube
ensations/
1 Control
Att
8 Tube
1 Control
RETAIL
Big Discount to Agent*
From this Price
Has Complete
A-B Power Unit
A REAL ALL ELECTRIC Radio with one of
the best A-B power units on the market — no
batteries needed — at the worWs lowest price.
This Marwood can't be excelled at ANY price.
If you have electricity in your home, just
plug into the light socket and forget bat-
teries. No more battery trouble and expense.
Costs less than 2c a day to operate. Always
have 100% volume. ALL ELECTRIC Radios
are high priced because they are new. We
cut profit to the bone and offer a $250.00
outfit for $98.00 retail price. Big discount to
Agents. Don't buy any Radio 'til you get
details of this sensational new ALL ELKC-
TRIC Marwood.
All Electric
or Battery Operation
AGAIN Marwood is a year ahead — with the
Radio sensation of 1928— at a low price that
smashes Radio profiteering. Here's the sensa-
tion they're all talking about — the marvt lous 8
Tube Single Control Marwood for BATTERY or
ALL ELECTRIC operation. Direct from the
factory for only $69.00 retail price — a price far
below that of smaller, less powerful Radios. Big
discount to Agents from this price. You can't
beat this wonderful new Marwood and you can't
touch this low price. Why pay more for less
quality? To prove that Marwood can't be beat
we let you use it on 30 Days' Free Trial in your
own home. Test it in every way. Compare it
with any -Radio for tone, quality, volume, dis-
tance, selectivity, beauty. If you don't say that
it is a wonder, return it to us. We take the risk.
New Exclusive Features
Do you want coast to coast with volume enough
to fill a theatre? Do you want amazing distance
that only super-power Radios like the Marwood
It can get? Do you want ultra-selectivity to cut
out interference? Then you must test this Mar-
wood on 30 Days' Free Trial. An amazing
surprise awaits you. A flip of your finger
makes it ultra-selective — or broad— just as
you want it. Every Marwood is perfectly
BALANCED— a real laboratory job. Its
simple one drum control ge ts ALL the sta-
tions on the wave hand with case. A beau-
tiful, guaranteed, super-efficient Radio in
handsome walnut cabinets and consoles.
A radio really worth double our low price.
Buy From Factory— Save Half
Why pay profits to several middlemen? A
Marwood in any retail store would cost
practically three times our low direct-
from-the-factory price. Our policy is high-
est quality plus small profit and enormous
sales. You get the benefit. Marwood is a
pioneer, responsible Radio, with a good
reputation to guard. We insist on the best
—and we charge the least. If you want next
year's improvements NOW — you must get
a Marwood— the Radio that's a year ahead.
AGENTS
Make Big Spare Time Money
Get yoxir own Radio at wholesale price. It's
easy to get orders for the Marwood from
your friends and neighbors Folks buy
quick when they compare Marwood quality
and low prices. \Ve want local agents and
dealers In each territory to handle the enor-
mous business created by our national
advertising. Make *1OO a week or more in
spare time demonstrating at home. No ex-
perience or capital needed. We show you
how. This Is the biggest season in Radio
history. Everybody wants a Radio. Oet In
now. Hush coupon for 30 .lays' Free Trial,
beautiful catalog. Agents' Confidential
Prices and Agents' New I'lan.
MARWOOD RADIO CORP.
5315 Ravenswood Avenue
Department A-l 7 Chicago, Illinois
^
RETAIL
PRICE
Big Di'count ,
i to A$enf
.
Price
Get Our Discounts
Before You Buy a Radio
Don't buy any Radio 'till you get our big discounts and
catalog. Save half and get a Radio that IS a Radio. Try
any Marwood on 30 Days' Free Trial at our risk. Tune
in coast to coast on loud speaker with enormous vol-
ume, clear as a bell. Let your wife and children oper-
ate it. Compare it with any Radio regardless of price.
If you don't get the surprise of your life, return it. We
take the risk. Don't let Marwood low prices lead you
to believe Marwood is not the highest quality. We
have smashed Radio prices. You save half.
6 Tube— 1 Control
This is the Marwood 6 Tube, 1 Control for BATTERY or
ALL ELECTRIC operation. Gets coast tocoant on loud
speaker with great volume. Only $47.00 retail. Big dis-
counts to Agents. Comes in handsome walnut cabinets
and consoles. This low price cannot be equalled by
any other high grade 6 tube Radio. Has the volume of
any 7 tube set. If you want a 6 tube Radio you can't
beat a Marwood and you can't touch our low price.
$47
RETAIL
PRICE
BigDiscoitnt
to Agents
frttni This
Price
MARWOOD RADIO CORPORATION
5315 Ravenswood Ave., I)«'i»t A-17, Chicago, 111.
Send Agents' Confidential Prices, 3O Days' Free
Trial. New Catiilofr and Agents' New Money
Making Plan. No obligation on my part.
Address
St. or R.F.D
City State..
RADIO BROADCAST ADVERTISER
NO. 485. BOSWORTH B6
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Two dials. Volume control:
variable grid resistances. Battery cable. C battery
connections. Antenna: 25 feet or longer. Cabinet size
15 x 7 x 8 inches. Price $75.
NO. 513. COUNTERPHASE SIX
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 12). Counterphase t.r.f. Two
dials. Plate current: 32 mA. Volume control: rheosta.
on 2nd and 3rd r.f. Coils shielded. Battery cable. C-
battery connections. Antenna: 75 to 100 feet. Console
size: 18J x 405 x 15} inches. Prices: Model 35, table,
$110; Model 37, console, $175.
NO. 514. COUNTERPHASE EIGHT
Eight tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 12). 'Counterphase t.r.f. One
dial. Plate current: 40 mA. Volume control: rheostat in
1st r.f. Copper stage shielding. Battery cable. C-battery
connections. Antenna: 75 to 100 feet. Cabinet size:
30 x 12J x 16 inches. Prices: Model 12, table, $225'
Model 16, console, $335; Model 18, console, $365.
NO. 506. CROSLEY 601 BANDBOX
Six tubes; 3 t.r.f., detector, 2 transformer audio. AH
01-A tubes. Neutrodyne. One dial. Plate current:
40 mA. Volume control: rheostat in r.f. Shielded.
Battery cable. C-battery connections. Antenna: 75 to
150 feet. Cabinet size: 175 x 5} x 7j. Price, $55.
NO. 434. DAY-FAN 6
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). One dial. Plate
current: 12 to 15 mA. Volume control: rheostat on r.f.
Shielded. Battery cable, C-battery connections. Output
device. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7
Prices: Day-Fan 6, $110; Daycraft 6, $145 including
loud speaker; Day-Fan Jr. not available.
NO. 435. DAY-FAN 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resist-
ance audio (01-A), 2 transformer audio (01-A and 12
or 71). Plate current: 15 mA. Antenna: outside. Same
as No. 434. Price $115.
NO. 503. FADA SPECIAL
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 20 to 24mA. Volume control:
rheostat on r.f. Coils shielded. Battery cable. C-battery
connections. Headphone connection. Antenna: outdoor.
Cabinet size: 20$ x 13J x 10} inches. Price $95.
NO. 504. FADA 7
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 43mA. Volume control: rheostat
on r.f. Completely shielded. Battery cable. C-battery
connections. Headphone connections. Output device.
Antenna: outdoor or loop. Cabinet sizes: table, 25J x
131 x Hi inches; console, 29 x 50 x 17 inches. Prices:
table, $185; console, $285.
NO. 436. FEDERAL
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t.r.f. One
dial. Plate current: 20.7 mA. Volume control: rheostat
on r.f. Shielded. Battery cable. C-battery connections.
Antenna: loop. Made in 6 models. Price varies from
$250 to $1000 including loop.
NO. 505. FADA 8
Eight tubes. Same as No. 504 except for one extra
stage of audio and different cabinet. Prices: table, $300;
console, $400.
NO. 437. FERGUSON 10A
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio
(01-A and 12 or 71). One dial. Plate current: 18 to 25
mA. Volume control: rheostat on two r.f. Shielded.
Battery cable. C-battery connections. Antenna: 100
feet. Cabinet size: 214 x 12 x 15 inches. Price $150.
NO. 438. FERGUSON 14
Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector
(01-A), 3 audio (01-A and 12 or 71). Special balanced
t.r.f. One dial. Plate current: 30 to 35 mA. Volume con-
trol: rheostat in three r.f. Shielded. Battery cable, C-
battery connections. Antenna: loop. Cabinet size:
24 x 12 x 16 inches. Price $235, including loop.
NO. 439. FERGUSON 12
Six tubes; 2 t.r.f. (01-A), detector (01-A), 1 trans-
former audio (01-A), 2 resistance audio (01-A and 12
or 71). Two dials. Plate current: 18 to 25 mA. Volume
control: rheostat on two r.f. Partially shielded. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet size: 22* x 10 x 12 inches. Price $85. Consolette
$145 including loud speaker.
NO. 440. FREED-EISEMANN NR-8 NR-9, AND
NR-66
Six tubes; 3 t.r.f. (01-A), detector '01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. NR-8, two
dials; others one dial. Plate current: 30 mA. Volume
control: rheostat on r.f. NR-8 and 9: chassis type
shielding. NR-66, individual stage shielding. Battery
cable. C-battery connections. Antenna: 100 feet
Cabinet sizes: NR-8 and 9, 19JxlOx 10}inches; NR-66
20 x 10! x 12 inches. Prices: NR-8, $90; NR-9, $100;
NR-66, $125.
NO. 501. KING "CHEVALIER"
Six tubes. Same as No. 500. Coils completely shielded.
Panel si/e: 11x7 inches. Price, $210 including loud
speaker.
NO. 441. FREED-EISEMANN NR-77
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2
transformer audio (01-A and 71). Neutrodyne. One
dial. Plate current: 35 mA. Volume control: rheostat on
r.f. Shielding. Battery cable. C-battery connections.
Antenna: outside or loop. Cabinet size: 23 x 10i x 13
inches. Price $175.
NO. 442. FREED-EISEMANN 800 AND 850
Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 trans-
former (01-A), 1 parallel audio (01-A or 71). Neutro-
dyne. One dial. Plate current: 35 mA. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery
connections. Output: two tubes in parallel or one power
tube may be used. Antenna: outside or loop Cabinet
sizes: No. 800, 34 x 154 x 13J inches; No. 850, 36 x 65} x
17}. Prices not available.
NO. 444. GREBE MU 1
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t.r.f. One,
two, or three dials (operate singly or together). Plate
current: 30mA. Volume control: rheostat on r.f. Bi-
nocular coils. Binding posts. C-battery connections
Antenna: 125 feet. Cabinet size: 22} x 9i x 13 inches
Prices range from $95 to $320.
NO. 426. HOMER
Seven tubes; 4 t.r.f. (01-A); detector (01-A or OOA);
2 audio (01-A and 12 or 71). One knob tuning control.
Volume control : rotor control in antenna circuit. Plate
current : 22 .0 25 mA. 'Technidyne" circuit. Completely
enclosed in aluminum box. Battery cable. C-battery con-
nections. Cabinet size, 8J x 19} x 9J inches. Chassis size,
6{ x 17 x 8 inches. Prices: Chassis only, $80. Table cabi-
net, $95.
NO. 502. KENNEDY ROYAL 7. CONSOLETTE
Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). One dial. Plate current:
42 mA. Volume control: rheostat on two r.f. Special
r.f. coils. Battery cable. C-battery connections. Head-
phone connection. Antenna: outside or loop. Consolette
size: 36} x 35} x 19 inches. Price $220.
NO. 498. KING "CRUSADER"
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 20 mA. Volume control: rheostat on r.f.
Coils shielded. Battery cable. C-battery connections.
Antenna: outside. Panel: 11 x 7 inches. Price, $115.
NO. 499. KING "COMMANDER"
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 25 mA. Volume control: rheostat on r f.
Completely shielded. Battery cable. C-battery con-
nections. Antenna: loop. Panel size: 12 x 8 inches.
Price $220 including loop.
NO. 429. KING COLE VII AND VIII
Seven tubes; 3 t.r.f., detector, 1 resistance audio, 2
transformer audio. All 01-A tubes. Model VIII has one
more stage t.r.f. (eight tubes). Model VII, two dials.
Model VIII, one dial. Plate current: 15 to 50 mA.
Volume control: primary shunt in r.f. Steel shielding.
Battery cable and binding posts. C-battery connections.
Output devices on some consoles. Antenna: 10 to 100
feet. Cabinet size: varies. Prices: Model VII, $80 to
$160; Model VIII, $100 to $300.
NO. 500. KING "BARONET" AND "VIKING"
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 19 mA. Volume control: rheostat in r.f.
Battery cable. C-battery connections. Antenna: out-
side. Panel size: 18 x 7 inches. Prices: "Baronet," $70;
"Viking," $140 including loud speaker.
NO. 489. MOHAWK
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio
(01-A and 71). One dial. Plate current: 40 mA. Volume
control: rheostat on r.f. Battery cable. C-battery con-
nections. Output device. Antenna: 60 feet. Panel size:
12} x &', inches. Prices range from $65 to $245.
NO. 543. ATWATER KENT, MODEL 33
Six tubes: 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71 or 1"). One dial. Volume control: r.f. fila-
ment rheostat. C-battery connection*. Battery cable
Antenna: 100 feet. Steel panel. Cabinet size: 21 Jx6|x6J
inches. Price: $90, without accessories.
NO. 544. ATWATER KENT, MODEL 50
Seven tubes; 4 t.r. f. (01-A) , detector (01-A), 2 audio
(01-A and 12 or 71 ). Volume control: r.f. filament rheo-
stat. C-battery connections. Battery cable. Special band-
pass filter circuit with an untuned amplifier. Cabinet
size: 20f x 13 x 7J inches. Price: $150.
NO. 452. ORIOLE 90
F ve tubes; 2 t.r.f., detector, 2 transformer audio.
All 01-A tubes. "Trinum" circuit. Two dials. Plate
current: 18 mA. Volume control: rheostat on r. f.
Battery cable. C-battery connections. Antenna: 50 to
100 feet. Cabinet size: 25} x Hi x 12} inches. Price
$85. Another model has 8 tubes, one dial, and is
shielded. Price $185.
NO. 453. PARAGON
Six tubes; 2 t.r.f. (01-A), detector (01-A), 3 double
impedance audio (01-A and 71). One dial. Plate cur-
rent: 40 mA. Volume control: resistance in r.f. plate.
Shielded. Battery cable. C-battery connections. Out-
put device. Antenna: 100 feet. Console size: 20 x 46
x 1 7 inches. Price not determined.
NO. 543 RADIOLA 20
Five tubes; 2 t. r. f. (99), detector (99), two trans-
former audio (99 and 20). Regenerative detector. Two
drum controls. C-battery connections. Battery cable.
Antenna: 100 feet. Price; $78 without accessories.
NO. 480. PFANSTIEHL 30 AND 302
Six tubes; 3 t.r.f. (01-A), detector (01- 2A), trans-
former audio (01-A and 71). One dial. Plate current:
23 to 32 mA. Volume control: resistance in r.f. plate.
Shielded. Battery cable. C-battery connections. An-
tenna: outside. Panel size. 17J x 8} inches. Prices: No
30 cabinet, $105; No. 302 console, $185 including
loud speaker.
NO. 515. BROWNING-DRAKE 7-A
Seven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio
(Hmu, two 01-A, and 71). Illuminated drum control.
Volume control: rheostat on 1st r.f. Shielded. Neutral-
ized. C-battery connections. Battery Cable. Metal
panel. Output device. Antenna: 50-75 feet Cabinet
30 x 1 1 x 9 inches. Price, $145.
NO. 516. BROWNING-DRAKE 6-A
Six tubes; 1 t.r.f. (99), detector (00-A), 3 audio
(Hmu, two 01-A and 71). Drum control with auxiliary
adjustment. Volume control: rheostat on r.f. Regenera-
tive detector. Shielded. Neutralized. C-battery connec-
tions. Battery cable. Antenna: 50-100 feet. Cabinet
25 x 11 x9. Price $105.
NO. 518. KELLOGG "WAVE MASTER,"
504, 505, AND 506.
Five tubes; 2 t.r.f., detector, 2 transformer audio.
One control and special zone switch. Volume control:
rheostat on r.f. C-battery connections. Binding posts
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel
7} x 25} inches. Prices: Model 504, table, $75, less
accessories. Model 505, table, $125 with loud speaker
Model 506, consolette, $135 with loud speaker.
NO. 519. KELLOGG, 507 AND 508.
Six tubes, 3 t.r.f., detector, 2 transformer audio. One
control and special zone switch. Volume control: rheo-
stat on r.f. C-battery connections. Balanced. Shielded.
Binding posts and battery cable. Antenna: 70 feet.
Cabinet size: Model 507, table, 30 x 13J x 14 inches
Model 508, console, 34 x 18 x 54 inches. Prices: Model
507, $190 less accessories. Model 508, $320 with loud
speaker.
NO. 427. MURDOCK 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 trans-
former and 2 resistance audio (two 01-A and 12 or 71)
One control. Volume control: rheostat on r.f. Coils
shielded. Neutralized. Battery cable. C-battery con-
nections. Complete metal case. Antenna: 100 feet.
Panel size: 9 x 23 inches. Price, not available.
NO. 520. BOSCH 57
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control calibrated in kc. Volume
control: rheostat on r.f. Shielded. Battery cable. C-
battery connections. Balanced. Output device. Built-in
loud speaker. Antenna: built-in loop or outside antenna.
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340
including enclosed loop and loud speaker.
NO. 521. BOSCH "CRUISER," 66 AND 76
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat
on r.f. Shielded. C-battery connections. Balanced
Battery cable. Antenna: 20 to 100 feet. Prices: Model
66, table, $99.50. Model 76, console, $175; with loud
speaker $195.
NO. 524. CASE, 61 A AND 61 C
T.r.f. Semi-shielded. Battery cable. Drum control.
Volume control: variable high resistance in audio sys-
tem. Plate current: 35 mA. Antenna: 100 feet. Prices:
Model 61 A, $85; Model 61 C, console, $135.
NO. 525. CASE, 90 A AND 90 C
Drum control. Inductive volume control. Technidyne
circuit. C-battery connections. Battery cable. Loop
operated. Model 90-C equipped with output device
Prices: Model 90 A, table, $225; Model 90 C, console
$350.
NO. 526. ARBORPHONE 25
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat.
Shielded. Battery cable. Output device. C-battery con-
nections. Loftin- White circuit. Antenna: 75 feet. Panel:
7; x 15 inches, metal. Prices: Model 25, table, $125;
Model 252, $185; Model 253, $250; Mode; 255, combin-
ation phonograph and radio, $600.
NO. 527. ARBORPHONE 27
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio
(01-A). Two controls. Volume control: rheostat. C-
battery connections. Binding posts. Antenna: 75 feet.
Prices: Model 27, $65; Model 271, $99.50; Model 272,
$125.
NO. 528. THE "CHIEF"
Seven tubes; six 01-A tubes and one power tube.
One control. Volume control: rheostat. C-battery con-
nection. Partial shielding. Binding posts. Antenna:
outside. Cabinet size: 40 x 22 x 16 inches. Prices:
Complete with A power supply, $250; without acces-
sories, $150.
NO. 529. DIAMOND SPECIAL, SUPER SPECIAL,
AND BABY GRAND CONSOLE
Six tubes; all 01 -A type. One control. Partial shield-
ing. C-battery connections. Volume control: rheostat.
Binding posts. Antenna: outdoor. Prices: Diamond
Special, $75; Super Special, $65; Baby Grand Console,
$110.
RADIO BROADCAST ADVERTISER
73
Everything that Radio Has to Give
Kingston service goes al! the way through,
and Kingston dealers know that this
company stands squarely behind its prod-
ucts. The new Kingston B Ba.tery elimina-
tor is fully guaranteed to be all and do all
that is claimed for it.
The Kingston B Supply Unit brings to your radio evenings a new
richness and a new delight — full tones, clearness and perfect reception
always! It maintains your set at its perfection peak, operates silently,
and forever removes the trouble and expense of batteries. The
Kingston is beautifully made, is
smartly finished in satin black, and
is built by experts with extreme
care and accuracy. There are pro-
vided three voltage terminals, each
adjustable over a wide range, mak-
ing possible any desired voltages
from 5 to 200. In keeping with
Kingston quality, the Raytheon
125 milliampere type BH tube is
used as a rectifier.
If your dealer can't supply you as^ us
KOKOMO ELECTRIC CO. KOKOMO, IND.
Type 2, for 11 0-1 20 Volt AC 50 or 60.
Cycle Current, $35.00.
For receiving sets having not more
than eight lubes and not having type
UXl?l power tube or equivalent,
Type ZA, for 110-120 Volt AC 50 or
60 Cycle Current, *-J2.50.
For all S*MS using type UX171 power
tube or equivalent and for all large
sets having nine or more tubes.
Type 2C, for 110-120 Volt AC 25, 30
or 40 cycle current, #47.50.
Price* include type BH Raytheon tube.
Any of these models will be furnished
with an automatic control switch built in
the unit for $2*0 additional. With
thls the B unit is automatically
vitched on or off when switch
i the radio set panel
is turned.
LEAK
CARBORUNDUM^ •-
SLIP a Carborundum Grid-Leak into your set and you will notice
an improved reception instantly.
Carborundum Grid-Leaks are quiet. They are dense solid rods of Car-
borundum that provide for an uninterrupted flow of current.
No chance for the creation of minute noisy arcs — no glass tube. They
can't disintegrate. They are unbreakable.
All standard values, both Grid-Leaks and Fixed Resistors.
The Grid-Leaks are tested for values at 5 volts — the Resistors at 90 volts.
No. 77 Carborundum Grid-Leaks, values 0.25, 0.50, 1 to 10 Megohms, each $0.50
No. 79 Carborundum Resistors, values 2500 and 5000 Ohms, each 1.00
No. 79 Carborundum Fixed Resistors, values 1 2,000, 25,000, 50,000, 75,000 and 100,000 Ohms, ea., .75
From
your dealer
or direct
THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y.
CANADIAN CARBORUNDUM CO., LTD., NIAGARA FALLS, ONT.
Sales Offices and Warehouses in
New York, Chicago. Boston, Philadelphia, Cleveland, Detroit, Cincinnati, Pittsburgh, Milwaukee, Grand Kapida
Tbe Carborundum Co., Ltd., Manchester, Eng. Deutsche Carborundum Werke, Dusseldorf, Get.
f Carborundum ii the Rejlitere.1 Trade Same u«ed by Tbe Carborundum Company for Sill- "[
I con Carbide. Tble Trade .Mark le tbe extln.i.e property of Tbe Carborundum Company. _1
The
Carborundum
Company
Niagara Falls, N.Y.
nd booklet 1 >-_•
jm in Radio"
74
RADIO BROADCAST ADVERTISER
NO. 530. KOLSTER, 7A AND 7B
Seven tubes: 4 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r.f. Shielded. Battery cable. C-battery connections.
Antenna: 50 to 75 feet. Prices: Model 7A, $125; Model
7B, with built-in loud speaker, $140.
NO. 531. KOLSTER, 8A, 8B, AND 8C
Eight tubes; 4 t.r.f. (01-A), detector (01-A), 3 audio
(two 01-A and one 12). One control. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery con-
nections. Model 8A uses 50 to 75 foot antenna; model
8B contains output device and uses antenna or detach-
able loop; Model 8C contains output device and uses
antenna or built-in loop. Prices: 8A, $185; 8B, $235;
8C, $375.
NO. 532. KOLSTER, 6D, 6G, AND 6H
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r.f. C-battery connections. Battery cable. Antenna:
50 to 75 feet. Model 6G contains output device and
built-in loud speaker; Model 6H contains built-in B
power unit and loud speaker. Prices: Model 6D, $80;
Model 6G, $165; Model 6H, $265.
NO. 533. SIMPLEX, SR 9 AND SR 10
Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio
(01-A and 12). SR 9, three controls; SR 10, two con-
trols. Volume control : rheostat. C-battery connections.
Battery cable. Headphone connection. Prices: SR 9,
table, $65; consolette, $95; console, $145. SR 10, table
$70; consolette, $95; console, $145.
NO. 534. SIMPLEX, SR 11
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio
(01-A and 12). One control. Volume control: rheostat.
C-battery connections. Battery cable. Antenna: 100
feet. Prices: table, $70; consolette, $95; console, $145.
NO. 535. STANDARDYNE, MODEL S 27
Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio
(power tubes). One control. Volume control: rheostat
on r.f. C-battery connections. Binding posts. Antenna:
75 feet. Cabinet size: 9 x 9 x 19} inches. Prices: S 27,
$49.50; S 950, console, with built-in loud speaker,
$99.50; S 600, console with built-in loud speaker,
$104.50.
NO. 481. PFANSTIEHL 32 AND 322
Seven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio
(01-A and 71). One dial. Plate current: 23 to 32 mA.
Volume control: resistance in r. f.. plate. Shielded
Battery cable. C-battery connections. Output device.
Antenna: outside. Panel: 17J x 8} inches. Prices: No.
32 cabinet, $145; No. 322 console, $245 including
loud speaker.
NO 433. ARBORPHONE
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All 01-A tubes. Two dials. Plate current: 16mA. Vol-
ume control : rheostat in r.f. and resistance in r.f. plate.
C-battery connections. Binding posts. Antenna: taps
for various lengths. Cabinet size: 24 x 9 x 10$ inches.
Price: $65.
NO. 431. AUDIOLA 6
Six tubes; 3 t.r.f. (01-A), detector (00-A). 2 trans-
former audio (01-A and 71). Drum control. Plate cur-
rent: 20 mA. Volume control: resistance in r.f. plate.
Stage shielding. Battery cable. C-battery connection.
Antenna: 50 to 100 feet. Cabinet size: 28} x 11 x 14}
inches. Price not established.
NO. 432. AUDIOLA 8
Eight tubes; 4 t.r.f. (01-A), detector (00-A), 1 trans-
former audio (01-A), push-pull audio (12 or 71). Bridge
balanced t.r.f. Drum control. Volume control : resistance
in r.f. plate. Stage shielding. Battery cable. C-battery
connections. Antenna: 10 to 100 feet. Cabinet size:
28} x 11 x 14} inches. Price not established.
NO. 542 RADIOLA 16
Six tubes; 3 t. r. f. (Ol-A), detector (Ol-A), 2 trans-
former audio (01-A and 112). One control. C-battery
connections. Battery cable. Antenna: outside. Cabinet
size: 16'/2 x 8Vi x 7Vx inches. Price: $69.50 without ac-
cessories.
NO. 456. RADIOLA 20
Five tubes: 2 t.r.f. (99), detector (99), 2 transformer
audio (99 and 20). Balanced t.r.f. and regenerative de-
tector. Two dials. Volume control: regenerative.
Shielded. C-battery connections. Headphone connec-
tions. Antenna: 75 to 1.50 feet. Cabinet size: 19} x
111 x 16 inches. Price $115 including all tubes.
NO. 457 RADIOLA 25
Six tubes; five type 99 and one type 20. Drum con-
trol. Super-heterodyne circuit. C-battery connections.
Battery cable. Headphone connections. Antenna: loop.
Set may be operated from batteries or from power mains
when used with model 104 loud speaker. Price; $165
with tubes, for battery operation. Apparatus for opera-
tion of set from the power mains can be purchased
separately.
NO. 493. SONORA F
Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Special balanced t.r.f.
Two dials. Plate current: 45 mA. Volume control:
rheostat in r.f. Shielded. Battery cable. C-battery
connections. Output device. Antenna: loop. Console
si/£: 32 x 45} x 17 inches. Prices range from $350 to
$-450 including loop and loud speaker.
NO. 494. SONORA E
Six tubes; 3 t.r.f. (01-A), detector fOO-A), 2 trans-
former audio (01-A and 71). Special balanced t.r.f.
Two dials. Plate current: 35 to 40 mA. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery
connections. Antenna: outside. Cabinet size: varies.
Prices: table, $110; semi-console, $140; console, $240
including loud speaker.
NO. 495. SONORA D
Same as No. 49'. except arrangement of tubes; 2
t.r.f., detector, 3 audio. Prices: table, $125; standard
console, $185; "DeLuxe" console, $225.
NO. 482. STEWART-WARNER 705 AND 710
Six tubes; 3 t.r.f., detector, 2 transformer audio.
All 01-A tubes. Balanced t.r.f. Two dials. Plate cur-
rent: 10 to 25 mA. Volume control: resistance in r.f.
plate. Shielded. Battery cable. C-battery connections.
Antenna: 80 feet. Cabinet sizes: No. 705 table, 26}
x 111 x 13}g inches; No. 710 console, 29j x 42 x 17}
inches. Tentative prices: No. 705, $115; No. 710
$265 including loud speaker.
NO. 483. STEWART-WARNER 525 AND 520
Same as No. 482 except no shielding. Cabinet sizes:
No. 525 table, 19} x 10 x 11 J inches; No. 520 console,
22} x 40 x 14 H inches. Tentative prices: No. 525, $75;
No. 520, $117.50 including loud speaker.
NO. 459. STROMBERG-CARLSON 501 AND 502
Five tubes; 2 t.r.f. (01-A). detector (00-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two dials.
Plate current: 25 to 35 mA. Volume control: rheostat
on 1st r.f. Shielded. Battery cable. C-battery connec-
tions. Headphone connections. Output device. Panel
voltmeter. Antenna: 60 to 100 feet. Cabinet sizes:
No. 501, 25} x 13 x 14 inches; No. 502, 28 )j x 50
A * 16J inches. Prices: No. 501, $180; No. 502, $290.
NO. 460. STROMBERG-CARLSON 601 AND 602
Six tubes. Same as No. 549 except for extra t.r.f.
stage. Cabinet sizes: No. 601, 27A x 16} x I4f, inches;
No. 602, 28} x 51} x 19i5 inches. Prices: No. 601, $225;
No. 602, $330.
NO. 486. VALLEY 71
Seven tubes; 4 t.r.f. (01-A), detect9r (01-A), 2 trans-
former audio (01-A and 71). One dial. Plate current:
35 mA. Volume control: rheostat on r.f. Partially
shielded. Battery cable. C-battery connections. Head-
phone connection. Antenna: 50 to 100 feet. Cabinet
size: 27 x 6 x 7 inches. Price $95.
NO. 472. VOLOTONE VIII
Six tubes. Same as No. 471 with following excep-
tions; 2 t.r.f. stages. Three dir.ls. Plate current: 2-
mA. Cabinet size: 26.J x 8 x 12 inches. Price $140.
35
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AMERICAN AUTO A RADIO MFG. CO. /(ATA
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BRUNO QUARTZITE TUNING COILS
have been repeatedly specified in new cir-
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The No. 99 Jr. Tuning Coil has been designed to
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length 200 to 575 meters. List price . . $5.50.
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Both Coils are perfectly made and wound with green
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BRUNO RADIO CORPORATION
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RADIO BROADCAST ADVERTISER
75
Cle-Ra-Tone
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Manufactured in Canada by the Benjamin Electric
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Push-Pall
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THE
GENERAL RADIO
Type 441 Push-Pull Amplifier
In a search for an amplifier combination which would give the
maximum in quality and volume, the push-pull method has proved
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While push-pull transformer coupling does not increase the ampli-
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increased. The reason for this is that distortion due to tube over-
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would be possible if the tubes were used as in other methods of coup-
ling. A further advantage of push-pull amplification when using an
A. C. filament supply is that hum voltages also cancel out, rendering
the amplifier very quiet.
The type 441 unit with two type 171 power tubes having a plate
voltage of 1 80 will give more volume and better quality than a single
transformer coupled stage using the type 210 power tube with 400
volts on the plate.
The General Radio Type 441 unit is completely wired and mounted
(as illustrated) on a brass base-board with conveniently located bind-
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with an existing set as a separate unit.
The type 441 may be used with either the UX-226, UX-326, or
UX-i/i, CX-37I tubes.
Type 441 Push-pull amplifier $20.00
The Type 441 unit is licensed by the Radio Corporation of America
for radio amateur, experimental, and broadcast reception only, and
under the terms of the R. C. A. license the unit may be sold only with
tubes.
Type UX-226 or CX-326 Amplifier Tube $3.00
Type UX-171 or CX-371 Amplifier Tube $4.50
GENERAL RADIO COMPANY
Cambridge Massachusetts
76
RADIO BROADCAST ADVERTISER
for Radio Fans with
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Automatic
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I
A KEY TO RECENT
RADIO ARTICLES
By E. G. SHALKHAUSER
THIS is the twenty-fourth in stallment of references
to articles which have appeared recently in var-
ious radio periodicals. Each separate reference
should be cut out and pasted on 4" x 6" cards for
filing, or pasted in a scrap book either alphabet-
ically or numerically. An outline of He Dewey
Decimal System (employed here) appeared last in
the January RADIO BROADCAST.
R402. SHORT-WAVE SYSTEMS. SHORT-WAVE
QST. July, 1927. Pp. 8-14. TRANSMISSION.
"Short-Wave Radio Transmission and Its Practical
Uses," C. W. Rice. Part i .
The ionization of the atmosphere through cosmic radia-
tion as well as through propagation of electron streams from
the sun determines the nature of electromagnetic waves, as
stated. How this ionization affects day and night and also
seasonal variations is explained from experimental data
obtained to date. Comparison is made between auroral
phenomena and the theory of ionization as well as the effect
of terrestrial magnetism on the motion of the electron. Skip
distance effect is said to be due to the bending of the waves
in the upper atmosphere, the degree of bending depending
on the wavelength.
Rjoi. 6. HIGH-FREQUENCY BRIDGE. BRIDGE,
QST. July, 1927. Pp. 15-20. H iib- frequency.
"A Bridge to Measure Capacity, Power Factor, Re-
sistance, and Inductance," J. Katzman.
The purpose of the article is to describe and explain the
important factors of the Wien Series Resistance Bridge
when used to measure C, L R and power factor accurately
to i'0 of i per cent.
R344J- TRANSMITTING SETS. TRANSMITTERS,
QST. July. 1927. Pp. 24-28. Tuning.
"Some Light on Transmitter Tuning," R. A. Hull.
The construction of a shielded oscillator and its use in
tuning transmitter circuits for good signal output are out-
lined. Good plate and filament supply regulation is one of
the main requirements. The proper method of tuning various
circuits to adjust the wavelength of the oscillator and the
antenna, and the correct amount of grid excitation to be
used are told. Key thumps can be greatly reduced by having
proper coupling and antenna tuning.
SHORT-WAVES.
Band," E. M. Guyer
R402. SHORT-WAVE SYSTEMS.
QST. July, 1927. Pp. 29-30.
"An Investigation of the 5-Meter
and O. C. Austin.
Some problems on the construction and the operation of
5-meter transmitters are related, photographs of several
sets being shown with a list of material fortheii construction
appended.
R342. AMPLIFIERS. KEYING
QST. July, 1927, Pp. 33-35. AMPLIFIERS.
" Keying the Amplifier," A. G. Shafer.
A keying system, whereby a specially constructed key is
placed in the grid circuit of one of the amplifier tubes, is
utilized to prevent key thumping. The system consists of
changing the capacity of the coupling capacity to such an
extent as to prevent proper transfer of energy from the
oscillator without actually breaking any part of the circuit.
R344-3- TRANSMITTING SETS. TRANSMITTER,
QST. July, 1927. Pp. 36-40. Short-Wave.
"A Constant Frequency Transmitter," W. H. Hoffman.
A non-crystal oscillator, capable of maintaining a con-
stant frequency output, yet flexible enough that the fre-
quency may be shifted to other amateur wavelengths, is
described and illustrated.
R344.5. ALTERNATING-CURRENT SUPPLY. SOCKET POWER.
Radio. July, 1927. Pp. 25-ff. "A — B — C"
"ABC Socket Power For Large Tubes," G. M. Best.
A discussion on the assembly and the operation of several
combination ABC socket power units and the results ob-
tained when used with a Browning-Drake receiver are given.
The Raytheon 35O-mA. tube is used with each combination.
All wiring details of the units, including those of the
Browning-Drake receiver, are shown.
Ri6o. RECEIVING APPARATUS.
Radio. July, 1927. Pp. 29-ff. Single-Control.
"Trouble Shooting the Single-Control "
Gilliland.
RECEIVER,
glt>
1 Set," M. P.
In adjusting single-control receivers foi selectivity the
following points are said to be of importance: Proper neutral-
izing of all radio- frequency stages; balancing of tuned cir-
cuits. For volume control a shunt resistance across the
secondary of the first audio transformer is recommended.
R3io. ELECTRON TUBES. ELECTRON
Radio. July, 1927. Pp. 47-ff. TUBES.
"Vacuum Tube Characteristics."
The characteristics of dry cell tubes, power tubes, high-mu
tubes, and special detector tubes, also of the new a.c.
filament tubes such as the ux-226, the ux-28o, the i/x-^Si.
the i x-}27, are given. The quadratron, the Kmerson multi-
valve, the Sovereign A-C tube, the Van Home A-C tube, the
new A-C Magnatron tubes and the Armor A-C 1 10 tube are
described.
Ri6o. RECEIVING APPARATUS. RECF.IVKK
Proc. I. R. H. May, 1927. Pp. 387-395. MEASUREMENTS.
"Notes on Radio Receiver Measurements," T. A. Smith
and G. Rodwin.
The comparison of radio receivers electrically involves
the three main points: sensitivity, selectivity and fidclitv,
a> ^;iU>d. The method of test and of making and interpret-
ing the curves presented are outlined.
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RADIO BROADCAST ADVERTISER
Six New Precision Radio Products
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Radio is an exact science. There is a right and a best way for every-
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DRAKE'S RADIO CYCLOPEDIA
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FREDERICK J. DRAKE & CO. Publishers
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RADIO BROADCAST ADVERTISER
Nature's
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Board
The Lata Balsa Reproducer, successful
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R 376.3. LOUD-SPEAKING REPRODUCERS. LOUD
Proc. I. R. I'. May. 1927. Pp. 363-376. SPEAKERS.
"Loud-Speaker Testing Methods," I. Wolff and A.
Ringel.
An electric oscillator method is used in obtaining quanti-
tative measurements in testing loud speakers. The output
of an oscillator, having a continuously variable frequency is
fed to the loud speaker. The results are recorded on a re-
volving drum mechanism. The curves, showing variation
of sound pressure against frequency, reveal interesting
characteristics, as explained.
antenna operating at one of its harmonics. Short waves of
2.66 meters were employed, and observations have been
made with the grounded and the ungrounded antennas.
The paper also gives the test results on a new wave pro-
jector devised by the author with special reference to high
angle radiation of short electric waves.
R344-3- TRANSMITTING SETS. TRANSMITTER.
Proc. I. R. E. May, 1927. Pp. 397-400.
"The Tuned-Grid Tuned-Plate Circuit Using Plate-Grid
Capacity for Feed-Back. A Derivation of the Condi-
tions for Oscillation," J. B. Dow.
Mathematical equations are developed showing the con-
ditions required for oscillation in the tuned-grid tuned-plate
circuit of a transmitter.
Ri62. SELECTIVITY OF RECEIVERS. RECEIVERS,
Proc. I. R f:. May, 1927. Pp. 401-423. Selective.
"Selectivity of Tuned Radio Receiving Sets," K. W.
Jarvis.
The question of modern receiver design, incorporating
selectivity, fidelity of reproduction, and adequate sound
volume, is d-scussed. The resonance circuit and its require-
ments are analyzed mathematically and curves presented
bowing relation between amplification and electivity of
radio-frequency stages. Discussing quality of reproduction
ihe problem of regeneration, the phase shift of the side
bands and the transient response of the circuit are mentioned.
Ri 1 3.3. DIRECTIONAL VARIATIONS. TRANSMISSION
Proc. I. K. E. May, 1927. Pp. 425-430. PHENOMENA.
" Radio Phenomena Recorded by the University of
Michigan Greenland Expedition — 1926," P. C. Oscan-
van. Jr.
The experiences encountered by the writer when using
short waves for transmission on Maligiak Fiord, North of
the Arctic Circle, are related. It was loted that when at-
tempting to receive signals from stations working on wave-
lengths of 50 meters or below, complete screening was f-
fected when the receiver was placed at the foot of a hill
which is of a height greater than 17 degrees from the
horizontal of the station. Photographs of the station are
shown.
R$oo. APPLICATIONS OF RADIO. APPLICATIONS,
RAD.O BROADCAST. Aug. 1927. Pp. 199-202. Paper
"Saving Paper!" J. Millen. weighing.
The device illustrated and described consists of an
oscillating circuit coupled to a tuned circuit, a thermal meter
;ecording the deflection when in resonance. The material
to be measured acts in the capacity of a dielectric, thus
changing the frequency of the resonant circuit, this change
being recorded on the thermal meter.
R 1 34.8. REFLEX ACTION. REFLEX
RADIO BROADCAST. Aug. 1927. Pp. 208-210. CIRCUIT.
"Have You a Roberts Reflex?" J. B. Brennan.
Improvements which can be made in the Roberts circuit
consist in increasing the sensitivity and selectivity, improv-
ing the quality of reproduction, making it more stable in
operation, and increasing its volume. These changes are
discussed in detail.
R376-3. LOUD-SPEAKING REPRODUCERS. LOUD
RADIO BROADCAST. Aug. 1927. Pp. 211-212. SPEAKERS.
"The Balsa Wood Loud Speaker."
Data on the assembly and the oroperties of the new Balsa
wood loud speaker are given. The wood is obtainable in
kit form, and by careful assembly of the parts a speaker of
excellent reproducing qualities is said to result. Suggestions
concerning changes and improvements are offered for those
who experiment with this type of loud speaker.
R344-3- TRANSMITTING SETS. TRANSMITTER,
RADIO BROADCAST. Aug. 1927. Pp. 213-217. Short-Wave.
"A Flexible Short-Wave Transmitter," H. E. Rhodes.
The construction of a portable telegraph-telephone trans-
mitter for short-waves, using tuned-plate tuned-grid circuit,
is outlined, many data being given concerning the
general characteristics of the circuit employed. The set
operates between 7900 kc. and 2650 kc. (38 to ! 13 meters).
A series of tests were carried on, the results of which are
shown graphically and discussed in detail. These include: i,
'I he effect of varying the grid leak resistance; 2, the effect of
varying the resistance of either the tuned-grid or tuned-
plate circuit; 3, the effect of varying the coupling between
the plate and the antenna coils; 4, the effect of varying the
plate voltage.
R2oo. RADIO MEASUREMENTS AND STANDARDIZATION.
RADIO BROADCAST. Aug. 1927. Pp. 224-226. TONE
"Judging Tone Quality," E. H. Felix. QUALITY.
The subject of distortion in radio receivers is discussed
from the standpoint of the listener when trying to dis-
criminate between good and poor tone quality. What is
desired is faithful reproduction throughout, from micro-
phone to loud speaker. Because of the importance of har-
monics in distinguishing different instruments it is es-
sential that frequencies up to 6000 cycles be reproduced.
Sug^csiiqns as to methods which can be used in judging the
reproducing qualities of receivers are offered.
R22O. CAPACITY. CAPACITY MEASUREMENTS.
RADIO BROADCAST. Aug. 1927. Pp. 227-228.
"Condenser, Coil, Antenna Measurements," K. Henney.
The measurements of variable and fixed condensers, dis-
tributed capacity of inductance coils and of antenna capac-
ity and inductance can readily be made with the aid of a
calibrated modulated oscillator. Data for the use of this
instrument and typical measurements are presented.
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Wholesale Vest Pocket Price List
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Short Wave Section
Our catalog contains a section
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AMPERITE is the only automatic filament
control that keeps the temperature or
voltage of the tube filament constant de-
spite variations in the "A" Battery voltage.
It guarantees improved tube performance
and increased tube life through always
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AMPEKITE. Price 81. 1O mounted (in I .
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Write for FREE "Amperite Book" of season'*
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50 FRANKLIN ST., NEW YORK
She "SELF-ADJUSTING" 'Mcartat
RADIO BROADCAST ADVERTISER
79
EWNCH
Improved Aristocrat
de lumDeck
New and Different
Here is an example of a real receiver made
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The list price for all the parts necessary is
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For
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The Deck includes, all mounted ready for
wiring
i •
1 Westinghouse 6" x 12" Micarta
Panel
5 Eby De Luxe Sockets
4 Lynch Cartridge Condensers
7 Lynch Metalized Resistors
_ 4 Lynch Special Mounts
The Deck is a Lynch innovation which
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The Lynch 5-Tube Deck
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"Resistance the Control
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, very thorough treatise on the proper use
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ARTHUR H. LYNCH, Inc.
General Motors Building
New York City
Sales Offices in Most Large Cities
Metal Cabinet for
Latest Hook-Ups
Model 250
For A. C. or Battery Sets
using panels size 7 x 18,
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Inside dimensions 25"
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Metal Panel and Chassis for Silver-
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Complete assembly consisting of panel
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oration, all fibre bushings and washers
included, also screws, bolts and hard-
ware accessories.
S. C. 2 Assembly Unit
(Silver-Cockaday)
Designed and drilled for this
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Metal Panels for Citizens Super Eight
Unipac Housing
Especially designed and provided for Constructed in accordance with Citi-
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Metal Panels and Chassis in All Standard Sizes
JOBBERS, DEALERS— WRITE FOR PRICES
Set Builders— If your dealer cannot supply, write direct
The Van Doom Company
160 North La Salle Street
Factory, Quincy, Illinois
Chicago, Illinois
80
RADIO BROADCAST ADVERTISER
Volume Control
for any Circuit
Centralab
Standard Radiohm
The exclusive Cen-
tralab feature of mak-
ing contact on a resist-
ance element by a
pressure shoe and tilt-
ing disc, assures long
life and permanently
noiseless adjustment.
Centralab Radiohms
with 2 terminals, and
Modulators with 3 terminals, provide gradual,
silent control of oscillation or volume.
Centralab Radiohms with resistance value of
1,000 ohms are used as stabilizing resistance in
Reflex or Superheterodyne. Also used in the
RF grid return circuits of tuned radio frequency
sets. They provide excellent control of regen-
eration when shunted across the tickler in such
circuits as Browning-Drake, Samson TC, Radio
Broadcast, Aristocrat and others employing feed-
back principle. 25,000 ohms are especially
adapted for the S-C circuits. 100,000, 200,000
and 500,000 ohms are the most satisfactory plate
circuit resistance for controlling RF oscillation
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to provide volume control.
There is a resistance and correct taper for every
circuit, providing a perfect control of the circuit,
with simplified panel appearance. Can be
smoothly varied throughout their entire range
from zero to maximum, and give full resistance
variation with a single turn of the knob. Non-
inductive; no sliding contacts carrying current.
Exact resistance values'are maintained as adjusted.
Resistances 3,000, 15.000, 50,000, 100,000,
200.000 or 500,000 ohms $3.00
Switch Type
Radiohm
Same construction as
Standard Radiohms
and combine with the
Radiohm a quick-act-
ing "A" battery
switch. This removes
one more knob from the panel and makes the set
simpler and easier to operate. Provides two es-
sential controls at little more than the price of
one. Turning the knob to the right, lights the
tubes and then increases volume. Turning the
knob to the left decreases volume and then cuts
off the battery. "A" battery switch parts are
spring bronze, nickel plated with positive acting
silver contacts.
200,000 ohms and 500,000 ohms. $a. jo
Centralab
Modulator
The ideal panel-
mounted volume con-
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and a special taper of
resistance to provide
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ume control from a whisper to maximum. A sure
cure for overloaded tubes and harsh amplifiers.
Resistances 250,000 or 500,000 ohms. . . . $2.00
500,000 ohms with "A ' battery switch
combined in one unit $2.30
At your dealer's, or C. O. D.
CENTRAL RADIO LABORATORIES
22 Keefe Avenue Milwaukee, Wis.
R}43. ELECTRON-TUBE RECEIVING SETS. RECEIVER
Neutrodyne, AC.
RADIO BROADCAST. Aug. 1927. Pp. 232-234.
"Constructing a Five-Tube Neutrodyne," H. E. Rhodes.
A shielded, two radio-frequency, detector and two audio-
frequency tube neutrodyne, using the new a. c. tubes, is
shown and details for its construction given. Great sensi-
tivity. selectivity and ease of operation are claimed for this
circuit arrangement.
. ELECTRON TUBES. ELECTRON TUBES,
RADIO BROADCAST. Aug. 1927. Pp. 238-^240. High mu.
"Use of Tubes Having High Amplification." A. V.
Lough ren.
The amplification characteristics of high-mu tubes are
treated. The discussion analyzes the frequency character-
istics of each stage in a resistance-coupled amplifier and
the choice of the amplification factor. Oscillographs and
curves show the results to be expected.
R27O. SIGNAL INTENSITY. SIGNAL INTENSITY,
Radio News. July, 1927. Pp. 12-13. Broadcast.
"The Service Area of a Broadcast Station," S. R. Winters.
Results of measurements made with a loop test set by
S- W. Edwards, radio supervisor of the 8th radio district.
on signal strength from several broadcast stations, are
given. These show to what extent steel buildings, static,
electrical disturbances and other noises affect radio re-
ception at a distance. The working standard of 10.000
micro-volts per meter intensity was used to determine a
reliable reception area about the station.
R}-,2-7. AUDIO-FREQUENCY AMPLIFIERS. TRANSFORMERS
Radio News. July, 1927. Pp. 25-ff. Coupling.
"Why Loud Speaker Coupling Devices are Necessary,"
I. F. Jackowski.
An explanation is given of the necessity of coupling the
loud speaker to the audio amplifier through some coupling
transformer and auxiliary apparatus, in order to bypass the
direct-current component of the power tube output energy.
R8oo. (535.3) PHOTO-ELECTRIC PHENOMENA. CRYSTALS,
Radio News. July, 1927. Pp. 32-ff . Photo-electric.
"Light-Sensitive Crystals, G. C. B. Rowe.
The construction of simple light-sensitive cells, using
ordinary metals such as copper, zinc, etc. or molybdenite
and the substance selenium, is described. The numerous
applications of such cells are mentioned and diagrams
show how such cells may be used by the experimenter.
ELECTRON Ti BES,
High mu.
R33O. ELECTRON TUBES.
Radio News. July, 1927. Pp. 50-51.
"A New Electron Tube," S. Harris.
A tube haying a fourth element has been developed for
use in circuits where objectionable feed-backs are en-
countered. With the aid of the fourth element, known as the
"shielded grid," the ejfectof plate to grid capacity has been
eliminated. It is stated that the amplification obtainable
wi.h this tube is as high as 200 per tube at 50 kc.
R38?. i. SHIELDS. SHIELDING.
Radio News. July, 1927. Pp. 52-ff.
"The Effects of Shielding,' H. A. Zahl.
The effect that shielding has on the electrical properties of
circuits is discussed in detail, with curves shown, and the
method of making the measurements is described.
R2oi. FREQUENCY, WAVELENGTH FREQUENCY.
MEASUREMENTS MEASUREMENTS.
Exp. W reless (London). July, 1927. Pp. 394-401.
"The Exact and Precise Measurement of Wavelength in
Radio Transmitting Stations," R. Braillard. (Con-
cluded).
The description of the wavemeter is continued from the
previous article and the method of standardization is out-
lined. Its accuracy is said to be exceptional, transmitters
being adjustable to a variation limit of To,3c5 of their wave.
R 1 3475. SUPER-HETERODYNE. SUPER-HETERODYNE.
Exp. Wireless (London). July, 1927. Pp. 402-411.
"Design and Construction of a Super-heterodyne Re-
ceiver," P. K. Turner. (Concluded}.
In the last of a series of articles on the super-heterodyne
the author discusses the intermediate stages of amplification
and the low-frequency stages, and proceeds to give a de-
tailed analysis of the actual construction of the set.
R8oo (621.354). BATTERIES, SECONDARY. BATTERIES,
Amateur Transmitter. April, 1927. Pp. lo-flf, Edison.
"Edison Storage B Batteries," H. Rodloff.
The construction of small Edison cells from standard parts
is described. Considerable information as to their character-
istics and their properties is related.
R382. INDUCTORS. CHOKE
Amateur Transmitter. May, 1927. P. II. COILS.
"Radio-Frequency Choke Design," Wm. Zeidlik.
In order to obtain maximum efficiency in the operation
of any shunt-fed transmitter, properly designed radio-
frequency choke coils are essential, as stated. The method of
determining correct coils for such purposes is outlined.
R8oo(62i.3i 1.7). RECTIFIERS. RECTIFIERS,
Amateur Transmitter. May, 1927. Pp. 12-15. Electrolytic.
"Electrolytic Rectifiers, Lead-Aluminum Type," J. E.
Hall.
The theory and the principle underlying electrolytic
rectifiers is given. Information concerning the electrolytes
used, the forming process, the heating of the cells and the
capacity of the units constructed, is outlined in detail.
Gen
. TRANSMITTER SETS.
TRANSMITTER,
Amateur Transmitter. June, 1927. Pp. y-ff. Short-Wave.
"Master Oscillator Kinks," K. M. Ehret.
The design and construction of a master-oscillator, power-
amplifier transmitter, using two ux-2io tubes are outlined in
detail. The circuit differs somewhat from the usual, but is
considered to give very good results and a sharp signal when
1 adjusted properly. Complete circuit diagram and list of
"'parts are presented.
RADIO PARTS DEALERS
PROFESSIONAL SET BUILDERS
and SCHOOLS and COLLEGES
Should first get our free
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Parts and accessories for
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F. D. PITTS COMPANY
219-223 Columbus Ave., Boston, Mass., U. S. A
Distributing Radio Since 1919
REMOTE
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H rile for illustrated descriptive circular
IMAGINE the pleasure of
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"Algonquin"
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Remote Control Radio Tuning Unit
Building a New A'GReceiver
o
Applications of tlieDouble-Gri rl^acuumTube
How to Build the Cooley Racl io I ' ' ;ture Receiver
Constructing Power-Amplifier B-Supply Units
A Directory of Manufactured Receivers
What B-Power Unit Shall I Buy?
ents
RADIO
TJBES
are designed and built to
combine all the qualities
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E. T. CUNNINGHAM, INC.
NEW YORK CHICAGO SAN FRANCISCO
Since 1915—
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Twenty different \
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RADIO BROADCAST ADVERTISER
99
rom one
radio fan to another
Pins screw in this way for
jacks running horizontally.
Pins screw in this way for
jacks running vertically.
For battery testing.
How to say "Merry Christmas"
is no problem — if the person you
wish to remember is "radio-
active." Give him what you'd
like yourself — a voltmeter.
If his is one of the newer sets,
get one of the new Westinghouse
Cabinet Portables. Plugs right
into the jacks provided — looks
and performs like a permanent
cabinet fitting, but is easily re-
movable for testing "A", "B"
and "C" batteries or for other
purposes.
Styles in voltmeters are
changed by this new Cabinet
Portable. The rich, antique
bronze finish — the clever ad-
justable features — make this a
fitting companion piece for the
most expensive radio receiver.
An accurate voltmeter warns
continuously of voltage varia-
tions that affect good reception.
Its use prevents prematurely
burned-out tubes and prolongs
battery life.
PRICE COMPLETE
Price
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7.00
Range
(0-5 and 15O) or
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West of Rockies to
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At your dealer's
Good dealers have other Westinghouse models. For instance,
the most accurate moving-vane instrument made, at $5.00. Or
a highly sensitive jeweled movement at $10.00. Either, a gift!
WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY
Offices in all Principal Cities Representative! Everywhere
Tune in with KDKA— KYW— WBZ— KFKX
Westinghouse
RADIO BROADCAST
DECEMBER, 1927
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XII, No. 2
Cover Design - - - - From a Design by Harvey Hopkins Dunn
Frontispiece - Television Apparatus of a European Scientist 102
Television in Europe William J. Brittain 103
The March of Radio - - - An Editorial Interpretation 105
How the Radio Commission Can Set Radio "Radio Industry" Standards
to Rights Why the South Has Few Stations
What Can the Commission Do? The New WEAF Transmitter
$100,000 to Improve Broadcasting News of the Patent Field
What to Tell the Consumer — and Where The Month in Radio
What Broadcasters Want
Applications of the Four-Electrode Tube • Theodore H. }Ja\\en 109
The Phonograph Joins the Radio Set - ' ' • »• i la
Make Your Own Radio Picture Receiver - - Austin G. Cooley 114
Beauty — The Keynote in the New Radio Receivers 118
What B Device Shall I Buy? • Howard E. Rhodes 120
Measuring the "Gain" of Your Radio Receiver Keith Henney 123
Book Reviews . , , , j^ I^
Inventions and Patents, Wright The Story of Radio, Dunlap
Loud Speakers - 126
Power Devices 127
Facts About the Fada "Special" Receiver - John F. Rider 128
Our Readers Suggest - 131
How to Improve Your Old Receiver - Edgar H. Felix 133
A Quality Five-Tube A. C. Receiver James Mil/en 135
A New "TwO'Ten" Power Amplifier William Morrison 138
The DX Listener Finds a Champion - - - John Wallace 140
"The Listeners' Point of View"
As the Broadcaster Sees It Carl Dreher 142
Radio As an Electro-Medical Cure-Ail Piezo-Electric Control of Stations
Some Catalogues The Small Broadcaster
"Radio Broadcast's" Laboratory Data Sheets - - - - - 146
No. 145. Loud Speakers No. r49. Circuit Diagram of an A.C. Audio
No. 146. B Power Device Characteristics ^ Amplifier
VT ..,-, . „ No. 150. Oscillation Control
No. 147. Gain No. I5r. Single Control
No. 148. An A.C. Audio Amplifier No. 152. Speech
Manufacturers' Booklets Available - - - '152
" Radio Broadcast's" Directory of Manufactured Receivers - - 154
What Kit Shall I Buy? ' - - - - - - - 170
From the Manufacturers •••'».' 174
AMONG OTHER THINGS. . .
"DROBABLY the most interesting article in this issue from
*- the point of view of the experimenter is the constructional
data and operating and assembly instructions on the Cooley
"Rayfoto" radio picture receiver. By the time this magazine
is in the hands of its readers, all the essential apparatus will be
available on the market and nothing will delay the experimenter
in his experience in this new field. RADIO BROADCAST is glad to
forward the names of readers who are interested in receiving
printed matter and late bulletins to manufacturers who are
supplying the various parts for the "Rayfoto" apparatus. After
the appearance of Mr. Cooley's November article, a great num-
ber of our readers wrote us for this information which has
been supplied. A letter should at once be addressed to the
undersigned, asking for additional data in case you have not
already written.
V\ WASHINGTON is the center of interest these days, what
* * with the International Radio Conference and the changes
in the Federal Radio Commission. The death of Commissioner
Dillon is a great loss to radio in the United States and it will be
next to impossible to fill his place. The resignation of Com-
missioner Bellows removes one of the ablest members of the
Commission, but President Coolidge has filled his place through
the appointment of Sam Pickard, former secretary to the radio
body. Mr. Pickard is a likeable and able individual and we
believe his appointment is a wise one. Carl H. Butman, of
Washington, was appointed as Secretary to succeed Mr. Pick-
ard. Mr. Butman has long served RADIO BROADCAST as its
Washington news representative and we are indeed pleased
that the Commission has so wisely chosen a man who knows
radio problems so well.
A WORD about the authors in this issue: William J.
•**• Brittain is an English writer on radio and scientific
topics who has just returned from a European trip to see what
is being done in television. Theodore H. Nakken is a research
engineer for the Federal Telegraph Company. He is a pioneer
in photo-electric cell work and is unusually familiar with radio
progress abroad. Austin Cooley, whose "Rayfoto" picture
apparatus has attracted national attention, is a native of the
state of Washington, received his technical training at M. I. T.,
and except for his trip in 1916 with the MacMillan Arctic
expedition, has been in New York for the past four years.
John F. Rider is a well-known New York technical writer who
is at work on an interesting series of "fact" articles about manu-
factured receivers.
T^HE next issue will contain another story about the Cooley
•*• "Rayfoto" radio picture system and its operation, as well
as interesting data about push-pull power amplification. An-
other of Mr. Rider's articles about manufactured receivers will
be featured as well as a wealth of constructional matter.
— WILLIS KINGSLEY WING.
Doubleday, Page & Co.
MAGAZINES
COUNTRY LIFE
WORLD'S WORK
GARDEN & HOME BUILDER
KADIO BROADCAST
SHORT STORIES
EDUCATIONAL REVIEW
LE PETIT JOURNAL
KL Eco '
FRONTIER STORIES
WEST WEEKLY
THE AMERICAN SKETCH
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OFFICERS
F. N. DOUBLEDAY, President
NELSON DOUBLEDAY, Vice-President
S. A. EVERITT, ^ice-President
RUSSELL DOUBLEDAY, Secretary
JOHN J. HESSIAN, Treasurer
LILLIAN A. COMSTOCK, Asst. Secretary
L. J. McNAUGHTON, Assi. Treasurer
DOLJBLEDAT, <PAGE & QOMPA^Y, Garden Qity, He
Copyright, 1927, in the United States, Newfoundland. Great Britain, Canada, and other countries by Doubleday, Page &• Company.
TERMS: 54.00 a year; single copies 35 cents.
A!! rights reserved.
IOO
RADIO BROADCAST ADVERTISER
101
Acme E4-B Supply, $35
Acme B Power Supply units were
the first on the market to use a
Raytheon tube as rectifier. The
E-4, above, is the latest B Power
Supply achievement of the Acme
This Ifear's Programs
Deserve Such a Speaker/
PROGRAMS now available to you have
become so great that they deserve
the finest speaker radio science has been
able to construct after years of experi-
ence—the Acme K-1A ($25).
With cones on both sides, each
13 inches in diameter, and with two
motors instead of one to "feed"
sound to these cones — you enjoy the
advantage of two perfect speakers
working as one.
ACME APPARATUS CORP.
Dept. R.B-3 Cambridge, Mass.
Gentlemen: Please send me a copy of the booklet
checked below. I enclose 10 cents for each copy.
Amplification without Distortion D
Power Supply for Radio Sets D
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And . . . what an addition, this Acme K-1A, tc
home furnishings! Its graceful design blends
with furniture background as no other can.
For resonant volume beyond belief . . . have
your dealer show you the Acme PA-1 Power
Amplifier ($12.50). It uses socket power
whether your set is electrified or not.
Makes a power speaker of your present
speaker without additional drain on stor-
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Acme's two booklets tell (l) how to im-
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Look for socket operation. Fill in the coupon below
it Symbol for the one you want.
ACME
~for amplification
TELEVISION APPARATUS OF A EUROPEAN SCIENTIST
HpH IS equipment constitutes the television receiver developed by M.
1 Holweck, who is collaborating with Edouard Belin in the design of
television equipment. M. Holweck is specializing in the receiving side of
the installation. The received picture appears on the small circular screen
at the top of the receiver shown in this illustration. Numerous other
European scientists are devoting their time to the development of tele-
vision schemes, and many and promising are the reports emanating from
the various laboratories. M. Belin is, of course, a Parisian and has
done most of his work in France. The short story which begins on the suc-
ceeding page is from the pen of one who has visited many of the pioneers
in the television field in Europe, and the information has, therefore, been
obtained at first hand.
VON M1HALY S TRANSMITTING APPARATUS
TELEVISION IN EUROPE
By WILLIAM J. BRITTAIN
rHAT is Europe doing towards
the furtherance of television?
America already knows quite a
lot about the work of Baird, and the public
company formed to develop his machines
has made his name known in most countries.
But aside from this, little is known of the
progress of the many experimenters in this
fascinating art on the other side of the
Atlantic.
Recently the author went from England
to find out what the Continental men are
doing, what their apparatus is like, and
whether they are preparing a surprise for
the world, and in Berlin was found the man
preparing the surprise. He is Denes von
iYiihaly, a young Hungarian, and chief
consulting engineer to A. E. G. (the General
Electric Company of Germany). An
engineer brought from America for the
purpose is making a simplified version of
Von Mihaly's apparatus to be shown in
Berlin and London as a preliminary to
forming television companies there.
The vital feature of Von Mihaly's method
is an oscillograph which consists of a
tiny mirror mounted on twin wires. The
mirror vibrates between two electro-mag-
nets at speeds which sometimes reach
thousands of times a second. Light re-
flected from the object — a face, a scene,
or whatever it may be — is focussed by a
specially constructed set of Zeiss lenses upon
the mirror. The mirror, vibrating rapidly,
sees each point of the object in turn, in the
manner necessary for television, and flashes
it to a photo-electric cell.
Von Mihaly has made his own cell, and
it sends out currents corresponding ex-
actly to the intensity of light or depth
of shadow of each tiny point as it is
reflected upon it.
In his receiving apparatus Von Mihaly
again uses vibrating mirrors. An electric
lamp, shining brightly or becoming dim as
the current from the transmitter is strong
or weak, is concentrated by lenses upon
mirrors which repeat the action of the
mirror at the sender and zig-zag a beam of
light over a ground glass screen. The vary-
ing light beam, covering the screen eight
times a second, makes up the picture.
To ensure that the sending and receiving
mechanisms are working exactly in time —
so that the mirror at the receiving end is
shining light upon the centre of the screen
at the same fraction of a second as the mir-
ror at the transmitting end is "seeing" a
bright part in the center of the object —
Von Mihaly uses a tuning fork arrangement
on the same principle as those that have
been used by experimenters in photo-
telegraphy. A tuning fork in the receiver,
kept vibrating by an electromagnet, acts
as a switch, regulating current to other
magnets which allow a wheel to progress
one cog for every impulse, and so regulate
the vibrations of the mirror. The apparatus
at each end now fills a table, but Von
Mihaly says he can simplify it to work as
a home set in conjunction with a one-tube
radio receiver.
Behind this assurance is a secret. The
secret is in a small black cylinder,' five
inches by two and a half inches. The inven-
tor calls it his "little black wonder." He
will not tell the world what is inside, but
told the author that with it it is possible
to do away with the great amplifiers neces-
sary in other systems.
"Television sets for the home," he said,
" will be simple and yet give a boxing match
or a horse race. They will be sold in a few
months for the equivalent of a hundred
dollars."
Von Mihaly has been working for thir-
teen years on television. He first became
interested when he was twenty, after hear-
ing a lecture on photo-telegraphy by Pro-
fessor Arthurn Korn. He carried on his work
for the Austria-Hungarian government
during the war, and on July 7, 1919, gave
his first crude demonstration of television.
Ministers in the laboratory of the Telephon
Fabrik in Budapest then saw on a screen
the images of the letters M. D. and REX
transmitted from the young engineer's
home laboratory in another part of the
city.
104
RADIO BROADCAST
DECEMBER, 1927
It was the writer's privilege to be present
at a recent demonstration of Mihaly's ap-
paratus. The results obtained were con-
siderably better than those of the earls-
demonstrations referred to above, and the
images were clearer than those seen by the
author on Baird's screen. On the picture
of a "televised" boy it was possible to see
the collar, the wavy outline of the hair,
the shape of the ear, the forehead, the
eye, the nose, and the mouth, the latter
merging'into shadow on the left side of the
face.
OTHER EXPERIMENTERS
PROFESSOR Max Dieckmann, whom
1 met in his station near Munich,
Germany, has up to the present no result
like this to show. He has achieved results,
but has scrapped the transmitter and other
apparatus that gave them.
"I used mirrors," he told me, "but I
came to the conclusion that no mechanism
could ever be made light enough and ac-
curate enough for television. I am therefore
trying to make use of electrons. By two
electro-magnets, alternated by currents of
different frequencies, I make the stream of
electrons — or the cathode ray — zig-zag
over the object, and I am now experiment-
ing with devices to register the result of
this 'exploring.'
"With electrons I think I have the real
instrument for television. Electrons are
almost weightless and can travel at any
speed we need. All mechanism has a weight
and inertia that in my opinion will always
drag down efforts at perfect television. By
perfect television I mean, of course, the
reception of images as fine as published
photographs. It is possible now to have
crude television. You can have a picture on
as large a screen as you like, but the larger
the screen is the larger must be the patches
making up the picture. Distance of trans-
mission, too, offers little difficulty. We must
concentrate on producing a finer image, and
I believe electrons will enable us to do it."
Professor Dieckmann is retaining his
PROFESSOR MAX DIECKMANN
former receiver which already uses elec-
trons. The receiver is like a bottle. The re-
ceived currents vary the flow of electrons
from a tube fixed to the neck of the "bot-
tle." By magnets similar to those in his new
transmitter the varying flow of electrons is
made to zig-zag over a screen at the bottom
of the " bottle " which glows as the electrons
touch it. When a strong current, showing
that a light part of the object is being en-
countered at the transmitter, sets off a
heavy flow of electrons, the screen glows
strongly at that part, and the glowing
patches make up the picture.
With Mr. Rudolf Hell, his chief assistant,
Professor Dieckmann is working with en-
thusiasm at his latest apparatus.
Mirrors form an essential part of the
apparatus of M. Edouard Belin, the scien-
tist famed for his systems for photo-
telegraphy, who has large stations at La
Malmaison, near Paris. M. Belin inspired
cartoons with a television machine thirty
years ago. His latest apparatus looks
businesslike.
VON MI-
H A L Y ' S
TELEVISION
RECEIVING
APPARATUS
Two rectangular mirrors, about half an
inch long, set at right angles, are made to
oscillate by cranks and connecting rods
driven by an electric motor. A beam of light
shines on the mirrcrs and is reflected zig-
zag in the usual way. For his object M.
Belin uses his hand. Light from the hand
as the beam passes over it is caught by an
eighteen-inch concave mirror at the bottom
of a drum which concentrates the light on a
photo-electric cell held by an arm half-way
down the drum. With this apparatus, M.
Belin told me. he can record fifty thousand
flashes of light and shade a second.
M. Holweck, collaborator with M.
Belin, is responsible for the receiver. He has
designed a special form of cathode ray
oscillograph in which as complete a vacuum
as possible is kept by an air pump, also
of his own design. M. Holweck is working
to perfect the fluorescent screen so that it
will vary its glow exactly according to the
strength of the stream of electrons. He has
also made the apparatus more sensitive so
that a difference of potential of five volts
between the grid and the filament will ab-
solutely cease the flow of electrons. This
means that slight differences of light and
shade in the object, and therefore, tiny
differences in the current received, are re-
corded on the screen.
Promising results are being obtained. At
present M. Belin is transmitting only the
silhouettes of his hand. On the screen the
outline of the hand can be seen clearly.
The hand can be seen to move, and the
fingers to bend. A silhouette of the profile
of a face, and a simple photographic nega-
tive, have been transmitted with equal
success.
"Our work is progressing gradually" said
M. Belin. "We have found it better to pass
over the object a bright spot of light rather
than illuminate fiercely the whole object.
It we used flood lighting to obtain the same
brilliancy as our spot light gives us over a
person's face the intensity would be insup-
portable.
" Earlier in the year we were sending over
our object in a thousand points; now we
have reached two thousand five hundred.
We cover the object eight times a second
which means that in our ordinary experi-
ments twenty thousand signals are flashed
a second. We are greatly encouraged by our
present results. In a few months we should
have something to offer the world."
This is the stage European inventors have
reached. Each one of them is watching care-
fully every step forward by other workers
and trying to go a step further. Von Mihaly
is confident that all his system needs now
is to be put on the market. Dieckmann and
his young assistants are working quietly
but eagerly. And all the time I was at the
establissement Edouard Belin I was filled
with the boyish enthusiasm which per-
meates the atmosphere there.
Of hopes and plans it would be possible
to write pages but in this article an attempt
has been made to keep plainly to facts to
let America know just what Europe is
doing in television.
THK M
NKWS AND IN rmPUH'ATIQN OK rilUUJ-'N T PAhlQ EVENTS
How the Radio Commission Can Set Radio to Rights
A THE peak of the radio season
approaches, we look upon the situa-
tion with considerable satisfaction.
Last year, broadcasting was in chaos and
the Radio Act had not been passed; this
year, progress has been made in the di-
rection of restoring order. Public interest in
radio is at a maximum; the Radio Show at
New York broke all records for attendance
at an industrial exposition. Manufacturers
and dealers report brisk sales. Broadcasting
now has the stimulus of two competing
chains. Everywhere there is activity and
progress.
The only sore spot in the radio situation
is in the regulation of broadcasting. The
Commission went about its task with dili-
gence as soon as it was formed. It cleared
the Canadian channels and put the stations
back on even ten-kc. channels. Then it
spaced the New York and Chicago broad-
casters at fifty-kc. intervals, forcing time
sharing in some cases to make it possible.
After these commendable steps had been
taken, the Commission confined its activi-
ties to juggling a channel here and switch-
ing a station there.
We understood that the assignments of
June 15 were merely an experiment, a stop-
gap measure effective only until a compre-
hensive plan of allocation could be worked
out, which would mean an end to the
heterodyne whistle. The persistently optim-
istic announcements of the Commission that
the broadcasting situation is now remedied
give the impression that the Commission
considers its major task completed.
At the opening of the Radio World's
Fair, Admiral Bullard pleaded for more
time to give the Commission an opportun-
ity to do its work; at the Radio Industries
Banquet, he made numerous proposals to
the radio industry, many of them no less
than amazing, but nowhere have we had a
simple, direct statement of the future plans
of the Commission. Does the Commission
consider its task virtually competed or
will it devote itself to a radical improvement
of broadcasting conditions?
The Admiral's speech at the banquet
contained some striking indications. Briefly,
he stated that broadcasters should find a
way to fix the responsibility for statements
made in radio advertising; that direct ad-
vertising stations should be taxed; that
radio ought to be a public utility regulated
by public service commissions; that pro-
vision should be made to link up broad-
casting for national sos calls, perhaps for
such occasions as the loss of the President's
racoon; that motors for electric elevators
should be re-designed; and most ingenuous
and amazing, that receiving sets should be
equipped with crystals to permit of greater
selectivity.
A few words at the very end of this as-
tounding speech were devoted to the Com-
mission's plans. With regard to the high
power stations serving the long distance
listener, "the Commission is looking for-
ward to a time when the listener, on any
night of good reception, can hear broad-
casting stations from the Atlantic to the
Pacific, from Canada to Mexico, without
interference, on channels cleared for them,
not by arbitrary rulings of the government,
not by fixed and necessarily discriminating
classifications, but by the normal, logical
process of demonstrated fitness and capac-
ity to render a great public service. Such a
development is entirely practicable on the
basis of allocations now in force. It requires
no sweeping changes, but only a clear pic-
ture of the ideal to be attained, and a steady
careful improvement of existing condi-
tions. ..."
Thus the ingenious Commission will by
"orderly and natural, rather than by auto-
cratic and arbitrary methods" bring us
A RADIO TOUR OF THE CONTINENT
Capt. L. F. Plugge, an English radio enthusiast,
spent the months of July and August on a tour
which the accompanying map shows. There were
two radio-equipped cars, one of which is illus-
trated. Each had a loop-operated super-hetero-
dyne and a short-wave transmitter operating on
6660 kc. (45 meters). Intercommunication was
attempted and reception conditions along the
route noted
these ideal listening conditions. No one,
unless it be the broadcast listener, will be
imposed upon; only stations which elect
by natural processes to eliminate them-
selves will be taken off the broadcasting
lists.
The listener unless he lives within the
shadow of a broadcasting station, that is,
in that short distance which engineers like
to call the service range, must put up with
disagreeable heterodyne whistles. Only if
we use "arbitrary" methods, which means
actually applying the regulatory powers
with which the Commission is endowed,
can we hope for fewer stations. The natural
tendency is toward increasing the number
of stations and the power they use. The
Commission leans upon a broken reed, if it
expects "normal, logical processes" to
eliminate stations. Rubber spine methods
cannot help the broadcasting situation.
There is only one solution, which we repeat,
like Cato and his "Carthage must be des-
troyed," and that is the elimination of at
least four hundred broadcasting stations.
What Can the Commission Do?
ECTION IV of the Radio Act author-
izes the Commission to classify broad-
^^ casting stations, to prescribe the
nature of service rendered by each, to assign
bands and powers, and to determine the
location of stations. There is no limitation
on how far it may go in its work of classi-
fication.
Why does not the Commission use these
powers? Why does it not classify broad-
casting stations as (i) national, (2) regional,
(3) local; divide the country into geographi-
cal areas and prescribe exactly how many
106
RADIO BROADCAST
DECEMBER, 1927
stations of each class shall be licensed in
each of those areas?
Public convenience and necessity clearly
establish the point that interference among
stations should not be tolerated and cer-
tainly the Commission should be competent,
if it earns its keep, to determine how many
stations of various powers will be accom-
modated in the present broadcasting band.
In fact, all of these points have been ana-
lyzed for it by qualified experts in precise
and unequivocal terms.
NATIONAL STATIONS, to which exclusive
channels should be assigned, might be de-
fined as follows: (i) Power, 10,000 watts or
over; (2) Service, fifty hours a week or
more; (3) Location, at least ten miles from
all centers of 100,000 or more population
and at a point more than fifty miles from
the nearest national station and not within
200 miles radius of more than five national
stations.
REGIONAL STATIONS, sharing channels
with other regional stations more than
1000 or 2000 miles distant: (i) Power,
2000 to 5000 watts; (2) Service, at least
twenty-five hours a week, and (3) Location,
not more than 100,000 population within
a five mile radius, nor more than five re-
gional stations within 100 miles.
LOCAL STATIONS: (i) Power, between 250
and 500 watts; (2) Service, at least twenty-
five hours; and (3) Location, such that there
are not more than five local service stations
within a hundred mile radius.
Such a program would, of course, require
the elimination of stations in a few of the
congested areas, a blessing to the radio
audience. The stations so eliminated need
not go out of business, but merely con-
solidate with others serving the same area.
Stations of less than 25O-watt power should
be ruled off the air at once, not because they
themselves contribute seriously to con-
gestion but because their channels might
better be assigned to national or regional
stations.
Concrete suggestions, which are not only
logical, but also require the exercise of some
of the "arbitrary" powers conferred upon
the Commission by law, may be in order.
We respectfully suggest the promulgation
and actual observance of regulations for the
accomplishment of four objectives, the con-
stitutionality of which cannot be ques-
tioned:
i. ALL STATIONS should be required to
adhere to their frequencies and those failing
to do so, after occupying their assigned
channels for more than thirty days, should
be fined $500 for each violation noted,
without any further consideration of their
cases. The Commission has been buncoed
by whining station managements into the
belief that staying on a channel requires
extraordinary equipment and engineering
genius. A station failing to adhere to its
channel is not technically competent and
not worthy of a franchise on the air.
Furthermore, after its fourth offense, a
station's license should be cancelled, with-
out further consideration of the case. The
ether space thus regained should not be
assigned to a new ether nuisance, but
A COMPLETE RADIO INSTALLATION ON AN AIRPLANE
Although the l/ille de Paris, the Sikorsky airplane built for Captain Fonck, the noted French flier,
never started toward Paris, plans for the flight were exceptionally complete. Top right shows the
small transmitter and a larger set below it. In the center is a regenerative receiver and at the extreme
bottom, the antenna reel. The motor generator unit is at the extreme left and supplies plate current
for the transmitter. The generator and propeller can be swung out through the fuselage when in use
utilized in relieving congestion where it
exists. The Commission's leniency with
regard to channel wobbling, to which it
attributes practically all heterodyning, is
a remarkable example of unwarranted
bashfulness and consideration the stations
don't deserve. The five hundred dollar
fine for each violation of the Commission's
regulations gives the Radio Act plenty of
teeth but, to our knowledge, the Commis-
sion has never tried them out.
2. THE COMBINATION and consolidation
of broadcasting in congested areas should
be encouraged by guaranteeing to the con-
solidators the combined broadcasting priv-
ileges of the stations so consolidated. For
example, four, full time, 5OO-watt stations,
combined into one, should be permitted a
power increase to 2000 watts, or two, half-
time stations, forming one, should receive
full time. Furthermore, all local and re-
gional stations, not sharing the same chan-
nel, which combine, should be guaranteed
privileged consideration on the basis of
program merit, should they seek to secure
full time on a single channel by challenging
another station.
3. POWER INCREASES to local and
regional stations shall not be granted where
congestion exists, unless other stations,
having a power equivalent to the increase,
be absorbed. Thus, for example, for a thous-
and-watt station in New York to jump to
1500 watts, it should be necessary for it to
absorb a 5OO-watt station.
National stations, on the other hand,
serving large areas, should be encouraged
to increase power, because they require
clear channels and failure to employ the
maximum power means that they are not
making full use of the channel assigned to
them.
4. THE COMMISSION, empowered to
assign hours of broadcasting to stations,
should conserve ether space by limiting
licenses only to hours actually used by the
stations concerned. It has left problems of
time division to the stations themselves,
instead of utilizing its power to help in re-
lieving congestions. There are many broad-
casting stations which are assigned fifty per
cent, of the time on a channel which use
only ten per cent, of it, while the other sta-
tion on the channel is required to remain
silent, although it has program material to
fill the unused time. In congested areas, the
assignment of the time should be based
upon the average hours which a station
broadcast over the same period in the pre-
ceding year. Increase over this time should
be granted only upon the basis of program
merit and service, or the unused time held
to encourage consolidations and to accom-
modate other stations.
The present assignment of forty channel:-
to New York and Chicago, nearly half the
ether space in the eastern part of the United
States, is an imposition upon the listener.
Yet new stations are being licensed in New
York and Chicago, although six stations in
each of those cities have coralled ninety
per cent, of the audience. This concentra-
tion of broadcasting facilities in two centers
DECEMBER, 1927
DEATH OF RADIO COMMISSIONER DILLON
107
of population forces the rural listener to
contend with heterodyning all over the
dials and precludes power increases in rural
areas where better and bigger stations are
actually needed.
The Federal Radio Commission has
worked long and hard with its problem.
It has done the best possible job without
seriously disturbing or curtailing the priv-
ileges of the broadcasting station owners.
But, so long as it fails to regard its duty as
serving the interests of the listening public,
and fails to use the ample powers conferred
upon it by the Radio Act to reduce the
number of stations on the air, ether con-
gestion will remain the unhealthy disease
of the broadcasting situation.
$100,000 to Improve Broadcasting
THE National Association of Broad-
casters appropriated the sum of
$100,000 to make a scientific study
of broadcasting. It plans to employ field
engineers and program specialists to visit
individual stations throughout the country.
The procedure of the Association in the
effective utilization of this fund has not
yet been established. If it is sensibly ad-
ministered, very valuable contributions
can be made in the technical, economic and
program problems of the broadcaster.
From the technical standpoint, studio
methods, as they affect transmission qual-
ity, and the correct operation of the broad-
casting stations to help in eliminating ether
congestion are fruitful subjects for research.
The Association might well help in de-
termining just what the capacity of the
broadcasting band is with regard to power,
service range and geographical location of
stations.
In the field of program technique, critical
study of the outstanding features and sys-
tematic examination of voice and musical
instruments which make good broadcasting
could be very helpful. An investigation of
the possibilities of building high grade
programs by the use of recording methods,
as suggested by Edgar H. Felix in a speech
before the Association, might also be
studied with a view to investigating its
practicability. Mr. Felix suggested the re-
cording of "scenes," blending the voices of
speakers and pick-up music through mixing
panels and the "editing" of programs much
as films are cut and assembled, until the
ideal feature is assembled. When thus worked
over and perfected, it may be presented as
often and through as many stations as its
popularity warrants, without further cost
for talent. This suggestion may result not
only in better planned and coordinated pro-
grams, but it may help to reduce the mount-
ing wire costs which commercial broadcast-
ers now meet.
In the field of commercial broadcasting,
a close study of the methods used to associ-
ate the commercial program with the pro-
duct of its sponsor and to secure the most
effective results in a manner pleasing to the
listener might help to increase the effective-
ness of commercial broadcasting, an end
© Henry Miller
THE LATE COL. JOHN. F. DILLON
Colonel Dillon, member of the Federal Radio
Commission from the Pacific Coast, died early in
October. His loss will be keenly felt by the
Commission and the radio world at large. A
practical radio man of wide experience, Colonel
Dillon had served in various technical capacities
in the Signal Corps, and as radio inspector in
charge of the Eighth District when headquarters
were in Cleveland in 1913 and 1914. He was later
transferred to San Francisco as Radio Supervisor
for the Sixth District and it was from this duty
that his appointment as a Radio Commissioner
called him. His wide practical experience with
government, amateur, and commercial radio
made Colonel Dillon one of the most valuable
members of the Radio Commission
which is necessary to aid economic stabiliza-
tion of broadcasting stations.
The National Association of Broadcasters
is to be commended for its foresight in mak-
ing this substantial expenditure, which is
likely to be returned many fold through
better broadcasting and larger audiences.
What to Tell the Consumer — And
Where
ATLICTED with the expanded cran-
iums resulting from mushroom
growth, the larger manufacturers of
the radio industry are often flattered into
advertising excesses which ultimately cause
financial embarassment. As typical of this
trend, we received a dealer notice, not long
ago, describing a new type of A, B, and C
power device which was to make its debut
to the world principally through three pub-
lications having a combined circulation of
over three million copies. Although a
prophet is not often recognized in his own
country, so frequently has the folly of plung-
ing into expensive national mediums been
demonstrated to the radio industry, that
most manufacturers first make an effort to
sell the merits of their products among the
more influential radio listeners.
The general public has been too fre-
quently fooled by innovations to become
immediate buyers through the medium of
an advertising flash in national weeklies.
They are inclined to consult the most ex-
pert enthusiast whom they can reach before
they are willing to risk their money on a
device which may fail. The more successful
manufacturers establish . their products
among the more influential groups of radio
buyers before they plunge recklessly into
national campaigns in behalf of products
which do not have behind them the weight
of acknowledged approval of the better in-
formed radio enthusiast. The influence of
the radio enthusiast, like halitosis, is often
the insidious element which prevents the
success of the national advertising cam-
paign which is not supported by the good-
will of well informed broadcast listeners
and constructors.
WHAT BROADCASTERS WANT
A LIST of hearings scheduled by the Federal
Radio Commission early in October indi-
cates the evils of requiring hearings upon all
applications, regardless of their merit. For ex-
ample, WBAW, Nashville, Tenn., a loo-watt sta-
tion, operated by a drug concern, seeks to in-
crease its power to 10,000 watts, making it
necessary for nineteen stations to defend them-
selves against this unwarranted incursion of
their service range by the drug store carrier.
There is no channel available for any new
io,ooo-watt stations anywhere.
Another hearing is demanded by WJBL of
Decatur, Illinois, operated by a dry goods store,
calling for a power increase which would damage
the service of ten stations, including such widely
recognized stations as WBAL and WJAX.
WORD, the Peoples Pulpit Association in
Chicago, seeks to occupy the channel of WTAS
and WBBM, both well established and serving
large groups. There is little question but that the
defending stations will be able to show the Com-
mission the presumptuousness of those demand-
ing these hearings, but it is unfortunate that
lawyers, witnesses and disorganization of station
staffs are required to do so.
"RADIO INDUSTRY" STANDARDS
LJ B.RICHMOND, Director of the Engineering
. Division of the R. M. A., perhaps inspired
by our suggestions as to the desirability of one
set of radio standards rather than two, in an
article in the R. M. A. News, suggests that the
R. M. A. and the N. E. M. A. should combine
their work of writing radio standards. Although,
as Mr. Richmond points out, the R. M. A. has
ten times as many members as the Radio Divis-
ion of the N. E. M. A., the long engineering ex-
perience of the older organization and the great
importance of the manufacturers comprising it,
makes its cooperation in writing standards of
vital importance. Mr. Richmond's fair exposition
of the situation is a long step toward affecting a
consolidation of the standards committees of
both organizations, vitally necessary if either of
them are to be in the least effective.
WHY THE SOUTH HAS FEW STATIONS
OENATOR Simmons of North Carolina re-
•J cently launched an attack upon the Federal
Radio Commission, declaring that it showed
favoritism to stations in the North. Illinois,
Nebraska and Missouri, with a population of
fourteen million, have more licenses to broadcast
than the eleven states of the south with their
population of twenty-seven million.
The Senator is correct in his facts, but he dis-
regards the point that the south has not been
sufficiently progressive to erect its share of sta-
tions with the consequence that the Northerners
have already filled their wavelength bands. So
long as the Commission disregards future needs
by filling the ether bands with New York and
108
RADIO BROADCAST
DECEMBER, 1927
Chicago stations, there is not room enough for
better broadcasting service in the more remote
areas.
HOW THE RADIO BEACON WORKS
1'HE radio beacon operated at Hadley Field,
New Jersey, the terminus of the New York-
San Francisco air mail route, has proved re-
markably satisfactory. Two directional antennas
are used, set at right angles. By means of a
mechanical keying device, the letter "A" (dot
dash) is sent from one antenna and the letter
"N" (dash dot) is sent from the second. The
transmissions are so timed that the dots and
dashes exactly interlock so that, at the points
where the signals from both transmitters are
received equally, a continuous dash is heard.
That point of equal signal strength is exactly
midway between the directional signals of the
two antennas. The radio listener aboard the
plane can determine from the signals he hears
whether he is exactly on the course or to the right
or to the left of his course, because, in the former
case, he will hear the steady dashes, while off his
course, he will hear either A or N, depending on
whether he is to the left or the right of it. The
closer to the landing field he approaches, the
more narrow the midpoint at which the signals
are heard to form dashes. A few hundred feet
from the beacon station, a deviation of ten or
twenty feet from the course is clearly indicated
by the signal in the headphones.
THE NEW WEAF TRANSMITTER
IN SPITE of its 50 kw., the initial broadcasts
of WEAF at Bellmore proved a disappointment
to many New York listeners who have depended
upon WEAF for their principal program service.
There are large areas within twenty-five miles
of New York which, due to the change of loca-
tion, now receive a weaker signal from the jo-kw.
transmitter than they did from the old 5-kw. at
West Street. There have been other instances
•when the removal of stations, even a short dis-
tance from the congested areas to permit increase
of power, have actually reduced the number of
persons served.
The transmitting apparatus at Bellmore is the
last word in perfected control. The operator in
charge sits before his desk and manipulates a
number of buttons controlling each operation in
the station, which has the proportions of a fair
sized power house. If one of the water-cooled
rectifier, oscillator or modulator tubes burns out,
a light indicates the faulty tube. Pressure of a
control button takes it out of service and connects
a substitute without interruption of broadcast-
ing.
The receiving set used to maintain the sos
watch has a range of several thousand miles and
will be used to advantage by WEAF'S operator.
WEAF'S sos watches already have the remarkable
record of being the first to hear sos calls in the
New York area and notify naval and coast
guards in one case out of each three and of hear-
in the sos simultaneously with naval and coast
guard stations in the same proportion. Most
broadcasting stations continue blithely on the
air through sos calls until the silence of the ether
around them impresses them with the fact that
there must be something wrong.
NEWS OF THE PATENT FIELD
CLEVEN claims of F. A. Kolster's patent
*-< 1,637,615, were declared invalid in a decision
by the Second Assistant Commissioner of Patents
on the grounds that the applicant's combination
claim to a radio compass having a coil form of
antenna was not novel and was well known at the
time the applicant entered the field, f t f THE
PATENT Office Gazette mentions the following
suits over radio patents: Westinghouse vs.
Allen Rogers, Armstrong 1,113,149; Radio Fre-
quency Laboratory, Inc. vs. Federal Radio Cor-
poration, Warren patent 1,603,432. ? f I THE
DUBILIER Condenser Company has filed against
the Radio Corporation of America on various
socket power patents, f f ? JOHN V. L. HOOAN
filed against the American Bosch Magneto Com-
pany, Stewart Warner Corporation, Freed-
Eisemann, Freshman, and Splitdorf for recogni-
tion of his patent 1,014,002, and also against a
large department store for its sale of Crosley,
Stromberg Carlson, Federal and Fada sets which
he alleges infringe his basic patent. I f I A. H.
GREBE and Company, Stewart-Warner, and the
Consolidated Radio Corporation (Wells Gard-
ner, Chicago and Precision Products Company,
Ann Arbor, Michigan) are now R. C. A. licensees.
The Month In Radio
THE Eastman Kodak Company suggests
that RADIO BROADCAST encourage the use
of the term "phototelegraphy" rather than
"telephotography" in referring to the radio
transmission of pictures. "Telephotography" is
used among photography experts to denote the
taking of pictures over long distances by the use
of special lenses, although Webster approves the
use of the term to describe the transmission of
pictures by radio or wire. Indeed, so extensive
has been this latter use in scientific circles that
it would require much more than the approval of
RADIO BROADCAST to bring about a change in
the accepted terminology. Perhaps a compromise
may be suggested which may help to eliminate
the confusion. Why not refer to telephotography
in the sense of transmitting pictures by wire or
radio, as "radio photography" or "wire phot-
ography," as the case may be? Iff RADIO will
perform a new feat in eliminating the isolation of
explorers when the Army Signal Corps and the
Pathe Company participate in their exploration
of the Grand Canyon of the Colorado. The expe-
dition will traverse the entire length of the canyon,
taking moving pictures and collecting data of
scientific and educational value. Accompanying
the explorers will be a radio telephone trans-
mitter which will be used to
link them with broadcasting
station KGO, from which
reports will be broadcast
through a chain of stations.
The explorers will venture into
dangerous and heretofore in-
accessible parts of the canyon.
Iff WE NOTE in the list
of changes ordered by the
Federal Radio Commission,
authorization to move KFKX
from Hastings, Nebraska, to
Chicago, Illinois. KYW has
shared its channel with KFKX.
The result of the move is to
give Chicago listeners the full
use of the channel without
increasing station congestion.
Nebraska and the great open
spaces, however, suffer a
curtailment of broadcasting
service, f f f KOIL is now
transmitting its regular pro-
grams on 491 o-kc. (61. 06 met-
ers), as well as its regularchan-
nel in the broadcasting band.
KOIL is a member of the Columbia chain, f * t
THE MACKAY Companies purchased the Federal
Telegraph Company's communication system,
according to a recent announcement. The Fed-
eral Company's equipment consists of high pow-
ered arc stations installed along the Pacific
Coast for point-to-point service in California,
Washington and Oregon, and ship-to-shore ser-
vice on the Pacific, f f f WE ARE opposed to
the radiation of the same program by stations
covering the same service area. The listener is en-
titled to as much variety as the congested ether
permits and the employment of two channels to
do what may be done effectively with one is a
waste of ether space. This practice is frequently
indulged in by chain stations. ? f f ANOVELUSC
of broadcasting was employed by the United
Gas Improvement Company of Philadelphia to
warn its customers that gas service had been
temporarily discontinued because of damage by
an accidental blast. Undoubtedly, this prevented
many accidents upon the resumption of service.
f f I THE American Agriculturist should be
able to write a volume on the service of radio to
the farmer as a result of the contest which it
recently announced. It offers not too large prizes
to farmers writing the best letters on the service
which radio renders them. There have been many
instances of thousands of dollars of saving
through weather and market information, f t I
f f I BROADCAST LISTENERS in Germany now
number 1,713,899, according to Wireless Age, an
increase of 78,171 in a three months' period.
t f f THIRTY MILLION dollars worth of radio
apparatus was involved in international trade in
1926, of which about thirty per cent, consisted of
American shipments, twenty-five of German,
and twenty per cent, of British. Exports from the
United States decreased twelve per cent, in 1926
as compared with 1925, but the figures for the
first half of this year show a revival of business.
During the first half of 1927, American exports,
were $3,705,861, an increase of $450,000 over
the same period for the previous year. Iff
OUR BRITISH contemporary, Popular Wireless,
made some measurements as to the radiation
range of a two-tube receiver, consisting of one
stage of r. f. and detector. The set was presum-
ably a non-radiating one, but actually its radia-
tions were readily heard at a distance of twelve
miles, although but fifty volts of plate battery
were used. The radiations were found to blanket
an area of nearly two hundred square miles in
which some five million people reside.
A TUG CAPTAIN WHO CAN TELEPHONE FROM
HIS BOAT
More than forty British-Columbian tug-boats, used in towing
lumber on the waterways, are equipped with 5O-watt radiophone
sets, tuned to 1507 kc. (199 meters). The view above shows a
Captain's cabin and the complete receiving and transmitting
installation
1T1-JT1C1 17/01 TIC?
UrUi JriJUil
AN ENGLISH SHIELDED-GRID TUBE
In England and on the Continent, four-electrode tubes have been available for
some time. The original research is credited to Schottky in Germany and the
"shielded-grid" tube which has recently appeared in this country is credited to
Dr. A. W. Hull
By THEODORE H. NAKKEN
A REVIEW of the progress of receiver
design, which is possible by turning
over the advertising pages of some early
radio magazines, would offer some surprising
evidence. We would see that mechanical im-
provements, refinements, and modern methods
have been the cause of radical changes in receiver
pattern, and have so simplified operation of
tuning as to make the modern receiver seem
as far in advance of its forbears as is the present-
day automobile ahead of the automobile of
fifteen years ago. Yet we would note that there
has been no basic change in the type of circuit
used. The regenerative receiver of ten years ago
still stands unchallenged as a sensitive device for
translating signals from a distant broadcasting
station.
In searching for the reason of this lack of
change in circuit arrangement, it will occur to
us that we have reached a limit, and that it is
almost impossible to obtain greater amplifi-
cation than the present-day receiver gives us.
And this limit is easily located as lying in the
inherent characteristics of the vacuum tube as
manufactured to-day. Even with its better fila-
ments and better all round design, the vacuum
tube of to-day has exactly the same funda-
mental characteristics as it had when first con-
ceived and built as an experiment. It follows,
then, that if any improvements in receivers are
to be expected, such improvements will not be
realized before radically improved vacuum tubes
are made available.
But if we boldly lay the lack of actual progress
at the door of the commercial vacuum tube, we
must state why the tube should be responsible
and how its inherent faults can be eliminated.
The indictment against the present-day vacuum
tube covers in the main two points — lack of
amplification and the tendency to cause oscil-
lations due to inter-element capacity. Another
charge that may be brought forward is in-
efficiency, but this is almost identical with its
lack of amplification. How to improve these
conditions seems at the present time more
important than all other efforts combined to
make better receiver circuits, and so we will try
to indicate shortly why the vacuum tube is
inefficient, and how we can largely do away with
the inter-element capacity, so as to get better
all around performance from any circuit.
The ordinary vacuum tube contains three
elements — filament, grid, and plate. The fila-
ment acts as a source of electrons when heated;
the plate, by virtue of its positive potential,
causes these electrons to be attracted to itself
and thus establishes a plate current; the grid,
interposed between filament and plate, governs
the amount of electrons that can reach the plate,
acting, therefore, as a controlling element of the
plate current. The grid, generally being held at a
negative potential, tends to prevent electrons
from wandering away from the source (the
filament). The plate attracts electrons only by
virtue of its high positive potential, and over-
comes the repelling effect of the grid.
Space Charge
Plate Field +
"-GridField-
FIG. I
In the three element tube there are three static
fields which govern the tube's functions. From
this diagram it is seen that there are two negative
fields, both of which impede the flow of electrons
to the plate
It is not only the grid that tends to repel the
electrons emitted by the filament but this repel-
lent action is also exercised by the electrons
themselves. In fact, we may say that the fila-
FOR the last four years, foreign radio periodi-
cals have contained a wealth of articles on
the advantages of the double-grid lube. These tubes
are chiefly used by our foreign neighbors because of
their economy, but it has been inevitable that these
lubes should make their appearance in this coun-
try. More than a year ago, two manufacturers
brought sample double-grid tubes to the Laboratory
but the time was not yet ripe for their general in-
troduction. In April, 1926, Dr. A. W. Hull of
the General Electric Laboratories described his
"shielded-grid" tube in the Physical Review and
on October ist the New York newspapers carried
the announcement of the Radio Corporation that a
"shielded" grid tube — the ux-222 — was 'in the
process of commercial development and would be
ready for the general public "some time in the
future." Believing that our readers would be inter-
ested in a review of important information on
double-grid tubes, thefollowing article was prepared
at our request by Mr. Nakken who is familiar with
the use and operation of multi-grid tubes on the
Continent. — THE EDITOR.
ment is surrounded by a cloud of electrons, which
therefore constitute a negative charge, trying to
drive the electrons back instead of allowing them
free passage to the plate. See Fig. i. Hence the
plate must not only overcome the effect of the
negative grid, but it also must nullify the effect
of this cloud of electrons, which generally is
called the space charge, in addition to its duty
to attract electrons and thus establish the plate
current.
There are two combined factors then which
tend to retard the flow of electrons from filament
to plate — space charge and the grid, and both
are counteracted by the plate potential. It
follows that part of the plate potential is utilized
only to overcome the repellent action of space
charge and grid, and of course, as far as amplifi-
cation goes, this part of the plate potential is
virtually useless. We may then say that the
statement to the effect that the tube is inefficient
is proved, the more so when it has been estab-
lished that, in most designs, only from 10 to 15
per cent, of the plate potential is actually avail-
able for the establishing of plate current, and
the remaining potential serves the purpose
indicated.
We know that the space charge is virtually a
constant and its effect is added to that of the
grid effect. The space charge, having its sphere
of influence much nearer to the source of elec-
trons than the grid, is much more powerful in its
action, and thus a variation in grid potential,
while representing a comparatively large change
of the grid action on the flow of electrons, is
decreased in its effect by the fact that it repre-
sents only a comparatively small change in the
total sum of the retarding action of grid and
space charge combined. Here again we may say
that the tube is proved to be highly inefficient,
but now in the sense that the presence of the
space charge prevents the grid from being fully
effective.
It follows from the foregoing remarks that the
main reason for the inefficiency of the vacuum
tube may be sought in the presence of the space
charge. In fact, if the latter were absent, we
would need only a small plate potential to obtain
the identical results as at present, with the
additional advantage that the grid would be
fully effective because the grid field would be the
only factor governing the magnitude of the elec-
tron flow to the plate, instead of only part of the
sum of two factors, of which the second one, the
space charge, is by far the greater. The truth of
the matter is that, if only the space charge were
absent, the grid effect would be from three to four
times greater than at present, i.e., without any
110
further changes in the tube the amplification
factor would jump from, say, 8 to 30, yet the
internal impedance of the tube would remain
the same
THE FOURTH ELEMENT
WHEN we consider the static fields present
in the vacuum tube we will see that we
can count three — space charge, grid field, and
plate field. The former two are negative while
the latter is positive. The space charge, as we
have seen, is a constant, or virtually so, and must
be nullified by part of the positive plate field.
If, then, a second positive field were introduced,
nearer the filament, and thus nearer the space
charge, a fairly low potential field would easily
nullify the latter's effect. Obviously this can
easily be done by a fourth element, which
would, of necessity, be placed either between
filament and grid, or between grid and plate.
This element, however, should not obstruct the
flow of electrons from filament to plate, hence it
should be an open structure, and for this reason
logically take the form of a very
open grid. In this way the four-
element (double-grid) tube was
born.
Let us consider for a mo-
ment that such a grid is placed
between filament and grid,
as in Fig. 2. Due to the con-
struction of the tube it is much
nearer the filament than the
plate, and as the influence of
such a field is inversely propor-
tional to the cube of the distance,
it becomes apparent that, if this
grid is placed at, say, one third
of the distance between filament
and plate, its field is 27 times
more effective than the plate
field. Thus, if in the ordinary
tube 90 volts is used on the
plate, approximately 3 volts would suffice on
this fourth element to completely do away
with the space charge effect. This, first of all,
increases the percentage effectiveness of any
RADIO BROADCAST
Auxiliary Fiel'
Space Charge-,
- Plate Field +•
Grid Field -
Auxiliary Field +
Space Charge -
FIG. 2
When an auxiliary positive field is introduced
into the tube, the negative field due to the fila-
ment is overcome, leaving the total negative
field (which is detrimental to the progress of elec-
trons to the plate) in a much reduced condition
potential change on the controlling element, the
grid proper, so that we reach automatically a
much higher amplification factor, and secondly,
Milestones in Vacuum Tube Progress
Edison discovered "Edison Effect" ....
Fleming experimented with Edison Effect .
Fleming patented the two-element rectifier tube
DeForest added third element to Fleming valve
Tubes used in transcontinental telephony .
Radio telephony from Arlington to Honolulu .
Introduction of "hard" tubes to general use .
Appearance of thoriated filaments 1923 ,
General use of power tubes 1926 I
Development of high-current low-voltage filaments 1927 I
Development of shielded-grid tube 1927 \
FIG. 3
This diagram is that of a single radio-frequency
amplifier using a double-grid tube, the inner,
grid being at a positive potential with respect to
the filament. The grid-plate capacity remains
unchanged
makes it possible to decrease the plate voltage
considerably, say to ten or fifteen volts, and still
retain a tube of the same general characteristics
as the three-element original.
It should be noted here, that we have assumed
that this fourth element is built into an ordinary
tube. The result then is that we have not in-
creased the capacity between the plate and grid,
and thus have not increased the tendency of the
tube to oscillate due to capacitive feedback.
This is a very important consideration, because
it is easy enough to build an ordinary three-
element tube with as high an amplification
factor, as is done with modern high-mu tubes.
But the latter is accomplished by narrowing the
grid, i.e., by increasing the plate-to-grid capacity,
and hence such tubes are almost completely un-
fit for radio-frequency amplification. In such a
tube the tendency for capacitive feedback is
increased tremendously, and this capacity affords
an easy path for the signal potentials to escape
via the plate and become ineffective. As will be
DECEMBER, 1927
seen in Fig. 3, there is nothing strange in the
hookup of a four-element tube, the extra elec-
trode being hooked directly to some part of the
B battery.
We will now consider the second possibility in
construction, i.e., that of placing the fourth ele-
ment between grid and plate. Of course it must
take the form of an open grid, as its purpose
again is only to create a positive field, to be used
to nullify the space charge effect.
Let us suppose that the tube is now so con-
structed that this element is placed halfway
between filament and plate, in which case it
follows that its effect on the space charge is
eight times greater than the same potential on
the plate. If, then, normally the plate has a
potential of 90 volts, a positive potential of 12
volts will be equally effective when applied to
the fourth element, so that once more the plate
voltage can be decreased to, say, 22^ volts. Due
to its open construction the positive grid offers
no obstruction to the flow of electrons, and itself
draws only a very small current. Once more we
make the grid fully effective in
its influence upon the flow of
electrons, so that the amplifica-
tion factor of the tube has been
materially increased.
But simultaneously we have
attained another effect, which
merits close investigation. The
positive grid, being held at a
constant positive potential by
the expedient of connecting it to
a point on the B battery, may
be stated to be constantly at a
certain potential above ground
potential. But after all, it is
grounded. As it is interposed be-
tween plate and grid, it has the
effect of splitting the capacity
between these two elements into
two capacities, in series as can
be readily seen in Fig. 4, because it acts the
same as if a grounded plate were inserted be-
tween two condenser plates. And as its structure
is very open, its capacity to each of the elements
Hih
1883
1896
1905
1907
1914
1915
1920
THE "INNER WORKS' OF AN ENGLISH SHIELDED GRID TUBE
One really ought to call them "shielded-plate" tubes, for the grid differs but little from that in
ordinary tubes, while the plate is housed behind the shield. This illustration and that which heads
this article are reproduced from Wireless World (London)
FIG. 4
If the outer grid of a double-grid tube is made
positive, the resultant grid-plate capacity of the
tube is greatly reduced. At the same time it is
possible to build tubes with much greater ampli-
fication factor. The plate-grid capacity is reduced
owing to the fact that two "condensers" are
now in series
of the tube is very small indeed, smaller in fact
than the capacity between plate and grid origin-
ally was. As the two capacities are in series, the
resultant capacity between plate and grid is
smaller than either one of the two, and hence
we have, in this particular construction of the
double-grid tube, almost completely eliminated
the plate-grid capacity, with all its baneful
effects on receiver efficiency.
Thus, this type of vacuum tube has even
greater advantages than when the positive grid
is placed between filament and grid. We have
created a tube which is highly efficient as to
DECEMBER, 1927
APPLICATIONS OF THE FOUR-ELECTRODE TUBE
111
FIG. 5
In this detector circuit the outer grid is positive,
the inner grid biased negative to prevent over-
loading
plate potential, its amplification factor has
been increased considerably, and the plate-grid
capacity has been largely eliminated, so that
the tube may be called self stabilizing.
No wonder then that the European amateur
uses these double-grid tubes quite extensively,
for the upkeep of a small receiver with tubes of
this kind is very economical.
Let us for a moment imagine what can be done
PLATE VOLTAGE
FIG. 9
Measurements made in the Laboratory of RADIO
BROADCAST show that when the inner grid is
positive, the mutual conductance of the tube
may rise to as high as 800 while the plate im-
pedance is 125,000 ohms, indicating a voltage
amplification factor of 100. Plate voltage-plate
current curves are shown here
1 with tubes of this kind. In an ordinary receiver
employing two r.f. stages we may be glad if we
! get a voltage amplification of about eight per
' radio stage, so that the total amplification before
detection is only sixty four. With tubes of this
new design, and an amplification factor of, say,
25, we get an amplification before detection of
625 under the same circumstances, and with
less trouble, because the capacitive feedback is
as much more easily controlled.
An ordinary detector gives an additional
amplification of about four, so that with the
commercial receiver and ordinary tube the de-
tector delivers a signal with a voltage amplifi-
cation of about 250. The new tube as a detector
would give an amplification of about 12, so that
its signal would represent an amplification of
I 7500 times after the two r.f. stages — and this is
I voltage amplification only.
Due to this enormous amplification, the con-
ventional condenser and grid leak should of
course be discarded for a negative potential on
the detector grid, as shown in Fig. 5, because
otherwise the detector would surely be over-
loaded.
For audio amplification the type of double-
grid tube used is almost immaterial, but as only
the one type (with extra element between plate
and grid) gives great advantage of decreased
inter-element capacity, and thus will be employed
in the r.f. stages, we may just as well use it for
the audio stages too. With a good three to one
transformer one stage will give us an amplifi-
cation of about 90, so that the total reaches,
after the first stage, 675,000, as against
FIG. 6
A transformer-coupled audio amplifier stage
using a tube whose outer grid is positive to reduce
the space charge and make the plate voltage
more effective
ordinary tubes, with the same transformer, 24
for one audio stage and a total amplification of
6000. One perceives that almost unlimited per-
spectives in receiver design are opened up, that
M
H
3
RADIO BROADCAST
LABORATORY
UX-222
Inner Grid- »22.5
£p - MS i
/
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1.0 1.2.
GRID VOLTS
FIG. IO
Grid voltage-plate current curves on the new
ux-222 tube with the inner grid positive. Note
that the grid voltage lines are only two tenths
volts apart indicating a large amplification factor
enormous volume may be expected, and distance
undreamed of may be covered.
A study of the diagrams will reveal that the
tubes are hooked up almost in the same way as
ordinary tubes, with the exception of the posi-
PLATE VOLTAGE
FIG. I I
The most interesting curve of all — the plate
voltage-plate current data with positive outer
grid. Note the negative resistance at low plate
voltages, the rapid rise when the plate voltage
equals that of the outer grid, and the very flat
straight portion where the tube is ordinarily
worked
FIG. 7
A resistance-coupled low frequency ampli-
fier with the outer grid of the tube positive
live grid connection. Figs. 6 and 7 show dif-
ferent audio stage hookups.
The names "double-grid" tube is in the
author's opinion, a misnomer. Generally we call
the controlling element the grid, and as the
fourth element in no way serves as a controlling
element, it should not be called a grid, but
simply the auxiliary element, or fourth element.
Others have called the peculiar action of the
fourth element between grid and plate a shield-
no V.
FIG. 8
The circuit of a special a. c. -operated double
grid tube in process of development.
ing one, and call a tube thus constructed a
shielded grid tube. It will be perceived that there
is a good reason for this name, because the grid
is actually more or less shielded against the plate
effect, causing it to be remarkably stable.
EDITOR'S NOTE
THE curves presented here were made in the
Laboratory and show the interesting charac-
teristics of the ux-222 — the R. C. A. "shielded
grid" tube. Followers of our tube articles should
note the extremely flat plate-current plate-
voltage curve indicating an impedance — with
the outer grid positive — of about 650,000 ohms,
the negative resistance or falling characteristic
at low plate voltages, and the high amplification
factor of 222 secured by multiplying the mutual
conductance by the plate impedance. If it is
possible to place a load in the plate circuit of
this tube, say at broadcast frequencies, of
650,000 ohms, a voltage amplification of 1 1 1 will
result, compared with the usual amplification of
about 10 for a single tube and its accessory
apparatus.
With the inner grid positive, the mutual con-
ductance rises, the plate impedance falls, and the
amplification factor drops to about 100. Under
these conditions the tube can be used in a resist-
ance— or impedance — coupled low-frequency
amplifier.
Experimenters will delight in this tube. Its pos-
sibilities are many and diverse. It will not revo-
lutionize the radio industry, newspapers to the
contrary, nor will it produce an entirely new era
in receiver design. 1 1 is just one more step toward
the ultimate goal of — what? RADIO BROADCAST
will publish additional data as it is available on
the use of tubes of this type.
The PHONOGRAPH Joins
By Way of Introduction
\ JOT many months ago, Carl Dreher suggested
1 ' in his department in RADIO BROADCAST,
that a radio broadcast program was almost the
most ephemeral thing in the world. Thousands
of dollars are spent to engage talent, wires
covering half a continent are hired, advertising
is scheduled in newspapers, several studio re-
hearsals are held, and finally the elaborate pro-
gram is put on the air. For an hour it lasts — but
it can never be repeated. If you did not hear it,
all the king's horses and all the king's men
couldn't put it into your loud speaker again.
If it is not possible to reproduce a complete
radio program in one's own home, one can at
least recreate the equivalent. A very great num-
ber of well-known radio artists are regularly re-
cording for each of the important phonograph
companies. Their records — electrically cut — are
available everywhere.
These pages list a few of the records made by
artists who are perhaps better known to the
radio listener than to the average purchasers of
phonograph records. Here are fine recordings
made by the ' favorities of the Atwater Kent
hour, and the famous artists of the Victor,
Brunswick and Columbia hours. As for the jazz
bands, the comedy duos, and other enter-
tainers with a more local fame, they, too, are
forever at your beck and call on the black discs.
One of the most important advances made in
recent years — for which we must thank the
scientists — is the great progress made in the re-
production of music and speech by electrical
means. All radio folk know how audio amplifica-
tion has been improved, what with new amplifiers
of excellent characteristics, better loud speakers,
and so forth. An equally important improve-
ment has taken place in the phonograph field.
Now the phonograph, with its electrically cut
records and its acoustically excellent exponential
horns or cone loud speakers, will rival the musical
fidelity of the best radio receiver.
NEW RECORDS BY RADIO FAVORITES
Released Since September
WHAT no WE Do ON A DEW-DEW-DEWY DAY
Is IT POSSIBLE?
THE TAP TAP
IF I HAD A LOVER
PRESIDENT COOLIDCE WELCOMES COLONEL LINDBERGH AT
WASHINGTON, D. C., JUNE 11, 1927 — PARTS i AND 2
PRESIDENT COOLIDGE WELCOMES COLONEL LINDBERGH AT
WASHINGTON, D. C., JUNE n, 1927 — PART 3
COLONEL LINDBERGH REPLIES TO PRES. COOLIDGE
COLONEL CHARLES A. LINDBERGH'S ADDRESS BEFORE THE
PRESS CLUB OF WASHINGTON. D. C , JUNE 1 1, 1927
COLONEL LINDBERGH'S SOUVENIR RECORD— Concluded
CIRIBIRIBIN (WALTZ SONG)
IL BACIO (THE Kiss) (ARIDTI)
INDIAN LOVE CALL (FROM ROSE-MARIE)
ROSE-MARIE (FROM ROSE-MARIE)
OLD BLACK JOE (FOSTER)
UNCLE NED (FOSTER)
ACTUAL MOMENTS IN THE RECEPTION TO COLONEL CHARLES
A. LINDBERGH AT WASHINGTON D. C., — PARTS i AND 2
AT DAWNING
THE WALTZING DOLL
KENTUCKY BABE
MIGHTY LAK' A ROSE
ANGELS WATCHING OVER ME
CLIMBIN* Up THE MOUNTAIN
SAM'S BIG NIGHT
THE MORNING AFTER
JUST LIKE A BUTTERFLY
JUST ANOTHER DAY WASTED AWAY
UNDER THE MOON
SING ME A BABY SONG
You DON'T LIKE IT — NOT MUCH
OH JA JA
Shilkret-Victor Orchestra
Kentucky Serenaders
Kahn's Orchestra
Shilkret and Victor Orchestra
Hon. Calvin Coolidge
Hon. Calvin Coolidge
Colonel Charles A. Lindbergh
Colonel Charles A. Lindbergh
Bori
Virginia Rea
Murphy
Tibbett
Victor Concert Orchestra
Vaughn De Leath
Utica Jubilee Singers
"Sam 'n' Henry"
Franklyn Baur
Marvin-Smalle
Stanley-Marvin
Vaughn De Leath
The Happiness Boys
20819
20827
35835
35836
35834
1262
4015
1265
20747
20668
20664
20665
20788
20758
20787
20756
Vidm
The public has suffered rapid education. They
have learned that faithful reproduction of the
original is possible in radio sets and in phono-
graphs alike. And if the growth of broadcasting
were not enough to sharpen the interest in
music of all kinds, the new phonographs and the
new records have come along to broaden the
domestic entertainment horizon.
The radio receiver has taken its place as a
musical instrument — a medium of entertain-
ment— along with the phonograph and the piano.
The radio set in the public consciousness is no
A COMBINATION
RADIO-PHONO-
GRAPH FROM
BRUNSWICK
The Brunswick
Panatrope.Radiola,
model ijSC. This
instrument con-
tains a Radiola 28
super-heterodyne
receiver with en-
closed loop, which
can be controlled
by the dial in the
front of the left-
hand panel. On the
right is the Pana-
trope and below it
the cone loud speak-
er working out of
a ux-2io amplifier
which is also the
amplifier for the
radio set. The in-
strument, complete
with all tubes for
6o-cycle a. c. oper-
ation lists at $i 150
longer merely a scientific marvel and mystery.
And since they are so closely related because of
what they can bring to the home, the phono-
graph and the radio set have been drawn closely
together in association of ideas and in actual
physical form. Those who wish to buy a combina-
tion radio-phonograph can choose many fine
models from five or six well-known manufactur-
ers. Those who already have a radio receiver
which they wouldn't trade for the royal throne
of Roumania can make their audio amplifier and
loud speaker do double duty in reproducing
phonograph records or a radio program — accord-
ing to the whim of the owner. All one needs be-
side a good loud speaker system is any kind of
turntable which will twist the record at an even
speed of 78 revolutions per minute, and a good
electro-magnetic pick-up. And there are many of
the latter on the market.
FAVORITES IN CHICAGO
"Sam 'n' Henry" — Correll and Gosden who
nightly disport before the twin microphones of
WON and amuse countless WON listeners. Their
verbal antics are embalmed on Victor records,
listed above
DECEMBER, 1927
113
the RADIO Set
New Records by Radio Favorites
SOMETHING TO TELL
STOP, Go!
I AIN'T GOT NOBODY
ROODLES
MY WIFE'S IN EUROPE TO-DAY
A LITTLE GIRL — A LITTLE BOY — A LITTLE MOON
BABY FEET Go FITTER PATTER
SOMETIMES I'M HAPPY
WHEN DAY Is DONE
No WONDER I'M HAPPY
AIN'T THAT A GRAND AND GLORIOUS FEELING?
MAGNOLIA
JUST A MEMORY (VOCAL CHORUS BY ELLIOT SHAW)
OY BELLS (VOCAL CHORUS BY VAUGHN DE LEATH)
OOH! MAYBE IT'S You {VOCAL CHORUS BY FRANKLYN BAUR)
SHAKING THE BLUES AWAY (VOCAL CHORUS BY FRANKLYN BAUR)
JUST A MEMORY
MY HEART is CALLING
No WONDER I'M HAPPY
JUST ONCE AGAIN
BABY FEET Go FITTER PATTER
THERE'S ONE LITTLE GIRL WHO LOVES ME
FANTASY ON ST. Louis BLUES
PARTS i AND 2
AIN'T THAT A GRAND AND GLORIOUS FEELING?
I AIN'T THAT KIND OF A BABY
LEONORA
PARES!
HERE AM I — BROKEN HEARTED
HAVANA
(VOCAL CHORUSES BY FRANKLYN BAUR)
SWANEE SHORE
MEET ME IN THE MOONLIGHT
Do You LOVE ME? — VOCAL CHORUS BY F. BAUR
HONEY — VOCAL CHORUS BY VAUGHN DE LEATH
AIN'T THAT A GRAND AND GLORIOUS FEELING?
Vo-Do-Do-DE-O BLUES
THAT SAXOPHONE WALTZ
1 COULD WALTZ ON FOREVER WITH You SWEETHEART
Gio-Ap, GARIBALDI
OH! YA! YA!
FOR THEE (POUR Toi) (GORDON)
FROM OUT THE LONG AGO (STRATTON AND DICK)
IUST ONCE AGAIN (CHORUS BY F. BAUR)
LOVE AND KISSES
ARE You HAPPY?
GIVE ME A NIGHT IN JUNE
SONG OF HAWAII
HAWAIIAN HULA MEDLEY
Two BLACK CROWS, PART }
Two BLACK CROWS, PART 4
MAGNOLIA
PASTA FAZOO LA
THE VARSITY DRAG
(VOCAL CHORUS BY BAUR, JAMES, AND SHAW)
DANCING TAMBOURINE
GOOD NEWS (VOCAL CHORUS BY BAUR, SHAW AND LUTHER)
LUCKY IN LOVE
Shilkret-V'ictor Orchestra
Coon-Sanders Orchestra
Fry's Million Dollar Pier Orch.
Vaughn de Leath
Radio Franks,
White and Bessinger
Harry Richman
Harold Leonard and His Waldorf-
Astoria Orchestra
Harry Reser's Syncopators.
Franklyn Baur
Ernie Golden and His Hotel
McAlpin Orchestra
Abe Lyman's
California Orchestra
Don Vorhees and His Earl Car-
roll's Vanieties Orchestra
Paul Ash and His Orchestra
Leo Reisman and His Orchestra
Cass Hagan and His Park
Central Hotel Orchestra
Harry Reser's Syncopators
The Columbians
Van and Schenck
Art Gillham-The Whispering
Pianist
Billy Jones and Ernest Hare
(Happiness Boys)
Barbara Maurel
Paul Ash and His Orch.
Ipana Troubadours
South Sea Islanders
Moran and Mack
Van and Schenck
Cass Hagan and His Park
Central Orchestra
The Radiolites
Fred Rich and His Hotel Astor
Orchestra
3590 Brunswick
3605
10780 Columbia
io66D
10830
10890
10870
io68D
10710
1081 D
10740
1 4oM "
10900 "
10980
n n D
10940 "
10920 •'
11140 Columbia
lloSD
THIS RADIO PROGRAM IS RECORDED
Colonel Lindbergh before the Washington
microphones which carried his welcome-home
ceremonies to the entire nation. Victor has made
four excellent records from this event.
FOR the first time, phonograph records of a
radio broadcast program are offered to the
public. Victor has the distinction of pioneering
and they offer three double-face records of the
national welcome to Colonel Charles A. Lind-
bergh at Washington. On these three records you
have the voice of President Coolidge, the inter-
spersed announcements of Graham McNamee,
a short address by Colonel Lindbergh, and his
longer speech at the National Press Club. It's
all there and if you close your eyes, it isn't hard
to imagine that the events are just taking place —
the cheers of the crowd, the applause which
interrupts the speakers, the blare of the bands,
and the quiet unruffled voice of Lindbergh.
The Victor Company arranged a direct wire
from Washington, culminating in their studios
through which their recording apparatus got the
same program as each of the broadcasting sta-
tions. The ceremonies were recorded on forty-six
record surfaces and finally edited down to the
six surfaces now available. It is a good job from
any point of view and Victor is to be congratu-
lated. It is time that some of the historic events
which are being offered to the radio listener with
impressive regularity were preserved in perman-
ent form. The next offering will be a champion-
ship fight, we suppose.
GUESS WHO
None other than Billy Jones and Ernest Hare —
known to Eastern listeners of WEAF on Friday
nights as the Happiness Boys. Their songs are
recorded by Victor and Columbia
A PHONOGRAPH-RADIO
COMBINATION FROM
VICTOR
"Automatic Electrola-Rad-
iola No. 955" is what Vic-
tor calls this beautiful
instrument. Records are
changed automatically and
groups of 12 can be played
without attention.
An 8-tube super-heterodyne
with enclosed loop operating
entirely from the light sock-
et through the power supply
for the vacuum tube ampli-
fier and the cone speaker
used alike for phonograph
and radio reproduction. The
radio receiver panel can be
used in three positions. List
price, $1550
THIS article is the third in the serifs explain-
ing the use and operation of the Cooley " Ray-
foto" picture receiving system. The Cooley ap-
paratus was demonstrated in actual operation at
the New York Radio show and attracted an as-
tounding amount of interest. Governor Alfred E.
Smith of New York, who made the opening address
of the Show, transmitted a part of a picture of
himself, reproduced by the Cooley system over wiz
and other stations of the Blue network. Many of
the readers of this article undoubtedly heard that
interesting broadcast. The subject of radio photo-
graph reception is so large that it can be discussed
only in part on each article. Our readers are ad-
vised to preserve carefully each of the articles in
RADIO BROADCAST on this system, beginning i^itb
the first story in the October, 1927, issue. Pictures
•will be sent by broadcasting stations, using their
regular assigned wavelength, and no tuning changes
in your present receiver are necessary. Readers are
urged to write us their experiences with the con-
struction of the recorder. The development of the
Cooley "Rayfoto" system opens for the first time
to the American experimenter an important "next
step" in radio development.
— THE EDITOR.
THE articles on the Cooley "Rayfoto"
system in theOctober and November issues
of RADIO BROADCAST explained how the
system works, told something of the results to
be expected, and gave some details regarding
the operation of a picture receiver. This third
article in the series gives some general and
particular information about the system, and
diagrams necessary for the construction of a
Cooley receiver are also presented.
Many of the units for use in the radio picture
receiver have been especially designed for the
purpose and therefore possess the necessary
characteristics for good results. They have been
designed to take care of the present requirements
of the receiver and are so flexible that they will
still be suitable for use as the system may be
gradually developed. Considerable care has
been taken in this matter so that it will not be
necessary to scrap any of the parts as the natural
development of increased speed of reproduction
and better quality are consummated. The
approved parts, which have all been carefully
tested, are made under the Cooley " Rayfoto"
trade mark.
Arrangements are now under way to supply
various broadcasting stations with phonograph
records which will enable them to put Cooley
pictures on the air. The radio editor of your local
newspaper is the best source of information.
The complete set-up for picture reception by
means of the Cooley system consists of three
distinct units — the radio receiver proper, the
amplifier-oscillator unit, and the printer as-
sembly. The first — the radio receiver — should be
capable of quality reproduction of radio pro-
grams for if it falls down in this respect it will
assuredly do so when called upon to detect and
amplify the incoming modulated wave which
has super-imposed upon it the audible note
representing the picture being transmitted.
Passing from the last audio stage of the re-
ceiver proper, the "picture signal" is further
amplified in the amplifier-oscillator unit and
it then modulates the output of the oscillator in
accordance with the modulation produced by
the picture. The varying output of the oscillator
is made to cause corresponding variations in the
output of the corona coil, and thus the intensity
of the needle point discharge is made to produce
an effect on the proper tallying with the original
By AUSTIN Q. COOLEY
picture. The corona coil is included in the second
unit although the actual needle at which the
discharge occurs is naturally a part of the third —
the printer-unit. This third unit consists of the
needle, the drum upon which the photographic
printing paper is wrapped, and the mechanism
which causes the drum to revolve. It is purchas-
able as a whole, for there are few who possess
the mechanical ability and facilities for the
construction of such an intricate piece of mechan-
ism.
The construction of the amplifier-oscillator
unit from the approved parts is a simple matter.
Fig. I shows a suggested layout while Fig. 2
is the schematic diagram. The following parts are
necessary for this unit:
TI — " Rayfoto" Amplifying Transformer
Ri — Variable Shunt Resistance for Primary of TI
R2 — 2OO-Ohm Variable Resistance Capable of
Carrying too Mils.
Ra — i2-Ohm Filament Rheostat, i-Ampere
Capacity
Rr— "Rayfoto" Relay
Tj — "Rayfoto" Modulation Transformer
Ca — o. i-Mfd. Condenser
Ri — o.oi-Meg. Grid Leak and Mounting
Ci, Q — o.ooo5-Mfd. Fixed Condensers
C4 — o.ooo5-Mfd. Variable Condensers.
LI — "Rayfoto" Corona Coil
L2 — Radio-Frequency Choke Coil
Si — Filament Switch
$2 — Push Button or Special Switch
Ji, J2, Js — Double Contact Short-Circuiting
Jacks
R6 — Filament Ballast Resistance
One Telephone Plug
Milliameter, o-aj-mil. Scale
Two Sockets
Fourteen Binding Posts
Base- Board
Panel
Brackets
"Rayfoto" Printer Unit
Although wide deviations from the layout
shown in Fig. i are permissible, it is also quite
possible that considerable "grief" will be experi-
enced in many cases where original schemes are
attempted. We therefore suggest that the home
constructor follow our plan of layout and con-
struction very religiously, at least on his first set.
The photographs indicate very clearly the
arrangement of the apparatus and the experi-
enced home constructor should have little
difficulty in putting the apparatus together.
All but the radio-frequency circuits may be
wired up in any convenient manner. We find
PICTURES RECEIVED BY THE COOLEY SYSTEM
These two photographs have not been retouched and were received at the demonstration at the
New York Radio Show. Governor Smith, in his radio address opening the Show let radio listeners
hear how his picture, above, sounded. The heading above shows Mr. Copley and a part of his appara-
tus as set up in operation at the Show. Governor Smith's picture is on the receiving drum
MAKE YOUR OWN RADIO PICTURE RECEIVER
115
that ordinary No. 18 rubber covered fixture wire
is very easy to handle and makes a reasonably
neat job. Each circuit should be properly tested
out, as will be explained later, before the wires
are laced up in bundles. The radio-frequency
circuit should be wired up with considerable
care, the use of bus bar wiring or rigid wires
having a fair amount of spacing between them,
being recommended. No particular care need be
taken to prevent losses in the radio-frequency
oscillator circuit. The secondary of the corona
coil, and its lead to the corona needle, however,
require very special attention. This subject will
be covered in another paragraph.
When the "Rayfoto" printer has been com-
pleted and set up with all connections to batter-
ies, proceed as follows for testing and adjusting:
Place two 2O1-A type tubes in the sockets and
see that the filaments are properly lighted and a
good range of brilliancy is controlled by the
rheostat, Rs, of the amplifier tube. With the
input terminals open, plug a pair of phones in
meter jack, J2, for the amplifier. Turn the fila-
ments on and off a couple of times to see if the
I MECHANICAL '
UNIT -*1
5O
- c
34 67 08 O9 O10
A + B- B+ 8+ B+
A.F use. Relay
Booster
FIGURE I
The circuit diagram of the amplifier and oscillator is given in this figure
RADIO BROADCAST Photograph
THE PRINTER UNIT COMPLETE
With its spring motor. If the user desires to use
the motor in a phonograph which he already has,
the illustration on the next page shows a special
unit made for that purpose
proper click is obtained in the phones. If it
sounds satisfactory, plug in the milliammeter.
If you find the milliammeter reading down scale,
reverse the connections to it. Adjust the C
battery until the plate current is a little less
than one milliampere. The plate voltage on the
amplifier should be about 180 volts and the C
bias to bring the plate current down to I mA.,
will have to be around 22j volts.
Now connect a piece of wire between the plate
terminal of the a. f. amplifier tube socket and the
B plus terminal of the modulation transformer T2,
and connect the input of the amplifier to the out-
put of the radio receiver. Tune-in any broadcast
signal and watch the milliammeter to see if it
varies in accordance with the incoming signal.
The phones may be plugged into jack J2 and the
gain control resistance, Ri, varied to determine
if the proper control is obtained.
Now connect the lead from the corona coil to
Input from
radio receiver A Bat.
r^~2 3^~4
AMPLIFIER AND OSCILLATOR
To trip magnet
mechanism on recorder
10 l'T~i2~~tt~14
RECORDER
Rubber bands holding
paper around drum
Box containing
spring motor
FIGURE 2
The suggested layout of apparatus shown in this drawing may be followed when you construct your amplifier-oscillator unit. The various identifying
letters 6n the parts refer to similar letters on the circuit diagram given in Fig. i. The lead from the corona coil, Li to the needle holder on the recorder
should not be over three feet in length and should be supported where necessary by silk thread. The parts for the oscillator-amplifier unit can be pur-
chased and then assembled at home, and no special precautions are necessary in constructing the unit. The wiring may be done in straightforward fashion.
The corona lead is a No. 38 wire and should be carefully handled, otherwise it will break. If the lead is broken by accident, unwind about three turns from
the coil to make a new lead. The record unit cannot be home constructed and must therefore be purchased as a complete unit. The recorder depicted in
this sketch is a complete unit containing a spring motor. Ri and Rs, not a part of the early model illustrated, may be located at any convenient point ia
the layout. A fixed condenser was used for €4 in the first model. It is preferable that it be variable as indicated above.
116
RADIO BROADCAST
DECEMBER,
the corona needle. Give this lead no more sup-
port than absolutely necessary. If this important
lead needs support, it should only be by suspend-
ing it from small threads. The lead should be
made as short as possible and in no case should
be over three feet long. Place a small piece of
Azo No. 4 photograph paper on the drum and let
the needle rest on it. The paper may be held
around the drum by means of two rubber bands.
Disconnect the input of the amplifier from the
radio receiver and connect the booster terminal
to about 90 volts of battery. Cautiously plug the
meter in the oscillator circuit jack, ]s. If the
meter registers over fifteen milliamperes, the
circuit is not oscillating properly. Adjust the
variable condenser until the current is brought
down to less than ten milliamperes.
Now watch the point of the corona needle to
see if a very small corona discharge takes place.
If not, re-tune condenser C4. If this does not
bring results, try the various taps on the oscil-
lator coil. If you are still unable to obtain any
visible corona, increase the booster voltage to
about 150 and try the different taps again. It
may be found that all the condenser capacity is
required to obtain a discharge. The length of the
lead wire should then be shortened or a small
fixed condenser, of about o.ooo5-mfd., may be
placed across the variable condenser. Only a good
mica condenser should be used. If the discharge
is strong enough to burn a hole in the paper,
the booster voltage should be reduced. The taps
should be tried to determine the best position
of maximum discharge.
With the printing circuit operating properly,
connect the input to the radio receiver and tune-
in any broadcast signal. Take off the short
circuiting wire on the trip magnet switch termi-
nals and allow the drum to revolve with the
needle riding on the paper. If the trip magnet
does not trip from the radio signals, release the
drum by operating the switch, 82 across the
relay circuit. Watch the needle point to see if
the corona varies with the incoming signal.
GENERAL HINTS
A FTER the "Rayfoto" printer and recorder
•** are set up for operation, trouble may be
experienced in many cases due to feed-back
from the corona circuit about which considerable
information was given in the November issue.
This trouble will depend greatly upon the
characteristics of the radio receiver. To help
avoid it, the experimenter should provide a
separate set of small 22j-volt B batteries for
the printer. As an additional precaution, the
printer and recorder should be placed at a con-
siderable distance from the radio receiver, say
eight or ten feet, if convenient. After the appa-
ratus is set up and working properly, attempts
may be made to reduce this distance. Also
experiments can be made with the battery
circuits to determine the feasibility of operating
the radio receiver and printer with the same B
batteries. The experimenter will be aided greatly
by the use of low-resistance B batteries. The
filaments of the tubes in the "Rayfoto" printer
may be operated from the same storage battery
used for the radio receiver. All the above pre-
cautions should be taken to prevent feed-back
before attempting to tune up the "Rayfoto"
printer. If feedback still occurs after tuning up
the printer, additional steps may be taken to
suppress it.
If there is any feed-back from the printer
circuit, the discharge will be strong and con-
tinuous. A high reading on the meter when no
signals are coming in indicates feed-back.
The last resort to prevent feed-back is to shield
the printer circuit. The shielding should not be
attempted before the unit is set up and ready
RADIO BROADCAST Photographs
THREE VIEWS OF THE AMPLIFIER-OSCILLATOR UNIT
The upper view taken from the side, shows the home-made relay mounted on the front panel and the
corona coil is in the foreground of the picture. The center view shows the front panel layout and a
top view is given below
MAKE YOUR OWN RADIO PICTURE RECEIVER
117
RADIO BROADCAST Photograph
USING A PHONOGRAPH AND ITS MOTOR
The printer unit depicted above is designed for use with any standard phonograph and utilizes the
spring motor in the phonograph for the operation of the drum
for operating because in many cases the shielding
will do more harm than good if it cannot be first
tested out in an experimental way.
Due to the different characteristics of radio
receivers, we cannot give information here that
will cover every case. In general, the proper re-
sults may be obtained by running very small
gauge grounded wires parallel to the corona feed
wire and separated from it by a number of inches.
This may necessitate re-tuning the oscillator
circuit. Experiments with shield wires and
shield plates will eliminate feed-back in most
cases.
In many cases it will help matters to adjust
the neutralizing on the radio receiver or slightly
de-tune one stage of radio-frequency amplifi-
cation.
With the printer circuit working properly, we
may now adjust the relay and trip magnet. Ad-
just the relay contacts so that they close before
the armature strikes the magnet pole. With the
contacts closed, you should be able to slide a
piece of thin paper (the thickness of this page)
between the pole and armature. The gap be-
tween the contacts when open should be equal
to two thickness of the paper used on the cover of
this magazine. If sparking is bad, it may be neces-
sary to increase this slightly. A condenser across
the contacts will do more harm than good as it
will cause the contacts to stick unless the spring
tension is excessive.
\\ith the trip magnet contacts open, adjust
the C battery so that the plate current of the
amplifier is about five mils. Adjust the spring
tension of the relay so as to barely hold the
contacts open with the five mils, in the circuit.
After this adjustment is made, return the C
battery adjustment to its original point.
The voltage for the trip magnet should be
as small as practical, consistent with strong
operation of the magnet. The power for this
magnet may be taken from the batteries operat-
ing the radio receiver if small batteries are used
for the printer circuits.
W:ith all the foregoing adjustments and tests
made, the experimenter is ready to test his set
out on picture signals. It is well to have the
developer and fixer solutions made up in advance
although it will not hurt to let the undeveloped
picture stand for a considerable time if the paper
is protected from light. Instructions will be
found on the developer tubes and fixing powder
cartons for making up the solutions so we will
not cover that information here. Regular trays
for the solutions should be used for the sake of
convenience although any enamel or glass tray
or dish will serve the purpose. In mixing up the
solutions, it will do no harm if they are made a
little more concentrated than the manufacturers
specify, using about 6oz. instead of Soz.of water.
With the trip magnet properly adjusted, the
speed of the drum should be adjusted and
checked by counting the number of revolutions
of the drum. If a converter drum speed of 100
r.p.m. is used, the recorder drum speed should
be about 105 r.p.m. The clutch should be free
enough on the first tests so that the turntable
will revolve with the drum in its locked position.
By loosening up on a set screw on the collar
directly below the spring, the clutch friction may
be regulated.
To receive a Rayfoto picture, tune-in signals
from the station transmitting the signals so that
they are received with maximum intensity. If
the meter in the amplifier circuit runs up over
fifteen mils, on the strong signals, reduce the
intensity by the volume control on the radio
set or the gain control on the printer amplifier.
In most cases it will be good practice to reduce
the radio-frequency input to the detector circuit.
The minimum signal should be between one
and four milliamperes. Adjustment of the mini-
mum signal is more important than that of the
maximum for if the minimum is too high, it will
operate the relay when it should not, and if too
low, it will cause irregular relay operation.
While the synchronizing pulse is being trans-
mitted from the station sending pictures, the
drum should revolve and trip regularly with
only a brief period of rest or lap. By regulating
the speed of the driving motor the lap can be
regulated. If the lap should be very long, you
will find that the speed is too slow and that the
drum is tripping only on every second synchron-
izing impulse. Increase the speed.
After the drum is adjusted to trip regularly,
a "range" should be taken: that is, the signal
should be increased to the point where the relay
trips from the minimum rather than the syn-
chronizing signal, and then the signal should be
decreased to the point where the relay does not
trip at all. The operating adjustment should be
about half way between the two points. The
operating range of the relay should be as large
as possible. If it is very small, it may be in-
creased by increasing the amplifier tube's C-
battery potential so that the plate current is
practically zero when no signals are being re-
ceived.
When the synchronizing adjustments are
made and the paper placed on the drum, you
are ready to start as soon as the picture signals
begin. The paper should be drawn up to fit the
drum tightly. If the center of the paper at the
lap bulges out very far, a rubber band may be
placed around the center of the drum and slid
along when the needle approaches it. Care should
be taken not to get the hand close enough to_the
corona feed wire to detune the circuit.
After the picture is received the paper is placed
in the developing solution until developed to the
proper density. It is then dipped in the washing
bath and placed in the fixing solution. After
remaining in the fixing solution for ten or fifteen
seconds, it may be removed temporarily for
observation purposes but should be replaced in
this solution for ten or fifteen minutes and
washed in running water for five or ten minutes,
if it is desired to preserve the picture indefinitely.
In some cases the experimenter will experience
excessive blurring, lack of detail, streaks in the
pictures, improper contrast, etc. In the next issue
of RADIO BROADCAST we will give more complete
information that will enable the experimenter to
clear out any such troubles should they arise.
The Freedom of the Air
EXCERPT from a news item in the New
York Times of May 3, 1927, under the
caption, "Pacifist Talk Hushed by Radio
Station WGL:"
"We are proud that Mrs. Corson is a woman,"
Mrs. Ford said, "proud that she comes from
Denmark, that country which upholds an ideal
of peace, that country which said to the enemy,
"If you must cut through our country, even if
you must cut through our women and child-
ren"—
At this juncture Mr. Isaacson cut out the mi-
crophone through which she was speaking and
substituted one in the studio through which
music was broadcast as a stopgap.
Mr. Isaacson later explained to the radio aud-
ience what had happened. In discussing the in-
cident later he said:
"We believe in free speech and I have always
been willing to extend the use of our station to
anyone to express his views, but there are certain
things which are dictated by good taste. This
was not the time nor the occasion for such a
speech."
Excerpt from a news item in the New York
Sun of July 18, 1927, under the caption, "Worm
Controversy To Be Aired from WGL:"
Fred B. Shaw, one time international fly fish-
ing champion, will have an opportunity to dis-
cuss President Coolidge and his angleworm
fishing to his heart's content to-night when
WGL will allow him to broadcast, uncensored, his
speech which was barred last week by another
station.
"Our broadcast policy has always upheld free
speech on the air," declared Dr. Charles D.
Isaacson, program director of WGL, in extending
the invitation to Mr. Shaw yesterday, "and for
that reason we are only too happy to extend the
privileges of our broadcast station to you."
A vexing question is thus cleared up for all
time. What is free speech a la Isaacson? It is
freedom to discuss angleworm fishing. But not
to discuss war.
Beauty the Keynote of
AN INSTALLATION that is completely self-
•rv contained — the Bosch Model 57. Although there
is a very efficient loop built in, provision has been made
for the use of an outside antenna where desirable. The
receiver employs seven tubes, and is tuned by a single
main dial. A cone loud speaker is harbored within the
cabinet. Price, $340. For power operation, $100. extra
'T'HE set builder can now obtain a cabinet for his receiver which is
•*• every bit as beautiful as those which house the most exjMMisive of
factory-built receivers. The Model 80 cabinet of the Musical Products
Distributing Company, New York, here illustrated, is in combination
walnut and su tin wood. The set compartment measures approximately 28
inches long, 10 inches high, and 15 inches deep. Price, $250.
118
the New Radio Receivers
Making the Most of
Surroundings
It is easy enough to discuss the
offerings of the current radio season
abstractly but one should visualize
this year's radio sets in the proper
domestic surroundings to appreci-
ate what great strides have been
made toward making radio a truly
domestic bit of furniture. The illus-
trations on these two pages show
radio equipment in home settings
and who will deny their grace?
I
AN INTERESTING design in loud speakers, the new Amplion
-r»- "Fireside." This loud speaker has a large cone mounted on a big
sound-board, exceptional fidelity of reproduction being possible. The
screen stand and long cord render the "Fireside" readily portable,
making it easy to plure the loud speaker uny where in the room or out-
side on the porch. The panelling is of embossed walnut, attractively
curved, combining a grille front and bark. The height is 36J inches, and
the cone is 16} inches. Price, $97.50, with 20-foot cord
ATYPICAL example of the trend of the more expensive radio receiver,
in which utility and beauty are in combination. We are taken back
by this Wiiithrop secretary to America's younger days, when money was
scarce and furniture was made to serve dual purposes. Nowadays a return
to this state of affairs is demanded since home space is so scarce. The radio
receiver built into the Winthrop is the popular Splitdorf single-control
six-tube set. The price, complete with power operation and loud speaker, is
$600.
119
By HOWARD E. RHODES
f If ^O WRITE of B power units in general
I terms, with the object of assisting in their
•^ wise selection, is not difficult because there
are simple rules that can serve to guide the pros-
pective purchaser. In the first place it should be
realized that the satisfaction which any power
unit gives in service frequently bears a close re-
lation to its cost, for power units can be built
to meet almost any price. Cheap units, con-
structed of inferior materials, are often capable
of giving as good results as more expensive de-
vices, during a single demonstration, but whether
the cheaper device will stand up for as long a time
in service is certainly open to question.
The first rule in the purchase of a B power
unit should be insistance upon a well-known
make, purchased through a reputable dealer,
for only from such a source can you be assured
of obtaining satisfactory service. One of the sim-
plest and most satisfactory methods of apprais-
ing a B power unit to make certain that it will
satisfactorily operate your receiver, is to give it a
trial lasting several days in your own home, un-
der actual working conditions. Only a reputable
dealer selling a good product can afford to do this
for you. A cut price dealer, with little or no in-
terest in his customer once the sale has been
made, cannot afford to sell a unit to you on the
basis of a trial lasting several days. The unit
purchased from a reputable dealer might cost
somewhat more, but the higher price is justified
because of the better service and greater assur-
ance of satisfaction which you can obtain.
There are many things about a B power unit
which must be taken more or less on faith.
You can't tell, by looking at the device, what
kind of chokes are used or if the condensers in
the filter circuit have a sufficiently high voltage
rating so as to prevent any possibility of break-
down. Then again, the design of the transformer
supplying the rectifier and filter circuit is some-
thing that cannot be examined when you buy
the unit. It is only by relying upon the reputa-
tion of the dealer and of the manufacturer whose
product he sells, that you can have any assur-
ance of a properly designed unit. If care is taken
in the selection and use of a B power device, it
will give satisfactory operation and lasting
service for years.
In the list appended, we have given the im-
portant characteristics of about twenty-five
well-known B power units. Since there are being
made at the present time about one hundred and
thirty of these units, it will be seen that the list
is by no means exhaustive.
The proper selection of a B power unit is a
matter of knowing the total plate-current drain
of the receiver and of then finding a device that
will supply the correct voltages to your receiver
at this current drain. You must make certain
that the maximum voltage available from the
device when supplying a milliampere load equal
to that of your receiver is sufficient to supply the
power tube you are using. The maximum output
voltage of the device should be 180 volts, or
slightly more if a 171 type tube, with 40.5 volts
grid bias, is used in the output ; if a 112 type tube
is used, with 9 volts grid bias, the maximum volt-
age should be about 135 volts. The information
given in the appended list includes the maximum
output voltage which the units will supply at
various current drains.
Of course, it is also essential that the power
unit be capable of supplying the other tubes in
the receiver with the voltages they require.
These voltages are obtained from voltage taps
on the power unit and in most cases the voltage
that is obtained from any one of these taps varies
with the current being drawn from it and the
other voltage taps, and for this reason it is not
possible to give any definite figures for the volt-
age output from these taps. Many power units
use adjustable or semi-adjustable resistances so
that the desired voltages can be obtained by
proper adjustment of the resistance. These re-
sistances should not be adjusted by guess but
should be adjusted with the aid of a high-resist-
ance voltmeter. This is a service any reliable
dealer can give you.
There are some power units (those using glow
tubes) which give practically constant output
voltages independent of the load. If such a unit
is purchased it may be connected to any receiver
with assurance that the actual voltages being
supplied to the receiver will be near enough to
those marked on the terminals of the power unit
for satisfactory operation.
As will be seen in the accompanying list, some
of the devices have been approved by the Na-
DECEMBER, 1927
tional Board of Fire Underwriters and many of
the other devices have been submitted for test
but have as yet not been approved. The sub-
mission of B power units to the National Board
of Fire Underwriters for their approval is a dis-
tinct step in the right direction. It gives the pros-
pective purchaser the assurance that the unit
conforms to definite standards designed to make
certain that the operation of the device will be
entirely safe.
The power input to a power unit is a measure
of the cost of operating the unit. The input power
to the average B power unit is about 25 watts,
which is the amount of power required by a
small electric light bulb. If we obtain power from
the electric light company at the rate of ten cents
per kilowatt hour, it will cost just about one
quarter of a cent per hour to operate the average
plate-supply device. To this cost of operating,
we should, of course, add depreciation on the
unit and the cost of tube renewals which must
be made on an average of once a year.
All B power units for use with an alternating-
current supply must use rectifiers of some sort.
A majority of units use a tube for this purpose,
but there are also quite a large group that use
electrolytic rectifiers; thousands of B power
units using either type of rectifiers have given
satisfactory service. When purchasing a power
unit avoid those using unknown makes of rec-
tifiers. Whether you purchase a power unit
WHAT B DEVICE SHALL I BUY?
121
current and delivers a steady fluctuating direct
current to the output terminals of the device.
Some power units use half-wave rectifiers and
others use a full-wave rectifier. In the first
case, only half of the alternating voltage is
used and when full-wave rectification is used
both halves of the alternating voltage wave
are utilized. The filter system may contain
either one or two sections. Whether a half- or
full-wave rectifier is used or whether a one- or
two-section filter is used is something that need
not particularly concern the prospective pur-
chaser. The design of the filter in either case
should be such as to eliminate any hum, and so
long as the device which you buy does not hum
excessively, you may be sure that the filter cir-
cuit has been correctly designed for the type of
rectifier used. The coils and condensers used in
the filter circuit do not become weak with age,
and a filter system capable of giving an output
voltage free from hum will continue to do so
unless some unit in the system completely fails.
"high-low" switch in "high" position); 140 at
20 mA., 120 at 30 mA., and 70 at 50 mA. (with
"high-low" switch in "low" position). Other
models supply about 10 volts less. Approval
pending by National Board of Fire Underwriters.
Raytheon rectifier is used. Two-section filter.
Adjustable output voltages. Model A-i for oper-
ation on 1 10 volts 50-60 cycles a.c.; Model A-},
25-40 cycles; Model A-4, 220 volts 50-60 cycles
a.c.; Model A-8, 1 10 volts 50-60 cycles a.c. Size:
Models A-i, A-3, A-4, 9x7x5} inches; Model
A-8, 3x7x10 inches. Prices, including rectifier;
Model A-i, $37.50; Model A-3, $42.50; Model
A-4, $42.50; Model A-8, §27.50.
BURNS, MODELS 75O-A, 750-6, AND 8oo-B
Maximum output voltage of Models 75O-A
and 750-6; 190 volts at 30 mA., and 180 volts
at ;o mA. Model 8oo-B, 205 volts at 20 mA.,
and it)o volts at 30 mA. Uses Raytheon rectifier.
Amplifier and detector voltages adjustable.
Two-section filter. Approximately 20 watts a.c.
input with 30 mA. load. Designed to operate
171 type power tubes. Size: Models 75O-A and
750-6; 7J x 10^ x 6f inches; Model 8oo-B,
4! x io| x jf. Prices: Models 75O-A and 750-8,
$47.50 with tube; Model 8oo-B, $35 with tube.
AMRAD, MODEL No. 280
Maximum output voltage; 200 at 20 mA., 180
at 30 mA., and 165 at 50 mA. Uses type 280
B POWER UNITS FOR YOUR RECEIVER
.The power unit at the left is the Erla Steadivolt BC Converter and it utilizes a Raytheon BH rectifier tube and a glow tube to maintain the output
constant at all loads. It v/ill supply up to 80 milliamperes at 180 volts. It lists at $40 including tubes. The Exide unit in the center and the Burns power
device at the right both contain adjustable resistance units to regulate the voltage at the various terminals and further information regarding these
two devices will be found in the listings on these pages
using an electrolytic or tube rectifier is a matter
of personal preference.
WHEN YOU USE A B-POWER UNIT
ALOUD hum audible in the output of a re-
ceiver operated in conjunction with a B
power unit may be due to coupling between the
receiver and the power unit itself. If the hum is
due to such a cause it can generally be eliminated
by placing the power unit in some other position
relative to the receiver. Also if hum is to be pre-
vented it is essential that the negative B be
grounded directly, and in some cases it is neces-
sary to connect a i-mfd. 2Oo-volt condenser be-
tween the grounded negative B terminal and one
side of the input power lead. If these simple
remedies do not eliminate the hum it is likely
that there is some defect in the unit itself and
the dealer should be consulted for, if the power
unit is operating properly it should produce
practically no audible hum in the output. Every
plate-supply unit must contain a transformer
designed to step up the input voltage to an
amount depending upon what output voltage is
required and upon what type of rectifying ele-
ment is used. The rectifier, whether it be a tube
or an electrolytic device, modifies the alternating
current obtained from the power supply and
changes it to a pulsating direct current. The filter
circuit smooths out the pulsation in the rectified
Facts About Some B Units
ACME APPARATUS Co., MODELS E-i, E-2, £-3,
AND £-4
Maximum output voltage of a.c. models: 205
at 20 mA., 185 at 30 mA., and 160 at 50 mA.
Uses Raytheon BH rectifier. Two adjustable
voltages. Two-section filter. Approved by Na-
tional Board of Fire Underwriters. Size: 8J x 3}
x 7f inches. Models E-i, £-3, and £-4 for opera-
tion on 1 10 volts 60 cycles a.c. Model E-2 for
operation on 120 or 220 volts d.c. Model E-i,
with cable, for one- to twelve-tube sets, 850;
Model E-2, with cable, for one- to twelve-tube
sets, §25; Model £-3, with cable, for one- to
eight-tubes sets, $85; Model £-4, with binding
posts, for one- to eight-tube sets, $35.
ACME ELEC. AND MFG. Co., MODEL BE-4O
Maximum output voltage; 200 at 20 mA., 185
at 30 mA., and 145 at 50 mA. Uses QRS rectifier.
Two adjustable voltages. Full-wave rectifier.
Two-section filter. Approved by National Board
of Fire Underwriters. For operation on 1 10 volts
50-60 cycles a.c. Recommended for five- to eight-
tube sets with power tubes. Size: 7! x 1 1 J x 3|J
inches. Price, with tube, $34.50.
ALL-AMERICAN, MODELS A-i, A-3, A-4, AND A-8
Maximum output voltage of Model A-8; 200
at 2omA., 180 at 30 mA., 140 at 5omA. (with
or 213 thermionic rectifier. One-section filter.
Fixed output voltages. Full-wave rectifier.
Twenty watts a.c. inpu, at 30 mA. load. For
operation on 100-120 volts 60 cycles a.c. Size:
ioi x 6J x 7j inches. Price, without tube, $45.
ARCO B POWER
Maximum output voltage: 180 volts at 50 mA.
Uses filamentless rectifier. Two-section filter.
Full-wave rectification. Fifteen watts input with
30 mA. load. Size: gf x 3$ x 8| inches. For opera-
ation on 1 10 volts 60 cycles a.c. Price, without
tube, $32.50.
BREMER-TULLY B POWER
Maximum output voltage: 216 at 20 mA.,
195 at 30 mA., and 1 50 at 50 mA. Uses Raytheon
BH rectifier. Output voltages adjustable by
fixed steps. Two-section filter. Full-wave recti-
fier. Seven watts input with 30 mA. load. Ap-
proved by National Board of Fire Underwriters.
Will supply receivers having up to ten tubes.
For operation on 110-115 volts 60 cycles a.c.
Size: 4j x gf x 6j inches. Price: $37.50, without
tube.
BASCO B POWER
Maximum output voltage: 250 at 20 mA.,
230 at 30 mA., 190 at 50 mA., and 175 at 60 mA.
Uses Raytheon BH rectifier. Two-section filter.
Full-wave rectification. Fixed detector voltage.
Other voltages variable. A special primary
rheostat functions to regulate output to supply
different types of power tubes. Twenty watts
122
RADIO BROADCAST
DECEMBER, 1927
input with 30 mA. load. Size: 12 x 45 x 7\ inches.
Price, with tube, $35.
KING, TYPES M AND V
Maximum output voltage: 238 at 20 mA., 215
at 30 mA., and 180 at 50 mA. Uses type 213
rectifier. One-section filter. Full-wave rectifica-
tion. Type M has variable detector and amplifier
voltages. Type V has variable detector voltage
and fixed 90, 135, and power tube taps. Twenty
watts input with 30 mA. load. Can supply up to
nine tubes. Size: Type V, 9! x 4^ x 7 inches;
Type M, 1 1 x 6 x 6 inches. Prices: Type M,
§45.00; Type V, $37.50.
EXIDE, MODEL 9-6
Maximum output voltage: 208 at 20 mA.,
MAJESTIC, SUPER-B POWER UNIT
Maximum output voltage: 186 at 20 mA.,
156 at 30 mA., and 112 at 50 mA. Adjustable
output voltages. Special "high-low" switch
gives two voltage ranges. Full-wave rectification.
Two-section filter. For operation on 1 10 volts
60 cycles a.c. Size: io| x 5! x 9 inches. Price,
complete with tube, $29. 50.
FRESHMAN, MODEL A
Maximum output voltage: 220 volts at 40 mA.
Uses tube rectifier in full-wave circuit. Adjusta-
ble output voltages. Two-section filter. Unit
supplies following C voltages: -45 -9, -40.
Thirty watts input with 30 mA. load. Designed
to supply sets using up to seven tubes. Price
complete: $45.
MUTER B POWER UNITS
Two types made, one for Raytheon BH tube,
the other for 2 1 3 or 280 type rectifier. Maximum
output voltage (Raytheon type); 200 at 20 mA.,
1. 80 at 30 mA., and 150 at 50 mA. Other type
gives output voltages about 10 volts lower.
Full-wave rectification. Two-section filter. Fixed
output voltages. Twenty-one watts input with
30 mA. load. For operation on 110-120 volts
60 cycles a.c. Prices: Raytheon model, $26.50;
other model, $24. 50.
30 mA. load. Adjustable detector voltage.
Rheostat in the primary to compensate differ-
ences in line voltage. Uses Raytheon type B or
BH rectifier. Size: iij x 45 x 8j inches. Price:
$34-50.
DIS-TON, TYPES D-6o AND D-25
Maximum output voltage: 215 at 20 mA.,
200 at 30 mA., and 185 at 50 mA. Adjustable
output voltages. Two-section filter. Full-wave
rectification. Fifteen watts input with 30 mA.
load. Unit uses two thermionic rectifiers. Sup-
plies C bias up to 22 volts. Self-contained milli-
ammeter indicates performance. Price $29.50,
without tubes. Type D-6o
Maximum output voltage: 120 at 20 mA., and
95 at 30 mA. Adjustable output voltage. One-
section filter. Half-wave rectification. Nine watts
input with 30 mA. load. Uses one thermionic
rectifier. Size: 10 x 4 x 6 inches. Price: $23.50,
with tube. Type D-25
THREE MORE LINE SUPPLY DEVICES
The Acme B power unit incorporating two variable resistances to compensate differences in load imposed on the device by different receivers is shown
at the right. The All-American Constant B is illustrated at the center and contains a "high-low" switch to adapt the device to difierent loads and line
voltages. The C potential as well as B potential can be obtained from the Valley unit at the left
194 at 30 mA., and 180 at 40 mA. Uses electro-
lytic rectifier, arranged in bridge circuit for full-
wave rectification. Two intermediate and de-
tector voltages adjustable. Two-section filter.
For operation on 105-125 volts 50-60 cycles a.c.
Ten watts input with 30 mA. load. Approved by
National Board of Fire Underwriters. Designed
to supply sets with six or more tubes. A 1 12 or
171 type power tube may be used. Size, 6§ x
n| x 9! inches. Price: $42 50.
GENERAL RADIO, TYPE 445
Maximum output voltage: 200 at 20 mA.,
185 at 30 mA., and 160 at 50 mA. Uses type 280
rectifier tube. Two-section filter. Output voltages
adjusted by means of sliding taps on wire-wound
resistance. C voltage available for power tube.
Twenty-eight watts input with 30 mA. load.
Designed to meet specifications of National
Board of Fire Underwriters. Automatic switch
breaks the i lo-volt a.c. input circuit when cover
is removed. Size: 154X7x7 inches. Price: $55.00,
without tubes.
pREED-ElSEMANN, MODEL l6
Maximum output voltage: 135 at 30 mA.
Uses type 280 rectifier tube. Also uses type 874
glow tube to maintain output voltages con-
stant independent of the load. Two-section filter.
Three C voltages available;-4j, -9, and -27.
Twenty-five watts input with 30 mA. load. For
operation on 105-120 volts 60 cycles a.c. Size:
7x7x9! inches. Price: $35.00, without tubes.
PRESTO-O-LITE "SPEEDWAY" B
Maximum output voltage: 188 at 20 mA., 175
at 30 mA., and 148 at 50 mA. Fixed output vol-
tages. Compensation for variations in line volt-
age obtained by adjusting three-point switch.
One-section filter. Full-wave rectification.
Twenty-five watts input with 30 mA. load.
Uses Raytheon BH rectifier. Size: 6x8x8 inches.
Price: $37.00, including tube.
SENTINEL, MODEL B-C
Maximum output voltage: 180 at 80 mA.
Uses two rectifier tubes. Two variable voltages.
Unit supplies two C voltages, -4! (fixed) and
-45 to -45. Voltage control to compensate
variations in line voltage. Beverly model is
equipped with special instrument used to read
the voltages being supplied by the various taps
on the power unit. Prices, including two tubes,
regular model, $44.50; Beverly model, $65.00.
SILVER-MARSHALL, TYPE 656
Maximum output voltage: 170 at 20 mA., 160
at 30 mA., and 140 at 50 mA. Unit uses ux-213
(cx-313) rectifier and ux-284 (cx-384) glow
tube. Glow tube maintains output voltages
practically constant independent of load. Two-
section filter. Twenty-five watts input with 30
mA. load. Size: 6j x 7^ x 5 inches. Price: $38.50.
STEWART, U-8o
Maximum output voltage: 190 at 20 mA., 175
at 30 mA., and 140 at 50 mA. Two-section filter.
Full-wave rectification. Thirty watts input with
STERLING, TYPE R-97
Maximum output voltage: 300 at 20 mA.,
286 at 30 mA., and 262 at 50 mA. Adjustable
output voltages. Full-wave rectification. Twenty-
five watts input with 30 mA. load. Unit supplies
C voltages up to 50 volts. Price: $55.00
VALLEY, MODEL 60
Maximum output voltage: High range — 250
at 20 mA., 220 at 30 mA., and 175 at 50 mA.;
Low range — 200 at 20 mA., 180 at 30 mA., and
140 at 50 mA. Uses Raytheon BH rectifier. Two
adjustable voltages. Two-section filter. Full-
wave rectification. Eighteen watts input with
30 mA. load. Size: 5! x 9! x g\ inches. Price:
$50.00, including tube.
VALLEY, MODEL 40
Maximum output voltage: 170 at 20 mA.,
145 at 30 mA., and 1 10 at 50 mA. Uses Raytheon
BH rectifier. Two adjustable voltages. One-sec-
tion filter. Full-wave rectification. Seventeen
watts input with 30 mA. load. Size: 9 x 4j x -]\
inches. Price: $37.50, with tube.
COMPO, MODEL B-C
Maximum output voltage: 180 at 50 mA.
Two-section filter. Full-wave rectification. Uses
Raytheon BH rectifier. Uses Raytheon BR
regulator tube to keep voltages constant. Unit
supplies adjustable C voltages up to 50. Twenty-
eight watts input with 30 mA. load. Size: loj
x 5! x 8J inches. Price: $57.50, with tubes.
Measuring the "GAIN of
your RECEIVER
•• *^
St
/req
romberg-Carlson engineers testing the audio-frequency characteristics of one of their No. 744 receivers. The apparatus consists of a "beat
equency" oscillator which produces the audio tones, and meters for measuring the extent to which these frequencies are amplified within
the receiver
UR present broadcasting structure is
made up of three intimately connected
components, the broadcasting station,
the receiving equipment, and the intervening
medium. The broadcasting station has one
raison d'etre — to translate smjnd impulses into
electrical waves; the receiver's only purpose is to
accomplish the opposite — to translate these
electrical waves back into sound impulses. The
intervening medium is the connecting link be-
tween the transmitter and the receiver, an in-
efficient link it is true, performing its task with
many vagaries, and for reliability's sake it might
be very well displaced by a metallic conductor.
The radio medium, however, has the advantage
that for broadcasting purposes, the communica-
tion is radiated in all directions, and is not con-
fined to a direct path between two points.
We have already outlined in the November
RADIO BROADCAST what the transmitter does
when it lays down a "field strength" about the
receiver, how this field strength is measured, how
much is necessary for various degrees of service,
and how field strength and the attributes of sets,
selectivity, sensitivity, and fidelity, are related.
It was pointed out that the greater the field
strength, or the more sensitive the receiver, the
more powerful the corresponding loud speaker
signal. We are now faced with the problem of
ascertaining how sensitive a receiver must be
to deliver a certain signal from a certain field
strength, how selective a set must be to shut out
unwanted signals in favor of the desired program,
and what the degree of fidelity must be to furnish
sufficient realism to make a receiving equipment
no longer a " radio" but a musical instrument.
What we must do is to answer the following
questions, presupposing a station to deliver a
certain field strength at a certain point:
By KEITH HENNEY
Director of the Laboratory
How loud will be the resulting signal from a
certain receiver? How can it be measured? What
will happen if another station a given number of
kilocycles away goes on the air and lays down a
certain field strength about the receiver? If the
receiver is sufficiently sensitive and selective,
how do these factors influence the fidelity?
100 1M>
MICROVOLTS INPUT
FIG. I
When one measures the output voltage of a re-
ceiver of several years ago as the input voltage is
changed, he gets a curve similar to those shown
above. Note the steep i3OO-kc. curve indicating
extreme sensitivity, and the decreasing sensitivity
as the radio frequency is decreased
Since radio receivers were first made, qualita-
tive answers to these questions have been the
stock in trade of all engineers. It is only within
the last year that quantitative answers have been
generally available, especially when one consid-
ers the receiver as a single unit, and desires
answers to his questions not with regard to the
component parts that make up that receiver but
with respect to the ensemble equipment. Meth-
ods for determining the characteristics of coils,
condensers, transformers, and other individual
units that go to make up a "radio," have been
known and used for several years. In England
great emphasis has been laid upon and many
arguments built around such measurements as
contrasted with those which include everything
in a receiver between antenna and loud speaker.
While it is true that the characteristics of such
units can be combined to produce a fair approxi-
mation of what the complete receiver will do, an
overall measurement carries much more convic-
tion to the engineer.
An interesting experiment was carried out at
station WOR some time ago, and more recently
by WLW, to enable listeners to determine how
low and how high in audio frequencies their
receivers were responsive. At WLW, where a
Wurlitzer organ forms part of the studio equip-
ment, continuous tones varying from the lowest
to the highest organ note were put on the air,
First the pure note of the open diapason was
transmitted and then it was played with various
harmonics added. This enabled the listener to
determine not only the acoustic limits of his
receiver and loud speaker but the change in
quality as the harmonics modulated the original
pure note.
In laboratory the business of performing the
same experiment or that of investigating the
124
RADIO BROADCAST
DECEMBER, 1927
sensitivity and selectivity of the receiver under
better controlled conditions consists in moving
the transmitter nearer the receiver, and decreas-
ing its power accordingly. This eliminates the
vagaries of the intervening medium, and when
the transmitter is finally connected metallically
to the receiver a set-up results which is suffi-
ciently flexible that everything can be varied and
measured at the same time. A miniature broad-
casting station is necessary. This must consist
of an r.f. oscillator whose output can be regulated
and measured, an audio-frequency oscillator
variable from the lowest to the highest audio
tone ordinarily broadcast and relatively free
from harmonics, and some means of combining
these two generators of electric and sound waves.
The Hazeltine Laboratories, under the direc-
tion of Chief Engineer MacDonald, made such
tests on receivers which were under development
there, and the results were published in the
Proceedings of the I. R. E. in February, 1927, the
first paper to be published in this country on
such laboratory practice. The emphasis here,
however, was more on component parts, such as
radio-frequency amplifiers, coupling coils, and
audio amplifiers than on the receiver as a whole.
The data as published were most interesting.
In a discussion of this paper, appearing in the
April, 1927, Proceedings of the I. R. E., H. D.Oak-
ley and Norman Snyder of the General Electric
Laboratories described the methods used several
years ago at the Schenectady Laboratory for
measuring receivers.
The equipment was housed in two shielded
rooms, one of which contained the radio and
audio oscillators as well as a control device for
regulating the voltage which was put on the
receiver under test in the adjoining room. A
standard Radiola 100 loud speaker was placed
across the output of the receiver, and the voltage
across it measured as the input voltage was
varied.
To test the sensitivity of the set, that is, to
tell how many output volts could be delivered
with a given input radio voltage, the following
procedure was carried out. The generator was
set going at a certain radio frequency and this
was modulated at 1000 cycles to a given degree
of modulation. The input to the receiver was
varied in small steps until the output tube over-
loaded. This was considered the upper working
limit of the receiver. A specimen curve of out-
put voltage plotted against input voltage is
shown in Fig. i . The receiver was a standard set
of several years ago, and is not indicative of the
better types of modern sets.
The data show that the receiver at 1300 kc.
was roughly 6.5 times as sensitive as at 560 kc.
and that to produce an output voltage of 16 at
1300 kc. required an input of only 51 microvolts
compared to 335 required at 560 kc. At 1000 kc.
the voltage required was roughly 175. The out-
put voltage at 560 kc. divided by the input volt-
age gives a rough voltage gain of 46,000; at 1000
kc. the ratio is 102,000 and at 1300 kc. the gain
is 300,000.
The data showed that the output voltage for
each of the three frequencies was proportional
to the input voltage squared, for which the de-
tector tube is responsible.
TESTING SELECTIVITY
TO TEST the selectivity of the receiver, it
was tuned to, say, 560 kc., and the output
voltage read as the transmitting generator in
the first of the two shielded rooms was varied in
frequency but kept at constant amplitude. The
receiver was then set at some other frequency
and a similar set of data was taken. Specimen
curves shown in Fig. 2, are taken from the
Proceedings of the I. R. E.
706050403020100102030405060TO
KILOCYCLES OFF RESONANCE
FIG. 2
These queer curves show the selectivity of a
rather poor receiver. At 560 kc. the set is se-
lective, at 1300 kc., curve C, it is as broad as the
proverbial barn door. They are indicative of a
poorly engineered receiver and were made on
sets sold several years ago
The curves plotted from data obtained in this
manner are given in Fig. 2, and show the field
strength required to produce a given signal which
differed from the frequency setting of the re-
ceiver by a certain number of kilocycles. For ex-
ample, if the receiver were accurately tuned to
560 kilocycles, a signal 10 kilocycles off reson-
ance, say 570 kc., required a field strength of
150 microvolts per meter to produce an inter-
fering signal. At 1300 kc., a signal 66 kc. away, or
1366 kc., having a field strength of 150 micro-
volts per meter, would produce the same inter-
ference.
In other words the receiver was roughly one
seventh as selective at 1300 kc. as it was at 560
kc. which, coupled with the fact that it was
nearly seven times as sensitive at -the same
frequency, may demonstrate why the higher
broadcasting frequencies were not so highly
regarded by engineers of transmitting stations
a year or so ago. There is no reason why a care-
fully designed and engineered receiver cannot
be equally sensitive over the broadcasting band
of 1000 kc. If the band were to be extended, in
the direction of still higher frequencies, the
problem placed upon design engineers would be
considerable, but would not be insurmountable.
Receivers of the present day are better than
these curves show. Methods of maintaining equal
gain over rather wide frequency bands are well
known, and up-to-date receiver manufacturers
make every effort to include in their products the
results of all well-known inventions. A receivei
which squawks at 1300 kc. and is practically
silent at 560 kc. is a poorly designed set, and
should not be placed in the same class as others
in which care has been taken to avoid just such
criticism.
The method of measuring and rating receivers
employed by the Radio Corporation of America
was described in The Proceedings of the I. R. E.
in May, 1927, by T. A. Smith and George Rodwin
An arbitrary loud speaker signal is set up and
all measurements are made with a view toward
determining the field strength required to pro-
duce this signal, which is that corresponding tc
an average audio-frequency (r.m.s.) voltage ol
1 5 across a 5Ooo-ohm resistance when a 4OO-cycle
note modulates the transmitter to a degree ol
50 per cent.
Having determined how much output voltage
the receiver will deliver when a certain input
voltage due to a certain field strength is im-
pressed on it, mathematics will tell how much
voltage or power will be delivered at other inpul
levels, up to the overloading point of the ampli-
fier tubes. The following relations express the
manner in which transmitter antenna power,
input receiver voltage, output voltage and powei
are interconnected:
Field strength a transmitter antenna current.
Field strength a square root of transmitter power
Input receiver voltage a field strength.
Output receiver voltage oc field strength squared.
Output receiver voltage a. transmitter power.
Output receiver power a output voltage
squared.
Output receiver power a input voltage to the
fourth power.
FIG. 3
The receiver is put through its paces in this shielded room at the General Electric Company
Only signals that are meant for the receiver arrive at its input via shielded wires; all others are
excluded by the shielding surrounding the six room surfaces
DECEMBER, 1927
MEASURING THE "GAIN" OF YOUR RECEIVER
125
Output receiver power a field strength to the
fourth power.
Output receiver power a transmitter power
squared.
The Greek letter alpha in the above relations
means "is proportional to."
Doubling the transmitter antenna current
multiplies the transmitted power by four, dou-
bles the field strength, doubles the input receiver
voltage, multiplies the receiver output voltage
by four, and multiplies the power into the loud
speaker by sixteen. These relations may be con-
nected to what happens in one's receiver by the
following facts. The average stage of audio am-
plification has a voltage gain of twenty-five, a
two-stage affair having a voltage gain of roughly
| 300, or 50 TU, if a 171 type tube is used as the
1 output tube. A good radio-frequency amplifier
! should have a voltage gain of about 50 TU, or
i 300, so that the overall gain in voltage from a
\ modern well engineered receiver should be in the
[ neighborhood of 100,000, or 100 TU. These
i figures in power amplification become respec-
j lively, for the two-stage amplifier and for the
omplete receiver, 30,000 and 10,000,000 — truly
mormous amplification.
In actual practice the R. C. A. engineers do
not measure the voltage across the resistance in
he output of the receiver while the input voltage
s varied. An interesting short cut is used in-
tead, which is possible from the phenomenon
accompanying the function of detection.
When the receiver is tuned to a carrier wave,
modulated or not, the average d.c. detector
current changes, increasing when a C bias de-
ector is employed, decreasing when the con-
ventional grid leak and condenser method is
used. Greater changes occur with greater field
itrengths. or the more nearly the receiver is
:uned to the incoming signals. The change in
detector plate current, then, is a measure of the
effectiveness of the field strength or the sensitiv-
ty of the receiver.
To produce the arbitrary 15-volt signal across
:he 5ooo-ohm resistance in the receiver output
requires a certain change in detector plate cur-
rent. Once this is determined the audio amplifier
can be dispensed with and all measurements may
>e made by noting the change in detector plate
current. This method obviates the necessity of
using modulated signals.
In the R. C. A. Laboratory the input voltages
FIG. 4
Signal generating apparatus used at the General Electric Laboratories for testing the characteristics
of receivers. This apparatus is housed in a shielded room, and consists of a Heising modulated gen-
erator capable of oscillating at any frequency in the present broadcasting band modulated at any
audio frequency between 40 and 10,000 cycles
are fed to the receiver through a dummy antenna
consisting of an inductance of 28 microhenries
which has a resistance of 2 ohms, a capacity of
0.0004 mfd., and a resistance of 23 ohms. The
curves obtained in this way show the same
general characteristics as those given in the
General Electric report, i. e., low gain at low
radio frequencies, high gain and poor selectivity
at high frequencies. At the same time there is
considerable loss of the higher audio frequencies
at the longer wavelengths, due to the excessive
sharpness of tuning, or selectivity.
While it is true that only a few of the larger
and better-known receivers are engineered with
these thoughts and these laboratory measure-
ments in mind, it is a fact that more and more
radio manufacturers are becoming aware that
good engineering is a priceless asset. The article
in this issue of RADIO BROADCAST on the Fada
receivers, by John F. Rider, and others to follow
on other well-designed receivers, proves this
statement. The Laboratory is preparing data on
manufactured sets using the methods of measure-
ments mentioned above and as fast as the ma-
terial is ready, it will be presented to RADIO
BROADCAST'S readers.
All About Patents
INVENTIONS AND PATENTS, THEIR DEVELOPMENT
AND PROMOTION. By Milton Wright, LL.B.
Published by the McGraw-Hill Book Com-
pany, Incorporated, New York. Price, $2.00.
Pages, 225.
A VERY useful contribution to the bewild-
ered inventor, throbbing with the thrill
of a discovery, is the sage and practical
counsel of Mr. Milton Wright, as embodied in
tlis new book, "Inventions and Patents." There
is nothing assuming about the writer's style;
the work is not overburdened with technical legal
arguments, although the subject is a highly
technical one, and there is no obscure language
to confuse the uninitiated.
The subject matter of the volume is devoted
broadly to all the problems which face the in-
ventor. He is told what is patentable and what is
not patentable, what constitutes a practical in-
vention, what steps to take to facilitate securing a
patent and how to protect it after it is secured,
how to select a good patent attorney, how a pat-
ent should be applied for, how to obtain financial
support, what the problems of marketing and
merchandising are, how to sell patents outright,
on a territorial and on a royalty basis, and what
steps to take against infringers. There you have
it in one long sentence; certainly the scope of the
book is broad enough to be a real aid to the
floundering inventor.
Valuable cautions and dangerous pitfalls,
which are the usual stumbling blocks to the un-
initiated patent seeker and inventor, are dis-
closed. For example, how to keep records which
aid in establishing date of conception and re-
duction to practice, is explained so that the in-
ventor, heeding the advice given, will have no
difficulty in later sustaining his invention in the
courts. And again, the vital subject of how to se-
lect a patent lawyer and how to get the greatest
value from his services is presented simply and
clearly. The book abounds in practical illustra-
tions which serve to clarify the force of the wri-
ter's arguments.
The reviewer does not hesitate to recommend
a thorough reading of this volume to all those
who believe they have a patentable idea and
those who contemplate obtaining a patent. It is
certain either to cause them to abandon the idea
because it offers little or no possibility for profit,
or else to secure a better and more easily pro-
tected patent. Considering that only one patent
out of a hundred secured by hopeful inventors
proves profitable, the discouragement of the
impractical is as valuable a service as the en-
couragement of the promising. In this respect,
Mr. Wright's dispassionate and constructive
point of view differs materially from the flam-
boyant literature and booklets which un-
scrupulous patent lawyers distribute in the hop2
of inveigling misguided inventors to obtain
patents, whether their ideas show promise or not.
— E. H. F.
A LOUD SPEAKER ELEMENT
This is the driving unit used in the type 20-20 cone speaker
manufactured by A. H. Grebe. The speaker is priced at $35.00
A PACENT OFFERING
This well made instrument uses a balanced armature con-
struction that insures quality reproduction. Price, $35.00
THE "ALGONQUIN" CONE
SPEAKER
An artistically designed cone priced at
$15.00, the product of the Algonquin Elec-
tric Company
A POWER CONE WITH B SUPPLY
The perfectly free mounting used in this Mag-
navox combination is responsible for its excel-
lent reproducing qualities. It contains a 210
power-amplifier and B supply. Price, $242.00
THE "NEUTROWOND" REPRODUCER
An attractive loud speaker finished
in American walnut. Price $35.00
AN INNOVATION
This interesting loud speaker made
by Frank B. Porter, Washington
utilizes the structure above the base
to conceal a tonal chamber. The ac-
tual element is with base. Various
models retail for from $50.00 to
$150.00
126
FADA
This 17-inch table cone sells for $25.00, Model
315 A. Fada manufactures other more expensive
models selling for up to $50.00
FOUR OR SIX-VOLT A-POWER
A combination storage battery and full-wave dry rectifier available in
four and six-volt models, made by Triple A Specialty Co., Chicago.
Price: either model. $39.50
THE BASCO A-B POWER UNIT
This device contains a B-Power unit anil n storage battery-trickle char-
ger combination. A visual indicator shows the state of charge of the
battery. Price $75.
A TWO AMPERE "TUNGAR" BATTERY
CHARGER
A well known product of the General Electric
Company for charging A and B storage batteries.
Price, $18.00
THE "ACME" B POWER UNIT
For use with receivers containing up to twelve
tubes, including a 171 type power tube. A Ray-
theun rectifier is used. Price: $50.00
ANOTHER B POWER UNIT
This unit supplies up to 135 volts at a 60 milliam-
pere load — mc-rc than enough for most receivers. Man-
ufactured by the All- American Company and priced
at $27.50
A POWER AMPLIFIER AND B SUPPLY
An A-B-C power supply for receivers using a.c. tubes. The uniteon-
tains one stage of power amplification using a 210 tube. Manufac-
tured by the Radio Receptor Co., New York, and priced at $60.00
127
FACTS ABOUT THE FADA "SPECIAL" SET
By John F. Rider
JUST as the research laboratory is the prime
mover of every business, whether cheese, steel,
or clothing, it is also the heart of the radio in-
dustry. The radio public is awakening to the
fact that research is a prime mover in the radio
industry; that research, and research only, can
produce faithful reproduction, ample volume,
satisfactory selectivity, ease of control, and per-
fect stability. The result is recognition of re-
search as the paramount factor, and consistent
with this recognition, is the gradual stabiliza-
tion of the industry — its gradual ascension to
an impregnable position.
Research is directly responsible for every
good receiver and for every development in ra-
dio receiver design since the day KDKA com-
menced its broadcasting activities. A good radio
receiver cannot be produced without a research
background.
As an example, let us consider a typical re-
ceiver, the design of which may be laid directly
at the door of research. This receiver consists
of three stages of radio-frequency amplification,
a non-regenerative detector and two stages of
audio-frequency amplification. It is known as
the Fada "Special." But before we can enter
into the mechanics of the receiver, we must first
ascertain why the electrical design used was se-
lected.
The problem placed before the engineering
department was the development of a radio re-
ceiver limited to six tubes. The apportioning of
the tubes was the first problem. How many
stages of radio-frequency amplification should
there be; and how many stages of audio-fre-
quency amplification? Having developed audio-
frequency transformers with known response
characteristics and known gain per stage, and
knowing that a two-stage audio amplifying
system using their transformers would give the
proper amount of amplification, the engineering
department decided upon two stages of trans-
former-coupled audio amplification. Since the
detector unit utilizes but one tube, the remain-
ing three tubes can be applied to the radio-
frequency system.
The development of the radio-frequency sys-
tem brings to light many interesting features.
Should the stages be tuned or untuned or a com-
bination of both? Should the stages be shielded,
and what material shall be used for the shield-
ing? Since the receiver utilizes an antenna as
the pick-up system, the three stages of radio-
frequency amplification will give a high degree
of sensitivity. The demand for selectivity neces-
sitates the use of tuned stages of radio-frequency
amplification. But the development of a three-
stage tuned radio-frequency amplifier does not
mean a simple decision to use three stages. Con-
sideration must be accorded to the wavelength
response of such a system. The average system
possesses wavelength characteristics which fall
in amplification as the wavelength is increased
i.e., the amplifying power of the radio-frequency
amplifier is high at the shorter wavelengths and
as the tuning dials are manipulated to tune to
the longer wavelengths, the amplification de-
creases, and at 550 meters is a fraction of that
at 250 or 300. meters. This situation must be
avoided; it is desirable that the receiver should
possess equal amplification over the entire broad-
cast frequency spectrum.
Since the allocation of frequencies to broad-
casting stations is such that excellent selectivity
can be obtained with two stages of well-designed
and shielded tuned radio-frequency amplifica-
tion, the third stage can be utilized to balance
the two tuned stages and give the system the
desired wavelength response characteristic. The
radio-frequency system would, therefore, con-
sist of two stages of tuned radio-frequency am-
plification and one stage of untuned radio-
frequency amplification.
The decision to shield the individual stages
was immediate, since shielding, if properly car-
ried out, is conducive to better radio receiver
operation and consequently better radio recep-
tion and better stability is thus attained in the
radio-frequency stages because coil interaction
is eliminated. By the elimination of coil inter-
action, neutralization is made more effective.
Better tone quality is also obtained, because by
eliminating coil interaction, the side-band char-
acteristics planned in the design of the tuned
stages are actually obtained. Selectivity is aug-
mented, because direct coil pick-up is precluded.
The elimination of coil pick-up also means
greater amplification in the radio-frequency
system.
The selection of the shielding material is
governed by the effect the shield has upon the
inductances used in each stage. In order to mini-
mize the electrical effect upon the coils, a ma-
terial with a high conductivity must be used,
since high conductivity means lower losses.
Aluminum was decided upon, and the shield
takes the form of a can, completely enclosing
the radio-frequency transformer. With the
shields of proper diameter and properly located
with respect to the coils, the losses introduced
are so small as to be entirely negligible.
In view of the fact that the radio-frequency
coils are shielded, it is possible to make use ol
the most efficient type of winding — the single-
layer solenoid. Without shields, a cascade sys-
tem employing such coils would be quite diffi-
cult to control. The selection of the single-layei
solenoid was also based upon the fact that il
can be wound with the greatest degree of ac-
curacy, particularly so when the winding fern-
is grooved, and the turns ar; wound in thes<
grooves.
The receiver is to be dual tuned, requiring
two condensers controlled by one drum dia
and another single condenser controlled by th<
other drum dial. Such control is simple becausf
of the precision methods employed in the test-
ing and matching of the coils and tuning conden-
sers. Each tuned transformer consists of three
windings, the primary, the secondary, and 2
neutralizing winding. Each of these winding;
is matched on a radio-frequency testing instra
ment, to within one eighth of one per cent. Th<
coil under test is plugged into an oscillator cir
cuit and a resonance point obtained with a Stan
dard condenser. This condenser is so graduates
that a 10 per cent, variation in resonance ii
spread out across the loo-division dial. The dia
settings for the resonance point for each winding
are noted and the coils segregated according tc
these figures. The result is that each group o
three coils consists of coils with windings whicl
never vary more than one eighth of one per cent
The same precision in testing applies to thi
tuning condensers, and because of the mechani-
cal design of these condensers, full accuracy ii
maintained during the operating life of tht
unit. Each completed tuning condenser is mad<
to within one per cent, plus or minus, of its ratec
capacity, and each condenser in a group of threi
is matched to within one eighth of one per cent
of the others. The matching of the variable con
densers is carried out by means of a specia
radio-frequency measuring instrument designe<
for the purpose.
The construction of variable condenser:
which will not vary more than one per cent, call:
for detailed engineering. The brass used for thi
plates must be very accurate, the toleranci
limit being 0.0005 °f a m'' 'n thickness. To as
sure perfect alignment of the condenser plates
and a smooth rotary action, large bearings an
used, these latter being approximately |" ii
diameter. To further assure perfect alignment o
the brass plates, each plate is individual!;
stipled and leveled.
But the precision construction and matchinj
of coils and condensers is not sufficient to assun
perfect operation. It is necessary to assure per
feet mechanical support for these units — sup
ports which will be identical in every receiver o
similar design. It is necessary to select a base fo:
the condensers which will assure easy operation
not for a short while, but for years to come
DECEMBER, 1927
FACTS ABOUT THE FADA "SPECIAL" SET
129
Again engineering comes to the fore, with a pressed steel chassis J"
thick, punched out on a loo-ton press. One operation punches all the
holes necessary and also forms the chassis. The result is uniformity of
mounting holes.
R. F. CHARACTERISTICS
WITH the condensers, coils, and shields on hand, we go back to the
radio-frequency system. The overall gain curve of the three-stage
radio-frequency amplifier, consisting of the two tuned stages and the one
untuned stage, is shown in Fig. i. Here we see a beautiful example of re-
search and engineering. With the exception of the zone between 200 and
212 meters, (1500 and 1410 kc.) the amplification does not vary more
than ii per cent, from 212 to 550 meters. Between 200 and 212 meters,
the curve rises with the increase in wavelength, and the difference be-
tween the lowest point, 200 meters, and the highest, 250 and 500 meters,
is only 17 per cent. With such small variance in amplifying power, the
owner can manipulate the dials of his receiver from 200 to 550 meters,
and know that the sensitivity of the system is practically uniform over
the complete scale.
But the design of a radio-frequency system does not consist solely of
the development of an amplifier which will possess the wavelength re-
sponse curve shown. It is also imperative to accord detailed consider-
ation to the shape of the resonance curve of each individual tuned stage,
since the resonance curve manifests a great influence upon the tone qual-
ity of the receiver. In this respect, there is a close association between
the radio-frequency amplifier and the audio-frequency system. Many
owners of radio receivers are unaware of the effect the resonance curve
of the radio frequency stages has upon the tone quality obtainable with
the receiver employing three stages of radio-frequency amplification.
Fans are too prone to overlook the side-band characteristics of the radio-
frequency stage. They forget that while the radio-frequency stage is
tuned to the frequency of the carrier wave, it is also necessary to con-
sider that this carrier wave is modulated by audio frequencies rang-
ing from 30 to 5000 cycles. Also that the effect of these modulating fre-
quencies is to create a modulated carrier wave whose frequency spec-
trum is 10,000 cycles wide. In other words, if the carrier wave (un-
modulated) is 750,000 cycles (400 meters) when modulated, this wave
is broadened to cover from 745,000 to 755,000 cycles. The 5000 cycles
above the carrier and the 5Ooo-cycle-band below the carrier constitutes
che side-bands. Hence the resonance curve of the radio-frequency stage
must be broad enough to cover this band of 10,000 cycles even though
the circuit is actually tuned to 750,000 cycles. If the curve is too sharp,
some of the higher side-band frequencies will be suppressed. If the
curve is too broad, selectivity will be marred. Hence both selectivity
and sideband suppression must be considered in the design of the radio
frequency amplifier. With a known value of "Q", which is the factor of
selectivity, being the ratio of the reactance to the resistance of the cir-
cuit at a certain frequency, it is imperative to know the side-band sup-
pression in the radio-frequency amplifier and to give it consideration
in the design of the associated audio-frequency amplifying equipment.
An example of various degrees of sideband suppression in tuned circuits is
-Neutralizing Condensers — --_.
'
Antenna
60
= 40
i-:
z
z
320
\ r
R.F. GAIN
^00 250 300 350 400
WAVELENGTH, METERS
FIG. I
450
500 550
The curve shows the gain from the antenna to the input to the detector.
The sensitivity of the r. f. amplifier is high and the amplification flat
110
Width of carrier.& side bands
in o ir>
rH Oil CM
Lower side band — •*"" ~"^— Upper side band
MODULATION FREQUENCIES
FIG. 2
Tuned circuits that are too selective impair quality. The outer curve shows
the response in a well-designed circuit
UX-171
FIG. 3
This is the complete circuit diagram of the Fada "Special" receiver.
The '.'amplification equalizer" shown above, consisting of an untuned
stage, especially responsive to the longer wavelengths accounts for the
excellent r. f. response curve in Fig. I
-CPower-C4!$
rr
*C -A + A -BjgB45 tB90*BPower
BATTERY CABLE
130
RADIO BROADCAST
DECEMBER, 1927
50
40
20
10
A.F. CHARACTERISTIC
V
100
FREQUENCY
CYCLES PER SECONO
1000
10,000
FIG. 4, OVERALL A. F. CHARACTERISTICS
shown in Fig. 2. Curve A shows 80 per cent,
suppression on 5000 cycles and curve B shows
15 per cent, suppression at 5000 cycles. Curve
B is broader than A, but the proper amount of
selectivity is obtained by virtue of the cumula-
tive effect of a number of stages.
THE DETECTOR
FROM the radio-frequency system we pass
on to the detector circuit. A choice of two
systems of detection is available — the grid bias
method or the grid leak-condenser arrangement.
Because of the increased sensitivity, resulting
in greater output, the grid leak-condenser sys-
tem is used.
From the detector we pass to the audio-
frequency amplifying system. We made mention
in a previous paragraph that transformers were
used, but the design of a transformer-coupled
audio amplifier cannot be. consummated by
simply deciding upon transformers. Sometimes
these characteristics of the transformers to be
used are exactly what the requirements call for;
sometimes they are not. With specific require-
ments on hand, audio-frequency transformers
must be designed to fill the need. The design is
a detailed process. First the tubes to be used
must be decided upon, and their electrical con-
stants must be taken into consideration. The
core material for the transformers must be
selected, and the inductance of the primary and
secondary windings must be calculated in order
that the transformer possess certain predeter-
mined characteristics. The method of winding
must be decided upon so that distributed capac-
ity is low and so that satisfactory response on
the higher audio frequencies is obtained.
Detailed consideration must be accorded to
the regeneration existing in the completed audio-
frequency amplifier. This is very important.
The overall response curve of a two-stage audio
system with regeneration in the amplifier will
differ from that of a single unit. If the single
unit is designed to match the radio-frequency
system, the operation of the completed two-stage
amplifier will be entirely different. It is also
essential to consider the loud speaker to be used.
This unit, too, possesses operating character-
istics which must be taken into account. The
combined operating characteristics of the radio-
frequency amplifying system and the audio-
frequency amplifying system must be such
as to produce best results with a particular loud
speaker or with a group of good loud speakers.
The completed two-stage audio amplifier of
the receiver under consideration — the Fada
"Special" possesses the overall audio frequency
characteristics shown in Fig. 4. The amplifica-
tion is shown on the ordinate or the left vertical
line. The audio frequencies are shown on the
abscissa or the horizontal line. The frequencies
are plotted on a logarithmic scale. As is evident,
the curve is practically flat from 50 to 1000
cycles, rises from 1000 to 3000 cycles, and' then
falls gradually to 5000 cycles. The maximum
difference in amplification between the lowest
and the highest points is only 12.5 per cent.,
which difference is negligible, since the average
ear will not discern intensity variations of such
small proportions.
The development of the receiver is com-
pleted. Let us now consider the engineering in-
volved in the testing of the receiver. Each re-
ceiver must undergo various tests during the
process of production. The designing of this
testing equipment is also in the hands of the
engineering staff. Without testing equipment
all the effort placed in the design of the indi-
vidual parts and systems will have been for
naught. Without a testing department the life
of a radio plant would be very short.
The first test is a continuity test of the as-
sembled chassis. This makes necessary testing
with meters in each and every circuit, showing
the voltage across the tube filament, the fila-
ment current, the plate current, the plate volt-
age and, continuity in the grid circuit. The fila-
ment current and filament-voltage meters show
the operating action of the units incorporated in
these circuits. The same is true of the plate-
voltage and plate-current meters. Open circuits
in the plate circuit will be shown on these me-
ters. By simultaneously testing all the circuits,
it is easy to select the faulty circuit if one is
present in the receiver. The location of the fault
is also noted. By having meters in every circuit
it is unnecessary to hunt haphazardly.
The second test is to determine the efficacy
of the neutralizing system, and the adjustment
of the neutralizing units. In this test the as-
sembled and wired chassis is connected to a
series of meters, and the input system is coupled
to a dummy antenna which obtains its energy
from a local radio-frequency oscillator. The
dummy antenna simulates an average outdoor
installation. The meters show excessive regen-
eration in any of the tuned circuits, when these
circuits are made resonant to the frequency of
the oscillator. The neutralizing system is then
adjusted until all signs of excessive regeneration
in the radio-frequency amplifying system dis-
appears. Incidentally, this same method of test-
ing is employed to determine the overall gain
of the radio-frequency amplifier.
When measuring the amplifying power of the
radio-frequency system, from the grid of the
first radio-frequency amplifying tube to the grid
of the detector tube, a constant predetermined
radio-frequency signal is fed into the radio-
frequency system. The input voltage is held
constant on all wavelengths covered by the
tuning system. The voltage across the grid fila-
ment circuit of the detector tube is measured
with a vacuum-tube voltmeter.
The third test applied to the receiver is the
"air" test, i.e., the receiver is connected to an
outdoor antenna and outside broadcasting sta-
tions are tuned-in. This test is a final check of
all the tests applied to the receiver during the
process of manufacture. The overall gain of the
radio-frequency amplifier and the audio-fre-
quency amplifier is again ascertained. With
respect to the measurements of the audio-fre-
quency system and the transformers used, each
transformer is individually tested against a
standard before being placed into service in the
amplifier. Then the completed two-stage unit
is again tested under actual operating condi-
tions. With a known constant input, the total
gain is finally measured with a tube voltmeter —
the last of a series of thorough and efficacious
tests.
WHAT THE CHASSIS LOOKS LIKE
i 6
Our Readers Suggest — "
TWO pages of RADIO BROADCAST will regularly
be devoted to publishing contributions from
readers who have made interesting improvements
in the use of ready-made radio products. These
suggestions may deal with complete radio receivers,
socket-power units, "kinks" in the placing of loud
speakers, or slight circuit or mechanical changes
in apparatus in general use. Our readers have a
wealth of experience along these lines and these
pages offer an opportunity for them to share their
findings. Typewritten contributions from readers
are welcomed which, if published, will he paid for
at our regular space rates. In addition, a monthly
award of $ I o will be paid for the best contribution
published each month. Address all contributions to
Complete Set Editor, RADIO BROADCAST, Garden
City, New York. — THE EDITOR.
A Short-Wave Converter for any
Radio Receiver
THERE is to-day sufficient material being
broadcast below 100 meters (3000 kc.) to
interest the serious fan and to justify the
•construction of simple apparatus for its reception.
In some cases the use of a short-wave receiver
will make possible the reception of important
programs beyond the range of the conventional
receiver. The construction of a short-wave re-
ceiver is often an expensive proposition, and con-
verters heretofore described have been rather
complicated affairs. It is the intention of the
writer to describe a simple and inexpensive con-
verter which, when attached instantly to any
broadcasting receiver, makes it possible to re-
ceive on wavelengths between 15 and 125 meters
(20,000 and 2400 kc.) No change is made in the
present receiver but by means of the converter
the former is alternately available for short- or
broadcast-wave reception.
THE SHORT-WAVE CONVERTER
The short-wave converter takes the form of a
very simple and incidentally highly efficient
short-wave receiver, the output of which is
connected to the audio-frequency amplifier of the
present broadcast receiver. A simple plug-in
arrangement makes the change a matter of a few
seconds.
The following is a list of the parts used in the
short-wave converter illustrated and described:
Li, L2, U— Set Aero Short-Wave Coils.
Ci — Amsco o.ooo25-Mfd. S. F. L. Condenser.
Lc — Silver-Marshall Choke. No. 275
Ri — Clarostat o-joo.ooo-Ohm Resistor.
RZ — Amsco 3-Megohm "Grid Gate-/' with
Mounting.
Rs — Amsco 2O-Ohm Rheostat.
C2 — Tobe o.ooo25-Mfd. Fixed Condenser.
Cs — Tobe o.ooi-Mfd. Fixed Condenser.
Three Four-Foot Lengths of Flexible Wire.
Sub-Panel Brackets, Hardware, and Old Tube
Base.
National Type C Dial.
Amsco Floating Socket.
7 x 12 x T"s Inch Celeron Panel,
yxiixj Inch Wood Baseboard.
Two "XL" Laboratories "Push" Binding Posts.
THE FRONT PANEL
The construction of the short-wave converter
is best described in the accompanying illus-
trations. However, a word regarding the con-
necting plug may be of assistance.
The three wires leading respectively from the
radio-frequency choke coil, A-battery minus, and
A-battery plus, are led to the base of a discarded
tube, as made clear by reference to Fig. i. The
glass of the old vacuum tube is broken off and
the base cleaned out. The three wires are soldered
to terminals inside the base, one to the A-plus
plug, one to the A-minus plug, and one to the
plate terminal. These terminals may be identified
by holding the tube base, bottom down and the
side pin toward you. With the base in this
position, the two rear posts are A plus and A
minus respectively from left to right, and the
left-hand front post is the plate terminal. The
base of the tube is now filled with a wax com-
pound, such as the top of a discarded B battery.
This is easily done by placing small pieces of the
wax in the tube base and melting them with a
hot soldering iron. The receiver may be wired
with bus bar, but the author found coded flexible
wire more convenient. All leads should be made
as short as possible.
The function of the choke coil is important.
If the Silver-Marshall one is not available, one
may be made by winding 100 turns of 26 d.c.c.
wire at random on a wood spool, 5 inch in
diameter with j-inch wooden core.
To operate the short-wave converter, remove
the detector tube from the regular broadcast
receiving set and place it in the tube socket of
the converter. Next select the plug-in coil from
the Aero set covering the wave band in which
you wish to receive, and plug it into the coil
jacks. Then insert in the detector tube socket
of the regular broadcast receiver the plug made
from the old tube base. When the antenna
and ground have been changed to their respective
posts on the converter, you are ready to listen-in.
To do so simply leave the loud speaker where it
is, or, if phones are used, these may be plugged
in as usual in any stage for which a jack is pro-
vided on your particular receiving set. Turn the
Clarostat until the receiver oscillates. Tune-in a
station and clear up the signal by a further ad-
justment of the Clarostat or rheostat as re-
quired.
PERRY S. GRAFFAM.
Boston, Massachusetts.
STAFF COMMENT
\A/HILE the importance of short-wave
" * reception cannot be overstressed, state-
ments regarding its immediate and direct utility
to the fan must be qualified. RADIO BROADCAST
does not care to encourage the use of radiating
short-wave receivers, and the more simple sets
necessarily fall into this category. Serious experi-
menters, broadcast enthusiasts desiring to take
up code work, and fans in isolated districts are,
however, undoubtedly justified in conducting
experiments along these lines. Mr. Graffam's
inexpensive arrangement offers perhaps the sim-
plest introduction into the realm of megacycles.
R.F. Choke
^MKKTi
1-4
FIG. 1
132
Short-wave reception is by no means an un-
alloyed bliss as some avid publicity men would
have us believe. Ninety-eight per cent, of the
transmissions carried on below 100 meters is
inter-communicative code work and the two per
cent, of radio telephonic transmission is often
marred by high speed fading.
Antenna Compensation in a Single-
Control Receiver
NE of the major problems in single-
control multi-tuned circuit receivers is
the elimination of the detuning effect
of the antenna on the first radio frequency
stage. Loose and variable coupling between the
antenna primary and the first r.f. secondary is
generally employed to compensate this influence.
These arrangements, unfortunately, often lower
the signal response of the receiver, and the set
still functions best with antennas of definite
electrical characteristics.
The arrangement proposed overcomes these
difficulties and offers the following advantages:
It eliminates the antenna effect on any receiver.
It can be attached to any receiver without
making more than one simple change.
No additional controls are required.
Sensitivity is never reduced. On the contrary
it is often increased.
Any length antenna may be used with the
receiver without making additional changes.
The device acts as a partial blocking stage in
case oscillations are set up in the tuned amplifiers.
In brief, the device causes the radio-frequency
impulses to be applied across a resistor to an
extra radio-frequency tube, which is outputted
to the original antenna primary.
The following is a complete list of parts neces-
sary to make the change:
Ci — o.oo I -Mfd. Coupling Condenser. LI — R. F.
Choke Coil. Socket. 2O1-A Type Tube. Ri — J-
Ampere Ballast Resistor. Sw. — Battery Switch.
R2 — lOOO-Ohm Resistor. Six Binding Posts.
This apparatus is easily wired on a baseboard
in accordance with the diagram, Fig. 2.
The antenna is disconnected from the receiver
and wired to post number one. The ground re-
mains connected to the receiver and is also wired
to post number two of the new stage.
Turn on the filaments to the receiver proper
and the switch to the extra stage. Run a wire
from the A battery plus post on the set to post
number four. The extra tube will probably light.
If it does not light, repeat the test with a wire
from the negative A post.
If the extra tube lights with one side grounded
and the other side connected to the A battery
circuit, it is an indication that one side of the A
circuit is grounded, as it will be in 90 per cent,
of receivers. If this is the case, proceed as follows:
Leave the wire that lights the filament con-
nected to post number four. Connect the an-
tenna post on the receiver to post number five.
If, upon making the tests with the filament
wires to post number four, the tube does not
light, indicating that the filament circuit is
not grounded in the receiver, the filament plus
wire should be connected to post four and the
filament minus wire to post three. The tube will
now light, of course.. Connect the antenna post
on the receiver to post number five, and terminal
six to the plus 90 volts, and the unit is ready for
operation.
There is no change in the operation of the
receiver whatever. If taps are provided on the
antenna primary of the original receiver, slightly
higher efficiency may be secured by experiment-
ing with them.
If the experimenter is a bit more of an expert,
RADIO BROADCAST
1 II I
u
1000 D
2
(
Jiallast C
<ReJ.istor <
I"'
swTl
i>3 A4 m
S 0.001 mfd
3 R.F. Choke
D6
<
FIG. 2
the filament lead, or leads, to the antenna
coupler tube may be led from the tube side of the
set switch, making it possible to operate the
antenna coupling tube by the same switch that
controls the set filaments.
HAROLD BOYD.
Winchester, Virginia.
AN EMERG-'
ENCY AN-
TENNA
Fifty turns of
bell wire are
usually satis-
factory
STAFF COMMENT
THE arrangement suggested by Mr. Boyd is
quite practicable and is already used in
several commercial and kit receivers. The tube
coupling device is in the nature of an untuned
radio-frequency amplifying stage, and, in some
instances, may result in increased sensitivity.
The r.f. gain, however, is generally small in
comparison with the utility of the arrangement.
One thousand ohms is about the optimum
value for the antenna coupling resistor. It seems
to make little difference whether the resistor is
inductive or not. The Lynch, Amsco " Metaloid,"
Carter, and Electrad are excellent resistors for
this purpose. A variable zero to 2000 ohm re-
sistor may be substituted for the fixed resistor
recommended by Mr. Boyd and used as a vol-
ume control.
In a few cases it may be found that the load
imposed by the coupling arrangement on the
first r.f. transformer is no more favorable to
tandem tuning than that of the average antenna.
This can be compensated either by adjusting the
compensating condenser across the first tuning
section (if the main condenser is so equipped),
or by winding a special primary over the first
secondary. From six to ten turns of wire may be
placed directly over the coil. One end is con-
nected to post number five in Fig. 2 and the other
terminal to plus 90 volts.
Increasing Response from a Loop
Receiver
AL receivers are more or less affected by
location, but the loop set seems to be
particularly susceptible to adverse con-
ditions imposed by position. This is due to the
fact that the loop is often surrounded by steel
building framework and similar obstructions
which the open antenna can rise above. Dis-
advantages of this nature were impressed upon
the writer when moving from the top floor of a
New York City apartment house to the second
floor of the same building. The receiver, a
DECEMBER, 1927
Radiola super-heterodyne, worked perfectly in
its original position eight floors higher up, but
lost perhaps seventy-five per cent, in sensitivity
when brought a hundred feet nearer the ground.
Its operation was brought up to normal by a
simple device, thrown together in five minutes.
A twenty-five foot antenna was strung on the
roof of the building. Three turns of wire, harmon-
izing with the wire on the loop, were wound
around the loop frame, twisting slightly about
the original loop wire to keep it in place. One end
of this extra wire was connected to the short
antenna, while the other end ran to ground.
Sufficient energy is transferred to the loop
circuit from the open antenna to compensate the
losses imposed by an inferior location.
A. J. HOWE.
New York City.
STAFF COMMENT
THE device recommended by our contributor
is, of course, a simple antenna coupler, the
extra turns of wire functioning as the primary
and the loop itself as the secondary. The arrange-
ment is effective. On the ordinary super-hetero-
dyne (that is other than the second harmonic
type) the shortest antenna giving satisfactory
reception should be used, to reduce the possi-
bility of radiation.
The directional effect of the loop is largely
eliminated by coupling to an open antenna in
this manner. However, the selectivity of the
super-heterodyne is such that this effect can be
safely dispensed with.
A coupling device of this type is made com-
mercially by the Jenkins Radio Company,
Davenport, Iowa.
A Temporary Antenna for the
Traveling Fan
EXTRA tubes and batteries are easily avail-
able in an emergency, but the occasion
where a spare antenna would save the day
is seldom provided for, so a word as to an ex-
cellent makeshift antenna may not be amiss.
A first class one, often equal to the average
outdoor variety, may be secured by wrapping
fifty turns of bell wire around a telephone desk
stand. See Fig. 3. One end of the wire is con-
nected to the antenna post on the receiver and
the usual ground is used.
The writer, an inveterate radio enthusiast,
discovered the possibilities of this arrangement
when traveling across the country with a Fada
neutrodyne, the operation of the receiver being
somewhat limited by the facilities of the average
hotel bedroom.
Subsequent experiments show this type of
antenna to be equally efficacious with other
receivers.
ALFRED A. MARKSON.
New York City.
STAFF COMMENT
THE use of the telephone as a substitute
antenna is by no means a novelty, although
the exact system of connection outlined here is
not that generally advocated, but probably as
efficient. The more widely used application of
this idea is found in the use of a small metal
plate upon which the telephone is stood, and
which is connected to the antenna binding post
of the receiver. Such metal plates, especially cut
for the purpose, are commercially available. As
the latter are not always immediately obtain-
able in an emergency, Mr. Markson's idea is a
useful one.
A radio set of other years can be brought up to date by improving the audio quality through
new transformers, tubes and loud speakers or by the purchase of a complete power-supply-
amplifier unit. These changes help greatly. R.f. Changes are not suggested
THE articles appearing in the September
and October issues of RADIO BROADCAST,
dealing with the judging and attainment
of good tone quality, resulted in hundreds of
letters from readers, asking specifically how cer-
tain makes of receivers could be converted to
give the high-grade tone quality described. It
was the writer's intention to answer the letters
directly in these columns, but their number grew
so large that it would require an entire issue of
the magazine to meet the demand for informa-
tion. This article is based upon the questions
raised in the letters and will serve as a concen-
rated answer to these letters.
Hundreds of thousands of radio enthusiasts
are owners of receiving sets sufficiently selective
:o be satisfactory, but falling far short of the
atest standards of tonal reproduction. So long
as the receiver meets the simple requirement of
>eing sufficiently selective, but not too selective,
t can be converted to give good tone quality.
The writer does not mean to imply that the
radio-frequency end of the modern receiver is
not as greatly improved as the audio end and
that the most satisfactory measure, after all, is
not to discard entirely the obsolete receiver.
But not everyone is in a position to employ
this remedy; some of us must reconcile ourselves
to tuning with several dials and to great sensi-
tiveness at the high frequencies, where it is not
especially needed, and lack of sensitiveness at
the low-frequency end, where it is most desired.
Simplicity of control, and equal amplification
throughout the wavelength scale, are features
embodied only in the latest receivers. But, given
satisfactory selectivity, an old receiver may be
greatly improved so far as tone quality is con-
cerned.
Exceedingly sharp tuning, such that high-
power stations within fifty ot a hundred miles
are heard with considerable volume only when
tuned-in precisely and always disappear with a
whizz and hiss when detuned but one or two de-
grees from exact resonance, indicates selectivity
too great for the attainment of good tone qual-
ity. Oftentimes a receiver behaving in this way
can be made to tune more broadly, so that
neither the low or high audio frequencies are cut
off, by installing a somewhat longer antenna.
Having once determined that the radio-
frequency end of the receiver does not tune too
By EDGAR H. FELIX
sharply, improvement of tonal quality is a mat-
ter of re-vamping the audio system. The essen-
tial requirements for good tonal quality are:
(i) Audio-frequency transformers of sufficiently
good quality to pass the entire tonal range; (2)
tubes of sufficient power and emission to ade-
quately handle signals of considerable magni-
tude (3) a power supply assuring correct A, B,
and C voltages to every tube under actual oper-
ating conditions; and (4) a loud speaker capable
of setting up sound waves throughout the audio
scale.
Prior to recent developments in transformer
design and material, resistance-, and impedance-
coupled amplification were the only systems,
within reach of the experimenter, capable of
handling broad tonal Jange. These systems under
proper conditions are not excelled in quality
output by high-grade modern transformers, but
require an extra stage so that they are not
easily incorporated in a manufactured receiver,
unless it is especially designed to accommodate
them. During the last year, transformer devel-
opment has reached such a point that two
stages may be used to give the best of tone qual-
ity.
Transformers can be manufactured at a cost
as low as forty cents, although the actual raw
materials which go into the better transformers
cost as much as eight times that figure. Expen-
sive iron alloys, which magnetize and de-
magnetize rapidly, and high-inductance wind-
ings, are essential if the entire tonal range is to
be amplified. Under no circumstances, can cheap
transformers serve as well as well known expen-
sive ones. In replacing transformers, to make the
job worth while, confine yourself to the best.
Some of the better receiving sets of earlier vin-
tages, are not equipped with suitable transform-
ers and the substitution of such makes as Amer-
tran, Ferranti, Silver Marshall, Thordarson,
General Radio, Rauland Lyric, Modern, All
American, Pacent, Sangamo, and Samson, to
mention some of the better ones, is decidedly
worth while.
REPLACING OLD TRANSFORMERS
TO DETERMINE whether such substitu-
tion is feasible, open the cabinet and ex-
amine the audio-frequency transformers. See if
they are easily removed and if the four terminals
are so marked that you can put labels on the
wires before you remove them, indicating the
correct filament, grid, plate, and B -(-terminals.
This will prevent confusion when you put the
new transformers in place. Adhesive tape is a
convenient form of label. Measure the space
available for transformers because cheap trans-
formers are often small. The high grade ones,
with which you replace them, are likely to be
somewhat larger and hence may not fit in the
space provided for the old transformers. Where
the problem requires moving of sockets and
other parts, your local dealer can replace the
transformers for you. His charge should be be-
tween two to five dollars, plus the cost of the
transformers themselves.
The next link in the chain of audio reproduc-
tion concerns the tubes used. You cannot hope
to secure good quality, if you do not use a power
tube in the last stage. The ux-2oi-A (CX-JOI-A)
tubes in the output stage are capable of only
moderate volume with good quality. If you are
attaining fair quality with such tubes now, after
replacement of the transformers they may prove
unsatisfactory, because the added energy in the
low frequencies, impressed upon the output
tube by the new transformers, will not be handled
satisfactorily.
In the case of the storage-battery receiver,
wired with but a single C battery connection,
both the first and second stages are usually sup-
plied with the same C battery voltage, generally
4J. Re-wiring of the set, however, is not neces-
sary to put in an ux-iyi (cx-3yi) or a ux-i 12
or cx-312. Manufacturers such as Na-Ald, have
developed special sockets with flexible cable con-
nections, enabling you to add the necessary grid
and plate voltages to operate power tubes, with-
out any wiring changes.
There is one exception to the general rule that
replacement of the transformers and addition of
a power tube will bring you better tone quality.
Certain reflex receivers, which enjoyed a fairly
wide sale three and four years ago, are not
adapted to this simple conversion. The use of a
grid bias and plate potential satisfactory for
audio purposes may render the radio-frequency
amplifier of these reflex sets quite unstable.
Many of these receivers are such heavy con-
sumers of plate current that discarding them is
an economy. It is not worth while to attempt to
134
RADIO BROADCAST
DECEMBER, 1927
improve them. You must treat them as you
would an inherited 1902 one cylinder-automo-
bile.
With dry-cell tube receivers, the largest out-
put tube available is the 120 type. This is a great
improvement in power handling capacity over
the 199 type, but it is still far from sufficient to
attain really good tonal quality. The further
down the tonal range the reproducing system
goes — and that is what gives body and richness
to music and naturalness to speech — the greater
must be the power available in the output tube.
The owner of such a dry-cell tube receiver
need not, however, abandon hope, because he
may employ a one-stage power amplifier, receiv-
ing its filament, grid and plate potentials, di-
rectly from the light socket, and employing the
ux-2io (cx-jio) in the output. This tube is of
even greater power handling capacity than the
ux-iyi (cx-37i) and, hence, capable of magni-
ficent tonal quality, provided good transform-
ers and reproducers are used in connection with
them. These light socket units may also be
used with storage battery outfits and are recom-
mended to B battery users. The use of a power
tube in the output stage considerably increases
B battery drain and, as a consequence, the use of
a light socket amplifier unit is an economy.
Such power supply devices are manufactured
by General Radio, Farrand, Radio Receptor.
Pacent, National, Timmons, Amertran, and the
Radio Corporation. They furnish A, B, and C
power, not only for the 210 or 171 tube, but also
B and in some cases C voltages for the receiv-
ing set itself. Adding these amplifier-power
supply devices to the existing receiver is a simple
matter. The tonal reproduction secured is still
dependent upon the grade of loud speaker and
first stage transformer used but, so far as avail-
able power is concerned, the purchase of a good
power amplifier and B supply unit settles that
question.
SELECTING A REPRODUCER
HAVING now supplied transformers which
actually amplify the entire range of tonal
frequencies, having installed tubes of adequate
power handling capacity, and having supplied
them with the correct A, B, and C voltages, it is
next necessary to obtain a loud speaker capable
of setting up sound waves throughout the entire
tonal range. A loud speaker which is seemingly
satisfactory with poor transformers and power
supply, often fails when the high-grade trans-
formers and tubes are wired into circuit, because
of the larger load and greater frequency range
thereby impressed upon it.
Remedying an audio system requires that the
entire audio system be put in good condition,
because any one weak link will destroy the ef-
fectiveness of all the other remedial measures.
If you have four worn out tires on your car,
replacing one, two, or three of them is not suf-
ficient to give you immunity from tire trouble.
Many a person, dissatisfied with tone quality,
has replaced his loud speaker and then wondered
why great improvement did not result. In fact,
it often happens that an exceptionally good loud
speaker will sound worse than a bad one with a
poor set. The good loud speaker sets up sound
waves in exact accordance with the electric
signal furnished it. A poor loud speaker may be
so designed as to exaggerate the low notes, thus
providing for their deficiency in a defective au-
dio system. When a good loud speaker is sub-
stituted, the absence of low notes, due to un-
suitable transformers, becomes more conspicu-
ously apparent.
Every reproducer has an actuating element
which sets up the sound waves — a sort of paddle
which sets up air vibrations. With good repro-
ducing systems, the loud speaker must be ca-
pable of setting up low frequencies as well as
high ones, and consequently the actuating ele-
ment, vibrating diaphragm, or cone surface, must
often be large if it is to be successful. The horn, if
one is used, must also be of large size, so that it
does not impede the radiation of low frequencies.
A long, goose-necked horn chokes off the low
frequencies, while a large exponential horn can
give you much of the true magnificence of the
organ.
The writer cannot attempt to list entirely
all good cones and horns, but he has personally
tested Western Electric, Farrand Sr., Balsa,
Rola, and Amplion, and found them capable of
handling the output of 171 and 210 type tubes
throughout the tonal range attainable by the best
of amplifier systems.
Inferior loud speakers fail not only because
they are incapable of mechanically setting up
waves by reason of small moving surface or con-
fined tubular horn areas, but also because the
electromagnetic unit is incapable of handling
the large output which is necessary to secure
good tone. With the 210 and 171 types of tubes,
an output transformer or choke and condenser
feed to the loud speaker is absolutely necessary
to eliminate the direct-current component from
the speaker winding. We desire only to have the
audio-frequency fluctuations in the loud speaker
winding so that magnetic saturation is avoided.
Silver-Marshall, General Radio, Federal, Na-
tional, Pacent, Samson, Thordarson, Amertran,
Muter, Amsco, and others make output devices.
One question which appeared in many of the
letters received was the demand for more vol-
ume, or specific questions to the same effect,
such as whether the use of a 171 tube would
increase volume. None of the measures described
have for their purpose the increasing of volume
output of the receiver. The use of large power
tubes simply increases the amount of signal vol-
ume which can be handled without distortion
due to overloading.
By using the grade of transformers, tubes, and
loud speakers mentioned, a signal so weak that
it can hardly be distinguished by the phones in
the detector output circuit is amplified to com-
fortable living room volume. If the signal is not
sufficiently strong to give such volume, the
remedy does not lie in additional audio-frequency
amplification but in the use of a more sensitive
receiving set. The best results are obtained if
the detector tube's output is a signal just strong
enough to be discernible in the headphones.
Those complaining of weak signals should look
to improving antennas and to increasing radio-
frequency amplification. The audio system
should not be expected to make up for deficien-
cies in the radio-frequency amplifier.
As a matter of fact, most of the receiving sets,
even those of two and three years ago, are ade-
quately sensitive. Many complaints of reduced
volume may be attributed to the continued use
of depreciated power supply and tubes, whose
filaments have lost their emission.
It is an essential requirement of good tone that
the power supply be adequate and that the
tubes have plenty of emission. There is only
one way that this can be determined definitely
and that is by measurement. Your dealer should
have a tube checker which he can bring to your
set, or you should take the tubes to a well
equipped radio store for testing. By taking out
one tube, substituting for it a plug, connected
by a flexible cord to the set checker or tube tester,
and placing the removed tube in a socket pro-
vided on the tester, the A, B, and C potentials,
and the plate-current output of the tube, can
be measured. The writer recently tested an elab-
orate set checker made by a concern in Detroit,
equipped not only to make the four measure-
ments mentioned, but also the voltage at the
terminals of the A battery, the completeness of
all the circuits and, the mutual conductance of
the tubes by the manipulation of a few well
marked switches. Every dealer should have
some such device. The use of a voltmeter does
not tell the full story and no dealer is in a posi-
tion to service adequately without measuring
devices such as those made by Jewel, Weston,
General Radio, Quick-Test, Hoyt, Hickok and
others.
There were many well-known and widely ad-
vertised makes of receivers which last year
became known for their mediocre tone quality
and which this season have effected extraordin-
ary improvements. The importance of tone
quality has been widely recognized and manu-
facturers have realized that they cannot remain
in the radio market unless their receivers are
capable of high-grade reproduction. Name, rep-
utation, price, and the willingness to submit
their product to the test and approval of the
recognized set expert, are guides to the set pur-
chaser. Many receivers, described in most al-
luring terms in general magazines, do not meet
the laboratory inspection of the expert. It is best
to confine your purchases to sets recommended
by well-informed enthusiasts who have some
familiarity with the technical phases of radio.
In the October issue, the writer gave suggestions
for tests which may be made at the dealer's
store when a receiver is being demonstrated,
to give indication of its tonal capacity. It is sug-
gested that the reader go over both the Sep-
tember and October articles before making pur-
chases.
To summarize, the conversion of an old re-
ceiving set to give good tonal quality requires:
(i). That the radio-frequency amplifier of
the receiver does not tune so sharply that near-
by signals are heard only when precisely in re-
sonance.
(2). Audio-frequency transformers be used of
a quality and price sufficient to assure that they
will amplify the entire range of frequencies
from stage to stage.
(3). The output tube be of sufficient power
capacity to handle the required range ampli-
tudes.
(4). The correct A, B, and C voltages be sup-
plied to the tubes.
(5). That the loud speaker be capable of
handling the tonal range.
In most cases, these objectives are attained by
replacement of the audio-frequency transform-
ers, installation of a power tube (in the case of
dry-cell sets, the addition of a one-stage power
amplifier and B supply which furnishes A, B,
and C power for a 210 or 171 type tube), and
finally, the use of a suitable reproducer.
A Quality Five-Tube A. C« Receiver
• ^^' /
By JAMES MILLEN
T^
_
I HIS article describes the construction of
an a.c. operated receiver, the new type a.c.
tubes being used to accomplish the electri-
fication. In the preceding article in this series,
published in last month's RADIO BROADCAST,
some general information on a.c. tubes was
given.
In explaining how to use these a.c. tubes with
an actual receiver, we have chosen a circuit which
embodies some of the features of the Browning-
Drake receiver. Strict adherence to the instruc-
tions contained in this article will result in a light
socket operated receiver equaling in sensitivity
and selectivity a receiver operated on standard
storage-battery type tubes.
Before going into details regarding the con-
struction of this a.c. receiver, we will point out
how the circuit differs from that of Browning-
Drake sets. First, let us consider the r.f. ampli-
fier. Most previous designs of the Browning-
Drake receiver have used a 199 type tube as the
r.f. amplifier, because the tendency for this tube
to oscillate is less than with a aoi-A type tube.
A. c. tubes, however, have characteristics similar
to the latter type, and since an a.c. tube is used
FRONT VIEW OF THE RECEIVER
in the r.f. stage of the receiver described here, it
becomes necessary to devise some practical
method of preventing this r.f. amplifier from
oscillating.
In Fig. 4 is shown, at "A," the circuit of the
original Browning-Drake radio-frequency ampli-
fier using Hazeltine neutralization; at "B" we
see the Browning-Drake circuit using the Rice
system of neutralization. At "C" is shown the
circuit arrangement for use of a 226 type a.c.
tube. In the grid circuit will be noticed a non-
inductive resistor, having an ohmic value of
approximately 1000 ohms. It is the use of this
grid resistor or, as it is more generally called,
"suppressor," that makes possible the balancing
of the circuit. As this resistor is not placed in the
tuned circuit, it has no detrimental effect upon
the selectivity of the receiver.
The arrangement shown at "C," Fig. 4, is
used in the final model of the receiver illustrated
in this article, and it will be noted that the plate
voltage is fed to the plate of the tube through a
choke coil, U, instead of through the primary
winding of the r.f. transformer. The former
method (feeding the voltage through a choke
coil) tends to somewhat stabilize the operation
of the receiver, especially when a socket-power
unit is used for the B supply.
The antenna is coupled to the first coil in the
usual manner, i.e., through a 50-150 micro-
microfarad midget variable condenser, to a
center tap on the coil. If the antenna is over 40
feet in length, the connections should be as indi-
cated in the diagram, but if a shorter antenna is
used, the lead from the midget condenser may
connect directly to the grid end of the coil in-
stead of the center. In congested localities, ex-
cellent reception, with greatly improved selec-
tivity, is obtained by using a j-foot length of
bus bar for an antenna. The bus bar should be
attached directly to the grid end of the coil.
THE AUDIO AMPLIFIER
THE audio channel employed is capable of
producing excellent tone quality and at the
same time lending itself equally well for use with
either the new a.c. tubes or the standard storage
battery tubes. The wiring of the audio channel
is shown in the complete circuit diagram. Fig. 2.
In the first stage is employed an impedance
6 b 6 b
2.5 1.5
A.C. Filament
Heating Transformer
To Light
Socket
FIG. I
Complete circuit diagram of the complete a.c. operated receiver
136
RADIO BROADCAST
DECEMBER, 192-;
•IWi-
T"
•T
"75
i "t^
c-1
.~~"t
r«- 1 *«*--
NOTE: Holes with No.28 Drill
unless otheiwisenolei
FRONT PANEL
FIG. 2
How to drill the front panel
coupling unit which is incorporated a radio-
frequency choke coil; in the second stage, resist-
ance coupling is used, while the third stage em-
ploys a special arrangement of resistance and
impedance with the impedance in the grid circuit
of the power tube so as to eliminate any tendency
of the amplifier to " motor-boat " when used with
some types of B power units. A tone filter, Ls, is
incorporated in the output circuit as a protective
device for the loud speaker.
As will be noted from thecircuitdiagram, Fig. I
resistance-capacity filters (Rs-Cy, Rz-Ce, and
R8-C8) are employed in the grid circuits of each
of the audio tubes. These filter circuits prevent
"motor-boating" and make the operation of the
audio amplifier entirely stable under all con-
ditions. The grid bias resistances, Ra and RS, as
well as the mid-tapped resistance, R2, across the
filament of the detector tube, are all of the fixed
variety so as to eliminate needless adjustment
and enable the home constructor to obtain the
same excellent performance from his receiver as
from the original laboratory model.
The various photographs, working drawings,
and circuit diagrams accompanying this article
give all the necessary details regarding the con-
struction of this receiver and only a few ad-
C7 C3
C2
C6 C10 C9
R4 R 2
FROM THE UNDER SIDE
The letters correspond with the parts list on page 137. On page 33 of RADIO BROADCAST for
November, 1927, appeared a back panel view of this set to which reference may be made
-- 20 '^ .
BASE PANEL
FIG. 3
How to drill the base panel
Make Two, Brass
+t£fr
*<w -
*
E
tS
^'
>
r
•1%1-^
i 1
BRACKET
DECEMBER, 1927
A QUALITY FIVE-TUBE A. C. RECEIVER
FIG. 4
' The circuit of "C" is used in this set. This
alteration in the usual Browning-Drake circuit is
necessary because of the special problems arising
from the use of a.c. tubes
ditional hints need be given in order to make
possible the easy construction of the receiver. '
As the illustrations show, the a.c. filament
heating transformer is not built into the set, it
being more convenient in this case to mount it
as a separate unit within the usual battery com-
partment of the console if the latter is employed.
The first construction step is to drill the front
and sub-panels in accordance with the details
given in Figs. 2 and 3.
The next step is to mount the condensers,
coils, sockets, and other parts on the sub-panel,
as shown in the illustrations. Then, the sub-panel
may be almost completely wired — all before
attaching the front panel, which merely carries
the dial, volume control resistor, and tickler
adjustment.
The small General Radio neutralizing con-
denser should be disassembled and built right
into the sub-panel after discarding the triangular
bakelite back.
In the receiver shown in the illustrations, the
resistor mountings and sockets were also dis-
assembled and the contacts remounted directly
on the sub-panel. Much needless work can be
saved however by retaining the bases of the
resistor mountings and sockets.
Instead of numerous binding posts the use of
two cables is recommended. One cable should
consist of the seven low-voltage a.c. leads to
the filament transformer while the other cable
should have four leads to the B power supply
unit.
As the loud speaker cord may be plugged
directly into the tip jacks on the front of the
tone filter, it is necessary to provide but two
binding posts — for the antenna and ground.
The wire to use for all connections as well as
the cables should preferably be No: 18 tinned
flexible rubber-covered wire. Such wire may be
obtained from Acme and Corwin in different
colors for making the cable and to facilitate the
tracing of the set wiring itself.
With many uy-22y type detector tubes it will
be found that the most satisfactory operation is
obtained when the heater voltage is slightly be-
low the rated 2.5 volts. For this reason it is
recommended that a 6-inch length of resistance
wire from an old 6-ohm rheostat be connected in
series with one of the a.j-volt a.c. leads, prefer-
ably right at the transformer terminal panel.
ADJUSTING AND OPERATING THE RECEIVER
THE adjustments necessary in order to obtain
the best performance from the~completed
receiver are few and easily made. First, connect
the antenna, ground, loud speaker, B-power
unit, and filament heating transformer, and then
turn on the i lo-volt supply and wait for about a
minute or so for the detector tube to reach its
proper operating temperature. If a high-resist-
ance voltmeter is available, the next step is to
set the detector B voltage to approximately 45
and the r.f. B voltage to 70. Should a suitable
voltmeter not be available, the r.f. and detector
B voltage may be set by guess work and then
readjusted for best results later. The next step
is to set the potentiometer, Ri, for minimum
hum. Generally this adjustment will be obtained
when the contact arm is somewhere near the
center of its arc. Occasionally, if the receiver
should develop a slight hum, a slight readjust-
ment of the potentiometer will remedy the
trouble.
The antenna series condenser should be ad-
justed so that the two tuning condenser scales
read somewhat alike.
The neutralizing condenser may now be ad-
justed so that the receiver does not oscillate at
the shortest wavelength when the tickler coil is
set for minimum regeneration. Generally the
proper setting is with the movable plate of the
neutralizing condenser turned in about a third
of the way.
When making any of these adjustments, the
volume control should be set for maximum vol-
ume in which position the receiver has the
greatest tendency to oscillate. The following is a
list of parts recommended for use in the receiver
described in this article:
LIST OF PARTS
TI — National B-DiE Tuning Unit
(Without Dial)
T2 — National B-D2E Tuning Unit
(Without Dial)
National Drum Tuning Control .
Li — National Impedaformer, 1st Stage
Type
La — National Impedaformer, 3rd Stage
Type
L3 — National Tone Filter ....
Ra — General Radio No. 439 Center-Tap
Resistor
Rs — Lynch 5OO-ohm Suppressor
Ci — Precise No. 940 Midget Condenser,
50-150 Mmfd
Cs — General Radio Midget Neutraliz-
ing Condenser
Re, R?, Rs — Lynch o. i-Meg. Standard
Metalized-Filament Resistors .
Rg — Lynch o.i-Meg. Type C Metal-
ized-Filament Resistors .
Rio — Lynch o.5-Meg. Standard Metal-
ized-Filament Resistors .
Rn — Lynch looo-ohm "Suppressor" .
Rs — Lynch 2ooo-Ohm Type P Wire
Wound Resistor
Ri — Lynch 2-Meg. Standard Metal-
ized-Filament Resistor .
Cs, Q, C?, Cs, Cio — Tobe i-Mfd. By-
pass Condensers
Cg — Tobeo.i-Mfd. Bypass Condenser.
Ria — Electrad Royalty Variable Re-
sistor, Type K
C4 — Sangamo o.ooo25-Mfd. Mica Con-
denser .... ...
Cs — Sangamo o.ooi-Mfd. Mica Con-
denser
U — Samson No. 85 R. F. Choke .
R4 — Carter 2o-Ohm Midget Potentio-
meter
Two Eby Binding Posts ....
Four — General Radio No. 439 ux
Sockets
One General Radio No. 438 UY Sockets
Eight Lynch Single Resistor Mountings
Bakelite Panel, 7x21 Inches .
Bakelite Sub-Panel, 9 x 20 Inches.
Wire, Etc .
137
$ 8.25
11.75
6.00
5.50
5 50
6. 50
.60
i.if
i 75
1.25
2.25
i .00
•50
•75
1.25
50
4.50
.60
TOTAL
ACCESSORIES
One cx-371 (ux-i7i) or Ceco j-yi
Tube
One cv-327 (uY-227) or Ceco R-27
Tube
Three cx-326 (uv-226) or Ceco R-26
Tubes
One ux-28o (cx~38o)
One National No. F226 Filament Heat-
ing Transformer
One B-Power Unit, National Type M .
TOTAL
$4.50
6.00
9.00
5.00
10.00
40.00
$74.50
Looking Back
THE STORY OF RADIO. By Orrin E. Dunlap,
Jr. Published by the Dial Press, New York.
Price $2.50; pages, 226; illustrations, 15.
THIS book, by the Radio Editor of the
New York Times, is a literary effort to
squeeze some more thrills out of radio
for the benefit of laymen who desire knowledge
but do not want to struggle for it. There is
nothing technical in its two hundred or so pages
but, in a journalistic and often very interesting
fashion, it gives a history of radio progress, and
manages to touch on such topics as transmission
theories, fading, radio direction finders, and
piezo-electric control. The various branches of
radio communication, such as aircraft work and
transatlantic radio telephone circuits, are des-
cribed; there are several pages on auditory
phenomena; short waves and television are not
neglected. The history of radio is told in the
first person, presumably by the spirit of the
ether, or some loquacious band of waves. The
effort to sustain an appeal to the imagination
results in some very silly passages, the worst
one appearing in the introduction :
Will the millions and billions of musical scores
and countless numbers of spoken words ever
return from the Infinite? Will the waves all roll
back some day, all intermingled, the music of
centuries, the works of all composers a hopeless
jumble, a babel of voices, all so powerful elec-
trically that the onslaught of invisible waves will
burn up the ether and radio will be no more?
The answer is that this catastrophe will posi-
tively not occur, unless at that time God sees
fit to suspend the second law of thermodynamics,
retroactively.
But, with the exception of some of the chap-
ter headings and captions, which have no con-
ceivable relation to the text, this drivel is not
representative of the contents of Mr. Dunlap's
book. He is, in point of fact, an old radio man,
and a Member of the Institute of Radio Engi-
neers, and when he remembers that there is
only one inimitable Judge Rutherford, he does
a good job. What he says is, in the main, ac-
curate, and jazzed up only within the limits
permissible in such a book. He has at his fingers'
ends, or in his scrap book, about all the interest-
ing things that have ever happened in radio,
and in "The Story of Radio" relates them for an
audience to which they will be utterly new.
The events of the war in the radio field dramatic,
sos episodes, the old Herald station, OHX, silent
these fifteen years, all live again in Dunlap's
pages, and it is pleasing to see their appearance
in a more or less permanent record. Give the
book to your son as a birthday present, if you
have not already bestowed it on him for Christ-
mas.
— C. D.
T1
T2
LI
T3
CX-316-B
0/-UX216-B
Xii
A
CX-310
»rUX-210
R1
CX-310
orUX-210
CX-374
erUX-274
C1,C2,C3,C4,C5.
B SUPPLY For
RECEIVER
A PUSH-PULL POWER AMPLIFIER
The amplifier illustrated above is designed to give excellent quality reproduction of radio programs. The push-pull amplifier uses two
cx-jio (ux-2io) power tubes which are capable of supplying to a loud speaker large amounts of undistorted power. The entire amplifier
is constructed on a pressed steel sub-base
A NEW "TWO-TEN" POWER AMPLIFIER
By William Morrison
THE combined push-pull power amplifier
and light socket B power unit described on
pages 163 and 164 of the July RADIO
BROADCAST has recreated considerable interest in
push-pull amplification. The device described
consisted of a single-stage push-pull power
amplifier built into a steel case and chassis
assembly which also housed the power supply
equipment. The latter furnished A, B, and C
power to the push-pull amplifier and B power
for the radio receiver as well. While this unit,
termed for simplicity a "Unipac," possessed
considerable merit, its power output, even with
a pair of 171 type power tubes, would appear to
be insufficient for really substantially distortion-
less reproduction, assuming that from 1.5 to 2
watts of power is required for good dance music
volume, and that the amplifying system should
possess a fairly flat frequency characteristic of
from 30 to 5000 cycles.
The undistorted power output obtainable from
the previously described unit is higher than is
generally obtained from receiver output stages,
and, in fact, is greater than is often obtained
from some of the more popular power packs em-
ploying a 210 type tube, the operating voltages
of which are often less than they should be.
As a result of the interest that has been dis-
played in this earlier push-pull "Unipac," a
higher-powered model has recently been de-
veloped employing a pair of ux-2io (cx-3io)
type amplifier tubes capable of delivering from
3 to 4 watts of undistorted power to a good loud
speaker. It is probably quite safe to say that this
is one of the most powerful receiving amplifiers
yet developed for the home constructor, and the
quality of reproduction it provides is really re-
markable. After listening to the push-pull
amplifier of the type described here, the signifi-
cance of the popular phrase "tube overloading,"
as applied to conventional receiving amplifiers,
is really brought home.
This newer combination is illustrated here-
with, and closely resembles the push-pull model
previously described. The new "Unipac" con-
sists of a full-wave rectifier, which may use
either ux-2i6a (cx-3i6-B) or the new ux-28i
(cx-38i) type tubes, and a push-pull amplifier
stage with the two ux-2io (cx-3io) power tubes.
A good idea of the details of the device may be
gained from the detailed circuit diagram, in which
the parts are lettered to agree with the list of
parts on the next page.
The power supply uses a large, full-wave
power transformer supplying 7.5 volts from
two separate windings for lighting the rec-
tifier and amplifier tubes. Its priimary is
designed for 105- to i2o-volt, 6o-cycle, lighting
circuits, while a split high-voltage secondary
supplies 550 volts a.c. (r.m.s.) to the plates of the
rectifier tubes. Due to good transformer design,
the ux-2i6-e (cx-3i6-s) rectifier tubes will
deliver from 500 to 530 volts of unfiltered d.c. at
a 106 mA load. This voltage is about all that
may safely be used upon 210 type amplifier tubes
Facts About This Amplifier-™—
Circuit: Single stage push-pull power ampli'
fier
Tubes, TWOCX-JIO (ux-2io) tubes in push-
pull amplifier, two cx-;i6-B (ux-n6-B)
rectifiers, one ex -374 (ux-274) glow tube.
Cost: $83.25, without tubes. (Tubes: $38.50)
This power amplifier is capable of supplying
3 to 4 watts of undistorted power to a loud
speaker. Complete A, B, and C power is ob-
tained directly from the light socket. The
rectifier and filter system are designed to
supply the power amplifier tubes with about
500 volts for the plate and the necessary C
bias. The unit is arranged to replace the
second audio stage in a receiver. The unit is
encased in a nicely finished metal cabinet
after a 4O-voIt drop has been allowed for in thi
filter system. The filter output is about 460 t<
490 volts d.c., of which 35 to 40 are used for (
bias on the amplifier tubes, the remaining 425 t<
450 volts being actual plate potential suppliec
to the push-pull amplifier. The rectifier life wil
be quite good since each ux-2i6-B (cx-3i6-B
is called upon to furnish only 53 mA., while thesi
tubes are actually capable of supplying 65 mA
A single ux-28i (cx^Si) rectifier would delive
nearly the same power output as the two 2i(
type tubes, but the use of a single half-wavi
rectifier, such as the type 281, is generally to bi
discouraged as increasing the filtration problem
and almost invariably resulting in an excessivel)
high value of hum in the loud speaker. Two 281
type rectifier tubes, however, will give a highe:
output than two 2i6-B tubes by about 50 to 6t
volts, and their use is recommended, not so muct
because of the increased power output, but be
cause of their probable longer life due to oxidi
coated filaments and rather generous design.
The filter system is substantially the same a:
is used in the smaller "Unipac," except for th(
use of looo-volt condensers, which are necessary
because of the high voltages used. A combinatior
selective and "brute-force" filter scheme is em-
ployed, resulting in very good filtration at high
current values.
The amplifier stage consists of a split winding
input transformer with a step-up ratio of 3:1 pel
tube, and a split winding output transformei
matching the impedance of the ux-2io (cx-3io)
amplifier tubes to that of a Western Electric 01
similar loud speaker at 30 cycles. The overall volt-
age gain of the amplifier is about 20 to 22 times,
CONSTRUCTION
THE construction of the "Unipac" is quite
simple, involving only the mounting of a
number of standard parts upon a standard steel
chassis, the wiring up of these parts, and the
DECEMBER, 1927
A NEW "TWO-TEN" POWER AMPLIFIER
139
THE POWER AMPLIFIER WHEN COMPLETED
IS HOUSED IN A METAL CABINET
final attaching of the cabinet or ventilated hous-
ing after the unit has been tested. The parts
needed are listed below:
POWER AMPLIFIER
Rectifier Tubes (cx-38[ or ux-a8i
Optional) $15 .00
One ux-274 or cx-374 Ballast Tube . 5 . 50
Two ux-2io or cx-jio Power Tubes 18.00
$38.50
The "Unipac" will furnish ample power to a
radio receiver at 45 and 90 volts with voltage held
constant by a potential dividing resistance and a
glow tube voltage-regulator, preventing high
open-circuit voltages to develop, which might
damage receiver condensers. The amplifier re-
places the conventional second audio stage of a
receiver, the input tipjacks connecting to the
first audio stage output terminals of the receiver,
and the loud speaker connecting to the output
jacks of the "Unipac."
In operation, all tubes will get quite hot, as
will the larger Ward-Leonard resistor. This
is correct, as is a slight warmth noticeable in the
power transformer core. It is necessary always
to see that the B minus post is grounded, directly
or indirectly through a condenser.
POWER TRANSFORMER
AND RECTIFIER
To light socket
110V.60-AC.
Ta — 328 Super Power Transformer
LI — 331 "Unichoke" .....
Ti — 230 Push-Pull Input Transformer
Tj — 23 1 Push-Pull Output Transformer
Five 5 1 1 Tube Sockets .....
Ci, C2, C3, €4, C6 — Type 662 Condenser
Block .........
Rz — 65 1 Resistor (Ward-Leonard) Set
Four Frost 253 Tipjacks ....
Ri — Frost FT64 Balancing Resistance
Van Doom 66 1 Steel Chassis and Cabi-
net, with Hardware .....
Three Eby Binding Posts (B — , +45,
+90) ........
Twenty-Five Feet Kellogg Fabricated
Hook-Up Wire ......
$18.00
8.00
10.00
IO.OO
2.50
18.00
7.00
.60
.50
•45
Unless otherwise noted, all the parts listed
above are manufactured by Silver-Marshall.
The tubes required for the operation of the
"Unipac" are as follows:
Two ux-2i6-e or cx-3i6-B Half-Wave
To
loudspeaker
45 Neg
B
To Set / To A Bat
liiVolt
C Battery
A iyi PUSH-PULL AMPLIFIER
The circuit of the 171 type push-pull amplifier described in the July, 1927, RADIO BROADCAST is given
above. This amplifier is capable of delivering about 2 watts of power to a loud speaker
I
I
Power Transformer
& Rectifier
Loud
Speaker
9045 Neg.
To Receiver
TOO
1 no VAC
Cord & Plug
to Light Socket |
A 210 PUSH-PULL AMPLIFIER
The circuit diagram of the super-power amplifier described in the article given in this illustration. The 55O-volt transformer, T3, at the right, sup-
plies the two rectifier tubes with sufficient voltage so that when it is rectified and filtered each of the power amplifiers will receive about 500 volts each.
A glow tube is incorporated in the circuit to maintain the voltages constant, independent of the load. The loud speaker is fed with energy through
an output transformer.
The Listeners' Point of View
THE DX LISTENER FINDS A CHAMPION
THE DX hound comes in for a lot of un-
warranted disparagement. He is viewed
askance by his more enlightened brethren
as a benighted soul with a perverse idea of what
radio ought to be used for. His greatest delight,
as they picture it, is in attacking his receiving
set with a screw driver and soldering iron, dis-
emboweling it and putting it together a different
way. He is said to prefer the faint whisper of call
letters from some mission station in heathen
Africa to hearing the Prince of Wales sing
Frankie and Johnny from the local station. In
his defense it has been iterated from time to time
that his experimenting made radio what it is
to-day. This vindication seems to us to be still
a pretty sound one.
There are two types of DX hounds, the radi-
cals and the conservatives. The extremists care
for nothing but distance. They will labor into
the small hours of the night to pick up the signal
of a station half a continent away. Their stand-
ard of reception fidelity is not exacting — all they
ask is that the fis be distinguishable from the
Ps. Once they have gained their quarry (which
Mr. Webster describes as "the entrails of the
prey, given to the hounds") their interest is
over and they start in pursuit of some other
station. We are in no special sympathy with this
hunting breed of DX hound, but we will not have
it said that he is quite useless. He has forced an
increase in the range of receiving sets.
But the conservative hound likes to have a
little sport with his catch after he's run it down.
Once he has got a distant station he labors
patiently at tuning it to shut off all extraneous
noises. Not until he has the program coming in
with the clarity of a local one is he satisfied.
Then, if the program is a good one, he listens to
it. With the pleasure he experiences from the
program is an added stimulation in the real-
ization that he is eavesdropping on a scene tran-
spiring some hundreds of miles away with no
connection between him and that remote city
but some great open space and an assortment
of ether waves. If a sympathy with his en-
deavours and an occasional emulation of them
makes us a DX hound, then — we are a DX
hound. Those who advance the protest that
radio is now so much a matter of fact that they
cease to marvel at its wonders present not half so
good a defense of their attitude as they do a
confession of their lack of imagination.
After all, the unique thing about radio is not
that it brings music into your home — the phono-
graph did that years ago — but that it conquers
distance. It was radio's ability to conquer
distance that gave it its initial impetus, that
seized the public imagination and bounded it
along to an unprecedentedly swift success. It
seems a bit of the basest ingratitude — a sort of
biting the hand that feeds you — for radio to turn
its back now on the characteristic that gave it
hirth. And, turning its back on it, it is, what with
its two latest developments: chain broadcasting
and wired broadcasting. Chain broadcasting,
with its extended use of telephone wires has made
the listener in large cities content to receive his
distant programs from a station perhaps a few
blocks away. Wired radio, while it still exists
only as a rumor, is likely to come any time soon.
Here the program will he circulated on the
By JOHN WALLACE
already existing electric power lines which
enter almost every civilized household, and the
program received will have spent no instant of
its life bounding on an ether wave. This seems
to us a distinct retrogression, technically at
least. Of course we do not argue that a trip
through the ether makes a program any better;
under present conditions the wired program is
frequently better in quality. But the one is
genuinely radio, the other simply glorified
telephony. In short, wired radio, and, to a lesser
degree, chain broadcasting, summarily renounce
the fundamental principle upon which radio was
founded — space annihilation.
This renunciation seems to us premature. The
possibilities of radio broadcasting have not been
completely exhausted. Hardly a score of years of
experimentation has been completed. Certainly
the idea is worth a score more.
It may be very practically objected that
atmospheric conditions, over which man has
no control, simply render it impossible to extend
further the range and reliability of radio re-
ception. This is practically true. Theoretically
it is false and since this is a theoretical article
we will press our point further. A demonstrable
increase in range has been effected within the
past few years by increasing the power of
transmitters and the efficiency of receivers.
There has been no sign from heaven to indicate
that this increase has reached its limit. So,
having utterly no knowledge of the mechanical
problems of radio, but an unbounded faith in
the uncanny powers of its technicians we argue
that they can further perfect it if they try.
But if interest in long range broadcasting is
abandoned it's a cinch they won't try.
Radio's unique contribution to what is drolly
referred to as the "progress" of civilization is
the conquering of space. We repeat ourself? As
a follower of radio programs we are well aware
that it has made an enormous contribution to
mankind by making music once again part of
his daily life. In this role it has been of incalcula-
ble benefit. However, this role, important as it is,
DAVID BUITOU'H
The gifted young conductor of the National
Concert Orchestra, regularly heard through the
red network of the National Broadcasting Com-
pany
is none the less a secondary one. It is possible
for a man in his home to survive the evening
without an after dinner concert, but a man at
sea on a ship with a hole in it is dependent upon
radio for his life. The city dweller can go to a
concert hall when he craves music and entertain-
ment, but the dweller at a lonely outpost in
Canada is dependent upon radio for any break
in the monotony of his existence. A catastrophe
such as a cyclone or an earthquake may cut off
wire communication with a devastated area but
radio may still be able to penetrate and convey
important, perhaps life saving, messages. Or,
to cite a fanciful but none the less valid instance
of the primary importance of radio as a long
distance agent: in time of war an invading force
could throttle all wired communication within
the nation but a few well entrenched trans-
mission stations could still reach the entire
populace.
As we have said, further extension of the
range of broadcasting, particularly in the face
of the apparently unsurmountable difficulties
it has already met, is dependent upon a sustained
interest in achieving this end. So we think the
vast army of DX hounds instead of being reviled
should rather be looked upon as a desirable
faction and, an important balancing element in
radio's development.
While, personally, we are most frequently
interested in the musical things radio has to
offer, we look forward to the time when it will
put us in easy touch with foreign shores. Perhaps
some further use will be made of short-wave
broadcasting and reception to this end. There
would be a kick in that which not even the
staunchest deprecator of DX could deny. But
such an entertaining, and indeed instructive,
state of affairs will not have been reached until
after we first overcome the not inconsiderable
distances in our own U. S. If we ever do this it
will be due to the persistency of the DX hounds.
What We Thought of the First
Columbia Broadcasting Program
SUNDAY, the eighteenth of September, wit-
nessed the debut of the long heralded
Columbia Broadcasting System. The even-
ing of Sunday, the eighteenth of September,
witnessed your humble correspondent, tear
stained and disillusioned, vowing to abandon for
all time radio and all its works and pomps. We
have since recovered and will go on with our
story. The broadcast divided itself into three
successive parts, descending in quality with
astounding speed.
PART ONE: THE VAUDEVILLE
This program came on in the afternoon, after
a half hour's delay due to mechanical diffi-
culties— a heinous sin in this day of efficient
transmission, but excusable, perhaps, in a half-
hour-old organization. This opening program, at
least, was auspicious. The performers were of
superlative excellence. Bits from a light opera
were well sung. A quartet gave a stirring ren-
dition of an English hunting song. A symphony
orchestra played some Brahms waltzes. A soloist
sang"Mon Homme" in so impassioned a fashion
DECEMBER, 1927
BAD COMMERCIAL BROADCASTING
141
that she must have swooned on the last note.
Then a dance orchestra concluded the program
with some good playing. The offerings were of
such high quality that it was doubly disconcert-
ing to have them strung together with a shoddy
'"continuity" — especially with such stupid and
overdone continuity as the "and-now-parting-
from-Paris-we-will-journey-to-Germany " type.
Continuity is a device used to bolster up weak
programs. It is a bit of psychological trickery
designed to keep the listeners listening even
while their own good sense tells them that there
is nothing being offered worth listening to. A
good steak doesn't need to be served with sauce,
but there's nothing like some pungent Worcester-
shire for camouflaging the defects of a bad one.
The items offered on this afternoon program were
good enough to serve ungarnished, and were
cheapened by the introductory blah.
PART TWO: THE UPROAR
"Uproar," let us hasten to explain, is Major
J. Andrew White's way of pronouncing Opera.
We seek not to poke fun at this announcer; he
is one of the best we have. (Though we think
both Quin Ryan and McNamee outdid him in
the recent fight broadcast). But his habit of
tacking Rs on the end of words like Americar
and Columbiar doesn't fit into a high-brow
broadcast as well as it does in a sports report.
The Uproar was "The King's Henchmen" by
Deems Taylor. Evidently no effort was spared to
make the broadcast notable. A good symphony
orchestra was utilized, capable singers were
employed, and Deems Taylor himself was in-
trusted with the duty of unfolding the plot. But
after all it was "just another broadcast." Musi-
cal programs into which a lot of talk is injected
simply will not work. One or the other has to
predominate. Either make it a straight recitation
with musical accompaniment — or straight music
with only a sparing bit of interpretative com-
ment.
Mr. Taylor's music for this opera is delightful,
the singing was admirable, but the total effect
was disjointed and unsatisfactory. The composer
outlined the story, but, enthralling as it may be
on the stage, it was impossible to visualize the
action with any degree of vividness from his
words. We felt continually aware that there was
really no action taking place, and the effort at
make believe was too strenuous and detracted
from an enjoyment of the music. It was less
effective, even, than a broadcast from the
regular Opera stage. Here the piece is likely to
be more familiar and it is possible to conjure up
its pantomime from remembrances of perform-
ances seen.
It is our humble and inexpert opinion that
program designers are barking up a wrong tree
and wasting a lot of energy in their unceasing
attempts to fit spoken words into musical pro-
grams. But if they will persist let us suggest that
they are going about the job in a blundering way
with no proper realization of its difficulty. All
present essays in this line fall into two classes:
those which attempt to relate starkly the neces-
sary information in a minimum number of words,
and those which attempt to give a spurious arty
atmosphere by the meaningless use of a lot of
fancy polysyllables.
Neither method works. The first is distracting
and effectively breaks up any mood or train of
thought that may have been induced by the
music. The fancy language system, besides
being obviously nauseating, takes up too much
time.
Program makers may as well realize soon as
later that the simple possession of a fountain
pen doesn't qualify a man for writing "script"
or other descriptive text. It is a job calling for
the very highest type of literary ability and one
that can't be discharged by just anybody on the
studio staff. The properly qualified writer should
be able to state the information tersely, but, with
all the vividness of a piece of poetry. Each word
he uses must be selected because it is full of
meaning, and of just the right shade of meaning.
Any word not actively assisting in building up a
rapid and forceful picture in the listener's mind
must be sloughed off. A further complication:
the words can't be selected because they look
descriptive in type, but because their actual
sound is descriptive. Altogether an exacting job;
it' would tax the ability of a Washington Irving.
It is highly improbable that a genius at writing
this sort of stuff will ever appear; the ether wave
is yet too ephemeral a medium to attract great
writers. But there is no question that scriveners
of some literary pretensions could be secured if
the program builders would pay adequately for
their services. This they will never do until they
realize the obvious fact that the words that
interrupt a program are just as conspicuous as
the music of the program itself. It is incongruous,
almost sacrilegious, to interrupt the superb train
of thought of Wagner or Massenet to sandwich
in the prose endeavours of Mabel Gazook,
studio hostess, trombone player and "script"
writer.
PART THREE: THE EFFERVESCENT HOUR
0 dear ! O dear ! Wbiiber are we drifting !
You have all heard the ancient story of the
glazier who supplied his small son with a sack of
stones every morning to go about breaking win-
dows. Comes now a radio advertiser who deals
in stomach settling salts with a program guaran-
teed to turn and otherwise sour the stomach of
the most robust listener. The Effervescent Hour
was the first commercial offering of the new chain
and far and away the worst thing we ever heard
from a loud speaker. We thought we had heard
bare faced and ostentatiously direct advertising
before, but this made all previous efforts in that
line seem like the merest innuendo. The name of
the sponsoring company's product had been
mentioned ninety-eight times when we quit
counting. An oily voiced soul who protested to be
a representative of the sponsoring company
engaged with announcer White in sundry badin-
age before each number, extolling the virtues of
his wet goods and even going so far as to offer
the not unwilling announcer a sip before the
microphone. Stuck in here and there amidst
this welter of advertising could actually be dis-
covered some bits of program! But such program
material it was. First the hackneyed "To
Spring" by Grieg. Then "Carry Me Back to Old
Virginia." Next some mediocre spirituals fol-
lowed by a very ordinary jazz band and culmi-
nating with a so-called symphony orchestra
which actually succeeded in making the exquisite
dance of the Fee Dragee from the "Nutcracker
Suite" sound clumsy and loutish — no mean
achievement.
One long interruption occured while special
messages were given to soda jerkers the country
o'er, inviting them to enter a prize contest for
the best encomium to the advertiser's wares. But
the most aggravating interruptions were the
frequently spaced announcements: "This is the
voice of Columbia — speaking." This remarkable
statement was delivered in hushed and rever-
ential tones, vibrant with suppressed emotion,
a sustained sob intervening before the last word.
It was positively celestial. We have given a
rather complete resume of this program, but it
may be warranted by the fact that probably not
a dozen people in the country, beside ourself,
heard it. No one not paid to do so, as we are,
could have survived it. Perhaps this indictment
of Columbia's opening performance is unkind in
the light of subsequent offerings. Our stomach
is still unsettled. Furthermore we will not make
use of any of the Effervescent Hour's salts to
settle it!
THIS MONTH'S prize for the ugliest and most
cacophonous coined name plastered on any
troup of radio performers is hereby awarded by
unanimous and enthusiastic vote to wow's pop-
ular entertainers the Yousem Tyrwelder Twins!
A FAMILIAR WBZ-WBZA PROGRAM GROUP
The Hotel Statler Ensemble Group, one of the best of the dinner orchestras in the New England
territory. From left to right: Helen Clapham, Hazel McNamara, Katherine Stang, leader, and
Virginia Birnie
AS IHh
SEES
KY f AU»
Drawing by Fran\!yn F. Stratford
Radio As An Electro-Medical Cure-Ali
THAT electricity plays a considerable role
in the physiological functions is a fact well
known and already extensively investi-
gated. But outside of the area of verified or veri-
fiable observations there is, as in every other di-
vision of science, a penumbra of dubious ideas,
and beyond that lies what Theodore Roosevelt
called, in one of the most apt of phrases, the
lunatic fringe. Roosevelt was concerned with the
field of politics, but politics have no monopoly of
lunatics — nor knaves. The two are frequently
coupled.
1 am forced to these melancholy reflections on
re-reading a newspaper article which was clipped
for me during the summer. Under the caption,
"Metal Lingerie As Radio Shield," it related the
adventures of an afflicted governess in the radio
realm. It seems that for years the lady suffered
from "mysterious burns, bruises, blisters, and
internal pains," which, of course, the doctors
were unable to explain or cure. Thereupon a
learned scientist (non-medical) came to her res-
cue. He subjected the sick woman to extensive
tests, including the effect of ultra-violet, infra-red
and X-rays, as well as short and long radio waves.
She was very sensitive to all these oscillations
and the professor decided that they might be
responsible for her pains. He designed for her
some metal screen lingerie to act as a shield
against the nefarious oscillations. The method
of keeping a ground on this intimate shield, as
the wearer moves about, is not disclosed. Nor,
unfortunately, are the results of the treatment
reported. The article does state, however, that
the afflicted woman, while previously in hospital
near a radio station, heard sounds like the wind
whistling through the shrouds of a ship, she
would awake in the night with pains in her neck
and ears, and hear a "dream-like voice." At this
time she spent ten weeks in an insane asylum
in the hope of being relieved.
There she was probably on the right track, and
the fact that she entered the asylum
voluntarily indicates some degree of
insight, with a favorable prognosis if
the patient came under the care of a
skilled psychiatrist able to give her
the requisite attention. She is almost
certainly a mental case. The fact that
she was bothered in the tests by elec-
trical oscillations proves precisely
nothing. If, as part of her psychosis,
she was convinced that electrical
waves made her ill, she would exhibit
symptoms during any tests in the
course of which she knew or suspected
such waves were being generated.
Even skin maladies may be of hys-
terical origin; this is the modern ex-
planation of the "stigmata" which, in
the Middle Ages, were taken for
crosses printed on the bodies of certain
persons by divine intervention, just
as people might be possessed by devils
through the machinations of Satan.
Both beliefs are still firmly held in
some parts, although their influence
as a whole has decreased inversely
with the spread of scientific ideas.
If radio waves were capable of exerting physi-
ological, effects professional radio workers -in
transmitting stations would certainly manifest
whatever symptoms could result. Spending eight
hours or more each day in an atmosphere where
the field strength is many volts per meter, some
of them, after thirty years, should be lamentably
corroded in sensitive regions. But 1 have never
heard of a radio man quitting a transmitting
station because the waves were hurting him.
I have seen them quit because they did not like
the cooking, or the shape of the superintendent's
nose, or the movies in the near-by town, but not
one of them ever seemed to realize that Hertzian
oscillations were whizzing through him at a
velocity of 186,000 miles a second and might
cause his vital juices to curdle. This seems to me
cogent evidence. While many individuals might
be resistant, surely among some thousand of
exposures a considerable amount of pathology,
definitely traceable to the ether waves, would by
this time have accumulated. As for the pitiably
feeble emanations a few miles from a station,
which cannot even be heard until they are
amplified on a grandiose scale, doing a man any
harm — that chance is about as great as One-
Eyed Connelly's hopes of becoming President of
the United States. And the possibility of benefit-
ing a patient physiologically, save incidentally
through entertainment or education, is equally
large.
But some of the apostles of the late Doctor
Abrams' medical credo know better. One of them
relates in a learned journal of his cult the story
of his efforts to benefit the human race by " Im-
provement in Electronic Diagnostic and Treat-
ment Apparati; Broadcasting Electro-Magnetic
Radio Treatment Waves." He has made his
diagnostic circuit bigger and better, he feels, by
adding "amplifying attachments" as follows:
I. A solenoid with its South attached to the
"HE SUBJECTED THE SICK WO-
MAN TO EXTENSIVE TESTS"
dynamizer and its North connected by wire to
the head-band electrode of the subject, thence,
through subject and grounded plates, to a metal
stob driven two feet into the earth.
2. The South end of diagnostic set is connected
to a second metal stob. These stobs are set eight
or ten feet apart on the magnetic meridian as
ascertained by the compass.
3. A small high-frequency machine for in-
creasing the electric tension to drive all possible
of the radiant force of disease through the diag-
nostic set and subject; and to stimulate the sub-
ject's reflexes so that they will act with their
highest efficiency. . . .
What the "stob" part refers to I cannot say.
The word is not in the dictionary.
But the Doctor continues:
Later I added a one-stage radio amplifier to
the above diagnostic outfit which multiplies its
findings four times. Instead of carrying the wire
leading from the last reflexophone to the head
band of the subject, it is carried to the positive
side of the one stage radio amplifier's transformer
and then a second wire is carried from the nega-
tive side of the amplifier's transformer to the
head-band electrode on the subject.
Now comes the actual radio application of the
idea. A two-stage radio amplifier, according to
the description, is attached to the "master
oscilloclast." The electronic treatment is thus
let loose on the world, first on a small scale:
In the electric store two doors away we secured
specimens for electronic examination of four
people and secured specimens from two people in
a store in the same building with the treatment
instruments. We then made electronic examina-
tions of the six specimens and recorded what in-
fections those people were carrying. After run-
ning the instruments some twenty days, we again
secured specimens from the same people and
made reelectronic examinations. We found that
four of the people were negative of their carried
infections — the other two not quite
negative but their infections had
greatly reduced, showing that only a
few more days of broadcasting would
render them negative.
These experiments proving to us
that infections could be destroyed at
a distance of one hundred fifty (150)
or more feet through air, brick walls,
glass doors, windows, etc., we decided
to broadcast the treatment waves out
for a mile or more. We had made a
five-stage radio-transmitting broad-
casting instrument that multiplied the
eighteen multiplication, of master ma-
chine, by fifteen hundred times mak-
ing a total multiplication of master
machine twenty-seven thousand
(27,000) times— we then had erected
a broadcasting aerial on top of a five
story building and connected by wire
the instruments, oscilloclast, two-stage
amplifier, one treatment short circuit-
ed unit and the five-stage radio-
transmitter to the aerial. We then
started up the instrument. Then we
secured a large radio receiving set
(with loud speaker) from the electric
company and set it up in a seven-
passenger automobile and three of us.
DECEMBER, 1927
A CRYSTAL-CONTROLLED STATION
a skilled electrician and radio mechanic, chauffeur
and myself, tuned at the curb in front of the elec-
'tric company and could hear the working of the
oscilloclast — we then drove five squares and
tuned in and could hear the instrument and at
intermediate points fora little more than a mile,
showing that the treatment waves were being
broadcast a mile or more.
We then secured specimens for electronic
examination from a distance of half a block up to
three miles and from many intermediate points.
The number of specimens secured from begin-
ning of broadcasting, from November i, 1926, to
present date, January 20, 1927, were thirty-
three. We have found that out of that number
twenty-three have been made negative — the
balance, ten, have been greatly reduced, showing
that it will only require a week or ten days further
broadcasting of the treatment waves to render
them negative.
The amplified treatment machines are run by
batteries that are fed from the electric light
socket and will last from four to six months;
otherwise batteries only last a few days. The
five-stage radio-transmitter is also fitted up with
a large battery supplied by electric socket and
it in turn supplies the dry batteries, making the
apparatus very efficient and durable.
... In the last six weeks or more, with broad-
casting outfit we have treated electronically a
population of fifty thousand (50,000) on an
average of two hours per day, making a total
of one hundred thousand (100,000) hours per
day. If the broadcasting electronic treatment
waves have rendered negative two-thirds of the
fifty-thousand (50,000) population and reducing
the other one-third, as was proven in the thirty-
three test cases (two-thirds made negative, one-
third reducing) taken out of the same population
we can readily see the great benefit and per day
value to the people. Giving the value of one dollar
per hour for treatment of each individual (which
is a low tariff fee) we have a total of $100,000.00
per day.
If a transmitter fed from batteries can benefit
the surrounding population to the extent of
$100,000. per day, conceive of the value of a 100-
kw. outfit devoted to the same philanthropic pur-
pose! Why not make it 10,000 kw., while we are at
it? Assuming that the professor's present equip-
ment has a capacity of 20 watts, the io,ooo-kw.
set would be worth §50,000,000,000. a day to the
citizens of the United States, on the valuation
basis assumed in the first place. This is of the
general order of the amount of business trans-
acted in the country in a year. It is clear, there-
fore, that a stupendous wealth producing agency
is in the hands of the electronic practitioner,
which, I suppose, makes him feel very bad.
For my own part, I have some qualms. By
broadcasting these electronic treatments, the
learned Doc cures all the people within reach
of their ailments. But why only the people?
Any such general specific must also be good for
animals. Horses will be cured of the blind stag-
gers, tubercular monkeys will rise from their
beds, sick cockroaches will report at the office fit
for work. The rats, pediculi, and bed-bugs
(Cimex leciularins) may benefit even more than
human beings, who may thereby be crowded off
the earth. I hope that the electronic broadcaster
will consider this aspect of the matter and quiet
my fears if he can.
Some Catalogues
ULLETIN No. i of H. F. Wareing and
Associates, on Modulator Reactors, will
prove of interest to some broadcasting
stations. This company, whose address is 401
Pereles Building, Milwaukee, Wis., is in the
business of supplying apparatus and service to
broadcasting stations. The first bulletin includes
a discussion of modulator reactor design, and a
price list of types stated to be suitable for trans-
mitters from 5o-watt to lo-kilowatt size. The
corresponding currents for which the chokes are
built vary from 0.25 to 5.00 amperes, at d.c.
voltages of 1000-5000. Ten- thirty-, and fifty-
henry reactors are available. Bulletins on other
broadcast station equipment are to be issued by
H. F. Wareing and Associates at intervals, ac-
cording to the announcement reaching us.
The Samson Electric Company of Canton,
Massachusetts, distributes a "Radio Division
Price List" including, besides the usual radio
parts sold to receiver constructors, such items as
microphone input transformers, tube-to-line and
line-to-tube transformers, mixer equipment,
and other specialized broadcast transmitter and
public address material. They have made up a
blueprint showing a small public address system
assembled with their parts. Provision is made for
microphone, radio set, and phonograph pick-up.
There are three 0.25 ampere (filament) tubes,
and apparently the output stage is push-pull,
using 5- or 7.5-watt tubes. On this basis the
volume capacity should approximately equal that
of the Western Electric 3-A size P. A. system.
Design and Operation of Broad-
casting Stations
1 8. Pie^o-Electric Control
THE field of piezo-electric phenomena
includes the generation of electrical po-
tentials in various substances by the
application of physical pressure, and, conversely,
changes in physical dimensions directly corre-
lated with electrical conditions. It is not a new
division of physics; the piezo-electric properties
of quartz, for example, were investigated by P.
and J. Curie in 1889. The effect itself was dis-
covered by the brothers some years earlier.
Prof. W. G. Cady, about eight years ago, began
the work which resulted in the application in the
radio art of crystal frequency control. He re-
ported his investigation of "The Piezo-Electric
Resonator" in the Proceedings of the Institute of
Radio Engineers, Vol. 10, No. 2, April, 1922.
Oscillating crystals are used as frequency stan-
dards in wave meters and monitoring units,
some practical forms much used by broadcasting
stations being those produced commercially by
the General Radio Company. RADIO BROADCAST
has printed two comprehensive articles by M. T.
Dow on crystal circuits and measurement ap-
plications (January and September, 1927). A
direct form of frequency control of particular in-
terest to broadcasters is that in which the trans-
mitter functions as a radio-frequency amplifier,
the master oscillator being a crystal-controlled
tube. Some recent engineering publications on
this aspect include three in the I. R. E. Proceed-
ings: A. Crossley: "Piezo-Electric Crystal-
Controlled Transmitters" (Vol. 15, No. i, Jan.,
1927); A. Meissner: "Piezo-Electric Crystals at
Radio Frequencies" (Vol. 15, No. 4, April, 1927);
and H. E. Hallborg: "Some Practical Aspects" of
Short- Wave Operation at High Power" (Vol. 15,
No. 6, June, 1927). In the present article an
attempt will be made to introduce the subject to
broadcast operators who have not worked with
crystal-controlled transmitters so that when
they are called on to operate such equipment
they will be in possession of some of the elemen-
tary facts.
In itself the use of a crystal is no guarantee of
frequency stabilization to any required degree of
accuracy. Some broadcasters seem to believe
that the use of a crystal in almost any kind of
holder, with some sort of radio-frequency am-
plifier following, will insure constant frequency
radiation. Actually a crystal is of little use unless
Choke
Main Plate Supply
THE CIRCUIT DIAGRAM OF A CRYSTAL-CONTROLLED TRANSMITTER
In actual practice, tubes A and B in the third stage generally consist of two banks of power tubes.
The filaments of only one set of tubes are lighted and they deliver power to the antenna circuit while
the other bank, with the filaments not lighted, acts as a neutralizing circuit to prevent the active bank
from breaking into self oscillation. In operation, if an accident happened to the active bank, the fila
ments could immediately be turned off and the filaments of what was the inactive bank turned on.
The latter bank of power tubes would then deliver power to the antenna while the other bank func-
tioned as a neutralizing condenser
144
RADIO BROADCAST
DECEMBER, 1927
very specific and delicate conditions of operation
are maintained for it.
A piezo-electric substance for radio crystal
control purposes must have certain internal
atomic properties, and it must be hard, durable,
and not easily broken down physically or electric-
ally. Quartz is the best commercial product so
far offered to fill these requirements. The manu-
facture of quartz crystals for radio purposes is a
specialized subject and, as few broadcasters are
likely to attempt grinding their own crystals,
need not be discussed here. The crystal should
be optically ground to oscillate at only one fun-
damental frequency. If the frequency is to remain
constant, the crystal must be maintained under
constant physical conditions as a prerequisite.
This includes an unvarying contact pressure and
temperature. When the temperature changes the
dimensions of the crystal change and the natural
frequency varies proportionately. The crystal
must be kept clean; a drop of oil or water in-
troduced between the holder and the quartz
slab will usually stop oscillations altogether. It
follows that in a broadcasting station installation
the crystals are usually kept in a dust-proof box
whose temperature is thermostatically controlled.
Some commercial crystals, in addition, are sealed
into small individual containers, provided with
lugs designed to slip under binding posts. The
actual contact with the crystal is inside the con-
tainer. If springs or screw clamps are used to
make contact with an open crystal care must be
taken, to secure parallel movement of the metal
surfaces, so that the crystal is not subjected to
pressure on part of its surface and left untouched
elsewhere. A loose contact leads to brushing,
heating, and possible cracking of the crystal. The
capacity of the crystal holder should be small
in order that its piezo-electric variations may
exert the maximum governing effect on the cir-
cuit of which the crystal is a part. It will be noted
that there is some design analogy between the
old-style crystal detector stand and the quartz
crystal holder of a modern tube transmitter;
each has protean forms. Some illustrations of
actual crystal holders will be found with the
RADIO BROADCAST papers mentioned in the
bibliography, and Crossley includes a detailed
description of the contact requirements in his
paper.
The radio-frequency energy in the initial
crystal circuit may amount to a fraction of a
watt, while the final stage may deliver many
thousand watts to the antenna. It is clear that
great care must be taken to prevent feed-back,
parasitic oscillations, and unstable circuit con-
ditions along the line. Under some conditions of
circuit imbalance the crystal is likely to overheat
and be damaged. The transmitter may stop oscil-
lating. In the endeavor to control regeneration
and secure circuit stability, designers have fre-
quent recourse to shielding and neutralization of
successive amplifier stages, and sometimes push-
pull radio frequency amplification is employed,
resulting in a series of balanced circuits anal-
ogous to those of low frequency telephone
practice.
In a crystal-controlled telephone transmitter,
modulation may take place in the final stage or
at an intermediate point after the crystal but
before the final stage. The advantage of modu-
lation at a low power level lies in the possibility
of securing ample modulator capacity relative to
the radio frequency energy to be modulated.
But if, for example, modulation takes place in
one of the earlier stages at a power level of, say,
50 watts, care must be taken not to impair the
audio-frequency characteristic of the transmitter
by cutting of the side bands in successive tuned
stages, and of course the power tubes must have
sufficient capacity to handle the peaks of modu-
lation. The Bell Telephone Laboratories engin-
eers seem to incline toward low power modula-
tion, while the Westinghouse and General Elec-
tric engineers prefer to wait until the full radio
frequency power is developed before impressing
the audio frequency on the carrier.
The power of successive stages depends on
tube characteristics and the use to which the
transmitter is to be put. Crossley shows a i 50-
6oo-kc. telegraph transmitter in which the
crystal controls a y.j-watt tube, which is followed
by a 5O-watt impedance-coupled amplifier, a i-
kw. tuned amplifier stage, and the final 2o-kw.
stage feeding the antenna. These figures and
some others in this paragraph represent the
nominal oscillator ratings of the tubes in ques-
tion; the powers actually developed are generally
less. Meissner mentions a telephone transmitter
in which, after the crystal tube, 5-watt,75-watt,
joo-watt, and j-kw. stages are found, the last
named supplying 3 kw. to the antenna. The Na-
tional Broadcasting Company's Bound Brook
telephone transmitter (made by Westinghouse for
R.C.A.) uses a y.j-watt tube in the crystal stage,
swinging a 2jo-watt tube, followed by two 250*5
in parallel (500 watts) before the final 4O-kw.
bank. Bellmore, built by General Electric for the
N. B. C., uses more stages; the crystal, likewise
governing a y.j-watt tube, is coupled to another
of the same size; then follow a 5o-watter, two
fifty-waiters in parallel (100 watts), a looo-watt
tube, a single 2o-kw. tube run at about a quarter
of its rating, and the final jo-kw. stage. In both
of these American transmitters, plate modulation
of the final power stage is used. In the Bellmore
transmitter the output of the crystal stage is
purposely kept low as one of the design consider-
ations, only about 0.5 watt being generated,
while Crossley mentions getting 21 watts from a
crystal-governed tube of the same type, in one
of the U. S. Navy experiments. This divergence
shows how design calculations determine operat-
ing conditions.
Fig. i is a schematic circuit diagram of a
crystal-controlled telephone transmitter without
the audio amplifier and the power supply to the
modulator and r. f. output stage. The power rat-
ings of the successive stages have been omitted
because, as indicated above, various sizes of
tubes might be employed in such a chain, ac-
cording to the final output required, the tube
characteristics, and other design factors.
The Small Broadcaster
IN A letter of some length, which we should
print in full if the space were available, Mr.
Robert A. Fox, formerly owner and manager
of Station WLBP of Ashland, Ohio, takes me
severely to task for my past animadversions on
incompetent broadcast technicians, which he ap-
parently thinks were aimed exclusively at small
stations, and then goes on to a penetrating dis-
cussion of the small stations' economic problems.
Mr. Fox points out that in arranging high
quality programs the small station is at a dis-
advantage, "for the simple reason that musicians
do not charge you for their time according to the
power of your station, but in accordance with
the number of hours required of them." The ad-
vertiser, on the contrary, will pay more or less
proportionately according to the power. The
members of the station staff are in the same posi-
tion as the musicians. The result is that one man
must sometimes assume the staggering burden
of acting as "station monitor operator, an-
nouncer (doing a nemo job of it), operator; chief
engineer as well as salesman, financier, publicity
agent, and program director," all this with one
assistant. Even then the structure collapses under
the fixed expense, and Mr. Fox concludes, "The
small broadcaster is economically doomed."
But, he insists, the failure is economic, not per-
sonal— "the fellows who have been operating
under 1000 watts have more brains than those
above 1000 watts."
They may not have more brains — nature does
not distribute brains according to antenna watts,
either in direct or inverse ratio — but they cer-
tainly have more courage. And, while economic-
ally they may be sick, they may yet survive, on
some other basis, to see a better day, No one can
say, at this juncture, that the small neighbor-
hood station will not find a place in community
life, with some form of cooperative support, in a
frequency band wherein it can serve local in-
terests without interfering with the large stations
and networks aspiring to national coverage, and
be in turn protected from interference by them.
As to the less material matter of my own atti-
tude toward such enterprises, it is a curious
commentary on our American attitude toward
criticism in general that when a man states
baldly, in public, unpleasant facts about institu-
tions or people, he is immediately suspected of
being hostile to those institutions and people.
That it is his right and duty, once he has set up
as a critic, technical or social, to discriminate be-
tween what he finds good and bad, is a basic fact
not sufficiently recognized among us, in radio and
elsewhere. There is still a lot of bad broadcasting
and incompetent operation going on. No one
with a pair of ears and the tonal discrimination
of a tomcat can think otherwise. There is also a
large and growing element of good showmanship,
efficient operation, and skilled personnel, among
both large and small stations, and 1 have not
been backward in giving credit to those responsi-
ble for such progress. The standards have been
lower among smaller stations, because of the lack
of resources and, sometimes, because of the lack
of time and skilled personnel. All these factors go
together. If a man tries to act as announcer,
engineer, operator, program director, and publi-
city representative of a station he will inevitably
turn out a half-baked job in each capacity. He
may be a hero, but he is not a broadcaster by
1928 standards. One may admire his courage
and still tell him what one thinks of his audio
frequency band and the quality of his sopranos.
As for constructive contributions, I have tried
to do my part by writing technical articles which
are of use largely to the smaller broadcasters, be-
cause the information contained in them is com-
mon property among the operators of the bigger
stations. Let that be weighed against my refusal
to be a member of a cheering squad.
RADIO BROADCAST ADVERTISER
145
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146
RADIO BROADCAST ADVERTISER
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The LYNCH BOOK
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The Radio Broadcast
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not out
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. An index appears twice a year dealing with the sheets
published during that year. The first index appeared on sheets Nos. 47 and 48, in No-
vember, 1926. In July, an index to all sheets appearing since that time was printed.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. I to 88, can be secured from the Circulation Department,
Doubleday, Page & Company, Garden City, New York, for Si oo Some readers have
asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any such errors do appear, a new Laboratory Sheet with the old
number will appear.
— THE EDITOR.
No. 145
RADIO BROADCAST Laboratory Information Sheet December, 1927
Loud Speakers
GENERAL CONSIDERATIONS
nHAS been realized for some time that a large
uiaphragm type of loud speaker is capable of giving
somewhat better frequency response than can be
obtained from a short horn. 1 hese large diaphragm
loud speakers have generally been called cones
because the large diaphragm in most cases takes
the form of a right circular cone.
There are certain essential characteristics which
must be striven for in designing a loud speaker of
this type. ^ hat we desire in the diaphragm is to
obtain a large surface of great stiffness or rigidity
and, at the same time, extreme lightness. If such a
material can be obtained, a very satisfactory loud
speaker could be made consisting simply of a sheet
of the material freely supported at the edge. Such
a material having a high ratio of stiffness divided
by mass is difficult to obtain, and it has been neces-
sary to devise diaphragm shapes which will give the
necessary stiffness and which will still be light. This
is the reason why a cone shape has generally been
used, for it will give the necessary characteristics.
Recently there was described in RADIO BROAD-
CAST the Balsa wood loud speaker, which repre-
sents an attempt to obtain a large flat diaphragm
using a light material, with the required stiffness
obtained through the use of slats radiating from
the center. Because of the extreme lightness of Balsa
wood it is possible to obtain in this way a very high
ratio of stiffness to mass.
It is, of course, essential that any loud speaker,
if it is to radiate sound effectually, be made as light
as possible so as to require only a small amount of
energy to move it. It is desirable that the entire
diaphragm shall move and that the major resis-
tance it encounters, in moving should be that due
to the energy required to move the air about the
diaphragm and set up sound waves in the air.
Any of the available energy that is used for other
purposes represents a loss.
An excellent book, WiVr/rss Loud Speakers, is
published in England by Iliffc and i;ons and writ-
ten by N. W. McLachlan. The author says, in
speaking of cone type loud speakers:
"There is a wide field for rrathematical and ex-
perimental work regarding the behavior of dia-
phragms of various shapes and sizes. By exact
measurement, coupled with analysis, it will be
possible to pave the way to better reproduction
and to evolve a diaphragm with qualities superior
to those now used. Until this is done we must re-
main in ignorance of the action of diaphragms at
various frequencies. The human ear may judge one
diaphragm to be better than another, but it cannot
give exact data."
No. 146 RADIO BROADCAST Laboratory
B Power Device Ch
TYPICAL CURVES
f\N THIS Laboratory Sheet are given a group 450
v of curves, supplied by the Raytheon Manu-
facturing Company, which show how the output
voltage of a typical B power unit varies with the 400
transformer voltage. The circuit diagram of the 375
rectifier and filter system used in making these
tests is given on the curve. The curves apply when 350
a type BH or similar tube is used as the rectifier. ...
These curves indicate the following facts:
(A.) That the slope of all of the curves is the 300
same. This is to be expected because the u ...
slope is determined entirely by the resis-
tance of the circuit, which docs not vary. § 250
(B.) That an increase of 50 volts in the trans- g
former voltage is effective in producing an ,- '
average of 75 volts increase in the output £ 200
voltage. g 176
(c.) That the output voltages of the system
at no load have approximately the same 150
value as the transformer voltages. 125
(D.) That the total resistance of the rectifier-
filter system is about 1340 ohms. (This 100
value is determined by dividing the dif- „
ference of any two voltages on the straight
portion of any one curve by the differ- 50
encc of the corresponding load currents.) 25
The resistance of the choke coils used was
information shee! December, 1927
laracteristics
j|
\
c
T
1;
51
•yL
);
i
-w
I
•
Tv"y3-
' I'
a
v
V
Voltage either
side of Trans,
rve CenlerTap
A 200
B 25C
C 300
D 350
\
s
s
\
S
•»>
Cu
\
V,
**,
*\
)
t
V
^
x.
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VI
*,
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••N
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^
S
V
V.
^
v.
^
^
•s
V,
s
~
N
^.
**
X
*
known to Ix; 600 ohms so lliat tin1 elfcv- ° 10 2o so 40 50 60 70 80 90 100
tive resistance of the rectifier is about LOAD IN MILLIAMPERES
740 ohms.
RADIO BROADCAST ADVERTISER
147
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RADIO BROADCAST ADVERTISER
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No. 147
RADIO BROADCAST Laboratory Information Sheet December 1927
"Gain"
SIMPLE MATHEMATICAL CALCULATION7
'"PHE diagram on this Sheet shows an ordinary
•*• tuned circuit with a source of high-frequency
voltage, e, in series with it. The voltage e can be
considered to be the voltage induced in the tuned
circuit from another coil, the primary of a radio-
frequency transformer for example. This voltage
will cause a current to flow in the tuned circuit
and the ratio of the voltage E, developed across
the entire circuit, to the voltage e, induced in the
circuit, is known as the "gain" of the tuned circuit.
The more efficient the tuned circuit is, the greater
will be the "gain." We will now derive a mathe-
matical expression for the "gain" of a tuned circuit.
The current, I, flowing in a tuned circuit at re-
sonance is:
K
where e = the voltage induced in the circuit and
R = resistance of the circuit. The current flowing
through the inductance coil, L, generates a potential
across the coil, determined as follows:
E = wLI (2.)
where d> = 6.28 times the frequency of the current,
L = inductance of coil in henries, and I has the
same meaning as in equation (1.) Substituting in
equation (2.) the value for I given in equation (1,)
we have:
and dividing through by e we get:
But, as stated previously, the ratio of E to e is
the gain of the circuit. Therefore:
,, .
Gam =
(4.)
This final expression indicates that, to obtain
greatest efficiency from a tuned circuit, it is essen-
tial that the ratio of the inductance reactance (toL)
to the resistance of the coil should be made as large
as possible.
E =
(3.)
No* 148 RADIO BROADCAST Laboratory Information Sheet December, 192?
An A. C. Audio-Frequency Amplifier
WHAT PARTS TO USE
'"PHE introduction of the new a. c. tubes makes
-*• possible the construction of an a. c. audio
amplifier with the necessary A, B, and C voltages
supplied directly from the light socket. The list
of parts necessary to construct such an amplifier
is given on this Sheet. The circuit diagram is given
on Laboratory Sheet No. 149.
An amplifier of this type is well suited for use
with a small receiver consisting of one or more stages
of radio- frequency amplification and a detector.
The circuit has been so designed that B voltages
for the r. f. and detector tubes can be obtained
from the audio amplifier device.
The following parts are necessary to construct
this amplier:
A — A. C. Tube, Type ux-226 (cx-326) or Equiva-
lent.
B — ux-171 (cx-371) or Equivalent.
TI, TT — Two High-Quality Audio Transformers.
Ts — Filament-Lighting Transformer to Supply
Tube A.
T^ — Power-Supply Transformer Designed for use
in 171 Type B Power Units.
Li, L-r— Filter Choke Coils.
Ls — Output Choke Coil.
Ci, G> — 1-Mfd. Bypass Condensers.
C3, C*— 2 Mfd. Filter Condensers.
Cs — 4-Mfd. Filter Condenser.
C6, C7, Cg— 1-Mfd. Filter Condensers.
Cfl — 2-4-Mfd. Fixed Condenser.
RI — 30-Ohm Center-Tapped Resistance.
Rs— 1500-Ohm Fixed Resistance Capable of Carry-
ing 4 mA.
R; — 2000-Ohm Fixed Resistance Capable of Carry-
ing 20 mA.
R4 — -Tapped Resistance for Use in Output of B
Power Units.
In wiring this amplifier, be sure to twist the fila-
ment leads to the two tubes, to prevent hum. C
bias for the first tube, A, is obtained from resis-
tance Ra, and resistance Rj supplies the output
tube with grid bias.
The input terminals of the amplifier should con-
nect to the output of the detector tube, terminal
No. 1 connecting to the plate and terminal No. 2
to the detector B plus.
To prevent hum it is essential that the negative
B be carefully grounded.
No* 149 RADIO BROADCAST Laboratory Information Sheet December, 1927
Circuit Diagram of an A. C. Audio Amplifier
Here is the circuit diagram of an alia. c. audio amplifier. The list of parts is given on Sheet No. 148.
RADIO BROADCAST ADVERTISER
149
Silent
Magic
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ever you will. Turn the dial
and your attentive ear does
the rest. That is all there is
to this magic of radio.
Or almost all. If a radio
set is to work at its very best,
attracting no attention to
itself, creating for you the
illusion that can be so con-
vincing, you must pay a
little attention to the kind
of power you give it. There
is but one direction, a
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Direct Current. Any other
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Radio Batteries
Radio is better with Battery Power
±-they last longer
radio set may put a hum
into the purest note of a
flute, a scratch into the song
of the greatest singer, a
rattle into the voice of any
orator.
Don't tamper with tone.
Beware of interfering with
illusion. Power that reveals
its presence by its noise is
like a magician's assistant
who gives the trick away.
Use batteries — use the Ever-
eady Layerbilt "B" Battery
No. 486, the remarkable
battery whose exclusive,
patented construction makes
it last longest. It offers you
the gift of convenience, a
gift that you will appreciate
almost as much as you will
cherish the perfection of
reception that only Battery
Power makes possible.
NATIONAL CARBON CO., INC.
New York 1 1 1 ^ ^ San Francisco
Unit of Union Carbide and Carbon Corporation
Tuesday night is Evcready Hour
Night — 9 P. M., Eastern Standard
Time
WEAF-JVeir York
WJAR-Prowdence
WEEI-Bosron
Wl-Phitadelphia
\fGK-Buffalo
WCAE-Pittsburgh
WOC- Davenport
KSD-Sf. Lout,
WSAI-flncinnali
WWJ— Detroit
WCN-CMcago
t. Paul
WDAF-Konsns City
\iRC.-Washington
\fGY-Schenectady
id WHAS-Louist>i/(e
•VSa-Atlanta
WSM-lVashville
•WMC-Memphis
Pacific Coast Stations —
9 P. M., Pacific Standard Time
KPO-KGO— Kan Francisco
KFOA-KOMO-S<.a((/e
KFI-tns Angeles
KG-W-Portland
T h
air is full of things you should n't miss
150
RADIO BROADCAST ADVERTISER
tomatic rower
Gbntfo
FOR
CHRISTMAS
The gift of gifts for the
set owner.
Makes radio more con-
venient because it hand-
les the switching of the
trickle charger and B
eliminator automatic-
ally. Controls charger
or eliminator separately
or both in combination.
When the set is turned
on the trickle charger is
cut out and the B elim-
inator is switched in.
When the set is turned
off the trickle charger is
cut in and the B elim-
inator is switched off.
Better reception and
greater satisfaction are
assured. The A battery
is charging when the set
is not in use. It is always
ready with plenty of
kick when the set is
turned on. The B elim-
inator is on only when
the set is in use; the
tubes last longer and
give better service, and
there is no waste of
power.
No. 444 — Series Type
#5.00
YAXLEY MFG. CO.
Dept. B
9 So. Clinton St., Chicago
No. 150
RADIO BROADCAST Laboratory Information Sheet
Oscillation Control
December, 1927
THE USE OF NEUTRALIZATION
TT HAS been pointed out many times that an or-
•*• dinary three-element tube has an inherent ten-
dency to oscillate due to the feed-back that occurs
from the plate circuit to the grid circuit through the
grid-plate capacity, indicated by dotted lines in
the accompanying diagram. This diagram repre-
sents the circuit of a single-stage of tuned radio-
frequency amplification, using the Rice system of
neutralization, and the following explanation will
make clear why the tube tends to oscillate and why
the tendency to oscillate can be overcome by using
some system of neutralization.
When a tube acts as an amplifier, the voltage
developed in the plate circuit is greater than the
voltage originally impressed on the grid circuit
and, consequently, if the plate circuit is coupled
to the grid circuit in any manner whatsoever, cur-
rent will tend to flow from the point of high poten-
tial, that is the plate, to a point of lower potential,
in this case the grid. If this current flowing to the
grid circuit has the same phase as the original sig-
nal impressed on the grid, then the grid voltage
will become somewhat greater and will be equal to
the original signal in the grid circuit plus the volt-
age induced in the grid circuit from the plate. An
increase in the grid voltage again produces an in-
crease in plate voltage which in turn reacts back
on the grid until the voltage is increased to a point
where the losses in the circuit are overcome, and
then the tube breaks into continuous oscillation.
It should be evident that if we can place in the
circuit some device that will impress a potential
on the grid kind ot an eqisjal and opposite to that
caused by the coup'mg between the grid and
plate, then the resu.tant effect will be zero and
the tendency for the circuit to build up and break
into continuous oscillatkwi will be nullified. The
Rice system of neutralization is one way of doing
this, the circuit foi which is shown in the accom-
panying diagram. The grid-plate capacity is ^hown
in dotted lines and this is the capacity through
which current flows from the plate to the grid cir-
cuit and which ordinarily ca\Bes the tube to oscil-
late. This caoacity is neutralized in the Rice sys-
tem by connecting condenser Cn as indicated.
Grid Plate Capacity
; ir-
No. 151
RADIO BROADCAST Laboratory Information Sheet December. 1927
Single-Control
BOOSTING SENSITIVITY
LABORATORY Sheet No. 33, October, 1926,
some facts were given regarding the tandem
tuning of several condensers, to decrease the number
of controls. It was pointed out that, to obtain
single control, it is necessary to overcome the
effect of the antenna circuit in some manner,
and that a common method of doing this is as in-
dicated in sketch A on this Sheet. The owner of a
receiver of this type may greatly increase its sen-
sitivity by connecting a variometer between the
antenna and ground posts as indicated in sketch
B. This, of course, adds one more control to the set
but in those cases where greater sensitivity is neces
sary, the additional control is justified.
The increase in sensitivity that results when the
variometer is used in the antenna circu't is due to
the fact that it brings the antenna into resonance
with the signals being received and the resultant
gain in amplification is practically equal to that
which would be obtained from an additional stage
of radio- frequency amplification.
In some cases when thir, variometer is usea, i-
will be found that the receiver tends to oscillate,
or actually does oscillate, when all of the circuits
are brought into resonance. Fortunately, however,
most single-control receivers have a volume control
in the radio- frequency system and it will be found
that, by cutting down the volume control, :. ooint
will be reached where the set will stop oscilliting
and usually the actual volume obtained with the
antenna circuit tuned will be rrnch greater than
that obtained before with the volume control turned
to the "maximum" position. The tendency of the
circuit to oscillate can also be lessened by some-
what decreasing the r. f. plate voltage.
Ist.R.F.
2nd. R.F.
No. 152
RADIO BROADCAST Laboratory Information Sheet December, 1927
Speech
SOURCES OF INFORMATION
nature of speech has be?n the subject of
many scientific inquiries and many of the in-
vestigations in connection with speech have been
recorded in various scientific journals.
Back in 1873, Alexander Graham Bell, familiar
to us as the inventor of tne telepnone, did con-
siderable work in analyzing speech and in "de-
vising methods of exhibiting the vibrations of
sounds opticallly," and much of the recent research
has been done by engineers and physicists associated
with the laboratories of the telephone companies.
A bibliography is given below of some of the im-
portant articles and books on the subject with
which we are familiar. This bibliography is by no
means complete in itself but if the references given
are studied it will be found that some of them con-
tain many references to other papers on the sub-
ject. I. B. Crandall's article, in the October, 1925,
Bell System Technical Journal, in particular, con-
tains about twenty-six references to other sources
of information on speech and related subjects.
REFERENCE SOURCES
Bell System Technical journal
C. F. Sacia and C. J. Beck; "The Power of Fun-
damental Speech Sounds." July, 1926.
I. B. Crandall: "Sounds of Speech." October,
1925.
C. F. Sacia: "Speech Power and Energy." Oct-
ober, 1925.
Irving B. Crandall: "Dynamical Study of the
Vowel Sounds." January, 1927.
C. R. Moore and A. S. Curtis: "An Analyzer
for the Voice Frequency Range." April, 1927.
Journal of the American Institute of Electrical
Engineers
Jones; "The Nature of Language." April, 1924.
Martin and Fletcher: "High-Quality Transmission
and Reproduction of Speech and Music:" March.
1924.
Maxfield and Harrison: "Method of High
Quality Recording and Reproducing of Music and
Speech Based on Telephone Research." March,
Books
Miller: Science of Musical Sounds. Second Edi-
tion. Macmillan.
Sabine: Collected Papers on Acoustics. Harvard
University Press.
RADIO BROADCAST ADVERTISER
151
great improvements
in radio power have been
TJ || •- _
Balkite
« A » Contains no bat-
A ftrj,The,.me
as Ballcite " AB," but for the " A"circuit
only. Enables owners of Ballcite "B" to
make a complete light socket installa-
tion at very low cost. Price $35.00.
Rallcite "B"
JjaiKllC Lt est i,vej devices
in radio. The accepted tried and proved
light socket "B" power supply. The
first Balkite "B," after 5 years, is still
rendering satisfactory service. Over
300,000 in use. Three models: "B"-W,
67-90 volts, $22.50; "B"-i35,* 135
volts, $35.00; "B"-i8o, 180 volts,
$42.50. Balkite now costs no more than
the ordinary "B" eliminator.
Balkite Chargers
Standard for ''A" batteries. Noiseless.
Can be used during reception. Prices
drastically reduced. Model "J,"* rates
2.5 and .5 amperes, for both rapid and
trickle charging, $17.50. Model "N"*
Trickle Charger, rate .5 and .8 am-
peres, $9.50. Model "K" Trickle
Charger, $7.50.
*Spedal models for 25-40 cycles at
slightly higher prices. Prices are higher
West of the Rockies and in Canada.
THIRST noiseless battery charging.
i Then successful light socket "B"
power. Then trickle charging. And to-
day,mostimportantofall,Balkite"AB,"
a complete unit containing no battery
in any form, supplying both "A" and
"B" power directly from the light sock-
radio dealer Balkite is a synonym for
quality.
Because the electrolytic rectification
developed and used by Balkite is so re-
liable that today it is standard on the
signal systems of most American as well
as European and Oriental railroads . It is
et, and operating only while the set is this principle that does away with the
in use. The great improvements in ra- necessity of using tubes for rectifying
dio power have been made by Balkite. current — that makes all Balkite Radio
The famous
Balkite electrolytic principle
This pioneering has been important.
Yet alone it would never have made Bal-
kite one of the best known names in
radio. Balkite is today the established
leader because of Balkite performance
in the hands of
its owners.
Because with
2,000,000 units
in the field Bal-
kite has a record
of long life and
freedom from
trouble seldom
equalled in any
industry.
Because the
first Balkite "B,"
purchased 5 years
ago, is still in use.
Because to your
"AB" Contains no battery.
A complete unit, replacing both "A" and "B" bat-
teries and supplying radio current directly from
the light socket. Contains no battery in any form.
Operates only while the set is in use. Two models:
"AB" 6-135,* 135 volts "B" current, $64.50;
"AB" 6-180, 180 volts, $74.50. Special model for
Radiola 28, $63.50.
Power Units, including the new Balkite
"A" and "AB," permanent equipment
with nothing to wear out or replace.
Balkite has pioneered — but not at
the expense of the public.
Radio power
with batteries or without
Today, whatever
type of radio set
you own, what-
ever type of pow-
er equipment you
want (with bat-
teries or without)
Balkite has it.
And production
is so enormous
that prices are as-
tonishingly low.
Your dealer will
recommend the Bal-
kite equipment you
need for your set.
FANSTEEL PRODUCTS COMPANY, INC., NORTH CHICAGO, ILLINOIS
Licensees for Qermany:
Siemens & Halske, A. G. Wernerwerk M
Siemensstadt, Berlin
Sole Licensees in the United Kingdom:
Messrs. Radio Accessories Ltd., 9-13 Hythe Rd.
Willesden, London, N. W. 1O
RdJlSTEEL 1
Balkite
o Tower Units
152
RADIO BROADCAST ADVERTISER
Perfect Radio Parts
for Discriminating
Set Builders
The BRADLEYUNIT-A
is a fixed resistor that is molded and
heat-treated under high pressure. It
does not rely on glass or hermetic
sealing for protection against mois-
ture. Is not affected by temperature,
moisture, or age. The ideal fixed
resistor for B-eliminator hookups.
i The BRADLEYOHM-E
• is standard
I
equipment
for accu-
rate plate
voltage
control on
many lead-
ing B-elim-
inators.
Scientifi-
cally-treated discs in the Bradley-
ohm-E provide noiseless, stepless
plate voltage control.
The BRADLEYLEAK
A vari-
able grid
leak that
provides
perfect
grid leak
adjust'
m e n t ,
thereby
provid-
ing the
best possible results with any tube.
The BRADLEYSTAT
The ideal
f i lament
control.
Gives noise-
less, stepless
control for
all tubes.
Can be easi-
ly installed
in place of wire wound rheostats,
When you build a set or B-elimina-
tor, demand Allen -Bradley Perfect
Radio Resistors to secure best results
• Electric Controlling Apparatus
• 27SGr«D(ieldAve. [fvD | Milwaukee. Wii
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
ID EADERS may obtain any of the booklets listed below by use*
*^- ing tbe coupon printed on page 168. Order by number only.
1. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS— A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
4. RESISTANCE-COUPLED AMPLIFIERS — A general dis-
cussion of resistance coupling with curves and circuit dia-
grams. COLE RADIO MANUFACTURING COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
6. B-ELIMINATOR CONSTRUCTION — Constructional data
on how to build. AMERICAN ELECTRIC COMPANY.
7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-
TION— Circuit diagrams and discussion. ALL-AMERICAN
RADIO CORPORATION.
8. RESISTANCE UNITS— A data sheet of resistance units
and their application. WARD-LEONARD ELECTRIC COMPANY.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
1 1. RESISTANCE COUPLING — Resistors and their ap-
plication to audio amplification, with circuit diagrams.
UBJUR PRODUCTS COMPANY.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
1 5. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE CONDENSERS — -A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their application to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
•17. BAKEUTE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
19. POWER SUPPLY — A discussion on power supply with
particular reference to lamp-socket operation. Theory
and constructional data for building power supply devices.
ACME APPARATUS COMPANY.
20. AUDIO AMPLIFICATION — A booklet containing data
on audio amplification together with hints for the construc-
tor. ALL AMERICAN RADIO CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE-
METER — Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
Eoshions in the circuit where audio- frequency chokes may
e used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio- frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED.
51. SHORT-WAVE RECEIVER — Constructional data on a
receiver which, -by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY— A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL. INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA— Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. RESISTANCE COUPLING — A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION.
60. RESISTORS— A pamphlet giving some technical data
on resistors which are capable of dissipating considerable
energy; also data on the ordinary resistors used in resistance-
coupled amplification. THE CRESCENT RADIO SUPPLY
COMPANY.
62. RADIO-FREQUENCY AMPLIFICATION — Constructional
details of a five-tube receiver using a special design of radio-
frequency transformer. CAMFIELD RADIO MFG. COMPANY.
63. FIVE-TUBE RECEIVER — Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
64. AMPLIFICATION WITHOUT DISTORTION — Data and
curves illustrating the use of various methods of amplifica-
tion. ACME APPARATUS COMPANY.
66. SUPER-HETERODYNE — Constructional details of a
seven-tube set. G. C. EVANS COMPANY.
70. IMPROVING THE AUDIO AMPLIFIER— Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used.
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM— A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY.
80. FIVE-TUBE RECEIVER — Data are given for the con-
struction of a five-tube tuned radio-frequency receiver.
Complete instructions, list of parts, circuit diagram, and
template are given. ALL-AMERICAN RADIO CORPORATION.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
, 82. SIX-TUBE RECEIVER — A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams,
and templates for the construction and assembly of socket
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Panel layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequency
transformers of special design. KARAS ELECTRIC COMPANY.
85. FILTER— Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A socket
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimental
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blueprint and necessary
data, for building an eight-tube receiver. THE GEORGE W.
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER — Data and blue prints
are given on the construction of a short-wave transmitter,
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES.
oo. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification are
given. ALDEN MANUFACTURING COMPANY.
93. B-SOCKET POWER — A booklet giving constructional
details of a socket-power device using either the BH or 313
type rectifier. NATIONAL COMPANY, INCORPORATED.
94 POWER AMPLIFIER — Constructional data and wiring
diagrams of a power amplifier combined with a B-supply
unit are given. NATIONAL COMPANY, INCORPORATED.
ipo. A, B, AND C SOCKET-POWER SUPPLY — A booklet
giving data on the construction and operation of a socket-
power supply using the new high-current rectifier tube.
THE Q. R. S. Music COMPANY.
101. USING CHOKES — A folder with circuit diagrams of
the more popular circuits showing where choke coils may
be placed to produce better results. SAMSON ELECTRIC
COMPANY.
ACCESSORIES
22. A PRIMER OF ELECTRICITY — Fundamentals of
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
25. ELECTROLYTIC RECTIFIER — Technical data on a new
type of rectifier with operating curves. KODEL RADIO
CORPORATION.
26. DRY CELLS FOR TRANSMITTERS — Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS—Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE— Battery life curves with general
curves on tube characteristics. BURGESS BATTERY COM-
PANY.
29. How TO MAKE YOUR SET WORK BETTER — A non-
technical discussion of general radio subjects with hints on
how reception may be bettered by using the right tubes.
UNITED RADIO AND ELECTRIC CORPORATION.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
31. FUNCTIONS OF THE LOUD SPEAKER — A short, non-
technical general article on loud speakers. AMPLION COR-
PORATION OF AMERICA.
32. METERS FOR RADIO — A catalogue of meters used in
radio, with connecting diagrams. BURTON-ROGERS COM-
PANY.
33. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
34. COST OF B BATTERIES — An interesting discussion
of the relative merits of various sources of B supply, HART-
FORD BATTERY MANUFACTURING COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. CHOOSING THE RIGHT RADIO BATTERY — Advice on
what dry cell battery to use; their application to radio,
with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR — Information on the care of
vacuum tubes, with notes on how and when they should be
reactivated. THE STERLING MANUFACTURING COMPANY.
54. ARRESTERS— Mechanical details and principles of the
vacuum type of arrester. NATIONAL ELECTRIC SPECIALTY
COMPANY.
55. CAPACITY CONNECTOR — Description of a new device
for connecting up the various parts of a receiving set, and
at the same time providing bypass condensers between the
leads. KUR/-KASCH COMPANY.
(Continued on page 168)
RADIO BROADCAST ADVERTISER
153
Vital Factors
in attaining
High Quality Reproduction
High quality reproduction depends upon three things:
correctly designed coupling units, proper use of ampli-
fier tubes, and an efficient reproducing device.
For over a decade the subject of audio frequency
amplification has been extensively studied in the labora-
tories of the General Radio Company with particular
attention given to the design of coupling units.
As a result of this exhaustive research the General
Radio Company has been, and is, the pioneer manufac-
turer of high quality Audio Transformers, Impedance
Couplers, and Speaker Filters.
The latest contribution to quality amplification is the
type 441 Push-Pull Amplifier, which is mounted on a
The Type 285 transformers give high nickel finished metal base-board and is completely wired.
and even amplification of a!) tones *
If the amplifier of your receiver is not bringing out
the rich bass notes and the mellow high tones as well as
those in the middle register why not rebuild your ampli-
fier for Quality Reproduction with General Radio coupling
Type 285
Audio Transformer
common to speech, instrumental, and
vocal music. Available in two ratios.
Type 285-H Audio Transformer.
Price $6.00
Type 285-D Audio Transformer.
Price $6.00
Type 367
Output Transformer
This unit adapts the impedance of
an audio amplifier to the input of any
cone type speaker, thus promoting
better tone quality and protecting the
speaker windings against possible dam-
age from A. C. voltages. Similar in
appearance to the Type 285.
Type 367 Output Transformer.
Price $5.00
units r
Write for our Series A of amplification booklets de-
scribing various amplifier circuits and units.
GENERAL RADIO COMPANY
Cambridge, Mass.
Type 373
Double Impedance
Coupler
Many prefer the impedance coupling
method of amplification to resistance
coupling as lower plate voltages may
be used and greater amplification may
be obtained. The Type 373 is con-
tained in a meta! shell and connected
in a circuit in precisely the same man-
ner as a transformer.
Type 373 Double Impedance Coupler.
Price $6.50
Type 387 -A
Speaker Filter
The Type 387-A consists of an in-
ductance choke with condenser. It
offers a high impedance to audio fre-
quency current and forces these cur-
rents to pass through a condenser into
the speaker, thereby improving tone
quality and protecting the speaker
windings.
Type 387-A Speaker Filter.
Price $6.00
Type 441 Push-Pull Amplifier
The Type 441 is completely wired and consists of two high quality push-pull trans-
formers, with necessary sockets and resistances mounted on a nickel finished metal
base board. It may be used with any power or semi-power tube to increase the un-
distorted output of the amplifier with the result that better quality is reproduced from
the loudspeaker with more volume than is obtained from other methods of coupling.
Licensed by the R. C. A. and through terms of the license may be sold with tubes only.
Type 441 Push-Pull Amplifier Price $20.00
Type UX-226 or CX-326 Amplifier Tube •• 3.00
Type UX-I7I or CX-37I Amplifier Tube " 4.50
Type 445 Plate Supply and Grid Biasing Unit
1 he Type 445 meets the demand for a thoroughly dependable light socket plate
supply and grid biasing unit that is readily adaptable to the tube requirements of any
standard type of receiver. Any combination of voltages from o to 100 may be taken
from the adjustable "B" voltage taps. A variable grid bias voltage from o to 50 is
also available. The unit is designed for use on 105 to 125 volt (50 to 60 cycle) A. C.
lines and uses the UX-28O or CX-3KO rectifier tube.
Licensed by R. C. A. and through terms of the license may be sold with tube only.
Type 445 Plate Supply and Grid Biasing Unit Price $55.00
Type UX-;8o or CX-38o Rectifier Tube " 5.00
ENERAl
LABORATORY EQUIPMENT
Parts and Accessories
154
RADIO BROADCAST ADVERTISER
"RADIO BROADCASTS" DIRECTORY OF
MANUFACTURED RECEIVERS
<J A coupon will be found on page 172. All readers who desire additional
information on the receivers listed below need only insert the proper num-
bers in the coupon, mail it to the Service Department of RADIO BROADCAST,
and full details will be sent. New sets are listed in this space each month.
KEY TO TUBE ABBREVIATIONS
99 — 60-mA. filament (dry cell)
01 -A — Storage battery 0.25 amps, filament
12 — Power tube (Storage battery)
71 — Power tube (Storage battery)
16-B — Half-wave rectifier tube
80— Full-wave, high current rectifier
81 — Half-wave, high current rectifier
Hmu — High-Mu tube for resistance-coupled audio
20— Power tube (dry cell)
10 — Power Tube (Storage battery)
00-A — Special detector
13 — Full-wave rectifier tube
26 — Low-voltage high-current a. c. tube
27— Heater type a. c. tube
DIRECT CURRENT RECEIVERS
NO. 424. COLONIAL 26
Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One to
three dials. Volume control: antenna switch and poten-
tiometer across first audio. Watts required: 120. Con-
sole size: 34 x 38 x 18 inches. Headphone connections.
The filaments are connected in a series parallel arrange-
ment. Price $250 including power unit.
NO. 425. SUPERPOWER
Five tubes: All 01-A tubes. Multiplex circuit. Two
dials. Volume control: resistance in r. f. plate. Watts
required: 30. Antenna: loop or outside. Cabinet sizes:
table, 27 x 10 x 9 inches; console, 28 x 50 x 21. Prices:
table, $135 including power unit; console, $390 includ-
ing power unit and loud speaker.
A. C. OPERATED RECEIVERS
NO. 508. ALL-AMERICAN 77, 88, AND 99
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Rice neutralized t. r. f. Single drum
tuning. Volume control: potentiometer in r. f. plate.
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,
25 x 38 x 18 inches; No. 99 console,'27j x 43 x 20 inches.
Shielded. Output device. The filaments are supplied
by means of three small transformers. The plate supply
employs a gas-filled rectifier tube. Voltmeter in a. c.
supply line. Prices: No. 77, $150, including power unit;
No. 88, $210 including power unit; No. 99, $285 in-
cluding power unit and loud speaker.
NO. 509. ALL-AMERICAN "DUET"; "SEXTET"
Six tubes; 2 t. r. f. (99), detector (99), 3 transformer
audio (99 and 12). Rice neutralized t.r.f. Two dials.
Volume control: resistance in r.f. plate. Cabinet sizes:
"Duet," 23 x 56x16} inches; "Sextet," 22}x 13} x 15}
inches. Shielded. Output device. The 99 filaments are
connected in series and supplied with rectified a.c.,
while 12 is supplied with raw a.c. The plate and fila-
ment supply uses gaseous rectifier tubes. Milliammeter
on power unit. Prices: "Duet," $160 including power
unit; "Sextet," $220 including power unit and loud
speaker.
NO. 511. ALL-AMERICAN 80, 90, AND 115
Five tubes; 2 t.r.f. (99). detector (99), 2 transformer
audio (99 and 12). Rice neutralized t.r.f. Two dials.
Volume control: resistance in r.f. plate. Cabinet sizes:
No. 80, 231 x 12} x 15 inches; No. 90, 37} x 12 x 12}
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi-
vidually shielded. Output device. See No. 509 for
power supply. Prices: No. 80, $135 including power
unit; No. 90, $145 including power unit and compart-
ment; No. 115, $170 including power unit, compart-
ment, and loud speaker.
NO. 510. ALL-AMERICAN 7
Seven tubes; 3 t.r.f. (26). 1 untuned r.f. (26), detector
(27), 2 transformer audio (26 and 71). Rice neutralized
t.r.f. One drum. Volume control: resistance in r.f.
plate. Cabinet sizes: "Sovereign" console, 30} x 60}
x 19 inches; "Lorraine" Hiboy, 25} x 53j x 17J inches;
"Forte" cabinet, 25} x 13} x 17} inches. For filament
and plate supply: See No. 508. Prices: "Sovereign"
$460; "Lorraine" $360; "Forte" $270. All prices include
power unit. First two include loud speaker.
NO. 401. AMRAD AC9
Six tubes; 3 t.r.f. (99), detector (99), 2 transformer
(99 and 12). Neutrodyne. Two dials. Volume control:
resistance across 1st audio. Watts consumed: 50. Cabi-
net size: 27 x 9 x 11J inches. The 99 filaments are con-
nected in series and supplied with rectified a.c., while
the 12 is run on raw a.c. The power unit, requiring two
16-B rectifiers, is separate and supplies A, B, and C
current. Price $142 including power unit.
NO. 402. AMRAD ACS
Five tubes. Same as No. 401 except one less r.f.
stage. Price $125 including power unit.
NO. 536. SOUTH BEND
Six tubes. One control. Sub-panel shielding. Binding
Posts. Antenna: outdoor. Prices: table, $130, Baby
Grand console, $195.
NO. 537. WALBERT 26
Six tubes; five Kellogg a.c. tubes and one 71. Two
controls. Volume control: variable plate resistance.
Isofarad circuit. Output device. Battery cable. Semi-
shielded. Antenna: 50 to 75 feet. Cabinet size: 10} x
SH x 16J inches. Prices: $215; with tubes, $250.
NO. 484. BOSWORTH, B5
Five tubes; 2 t.r.f. (26), detector (99), 2 transformer
audio (special a.c. tubes). T.r.f. circuit. Two dials^
Volume control: potentiometer. Cabinet size: 23 x 7
x 8 inches. Output device included. Price $175.
NO. 406. CLEARTONE 110
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All tubes a. c. heater type. One or two dials. Volume
control: resistance in r. f. plate. Watts consumed: 40.
Cabinet size- varies. The plate supply is built in the
receiver and requires one rectifier tube. Filament sup-
ply through step down transformers. Prices range from
$175 to $375 which includes 5 a.c. tubes and one rectifier
tube.
NO. 407. COLONIAL 25
Six tubes; 2 t. r. f. (01-A), detector (99), 2 resistance
audio (99). 1 transformer audio (10). Balanced t.r.f.
circuit. One or three dials. Volume control: Antenna
switch and potentiometer on 1st audio. Watts con-
sumed: 100. Console size: 34 x 38 x 18 inches. Output
device. All tube filaments are operated on a. c. except
the detector which is supplied with rectified a.c. from
the plate supply. The rectifier employs two 16-B tubes.
Price $250 including built-in plate and filament supply.
NO. 507. CROSLEY 602 BANDBOX
Six tubes; 3 t.r.f. (26), detector (27), 2 transformer
audio (26 and 71). Neutrodyne circuit. One dial,
Cabinet size: 17J x 5} x 7| inches. The heaters for the
a.c. tubes and the 71 filament are supplied by windings in
B unit transformers available to operate either on 25 or
60 cycles. The plate current is supplied by means of
rectifier tube. Price $65 for set alone, power unit $60.
NO. 408. DAY-FAN "DE LUXE"
Six tubes; 3 t.r.f., detector, 2 transformer audio. All
01-A tubes. One dial. Volume control: potentiometer
across r.f. tubes. Watts consumed: 300. Console size:
30 x 40 x 20 inches. The filaments are connected in
series and supplied with d.c. from a motor-generator
set which also supplies B and C current. Output de-
vice. Price $350 including power unit.
NO. 409. DAYCRAFT 5
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All a. c. heater tubes. Reflexed t.r.f. One dial. Volume
control: potentiometers in r.f. plate and 1st audio.
Watts consumed: 135. Console size: 34 x 36 x 14 inches.
Output device. The heaters are supplied by means of
a small transformer. A built-in rectifier supplies B
and C voltaces. Price $170, less tubes. The following
have one more r.f. stage and are not reflexed: Day-
craft 6, $195; Dayrole 6, $235; Dayfan 6, $110. All
prices less tubes.
NO. 469. FREED-EISEMANN NR11
Six tubes; 3 t.r.f. (01-A). detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Volume control: potentiometer. Watts consumed: 150.
Cabinet size: 19} x 10 x 10} inches. Shielded. Output
device. A special power unit is included employing a
rectifier tube. Price $225 including NR-411 power unit.
NO. 487. FRESHMAN 7F-AC
Six tubes; 3 t.r.f. (26), detector (27), 2 transformer
audio (26 and 71). Equaphase circuit. One dial. Volume
control: potentiometer across 1st audio. Console size:
24} x 41} x 15 inches. Output device. The filaments and
heaters and B supply are all supplied by one power unit.
The plate supply requires one 80 rectifier tube. Price
$175 to $350, complete.
NO. 421. SOVEREIGN 238
Seven tubes of the a.c. heater type. Balanced t.r.f.
Two dials. Volume control: resistance across 2nd audio.
Watts consumed: 45. Console size: 37 x 52 x 15 inches.
The heaters are supplied by a small a. c. transformer.
while the plate is supplied by means of rectified a.c
using a gaseous type rectifier. Price $325, including
power unit and tubes.
NO. 517. KELLOGG 510, 511, AND 512
Seven tubes; 4 t.r.f., detector, 2 transformer audio.
All Kellogg a.c. tubes. One control and special zone
switch. Balanced. Volume control: special. Output de-
vice. Shielded. Cable connection between power supply
unit and receiver. Antenna: 25 to 100 feet. Panel "1$
x 27} inches. Prices: Model 510 and 512, consoles, $495
complete. Model 511, consolette, $365 without loud
speaker.
NO. 496. SLEEPER ELECTRIC
Five tubes; four 99 tubes and one 71. Two controls.
Volume control: rheostat on r.f. Neutralized. Cable.
Output device. Power supply uses two 16-B tubes.
Antenna: 100 feet. Prices: Type 64, table. $160; Type
65, table, with built-in loud speaker, $175; Type 66,
table, $175; Type 67, console, $235; Type 78, console,
$265.
NO. 538. NEUTROWOUND, MASTER ALLECTRIC
Six tubes; 2 t.r.f. (01-A), detector (pl-A), 2 audio
(01-A and two 71 in push-pull amplifier). The 01-A
tubes are in series, and are supplied from a 400-mA.
rectifier. Two drum controls. Volume control: variable
plate resistance. Output device. Shielded. Antenna:
50 to 100 feet. Price: S!60.
NO. 413. MARTI
Six tubes: 2 t.r.f., detector, 3 resistance audio. All
tubes a.c. heater type. Two dials. Volume control'
resistance in r.f. plate. Watts consumed: 38. Panel size
7 x 21 inches. The built-in plate supply employs one
16-B rectifier. The filaments are supplied by a small
transformer. Prices: table, $235 including tubes and
rectifier; console, $275 including tubes and rectifier;
console, $325 including tubes, rectifier, and loud speaker.
NO. 417 RADIOLA 28
Eight tubes; five type 99 and one type 20. Drum
control. Super-heterodyne circuit. C-battery connec-
tions. Battery cable. Headphone connection. Antenna:
loop. Set may be operated from batteries or from the
power mains when used in conjunction with the model
104 loud speaker. Prices: $260 with tubes, battery
operation; $570 with model 104 loud speaker, a. c.
operation.
NO. 540 RADIOLA 30-A
Receiver characteristics same as No. 417 except that
type 71 power tube is used. This model is designed to
operate on either a. c. or d. c. from the power mains.
The combination rectifier — power — amplifier unit uses
two type 81 tubes. Model 100-A loud speaker is con-
tained in lower part of cabinet. Either a short indoor
or long outside antenna may be used. Cabinet size:
42Vi x 29 x 17% inches. Price: $495.
NO. 541 RADIOLA 32
This model combines receiver No. 417 with the model
104 loud speaker. The power unit uses two type 81
tubes and a type 10 power amplifier. Loop is completely
enclosed and is revolved by means of a dial on the panel.
Models for operation from a. c. or d. c. power mains.
Cabinet size: 52 x 72 x 17% inches. Price: $895.
NO. 539 RADIOLA 17
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 27). One control. Illuminated dial.
Built-in power supply using type 80 rectifier. Antenna:
100 feet. Cabinet size: 25,", x 7% x 8'/8. Price: $130
without accessories.
NO. 545. NEUTROWOUND, SUPER ALLECTRIC
Five tubes; 2 t.r.f. (99), detector (99). 2 audio (99
and 71). The 99 tubes are in series and are supplied from
an 85-mA. rectifier. Two drum controls. Volume con-
trol: variable plate resistance. Output device. Antenna:
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:
$150.
NO. 490. MOHAWK
Six tubes; 2 t.r.f., detector, 2 transformer audio. All
tubes a.c heater type except 71 in last stage. One dial.
Volume control: rheostat on r.f. Watts consumed: 40.
Panel size: 12} x 8| inches. Output device. The heaters
for the a.c tubes and the 71 filament are supplied by
small transformers. The plate supply is of the built-in
type using a rectifier tube. Prices range from $65 to
$245.
NO. 522. CASE, 62 B AND 62 C
McCullough a.c. tubes. Drum control. Volume con-
trol; variable high resistance in audio system. C-battery
connections. Semi-shielded. Cable. Antenna: 100 feet.
Panel size: 7 x 21 inches. Prices: Model 62 B, complete
with a.c. equipment, $185; Model 62 C, complete with
a.c. equipment, $235.
NO. 523. CASE, 92 A AND 92 C
McCullough a.c. tubes. Drum control. Inductive
volume control. Technidyne circuit. Shielded. Cable.
C-battery connections. Model 92 C contains output
device. Loop operated. Prices: Model 92 A, table, $350;
Model 92 C, console, $475.
BATTERY OPERATED RECEIVERS
NO. 542. PFANSTIEHL JUNIOR SIX
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio.
Pfanstiehl circuit. Volume control: variable resistance in
r.f. plate circuit. One dial. Shielded. Battery cubic. C-
battery connections. Etched bronze panel. Antenna : out-
door. Cabinet size: 9 x 2O x 8 inches. Price: $80, without
accessories.
NO. 512. ALL-AMERICAN 44, 45, AND 66
Six tubes; 3 t.r.f. (01-A, detector) 01 -A, 2 transformer
audio (01-A and 71). Rice neutralized t.r.f. Drum
control. Volume control: rheostat in r.f. Cabinet sizes:
No. 44, 21 x 10 x 8 inches; No. 55. 25 x 38 x 18 inches;
No. 66, 27J x 43 x 20 inches. C-battery connections.
Battery cable. Anienna: 75 to 125 feet. Prices: No. 44,
$70; No. 55, $125 including l«ud speaker; No. 66, $200
including loud speaker.
NO. 428. AMERICAN C6
Five tubes; 2 t.r.f, detector, 2 transformer audio.
All 01-A tubes. Semi balanced t.r.f. Tnrce dials. Plate
current 15 mA. Volume control: potentiometer. Cabinet
sizes: table, 20 x 8} x 10 inches; console. 36 x 40 x 17
inches. Partially shielded. Battery cable. C-batler>
connections. Antenna: 125 feet. Prices: table, $30
console. $(if> including loud speaker.
RADIO BROADCAST ADVERTISER
155
ALL
METAL
SHIELDED
SIS
MAGNIFICENT TONE- SUPER SELECTIVE-POWERFUL DISTANCE GETTER \
or Battery Set.'
t
Risers Say:
Reports from us era everywhere
leave little fur us to add. These are
only a few of the many in our files
and which we receive daily. Se
.
TRICO MANY SETS-MIRACO BEST
Miraco is best set I've ever heard.
It's just the set I've always wanted
and I've had so many setslgot justa
little hard-boiled about believing
there were any sets perfect. I sure
got ray wish. I've had just 104 sta-
tions. There's about a station to
each number on dial. I get KFI
(Cal.) every night. Had PWX last
night and got 6KAV tonight good
and loud.— FRANCIS ARM-
BRUSTER. Cleveland, Ohio.
P.is. Youpackyoursetswonderful.
HE KNOWS SETS-READ THIS
I have built radios since they first
made their appearance and it has
been my pleasure to build, repair
and self them. For quality, selec-
tivity and sensitivity it is my firm
belief that the Miraco cannot be
excelled. I have proven beyond any
shadow of doubt that it will out-
perform any other radios. I bring in
the farthest distance with little or
no effort. TheMiracoalsogivesme
tone quality. — URBAIN BARIL,
Jr., Fall River, Mass.
MIRACO EXCELS EXPENSIVE RADIOS
The Miraco set and loud speaker
beat anything around here, regard-
less of price. Have tried them out
against a $200 outfit. Have logged
140 stations, coast tocoast. — E. J.
CARR1FRE, Bathgate, N. D.
HEARS CUBA, CANADA. MEXICO
Afriend visited here that has close to
S300in a radio — but no better tone
and no plainer than the Miraco.
Have gotten
America's big, old, reliable Ra-
dio Corporation* (8th successful
year) guarantees in its big:,
powerful, latest 6, 7 and 8 tube
Miraco Beta "the finest, most
enjoyable performance obtain-
able in high grade radios."
Unless 30 days' use in your
homef ully satisfies you a Miraco
is unbeatable at any price for
beautiful, clear cathedral tone,
razor-edge selectivity, power-
ful distance recpption, easy
operation, etc. — don't buy it!
Your verdict final. Save or
make lots of money on Bets and
equipment" write for testimony
01 nearby users and Amazing
Special Factory Offer.
Miraco's work equally fine
on "AC" electric house
current or with batteries.
Take your choice. Many thou-
sands of Miraco users— who
bought after thorough com-
parisons—enjoy programs Coast
to Coast, Canada to Mexico,
loud and cleat — with the mag-
nificent cathedral tone quality
of costliest seta. Don't con-
fuse Miraco's with cheap,
"squawky" radios. Miraco's
have finest parts, latest ap-
proved shielding, metal chassis,
etc.— as used in many $200 sets.
Deal Direct
with Big Factory
Your Miraco reaches you com-
pletely assembled, rigidly test-
ed, fully guaranteed. Easy to
connect and operate. 3O days'
trial free. S year guarantee if
you buy. You take no risk, you
insure satisfaction, you enjoy
rock -bottom money -sav-
ing prices by dealing direct
with one of radio's oldest, most
successful builders of fine sets.
8th successful year in the radio
manufacturing business.
USER-AGENTS! Make bis profits showing Mlraca
to friends. Get Our Special Wholesale Prices!
• MIDWEST RADIO CORPORATION, Cincinnati, O.
BEAUTIFULLY ILLUSTRATED CATALOG
AND AMAZING
SPECIAL OFFER
SEND NO MONEY— 30
DAYS' TRIAL, Special
sale Price Offer to User-Apents, Bank
:es, testimony of nearby iairacou^crg
proof you want— sent with catalog:.
mail coupon right now j
f
User-Agents
one dial
METAL SHIELDED
CHASSIS
MIRACO "Powerpluss"
— both in 8 and 7 tube models —
havr magnificently beautiful,
clear cathedral tone quality. I urn
one dial for stations everywhere.
Ultra-t elective. Miraco multistage
distance amplification gives "power*
plus" on fir-oif stations. Latest
all-metal shielded chassis. Illun.fn-
ated dial. Fully guaranteed. Try
one jrte far JO days I Choice ot
beautiful cabinets.
RETAIL LIST
ElectrifyJVny Radio
MIDWEsflNO-BATTERY
BIG
DISCOUNT
TO
User- Agent
COUPON
NOT
ORDER
outbatteries! WriteforMiciwertprlcee
and discounts. Midwest Units are highest
trade— laatiDgly dependable. QUMt la o
etioD, fully guaranteed.
CUTS THRU NEW YORK LOCALS
I can get distance thru the locals I
when they are all on early i n the I
evening. — J. F.LOGAN, Rock-
X away Beach. New York.
Another Big Bargain! Famous pow-
erful big Miraco Super 6, 1928 model-
ultra selective ! Thousands find it out-
performs sets of much higher price.
3O Days' Trial Free. Fully
Guaranteed.
r MIDWEST RADIO CORPORATION
Pioneer Builders ofSet$
406— K Miraco Building, Ou.cini.ati, Ohio.
Without obligation, send free catalog, AMAZING SPECIAL OFFER, testimony of
nearby Miraco users. D User Q Agent D Dealer
NAME
I ADDRESS
1.56
RADIO BROADCAST ADVERTISER
NO. 485. BOSWORTH B6
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Two dials. Volume control:
variable grid resistances. Battery cable. C battery
connections. Antenna: 25 feet or longer. Cabinet size
15 x 7 x 8 inches. Price $75.
NO. 513. COUNTERPHASE SIX
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 12). Counterphase t.r.f. Two
dials. Plate current: 32 mA. Volume control: rheostat
on 2nd and 3rd r.f. Coils shielded. Battery cable. C-
battery connections. Antenna: 75 to 100 feet. Console
size: 18f x 40} x 15j inches. Prices: Model 35, table,
$110; Model 37, console, $175.
NO. 514. COUNTERPHASE EIGHT
Eight tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 12). Counterphase t.r.f. One
dial. Plate current: 40 mA. Volume control: rheostat in
1st r.f. Copper stage shielding. Battery cable. C-battery
connections. Antenna: 75 to 100 feet. Cabinet size:
30 x 12} x 16 inches. Prices: Model 12, table, $225;
Model 16, console, $335; Model 18, console, $365.
NO. 506. CROSLEY 601 BANDBOX
Six tubes; 3 t.r.f., detector, 2 transformer audio. All
01-A tubes. Neutrodyne. One dial. Plate current:
40 mA. Volume control: rheostat in r.f. Shielded.
Battery cable. C-battery connections. Antenna: 75 to
150 feet. Cabinet size: 17J x 5} x 7|. Price, $55.
NO. 434. DAY-FAN 6
Six tubes: 3 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). One dial. Plate
current: 12 to 15 mA. Volume control: rheostat on r.f.
Shielded. Battery cable, C battery connections. Output
device. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7.
Prices: Day-Fan 6, $110; Daycraft 6, $145 including
loud speaker; Day-Fan Jr. not available.
NO. 435. DAY-FAN 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resist-
ance audio (01-A), 2 transformer audio (01-A and 12
or 71). Plate current: 15 mA. Antenna: outside. Same
as No. 434. Price $115.
NO. 503. FADA SPECIAL
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 20 to 24 mA. Volume control:
rheostat on r.f. Coils shielded. Battery cable. C-battery
connections. Headphone connection. Antenna: outdoor.
Cabinet size: 20} x 13J x 10i inches. Price $95.
NO. 504. FADA 7
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 43mA. Volume control: rheostat
on r.f. Completely shielded. Battery cable. C-battery
connections. Headphone connections. Output device.
Antenna: outdoor or loop. Cabinet sizes: table, 25} x
13} x 11} inches; console, 29 x 50 x 17 inches. Prices:
table, $185; console, $285.
NO. 436. FEDERAL
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t.r.f. One
dial. Plate current: 20.7 mA. Volume control: rheostat
on r.f. Shielded. Battery cable. C-battery connections.
Antenna: loop. Made in 6 models. Price varies from
$250 to $1000 including loop.
NO. 505. FADA 8
Eight tubes. Same as No. 504 except for one extra
stage of audio and different cabinet. Prices; table, $300;
console, $400.
NO. 437. FERGUSON 10A
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio
(01-A and 12 or 71). One dial. Plate current: 18 to 25
mA. Volume control: rheostat on two r.f. Shielded.
Battery cable. C-battery connections. Antenna: 100
feet. Cabinet size: 21} x 12 x 15 inches. Price $150.
NO. 438. FERGUSON 14
Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector
(01-A), 3 audio (01-A and 12 or 71). Special balanced
t.r.f. One dial. Plate current: 30 to 35 mA. Volume con-
trol: rheostat in three r.f. Shielded. Battery cable, C-
battery connections. Antenna: loop. Cabinet size:
24 x 12 x 16 inches. Price $235, including loop.
NO. 439. FERGUSON 12
Six tubes; 2 t.r.f. (01-A), detector (01-A), 1 trans-
former audio (01-A), 2 resistance audio (01-A and 12
or 71). Two dials. Plate current: 18 to 25 mA. Volume
control: rheostat on two r.f. Partially shielded. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet size: 22( x 10 x 12 inches. Price $85. Consolette
$145 including loud speaker.
NO. 440. FREED EISEMANN NR-8 NR-9, AND
NR-66
Six tubes; 3 t.r... (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. NR-8, two
dials; others one dial. Plate current: 30 mA. Volume
control: rheostat on r.f. NR-8 and 9; chassis type
shielding^ NR-66, individual stage shielding. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet sizes: NR-8 and 9, 19 j x 10 x 10} inches; NR-66
20 x 10} x 12 inches. Prices: NR-8, $90; NR-9, $100;
NR-66, $125.
NO. 501. KING "CHEVALIER"
Six tubes. Same as No. 500. Coils completely shielded.
Panel size: 11 x 7 inches. Price, $210 including loud
speaker.
NO. 441. FREED EISEMANN NR 77
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2
transformer audio (01-A and 71). Neutrodyne. One
dial. Plate current: 35 mA. Volume control: rheostat on
r.f. Shielding. Battery cable. C-battery connections.
Antenna: outside or loop. Cabinet size: 23 x 10} x 13
inches. Price $175.
NO. 442. FREED-EISEMANN 800 AND 850
Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 trans-
former (01-A), 1 parallel audio (01-A or 71). Neutro-
dyne. One dial. Plate current: 35 mA. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery
connections. Output: two tubes in parallel or one power
tube may be used. Antenna: outside or loop. Cabinet
sizes: No. 800, 34 x 15J x 13J inches; No. 850, 36 x 65J x
17}. Prices not available.
NO. 444. GREBE MU-1
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t.r.f. One,
two, or three dials (operate singly or together). Plate
current: 30mA. Volume control: rheostat on r.f. Bi-
nocular coils. Binding posts. C-battery connections.
Antenna: 125 feet. Cabinet size: 22} x 9} x 13 inches.
Prices range from $95 to $320.
NO. 426. HOMER
Seven tubes; 4 t.r.f. (01-A); detector (01-A or OOA);
2 audio (01-A and 12 or 71). One knob tuning control.
Volume control: rotor control in antenna circuit. Plate
current: 22 io25mA. "Technidyne" circuit. Completely
enclosed in aluminum box. Battery cable. C-battery con-
nections. Cabinet size, 8| x 19} x 9i inches. Chassis size,
6J x 17 x 8 inches. Prices: Chassis only, &80. Table cabi-
net, $95.
NO. 502. KENNEDY ROYAL 7. CONSOLETTE
Seven tubes; 4 t.r.f. (01-A), detectx>r (00-A), 2 trans-
former audio (01-A and 71). One dial. Plate current:
42 mA. Volume control: rheostat on two r.f. Special
r.f. coils. Battery cable. C-battery connections. Head-
phone connection. Antenna: outside or loop. Consolette
size: 36} x 35} x 19 inches. Price $220.
NO. 498. KING "CRUSADER"
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 20 mA. Volume control: rheostat on r.f.
Coils shielded. Battery cable. C-battery connections.
Antenna: outside. Panel: 11 x 7 inches. Price, $115.
NO. 499. KING "COMMANDER"
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 25 mA. Volume control: rheostat on r.f.
Completely shielded. Battery cable. C-battery con-
nections. Antenna: loop. Panel size: 12 x 8 inches.
Price $220 including loop.
NO. 429. KING COLE VII AND VIII
Seven tubes; 3 t.r.f., detector, 1 resistance audio, 2
transformer audio. All 01-A tubes. Model VIII has one
more stage t.r.f. (eight tubes). Model VII, two dials.
Model VIII, one dial. Plate current: 15 to 50 mA.
Volume control: primary shunt in r.f. Steel shielding.
Battery cable and binding posts. C-battery connections.
Output devices on some consoles. Antenna: 10 to 100
feet. Cabinet size: varies. Prices: Model VII, $80 to
$160; Model VIII, $100 to $300.
NO. 500. KING "BARONET" AND "VIKING"
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t.r.f. One dial.
Plate current: 19 mA. Volume control: rheostat in r.f.
Battery cable. C-battery connections. Antenna: out-
side. Panel size: 18x7 inches. Prices: "Baronet," $70;
"Viking," $140 including loud speaker.
NO. 489. MOHAWK
Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio
(01-A and 71). One dial. Plate current; 40 mA. Volume
control: rheostat on r.f. Battery cable. C-battery con-
nections. Output device. Antenna: 60 feet. Panel size:
12} x 8J inches. Prices range from $65 to $245.
NO. 543. ATWATER KENT, MODEL 33
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71 or 12). One dial. Volume control: r.f. fila-
ment rheostat. C-battery connections. Battery cable.
Antenna: 100 feet. Steel panel. Cabinet size: 21 ix6f x 61
inches. Price: $75, without accessories.
NO. 544. ATWATER KENT, MODEL 50
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 12 or 71 ). Volume control: r.f. filament rheo-
stat. C-battery connections. Battery cable. Special band-
pass filter circuit with an untuned amplifier. Cabinet
size: 20J x 13 x 7J inches Price: $120.
NO. 452. ORIOLE 90
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All 01-A tubes. "Trinum" circuit. Two dials. Plate
current: 18 mA. Volume control: rheostat on r. f.
Battery cable. C-battery connections. Antenna: 50 to
100 feet. Cabinet size: 25} x 11} x 12} inches. Price
$85. Another model has 8 tubes, one dial, and is
shielded. Price $185.
NO. 453. PARAGON
Six tubes; 2 t.r.f. (01-A), detector (01-A). 3 double
impedance audio (01-A and 71). One dial. Plate cur-
rent: 40 mA. Volume control: resistance in r.f. plate.
Shielded. Battery cable. C-battery connections. Out-
put device. Antenna: 100 feet. Console size: 20 x 46
x 17 inches. Price not determined.
NO. 543 RADIOLA 20
Five tubes; 2 t. r. f. (99), detector (99), two trans-
former audio (99 and 20). Regenerative detector. Two
drum controls. C-battery connections. Battery cable.
Antenna: 100 feet. Price: $78 without accessories.
NO. 480. PFANSTIEHL 30 AND 302
Six tubes; 3 t.r.f. (01-A), detector (01- 2A), trans-
former audio (01-A and 71). One dial. Plate current:
23 to 32 mA. Volume control: resistance in r.f. plate.
Shielded. Battery cable. C-battery connections. An-
tenna: outside. Panel size: 172 x 8} inches. Prices: No.
30 cabinet, $105; No. 302 console, $185 including
loud speaker.
NO. 515. BROWNING-DRAKE 7-A
Seven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio
(Hmu, two 01-A, and 71). illuminated drum control.
Volume control: rheostat on 1st r.f. Shielded. Neutral-
ized. C-battery connections. Battery Cable. Metal
panel. Output device. Antenna: 50-75 feet. Cabinet,
30 x 11 x 9 inches. Price, $145.
NO. 516. BROWNING-DRAKE 6-A
Six tubes; 1 t.r.f. (99), detector (00-A), 3 audio
(Hmu, two 01-A and 71). Drum control with auxiliary
adjustment. Volume control : rheostat on r.f. Regenera-
tive detector. Shielded. Neutralized. C-battery connec-
tions. Battery cable. Antenna: 50-100 feet. Cabinet,
25 x 11 x9. Price $105.
NO. 518. KELLOGG "WAVE MASTER,"
504, 505, AND 506.
Five tubes; 2 t.r.f., detector, 2 transformer audio.
One control and special zone switch. Volume control:
rheostat on r.f. C-battery connections. Binding posts.
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel:
7} x 25} inches. Prices: Model 504, table, $75, less
accessories. Model 505, table, $125 with loud speaker.
Model 506, consolette, $135 with loud speaker.
NO. 519. KELLOGG, 507 AND 508.
Six tubes, 3 t.r.f., detector, 2 transformer audio. One
control and special zone switch. Volume control : rheo-
stat on r.f. C-battery connections. Balanced. Shielded.
Binding posts and battery cable. Antenna: 70 feet.
Cabinet size: Model 507, table, 30 x 131 x 14 inches.
Model 508, console, 34 x 18 x 54 inches. Prices: Model
507, $190 less accessories. Model 508, $320 with loud
speaker.
NO. 427. MURDOCK 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 trans-
former and 2 resistance audio (two 01-A and 12 or 71).
One control. Volume control: rheostat on r.f. Coils
shielded. Neutralized. Battery cable. C-battery con-
nections. Complete metal case. Antenna: 100 feet.
Panel size: 9 x 23 inches. Price, not available.
NO. 520. BOSCH 57
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control calibrated in kc. Volume
control: rheostat on r.f. Shielded. Battery cable. C-
battery connections. Balanced. Output device. Built-in
loud speaker. Antenna: built-in loop or outside antenna,
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340
including enclosed loop and loud speaker.
NO. 521. BOSCH "CRUISER," 66 AND 76
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat
on r.f. Shielded. C-battery connections. Balanced.
Battery cable. Antenna: 20 to 100 feet. Prices: Model
66, table, $99.50. Model 76, console, $175; with loud
speaker $195.
NO. 524. CASE, 61 A AND 61 C
T.r.f. Semi-shielded. Battery cable. Drum control.
Volume control: variable high resistance in audio sys-
tem. Plate current: 35 mA. Antenna: 100 feet. Prices:
Model 61 A, $85; Model 61 C, console, $135.
NO. 525. CASE, 90 A AND 90 C
Drum control. Inductive volume control. Technidyne
circuit. C-battery connections. Battery cable. Loop
operated. Model 90-C equipped with output device.
Prices: Model 90 A, table, $225; Model 90 C, console,
$350.
NO. 526. ARBORPHONE 25
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat.
Shielded. Battery cable. Output device. C-battery con-
nections. Loftin-White circuit. Antenna: 75 feet. Panel:
7} x 15 inches, metal. Prices: Model 25, table, $125;
Model 252. $185; Model 253, $250; Model 255, combin-
ation phonograph and radio, $600.
NO. 527. ARBORPHONE 27
Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio
(01-A). Two controls. Volume control: rheostat. C-
battery connections. Binding posts. Antenna: 75 feet.
Prices: Model 27, $65; Model 271, $99.50; Model 272,
$125.
NO. 528. THE "CHIEF"
Seven tubes; six 01-A tubes and one power tube.
One control. Volume control: rheostat. C-battery con-
nection. Partial shielding. Binding posts. Antenna:
outside. Cabinet size: 40 x 22 x 16 inches. Prices:
Complete with A power supply, $250; without acces-
sories, $150.
NO. 529. DIAMOND SPECIAL, SUPER SPECIAL,
AND BABY GRAND CONSOLE
Six tubes; all 01-A type. One control. Partial shield-
ing. C-battery connections. Volume control: rheostat.
Binding posts. Antenna: outdoor. Prices: Diamond
Special, $75; Super Special, $65; Baby Grand Console,
$110.
RADIO BROADCAST ADVERTISER
157
ensations.
STubelCont
8 Tube
RETAIL
Big Discount to Agent*
From this Price
Has Complete A-B Power Unit
A REAL ALL ELECTRIC Radio with one of
the be«t A-B power units on the market— no
batteries needed — at, the world's lowest price.
This Marwood can't be ex relied at ANY price.
If you have electricity In your home, just plug
into the light socket and forget batteries. >o
more battery trouble and expense Costs less
than £c a day to operate. Always have lOO^
volume. ALL ELECTRIC Radios are high
priced because they are new. We cut profit
to the bone and offer a *250.0O outfit for
$!>H.OO retail price. Big1 discount to Agents.
Don't buy any Radio 'til you get details of this
sensational new ALL ELECTRIC Marwood.
All Electric
or Battery Operation
AGAIN Marwood is a year ahead — with the
Radio sensation of 1928 — at a low price that
smashes Radio profiteering. Here's the sensa-
tion they're all talking about — the marvelous 8
Tube Single Control Marwood for BATTERY or
ALL ELECTRIC operation. Direct from the
factory for only $69.00 retail price — a price far
below that of smaller, less powerful Radios. Big
discount to Agents from this price. You can't
beat this wonderful new Marwood and you can't
touch this low price. Why pay more for less
quality? To prove that Marwood can't be beat
we let you use it on 30 Days* Free Trial in your
own home. Test it in every way. Compare it
with any Radio for tone, quality, volume, dis-
tance, selectivity, beauty. If you don't say that
it is a wonder, return it to us. We take the risk.
New Exclusive Features
Do you want coa.«t to coast with volume enough
to fill a theatre? Do you want amazing distance
that only super-power Radios like the Marwood
8 can gel? Do you want ultra-selectivity to cut
out interference? Then you must test this Mar-
wood on 30 Days' Free Trial. An amazing
surprise awaits you. A flip of your finger
makes it ultra-selective — or broad — just as
you want it. Every Marw ood is perfectly
BALANCED— a real laboratory job. Its
simple one dial control gets ALL the sta-
tions on the wave band with ease. A beau-
tiful, guaranteed, super-efficient Radio in
handsome walnut cabinets and consoles.
A radio really worth double our low price.
Bay From Factory — Save Half
Why pay profits to several middlemen? A
Marwood in any retail store would cost
practically three times our low direct-
from- the- factory price. Our policy is high-
est quality plus small profit and enormous
sales. You get the benefit. Marwood is a
pioneer, responsible Radio, with a good
reputation to guard. We insist on the best
— and we charge the least. If you want next
year's improvements NOW — you must get
a Marwood — the Radio that's a year ahead.
AGENTS
Make Big Spare Time Money
Get your own Radio at wholesale price. It's
euwy to get orders for the Marwood from
your friends and neighbors. Folks buy
Quick when they compare Marwood Quality
and low prices. We want local agents and
dealers In each territory to handle thf? enor-
mous business created by our national
advertising. Make #10O a week or more in
spare time demonstrating: at home. No ex-
perienre or capital needed. We show you
how. Tills is the biggest season in Radio
history. Kverybody wants a Kndlo. Get In
now. Rush coupon for 3O days* Free Trial,
beautiful catalog. Agents* Counde iitiul
Prices and Agents' New Plan.
MARWOOD RADIO CORP.
5315 Ravenswood Avenue
Department B- 1 7 Chicago, Illinois
Get Our Discounts
Before You Buy a Radio
Don't buy any Radio "I ill you get our big discounts and
catalog. Save half and get a Radio that IS a Radio. Try
any Marwood on 30 Days' Free Trial at our risk. Tune
in coast to coast on loud speaker with enormous vol-
ume, clear as a bell. Let your wife and children oper-
ate it. Compare it with any Radio regardless of price.
If you don't get the surprise of your life, return it. We
take the risk. Don't let Marwood low prices lead you
to believe Marwood is not the highest quality. We
have smashed Radio prices. You save half.
6 Tube— i Control
This is the Marwood 6 Tube, 1 Control for BATTERY or
ALL ELECTRIC operation. Gets coast to coast on loud
speaker with great volume. Only $47.00 retail. Big dis-
counts to Agents. Comes in handsome walnut cabinets
and consoles. This low price cannot be equalled by
any other high grade 6 tube Radio. Has the volume of
any 7 lube set. If you want a 6 tube Radio you can't
beat a Marwood and you can't touch our low price.
$47
RETAIL
PRICE
BigDiscount
to Agents
from This
Price
MARWOOD RADIO CORPORATION
5315 Ravens wood Ave., Dcpt. IM7, Chicago, 111.
Send Agents' Confidential Prices, 30 Days' Free
Trial. New Catalog and Agents' New Money
Making Plan. No obligation on my part.
Name
St. or R.F.D
City State..
1.58
RADIO BROADCAST ADVERTISER
NO. 531. KOLSTER, 8A, 8B, AND 8C
Eight tubes; 4 t.r.f. (01-A). detector (01-A), 3 audio
(two 01-A and one 12). One control. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery con-
nections. Model 8A uses 50 to 75 foot antenna; model
8B contains output device and uses antenna or detach-
able loop; Model 8C contains output device and uses
antenna or built-in loop. Prices: 8A, $185; 8B, $235;
8C, »375.
NO. 532. KOLSTER, 6D, 6G, AND 6H
Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r.f. C-battery connections. Battery cable. Antenna:
50 to 75 feet. Model 6G contains output device and
built-in loud speaker; Model 6H contains built-in B
power unit and loud speaker. Prices: Model 6D, $80;
Model 6G, $165; Model 6H, $265.
NO. 533. SIMPLEX, SR 9 AND SR 10
Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio
(01-A and 12). SR 9, three controls; SR 10, two con-
trols. Volume control: rheostat. C-battery connections.
Battery cable. Headphone connection. Prices: SR 9,
table, $65; consolette, $95; console, $145. SR 10, table
$70; consolette, $95; console, $145.
NO. 534. SIMPLEX, SR 11
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio
(01-A and 12). One control. Volume control: rheostat.
C-battery connections. Battery cable. Antenna: 100
feet. Prices: table, $70; consolette, $95; console, $145.
NO. 53S. STANDARDYNE, MODEL S 27
Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio
(power tubes). One control. Volume control: rheostat
on r.f. C-battery connections. Binding posts. Antenna:
75 feet. Cabinet size: 9 x 9 x 19} inches. Prices: S 27,
$49.50; S 950, console, with built-in loud speaker,
$99.50; S 600, console with built-in loud speaker,
$101.50.
NO. 481. PFANSTIEHL 32 AND 322
Seven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio
(01-A and 71). One dial. Plate current: 23 to 32 mA
Volume control: resistance in r. f. plate. Shielded
Battery cable. C-battery connections. Output device.
Antenna: outside. Panel: 17} x 8} inches. Prices: No.
32 cabinet, $145; No. 322 console, $245 including
loud speaker.
NO 433. ARBORPHONE
Five tubes; 2 t.r.f., detector, 2 transformer audio.
All 01-A tubes. Two dials. Plate current: 16 mA. Vol-
ume control : rheostat in r.f . and resistance in r.f. plate.
C-battery connections. Binding posts. Antenna: taps
for various lengths Cabinet size: 24 x 9 x 10 j inches.
Price: $65.
NO. 431. AUDIOLA 6
Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Drum control Plate cur-
rent: 20 mA. Volume control: resistance in r.f. plate.
Stage shielding. Battery cable. C-battery connection.
Antenna: 50 to 100 feet. Cabinet size: 28J x H x 14i
inches. Price not established.
NO. 432. AUDIOLA 8
Eight tubes; 4 t.r.f. (01-A), detector (00-A), 1 trans-
former audio (01-A), push-pull audio (12 or 71). Bridge
balanced t.r.f. Drum control. Volume control: resistance
in r.f. plate. Stage shielding. Battery cable. C-battery
connections. Antenna: 10 to 100 feet. Cabinet size:
28J x 11 x 14j inches. Price not established.
NO. 542 RADIOLA 16
Six tubes; 3 t. r. f. (Ol-A), detector (Ol A), 2 trans-
former audio (01-A and 112). One control. C-battery
connections. Battery cable. Antenna: outside. Cabinet
size: 16>/4 x 8'/4 x 7'A inches. Price: $69.50 without ac-
cessories.
NO. 456. RADIOLA 20
Five tubes: 2 t.r.f. (99), detector (99), 2 transformer
audio (99 and 20). Balanced t.r.f. and regenerative de-
tector. Two dials. Volume control: regenerative.
Shielded. C-battery connections. Headphone connec-
tions. Antenna: 75 to 150 feet. Cabinet bize: 19 j x
11 J x 16 inches. Price $115 including all tubes.
NO. 457 RADIOLA 25
Six tubes; five type 99 and one type 20. Drum con-
trol. Super-heterodyne circuit. C-battery connections.
Battery cable. Headphone connections. Antenna: loop.
Set may be operated from batteries or from power mains
when used with model 101 loud speaker. Price; $165
with tubes, for battery operation. Apparatus for opera-
tion of set from the power mains can be purchased
separately.
NO. 493. SONORA F
Seven tube*; 4 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Special balanced t.r.f.
Two dials. Plate current: 45 mA. Volume control:
rheostat in r.f. Shielded. Battery cable. C-battery
connections. Output device. Antenna: loop. Console
si,;e: 32 x 45J x 17 inches. Prices range from $350 to
$450 including loop and loud speaker.
NO. 494. SONORA E
Six tubes; 3 t.r.f. (01-A), detector COO-A), 2 trans-
former audio (01-A and 71). Special balanced t.r.f.
Two dials. Plate current: 35 to 40 mA. Volume control:
rheostat on r.f. Shielded. Battery cable. C-battery
connections. Antenna: outside. Cabinet size: varies.
Prices: table. $110; semi-console, $140; console, $240
including loud speaker.
NO. 530. KOLSTER, 7A AND 7B
Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r.f. Shielded. Battery cable. C-battery connections.
Antenna: 50 to 75 feet. Prices: Model -7A, $125; Model
7B, with built-in loud speaker, $140.
NO. 495. SONORA D
Same as No. 494 except arrangement of tubes; 2
t.r.f., detector. 3 audio. Prices: table, $125; standard
console, $185; "DeLuxe" console, $225.
NO. 482. STEWART-WARNER 705 AND 710
Six tubes; 3 t.r.f., detector, 2 transformer audio.
All 01-A tubes. Balanced t.r.f. Two dials. Plate cur-
rent: 10 to 25 mA. Volume control: resistance in r.f.
plate. Shielded. Battery cable. C-battery connections.
Antenna: 80 feet. Cabinet sizes: No. 705 table, 26t
x 11} x 13}| inches; No. 710 console, 29| x 42 x 17?
inches. Tentative prices: No. 705, $115; No. 710,
$265 including loud speaker.
NO. 483. STEWART-WARNER 525 AND 520
Same as No. 482 except no shielding. Cabinet sizes:
No. 525 table, 19} x 10 x 11} inches; No. 520 console,
225 x 40 x 14 U inches. Tentative prices: No. 525, $75;
No. 520, $117.50 including loud speaker.
NO. 459. STROMBERG-CARLSON 501 AND 502
Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two dials.
Plate current: 25 to 35 mA. Volume control: rheostat
on 1st r.f. Shielded. Battery cable. C-battery connec-
tions. Headphone connections. Output device. Panel
voltmeter. Antenna: 60 to 100 feet. Cabinet sizes-
No. 501, 255 x 13 x 14 inches; No. 502, 28 !J x 50
,7, x 16J inches. Prices: No. 501, $180; No. 502, $290.
NO. 460. STROMBERG-CARLSON 601 AND 602
Six tubes. Same as No. 549 except for extra t.r.f.
stage. Cabinet sizes: No. 601, 27^ x 16J x 14A inches;
No. 602, 28? x 51} x 19| inches. Prices: No. 601, $225;
No. 602, $330.
NO. 472. VOLOTONE VIII
Six tubes. Same as No. 471 with following excep-
tions; 2 t.r.f. stages. Three dials. Plate current: 2-
mA. Cabinet size: 26i x 8 x 12 inches. Price $140.
NO. 546. PARAGON "CONGRESS"
Six tubes; 2 t.r.f. (01-A), detector (01-A), 3 impedance-
coupled audio (two 01-A and 12 or 71). One main con-
trol and three auxiliary adjustments. Volume control:
resistance in r. f. plate circuit. Plate current: 40 mA. C
battery connections. Tuned double-impedance audio am-
plifier. Output device. R. F. coils are shielded. Cable or
binding posts. Cabinet size: 7x18x9 inches. Price $90.00;
without cabinet. $80.00.
Crystal Clear Tones
Tone quality is what radio listeners want. Volume and
distance mean nothing if the tones are blurred.
The Carborundum Stabilizing
REG. U. S.PAT. OFF. ^^
Detector Unit
brings you natural tones clear as crystal with assured volume
and selectivity.
A tone perfecting unit that can be used on practically
any set.
.50
in U.S. A. Dealer or direct. Or the Car-
borundum Detector alone for $1.50.
i-,1 Trade Name used \-j The Carborundum Company for gill.
rk it the excluiiv« property of The Carborundum Company.
THE CARBORUNDUM COMPANY
NIAGARA FALLS, N. Y.
CANADIAN CARBORUNDUM Co., LTD.
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llook'itp Book D- 2
RADIO
BROADCAST
How to Use the Screen- Grid Tube
A Directory of Manufactured Receivers
Hints onOperatincftour CooleyRayfoto Receive
The Phonograph Joins tKe Radio Receiver
A Push-Pull Amplifier and B Supply
Inside the Complete Receiver
i
35 Qmts
'X^pr JAN -*92
Vitv. jVew Uork^ -J
RADIO!
TUBES
SINCE 1915
STANDARD f OR ALL SETS
CUNNINGHAM'
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gifts
that bring happiness at
Christmas time and
throughout the year
Radio sets and radio equipment make
immensely popular Christmas gifts.
To assure the utmost in Yule-tide Radio
enchantment, see that Cunningham Radio
Tubes are on duty in every socket. Every
owner of a radio will be delighted to re-
ceive a set of new tubes.
Buy them in combination of five or more.
Your dealer will tell you the correct types
of Cunningham Radio Tubes for which
any radio set is designed.
Don't use old tubes with new ones.
Use new tubes throughout.
E. T. CUNNINGHAM, Inc.
New York Chicago San Francisco
• I
RADIO BROADCAST ADVERTISER
191
Improve
Reception!
ELECTRAD
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bles at the entrance point
of your aerial and have bet-
ter reception by using: this
superior constructed Lead-in.
Bends any shape to fit around
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full 10 inches, covered with water-
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strip heavily tinned to prevent
corrosion.
Protect yourself by looking for
the Electrad name. Price 40c
each. At your dealers.
Write for Descriptive
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mation that is right up to the
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FROST-RADIO
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"What S.-t Shiill I Build?"
telK much about the newest
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Power
ft
Quality
\ PUSH-PULL amplifier in that last stage provides the speaker with ample
•**• power to sustain a high volume level without tube overloading, transmit-
ting the full effects of large swings in intensity common in orchestra music.
This balanced type of amplifier draws no alternating current from the plate
supply, a fact of great importance if socket power is used, as the impedance
of the power unit does not affect the amplifier. This results in improved re-
production of sustained notes, particularly of low frequency.
Other advantages of the push-pull system are, a reduction in hum when al-
ternating current is used for filament supply and for equal power outputs, a
reduction in the plate voltage required.
The amplifier is supplied completely wired.
Type 441 amplifier
For use with UX 226, CX 326, UX 171, CX 371, UX 210, or CX
310 tubes.
Input inductance 30 henries.
Input turns ratio i :2.25.
Output impedance ratio 12:1.
(whole primary to secondary)
Price completely wired $20.00.
Licensed by the Radio Corporation of America for radio amateur, experi-
mental and broadcast reception only and under the terms of the R. C. A.
license the unit may be sold only with tubes.
GENERAL RADIO
LABORATORY EQUIPMENT
PARTS and ACCESSORIES
If we can be of help to you in supplying technical
information, we welcome your correspondence. Write
for our Series A of amplification booklets describing
various amplifiers, circuits and units.
GENERAL RADIO CO.
Cambridge, Mass.
RADIO BROADCAST
JANUARY, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEV EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XII, No. 3
Cover Design »*.•••• From a. Design by Harvey Hopkins Dunn
Frontispiece - ' - In the Laboratory of a Tube Manufacturer 194
Radio Enlists the Helium Atom - Volney G. Mathison 195
The March of Radio
An Editorial Interpretation 198
Can the Serious Problem of Radio Patents Be What Readers Say About Broadcasting
Settled?
The Prospects of a Patent Pool
The Commission Announces a New Policy
Conditions
Broadcasting Bands Changed
Broadcasting Notes
The Commission Suggests Synchronization News of the Patent Field
Schemes
Among the Manufacturers
Push-Pull Amplification— Why? - Howard E. Rhodes 202
The Phonograph Joins the Radio Set • 206
The Screened Grid Tube • Keith Henney 208
What Set Shall I Buy? - Edgar H. Felix 211
"Our Readers Suggest — 213
Why I Installed a Cooley Picture Receiver • - Edgar H. Felix 215
Suppressing Radio Interference - - - A. T. Lawton 217
Are Programs Going in the Wrong Direction? - John Wallace 219
The Listeners' Point of View
A Vacuum'Tube Voltmeter - The Laboratory Staff 221
Radio Folk You Should Know 225
(i.) Ralph H. Langley Drawing by Franklyn F. Stratford
Some Fine Receivers and Their Chassis - 226
"Strays" from the Laboratory - 228
How Reliable are Short Waves? High-Powered Bunk
Mathematics of the Audio Transformer New Apparatus
Concomitants of Good Quality - .- 230
How the "Synchrophase" Seven Was Developed John F. Rider 232
As the Broadcaster Sees It Carl Dreher 235
"Radio Broadcast's" Laboratory Information Sheets 238
No. 153. Standard' and Constant-Frequency No. 157. Table for Wavelength-Freauency
Stations Conversion
No. 154. The na-A and 171-* Type Tubes No. 158. The Three-Tube Roberts Reflex
No. 155. Wave Traps No. 159. Diagram of Three-tube Roberts
No. 156. Wavelength-Frequency Conversion Reflex
No, 160. Fading
Manufacturers Booklets Available - - 244
"Radio Broadcast's" Directory of Manufactured Receivers 246
A Key to Recent Radio Articles E. G. Shall<hauser 255
What Kit Shall I Buy? •..•>'*, 257
AMO^G OTHER THINGS. . .
IT IS a sad duty to record the death of the Chairman of the
Federal Radio Commission, Admiral W. H. G. Bullard,
which occurred in Washington on Thanksgiving Day. Admiral
Bullard, who served in the United States Navy for thirty-six
years, for a very long time was close to the center of radio in
almost all of its branches. His loss will be keenly felt, not only
by those who knew him as a likable and able individual but
especially by the Radio Commission itself. When the Radio
Commission went to work on March 15, two of its members
had a background of technical radio experience. These two men
were Admiral Bullard and Colonel Dillon. Death has removed
both. The Commission at this writing now consists of Acting-
Chairman E. O. Sykes, O. H. Caldwell, Sam Pickard, and
H. A. Lafount. Not one of these members has a technical radio
background which would enable them to better struggle with
the complicated problems which confront them.
THE reports of international conferences, on whatever
subject, usually make rather dull reading for the general
public and the Washington Radio Conference has beer. 11O
exception to this rule. The proceedings may not be exciting, but
the results are certainly important. There has been no revision
of international agreement since the London conference of 1912,
and radio progress has been so rapid since then that the articles
of that Convention were hopelessly inadequate to meet present
needs. There have been many rocks and shoals in the way of
the present conference, which, at this writing, has just wound
up its work, but through good management and a praiseworthy
desire for general accord, the delegates have succeeded in
drawing up a Convention which well meets the needs of radio
today. Not the least important decision reached at Washington
was that dealing with the international assignment of channels
in the frequency spectrum. In that respect, we are glad to note,
the future needs of short-wave communication, broadcasting,
commercial, and amateur work were provided for. The ama-
teurs had a hard fight, but room has been saved for them — a
result of which the broad-minded directors of the American
Radio Relay League may well be proud.
THE issue of RADIO BROADCAST before you contains some
extremely interesting articles. The story by Howard
Rhodes on the problems of push-pull amplification is distinctly
helpful and should cast much light on a form of amplification
which is again being revived after several years of comparative
disuse. . . . Those who are anxious to know what the new
screened-grid tube will do will find Keith Henney 's article very
valuable indeed. As soon as possible, RADIO BROADCAST will
give its readers data on receiving circuits which can be used
with the tube; the latter has just been released for general sale.
THOSE of our readers who would like to have their names
forwarded to the manufacturers of the special apparatus
necessary to construct a Rayfoto receiver may send letters to
the undersigned, and printed matter containing detailed in-
formation will be sent them. . . . The next RADIO BROADCAST
will contain an article describing a new super-heterodyne,
entirely operated from a. c., which has much to recommend it,
both from the design and appearance point of view. There
will also be many other articles of interest.
— WILLIS KINGSLEY WING.
Doubleday, Page & Co.
MAGAZINES
COUNTRY LIFE
WORLD'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
SHORT STORIES
EDUCATIONAL REVIEW
LE PETIT JOURNAL
EL Eco '
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WEST WEEKLY
THE AMERICAN SKETCH
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Doublfday, Page & Co.
OFFICERS
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Company. All rights reserved.
RADIO BROADCAST ADVERTISER
193
OUJu
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THORD ARSON 171 TYPE
POWER AMPLIFIER
Built around the Thordarson Power Compact R-171, this
Power amplifier supplies "A," "B," and "C" current for one
t/X- 171 power tube and B-voltage for the receiver. Employs
Raytheon B. H. rectifier.
THORDARSON 210 TYPE
POWER AMPLIFIER
This amplifier, mounted on a special metal chassis, uses the
Thordarson Power Compact R-21Q. Provides "A," "B," and
"C" current for one UX.-21} power tube and "B" voltage for
the receiver. Employs one 216-B o/ 281 rect:fier.
A Home Assembled
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Give your radio set a chance to reproduce real
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Write today for complete constructional booklets
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THORDARSON 210 PUSH-PULL
POWER AMPLIFIER
This heavy duty power amplifier operates two 210 power tubes
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Transformer T-2098, and Double Choke Unit T-2099.
THORDARSON ELECTRIC MANUFACTURING CO.
"Transformer Specialists Since 1895
WORLDS OLDEST AND LARGEST EXCLUSIVE TRANSFORMER MAKERS
and Kingsbury Streets — Chicago. 1 'II. USA.
In the Laboratory of a Tube Manufacturer
Where diligent investigation precedes production of any new kind of tnhe
likely as not, discarded. It is said that about 99 per cent of these hand-mud.,
expcnmental tubes are discarded without even bei ,K put into prudSot ton Whin
we cons,der the expense of such tireless research, more and ,,,"",!, we' recog
m*. the og,c ,,f ,he statement that it is only ,he larger and more "moneyed*'
manufacturers who are capable of producing dependable radio equipment
194
STUDYING GASES IN THE LABORATORY
Looking into the depths of ionized helium atoms with a spectroscope. Charles Grover Smith,
who is shown in this picture, spends considerable of his time studying gases, especially helium
RADIO ENLISTS THE HELIUM ATOM
By VOLNEY G. MATHISON
IT'S all so useless, that's why I'm quitting,"
complained the young college graduate to
the chief of the laboratory in which he had
lately gotten a job. "What can ever come out of
measuring the ohmic resistances of a cubic mil-
limeter of about a million different substances
under a couple of hundred different tempera-
tures? That's the job you've given me — nothing
but an endless measuring of ohms. -If this is
what you call scientific research —
"It is," interrupted the electro-chemist.
" It's the backbone of it — prolonged patience at
tedious work."
"Seefns tedious enough. But I could stand that
if I could see some results ahead. I can't see
any."
"Well, there may be no directly important
outcome of what you're doing. You are simply
adding to the stock of scientific knowledge in a
prosy way, working on a huge book of tempera-
ture-resistance tables. You can't tell in advance
what it may lead to. Take, for example, the
helium-gas rectifier tube used in radio B-supply
devices. It was never invented, it just grew out
of a lot of laborious work like this. American
factories are turning out about 20,000 of these
tubes a day at present and the patent profit is
close to a dollar and a half apiece. There's a
return to pure research at the rate of something
like $30,000 a day. That soon pays for a lot of
slow laboratory grinding, doesn't it?"
"Yes," reiterated the young graduate, "but
that tube wasn't developed by any such work as
I'm doing here — measuring the resistances of
rust, rocks, roots, cocoanut shell, and the end
years away. It's all so discouraging!"
As a matter of fact, the helium-gas tube for
B-devices was the result of a great amount of
purely scientific work of the tedious and rather
unfocussed sort that this discouraged young
chemist was assigned to, though, perhaps, the
experiments involved were a good deal more
technical. A few years ago we began studying
the actions of electrons in gases. At that time
nobody knew much about electrons — maybe we
don't yet— and the experiments were entirely
general in kind. The aim was to find out some-
thing, not to invent something. One young fellow
had the job of finding out definitely whether or
not electrons emitted from a cathode into a tube
of gas passed through the gas without colliding
with its atom centers.
An atom of any kind of substance, as nearly
every one now is aware, consists of a group of
protons and electrons surrounded by planetary
electrons. The space in between seems to contain
nothing but electric tension, though now late in
1927 we are about to believe that this tension
consists of a flurry of particles called etherons
that are so small they make an electron look
like a balloon in comparison with an apple, and
move almost twice as fast as light. Matter.even
"95
solid steel, is nearly all emptiness, and it is the
crudeness of our undeveloped physical senses
that makes us think otherwise.
So this young man set about trailing a lot of
wandering electrons through a wilderness of gases
to find out what they did in there. He had a
photographing outfit that would show the paths
of the electrons. Many gases and pressures had
to be tried. In one series of experiments each
photograph showed the flight of 200,000 elec-
trons, and that young man took 100,000 photo-
graphs separately, one after the other, before he
got one collision of an electron with the middle
of an atom of the gas under test. He kept on, and
got a total of eight collisions in 400,000 photo-
graphs. Even when it is possible to use a fast
automatic machine to take such photographs,
they all have to be individually and laboriously
examined.
The photographer found out something else.
He found out that when an electron hit an atom
of gas square in the middle, it blew the atom to
pieces, producing a shower of unattached elec-
trons, and unsmashable groups of electrons and
protons that were named alpha particles. Alpha
particles were identified with a spectroscope as
being the same as a mysterious gas which had
been seen by astronomers pouring over the sun,
and which they had named helium — a "sun"
word.
The alpha particles or helium atoms can be
196
RADIO BROADCAST
JANUARY, 1928
quite easily robbed temporarily of one planetary
electron, but they cannot be further broken up
except with the most extreme difficulty. Helium
gas was therefore recognized as a valuable elec-
trical conducting medium that would tend to
act at all times with unchanging properties and
that would refuse to eat, corrode, or combine in
any way with the metal tips of the electrodes by
which electricity would be fed into the gas. No
particular electrical use for this gas had yet
been thought of, though it was proposed that
metal-ended glass cartridges of helium might be
valuable as ultra-stable resistors capable of
withstanding enormous currents and pressures.
In photographing the flights of electrons
through helium gas, it was observed that, when
an electron struck an atom of helium, the elec-
tron ran off with one of the planetary electrons
of the helium atom, carrying it to the anode.
A sketch of this performance would be almost
inconceivably out of proportion
since there would have to be rep-
resented the trillions times trillions
of atoms in the tube, while elec-
trodes about the size of the state
of Georgia would be necessary to
preserve the proper scale if the
atoms were one half inch across.
If the helium nucleus were drawn
the size of a pea, the planetary
electrons would properly be placed
a quarter of a mile away. Such is
the ghastly emptiness of matter —
of even the "solid" walls of a
glass tumbler from which we drink
billions of electrons and protons in
the peculiarly ordered state we call
water; and of the stout iron bars
upon which the jail-bird leans his
head. But solidity, although physi-
cally an illusion, is nevertheless real
because it is a manifestation of
a powerful electrical condition.
To return now to the story of
the doings in the helium tube un-
der electrical pressure, we learn
that the unfortunate gas atom that
has lost an electron is said to be
"ionized." This is all that ioniza-
tion means, i. e., a breaking away
of electrons from gas atoms. It,
the ionized atom, is over-positively
charged and flies with terrific force
toward the negative or cathode
element, which it strikes violently
and from which it extracts an
electron from the inflowing stream
in the wire leading to the cathode
— the entrance element from the outside supply.
The gas atom, now once more in a normal state,
rebounds from the cathode and flies about
jubilantly until it is again robbed of an electron,
when it instantly goes through the perform-
ance just described all over again.
One remarkable thing about this action which
is not yet understood is the fact that the bom-
bardment of the cathode by ionized gas particles
causes a liberal release of free electrons — of extra
electrons beside those taken to balance the
ionized atoms. In other words, by hammering a
negative electrode with positively charged gas
particles, we get a discharge of electrons. Per-
haps the "yanking" out of the electron needed
by the atom for itself is so violent that several
extra electrons are hustled out along with it.
Some of these extra electrons in their flight to
the positive or exit element collide with other gas
molecules, and the action, the pounding of gas
particles on the cathode and the emission of elec-
trons, is continuous as long as electrical pressure
is applied to the device. A current consequently
flows through the tube. In this manner elec-
tricity gets through a cold-electrode rectifier
tube.
HOW A TUBE RECTIFIES
HpHE foregoing does not explain how current
* gets through the tube in only one direction.
It would seem that, when the tube is put in an
a. c. circuit, each element would become alter-
nately an anode and a cathode, an exit and
an entrance, and that the flow would be equally
back and forth through the gas in the tube.
But since the current flow depends upon hitting
an electrode with gas particles, it becomes ap-
parent that, by making one electrode big and the
other one little, you can facilitate the hitting in
one direction and minimize it in the other. When
the larger electrode is negative, it will get thor-
oughly hammered with gas particles and will
release many electrons; consequently, a large
BEHIND THE SCENES IN THE LABORATORY
Preparing a globe of pure helium for research experiments. This kind of
work never stops, and in every progressive tnbe concern, the laboratory
is always ahead of the factory — is always working on " something better."
current will flow through the device. On the other
hand, when the smaller electrode goes negative
under the reversing a. c. current, it will not be
battered so much by the flying gas particles as
the other electrode was and therefore will not
emit many electrons. A small current will, how-
ever, flow. The big electrode is a better emitter
because it has more surface for the gas particles
to "rip" electrons out of. When the big electrode
is positive and the small electrode is negative,
the ionized gas atoms do fly toward the small
electrode but most of them miss it because it
is comparatively hard to hit. Some particles
strike the small element while it is negative and
release electrons which fly across to the large
electrode. This produces a "back-current"
through the tube. All helium-gas rectifier tubes
have this "back-current." The amount of it
determines the efficiency of the rectifier and it
usually is but a small percentage of the current
in the other direction.
The "back-current" is reduced by making
the anode small and hard, while the other large
electrode is treated with radioactive earths to
encourage it to release electrons. Besides the
difference in size of the bombarding areas of the
two elements, the electric field produced by the
smaller electrode is less attractive to the ionized
gas particles than that of the larger one, with the
result that it is hit less violently.
Both of the elements are made principally of
nickel, which has been purified in a hydrogen
furnace to remove all impurities.
The description so far has dealt with a tube in
which there are only two elements. The usual
helium-gas rectifier tube has three elements —
a hat-shaped or tubular cathode and two anodes.
This is simply two rectifier tubes in one, using a
common cathode, and enables both halves of the
a. c. wave to be used. The action here is exactly
the same as that already described, except that
the emission of electrons is alternately from the
cathode to first one anode and then to the other —
to each one as it becomes positive
in turn. And the cathode is almost
continuously under bombardment,
because it is always negative with
respect to one anode or the other.
At the same time that the flight of
electrons takes place from the
cathode to the positive anode, a
"back-current" emission travels
from the temporarily negative
anode toward the cathode. Some
electrons also fly between the two
anodes, causing "leak" current.
These "leak" and "back-cur-
rents," while not wanted, cannot
be entirely eliminated, and as long
as they are small, cause no serious
trouble. In the factories, each tube
is tested on a machine that meas-
ures the "back-current," and if
excessive, the tube is discarded.
Too much "back-current" through
a tube will cause a B-device to
hum.
It is worth pointing out that the
popular 'conception of the move-
ment of electricity through a B-
device rectifier and filter system
is erroneous. The general idea is
that a "positive current" gets
across the rectifier tube into the
filter where it is tanked arid choked
into smoothness. But it should be
remembered that current is purely
electronic flow — it consists only of
moving electrons in a conductor —
and these electrons flow only from
negative to positive. It is very con-
fusing to the novice and entirely unnecessary to
say that the current flows one way and the elec-
trons the other. There is no such current flowing
against the movement of the electrons. It simply
doesn't exist. In the early days of electrical
science, long before any kind of a radio vacuum-
tube had even been thought of, experimenters
misunderstood some of the actions of electricity,
and the positive-to-negative idea of current flow
was one of the consequences of their lack of
knowledge. In the business of science, there is
no sensible reason for compromising with mis-
takes or twisting them around to meet new facts,
as is being attempted all the time in religion;
they should be simply left out of the story.
The electrons flowing in a B-device circuit
enter the negative wires, pass direct to the fila-
ments of the vacuum-tubes in the radio receiver,
are emitted from the hot filaments to the plates,
pass from the plates through the various circuits
to the positive lead of the B device, thence
through the chokes to the cathode element of the
rectifier tube, and from this point they are
JANUARY, 1928
RADIO ENLISTS THE HELIUM ATOM
197
sprayed alternately to the anode elements as
these become positive in turn under the inductive
action of the a. c. current in the primary power-
supply windings. The filter chokes and tanks pre-
vent a voltage and current fluctuation in the
line during the intervals between the spraying
or emission surges through the rectifier tube.
So deeply ingrown is the current-flow con-
ception that in a recent issue of a well-known
radio magazine there was a cut of a helium-gas
tube with the hat-shaped cathode marked
"anode" and the two anodes marked "cath-
odes." The accompanying text used the same
terminology, which was wrong even in the light of
the old theory. It should be clear that the posi-
tive side of a B-device filter is of negative
potential compared to the ends of the secondary
winding of the power transformer to which the
rectifier-tube anodes are connected. The large
cathode of a helium rectifier is equivalent to the
incandescent filament of the filament type tube.
WHY A TUBE DETERIORATES
CINCE the helium-gas rectifier tube contains
^ no heated filament emitter to burn out or
become lifeless through deterioration, many
usersof thedevice feel that it ought to last almost
forever — for years and years at any rate, and
wonder why it sometimes has a short life.
As a matter of fact, the developers of the tube
themselves thought at first that it would have a
life of 10,000 hours or more of continuous use,
but soon found that such was not the case. The
principal thing that brings the life of a helium-
gas rectifier tube to an end is the fact that the
helium gas in the bulb disappears. Helium gas is
inert, it will not combine with anything, so far
as we know at present; it is genuinely strange,
therefore, that it should disappear from a her-
metically-sealed bulb. It seems that the ionized
gas particles pound the cathode with such force
that some of them are driven deep into the metal
and stay there — become occluded or imprisoned.
After a certain length of time so many gas
atoms are bound in the metal that the tube be-
comes very hard, the vacuum rises, and the
bombardment of the cathode becomes meager,
owing to the reduced number of molecules of
gas to do the battering. The current output of
the tube then falls off to such a point that it
must be discarded.
The life of many a good helium-gas tube has
been quickly brought to an end through the
breaking down of condensers in filter circuits.
Cheap inferior condensers in both home-made
and factory-built power devices usually go to
pieces after a few weeks or months of use, with
the result that the rectifier tube is placed in a
dead short-circuit. The heavy current flow
quickly burns off the tips of the anodes in the
tube. The helium gas itself cannot be injured by
any current. Helium gas will carry currents so
great that they will instantly explode copper
conductors of the same cross-sectional area;
but under such currents the gas particles quickly
drive themselves deep into the negative elec-
trodes and are as good as lost.
Some of the cheaper helium-gas tubes now on
the market may be short-lived through the
presence of impurities in the helium, which would
destroy the electrodes. Extremely pure helium
must be used. This gas is purified by passing it
through copper tubes filled with cocoanut char-
coal and maintained at the temperature of liquid
air — more than 250° below zero, Fahrenheit; then
to a steel reservoir; then to a second battery of
tubes of charcoal surrounded with liquid air
to remove oxygen or nitrogen which might come
away from the walls of the reservoir. The helium
is admitted until the charcoal is partly loaded
with it; next it is pumped off with vacuum
pumps and the impurities remain in the char-
coal, which is itself purified and used over again.
It is interesting to consider that absolute
purification of anything, liquid, gaseous, or solid,
is almost impossible. Imagine for a moment that
you could mark molecules in some such way
that you could identify them when you saw them
again. Assume that you took a glass of water
with the molecules of water all thus marked and
stirred it into the waters of the oceans of this
earth, that you waited a couple of million years
for thorough mixture, and that you then walked
up to the nearest hydrant in your vicinity and
casually drew a glass of water, you would find
about 2000 of your marked molecules in it! Of
course, we may be a few molecules out on this
estimate, but that is roughly the correct mathe-
matical number, because there are 2000 times
as many molecules in a glass of water than there
are glasses of water on the earth.
Again, molecules of air, if admitted into a
highly-evacuated 25-watt electric light bulb
through a hole so small that they had to flow in
single file, would take about 100,000,000 years
to fill it to atmospheric pressure. A little re-
flection will show that "purity," like everything
else, is probably only a relative condition.
"Some of 'em is more pure, and some of 'em is
less pure, but none of 'em is all pure," said the
sour cynic, and while he wasn't speaking of gases,
and was not a scientist for that matter, he was
uttering profound truth.
THE TIN "HAT"
VA/HAT is the queer tin "hat" for in the
* " modern gaseous rectifier tube? Nobody
outside of the research laboratories 'seems to
know. Even some of the "bootleggers" making
these tubes don't know.
In the early experimental forms of the helium-
gas tube, great trouble was met with owing to
the disruption of the cathode element under the
hammering of the ionized gas atoms. The earlier
tubes had disk shaped cathodes, and the gas
atoms pulled out electrons with such violence
that tiny pieces of solid metal were often ripped
loose from the electrode. These metal bits were
thrown against the glass walls of the tube,
blackening it, and resulting in the speedy
destruction of the cathode.
For this reason the peculiar tin-hat form of
cathode was evolved because, with this arrange-
ment, the bombardment of the cathode and emis-
sion of electrons is entirely internal. The action
all takes place inside of the electrode. If a bit of
metal is torn from the cathode at any point, it is
hurled across the inner chamber and thrown
back onto the element somewhere else. There is
no loss of metal because the cathode is continu-
ally built up as fast as it is torn down.
It seems that, if we, as human beings, could be
temporarily reduced to the size of, say, an atom,
together with a corresponding ability to see
small objects, and were then placed upon the
cathode of an operating helium-gas rectifier tube,
we would have an impression of standing among
ranges of heaving mountains of metal in a state
of furious convulsion and uproar, bombarded
with enormous meteors of helium and full of
volcanic upheavals and earthquake-like shocks,
while electrons would arise like clouds of steam
on all sides, or spurt out like fiery sparks.
.
A VIEW OF THE LABORATORY IN WHICH THE HELIUM-GAS RECTIFIER TUBE WAS PERFECTED
I HI- MA
NFWS AND INimPKHATIQN OF r.UUUI-'NT UAmQ KVHNI I V~
Can The Serious Problem of Radio Patents Be Settled?
THE recent adjudication of several
important patents, such as those of
Hazeltine and Alexanderson, has
forced upon the radio industry the long
deferred day of reckoning with inventive
genius. Conscientious and established man-
ufacturers have proceeded promptly to ob-
tain licenses under Radio Corporation
patents which make available to them the
work of some of the world's greatest labora-
tories. By assuming an annual royalty
guarantee of one hundred thousand dollars
a year, charged at the rate of 75 per cent,
of the cost of radio receivers, they become
licensed under R. C. A., A. T. & T., West-
ern Electric, General Electric, Westing-
house and Wireless Specialty patents.
Having assumed this substantial burden,
the licensees considered their patent diffi-
culties disposed of. But some quickly found
that licenses under Hazeltine and Latour
patents are also necessary to freedom from
patent difficulty and, probably quite re-
luctantly, signed the Hazeltine licenses with
the additional burden of a 25 per cent,
royalty and an annual guarantee of thirty
thousand dollars a year. This duty per-
formed, the manufacturer dismissed patent
trouble and consecrated himself to the
problem of selling newer and better radios.
And then came the independent inventor
to disturb his peace of mind. Old patents
were dug up, demanding recognition. New
patents, just issued, added to the swarm.
Some of these inventions are as worthy of
recognition as those covered by the Radio
Corporation license. Others may be worth-
less and which will not withstand the test
of adjudication.
The weary manufacturer's answer to
those demanding additional royalties is be-
coming less and less courteous. He is now
paying all that the traffic will bear. Unless
some remedy is offered, his answer to patent
holders soon will be: "A plague upon your
patents!"
The Prospects of a Patent Pool
SOME manufacturers have united in de-
fensive groups to protect themselves
against the swarm of inventions which
now confronts them. They foresee the neces-
sity for so great an increase in the price of
radio receivers by reason of patent royalties
that the public will no longer be able to
afford them. Faced with the alternatives of
excessive royalties or occasional injustice
to the legitimate inventor, the manufac-
turers have, quite naturally, tended to the
latter course.
No doubt, some of the inventors, whose
claims for royalties are being disregarded
or opposed, will eventually win adjudica-
tions, and triple damages, if they are suf-
ficiently patient and prosperous to afford
the protracted legal battle which must pre-
cede such a result. It is quite possible that
combined resistance to the inventor may,
in some cases, prove costly, because it is
not reasonable to assume that Radio Cor-
poration, Latour and Hazeltine patents
are the only ones which will be favorably
adjudicated.
Combined resistance, however, is the only
course open to the manufacturer because
there are too many unadjudicated patents
demanding attention. It would be suicidal
to agree to a license under all of them; the
cost of radio sets to the consumer would
double and sales resistance would fourfold.
Most of the executives in the radio field
wish to concentrate their attention on the
design, manufacture and merchandising of
radio equipment, but patent problems now
require an alarming proportion of their
time. Naturally, the leaders of the radio
industry are nervous. At every trade con-
vention and meeting, we hear talk of an
all-inclusive patent pool.
Unfortunately, no patent pool can be
successfully organized unless it has the
unanimous support of all radio manufac-
turers and patent holders. To relieve the
patent situation economically and pain-
lessly, there must be a single, powerful,
radio trade organization. Nevertheless, the
N. E. M. A. and the R. M. A. still— to
all outward appearances — indulge in short-
sighted rivalry. An unofficial canvass of
ninety per cent, of the membership of one
of these organizations reveals that all but
two were in favor of consolidation. To make
a consolidation possible, one or two leaders
in the R. M. A. must for a moment forget
that their organization has the largest
number of members and the youngest
blood, and one or two members of the
N. E. M. A. must forget some remarks
made several years ago over matters long
since settled. And both groups must cease
suspecting each other.
CHANGES IN THE FEDERAL RADIO COMMISSION
© Hcmy Miller
Henry A. Bellows, Sam Pickard.and Carl H. But man. Commissioner Bellows was appointed from the Minneapolis district where he had long ably managed
wcco. His resignation, effective November ist, left a vacancy which was filled by the President in appointing Sam Pickard who has been Secretary to
the Commission since its appointment. Carl Butman is the new Secretary succeeding Mr. Pickard and has many years of experience in Washington as
news correspondent, specializing in radio, to aid him in his new post. Mr. Butman has for some time been Washington correspondent for RADIO BROADCAST
,98
JANUARY, 1928
ACTIVITIES OF THE RADIO COMMISSION
199
The industry is headed for one of the
most dangerous shoals in its career. Doubt-
less, it will weather it successfully. But
how long the shoal will impede its progress
depends upon how successful it is in placing
the ship in the hands of one pilot, instead
of two squabbling deck hands, to guide it
past the patent whirlpool. It will require
leadership of the highest order to establish
a patent pool.
In the future, there will be a new and
greater industry, much greater than we
imagine to-day. The radio receiver is but
a nucleus of a home entertainment device
which will rival the automobile in useful-
ness and entertainment value and, in the
end, its gross sales figures will be as large
as those of the envied motor car industry.
The radio receiver, the phonograph, the
motion picture machine and the television
receiver will, some day, be available in a
single, compact, home-entertainment de-
vice. The public will pay as much for a
versatile means of home entertainment as
for an automobile to take them away from
home. The more the leaders of the radio
industry concentrate upon the develop-
ment of radio and the establishment of its
true market, the sooner they will have a
five-billion-dollar industry. At present, the
most vital aid in that objective would be
turning over radio's patent problems to a
patent pool. The alternatives are continued
squabbles, continued patent fights, and a
radio market still limited to about ten per
cent, of the American public.
The Commission Announces a
New Policy
THE Federal Radio Commission re-
cently announced a long list of al-
location changes which have been
made with the purpose of improving the
channels of a few of the leading stations of
the country. The Commission it is ru-
mored, will hereafter work on the theory
that there are a few leading, national sta-
tions, which are the favorites of listeners
all over the country and therefore deserve
clear channels, entirely free of interference
to the limit of their range. This is the basis
upon which several years ago Secretary of
Commerce Hoover worked out the plan of
Class A and Class B broadcasting stations
and urged on the commission in these
columns for more than a year.
Following this plan, WHAZ, which shared
time with WGY, was shifted to share time
with WMAK, giving powerful and popular
WGY a full channel. WJAR, Providence, was
shifted from 620 kc. to 800, eliminating
widespread heterodyning with WEAF, ten kc.
off, experienced throughout southern New
England. WEEI, Boston, was shifted from
670 to 650 kc., avoiding a heterodyne im-
posed upon it by a Chicago station. WTRL,
a little station in Tilton, New Hampshire,
formerly occupying a channel adjacent to
wjz, was shifted downward in order to
eliminate a whistle which it thrust on wjz's
carrier in large parts of New England.
WDWM of Asbury Park, New Jersey, was
shifted so as to eliminate conflict with
WSAI'S carrier. WNAC of Boston and WEAN
of Providence, Columbia chain members,
were made channel-sharing stations, prob-
ably in the interests of better management,
and moved quite far into the unpopular
higher frequency region. WCAU, a Philadel-
phia advertising station and now a mem-
ber of the Columbia network and WKRC of
the same chain were demoted from the
lower frequency region. WOR now has wos
of Jefferson City, Missouri, as a channel
neighbor instead of wsui, Iowa City. We
believe the Missouri station is more power-
fully received in Newark and will therefore
accentuate slightly the whistle which
already mars WOR'S programs.
Another station to benefit by the Com-
mission's reallocation is KSD, St. Louis,
which is given full time. KSD is one of the
pioneers of broadcasting and is deserving
of the consideration which the Commission
has shown.
The conclusion that N. B. C. stations
have fared better than Columbia chain
stations is inescapable, but it must not be
forgotten that the former do include most
of the pioneer stations of the country which
have served faithfully and well for years,
while most of the latter have not yet won
their spurs in public estimation. Clearing
the channels of the N. B. C.'s leading sta-
tions cannot be criticized, but it might have
been better policy to have concentrated
less on Columbia stations when the de-
moting process was begun.
The Commission Suggests
Synchronization Schemes
IN A speech before the American In-
stitute of Electrical Engineers, Com-
missioner O. H. Caldwell made some
remarks about the problems of maintaining
a broadcasting station on its assigned fre-
quency. He mentioned three methods of
accomplishing this purpose, one well known
and widely used, one successfully used ex-
perimentally but economically prohibitive,
and a third which is a rather unfortunate
suggestion. It is the Commissioner's idea
that, if complete frequency stability could
be secured and the heterodyne interference
between stations now assigned to the same
channels eliminated, more stations could
safely occupy the same channel. While this
is true, it must be realized that the audio-
frequency components of two stations on
the same channel also affect each other.
When the distant station does not come in
with sufficient volume to cause cross talk,
it often causes irregular distortion.
Cyrstal control, the first method sug-
gested for synchronizing carriers, is not
sufficiently stable to solve the problem.
Temperature and humidity changes affect
the frequency of the crystal and, conse-
quently, it does not give the absolute regu-
lation necessary for successful occupancy
of the same channel by two broadcasting
stations whose carrier ranges overlap.
The second method suggested, the use of
a wire circuit for the transmission of a con-
A WIRELESS STATION IN 1904
A 35-kw. spark transmitter was erected by the old De Forest Company for the Navy near San Juan,
Porto Rico. The illustration shows the receiving installation with Mr. Irodell, operator for the De
Forest Company using the receiving equipment which consisted of a "pancake" tuner and an electro-
lytic detector. It was not until 1906 that a carborundum detector was substituted for the electro-
lytic one. The call signal of this station, which may be recalled by old-timers, was SA.
200
RADIO BROADCAST
JANUARY, 192!
trolling frequency, which has been success-
fully employed by WBZ and WBZA at
Springfield and Boston, has the disadvan-
tage of being prohibitively expensive. For
example, if WOR attempted to eliminate the
heterodyne whistle caused by wos at
Jefferson City by this method, it would
probably cost some fifty thousand dollars
a year. To stabilize the whole broadcasting
structure would require perhaps five years
to erect sufficient telephone channels for
the purpose and an expenditure of perhaps
twenty million dollars a year in mainte-
nance.
The third suggestion made by the Com-
missioner was prompted by a suggestion
from WDRC of New Haven, Connecticut,
a 5OO-watt station. A heterodyne whistle,
originating from the carrier of WAIU, a
jooowatt station in Columbus, Ohio,
about 500 miles distant, had been suffi-
ciently annoy ing to require drastic measures.
To solve this problem, a receiving station
was installed five miles from New Haven,
connected by wire lines with WDRC'S trans-
mitter. By tuning this receiving set care-
fully so that the heterodyne whistle is
eliminated, WDRC'S carrier is adjusted to
coincide with that of WAIU. So long as the
operator is vigilant and skillful, there is no
heterodyne whistle.
But, if the whole broadcasting structure
depended for frequency stability upon
manual control, it would become a sorry
mess. One need but recall the days of the
regenerative receiver, with its heterodyning
carrier of but a tiny fraction of a watt.
Then imagine manually controlled broad-
cast transmitters with hundreds and thou-
sands of watts power, trying to establish
zero beat with each other. The incident
again emphasizes the fact that the Com-
mission is sadly in need of technical assist-
ance which will help the members to grap-
ple more wisely with their problems. Any
competent engineer could have pointed out
the dangers of this ingenuous panacea.
What Readers Say About Broad-
casting Conditions
THE following are quotations from readers
of these editorials. George Madtes, Radio
Editor of the Youngstown Vindicator,
writes: "1 have no doubt that the re-allocation
of frequencies has materially helped stations in
New York and Chicago, but it has not attained
the Commission's apparent goal — an arrange-
ment which would permit listeners everywhere to
enjoy the stations nearest them. We are within
fifty miles of stations in Cleveland, Pittsburgh
and Akron and depend upon them for local
service. Our four main stations in these cities,
WTAM, KDKA, WCAE, and WADC are often hetero-
dyned and WADC and WCAE are almost invariably
useless at night."
W. W. Muir of Lockport, New York writes:
"One cannot help but notice the difference be-
tween the stations which are operating in the
few wave bands on which there is only one station
and those operating on the frequencies on which
there are more than one station. The stations
which are operating on exclusive channels are
usually free from distortion, the signal being
strong and clear. The stations which are operat-
ing on wavelengths on which there are more than
one station show a decided tendency to be mushy
and weak, and have a wide variation in signal
strength from moment to moment One cannot
help speculating what is apt to take place in the
future. We know that the American public have
had lots of things put over on them without
complaint. It is hard to believe that they will be
willing to stand for the huge joke that it is
possible to successfully operate more than one
powerful broadcasting station on a single fre-
quency without serious interference."
Another correspondent writes from Wyoming
to the effect that KOA, Denver, is the principal
reliance for summer and winter reception of the
entire state. The Federal Radio Commission has
ordered that station to cut its power in half after
seven in the evening. Continuing, he writes: "Prac-
tically every strong station near the east coast is
located on the same frequency as some powerful
station on the west coast. While probably they
do not interfere in their home territory, the
heterodyne of the two completely ruins reception
in the Rocky Mountain region. Before the recent
changes, we could usually depend on woe,
HOW VISITORS SEE THE ATWATER KENT FACTORY
Davenport, and wcco, St. Paul, for WEAF pro
grams, but have been unable to locate either fo
a long time."
Another correspondent .vrites from Ohio tha
he is located "forty-eight miles air line fron
WTAM, 102 miles from wWj and 95 miles fron
WAIU . . . WTAM fades so badlv at night that i
is worse than useless, wwj is 'crowded to death
on both sides. There is not one station in thi
group, or any other station, that can be receive!
here without heterodyning. Yet the Chairman o
the Federal Radio Commission reports the dis
trict very much improved. It is all bunk. Som
stations must be eliminated."
INTERNATIONAL CONFERENCE CHANGES
BROADCASTING BANDS
'"THE International Radio Telegraph Con
* ference at this writing is still in session ii
Washington. Very few of the articles of the nev
international agreement have yet been adopted
Some opposition has appeared to the Americai
proposal that no more spark stations shall b
licensed and that steps be taken to eliminat
gradually those in existence with a view to thei
complete disappearance in 1935. The eliminatioi
of spark transmitters is proposed largely in thi
interests of the broadcast listener.
In the matter of frequency allocations, th<
amateurs, as usual, have defended their positioi
with great heat. The Japanese delegation, ii
particular, was far from cordial in its attitudi
toward amateurs. The British, French and Ger
man governments sought lower frequency
channels for broadcasting in the 1000-, 1300-
1500- and i8oo-meter regions, in addition to thi
usual bands in general use. It was finally decide(
to consolidate these requests for a longer wavi
broadcasting band of setting aside 1500 to ij5<
meters (200 to 194 kc.)'for the purpose, provid
ing about two channels with ten-kc. separation
At this writing, this band is not yet officially
approved, but is likely to stand.
The Committee on frequency allocation, whili
favorably inclined toward the recommendation:
of the American delegation for the broadcastinj
band, does not, at this writing, plan to devoti
the entire 500- to i 5Oo-kc. region to broadcastinj
purposes. In the plan announced, it proposes t<
utilize the lower 200 kc. (i.e. from 130010 ijookc
or 230 to 200 meters) for both broadcasting anc
ship stations. This does not mean that the 27;
American broadcasting stations, now occupyinj
that part of the band, will have to get off, but i
is likely that ship interference will develop a
this end of the broadcasting channels. This movi
on the part of the International Teiegrapl
Conference will undoubtedly accentuate stil
further the need for curtailing the number o
broadcasting stations on the air in the Unitec
States.
BROADCASTING NOTES
THE National Broadcasting Company and th<
British Broadcasting Company will cooper
ate in several short-wave international pro
grams. In 1924, wjz participated in the first at
tempt at international broadcasting by relay
A dance music program from the Savoy Hote
was radiated from England and intercepted a:
Houlton, Maine, and from there sent by wire t<
wjz, in New York. The fading experienced or
the i6oo-meter wavelength, (187 kc.) upon whicl
the program was relayed, was sufficient to dis
courage further attempts along these lines a
that time. With the development of short-wavt
transmitters, however, more reliable results ma)
be expected, f ? f IN A statement of its policj
on international broadcasting, the British Broad-
casting Company lays considerable stress upor
the failures of previous attempts along thes(
JANUARY, 1928
BRIEF NEWS ABOUT IMPORTANT RADIO MATTERS
201
[lines. It describes an experimental relay of pro-
i grams for Sidney as barely recognizable; a paral-
lel attempt to relay Melbourne a few days later
as a complete silence. It regrets that so much
emphasis has been laid upon the possibilities of
international broadcasting and points out that
considerable development work is necessary be-
fore we can hope for regular and reliable inter-
national broadcasting. I I t E. T. SOMERSET
writes us from Sussex, England, that he enjoys
WGY, wjz, WLW, WEAF and KDKA on their regular
broadcasting channels, but American programs
come in with much greater regularity on the high
frequencies. 2XAZ, WGY'S short-wave twin is the
star performer, with KDKA on twenty-six meters
and ZXAF following. He has also heard with
great clarity, 2XAH, WRNY and WLW on its short
wave, and ANH, Radio Malabar, Bendosng, Java,
on 17.4 meters and last, but not least, 2ME,
Sidney, Australia. It gave him a particular thrill,
he writes, to hear the clock striking four A. M. in
Sidney, when it was still seven p. M., British
summer time, of the previous night. Mr. Somer-
set advises American fans to listen for 5 OB,
Daventry, England, on a frequency of 610 kc.
with 30 kw. output, and Langenberg, Germany,
with a 25 kw. output on a frequency of 640 kc.
Iff SAM PICKARD, who first gained fame in
radio circles as director of the Department of
Agriculture Radio Service, has been made Fed-
eral Radio Commissioner to succeed Henry A.
Bellows, recently resigned to resume the manage-
ment of wcco. The Commission loses Mr. Bel-
lows because the gentlemen of the Congress
failed to confirm his appointment. He was a use-
ful and hardworking Commissioner. Mr. Pickard
is qualified to serve on the Commission because
of his familiarity with its problems as its former
secretary. Carl H. Butman now becomes Secre-
tary of the Commission. He is well known to the
newspaper fraternity and may be helpful to the
Commission, not only as an efficient secretary,
but 'n advising it how to handle its relations with
the press and the public. I I f " I HAVE come to
the conclusion that it is not a practical or even a
theoretical advantage to a broadcaster to sponsor
a program through any small station. The com-
panies that are marketing national products can
use radio advertising to excellent advantage but
for local companies to broadcast through a small
local station is not good advertising, in my opin-
ion. Their efforts are so mediocre in comparison
with the programs sponsored by the big com-
panies and transmitted through the high power
of a well equipped, well operated station, that a
bad impression is made and no benefit is derived."
That is the statement, not of a newspaper pub-
lisher, but of Mr. Robert A. Fox, of Ashland,
Ohio, who owned and operated station WLPC.
Realizing that the small station serves little use-
ful purpose, WLPC requested the Federal Radio
Commission to cancel its license and its owner
now states that he wishes "about two hundred
more stations, now operating, would do the
same." f I f THE DEPARTMENT OF AGRICULTURE
Farm Radio Service is being broadcast by
eighty-nine radio stations in thirty-four states.
Each of these stations will broadcast one or more
of the eleven regular farm and household radio
services prepared and released by the U. S. De-
partment of Agriculture. Such services as these
help to sell radio to the farmer.
NEWS OF THE PATENT FIELD
I EE DEFOREST won a victory over Edwin
*-• Armstrong in the United States Circuit Court
of Appeals at Philadelphia, which decided that
he is the inventor of the regenerative or feed-back
circuit and the oscillating audion. Since the right
to use both DeForest and Armstrong patents is
included in the R. C. A. license, the decision does
not affect the R. C. A's licensees particularly.
Certain companies, however, operated under
licenses granted by Armstrong before his patent
was acquired by the Westinghouse Company,
appear, through this decision, to be liable for
royalties under the DeForest patent. There is
a possibility that this case may now reach the
Supreme Court, although that body has the
power to refuse to consider the matter. ? f f THE
MACKAY interests announce that the DeForest
victory places them on an equal footing with the
Radio Corporation of America in the field of
wireless communication. They will undertake
immediate steps to establish short-wave wireless
systems across the Pacific Ocean and throughout
the United States, f f J PATENT No. i ,639,042,
recently issued to Wilford MacFadden of
Philadelphia and assigned to the Atwater Kent
Manufacturing Company, describes the use of
a potentiometer for the stabilization of radio-
frequency amplifiers. This system was used ex-
tensively before the neutrodyne systemof stabili-
zation was developed, f f ? THE DUBILIER
Condenser Company has notified a number of
manufacturers of the scope of patents 1,635,1 17,
1,606,212, and 1,455,141, describing plate-
current supply devices and power amplifiers.
Included among prospective defendants under
these patents are various Radio Corporation
licensees. One of these patents describes a power
system comprising rectifiers, filter and choke
circuits, using a. c. on the filaments; another, a
two-stage power amplifier with
alternating current on the fila-
ments and a C battery used to
obtain grid bias; plate potential is
obtained from a thermionic recti-
fier.
AMONG THE MANUFACTURERS
TH E Sonora Phonograph Com-
pany, manufacturers and dis-
tributors of phonographs and radio
sets, the Bidhamson Company, a
patent holding corporation, organ-
ized by John Hays Hammond, Jr.,
Lewis Kausman and others, and the
Premier Laboratories, headed by
Miller Reese Hutchinson, have
recently merged to form a corpora-
tion devoted to the manufacture
of acoustic devices, f f f ARTHUR
D. LORD, receiver in equity of the
DeForest Radio Company, has
filed a complaint with the Federal
Trade Commission on Clause IX
of the R. C. A. license contract.
This clause specifically forbids
R. C. A. licensees to equip and
sell licensed radio sets without
equipping them with R. C. A. or
Cunningham tubes to make them
initially operative. In his com-
plaint, Mr. Lord claims that the
consumer is penalized because he
is forced to take a tube which
otherwise might not be his choice.
The clause is obviously aimed at
independent tube manufacturers.
He expfesses the belief that this is
an attempt at monopoly and re-
straint of trade, a direct violation
of the Federal Trade Commission
Act, the Clayton Act and the
Sherman Anti Trust Law. if "f I
IN FULL page newspaper advertise-
ments in the principal newspapers
of the country, Mr. A. Atwater
Kent announced a price reduction
of twenty per cent, in his receiv-
ing sets. This reduction, says the
announcement, is made possible by tremendous
increase in production facilities. Particularly in
the lower price classes, we may expect an era of
intensive price competition with consequent ad-
vantages to theconsumer. I t f POWELCROSLEY,
JR., has announced that his Bandbox model will
probably not be changed for several years. This
is the first time that a manufacturer has ven-
tured such a prediction, fit THE STEWART
WARNER Speedometer Corporation, which has
long defied the R. C. A. in patent matters, is the
most recent addition to the ranks of those com-
mitted to a 75 per cent, royalty.
A STATEMENT by Dr. J. H. Dellinger,
calls attention to a general current mis-
understanding regarding short-wave beam com-
munication. The international short-wave beam
links confine the radiated energy to a thirty-
degree arc which is indeed not concentration in a
single narrow path. It represents merely. Doctor
Dellinger points out, an economic advantage
and not a secrecy system.
Science has been unable to affect a concentra-
tion of radiated wave energy, either light, sound,
or heat, in a perfect single beam by the aid of
any form of reflector, and there seems little
ground for hope that we shall soon achieve it
with radio telegraphy or telephony. The concept
that we may reduce beam transmission to a
concentration comparable to that obtainable by
wire communication is now untenable.
THE NEW COAST GUARD SHORT-WAVE
TRANSMITTER
B. J. Fadden, chief radioman aboard the U. S. C. G. Modoc in
ice patrol duty is shown standing beside the 35.5-meter
(85oo-kc.) transmitter. The transmitter on this wave is used
for direct communication between the Modoc while in the
North Atlantic ice fields and headquarters in Washington
RADIO BROADCAST Photograph
MAKING FINAL ADJUSTMENTS ON THE PUSH-PULL AMPLIFIER DESCRIBED IN THIS ARTICLE
Measurements of the grid bias voltage are being made. Note the electro-dynamic Magnavox loud speaker in the background. A circular baffle-
board has been attached to it in the laboratory
PUSH-PULL AMPLIFICATION— WHY?
By HOWARD E. RHODES
THE essential prerequisites for faithful
reproduction from a radio set are, first,
a properly designed receiver capable of
giving reasonably distortionless amplification
and, secondly, a good loud speaker fed with
power from a source able to supply the necessary
energy without overloading. Much of the dis-
tortion in receivers is due to tube overloading,
which usually occurs to the greatest extent in
the last audio tube. The cure for this condition,
obviously, is to use a tube, or combination of
tubes, in the output circuit that has a high
enough power rating so that over-
loading will not take place. As will
be brought out in the following dis-
cussion, this requires that "power"
tubes be used in the output circuit
of the receiver, and at the end of
the article some constructional de-
tails will be given regarding a push-
pull amplifier employing 210 type
tubes. Such an amplifier will deliver
a large amount of power to a loud
speaker without overloading.
Let us first determine approxi-
mately what requirements are nec-
essary in the output of a receiver
to prevent serious overloading. By
the term "overloading," in this dis-
cussion, we mean that the input
voltage on the grid of the tube is
so great as to cause the grid to be-
come positive at times so that cur-
rent begins to flow in the grid circuit.
In the operation of any ordinary
amplifier, care must be taken that
the signal input voltage is never
great enough to cause grid current to
flow for, when this does occur, the
input signal will be badly distorted. In deter-
mining the characteristics of an amplifier to pre-
vent overloading, we must assume certain values,
with the result that the final answer will not be
exact, but should nevertheless give a good idea
of what conditions must be met. Suppose, to
take an average case, that an orchestra is
broadcasting and that the ratio of power be-
tween the fortissimo and pianissimo passages as
played by the orchestra, is a million to one,
corresponding to a power ratio of 60 TU. Be-
cause of the characteristics of the amplifier
RAD.O B«O»DCASI Photograph
A CLOSE UP
Showing the plug which provides for variations in line voltage
2O2
used to pick up this music, it is necessary to
cut down this power ratio somewhat so as to
keep the pianissimo passages above the noise
level and to prevent the fortissimo passages
from overloading the amplifier. In practice,
this ratio is cut down in the control room at the
broadcasting station by an operator in charge of
the gain control. The power ratio is, after being
cut down, generally about 40 TU into the
amplifier system. This corresponds to a ratio
of ten thousand to one. Let us assume that this
ratio is maintained throughout the entire broad-
casting and receiving system, a con-
dition which will be true if there
is no overloading at any point. Sup-
pose that the energy in the pianis-
simo passages as they are reproduced
by the loud speaker is 3 microwatts
(0.000003 watts).
I o get an idea of what this
amount of energy represents, it may
be compared to the average speech
power delivered by a person speak-
ing, which is about 10 microwatts.
The energy associated with the
fortissimo passages will be 10,000
times as great, or 0.03 watt. It is
now necessary to assume a figure
for the average efficiency of the
loud speaker, but because the effi-
ciency of a loud speaker varies con-
siderably over the range of audio
frequencies, it is hardly accurate to
assume an average efficiency and
have it mean very much. We wilt
do so in this case, however, merely to
get some idea of how much power is
required. The efficiency of a loud
speaker is very low, we will assume
f
JANUARY, 1928
PUSH-PULL AMPLIFICATION— WHY?
203
it to be 3 per cent., which means that, in order
to obtain a given amount of sound energy, we
must supply the loud speaker with many times as
much electrical energy. The amount of electrical
energy required is found by dividing the sound
energy output by the efficiency of the loud
speaker; in this case we must divide 0.03 watt
by 0.03 (3 per cent.) and the quotient, one
watt, is the amount of energy the power tube
in the receiver must be capable of delivering to
the loud speaker during the fortissimo passages.
Now let us see what tube or combination of
tubes is capable of supplying this power.
The maximum amount of undistorted power
that can be obtained from various tubes is
given below.
TABLE NO. i
PARALLEL
ARRANGEMENT
(i.) Requires only half as
much input foliage from
receiver to give same out-
put as push-pull ar-
rangement.
(2.) Distortion due to over-
load quite noticeable.
(3.) Voltage gain somewhat
higher.
(4.) Plate Impedance four
times smaller than push-
pull arrangement.
(5.) Distortion due to cur-
vature of tube charac-
teristic not eliminated.
(6.) Some hum may result
if filaments are oper-
ated on a. c.
PUSH-PULL
ARRANGEMENT
Requires twice as much
input voltage from receiver
to give same output power
as parallel arrangement.
Slight overload (about 25
per cent.) possible without
noticeable distortion.
Voltage gain is somewhat
lower.
Plate impedance four times
greater than parallel ar-
rangement.
Distortion due to curvature
of tube characteristic elim-
inated.
Any a. c. bum from fila-
ments eliminated due to push-
pull arrangement
TABLE NO. 2
OUTPUT
RESISTANCE
INCREASE
IN CURRENT
DECREASE
IN CURRENT
10,000
5,000
1,000
5
7
'4
I
1 1
TUBE
TYPE
PLATE
VOLTAGE
GRID
VOLTAGE
UNDISTORTED
OUTPUT
WATTS
'99
90
- 4-5
0.007
1 20
'35
-22.5
0. 1 IO
2O I -A
90
-90
0.055
112
"57
-10.5
0.195
171
180
-40.5
0.700
2IO
450
-38
i .700
We shall endeavor to explain now how the push-
pull amplifier eliminates a certain type of dis-
tortion which exists in a simple single-tube am-
plifier. It is necessary to start the discussion by
examining in some detail the characteristics of a
cx-3io (ux-2io) type tube (or, for that matter,
any tube).
When two tubes are used in a push-pull ar-
rangement the maximum power output of the
combination is twice that of a single tube.
It is evident from the table that
the only tubes delivering, in push-
pull arrangement, more than I watt
of power are the 171 and 210 com-
binations, and, therefore, these com-
binations are most satisfactory for
supplying a loud speaker with the
necessary amount of undistorted
power. In practice it will be found
that a push-pull amplifier can be
overloaded, but this amount of
overload is so small as to be negligible.
This treatment of the problem is not exact.
It was necessary to assume an average value for
the power associated with the pianissimo pas-
sages and this first assumption determines how
much power will be required for the fortissimo
passages. It is also true that a considerable
amount of distortion can be present in the
output of a loud speaker without being evident
to most of us. The figures do, nevertheless, give
an idea of why power tubes must be used, and
show that present-day loud speakers cannot
be supplied with sufficient undistorted power
from tubes other than the 171 or 210 type.
Marked improvement in the efficiency of loud
speakers will some day make other tubes with
a lower power output suitable for use in the last
stage of a receiver, but until such an improve-
ment is made, we must make certain that we
have plenty of power handling capacity avail-
able in the receiver's output.
PUSH-PULL OR PARALLEL TUBES?
A T THIS point there might be some question
•"* regarding the relative merits of a push-
pull amplifier with two 210 tubes and a parallel
arrangement of the same tubes. Let us list the
advantages and disadvantages of the two ar-
rangements.
The italics indicate with which arrangement
the advantage lies. Although point No. 4 was
indicated as an advantage for the parallel ar-
rangement, it is possible, by the use of a special
push-pull output transformer, to compensate the
higher plate impedance of the push-pull circuit,
and the two arrangements will then be equal
in this respect. Point No. 5 has not, as yet, been
explained, but it is the most important reason
for the existence of the push-pull arrangement:
FIG. I
Grid voltage -plate current curves of a 210 type tube
In Fig. i we have drawn several curves for a
single tube of the 210 type with a plate voltage
of 400 and a grid bias of -35 volts, and these
curves show the relation between the plate cur-
rent and the grid voltage with various load
resistances in the plate circuit. The curve marked
1000 was made with a looo-ohm resistance in
the plate circuit and the curves marked 5000 and
10,000 were made with resistances of 5000 and
10,000 ohms respectively in the plate circuits.
These curves are dynamic characteristics in the
sense that they indicate how the plate current
will vary with different loads in the plate circuit.
If a signal having a value of, for example, 10
volts, is impressed on the grid of this tube, it
will cause the grid voltage to vary 10 volts either
side of its average value of 35 volts. Such a sig-
nal voltage is represented in Fig. I by the curve,
marked "signal voltage," drawn below the grid
voltage axis. If the change in plate current due
to this voltage is determined on the io,ooo-ohm
curve by reading the values of plate current at
each extremity, we find that, when the voltage
is positive, 'the current rises to 21 milliamperes
and that, when the voltage is negative, the cur-
rent decreases to 1 1 milliamperes, a drop of 10
milliamperes.
The signal voltage of 10 volts has, therefore,
caused the plate current to increase and decrease
an equal amount with respect to the average
value, the increase and decrease being 5-milli-
amperes in this case. If the same measurements
are made on the 500o-ohm curve we find that
the plate current increases 7 milliamperes above
the average value but only decreases 6 milli-
amperes. On the looo-ohm curve the increase is
14 milliamperes and the decrease is only 11
milliamperes. These values have been arranged
in the form of a table:
This table indicates clearly that, as the resist-
ance in the output circuit of the tube decreases,
the increase and decrease in plate current due
to a given signal become unequal. This represents
distortion because it indicates that the positive
side of the input voltage produces a relatively
greater change in the plate current than does
the negative side.
100 LOUD SPEAKER CONSIDERATIONS
AND now let us consider the
^* loud speaker. The impedance of
a loud speaker is a function of fre-
quency and increases with increase
in frequency. At low frequencies,
therefore, the loud speaker will have
a comparatively low impedance and
the tube feeding the loud speaker
will then operate on the character-
istic corresponding to a low-resist-
ance load in the plate circuit. This
characteristic is indicated by the
looo-ohm curve in Fig. i. At me-
dium frequencies, where the loud
speaker's impedance is higher, the
tube will operate on a characteristic
similar to the 5OOO-ohm curve, and
at high frequencies the tube will
operate on a characteristic similar
to the io,ooo-ohm curve. As in-
dicated by the figures in table No. 2,
the io,ooo-ohm curve is quite
straight and therefore produces
little distortion. A small amount of distortion is
produced by the 5OOO-ohm curve, but much
greater distortion occurs when the tube operates
along the jooo-ohm curve. When a loud speaker
is operated from a single 210 type tube, this dis-
tortion occurs and, if possible, it would evi-
dently be of advantage to arrange the circuit
so that no distortion of this type is produced.
This leads us to consider push-pull amplifica-
tion.
The circuit diagram of a push-pull amplifiei
is given in Fig. 2. In some push-pull arrange-
ments the output choke, L, is replaced by a
transformer, but the circuit will function with
a simple choke coil as indicated. When a signal
is induced in the secondary of the input trans-
former, T, the voltage relations are as indicated
by the plus and minus signs on the diagram. It
will be noted that the voltage at one end of the
transformer is positive relative to the. voltage
at the other end, which is negative. The signal
voltage impressed on either grid is one half the
total voltage across the transformer. Since the
two grids are at relatively opposite potential
the plate current changes will also be opposite
Input
Speaker
FIG. 2
The circuit connections for a push-pull amplifier
204
RADIO BROADCAST
JANUARY, 1928
in nature. Referring to Fig. I, this means that,
during the time that the grid of tube No. 2 goes
positive, the plate current will increase, and that
the plate current of No. 2, as the grid goes
negative, will decrease. In Fig. 3, we have
represented at A the signal induced in the
secondary of the input transformer, T, curve A-i
indicating how the voltage on the grid of tube
No. i varies and curve A-2 indicating the vari-
ation of voltage on the grid of tube No. 2. It
should he noted that the voltages are similar,
that there is no distortion, and that the voltages
are in opposite phase relation to each other
(when one is positive the other is negative).
Now these voltages cause changes in plate cur-
rent in accordance with the curves given in Fig.
I, and if the particular signal being amplified is
low in frequency, the loud speaker's impedance
will be low and the tube's characteristic will have
a form similar to the looo-ohm curve. This
curve will produce unequal changes in plate cur-
rent (see table No. 2) and the curves at B-i
and B-2 in Fig. 3 indicate the change in plate
current due to the voltages impressed on the
grid. It should be noted that these two curves
are distorted (the positive halves are larger
than the negative halves) although the distor-
tion of the two curves is similar in nature.
These curves at B can be split into two parts,
as indicated at C, C-i and C-2 represent plate
current variations exactly similar in form to
the grid voltage variations and C-j and C-4
represent additional plate current variations
due to the curvature of the tube characteristic.
The point of interest here is that, although the
variations in plate current indicated by C-i and
C-2 are out of phase (as they should be) the dis-
torted parts represented by C-3 and C-4 are in
phase; that is, they are both positive or negative
at the same time. In order to have current flow
through the loud speaker, the a. c. voltage at one
plate must be opposite in sign relative to the
voltage at the other plate. We might consider
that the plate whose voltage is negative tries to
"pull" some current through the loud speaker
while the plate whose voltage is positive tries
to "push" some current through the loud
speaker, and this gives us an idea of why such
an amplifier is termed ''push-pull." C-} and C-4,
indicating the distorted part of the plate cur-
-C-3
FIG. 3
These curves are used to explain how a push-pull amplifier operates
rent variation produced by the curvature of the
tube characteristic, are such that both plates
are relatively positive at the same time. These
currents, therefore, cannot force any energy
through the loud speaker. The only current
flowing through the loud speaker is indicated by
C-i and C-2, and it is undistorted. In this way
two tubes in a push-pull arrangement eliminate
Gain
0 5 10 15 20 25 30 35 40
VOLTS ACROSS PRI. OF INPUT TRANSFORMER
FIG. 4
What happens when an amplifier is overloaded
can be determined from these curves. They are
explained in the text, col. 3, page 204
RADIO BROADCAST Photograph
THE LAYOUT OF THE PUSH-PULL AMPLIFIER FROM ABOVE
Nod. c. plate current can flow through the loud speaker, and blocking condensers are therefore
not necessary in this amplifier for this purpose. However, in the arrangement shown the loud speaker
itself is at a potential of 500 volts above ground and a serious shock will be had if the loud speaker
and a grounded object are touched at the same time. In order to make the installation entirely safe
it is a good idea to connect a 4-mfd. high-voltage condenser in series with each lead to the loud
speaker terminals
a form of distortion present in a simple circuit
using a single tube.
In Fig. 4 are given a group of curves obtained
from some data on the Samson push-pull ampli-
fier illustrated in this article. The three curves
shown in solid lines were made using a single
210 type tube. Note how the gain begins to fall
off when the voltage on the grid reaches about
18 volts and this point also corresponds approxi-
mately to the point at which grid current begins
to flow. The power output also begins to flatten
out after more than 18 volts is placed across the
input. These three effects, a decrease in the gain,
the presence of grid current, and a falling off in
power output, are all definite indications of over-
loading. The dotted curve indicates the power
output obtained from two 2io's in a push-pull
amplifier. This curve also begins to fall off
slightly after about 18 volts has been placed on
the input, but the change is not as rapid as in
the case of a single tube. The power output of
the push-pull amplifier at the point where grid
current begins to flow is twice as great as that 01
a single tube.
The Samson push-pull amplifier illustrated
in this article is an excellent example of a well-
designed unit. The major characteristics of this
amplifier are as follows:
(i.) The unit consists of two 210 type tubes in
a push-pull arrangement fed from an input
push-pull transformer. The unit is designed
to connect to the output of the first audio
stage in a receiver, and thereby makes pos-
sible the attainment of better quality than
can be obtained from the smaller tubes or-
dinarily used in a receiver.
(2.) The power transformer and choke coils have
been enclosed in a nicely finished metal
case with the various leads brought out
through a small terminal box at one end.
At the other end of the transformer is a
special plug, a Samson feature, which can
be turned to different points to compensate
differences in line voltage. The condenser
bank is also enclosed in a metal case.
(3.) The device will supply B power to a re-
ceiver. The circuit incorporates a glow
tube which maintains the output voltages
from the various terminals practically con-
stant independent of load, and this makes
it possible to use the device with almost
any receiver with assurance that the vol-
tages marked on the terminals will be equal
to the actual voltages delivered by the de-
vice. The following voltages are available;
180, 135, go, 6y|, and a variable tap so that
accurate adjustment of the detector voltage
can be made. The 210 type tubes receive
about 500 volts and the C bias is about 40
volts. The device also supplies C potentials
as follows: -4.5, -9, and -43.
The circuit diagram of this power amplifier is
given in Fig. 5. The following parts were used
in the amplifier illustrated in this article.
JANUARY, 1928
PUSH-PULL AMPLIFICATION— WHY?
205
LISTS OF PARTS
TL — Samson Power Block, Type 210,
Containing Power Transformer and .
Two Filter Choke Coils . . . . f 37.00
Tobe Condenser Block, for Samson
Power Amplifier, Containing the
Eleven Necessary Condensers . . 38.00
R; — Electrad y2oo-Ohm Type C "Tru-
Volt" Resistance, 50 Watts . . . 2.25
Ro — Electrad 42o-Ohm Type C "Tru-
Volt" Resistance, 25 Watts . . . 1.50
R, — Electrad 5O,ooo-Ohm Variable
Resistance, Type T-joo .... 3.50
R< — Tobe io,ooo-Ohm Veritas Resist-
ance 1.10
T — Samson Input Push-PuII Trans- \
former, Type Y (
Lr- Samson Output Push-PuII Choke, (
TypeZ J
12 — Eby Binding Posts .... 1. 80
4 — Benjamin Sockets 3.00
2 — RCA ux-2io (Cunningham cx-
310) Tubes 18.00
i — RCA ux-8y4 (Cunningham cx-
376) Tube 5.50
i — RCA ux-28i (Cunningham cx-
381) Tube 7.50
TOTAL
$138.65
The circuit diagram has been marked with
figures corresponding to the terminal markings
on the power block and the condenser block.
The arrangement of the apparatus on a single
large baseboard makes it a simple matter to
construct it and the circuit diagrams and pho-
tographs given herewith should supply all the
necessary information.
All of the transformer cases, and also the
case of the condenser block, should be con-
nected to the negative B, as indicated in the
schematic diagram, to prevent hum. This
grounding can generally be most readily accom-
plished by running a lead from the negative B
to the mounting screws of the various units.
The wire can be fastened under these mount-
ing screws. Remember that the voltages de-
livered by the transformer are very high and
therefore care is necessary in making all of
the connections. The 5O,ooo-ohm resistance is
the only variable control in the entire unit, and
it is used to obtain accurate adjustment of the
detector voltages.
When the construction has been completed,
the special plug on the power input side of the
Samson transformer may be inserted in the
correct manner and connected to the a.c. light
socket. When this is done, the tubes should
light and the regulator tube should glow with
a pinkish light.
In operation, the transformer block may be-
come somewhat warm, but if it becomes so hot
that the hand cannot be comfortably held on it,
it indicates some error in the wiring. The input
terminals of the device should be connected to
the output of the first stage of the receiver and
the loud speaker then be connected to the out-
put of the amplifier.
If carefully constructed and properly operated,
the unit will be found capable of giving excel-
lent reproduction.
Caution: Ground here only
if A Battery is not groundec
180V O
135 v.O
-4.5V. O
-43V. O
F- F+
874 Regulator
Tube Connections
FIG. 5
This is a complete circuit diagram of the Samson push-pull power
amplifier. The various numerals on the units correspond with
the markings on the terminal blocks on the various parts; num-
bers in circles indicate terminals on the condenser block. This
amplifier employs two 210 type tubes in the push-pull circuit, a
type 281 tube as the rectifier, and an 874 type regulator tube.
The connections to the socket holding the latter tube are indicated
in the diagram. The P and F minus terminals on the socket
are connected in the filter circuit as shown at the point marked
"874 BK." on the diagram. The two corresponding contacts on the
tube are short-circuited inside of the tube base during the process
of manufacture and, therefore, if the regulator tube is removed
from its socket while the power is on, the circuit is automatically
opened and damage to the filter condensers thus prevented. The G
post on the socket connects to the + go voltage tap and the
F + terminal connects to B minus
Condensers
Mounted in
One Block
TTTTTTT
R«
-1500V. O.C. '~-400V.D.C.
C BLOCK
-200V.D.C.
'/TO JUDGE by the sale of radio-phonograph
-*• combination instruments and the popularity of
the various electromagnetic pick-up units, the
phonograph and the radio set in combination are
climbing to high favor among radio users. If you
have a good radio receiver and loud speaker, the
purchase of a magnetic pick-up makes your old
phonograph up to dale and all the fine new electrical
recordings then pour out of your loud speaker
sounding as well as the best radio program. This
magazine and others have contained descriptions on
how to bring the old phonograph up to date using the
electromagnetic pick-up. These pages on the enter-
tainment that the radio-phonograph offers to the
user are a regular feature of RADIO BROADCAST.
It is not enough to know that the combination of the
radio and phonograph provides a flexibility of home
entertainment that is astounding — we feel our
readers would also like to know what the disks
actually offer. These columns discuss only the
records made by artists well known to broadcasting.
— THE EDITOR.
A New Use for Records
TN THE days when life was simpler, we thought
of the phonograph merely as an instrument
for the diversion of the multitude of home-loving
folk, who were enabled by it to listen to jazz or
classical music without budging an inch from
their Franklin stoves. Then someone realized
that by preserving on its records the speeches,
music and other audible accompaniments of
events of national importance the phonograph
could be made to have a definite historical im-
portance. And now the phonograph has had
another burden laid upon it, that of delivering
speeches for important individuals at gatherings
at which they cannot themselves be present.
This was actually done at the opening of the fifth
annual convention of the American Institute of
Steel Construction in Pinehurst, North Carolina,
on October 25. Secretary of Commerce Herbert
Hoover was asked to deliver the speech of wel-
The PHONOGRAPH
A CLOSE-UP OF VICTORS NO. 955
" ELECTROLA"
This illustration shows the radio panel of this
elaborate combination radio phonograph model.
The radio panel can be tipped for convenience in
operation as shown here, or it can be tilted up-
right. Pilot lights make tuning easy. This instru-
ment, completely electrically operated will play
12 records without stopping, contains built-in
loop, power loud speaker (shown behind the grille
above) and power supply. Price complete, $1550
come at this convention, but he could not take
the time to make the trip there and back. The
Institute, determined to have the speech, en-
listed the services of the Victor Company, who
made a record of a speech which Mr. Hoover
delivered in his own office in Washington, and on
October 25 this record was reproduced in Pine-
hurst before the convention. As Mr. Hoover
himself remarked, one of the advantages of this
method is that it puts a definite time limit on
speeches. What a unique device for curtailing
long-winded recitations! And what a splendid way
to eliminate superfluous oratory, for as the Secre-
tary also noted, and as all who have broadcast
well know, a microphone is about as inspiring
an audience as a bathroom door knob! We
foresee a great future for this branch of phono-
graph service.
A Review of Recent Records
BUT though the phonograph now has a Mis-
sion it still continues to provide amusement
and entertainment for those who want it. And, as
far as we can see, the recent output of records is
much the same as ever; there are many good
records, a few poor ones, and a goodly supply
of in-betweens. Of the latter the majority seem
to be instrumental dance records. The orchestras
which play for these are admirable and the record-
ing of their playing is in most cases all it should
be, but the selections on which they waste their
talent are just about zero in musical worth. The
result is like apple pie without the apple. Alas
for more Gershwins and Berlins!
On the Victor, Columbia and Brunswick lists
are many names familiar to those who sat at
home turning the dials of their radio sets through
the long winter evenings of 1926-27. They will
recognize numerous regular performers and
others who have made only a limited number of
ethereal bows on such programs as Atwater Kent,
Eveready, and Victor. New names are being
added daily to this register of recording-broad-
casters and now that Columbia has its aerial
chain, we can expect even more.
Of the recent dance records, Who Do You Love?
and /'// Always Remember You played by Paul
Whiteman and His Orchestra (Victor) head the
list. This famed outfit have taken two of the best
songs now extant and by decorating them with a
trick orchestration in the inimitable Whiteman
manner have made an unusually good record out
of them.
Is It Possible? and Just Call On Me played by
Leo Reisman and his Orchestra (Columbia) is
another grand record. If we hadn't always lived
in the belief that Whiteman had no equal, we
would say this was as good as the first record on
our list. We will say it. Anyway, it is pretty
smooth music and we defy you to keep your feet
still when you listen to either number.
Gorgeous by Johnny Hamp's Kentucky
Serenaders would be an asset to any collection of
dance records and its companion on the opposite
side, There's a Trick in Pickin a Cbick-Cbick-
THE UTICA JUBILEE SINGERS
There are those who are not especially impressed
by negro spirituals. But if you like these interest-
ing melodies and want to hear them sung as they
should be sung, listen to this group on wjz and
associated stations at 9:45 eastern time Sunday
evenings. They have made one double-faced
recording for Victor, one of the finest recordings
of the kind we have heard
206
Chicken by Nat Shilkret and His Vic-Vic-Victor
Orchestra is just as full of pep. (Victor).
Habitual listeners-in on Harold Leonard and
his Waldorf Astoria Orchestra will want his
latest Columbia product, Just A Memory and
Joy Bells. You don't have to be told it is good.
Once Again and No Wonder I'm Happy
as played by Ernie Golden and his Hotel Mc-
Alpin Orchestra will have the ring of familiarity
to those who tune-in on station WMCA. They are
good snappy numbers. (Brunswick.)
Having heard excellent reports of the new
Broadway show "Good News" we were disap-
pointed in the three numbers from it which have
found their way onto the rubber discs. The title
number, Good News, and Lucky in Love have been
recorded for Columbia by Fred Rich and his
Hotel Astor Orchestra, and Cass Hagan and his
Park Central Hotel Orchestra have done The
Varsity Drag (also Columbia). If you are one of
those who raved over the show you may enjoy
the records. You may also like Dancing Tam-
bourine by the Radiolites on the reverse side of
The Varsity Drag, though we can't enthuse over it.
If you stuff cotton in your ears during the
seconds devoted to the vocal chorus in Baby Feet
Go Fitter Patter you may agree with us that this
record by Abe Lyman's California Orchestra
(Brunswick) is one of the best that have appeared
in many moons. In addition to an aversion to
vocal choruses in general we detest the words to
this particular song. It was an error on someone's
part to attach such a silly lyric to such an excel-
lent tune. However, it's short and the few seconds
one sacrifices to get through it are a drop in the
bucket and the rest of the record is fine. The other
side carries There's One Little Girl Who Loves Me,
also played by Abe Lyman, and also good.
Another of the better records slightly marred
by a vocal chorus is No Wonder I'm Happy and
Sing Me a Baby Song by the George H. Green
Trio with Vaughn De Leath doing the vocalizing.
(Columbia.)
The Ipana Troubadours, smile vendors under
the direction of S. C. Lanin, have done a fine
job with Are You Happy? and A Night in June,
of which Frank Harris carols the chorus. (Colum-
bia.)
Inhabitants of Mayor Thompson's Strictly
American City will welcome a Columbia disk
made by one of Chicago's Municipal Heroes,
Paul Ash, and his Orchestra. Just Once Again
is excellent and its vocal chorus by Franklin
Baur makes us eat some of our words just
uttered; we must admit it is an addition to the
Joins the RADIO Set
record. In self-justification we insist that Frank-
lin Baur is an exception. The reverse of the record
Lone and Kisses, is not quite up to the Paul Ash
standard but that doesn't mean it is bad.
Several other records get only half a vote due
to the fact that one face of record is good and
the other not. Stop, Go ! executed by Nat Shil-
kret and the Victor Orchestra has a unique
rhythm, better than any other number on the
list but Something To Tell is only moderate.
Me and My Shadow by Phil Ohman and Victor
Arden and their Orchestra is good; Broken
Hearted is not. Even Paul Whiteman could not
do much better with that last number but
Collette on the reverse makes the record decidedly
worth buying. (Victor). Don Voorhees tried some-
thing tricky with Soliloquy (which we are told
belongs to the new school of music ushered in
by the Rhapsody in Blue) and was not very suc-
cessful, but his more orthodox My Blue Heaven
is exceedingly good. Just a Little Cuter falls rather
flat but Marionette is excellent dance music.
Both come from the orchestra under the baton
of Ben Selvin and are recorded by Brunswick.
We dont care much for Cheerie Beerie Be or
Waters of the Perkiomen even though played by
Leo Reisman and his Orchestra. Roodles and /
Ain'l Got Nobody are not as good as they ought to
be coming as they do from Coon-Sanders Orches-
tra. And we were very much disappointed in
Who's That Pretty Baby? and Barbara by Paul
Specht and his Orchestra. The fault lies in each
case not with the orchestras but with the stupid
selections they play.
AND NOW FOR COMEDY
OF THE good humorous records recently is-
sued by far the best is Two Black Crows,
Parts 3 and 4. (Columbia). Of course we don't
need to describe it. Everyone knows Moran and
Mack and their riotously funny dialogues. What,
you dont? Well, go right down to the corner
music store and buy this record and their first
one, Two Black Crows, Parts i and 2. You will
remember us in your prayers.
Next in order of importance comes that grand
song perpetrated by the Happiness Boys, Billy
Jones and Ernest Hare, Since Henry Ford Apolo-
gi^ed To Me. (Victor.) It is worth seventy-five
cents just to hear this record once, which is fortu-
nate, for we wouldn't give a nickel for the song on
the reverse side, / Walked Back From The Buggy
Ride, by Vaughn De Leath and Frank Harris.
Then the famous Sam and Henry combination
(Correll and Gosden of WGN) offer two dialogues
called Sam's Big Night and The Morning After.
(Victor.) They are both labelled comic dialogues
but oh! the pathos of Sam's refrain, "Henry,
Henry, I'se sick! My head's bout to kill me! ... I
b'lieve I'se gonna die!" It almost makes you want
to sign the pledge.
Of the many popular vocal records we nomi-
nate for first place, a work of art by the Happiness
Boys, You Dont Like It— Not Much and Oh Ja Ja.
(Victor.) This is typical of what they offer to the
audience of WEAF every Friday night and it's
good! Personally we like them best of all the
regular aerial performers, It's personality that
does it — plus good voices.
Van and Schenck sing Magnolia and Pasta-
fa^oola for you on a Columbia record. The Radio
Franks present No Wonder I'm Happy and When
Day Is Done. (Brunswick). And Johnny Marvin
and Ed Smalle do a little duet with Just Another
Day Wasted Away on a Victor. Ml of these are
good. But on the back of the last mentioned disk
is Just Like a Butterfly sung by Franklyn Baur.
Personally, as little Alice said in Peggy Ann, we'd
rather have a baked apple. No matter how good
the voice, the song is terrible! We feel just as
strongly about Baby Feet Go Fitter Patter as we
have hinted before, and when it is sung by
Vaughn De Leath we see spots before our eyes.
She could make Turkey in the Straw sound like a
sentimental ditty and when she has something
as mawkish as this to start with . . . words fail us.
In case you are still interested in the record the
opposite side bears another song by the same
lady, Sometimes I'm Happy (Brunswick).
The Sunflower Girl of WBAP vocalizes You
Went Away Too Far and / Hold The World in
The Palm of My Hand on a Columbia disk. We
cannot say she sings them because she has one
of those rough and tumble shouts so often heard
on the vaudeville stage. It is about as far from
being musical as anything could be, but for that
sort of thing, she will do.
We don't feel strongly one way or another
about Charmaine! and The Far-Away Bells sung
by Franklyn Baur (Columbia), Ain't That a
Grand and Glorious Feeling? and Magnolia, sung
by Harry Richman (Brunswick), or Flutter By,
Butterfly and I'd Walk a Million Miles by Art
Gillham and his Southland Syncopators (Colum-
bia).
RED SEAL RECORDS AND SUCH
TURNING now to the sublime we find several
red seal records made by operatic stars from
the Metropolitan firmament, who twinkled be-
fore microphones upon occasion last winter,
Lucrezia Bori, the beautiful Spanish soprano
who is as lovely to look upon as she is to listen to
(though you couldn't tell that when you heard
her sing in the Victor radio concerts or in the
Atwater Kent hour) presents us with the lovely
old waltz song by Pestalozza, Ciribiribin, and
// Bacio by Ardit. (Victor).
Another soprano who was presented to the
radio audience by Atwater Kent is Hulda
Lashanska In company with Paul Reimers,
tenor, she records for Victor two simple but ex-
tremely lovely old German folk songs, Du, Du
Liegst Mir Im Her^en and Ach, Wie I si's Moglich
Dann. The harmony of the first selection is par-
ticularly notable.
It was a Victor hour that launched Emilio De
Gogorza's baritone voice on the ether waves and
it is a Victor record which presents his voice
again for your permanent enjoyment. He sings
two favorites, 0 Sole Mio, and Santa Lucia.
We think it would be a grand idea for everybody
to have this record in his home, if for no other
reason than just so that whenever he hears the
song murdered by a would-be artist he can play
the record on the phonograph and reassure him- _
self that the song is all right after all.
We presume it is rank heresy to say that we
prefer to hear the Utica Jubilee Singers sing
Old Black Joe than to hear Lawrence Tibbett.
Tibbett's voice is marvelous, of course, and it is
perfectly trained, but he cannot manage this
negro melody as expressively as the Utica Jubilee
Singers do. If this be treason. . . . The reverse of
the record is Uncle Ned. We have never heard
the Jubileers sing this but we will wager our two
cents that they could do it more to our satis-
faction than the Metropolitan star has done.
Both these songs are so worn out that they need
all the expression that can be put into them.
The Utica Jubilee Singers have done a record
for Victor, Angels Watching Over Me and Climbin'
Up the Mountain. It's perfect! We can say no
more. Incidentally it is interesting to note that
these singers have just returned from a concert
tour of Europe where they were greeted with
great acclaim, so their popularity is no longer
limited to this continent. They are now heard
from wjz and others on that chain Sunday nights
at 9:45, eastern time.
Virginia Rea, staff artist for Eveready, has
recorded a popular number which Victor thought
good enough for a red seal record, Indian Love
Call from Rose-Marie; and Lambert Murphy,
whom you undoubtedly heard in an Atwater
Kent hour, has recorded the title number from
the same musical play on the reverse of the rec-
ord. Though we saw this show at regular in-
tervals through the winter of 1924-25 and heard
these numbers on hand organs for the next two
winters, we still like them.
ERNIE GOLDEN OF WMCA
He leads the Hotel McAlpin Orchestra, regularly
heard through WMCA of New York. The Hotel
McAlpin Orchestra has recorded many good
dance numbers for Brunswick
207
AN ELECTRIC RADIO-PHONOGRAPH FROM
FRESHMAN
This instrument, completely a. c. operated pro-
vides the usual Freshman receiver, electric turn-
table, electric pick-up, record space and loud
speaker which serves for radio or phonograph
music. Complete with a. c. tubes. $350
UX-222 TUBES
Some idea of the con-
struction of the new
R. C. A. screened grid
tube may be obtained
from this illustration
The extra connection
is made to the metal
cap atop the tube. Eby
new type sockets are
shown
ITT T
JLU
STUDENTS of the characteristics and ap-
plications of the vacuum tube, and of
circuits to do with it, may find them-
selves somewhat bewildered by the apparent
complexity of the screened grid tube when they
begin their researches into its idiosyncrasies.
They will be impressed at once with the thought
that this tube is no ordinary structure, and will
appreciate more such names as Schottky of
Germany and Hull of the United States — names
actively associated in its development. Experi-
menters here have yet to become familiar with
the new tube, which has already taken its share
of space in English, French, and German radio
periodicals, and it is certain that, with the Radio
Corporation's announcement of the ux-222, not a
FIG. I
The plate current of a screened grid tube varies in
strange fashion, as these curves show. In these
data the effect upon the plate current of changing
the plate voltage, with several values of bias
voltage, is given. The normal bias is about 1.5
volts, with 45 volts positive on the screen, and
about 135 on the plate
By KEITH HENNEY
Director of the Laboratory
great length of time will elapse before it will be
possible for anyone to obtain these interesting
and useful screened grid tubes.
American writers, too, will have considerable
to say about the double-grid tube, of which the
screened grid tube is a type, as they become
more familiar with its operation, and as its pos-
sibilities become more apparent.
Imagine a tube with an amplification factor of
about 250, and such a small grid-to-plate capacity
that it has little tendency to oscillate even
though the plate circuit be made highly inductive
in reactance. The nearest approach is the stand-
ard "high mu" tube with an amplification fac-
tor of about 30, but, unfortunately, with
sufficient capacity to make oscillation inevitable
if sufficient inductance is included in its plate
circuit to transfer energy efficiently to a subse-
quent circuit. The screened grid tube, of which
the ux-222 (cx-322) is the precursor, is a most
unusual tube. What are its characteristics, its
possibilities, its weak points?
Physically it is complicated by having a fourth
element within the glass bulb. Picture a cylin-
drical construction with a 3.3-volt filament in
the center, surrounded by a rather coarse grid,
then, at some distance, another fine mesh grid,
then a cylindrical plate, and the whole sur-
rounded by another very fine grid of about forty
spiral turns. The latter two grids, connected in
parallel, form one electrode, thus constituting the
extra element in the tube. It would be more
accurate, for geometrical reasons, to call this
tube a screened plate tube, but electrically, as
we shall see, it is really the grid which is pro-
tected from alternating voltages impressed upon
the plate.
The inner coarse grid is connected to a small
metal cap which sits on top of the bulb, where the
tip used to be, making the overall height about
three quarters of an inch higher than standard
tipless tubes. The screening grid connects to the
usual grid terminal in the base so that the tube
fits into the standard ux or uv socket.
As pointed out in the December, 1927, RADIO
BROADCAST by Mr. T. H. Nakken, there are two
types of double-grid tubes, those in which the
inner grid is positive, known as the space-charge
tube, and those in which the outer or protective
grid is positive. The ux-222 may be used either
208
way. Let us consider first its action as a shielded-
grid device. In this case the outer grid is positive.
We shall place 3.3 volts on the filament, make
the inner grid negative, place about 45 volts on
the shield, and read the plate current as the plate
voltage is changed. The result is shown in Figs. I
and 2.
When this is done there are unusual results:
First, the plate current rises, as is customary with
increase in plate voltage. Then the plate current
begins to decrease, giving the tube a characteris-
tic like that of the electric arc, i.e., decreasing
current with increased voltage; next, after a
sharp minimum, the current rises almost per-
FIG. 2
If any reader of RADIO BROADCAST feels that he
knows all there is to know about tubes, let him
explain the sudden and extensive changes in
plate current with change in plate voltage in-
dicated in these graphs. With even greater screen
voltages than are shown here, the plate current
may be reduced to zero or even go negative (re-
verse its direction of flow) at some positive plate
voltage
JANUARY, 1928
THE SCREENED GRID TUBE
209
pendicularly and finally flattens out to become
practically horizontal. All of this is contrary to
what happens in standard tube practice and, to
the student of physical phenomena, is extremely
interesting.
The slope of this plate voltage- plate current
curve represents the plate impedance and, if
plotted, an extraordinarily large scale graph would
be required owing to the extent to which it
changes. For example, in Fig. i it is 74,000 ohms
near the origin, then it suddenly goes negative
to the extent of 100,000 ohms, then positive
about 10,000 ohms, and finally becomes about
three-quarters of a megohm in value! The tube
has a negative resistance, or a dynatron effect,
at low plate voltages.
These rapid and extensive changes in internal
resistance are due to the varying proportions of
current taken by the shield and the plate, both
of which attract negative electrons, and to a
certain amount of secondary emission which
takes place within the tube. At the present mo-
ment, however, the detailed explanation of these
effects must give way to the more practical in-
formation regarding the tube. We are more in-
terested in this article in how the tube works than
in "why." It is sufficient to state that the sum
of the currents taken by the shield and the plate
is constant, the plate current increasing when
the shield takes fewer electrons, and vice versa.
Uhder usual operating conditions, i.e., high
plate voltages, the shield takes very little current
indeed.
Grid voltage -plate current curves appeared on
page 1 1 1 of RADIO BROADCAST for December,
1927, and will not be repeated here. They con-
form to what one secures from other tubes of the
general-purpose type. They indicate a mutual
conductance of about 300 to 400 under average
conditions, and an amplification factor of about
250 to 300, values which should be compared to
those of standard tubes in Table i. It is difficult
to measure these factors on the ordinary bridge
because of the extraordinarily high values of
mu and plate impedance involved, and the better
plan is to pick them from characteristic curves
as we have done here.
MATHEMATICS OF THE TUBE
THE screened grid tube is designed primarily
for radio-frequency amplification and, to
understand its possibilities in amplifier circuits,
we must examine somewhat more critically
than usual the processes involved in the ordinary
amplifier. Naturally we must have an input and
output circuit, and for general analytical pur-
poses we shall consider Fig. 3.
The purpose of the transformer in such cir-
cuits is not, as many would have us believe, to
increase the voltage step-up from tube to tube,
but to obtain a proper impedance for the ampli-
fier plate circuit to look into. Mathematics will
show that the maximum voltage amplification
will be obtained when the effective primary
impedance of the transformer is equal to the
internal resistance of the tube, and that under
these conditions this amplification is:
K
where RP= tube impedance, L = secondary
inductance, R5 = secondary resistance, and
o> = 6.28 x frequency.
If the effective resistance of the tuned circuit
at resonance is higher than that of the preceding
tube impedance, a step-down transformer must
be used. This effective resistance may be found
mathematically by substituting the proper values
in the following expression :
FIG. 3
A diagrammatic representation of the ordinary
interstage radio-frequency amplifier, consisting
of a transformer, tuned to the frequency desired,
connecting two tubes. The voltage gain at
resonance is given in the form of two equations
where L = inductance, Rs = high-frequency re-
sistance, W = 6.28 x frequency.
If we use an inductance of 250 microhenries
having a resistance of 15 ohms at 1000 kc., this
effective resistance will be:
(250 x io-«)!x (6.28 x io«)»
Ro = — ' '— = 177,000 Ohms
and if the previous tube is a 201 -A with an im-
pedance of 12,000 ohms we shall be compelled
to use a step-down transformer to secure maxi-
mum amplification and to prevent short
circuiting the secondary, to the impairment of
the selectivity. Using a tube and coil of these
FIG. 4
For analytical purposes the two-winding trans-
former of Fig. 3 may be replaced by this auto
transformer. The same conditions for maximum
voltage amplification obtain
characteristics, and with the proper primary,
the maximum amplication will be:
K
8 250 x 10-* x 6.28 x 10*
max = i * y-
15.0 (Approx.)
12.000 x 15
When any receiver designer states that he gets
a uniform amplification per stage of much over
this, he has neither used his mathematics nor
Ro
FIG. 5
In the ordinary tube, some electrostatic lines of
force connect the plate and grid because they
are at different potential. This means, simply,
that some capacity exists between them and it
is this capacity that causes trouble in the usual
high-frequency amplifier
his vacuum-tube voltmeter to substantiate his
statement.
This transformer, with its two windings, can
be replaced by an auto transformer for all prac-
tical purposes, as shown in Fig. 4. An auto
transformer, it will be remembered, is used in the
" Universal" receiver previously described in this
magazine and in the R. B. "Lab." Circuit, when
the plate or primary coil is reversed. The imped-
ance of the circuit, looked at from the preceding
tube, must equal the impedance of that tube,
and the position of the tap regulates the effective
transformation ratio, so that this condition is
realized, since the ratio of impedances across
secondary and primary is equal to the square of
the turns ratio.
If we use a special radio-frequency tube with
a higher amplication factor and higher impedance,
such as the Ceco Type K, we must move the
tap higher toward the grid end, or use more
primary turns if we use a transformer, while if a
1 12 type tube is used with its lower impedance,
the tap can be brought further down. Table i
gives essential data on existing tubes. The ap-
proximate turns ratio, in the auto transformer
case, can be found by substituting the value of
plate impedance in the following equation:
60000
Turns Ratio = ^ .
' Rp
TABLE i
TUBE
V-
RP
Gm
TURNS
RATIO
199
6.25
16,600
380
I.QO
2O I -A
8.00
12,000
675
2.25
1 12
8.00
5,000
1,000
35
2IO
7.70
5,000
1-540
3-5
171
3.00
2,000
1,500
5-5
222
250.00
7OO,OOO
400
i .0
"K"
13.00
16,800
780
1-9
Now all of this sounds simple to carry out but,
practically, there are difficulties ahead — most of
them due to the fact that the tube does not act
like a one-way street. Some traffic always goes in
the opposite direction, because of the grid-plate
capacity. As soon as we get the tap on our auto
transformer moved high enough toward the grid
end to secure maximum amplification, we include
sufficient inductance in the plate circuit of the
amplifier to make it oscillate, and trouble begins.
Therefore we must do one of two things: we
must either move the tap down, and lose ampli-
fication because our equal impedance condition
is no longer satisfied, or we must play neutraliza-
tion tricks on the amplifier to keep it from oscil-
lating, with perhaps slight loss in amplification
as the price of stability.
Here is where the screened grid comes in.
Suppose, as in Fig. 5, we have the plate receiving
electrons from the filament after passing through
the grid in straight lines. Because of the fact that
the grid and plate are at different potential there
will be electrostatic lines between them, repre-
sented by the curved lines. In other words, there
is some connection between the plate and the
grid, other than that produced by the passage of
negative electrons. Now if we surround the plate
by a fine grid which is grounded, as shown in Fig.
6, these electrostatic lines do not reach the grid,
and the latter is free to function only as a control
on the flow of electrons. If, in addition, we make
this shield positive with respect to the filament
and grid, we neutralize some of the space charge
which, in turn, boosts the amplification factor to
a very high degree.
If the plate is completely screened, the tube
will be a one-way repeater, there will be no tend-
ency to oscillate in the familiar tuned grid-
tuned plate circuit, and a little mathematics will
210
show that the amplification is a factor of the
mutual conductance of the tube and the external
impedance. This external impedance is the effec-
tive resistance of the tuned circuit, as already
mentioned, and varies as shown below for average
coils at usual frequencies. The possible voltage
amplification may be easily calculated, with an
assumed mutual conductance of 400 micromhos
and an infinite plate impedance.
RADIO BROADCAST
FREQUENCY,
KILOCYCLES
Ro = LW OHMS
AMPLIFICATION
Gm x Ro
Rs
100
1,000
10,000
400,000
100,000
10,000
200
40
4
These values of amplification are considerably
greater than is possible with standard tubes such
as we all use at the present time. At 1000 kc.
(300 meters) the average gain in modern receivers
may be as high as 10, and not many sets can do
as well without some loss of stability.
Actually, however, these values in the table
with the 222 tube will not be attained, since the
assumptions on which they were calculated,
infinite plate impedance, no grid-plate capacity,
and an effective resistance in the plate circuit of
100,000 ohms, are not realized. Since the tube's
internal impedance is of the order of a half
megohm, or greater, which is considerably more
than can be attained by average coils or by coils
which will not cut side bands, there is no use in
FIG. 6
If a grounded shield is placed around the plate,
the lines of force from grid to plate will be inter-
rupted, and fewer changes of plate voltage will
affect the grid — in other words, the grid is
shielded from the plate
above. If this resistance is equal to that of the
tube, approximately one-half the mu of the tube
may be realized. With 100,000 ohms in the plate
circuit approximately one seventh of the ampli-
fication factor, or about 35 may be expected.
For maximum voltage gain the effective resist-
JANUARY, 1928
amplifier, which had attached to its input a single
wire antenna about 35 feet long, and a ground.
With the brass box containing a Rice neutral-
ized amplifier, using a aoi-A tube, and with the
best position of the plate tap on the detector
coil (see Fig. 8), the voltage upon the input to
the detector was measured. Then the screened
grid tube was used, the whole coil being used
in its plate circuit, and the neutralization ap-
paratus was done away with. The voltage was
again measured with exactly the same input, and
at the same frequency — 500 kc. In this case the
output voltage was a little over three times the
best that could be obtained with the 2OI-A eft*
cuit. Resonance curves showed that the two
circuits were about equally selective.
If the 20 1 -A tube gave an amplification of ten,
which is reasonable, the new tube had an indi-
cated voltage gain of over 30, which seems to fit
in with our calculations explained previously.
Two stages would give a gain of 900 compared
with 100 for two 201 -A amplifiers, or approxi-
mately 20 TU, which has about the same effect as
adding one stage of audio to existing receivers.
With the antenna described, and with but two
tuning circuits, there was no difficulty in sepa-
rating WEAF and wjz, 50 kc. apart, when the
former was 8 miles away with 50 kilowatts of
power in the antenna and the latter was roughly
30 miles distant with somewhat less power.
Measurements showed that, with the screened
grid tube, WEAF delivered over 4.5 volts to the
detector, sadly overloading it.
0.0002
Oscillator
FIG. 7
In the Laboratory this arrangement of apparatus was used to discover
the voltage delivered to a detector when the screened grid tube was used
as an amplifier. The meter in the detector plate circuit read the change
in plate current when a. c. voltages were applied to its grid. It was a
calibrated detector, or vacuum-tube, voltmeter
+ 90
FIG. 8
Here the vacuum-tube voltmeter was applied to the output
of a standard Rice neutralized amplifier. The difference
between the input voltage in this case and that in Fig. 7
determines the gain in using the screened tube. The meter
used in the calibrated detector was a Westinghouse 200-
microampere meter, type PX
using a step-down transformer to couple the out-
put of the tube to a succeeding stage, and the
whole coil may be used without danger from
oscillation.
With the entire coil in the plate circuit, as
shown in Fig. 7, the amplification per stage may
be figured by somewhat simpler mathematics.
In this case we have a simple tuned impedance
in the plate circuit of the tube, which at reso-
nance has an effective resistance, as explained
_CX322
UX301-A
>18° 0.006
FIG. 9
When the grids of the ux-222 (cx-322) are reversed, i.e., the inner grid
is made positive, the amplification factor and plate impedance fall to
more usual values, and the tube can be used as an audio- or intermediate-
frequency amplifier.
ance muu be high, that is, we must use excep-
tionally good coils of high inductance and low
resistance with the probability that fidelity will
suffer.
In the Laboratory a simple set-up was em-
ployed to examine the tube's behavior. The
circuit is shown in Fig. 7 and, as may oe seen,
consisted of a single amplifier tube followed by a
non-regenerative C bias detector which could be
calibrated in volts input against change in d. c.
plate current.
The shielded tube and
its accessory input ap-
paratus was carefully
enclosed in a tight brass
bo.\ which was grounded.
The audio amplifier was
useful as a kind of moni-
toring stage to follow
what was happening in
the preceding circuits.
It made it possible to in-
sure against the amplifier
oscillating, etc. A 1000-
cycle modulated signal
was induced into the
The tube may also be used as a space charge
grid affair, where the inner grid is positive with
respect to the filament and the fine structure
which ordinarily screens the plate is used as the
signal grid. To test its capabilities the circuit
shown in Fig. 9 was used. W ith an input voltage
of o.i, the gain was about 30, from 60 to 30,000
cycles, and then fell slowly. At the higher fre-
quencies the tube capacities (in the space
charge grid tube the capacities are much greater
than in the screened grid connection) shunt the
output resistance, with consequent loss of am-
plication.
Here, then, is a tube which must henceforth
be carefully considered by all designers of
radio equipment, for amplification of the very
high frequencies, those of intermediate range
such as are used in super-heterodyne receivers
and broadcast frequencies, and again at the
low audible tones. In all of these ranges it seems
probable that greater amplification will be se-
cured than has been possible with ordinary or
high-mu tubes. In subsequent articles, we shall
discuss the design problems at greater detail and
have something to say about the problem of
selectivity and fidelity of reproduction.
WHAT
riTHOUT repeating the old arguments
which earn for radio the title "the
ideal Christmas gift," we are certain
that more people select a new radio at this
season than at any other. The fundamentals of
good selection do not change from year to year,
but the improvements which come with each
new season always bring with them new factors
to consider when purchasing. Indeed, the
constant improvement of the radio receiver
leads some to await new developments, expect-
ing some sort of radio millennium.
Improvement will always continue in the radio
art, and he who awaits perfection will neither
purchase nor enjoy radio. Were the same policy
followed with respect to the purchase of motor
cars, some forty million people would still be
walking because the ultimate automobile, after a
quarter of a century has been devoted to de-
velopment in this field, is not yet here.
The radio receiver of to-day is a product which,
both from the musical and technical standpoint,
is capable of many years of service. It will not be
greatly outclassed in the musical quality of its
output for a long time. In sensitiveness, selec-
tivity, fidelity of reproduction, simplicity of
control, and convenience of maintenance, it
has reached high standards. In appearance,
efficiency, compactness, simplicity of installa-
tion, and automatic operation, considerable
progress may still be looked forward to, but none
of these factors mean great changes in the funda-
mental output of the radio receiver, that is,
reproduced musical programs. We have passed
through the period of revolution and have come
to the era of refinement in this radio world of
ours. There is no longer any excuse for delay in
purchasing a high-grade manufactured re-
ceiver.
Maintenance convenience is the keynote of
1927*5 advances. The last word in installation
instructions now is: "Plug the cord in the light
socket, turn the set switch, and tune." This is
indeed a contrast to the requirements of former
years. There were antennas to install, batteries
to connect with multi-colored cables, chargers
to wire, power amplifiers to plug in, and loud
speakers to attach. Between these two ex-
tremes, there are several stages of convenience,
each of which is still represented in this year's
products. The term "light socket operation,"
for example, is applied to power systems varying
considerably in convenience, and is a very
flexible term. It is advisable, therefore, to as-
certain exactly what type of receiver and what
degree of convenience you buy.
There are several ways of powering a receiving
set "directly from the light mains." Filament
power might be supplied from a storage battery-
trickle charger unit and plate power from a
rectifier unit operating directly from the power
mains; or both filament and plate power may
come directly from the mains through a rectifier
unit; in another case the filament power may be
delivered directly from the line to a set using
alternating-current tubes, through a step-down
transformer, and plate power obtained through a
rectifier unit.
The field of usefulness for the storage battery
receiver is far from exhausted. Its lower manu-
facturing costs give it a price advantage, at no
sacrifice in attainable performance, over the
alternating-current powered receiver. Because
of lower cost, it is destined to remain in the
211
SET SHALL
I BUY?
By
EDQAR H. FELIX
radio market for a long time to come. Mag-
netically controlled trickle chargers, which turn
on automatically when the set switch is turned
off, reduce the maintenance responsibility placed
on the user of a storage battery to a minimum.
Precautions against overcharging, and occasional
filling of the cells with distilled water, are the
only attentions required. Indeed, this type ol
storage battery receiver is often sold to the un-
initiated buyer as the last word in socket powei
operation.
Large storage batteries, used almost ex-
clusively with receiving sets four and five years
ago, are likely to require replacement after two
to five seasons, the period of service depending
upon the care taken of the storage battery by its
owner, and the quality of the battery itself.
Bear in mind, when such replacement becomes
necessary, that the reliability of many an old
receiver would be greatly improved by the pur-
chase of a trickle charger outfit, a suggestion
which may be of value to many persons desiring
to give a Christmas gift costing twenty to
thirty dollars.
A device of interest to every storage-battery
set owner is the "Abox," which may be sub-
stituted for the storage battery or trickle charger-
storage battery combination. The "Abox" re-
quires no maintenance attention and operates
on an entirely different principle from the storage
battery-trickle charger combination. Other
manufacturers are marketing devices similar in
principle to the "Abox." Balkite might be cited
as an example.
A comprehensive article on A-power units, in
which twenty or so A units were listed, and their
characteristics noted, appeared in the November,
1927, RADIO BROADCAST, beginning on page 30 of
that issue.
TUBE POWER UNITS
D ECEIV1NG sets having A, B, and C power
^ *• supplied from vacuum- or gas-tube rectifier
units incorporated in the set, require no main-
tenance other than renewal of rectifier tubes.
There is no periodic adding of distilled water to
battery or chemical charger, nor is there any
other maintenance problem in connection with
212
RADIO BROADCAST
JANUARY, 1928
these sets. There are a large number of receivers
of this type on the market. With skillful engineer-
ing and high-grade components, they offer care-
free and high-quality reception. If carelessly
designed, they may give a marred output because
of excessive hum, and unreliability of service due
to failures in vital parts. It should not be
thought, however, that a set is necessarily good
because it does not hum. If poor audio trans-
formers are incorporated they may not be
capable of amplifying the low-frequency hum
produced by alternating current. The problem
of the uninitiated in distinguishing between the
inferior and the superior type is perplexing. The
name and reputation of the manufacturer, the
endorsement of men technically qualified to
judge radio products, and the pages of high-
grade publications, which censor and check the
statements made in their advertising columns,
are helpful sources of information and guidance.
Practical tests can be made by the technically
untutored buyer, when a set is being demon-
strated, which will protect him against the pur-
chase of a power set of inferior design. The
principal characteristic of a poorly designed re-
ceiver, deriving its A, B, and C potentials di-
rectly from the light mains, including both those
employing rectifier systems and those using a. c.
tubes, is the excessive hum experienced when the
set is adjusted to sensitive reception.
A dealer, selling a radio set subject to hum,
is likely to concentrate his demonstration upon
the reception of strong, near-by stations. Ask
him to tune-in a weak station, preferably one
fifty or a hundred miles away, during the day-
time, or one several hundred miles away at night,
requiring that the sensitivity or volume control
be turned up all the way to get the station
comfortably. Then slightly detune the set.
Without the covering effect of the music, you
should then get a direct indication of how much
the receiver hums under unfavorable conditions
provided, of course, that a loud speaker is used
which reproduces the very low notes. To be en-
tirely satisfactory, the hum should be so weak
that it cannot be heard in a quiet room ten feet
from the loud speaker which the prospective
purchaser will use.
It is quite possible to attain this standard
but it costs money. A great discrepancy in price
between two sets having the same sensitiveness,
tone quality, and appearance, is often accounted
for by the complete absence of hum in the more
expensive receiver. The hum test is a simple one
and should be made by every purchaser, re-
gardless of his technical qualifications.
MEETING MODERN STANDARDS OF FIDELITY
I F THERE is one quality in radio receiving sets
* which has been appreciated by manufacturers,
it is the ability to produce good tone. The judg-
ment of a receiver's tone quality has already
been fully discussed by the author in three recent
issues of RADIO BROADCAST and hence it is un-
necessary to repeat in great detail the factors
applying to this most important requirement.
Briefly, to obtain good tone quality requires
that the set have: (i) Adequate power supplied
the loud speaker by the use of a ux-171 (cx-
371) type output tube, or even by the still more
powerful ux-2io (cx-3io) type tube; (2) an
audio amplifying system which covers the tonal
scale and (3) a loud speaker adequate to handle
the volume and tonal range supplied it. To the
non-technical reader, these requirements may
seem difficult to appraise. But a simple test re-
veals a great deal about the tonal capacity of a
receiver. Ask the dealer to tune-in a strong,
near-by signal and bring it to full volume. Al-
though the music is uncomfortably loud, using
the output tubes mentioned, it should not, even
with very strong signals, be scratchy, stringy, or
drummy. Music should be simply loud with tonal
quality unaffected.
The second test is to listen critically with the
set at moderate volume for the instruments pro-
ducing low tones, like the 'cello, drums, or the
organ. If these appear to be in their proper pro-
portion, without being overshadowed by the
treble, the receiver is capable of handling low
tones.
There is much danger of selecting a set which
exaggerates the low tones, a characteristic easily
demonstrated in speech. A low, throaty, ringing
effect, which makes words difficult to under-
stand, is an indication of over amplification of
low notes. A receiver omitting low notes,
usually gives harsh, unsympathetic, but clear
speech. Speech over the telephone is quite easily
understood, but the rich, sympathetic quality
of a good voice is lost because of absence of low
tones in telephone transmission.
TESTING FOR SELECTIVITY
CELECTIVITY is necessary under modern
'••' receiving conditions, particularly in con-
gested areas. Generally speaking, the more
tubes a set has, the more likely it is to be selec-
tive, because each stage of radio-frequency
amplification adds another filter circuit. It does
not necessarily follow, however, that a great
number of tubes means great selectivity any
more than a great number of cylinders means
great power in an automobile.
The pick-up system used is a valuable guide in
determining the selectivity. Given an equal
number of stages of radio-frequency amplifica-
tion, an antenna set is likely to be less selective
than one with a loop. A receiver lacking in
selectivity, can often be improved by shortening
the antenna.
Selectivity is simply tested but it is hardly
possible to set down any definite procedure since
local conditions play an important part; while
a receiver may be perfectly satisfactory in one
district, it might fail badly elsewhere, where
the conditions and requirements are different.
There are some receiving sets so lacking in
selectivity that the nearest station (we do not
mean a so-called "super-power" station) can be
heard over one-fourth to one-eighth of the entire
dials' scales, while a few, high-grade receivers
pick up the same station over only two or three
degrees of the dial. The signal should tune-in
fairly sharply without long fringes over which it
is heard weakly above and below the point where
it is heard at full volume. The selectivity with
a weak and distant station is no indication of the
receiver's performance under ordinary condi-
tions.
EVALUATING SIMPLICITY OF CONTROL
THE third factor, and one of great impor-
tance, if the entire family is to use the
receiver, is its simplicity. Only three controls are
essential to the operation of the receiver: (i.) An
"on-off" switch; (2.) a volume control and (3.)
station selector. The "on-off" switch should take
care of all power supply connections, such as
those of the chargers and power supply units,
as well as the filaments of the tubes them-
selves.
The volume control should enable you to bring
the loudest, near-by station down to a whisper,
without impairing its quality, while the station
selector should give you the complete parade of
broadcasting stations, up and down the scale,
without requiring any other adjustment. Set
the volume control to a weak station and turn
the dial from top to bottom and the stations
should come in in the order of their frequency,
this depending, of course, on their power and
distance.
If, at the low end of the dial, the tone quality
of the station cannot be cleared up without cut-
ting down the volume control, the receiver is not
properly balanced and probably radiates, and
thus interferes with other receivers on the short
wavelengths. The functioning of volume control
and station selector should not be interdepend-
ent.
When two station selectors are used, which is
frequently the case, one may be calibrated in fre-
quencies, so that the dial may be set to a desired
station accurately, and the other arbitrarily
calibrated from i to 100, suiting it to antennas
of different length. It is not inconvenient tc
operate a receiver with two station selectors,
although the ideal arrangement provides but
one.
Receivers having a single station selector and
designed for antenna (as opposed to loop)
operation, generally require an extra stage ol
radio-frequency amplification generally untuned.
This extra stage only contributes little amplifica-
tion and does not materially affect the selectivity.
Because of this consideration, the fallacy of
rating a receiver's capabilities by the number of
tubes it possesses is obvious. Its sensitiveness
and selectivity are dependent upon the number
of stages of tuned radio-frequency amplification.
The buyer is often perplexed by the great
number of receivers, apparently similar, but
possessing a wide range of price. The factors of
tone quality, selectivity, and volume capacity
may be roughly tested upon demonstration, but
unreliability develops only in service. Beware
of the receiver that is too cheap, particularly
one having power supply incorporated in it,
because filter condensers may break down and
mechanical difficulties may arise in service. It
is true that very large quantity production de-
creases costs but, as with everything else, you
do not get something for nothing. The extra
cost of purchasing a set having back of it the
name of a well-known manufacturer, is a protec-
tion against the hidden factor of unreliability.
There is no reason for tolerating an unreliable
receiver because the instrument which the buyer
has at his command nowadays requires virtually
no attention other than the periodic renewal of
tubes.
The question is often asked, " How much does
a good radio cost?" or "What is the best radio
set for the money?" There are so many different
requirements which must be met, dependent
upon receiving conditions where the set is to be
installed, and so wide a variation in the skill and
temperament of the users, that such general
questions cannot be answered.
The qualities every discriminating listener
looks for are good tone, reliability, selectivity,
convenience, and simplicity.
The prospective purchaser of a radio receiver
should be fully cognizant of his requirements
before setting forth to the radio store-. He may
also decide how far he will go in cost to secure
the degree of maintenance convenience he
desires, as already considered. He will confirm
the quality of design of the power supply by
listening for hum with the receiver set at maxi-
mum sensitiveness with no station tuned-in; its
volume capacity and selectivity by tuning in the
loudest near-by station to maximum volume; its
tonal range by listening for low and high tones;
and its simplicity by checking the exact number
of operations required to tune-in a desired sta-
tion. With the aid of these precautions, he will
know just what he is buying and be able to com-
pare intelligently one receiver with another.
"Our Readers Suggest-
OUR Readers Suggest. . ." is a regular feature
of RADIO BROADCAST, made up of contri-
butions from our readers dealing with their experi-
ences in the use of manufactured radio apparatus.
Little "kinks," the result of experience, •which give
improved operation, will be described here. Regular
space rates will be paid for contributions accepted,
and these should be addressed to " The Complete
Set Editor," RADIO BROADCAST, Garden City, New
York. A special award of $10 will be paid each
month for the best contribution published. The
award for the December prife contribution "An-
tenna Compensation in a Single-Control Receiver"
goes to Harold Boyd of Winchester, Virginia.
— THE EDITOR.
Eliminating the Loop
FREQUENTLY suggested method of
increasing the sensitivity of loop re-
ceivers is that of coupling the loop to a
short antenna. This, of course, is a feasible
proposition, but when coupling to any sort of an
open antenna, why not eliminate the loop
altogether?
The system generally advocated when a loop
is used in conjunction with some kind of antenna
is that of winding several extra turns of wire on
the loop-frame and connecting the short antenna
span and a ground lead to the two ends of these
extra turns of wire. The combination of the loop
with an extra winding thus constitutes a simple
coupler, but one of rather extravagant dimen-
sions. There is no reason why the size of the
coupler cannot be reduced to more conventional
dimensions, and an ordinary antenna coupler,
such as an Aero or Bruno-Coil, substituted for
it. The loop-antenna combination will be no more
sensitive than the antenna-small coupler
arrangement.
It requires no technical skill to effect the
change. The coupler consists of two windings,
a primary winding having relatively few turns —
from six to twenty — and the second-
ary, having about fifty turns of wire.
The primary should be connected be-
tween antenna and ground while the
secondary should be substituted for
the loop, as shown in Fig. i .
It is desirable to obtain a coupler of
the correct size for the tuning con-
denser. If the connections from the
loop are traced, they will be found to
lead to a variable condenser. In the
majority of cases this condenser will
have a capacity of 0.00015 mfd. The
capacity of the condenser can almost
always be determined by counting the
plates. A condenser having approxi-
mately thirteen plates has a capacity
of 0.0003 mfd.; one having about 17
plates is probably 0.00035 mfd.; with
23 plates, the capacity will be near
0.0005 mfd. In purchasing a coupler,
specify the size condenser it is to be
used with. In the few instances where
it is difficult to determine the exact
THE CROSLEY "LOWAVE
Used with a Stromberg Carlson "Treasure
Chest. "See descriptive matter in the box below
capacity, obtain a coupler for a o.ooo3-mfd.
condenser. If you find that the receiver no longer
responds to the shorter wavelengths, or that the
longest desirable wave is attained with a con-
siderable portion of the tuning condenser unused,
a few turns can be taken from the secondary.
It is a simple matter to wind your own coupler.
The following tables give the correct number of
turns of wire:
CONDENSER
TUBING
DIAMETER
WIRE
D.C.C.
TURNS
PRI.
SEC.
13 Plates
0.0003 Mfd.
This Coil
3-1"
H"
-las an Induct;
No. 24
No. 24
No. 28
nee of 282 J
14
16
18
1 icrohen
55
64
70
nes
17 Plates i 3-j"
0.00035 Mfd. 3"
No. 24
No. 24
No. 28
12
<4
16
49
I8
64
as an Inductance of 245 Microhenries
23 Plates
0.0005 Mfd.
-
No. 24
No. 24
No. 28
40
40
50
f '""
This Coil Has an Inductance of 175.6 Microhenries
-ARE You INTERESTED IN SHORT WAVES?"
. 1 am using a simple electric light plug antenna
made by Dubilier. The substitution for the loop
was effected in this case not because of poor sensi-
tivity, but merely for esthetic reasons — to do
away with the unsightly loop. The successful
use of this system is by no means confined to
super-heterodynes and may be applied to any
loop receiver.
A. J. HOWARD
New York City.
Combining Horn and Cone
CERTAIN of the cone type loud speakers
^-* now on the market are designed to com-
pensate the failure of the usual two-stage
transformer-coupled amplifier to satisfactorily
amplify the very low
audio frequencies. The
customary audio ampli-
fier feeding into such a
loud speaker gives a very
satisfactory overall
characteristic. If, how-
ever, the audio amplifier
itself is designed to give
a slightly rising low-
Antenna \ 7
Primary
Ground
LAST month in this department we published the description
of a simple home-made short-wave converter, an auxiliary
attachment which makes it possible to receive wavelengths as
short as 18 meters (16,700 kc.) on any receiver. RADIO BROAD-
CAST Laboratory has recently received a commerical in-
strument, the Crosley "Lowave," of somewhat similar design.
Its adaptation to a Stromberg Carlson "Treasure Chest" re-
ceiver is shown in an accompanying photograph.
The Crosley "Lowave" is an especially designed circuit
employing three tubes, and so arranged that the radio-fre-
quency amplifier of the broadcast receiver is also utilized. The
"Lowave" is connected to batteries according to directions,
and one wire is led from it to the antenna post of the broadcast
receiver. A small switch on the front of the panel throws the
short wave attachment in or out of the circuit.
In tuning over the very high frequencies with such a con-
verter, many broadcasting stations will be heard, but a great
majority of them carry a badly distorted signal, which no
amount of tuning will clear up. These are the harmonics of
standard broadcasting stations, the frequency characteristics
of which are invariably badly garbled. True short-wave
broadcasting will be received as clearly as long-wave reception.
THE LABORATORY STAFF
frequency characteristic,
or even "straight-line"
amplification, and it be
used to feed into a cone
of the type described,
the bass is emphasized
to such an extent that
a sense of frequency
distortion is intro- FIG. I
duced.
A three-stage audio amplifier was hooked
up in conjunction with a Radio Corporation of
America cone loud speaker, model 100 A. The
resultant reproduction gave the effect of exag-
gerated bass. A very great improvement in the
quality was accomplished in the following man-
ner: A Radiola horn type loud speaker
was obtained and connected in series
with the model looA cone. The horn
was shunted by a Centralab Modula-
tor, variable from o to 50,000 ohms,
as suggested in Fig. 2. Without this
shunt, the proportion of the total load
taken by the horn would have been
excessive, on account of the higher im-
pedance of its windings. With the shunt
resistance set at about 25,000 ohms,
the load seemed to be about equalized
between the two loud speakers. Be-
tween 25,000 ohms and 50,000 ohms
the effect of the horn was more pro-
nounced, while from 25,000 down to
zero, the cone predominated. At a
setting of zero the horn was completely
shunted from the circuit.
The particular cone used in this
circuit gave excellent reproduction of
the bass, while the horn brought out the
treble clear and distinct. The reproduc-
tion resulting from this combination of
213
FIG. 2
214
about 20,000 ohms was the most pleasing the
writer has ever listened to. By the turn of a single
knob it was possible to bring out the bass or
treble to any relative degree to suit the particular
ear of the listener.
D. C. REDGRAVE
Norfolk, Virginia.
Another Cone and Horn Combination
I IKE many other radio fans I recently dis-
*-' carded my horn loud speaker for a cone.
When listening attentively, I decided that the
cone slighted the higher frequencies somewhat
so 1 dugout the old horn, which rather favors the
high notes, with the idea of using the two loud
speakers in combination. But the impedance of
the loud speakers were so poorly matched that
some balancing arrangement had to be devised.
1 evolved the scheme illustrated in Fig. 3,
employing a half-
megohm potentio-
meter, such as is
often used for a
volume control. As
the slider is moved,
one loud speaker is
cut in and one eli-
minated.
I soon found,
however, that I
needed a better
criterion than my
ears to place the
slider where it be-
longed, so I plugged
a pair of good
phones in the de-
tector plate circuit
and adjusted the potentiometer until the loud
speakers duplicated the pitch of the telephone
receivers.
H. D. HATCH
Boston, Massachusetts
STAFF COMMENT
THE choice of the systems outlined above
by our two readers rests pretty much on the
convenience of what you have in the way of a
variable resistor. Fig. 3 provides a greater
variation in loud speaker selection than Fig. 2
but sufficient variation can be secured with the
latter for the purpose of correct balance. In the
arrangement shown in Fig. 2 the variable
resistor should always be connected across the
loud speaker having the higher impedance,
/'. e., the loud speaker that seems to produce the
most sound when the resistor is disconnected.
Mr. Hatch's system for adjusting the relative
intensities of the two loud speakers is worthy
of special note. While a preference may exist
for an emphasis of high or low notes (adjusting
to suit individual tastes), this is not necessarily
natural reproduction. The phone test method
probably provides as correct a balance as can be
achieved without elaborate equipment.
C Bias from B Socket Power Units
IN THIS department for November, 1927, an
* interesting item was published showing how a
B socket power device could be changed to sup-
ply grid bias voltages as well as plate potentials.
In effecting this change, it was necessary to "get
inside" the device, break a connection, and
make several additions. This method is quite
practicable, but there is always a general disin-
clination to "monkey" with a commercial set-up.
It is possible to obtain the C bias potentials
by application of external resistors — no change
whatever being necessary in the device itself.
RADIO BROADCAST
In so doing, several possible faults in the device
can be corrected, such as break down of resistors,
as may be evident in noisy reception and poor
voltage regulation. It is also possible with the
external arrangement to secure voltages other
than those supplied by the original device for
special sets or purposes.
The additional device takes the form of an
entirely separate set of resistors, which is
connected between the high-voltage and negative
posts on the old power unit. The resistors are
tapped to supply the desired B and C potentials
and are mounted on a base-board.
The number of resistors required is determined
by the number of voltage outlets. We shall need
one Amsco "Duostat" to supply two variable
"C" biases, while one resistor will be required
between the negative tap and the lowest positive
plate tap, and another resistor for each additional
plate tap. The Amsco "Duostat" is equipped
with two variable arms, making it possible to
secure two variable C bias potentials with the
one resistance unit.
The average arrangement is shown in Fig. 4,
which requires three fixed resistors in addition
to the " Duostat. " The fixed resistors may be any
satisfactory power resistor, such as those of
Electrad, Amsco, Metaloid, Ward Leonard,
Durham, Carter, etc.
The method of calculating the values of the
resistors takes into consideration the probable
plate current drain through each resistor, and is
best illustrated by the example of Fig. 4.
An arbitrary value of ten milliamperes is
chosen as the loss current — the current through
the resistors over and above that drawn by the
receiver. The presence of this loss current reduces
the variations in voltage with slight differences
in load. The higher the loss current the better
the voltage regulation.
The output from the average power device
receiver combination under load is about 200
volts. By an application of Ohm's Law, which
tells us that the resistance is always equal to the
voltage drop divided by the current in amperes,
or one thousand times the voltage drop divided
by the current in milliamperes, it is a simple
matter to determine the total resistance neces-
sary. The equation in this case is:
P. 2OO X (OOO
R = =20,000 Ohms
10
So the total resistance of the "bridge" will be
20,000 ohms, 2000 of which is already appor-
tioned to the "Duostat," Rt. It remains to
calculate the values of RI, R2, and RS. To do this,
we must consider the probable plate currents
through these resistors. A 201 -A type tube,
properly biased, draws the following currents:
r. f. amplifier, 90 volts, 4 milliamperes; detector,
45 volts, 1.5 milliamperes; a. f. amplifier, 90
volts, 2 milliamperes.
20,000 Q
To B + Max. on B
Device and + B Max. on Set
>
>
+ 9
>
:: :::
I
+ 4
>
> —
>
-
-B
>
>
>
>
>
-
=
-C
- C (12-40 V.)
JANUARY, 1928
We shall consider a receiver which comprises
three r. f. tubes, detector, and two audio tubes,
the last of which should be a power tube
functioning directly from the highest voltage. So
the first five tubes are all we have to consider now
in designing the resistor bank.
Refer once more to Fig. 4. The current through
Ri is 10 milliamperes loss current, plus 12
milliamperes r. f. current, plus 1.5 milliamperes
detector current, plus 2 milliamperes ist audio
current, or a total current of approximately 26
milliamperes. The voltage drop is 200 volts less
90 volts, or 1 10 volts. By Ohm's Law, the value
of the resistor will be:
I 1O X IOOO_
26
•4200 Ohms
R2 carries a loss current of 10 milliamperes
plus the detector plate current of 1.5 milliam-
peres. The voltage drop is from 90 volts to 45
volts. The calculation here is:
Ri
-=3900 Ohms
11.5
Only the value of Rs remains to be
calculated. As the sum total of all the
other resistors is 10, 100 ohms,
obviously should
have a value of
9900 ohms — or,
say, 10,000 ohms.
The resistors
should always be
capable of dissipat-
ing sufficient watt-
age. The wattage
is equal to the volt-
age d rop across
any particular re-
sistor times t h e
current in milli-
amperes divided by 1000. The wattage in
therefore is:
1 10 x 26
FIG. 3
Wi
= 2.86
To B - on B Device
FIG. 4
A five-watt resistor should be used, thus
insuring perfect safety.
Similarly Rj'should be a i- or 2-watt resistor,
and Rs the same.
In the majority of cases the reader will not
have to make the calculations outlined above,
for the resistor bank _hown in Fig. 5 is well
adaptable to the average B power device and
receiver.
The resistor bank is merely connected to the
old B power unit at the high-voltage and nega-
tive posts. No other posts on the B device are
connected, the various voltages now being drawn
from the new resistors.
JOHN J. WILLIS
Batavia, Illinois.
STAFF COMMENT
\J( R. WILLIS suggests a simple way of ob-
** * taining various B and C voltages from B
power device other than those for which the
device was originally designed. No changes
whatever are made in the B unit itself. This
arrangement, however, is practical only in the
case of B device supplying voltages of 220 or
more with a drain of 35 milliamperes, since the
obtainment of C bias will reduce the voltage of
the maximum B tap by an amount equal to that
of C voltage. Thus, a device ordinarily capable
of delivering 220 volts will still deliver sufficient
voltage (180 v.) for best operation of a 171 type
tube after a reduction of 40 volts is made to
provide for C bias. The output of your present
B device can be determined frtfm the manufac-
turer's specifications accompanying it.
The resistor unit should be bypassed with i-
mfd. condensers, as indicated by the dotted lines
in Fig. 4.
L. Bamherner Sc Co. Photograph
A COMPLETE COOLEY RAYFOTO RECEIVING^ INSTALLATION
The incoming radio signals from a standard broadcasting station are received on a standard Freed-Eisemann broadcast receiver the audio output of which
is connected to the printer unit and thence to the recorder at the extreme right. Station WOR, on November 5, 1927, transmitted the first series of radio
pictures ever to be sent from a broadcasting station which were successfully received by an installation similar to this. This complete Cooley receiver
was demonstrated early in November at a special radio show held at the Bamberger store in Newark. There are only two essential units to the Cooley
Rayfoto receiving apparatus and they are shown on the table at the right of the loud speaker. Any good broadcast receiver can be used to pick up
the Rayfoto signals. The recorder at the extreme right is not the type usually supplied, which is furnished without the spring phonograph motor. The
commercial recorder may be attached to the turntable of any standard phonograph, thus decreasing the expense
WHY I INSTALLED A COOLEY PICTURE RECEIVER
EFORE me, as I write, is a photograph
of a lady. I treasure it highly. Her face is
rather indistinct; in fact, I doubt if I
could recognize her from the photograph. Al-
though the circumstances surrounding the ac-
quisition of this photograph are highly romantic
and thrilling, I neither hope, seek, nor expect to
make her acquaintance. Yet her picture will
always remain a treasured memento. It is the
beginning of a beautiful friendship, a new ad-
diction which will make my charming wife still
more thoroughly a radio widow. My new absorb-
ing interest is the radio reception of photographs
and the valued curio is the first photograph ever
received on a home-assembled radio picture
receiver from any broadcasting station.
Not many months will pass before picture
tvansmission will be a regular feature of broad-
casting programs. I do not say this because I
have inside information, but because picture
reception is an inevitable step in the progress of
broadcasting. The only hindrance so far has been
the fact that no simple and inexpensive appara-
tus has been available, a problem which has
been solved by the appearance of the Cooley
Rayfoto System.
It is easy to speculate on the possibilities
of picture reception. Most people think of it as a
means of seeing broadcasting artists performing
in the studio. Although such a use of picture
transmission is quite feasible, it is only a minor
application. Imagine a ringside description of a
champion prize-fight coming through the loud
speaker, while near-by your Rayfoto recorder is
grinding out one picture after another of the
high lights of each round. Or, imagine the
ceremonies at the take-off of the first transatlan-
tic air liner, accompanied by pictures of the
immense bird taking on its cargo, taking off with
its load, and finally disappearing in the distance.
The new medium has all the diverse possi-
bilities of tonal broadcasting and it will add a
new lure to radio reception. Perhaps my imagina-
tion runs away with me because I have just
By Edgar H. Felix
made my first radio picture, but I firmly believe
that it is only the first of hundreds, each of im-
proved quality, which I shall pick out of the air.
On November 5, 1927, WOR, the broadcast-
ing station of L. Bamberger & Co., Newark,
New Jersey, put the first picture on the air from
a public broadcasting station. It was only a pre-
liminary test, to precede a public demonstration.
So far as I know, my picture receiver was the
only one, not installed at an experimental
laboratory, capable of receiving the picture. But
so great has been the interest manifested by set
builders in picture reception that I am sure
thousands of picture receivers will be in opera-
tion within a few weeks.
Picture transmission by wire and radio is not a
AUSTIN G.
© Bachrach
COOLEY
new art. Pictures flash across the Atlantic by
the Ranger system almost daily. The Jenkins
system has been available to amateurs for years.
The A. T. & T. has been transmitting high-
quality pictures over wire lines to all parts of the
country for some time. But most of these systems
require either expensive receiving apparatus or
more than one broadcasting channel, so that they
are hardly suited to widespread use without
considerable development.
THE COOLEY SYSTEM IS SIMPLE
THE Cooley Rayfoto system is rugged and
inexpensive. It uses but a single radio tele-
phone channel for transmission. The parts for a
picture recorder cost no more than those re-
quired for a good six-tube home built receiver.
The quality — and quality in picture reception
means detail and accuracy in shading — is not
below the standard of tonal reception quality
which we had in 1921 and 1922, a quality
sufficient to set the world on fire with a broad-
casting boom. There is no reason to doubt that
picture reception will improve as rapidly as did
tone quality in a like period. In fact, all of the
experience gained with tone broadcasting is
directly applicable to the broadcasting of pic-
tures.
The constructional details of the Cooley sys-
tem have been given completely in this magazine.
The radio element of the Cooley apparatus is no
more difficult to assemble than a two-tube radio
set. Essentially, it is a stage of audio-frequency
amplification, coupled so as to modulate the out-
put of an oscillator. It can be assembled and
wired in two hours. The rest of the work is con-
necting power supply, setting the mechanical
unit on the phonograph, and adjusting the
relay, corona discharge, and phonograph motor
speed. Mr. Cooley, in his articles, has described
these matters in some detail; my only purpose
in mentioning them here is to give you an idea of
how easy it is to get the Cooley receiver in
working order.
216
RADIO BROADCAST
JANUARY, 1928
To receive this treasured picture of mine, we
adjusted the Rayfoto relay by tuning-in a musi-
cal program. A few moments of tinkering with a
screwdriver and the relay tripped at each loud
modulation peak. Mr. J. L. \Vhittaker, who did
most of the hard work while I looked on, had the
relay working in two minutes.
Adjusting the corona offered no special
difficulties. By tuning the variable condenser
across the oscillator coil, the corona starts as
soon as the oscillator starts going. There really
isn't anything to it. To get the modulation cur-
rent right, you plug in the meter to set the input
at the correct value. It's only a matter of juggling
the input volume control.
Synchronizing the phonograph motor when
everything else is working properly is simple
when you know how. The phonograph motor
should revolve just rapidly enough so that the
synchronizing signal releases the drum at each
revolution. When it does so, the drum stops
with a firm click and then resumes turning
with hardly a perceptible stop. When it is work-
ing just right, the drum stop makes its click
with perfect regularity, about as loud as that of
a typewriter key against the platen. If the speed
is decreased below this point, there is a drop in
the intensity of the clicks and a few may skip
entirely. That is the critical speed, when the
drum is at "zero beat" with the transmitting
drum. At that speed, the synchronizing signal
is not utilized in releasing the drum; at a slightly
faster speed, when the clicks are regular, it is in
proper adjustment.
These three adjustments ,nade, and you are
ready to receive the picture. vVe got the first one
quite well, but we did not get the second one.
First the grid leak went wrong, dimming the
corona. Then the phonograph needle slipped off
the bushing. Then the relay stuck. And, finally,
the A battery went down. Of course, we didn't
get the second picture!
So, you see, there is plenty that may happen
when you get your first picture with a Cooley
receiver. You have reason to be proud of a suc-
cessful result. Of course, when there are plenty
of pictures on the air,
you won't have to meet
all of your troubles in
two short minutes. And,
more important, is the
advantage to be gained
if you have a phono-
graph record of a Cooley
picture transmission. 1
recorded the Cooley
transmissions from WOR
The author receiving pic-
tures by means of a
Cooley Rayfoto receiver
on a high-quality Dicta-
phone. By reproducing
these records with an
electric pick-up, every
element of the picture
receiver can be put in
working order before
transmission begins.
Such records can prob-
ably be used for trans-
mission purposes so that
all the broadcasting
station needs to put
Cooley pictures on the
air is a phonograph record and a phonograph.
THE GATEWAY TO TELEVISION
PICTURE transmission is the gateway to
television and every red-blooded experi-
menter longs for the opportunity to become
familiar with its problems by actual experience.
The Cooley system sends the picture in one
minute and to increase this speed of transmission
sufficiently to get motion pictures requires a
thousandfolding of this speed. Considering the
magnitude of the improvement required, it
seems impossible that the Cooley system can
TWO PICTURES RECEIVED ON A RAYFOTO RECEIVER
The picture on the right shows the effect of improper adjustment of the oscillator in the Rayfoto printer
unit. The white streaks are produced when the oscillator suddenly stops oscillating. The left-hand
picture indicates the improvement in results after the oscillator has been adjusted. For best results
the oscillator should not be tuned exactly to the point at which the maximum corona discharge is
obtained since, when so adjusted, it is rather critical and easily stops oscillating. The variable con-
denser controlling the oscillator circuit should always be slightly detuned from that point at which
maximum corona discharge is obtained
ever be the basis for television. A fundamental
and startling invention is necessary before so
great an increase of speed can be hoped for.
There have been demonstrations of television
already, but all use electrical machinery so
complex and expensive that the tests really
proved that television is not .yet a practical pos-
sibility with our present knowledge.
Someone will some day accomplish the es-
sential invention to make television practical.
Very probably the discoverer will be someone
who has worked with picture transmission. And
the man who does make television possible will
go down as one of the world's greatest inventors.
Thousandfolding the speed of any process is a
large order. But remember that only twenty-
five years ago, when radio telegraphy made its
appearance, the detector used was a glass tube
filled with iron filings. Electromagnetic waves
caused these iron filings to congeal or cohere so
that the current from a local battery flowed
through them. This operated a sounder. The iron
filings were agitated by the clapper of a bell so
that they would de-cohere or interrupt the bat-
tery current as soon as the radio wave ceased
flowing through it. With this crude apparatus,
transmission of two, three, four, and five words a
minute was the maximum possible. Ranges were
matters of a few miles.
Then came the invention of Marconi's mag-
netic detector. This greatly increased both
speed and range. And then the really revolution-
ary vacuum tube. Now, with high-speed radio
telegraphy, we send thousands of characters a
minute. From many of the long-wave, trans-
oceanic stations, you can hear the myriad of dots
and dashes, so rapid that you cannot distinguish
between them. The step from the coherer to
radio telephone transmission and reception is no
greater than that necessary from telephotog-
raphy to television. Undoubtedly, someone will
make that essential invention to make television
possible and 1 hope it will be an American
amateur experimenter, who has enough vision
to see in the crude, simple, telephotographic ap-
paratus available to him to-day the possibilities
of the great new science and art of the future.
ssin
Every Conceivable Source of Radio Interference Is Considered, Remedial Suggestions Being
Offered — Farm Lighting Plants, Railway Signals, Telegraph Lines, Stock Tickers, Street
Railways, and Interference Originating in the Receiver Itself, Are Taken up in This Chapter
By A. T. LAWTON
THE studies made by the author in the
elimination of interference have been so
extensive that it would be hardly possible
to combine the various chapters in one issue.
An endeavor has been made, however, to elim-
inate cross references so that each article in
the series may be complete in itself. The forms
of interference covered in the two previous chap-
ters, printed in the September and November,
1927, issues of RADIO BROADCAST, dealt with
interference originating at the following sources:
Oil-burning furnaces, X-ray equipment, dental
motors, motion-picture theatres, telephone ex-
changes, arc lamps, incandescent street lamps,
flour mills, factory belts, electric warming pads,
and precipitators. The information printed re-
sults from a two-and-a-half-year study by the
author in more than 132 cities. The first form of
interference considered in the present chapter,
is that originating in farm lighting plants.
FARM LIGHTING PLANTS
INTERFERENCE from this source is confined
* to rural districts. The characteristic click,
click, corresponding to the ignition spark, re-
veals the source at once; rarely do we get trouble
from the commutator.
This continuous clicking is very loud on near-
by radio receivers and because of the large num-
ber of plants in operation in communities not
served by electric power companies, the total
interference is very annoying.
Complete elimination of the disturbance
created is a relatively simple matter. Nearly all
these plants, being bolted down to a wooden
platform, are insulated from the ground and two
2-microfarad condensers in series, midpoint con-
nected to the engine frame, and bridged across
the outgoing d.c. feeders, will clear up the click-
ing. Ground connection of the series wire should
not be made to a water pipe or earth rod in this
case. Even i-microfarad condensers will be
found suitable for small plants.
If the engine bed is of concrete or the plant is
grounded in some other way, complete elimina-
tion is not obtained by the above method al-
though the reduction (about 80 per cent.) is
material. The remaining interference is not likely
to be serious. However, where it is desired to
clear this out also, choke coils should prove
effective.
It is not uncommon to find the exhaust pipe of
such plants carried to a muffler drum in the
ground; such a connection to earth offsets the
effect of the condensers and more satisfactory re-
sults will be obtained if this pipe is cut and a
section of asbestos or other suitable piping in-
serted.
Further experimental work is required in the
cases where Electrical Inspections call for the
grounding of small lighting plants. Possibly a
fine wire choke coil, say, of No. 26 wire, bridged
by a standard lightning arrester, would be
satisfactory, the coil preventing the accumula-
tion of any static charge and the arrester taking
care of any abnormal surge superimposed on the
system from outside sources.
As a precaution, all leads around the plant
proper, either high- or low-tension, should be
cut as short as possible.
Where one or two of the storage cells are used
to operate a radio set as well as light the residence,
complete elimination of the trouble for that
particular set becomes difficult.
Prior to arriving at suitable preventive
measures in the various plants investigated, ex-
periments were carried out directly on the igni-
tion system but all methods tried proved of no
avail. In the case of "make and break" type
ignition, condensers applied directly to the igni-
tion system stalled the e'ngine, apparently neu-
tralizing the effect of the inductance coil, but
were quite effective on the outgoing lines and, of
course, did not interfere with normal operation.
In all cases attachment of the condensers is
made at the switchboard, under the same ter-
minals to which the two lighting mains are con-
nected.
RAILWAY SIGNALS
RAILWAY "wig-wag" signs and crossing
bells give rise to heavy clicking radio inter-
ference. Fortunately, their periods of operation
are limited, but where the trouble is material
it can be cleared up by shunting the operating
contacts with a resistance of about 350 ohms.
This applies to low-voltage d.c. operated bells
and signals.
To Key
0.5 mfd.
Condensers
Chokes^
n
000000000(7
For types operating on 400-600 volts it is
necessary to bridge each individual set of contacts
with a resistance of the above order.
The vibrating reed type battery charger used
in conjunction with these signals is a real offender.
Interference from this source has given rise to a
large number of complaints but, generally speak-
ing, railway companies are averse to tacking
on any surge traps to this equipment and in the
dozen or so cases cleared up, the operating com-
pany took the chargers out bodily and sub-
stituted a type which is silent so far as radio
interference is concerned.
I
LAND LINE TELEGRAPH AND STOCK TICKERS
RAPID clicking interference from the above
equipment is a serious matter in towns and
smaller cities. Not that there is less telegraph
activity in the larger centres, but in the places
referred to a comparatively greater number of
residences and radio dealers are located in the
vicinity of the telegraph offices.
Normal operation of the keys and repeaters
set up a vigorous highly damped wave which
breaks in on practically any setting of the dials
of the average radio set. The clicking from stock
tickers is severe even where the wires are en-
closed in lead-sheathed cable.
Since it is necessary to apply suppressive meas-
ures to each individual line, the factor of cost
looms large when we consider the number of
lines entering the average city office. Where
only a few lines are concerned it is usual to place
a i -microfarad condenser across the key con-
tacts inserting in each condenser lead a resistance
of about 20 or 30 ohms.
Strictly speaking, only one resistance unit is
required but it makes a very great difference
which contact of the key this resistance lead is
connected to. If the condenser alone is used, re-
duction of the interference may be noted but
the resultant arcing at the contacts is prohibitive.
It is ordinarily supposed that the condenser in
this case should absorb the spark; rather, it
turns the spark into an arc and resistance is re-
quired to overcome this.
We must remember that many variables enter
here; at a given time, one leg of the key may be
to ground and the oth'.r leg to line, positive or
Line
FIG. I
The circuit employed
to eliminate interference
caused by key clicking.
An obstinate case was
eliminated by applica-
tion of a surge trap, as
shown in this diagram
Chokes- 130 turns No.26 D.C.C. wire on wooden core 15/diam.
217
218
RADIO BROADCAST
JANUARY, iga8
negative. Again, the key may be cut in on a
through line, positive or negative either way,
and these conditions are likely to be re-
versed many times in the course of a day
through jack plugging operations at the switch-
board.
In most cases these clicks are unreadable; they
occur at the break of the key, not on the closing
of the circuit, but in the immediate vicinity of
a telegraph office, radio interference may be noted
from the local or sounder circuit. This is readable
and can usually be eliminated by bridging the
relay contacts of the local circuit with a one-half
microfarad condenser without any series re-
sistance.
Occasionally, complications enter into the
situation, making necessary the use of full surge
traps. An obstinate case of key clicking was
cleared up only after applying the surge trap
described in Fig. i.
Another difficult case, in connection with a
set of repeaters, required choke coils as described
in Fig. 2 in each line and o.5-mfd. condensers,
series arrangement midpoint grounded, across
the repeater contacts.
• Duplex and quad circuits require individual
treatment; much experimental work is required
before standard eliminators can be recommended
for these and the various types of stock tickers
in daily operation.
RADIO RECEIVERS
MUCH of the so-called inductive interference
has its origin in the broadcast listener's own
set. It might be due to any one of the following
causes:
(i.) Loose antenna or ground connections will
give rise to serious clicking noises when
shaken by wind or other agency.
(2.) Loose or corroded connections at the A
battery will cause flickering of the tubes
and consequent clicking.
(}.) Internal defects in any one cell will cause
harsh grating noises. This can be checked
with a telephone transformer and pair of
headphones, the secondary of the trans-
former being connected to the battery and
primary to the phones.
(4.) Defective B batteries cause a "chirping" or
clicking interference. It doesn't follow that
because a B battery registers full voltage,
22! or 45, that it is in good condition. One
high-resistance cell of the many incorporated
in this battery can render the battery unfit
for use although on open circuit it reads up
to full strength.
(5.) Oxidized contacts of the tube prongs or
spring contacts of the sockets are fruitful
sources of trouble. These should be scraped
occasionally and the spring strips pulled up
gently to insure that good contact is being
made.
(6.) Broken lead-in wires cause poor reception
and clicking noises. Naturally, a lead-in
wire must be insulated where it enters the
building but the practice of using covered
wire all the way down from the horizontal
portion of the antenna is not to be recom-
mended. From swinging in the wind, this
wire often breaks inside the insulation but
is held up by the fabric so it appears to be
continuous whereas the wire itself is sepa-
rated an eighth of an inch or more.
(7.) Concealed house light wiring in the walls
will cause humming noises if the radio set is ,
installed close up to such partitions. This is
especially noticeable in the case of single-
circuit receivers.
In the case of abnormal humming it is
probable that the main supply line (three-
wire system) is badly out of balance or the
wrong side of the house lighting system is
grounded. This latter will not necessarily
blow the fuses.
A and B supply devices designed for
sixty-cycle supply will also give some similar
trouble when used on twenty-five cycle lines.
Various stray noises will, of course, result from
defective tubes, shaky splices, poor construction,
connections soldered with acid flux, etc. Before
assuming that any given interference comes
from the outside, broadcast listeners should dis-
connect the antenna and ground wires and note
if the interference weakens or disappears. If it
does, the source of the trouble is outside. If it
remains the same and is not responsive to tuning,
the trouble, nine times out of ten, is in the set it-
self.
Unshielded sets may pick up outside inter-
ference without the antenna or ground being
attached, but a decided weakening will be ob-
served when these are disconnected and this is
sufficient proof that the disturbance is not in-
ternal.
As a test, the house lighting supply switch
should be opened for a moment. If the inter-
ference disappears coincident with this, all lights
and electrical apparatus in the residence should
be checked over for possible faults. A lamp loose
in its socket can cause quite a lot of trouble.
Partial shorts in the interior wiring will cause
trouble over a fairly wide area; such a case
-_*
A-*" B-%" C-%r D-2V E-%"
Hardwood Bobbin. approx 300
turns No.22 (about 125 ft)
FIG. 2
occurred recently where a long nail driven in an
attic floor brought a concealed power wire in
contact with the grounded plumbing.
ELECTRIC STREET RAILWAYS
INTERFERENCE from this source presents a
1 problem for which no really satisfactory solu-
tion has been found. Without question, many
radio sets are unnecessarily interfered with
by this agency and in such cases relief is possible.
The steady interference under a street-car line
is violent; fifty feet either side of this it is almost
negligible. Only when cars go by or some very
abrupt alteration of the line energy values occurs
do we get trouble at this distance.
The following actual test is interesting: On a
radio set, the antenna of which ran parallel to a
car line, broadcast programs were rendered
valueless as mediums of entertainment but when
this antenna was changed to run at right angles
to the line, good reception became possible. The
effect was decided.
If your antenna is at present installed at the
front of the building, facing the car line, shift it
to the rear as far as possible. If conditions per-
mit, run it at right angles to the line of inter-
ference. It is surprising what a difference one
or two feet variation in the plane will make
here and we suggest when installing, permanently
fixing one end of the horizontal portion and tem-
porarily attaching the other end of the horizontal
part to a pole which may be carried backward
and forward on the roof to test out the exact
position of minimum interference.
Relative intensity of the interference is noted
at each setting and a permanent pole fixed at the
proper point. We must remember that lighting
and power circuits nearer the residence than the
trolley feeder are concerned in transferring this
disturbance to the antenna, and distortion of di-
rection is pretty sure to occur.
Sparks at the trolley wheel cause clicking inter-
ference; large arcs cause none. The bigger the
flash, the less the interference. Cars going up
grade on full power cause decidedly less inter-
ference than cars coasting with practically all
power off, only the lights or heaters being in
operation. Trolley shoes are no improvement over
wheels. Catenary suspension makes no difference.
If the positive lead of the station generator
goes direct to the trolley wire, interference will
probably result. If this lead goes to the series
field winding first, the free end of the series field
going to the line, the choking effect of the coils
tends to suppress any commutator interference.
In addition to checks on the usual 6oo-volt
d. c. systems, observations were carried out on:
(a.) Pantograph System, 6600 volts a.c. copper
trolley wire.
(b.) 1 5oo-volt d.c. system using shoes. Copper
trolley.
(c.) 24Oo-volt d.c. pantograph. Copper trolley,
(d.) ijoo-volt system d.c. shoe contact. Entire
system steel trolley wire.
A great many variable factors entered into the
results and for scientific purposes the data ob-
tained are not considered satisfactory. Much
time and effort and expense have been devoted to
the whole problem of interference from electric
railways but, so far, results have not been very
encouraging.
It must not be concluded, however, that the
proposition is hopeless; greater efforts are being
made in every city to keep the rail bonding in
good shape and it is probable that more careful
attention to car motors and equipment generally
will tend to alleviate the situation.
Peculiar effects are often observed on radio
sets installed in the vicinity of a car line. It is
not uncommon to find that a passing car, even
when causing little or no radio interference, will
"take away," temporarily, the program being
received. As soon as the car moves away a few
hundred feet the program comes back, without
any alteration of the set tuning whatever.
Again, in two widely separated instances, and
some distance away from the car lines, the dis-
turbance on residence radio receivers amounts
to a continuous loud roar. Immediately outside
both residences no interference can be picked up
on a standard six-tube super-heterodyne receiver.
Evidently this was a case of electrolysis since
an exploring coil on the water piping indicates
fluctuating current in the plumbing system.
Concealed pipes and wiring in these residences
carry the surge also and loop reception is prac-
tically no better although the ground wire to the
water pipe is cut off.
One of the most curious and perplexing cases
of radio interference that we know of had its
origin in an electric street railway system. This
particular noise affected only three residences,
all fairly close together. All efforts to locate the
trouble failed but the plumber solved the prob-
lem. It so happened that the drain pipe of the
centre house became blocked; on digging this
up it was found to be full of a fibrous growth
and at a crack in the pipe a mass of roots had
come through and grown out in the direction of
the railway tracks, close up to the rails, in fact.
This offshoot evidently served as a conductor
to electrify the plumbing fixtures of the three
houses concerned and as the radio set grounds
were attached to this, every variation in the rail-
way line voltage set up a disturbance on the
radio receivers. When the drain pipe was cleaned
and replaced, all interference disappeared.
The Listeners' Point of View
ARE PROGRAMS GOING IN THE WRONG DIRECTION?
lOMETlMES when we sit ourself down
to pound out this monthly manifesto
concerning matters radio, we attack the
job with great gusto and enthusiasm. We are
filled with a vast faith in radio's achievements
and possibilities and garner a certain amount of
personal satisfaction in making our small critical
contribution to radio's great ends.
There are other times when we entertain grave
misgivings as to whether the subject is actually
worth the fifteen clean sheets of typewriter
paper we employ to comment on it. Such doubts
assail us this very minute. Probably when we are
effusing enthusiastic utterances about radio
entertainment we are writing romance, and to
admit that it is pretty punk is simply to be realis-
tic. Though if you be of the other turn of mind
you may claim that it is the former that is realism
and that the latter is rank pessimism — which
suggests an appropriate variation of Cabell's
ingenious epigram: The optimist thinks that radio
has now reached the greatest heights of achieve-
ment. The pessimist, alas, is afraid that he's
right!
Whatever roseate promises radio may have
seemed to have held in the past we are at present
thoroughly convinced that things have reached
a sorry pass and that radio is standing still —
smug, self-satisfied, and inutterably banal. One
robin does not make a summer and the indubi-
tably good program to which you may point here
and there (only too infrequently!) isn't enough
to raise radio to the standard it ought to be
maintaining.
If two years ago someone had told us that by
the end of 1927 programs would have only at-
tained the level they now actually occupy we
would have pooh-poohed him as a person in-
capable of reading the signs and portents. At
the rate things were progressing in 1925 there
was every indication that another two years
would find us surfeited with high-class program
material, of such high standard that we would
be loath to absent ourselves from our receiving
sets for two nights in a row.
As we look back several years, the greatest
hope for improved programs then seemed to lie
in the ever increasing number of sponsored pro-
grams. Great industries were going to start pour-
ing their gold into the radio stations in payment
for indirect advertising — more properly, radio
publicity — and great things were going to result.
Herein was the solution of all our difficulties:
without government operation; without levying
of taxes; without philanthropic financing, we
were going to lead the world in program stand-
ards by utilizing our great American asset — Big
Business.
Well the dismal fact of the matter is that none
of these things has come about. And the ironical
conclusion to which we are forced is that the
rise of the sponsored program is responsible for
the stand-still that radio has reached at the dawn
of this year of grace 1928. In fact, stand-still is
putting it mildly; the state of affairs is more
exactly a retrogression. All the money, all the
ingenuity, and all the labor that is being devoted
to the designing of programs is being diligently
devoted to efforts in the wrong direction — with
the result that radio is going to the dogs at a
breakneck speed, so rapidly in fact, that to check
it will require no little effort.
By JOHN WALLACE
LET US LOOK AT THE GUIDE POSTS
\A7HAT is the right direction? It would seem
• ' that program makers are too embroiled in
their business to glance at the guide posts, too
pressed by the strenuous and unceasing job of
making programs to take a moment or two off
for a little rational reflection on what their job
is all about. They persist in refusing to take
account of the fact that radio is a new medium,
a unique medium and, like any other medium,
endowed with its peculiar limitations and
peculiar possibilities. Pig-headedly they persist
in attempting to reconcile with their duties the
traditions of the drama, the opera, the music hall,
and the vaudeville stage. This observation has
Radio Times, London
IGOR STRAVINSKY
The British Broadcasting Company, on a recent
Sunday afternoon symphony program, presented
the modernist composer, Igor Stravinsky, con-
ducting a program of his own works. This is
an event in radio annals. True, Stravinsky has
been "outmoderned" by a group of still younger
composers but his compositions are still quite far
in advance of the popular taste. It's likely that
no American station would have, nor will have
for many years, the temerity to present a pro-
gram of such dubious popular appeal. This does
not indicate that the Britisher is any more
sophisticated in his tastes than the American;
it is our guess that the B. B. C. is enabled to
essay such a high-brow program simply because
it is non-competitive. On Mr. Stravinsky's pro-
gram appeared the Overture to Mavra, the
Suite from the Fire Bird and a Concerto for
Pianoforte with Accompaniment of Wind
Instruments. The latter was a premier English
performance. The above portrait is from a draw-
ing by the famous French artist, Picasso.
been made often before. We are a trifle abashed
at shouting the same tune again. But probably
it will have to be stated many times more^-
and certainly by others than ourselves — before
it sinks in.
Without annoying you by enumerating radios'
219
limitations, which you know as well as we (unless
you happen to be a program designer, in which
case you probably don't), we will proceed to the
proposition that the one species of entertain-
ment that radio is by its intrinsic nature best
fitted to put across is instrumental music.
Music is the only existing mode of entertain-
ment that can be assimilated solely by the un-
aided ear. The radio (together with the phono-
graph) is the only existing entertainment device
which can reach nothing but the ear. Obviously
they were made for each other! They should be
joined in holy wedlock and wander hand in
hand through the new mown hills, happily ever
after.
Instrumental music should be the backbone
of the radio program; it should predominate
every program; it should be the piece de resist-
ance with all the other little absurdities of broad-
casting arranged around it like the potatoes
around a roast beef. Plays, where you can't see
the players, speeches where you can't see the
speakers, comedy, where you can't see the
comedians — all such like stuff is mere piccalilli
and sauce.
So the business of broadcasting is music.
And by music we mean music at its fullest reali-
zation, which is that of the instrumental en-
semble— the symphony, the little symphony,
or the chamber group.
In the field of the representative arts are
many different mediums — water color, etching,
caricature, wood cut, lithograph, miniature, pen
drawing, fresco, and countless other specializa-
tions. But it is finally in the oil painting that
graphic art finds its complete expression. Beside
it all other artistic endeavors fall into compara-
tive insignificance. It contains within itself the
whole total of their qualities and infinite other
ones of its own.
A perfect analogy exists in music. Vocal music
is all right in its way, as are also organ recitals,
piano gymnastics, jazz bands, and marimba-
phones. But they are all dwarfed by the sym-
phony orchestra. The orchestra not only can do
all the things that they can do, but can do them
better — and with its great musical resources can
secure added effects that they can't possibly
aspire to.
Of course it is always necessary to get back to
the cold fact that, in America at least, the station
manager's only business is to give the listeners
what they want. But don't they want orchestral
music? There has been much talk about how the
taste of the listening public has been elevated
by radio and much proclaiming that Mr. Average
Citizen has reached a stage of enlightenment
where he can actually enjoy serious musical
compositions. We are inclined to believe that
this is true. Moreover, there are thousands of
people in the country who needed no "educat-
ing" but who already liked such music. It seems
fair enough to deduce that genuine music is
the "what-they-want" of a sizable section of
listeners and potential listeners.
In view of the fact that orchestral music is the
best thing that a station can put across, and the
best thing that a listener could listen to, it seems
fair enough further to deduce that there ought to
be a certain amount of it in the air of an evening,
available for such persons as wish to seek it out.
But is it there?
220
RADIO BROADCAST
JANUARY, 1928
THE HORRIBLE EVIDENCE
BY WAY of confirming our suspicion that
there isn't, we sat ourself down at our
receiver the other night and proceeded systemati-
cally to get a cross section of what was on the air.
At 8:15 p. M. (Central time) we started at the top
of the dial and worked our way patiently to the
bottom, recording everything that was going on
within our receiver's range. The stations en-
countered extended from Colorado to Texas to
New England. At 9:35 P. M. (Central time) the
chore was concluded, and if you entertain any
delusions that there are a lot of fine things on the
air awaiting the turn of a dial, gaze at the cold
and cruel statistics we found on our tablet:
1 JAZZ PIANO, playing "Ain't She Sweet."
2 JAZZ ORCHESTRA, dance music.
3 COUPLE AT A PIANO, wise cracks, request
numbers, ballads.
4 SENTIMENTAL SONGS, "Sweetheart of Sigma
Chi," etc.
5 SOPRANO, singing the Brindisi from "Lucre-
zia Borgia."
6 BARITONE, singing unidentifiable ballad.
7 SERMON, of the vocal-cord-splitting variety.
8 TENOR, popular ballad, "I'll Forget You."
9 DANCE ORCHESTRA, playing "Rio Rita."
10 OLD TIME FIDDLING, with "swing your
partners," etc., interpolations.
1 1 STRING TRIO, playing semi-popular airs.
12 CHORAL GROUP, in the finale of a light
opera.
13 SOPRANO, singing the Shadow Song from
" Dinorah."
14 SOPRANO, singing "Just a Wearyin' for
You."
15 CHURCHILL SISTERS, singing "Say Au
Revoir but Not Good-bye."
16 SOPRANO, singing some light ditties in
French.
17 DRAMATIZATION, of Rip Van Winkle.
18 TENOR, solo.
19 STRING TRIO, playing Saint-Saens' "Swan."
20 WEATHER REPORT.
21 DANCE ORCHESTRA.
22 NOVELTY SONG, with banjo.
23 HAWAIIAN GUITAR AND MANDOLIN, duet.
24 TRAVEL, talk on Starved Rock, Illinois.
25 FEMALE, reciting poetry.
26 MALE QUARTET, singing " Bye and Bye."
27 PRIZE FIGHT.
28 BRASS BAND, playing "Moonlight Wonder-
ings."
29 JAZZ ORCESHTRA.
30 TENOR, singing Welsh folk songs.
31 TENOR, singing popular ballad, "Lone-
some."
32 PIANOLOGUE.
33 TENOR, singing sentimental ballad.
34 VIOLINIST, playing Beethoven — Opus 12
Number i.
35 TENOR. "A Robin Sings in the Apple Tree."
36 TRIO, playing semi-classics.
37 ORGAN, "Pale Hands I Loved," etc.
38 BASS, soloist.
39 DANCE orchestra, "On a Dew Dew Dewy
Day."
40 FEMALE duet, sloppy ballad.
41 MALE CHORUS, college songs.
And there you are! Nowhere was the orchestral
program we had set out in search of. Twenty of
the forty-one programs were vocal, practically
fifty per cent.! And this in spite of the fact that
vocal transmission is one of the lesser effective
things broadcasting is capable of. Only three of
the programs encountered seemed to hold any
promise of suiting our mood of the moment,
numbers 5, 13, and 34. But a return to these dial
positions found the stations already shifted to
something trifling.
But perhaps, we reflected magnanimously, we
had picked out the wrong hour of the evening.
So the following night we repeated the pro-
cedure, commencing at 7:15 P. M. Central time,
and running through to 8:20. Behold our second
log:
1 SOPRANO, singing Nevin's " Rosary."
2 DANCE ORCHESTRA, jazz.
3 BARITONE, solo "Young Tom o' Devon."
4 JAZZ ORCHESTRA.
5 DANCE ORCHESTRA.
6 DANCE ORCHESTRA.
7 DANCE ORCHESTRA — (what, another!).
8 ORGAN, Mendelssohn's A Major Organ
Sonata.
9 MALE QUARTET, "Back Home Again in
Indiana."
10 BANJO, solo with piano accompaniment.
1 1 TALK, on something or other.
12 PIANO, solo.
13 NEGRO SPIRITUAL, "I Heard From Heaven
To-day."
14 PLAY, Julius Caesar.
15 SMALL ORCHESTRA, playing "Gypsy Sweet-
heart."
16 BAND, playing march tune.
17 VIOLIN, Schubert's "Ave Maria."
18 VOCAL DUET, semi-popular songs.
19 BIBLE READINGS.
20 TENOR, singing sloppy ballad.
21 TRIO, playing light stand-bys.
22 COUPLE, singing novelty songs about sweet
mammas.
23 DANCE ORCHESTRA.
24 SPEECH, by some labor leader.
25 STRING QUINTET playing Handel's Water
Music Suite — but, alas, even as we listened,
this changed into a soprano solo!
Such Was our clinic — sixty-six cases examined
over a period of two hours and twenty minutes
of the most favorable broadcasting time of the
evening. It may be objected that we didn't
examine all the programs of all the stations dur-
ing that time period, but we see no argument to
show that the cross section we observed was
other than representative. Representative, for
the most part, of a lot of inanities that only the
veriest imbecile, with the meagerest amusement
resources conceivable, could dignify with the
name of worthwhile entertainment.
Of these sixty-six programs not a single one
was orchestral. The few trios we ran across were
simply doing their five or ten minute/ turn on a
well scrambled variety hour.
WE DON'T NEED SO MUCH VARIETY
T"*HIS frantic search for variety is one of the
* silliest things in the whole radio broadcast-
ing business. Variety has been set up on a
pedestal as the one goal to be achieved. The
means used to secure it are devious and dull.
Variety is necessary, of course, but there are
other sorts of variety than that of the vaude-
ville show. Program directors do not realize that
music, real music, contains within itself all the
variety that is necessary. If program arrangers
only realized it, their job has already been done
for them by the great composers.
Practically every hour of program furnished
by the broadcasters to-day is a variety program.
And where every program is a variety program
would it not be a variety to introduce a program
that is not a variety program?
We throw out the foregoing sound suggestion
to whomsoever chooses to make use of it (fearing
the while that no one will).
To the rising tide of sponsored programs is
due the blame for the overwhelming number of
variety programs which is rapidly reducing radio
t6 the level of a gigantic and worthless vaudeville
show. In any schedule of entertainment it is the
light frivolous item, introduced to break the
monotony, that is the brightest thing on the
program. This principle is borne in mind by the
advertiser when he decides to produce a broad-
cast program of his own. He will make his pro-
gram snappy and ever changing, he reasons,
and thus make it stand out in high relief against
all the others. Unfortunately every other ad-
vertiser goes through precisely the same sort of
reasoning. The result is that sponsored programs
are all as alike as peas in a pod, and no pea is
any more novel or attention compelling than its
neighbor on the left or on the right. All are deal-
ing in olives and chilli sauce, nuts and caviar.
None is willing to supply the meat of the repast.
This meat must be orchestral music of solid
musical worth.
If broadcasting, considering it as a whole, were
maintaining a proper balance in its offerings —
a thing it must eventually do or go out of busi-
ness— it would be possible to find good music,
played by competent orchestras, at at least ten
places on the dial at any hour of the evening. Its
present condition, that of having no respectable
music to offer, is certainly not a healthy one.
Some stations used to maintain fair sized
orchestras as a staff feature, but their number is
rapidly diminishing — the very reverse of what
should have happened. If radio had progressed
in its proper channel we would now have some
ten or twenty symphony orchestras throughout
the country bearing as their titles the names
of the stations which organized them, and being
secondary in musical importance only to the old
established symphonic societies. It is expensive,
certainly, to maintain a large orchestra but when
it comes to hiring dance bands or opera singers
expense seems to be no important item to the
broadcasting stations.
If expense is not the drawback it must be that
there is still a lingering fear that not enough
people will listen to a highbrow orchestral broad-
cast to make it worth while. This fear, as we
have already stated thirteen different ways, is
ungrounded. The Damrosch programs (an excep-
tion we advance in further proof of our point)
seem successful enough. And witness the way the
populace is clamoring for more sophisticated
orchestration of its dance music. They go wild
over Paul Whiteman's rendition of "When Day
is Done." If they like this why wouldn't they
enjoy the compositions of Stravinsky and others
of the modern school. Katscher's piece is simply
a shoddy and ineffectual mimicking of the works
of these composers. There are tunes in the
Beethoven symphonies as simply melodious as
anything Victor Herbert ever wrote. No one
who likes jazz effects could fail to be pleased by
Casella, for instance, or Sowerby. We defy any-
one but the stupidest moron to listen to the first
movement of the Cesar Franck symphony with-
out craving to ' hear it repeated. Schelling's
"Victory Ball" could sweep any Rotarian off his
feet. The use of the human voice in Bloch's
"Symphony Israel" is incomparable, but not
incomprehensible. Ravel's "Waltz" makes those
of the light operas tame indeed. Tschaikowsky's
"Manfred" symphony, for those who would
weep, is forty times more lugubrious than
"Hearts and Flowers." The name of Bach could
terrify no one who had heard Abert's arrange-
ment of his Chorale and Fugue. Scriabin's
Third Symphony is of such emotional ferocity
that it could emotionally unstabilize a brassy
monkey. And as for soul satisfying harmony,
better than any organ chords is the passacaglia
that concludes Brahms' Fourth Symphony.
RADIO BROADCAST Photograph
USED IN THE LABORATORY
The photograph of the vacuum-tube voltmeter shown schematically in Fig. 2 indicates a simple breadboard layout. The equipment includes a Yaxley
potentiometer, a Pacent rheostat, an Alden socket, Mountford and Crescent resistances, a Sangamo "Parvolt" condenser, and several Fahnestock clips
A VACUUM-TUBE VOLTMETER
IN THE study of radio-frequency phenomena,
experimenters have always been more or less
handicapped by their lackof accurate measur-
ing instruments. It is a simple matter, compara-
tively, to build a meter that will cover a consider-
able range when one works at 60 cycles, or at
fairly high values of current and voltage, but let
the research student attempt to measure currents
at a million cycles and of a few microamperes, or
voltages of a few microvolts, and his problem has
increased in difficulty many fold.
The advent of the vacuum tube has made
material progress possible in the realm of radio-
frequency measurements, so much progress, in
fact, that it is now possible to buy a book that
deals with nothing but measurements at fre-
quencies far beyond those used for household
purposes, and at values of current and voltage
that are prefixed by the word "micro." Such a
book, Radio Frequency Measurements, by E. B.
Moullin, was reviewed in RADIO BROADCAST for
October, 1926; no serious experimenter can afford
to be without it.
In the present-day radio laboratory there will
generally be found, on one hand, a vacuum tube
generating currents and voltages of practically
any frequency and any amplitude (the modulated
oscillator described in the June, 1927, RADIO
BROADCAST is an example), while on the other
hand is another tube, perhaps exactly similar in
type to the generator, the purpose of which is to
measure the output of the first tube.
This latter tube, variously known as a "peak"
voltmeter, or a vacuum-tube voltmeter, is the
laboratory's most versatile and useful instrument.
It can be used to measure voltages and currents
of any amplitude and frequency, to measure the
voltage or power amplification of audio- or radio-
frequency amplifiers, the field strength of distant
stations, the high-frequency resistance of a coil
or condenser, as a level indicator in broadcasting
stations or remote control stations — anywhere
in fact where a meter is required which takes so
little power from the circuit being measured that
its presence causes no error in measurement.
Briefly, the vacuum-tube voltmeter is a tube act-
ing as a detector, or distorting device, so arranged
that alternating potentials on the input may be
read as direct current in the output. Unlike other
translating mechanisms, the vacuum-tube volt-
meter has no moving parts, there is little to wear
By THE LABORATORY STAFF
out, it has nothing in its construction that is not
easily replaceable and, best of all, it can be made
to consume almost no power from the source to
which it is attached.
Why is such an instrument necessary, and
what are its particular qualifications compared
to voltmeters with which we are all familiar? Let
us suppose, for example, that we wish to measure
the voltage delivered by a dynamo which will
light a hundred 4O-watt lamps, that is, will deliver
4000 watts, or 4.0 kilowatts. Suppose our ordin-
ary moving-coil voltmeter has a resistance of
10,000 ohms and that when placed across the
terminals of the dynamo it registers 100 volts,
how much current and power does it take from
the generator?
Ohm's law, which states that the number of
amperes flowing in a circuit is equal to the voltage
of the circuit divided by its resistance, tells us
that o.oi amperes will flow, and when we multi-
ply this value of current by the voltage across
the meter we find that the product, i.o watt, is
the actual power required by the meter to give
the proper deflection. Now this one watt is a very
small part of the power that can be delivered by
the dynamo, one four-thousandth as a matter of
fact. It will readily be seen that the error of read-
ing of the meter, due to the current it consumes
itself, will be so small in this case as to be negligi-
ble.
But suppose our dynamo still had a terminal
voltage of 100, but was so small that it could
supply only one watt of power? How can we
measure its output? It is at once obvious that
xu —
~~M
c
If
ti-Ampsl,
* ?=z^ —
™ C \
"ci Sr
ill1'
ilililiJ
tf.\— "Wl'l"
C B
FIG. 1
A C-battery detector and a direct-current meter
are the principal parts of a vacuum-tube voltmeter
221
we cannot use the same voltmeter for it would
consume all the power the dynamo is capable
of supplying.
The answer lies in making the resistance of
the meter so high compared to the resistance of
the source of power, the dynamo, that very little
current flows through it, and consequently, very
little power is drawn from the source, which, in
turn, means that applying the meter to the tiny
one-watt dynamo will not short-circuit it, as
would be the case with a low-resistance voltmeter.
This problem has resulted in the design of high-
resistance voltmeters useful in measuring the
output voltage of plate-voltage supply units.
The problem is even more complicated when
we wish to measure alternating currents or
voltages of very small magnitude, or at very high
frequencies. There is a very definite need for a
voltmeter or an ammeter that will measure any
values of current, or voltage, at any reasonable
frequency, and without taking appreciable power
to operate it.
The vacuum-tube voltmeter is such a device.
Its input resistance can be made so high that it
consumes practically no current from the source
being measured, and aside from a small input
capacity which may require slight retuning when
working with tuned circuits, it has so little effect
on the circuit that its presence may be neglected.
C-BATTERY METER
THFRE are several types of vacuum-tube
voltmeters, the C-battery detector type
being the simplest and perhaps the most gener-
ally useful. The one described in this article has
been designed for reading small values of a.c.
voltage although it may be adapted for reading
any desired maximum value.
The circuit diagram of a C-battery type of
voltmeter is shown in Fig. I. As can be seen, it is
quite simple, consisting only of the tube and its
necessary batteries, and a direct-current meter
which, for all ordinary measurements, should
read not over 500 microamperes.
The question, " how can a direct-current meter
in the plate circuit of a detector be made to meas-
ure alternating voltages placed on the grid-fila-
ment circuit of the tube?" naturally arises.
222
RADIO BROADCAST
JANUARY, 1928
Builders of plate-supply units, and owners of
power amplifiers, who have placed a milliam-
meter in the plate circuit of the power tube, and
watched its deflections under strong signals, have
possessed the essential part of a vacuum-tube
voltmeter — an overloaded tube. Whenever a
signal came along which was greater than the C
bias could handle, the average plate current
changed and caused variations of the milliam-
meter needle.
But why does the needle wobble?
The normal plate current, as indicated by the
milliammeter, is fixed with a fixed value of grid
bias and a given plate voltage. When small a.c.
voltages (the incoming signals) are placed on
the grid circuit, the C bias is changed accordingly
and in the plate circuit appears a magnified rep-
lica of these input voltages. In other words, the
actual voltage on the plate of the tube varies
with the input grid-filament voltage and natu-
rally the plate current changes accordingly. If
these changes are rapid and symmetrical, so that
an increase in current is followed by an equal de-
crease, the average value of the plate current
will remain the same and the milliammeter
needle does not move. It is these a.c. plate
currents which are amplified and which produce
signals; the d.c. current is only a necessary and
not directly useful part of the process.
If the changes in plate current are not sym-
metrical with respect to the value when no a.c.
input is applied, the average value of plate
current is different, and the plate milliammeter
needle jumps about if this average value changes
rapidly. The relative amount of plate current
change, and whether it decreases or increases
from the steady d.c. value with no input, depends
upon the fixed C bias, so that we can make the
complete unit, tube and meter, into a sensitive
indicator of small a.c. voltages if we choose the
plate and grid voltages correctly.
(i-Amps
FIG. 2
Here is the circuit diagram of the vacuum-tube
voltmeter described in this article. The addi-
tional apparatus not shown in Fig. I constitutes
a bucking-voltage device to keep the normal
plate current out of the microammeter and, of
course, the filament battery and rheostat
The vacuum-tube voltmeter, then, consists of
a tube so biased that input a.c. voltages cause
large changes in average d.c. plate current. To
make it into a calibrated meter, one merely places
known a.c. voltages on the input, reads the plate
current change, and plots a curve (typical curves
are shown in Fig. 4). The purpose of the bypass
condenser, Q, shown in Fig. i, is to improve the
rectifying or distorting property of the tube.
To prevent the device taking power from the
source being measured, the C bias must be great
enough that input peak voltages do not make the
grid go positive at any time. In practice the bias
is such that the normal d.c. plate current is very
near zero; this near-zero current is prevented
from going through the microammeter by a
FIG. 3
Some calibration curves.
Each curve was made
with a different a.
c. voltage input. Note
how rapidly the plate
current increases with
small increases of plate
voltage
RADIO BROADCAST
LABORATORY
199
Ey=-5.8
EF-3
7
7
•
200
180
t
r /
/
120
I
100
80
60
40
20
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
ED
"bucking" voltage secured from a battery or a
potentiometer across the A battery, as shown in
Fig. 2. The high resistance prevents shunting
the meter with the potentiometer. The reason for
preventing the normal d.c. plate current going
through the meter is so that the latter's range
will not be limited by having to register both the
normal current and the current produced in the
process of measurement.
Any type of tube may be used. For conveni-
ence, the small 199 type tubes are used in the
Laboratory, and should be used with the voltages
specified here.
One simple form of vacuum-tube voltmeter
used in the Laboratory is shown in the photo-
graph on page 22 i and another type, housed in
a Ware radio cabinet, on page 223. The microam-
mefer in the first picture (that at the top of page
221) is a Westinghouse instrument Model PX
and has a maximum range of 200 microamperes.
It is also possible to obtain this model with a
full-scale deflection of 500 microamperes. These
are particularly good instruments for this work,
since the scale length of four inches makes it
easy to read accurately, and the little button at
the left, when pushed, removes a shunt which
protects the meter from overload. In other words,
the meter is always protected until one pushes
the button, and in a vacuum-tube voltmeter
of the type described here, this is a very valuable
feature.
The two Westinghouse meters list at about
$35. Weston makes a model 301 meter in two
ranges which are suitable for tube voltmeters,
one with a full-scale deflection at 200 micro-
amperes listing at $33 and another, a i-milliam-
pere (1000 microamperes) meter at $12. Jewell
makes similar instruments at about the same
prices. In the photograph on page 223 a Weston
l.5-milliampere (1500 microamperes) meter is
shown.
CONSTRUCTION OF THE VOLTMETER
TH E photograph on page 22 1 shows how sim-
ple the vacuum-tube voltmeter may be. The
small single-pole double-throw switch at the
left is used to short the input by connecting the
grid directly to the negative post of the C battery
when circuits to be measured are being set up.
There is no need to place the apparatus in such a
small space as shown in this photograph, al-
though the grid lead between voltmeter and ex-
ternal apparatus under test must be as short as
possible, and well protected from other leads
carrying a.c. voltages.
A list of the apparatus used in the voltmeter
shown in Fig. 2 follows. Any of these parts may
be substituted by others that are well made,
and none of the values of resistance, etc., are
critical.
One Tube Socket.
RI — jo-Ohm Rheostat.
RI — 4OO-Ohm Potentiometer.
Rs — 2O,ooo-Ohm Resistance.
Ci — i-Mfd. Bypass Condenser.
One S.P.S.T. Switch.
7 — Clips (or Binding Posts).
One Binding Post, Insulated from the Baseboard.
Microammeter.
The experimenter who builds such an a.c. volt-
meter for the first time must remember that he
has in the circuit a very sensitive and, therefore,
expensive meter, namely, the plate current read-
ing device If the grid circuit of the tube is left
open, or if any one of several accidents happen,
the meter will be blown up, and all experiments
will terminate in an abrupt and disheartening
manner. Every step in the construction, calibra-
tion, adjustment, and operation must be watched
with great caution, and adjustments should be
JANUARY, 1928
A VACUUM-TUBE VOLTMETER
223
made only after due deliberation of what will
happen once the proposed adjustment is carried
out. After the experimenter becomes familiar
with his apparatus, he will be able to proceed
rapidly from calibration to operation, and to have
such a feeling for his instrument that he can pre-
dict what each change in voltage, etc., will pro-
duce.
CALIBRATION
THE first job after the assembly of the
vacuum-tube voltmeter is the calibration
process. This is a fairly simple operation and
need not be baulked at by the experimenter with
average experience in handling measuring instru-
ments. Before starting, bear in mind that too
much current in the plate circuit of the tube will
ruin the meter, so every step should be proceeded
with gradually and with the utmost care.
But before the actual calibration is started,
we must decide upon the voltage of the C and
B batteries in the voltmeter circuit itself (the A
voltage is, of course, that recommended by the
manufacturer of the tube used). We are assuming
in these experiments that a 199 type tube will be
used. The microammeter should not be con-
nected in circuit until the potentiometer switch
arm is thrown as far as possible towards the
negative end or, preferably, a small piece of
paper should be slipped under the movable con-
tact to insulate it from the wire beneath. This
prevents any of the voltage across the potentio-
meter, due to the filament battery, flowing
through the microammeter until needed. Since
this current is backwards with respect to the
meter, it may damage it until some plate current
flows. Now adjust the filament rheostat until
the voltage is normal.
Before proceeding further, we will test the
circuit to see that everything is satisfactory (the
actual calibration has not yet begun). We short-
circuit the input to the tube by connecting to-
gether points X and Y, Fig. 2. Assuming that the
microammeter has been connected in circuit and
that the B and C batteries are of satisfactory
value, a current will flow in the plate circuit and
will be indicated by a deflection of the meter
needle. The value of this current is dependent
upon the voltages of the B and C batteries. Thus
it will be seen that the value of these batteries
is all important for if they are of such value as
to give a larger plate voltage than the microam-
meter can indicate, it will be at this point that
the abrupt and disheartening termination of ex-
periments will occur. Do not, therefore, play
about with different values of plate and grid
voltages unless you know just what you are
doing.
With a 199 type tube, we recommend that
the B voltage be 45 and the C voltage be 9 to
start with. Under these conditions a reading of
6 microamperes was obtained in experiments in
the Laboratory. Fig. 3 shows some typical
curves which were obtained in the Laboratory.
They were obtained with a 199 type tube using
a grid bias (Eg) of 5.8 volts and a filament voltage
(Er) of 3. Of the several curves shown, only that
marked A.C. = O interests us at the moment.
The term A.C. = O indicates that there is no
alternating-current input to the vacuum-tube
voltmeter (in other words, X and Y are shorted.
See Fig. 2). We note in the curve A.C. = O how
rapidly the plate current increases with small
increases in plate voltage. At 40 volts plate po-
tential (Fp), for example the plate current (Ip)
is 1 10 microamperes (n Amps.). If with, say, forty
volts plate potential, we increased the grid volt-
age, the plate current would decrease. The other
curves in Fig. 3, incidentally, show the effect of
placing an a.c. input across the terminals X and
Y; in other words, they represent microammeter
FIG. 4
Here are some typical calibration curves. The
deflections of the microammeter needle caused by
various a.c. input voltages are plotted, together
with the effect of increasing the plate voltage
(Ep) for a given value of C bias (Eg)
deflections due to the sum of the normal plate
current and the current caused by input a.c.
voltage.
We have digressed a little to go into a brief
explanation of the curves in Fig. 3. We had previ-
ously arrived at that point where it was recom-
mended that the experimenter use 45 volts B
battery and 9 volts C battery. Under these con-
ditions, it was stated, a plate current of 6 micro-
amperes was obtained in the Laboratory. Do
not expect, however, to get a similar reading.
Every tube will vary. It is quite possible that
you will get no reading whatsoever. Perhaps the
reading will be higher than 6 microamperes.
Should there be no reading on the microam-
meter, slightly reduce the C voltage until a read-
ing of a few microamperes is apparent. It is quite
possible that a C battery quite a little smaller
than a g-volt one will ultimately be used, but the
large value is recommended for safety's sake.
The larger the C battery the smaller the plate
current and, therefore, the greater the margin
of safety.
Suppose that we have adjusted our batteries
and have obtained a reading of 10 microamperes.
We are satisfied that everything is working as it
should, and take the next step, which is to bal-
ance out this lo-microampere reading. If we do
not balance it out it will always be present when
we are measuring a.c. voltages applied across X
and Y and, therefore, the microammeter will
not be used to its full advantage. That is to say, if
the meter is always indicating 10 microamperes
with no input across X and Y, its range will be
reduced when an a.c. voltage is applied. True
indeed, with a 2oo-microampere meter this 10
microamperes only represents one fiftieth of the
whole scale, but possibly the combination of B
and C voltages used will give a greater plate
reading, perhaps 50 microamperes (such a high
value would not be probable with a 199 tube and
45 volts B and 9 volts C), which certainly should
be balanced out. The balancing out is accom-
plished by removing the piece of paper which we
previously slipped underneath the potentiometer
arm and adjusting the latter — slowly — until
the needle on the meter reads zero. Some experi-
menters prefer their meters to indicate a few
microamperes current when there is no a.c. input
across X and Y so that any possible back deflec-
tion of the needle will not harm the meter.
The actual calibration of the instrument is
our next job, and it is not an extremely difficult
VERY COMPLETE
VACUUM-TUBE
VOLTMETER
The complete in-
strument may be
dressed up to look
like this if you do
not care for the
breadboard layout
shown in the photo-
graph on page 22 1 .
Voltmeters to read
the B and C poten-
tials are included
RADIO BROADCAST Photograph
224
RADIO BROADCAST
JANUARY, 1928
one. Fig. 4 shows four typical calibration curves
made with different values of plate potential.
After one has become familiar with the vacuum-
tube voltmeter described here, the voltages may
be adjusted and all kinds of different curves ob-
tained.
For the process of calibration, some known
source of a.c. is necessary.
A fairly accurate calibration may be made by
using one of the many step-down transformers
that are now being used to supply filament
voltage to a.c. tubes. With the primary connected
to the I lo-volt a.c. house supply the secondary
voltage from one of these units will give several
points on a perfectly good calibration curve. For
example, a transformer which supplies filament
power to a receiver using 226, 227, and a power
tube, has the following voltage taps available:
5, 2.5, 1.5, 0.75. These voltages can be added
to or subtracted from each other by connecting
the windings to aid or to buck each other. Fig. 5
shows the complete vacuum-tube voltmeter with
the accessory equipment for calibrating it. If,
during calibration, but before the maximum
known voltage to be applied across X and Y has
actually been applied, the microammeter needle
is dangerously near the maximum deflection
point, it will be necessary to increase the C bias
and commence the calibration again.
Vacuum-tube voltmeters can be calibrated by
any Laboratory at small cost and it is probable
that the constructor can procure such a calibra-
tion near-by. The reader should remember that
the tube which is to be used should be sent with
the instrument and that the whole unit should
be very well packed.
The calibration of the instrument is practically
independent of frequency, so that the experi-
menter can compare voltages in circuits operat-
ing at audio, intermediate, or broadcast frequen-
cies. He can measure the voltage step-up in an
audio transformer or amplifier, or the output of
two radio-frequency amplifiers, or plot the
resonance curve of an intermediate frequency
stage.
It will be noted that the input of the tube
looks directly into the device whose terminal
voltage is being measured. If d.c. flows through
this device, it will be impressed across the input
to the voltmeter and ruin either the calibration
or the plate meter, or both. Some means, such
as that shown in Fig. 6, must be provided for
isolating the voltmeter from d.c. potentials ex-
isting in the circuit under measurement, when,
for example, the output voltage of a resistance-
coupled amplifier tube is being measured. With
this arrangement the
short-circuiting switch
shown in the photograph
on page 221 may be
omitted, since the grid is
always at a safe d.c.
potential with respect
to the filament. Fre-
quencies in the same
range, that is, all audio
tones, or all frequencies
in the broadcast band,
will give similar calibra-
tion curves.
If the experimenter
has no means of calibrat-
ing his instrument, he is
not so unfortunate as
might be supposed. He
may make use of the fact
that the deflections of
the microammeter are
roughly proportional to
the input a.c. voltages
squared. Thus he may
get two deflections re-
presenting the gain, say,
of two amplifiers. He
need not know the actual voltages provided he
knows roughly how much greater one is compared
to the other. All he needs to do is to divide one
0.006 mfd.
xo
A suitable set-up for
transformer which is
taps on the secondary.
and these
FIG. 6
When the vacuum-tube voltmeter is used to
measure an a.c. voltage across the terminals of
which is also a direct-current voltage, some
means must be employed to prevent this d.c.
from getting on the grid of the tube. Condensers
as shown here will accomplish this. The diagram
shows measurements being made on a resistance-
coupled amplifier
li-Amps
FIG. 5
calibrating the vacuum-tube voltmeter. T is a
used with a.c. tubes and, therefore, has several
. Thus several known voltages may be obtained,
plotted as a graph, similar to Fig. 4
deflection by the other and extract the square
root. This will be the ratio of the voltages.
The home constructor should be warned again
to carefully watch every step when experiment-
ing with the vacuum-tube meter and to be very
careful of the microammeter. One mistake and
the meter is gone. Always, at the conclusion of an
experiment, remove the meter from the circuit
first.
Those who wish to read further about the
vacuum-tube voltmeter will find a most inter-
esting and instructive series of articles in the
English paper, Wireless Experimenter and Wire-
less Engineer, for October and November, 1926.
Part of this material was republished in this
country in Lefax leaflets in February, 1927, and
forms the best background for the serious
student of this instrument. It is possible to pur-
chase from the Cambridge Instrument Company,
of Ossining-on-Hudson, New York, a vacuum-
tube voltmeter calibrated and "ready to go."
It is a beautiful instrument, although somewhat
expensive. The owner, however, may rest assured
that he has the best possible apparatus for
measuring small a.c. voltages, radio-frequency
currents, the gain of his amplifiers, both audio
and radio, and for the performance of a hundred
valuable experiments.
RADIO BROADCAST Photograph
SOME METERS USED IN THE LABORATORY
The vacuum-tube voltmeter, although an invaluable asset to the RADIO BROADCAST Laboratory, by no means holds a monopoly in usefulness. Here are
just a few of the dozens of meters always in use in the laboratory. Included are instruments by Weston, Sterling, Jewell, Dongan, and Hoyt
RADIO FOLK YOU SHOULD KNOW
I. RALPH H. LANQLEY
Drawing by Fran^Iyn F. Stratford
DALPH H. LANGLEY, Assistant to the
*^- President of the Crosley Radio Corpora-
tion, and, in that capacity, manager of most of
the operations carried on by the Crosley inter-
ests, was born in New York City on January
5, 1889. As this article goes into print he is,
therefore, still two years short of the forty
mark. By training, and probably by primary
inclination, he is an engineer, but his vision has
never been limited to screw-heads and tuning
knobs; of late years he has become increasingly
an executive figure. An administrator of thirty-
eight would be considered very young in most
lines of business, but in the radio industry there
are a number of them. The fact is that no one
can have more than thirty years or so of radio
experience, and only a handful of men can point
to anything like that. The twenty-year candi-
dates, even, are few. In the case of all such vet-
erans, the early years of experience have a value
which is mostly sentimental, for the modern
structure of the industry, with its complexities
of mass production and public relations sprang
up suddenly after the war. Mr. Langley's years
of contact with the radio art amount to about
nineteen, or half his age, which is quite enough
in a field where the race is to the swift rather
than the old.
Mr. Langley was born in New York City and
lived there until 1916. His boyhood residence
was near Morningside Park, under the hill on
which the buildings of Columbia University
were being erected. Young Langley, gazing at
the newly created campus, formed an ambition
to drink of knowledge at that fountain, but, as
yet, he did not see how the project was to be
financed. After finishing his elementary school
course, however, he went to De Witt Clinton
High School, 1904-1908, and towards the end
of his secondary school course succeeded in
winning a scholarship which enabled him to
enter Columbia.
During the following winter, Mr. Langley's
father died, and the son gave up college to take
a position with the New York and Queens
Electric Light and Power Company. But at
Columbia, in the college "Wireless Club," the
radio virus had already got into him, and in May,
1910, at the invitation of Emil J. Simon, he
turned from electric power to work in Dr. Lee
DeForest's laboratory at Park Avenue and 4151
Street, where many strange wonders were being
performed. Here he met Frederick A. Kolster
and other men now prominent in the radio indus-
try of to-day, which had its feeble and often
abortive beginnings in just such laboratories. In
those early days the courage of the workers
made up for the scarcity of good milliammeters.
A half year in DeForest's laboratory probably
did Langley good, but a school teacher friend,
James F. Berry, who had advised him before,
now convinced the young man that he would be
heavily handicapped in his later career if he did
not complete his university course while there
was still time. Mr. Langley took the advice and
went back to college in the fall of 1910, repeating
the sophomore year. But he did not give up
radio. The summer of 1911 he spent working
with E. J. Simon once more, this time for the
International Wireless Telegraph Company
(wasn't it the National Electric Signaling Com-
pany then?) at Bush Terminal in Brooklyn.
Here he met S. M. Kintner, now in charge of
the research activities of the Westinghouse Com-
pany. The summer of 1912 found him with the
Wireless Improvement Company.
Mr. Langley graduated from Columbia Uni-
versity as an Electrical Engineer in 1913. Edwin
H. Armstrong was one of his classmates, and
RALPH H. LANGLEY
Michael I. Pupin one of his professors. Professor
Arendt, another of Langley's preceptors, had
a poor opinion of the wireless game, and advised
the young engineer to stay out of it, but Langley
promptly joined the Wireless Improvement
Company once more.
During the three years Mr. Langley put in
with the Wireless Improvement Company, then
under the guidance of Colonel John Firth, most
of his work was with various types of joo-cycle
quenched spark transmitters. The J kw. sub-
marine transmitter was one of his early design
jobs. Mr. Langley's interests were not, however,
confined to commercial matters. He had joined
the Institute of Radio Engineers as an Asso-
ciate in 1912, and in 1914 served as Assistant
Secretary. In 1916 he was advanced to the grade
of Member of the Institute. In that same year,
at the invitation of David Sarnoff, he joined the
engineering staff of the Marconi Company, and
went to work at the Aldene factory, of which
Adam Stein, Jr., was Works Manager. Roy A.
Weagant was Chief Engineer of the Marconi
Company during the period of Mr. Langley's
connection with the firm. The Marconi Company
was handling war-time orders, principally for the
armed forces of the United States. In 1917 the
plant was greatly enlarged, and, running on
three shifts twenty-four hours a day, must have
employed in the neighborhood of one thousand
men. New types of quenched spark transmit-
ters were designed for submarine and aircraft
use. In the meantime the manufacture of the
standard Marconi marine transmitters and re-
ceivers, with auxiliary apparatus, such as Ley-
den jar condensers, had to be continued, and
in the shops one would see standing side by side
models of Naval receivers of the SE Types,
225
with their heavily-varnished bank-wound coils,
the older Type 106 tuners in their black cases,
and cheap little cargo receivers which looked
as if they had just come out of the five-and-ten
cent store. But Mr. Langley's concern at this
time was with the transmitters, so much so that,
in 1918, one of them almost ended his career.
This distinction would have gone to the 250-
watt aircraft transmitter, equipped with the
General Electric pliotrons of the same rating.
During one of the tests of the transmitter,
Langley, having shut off the filaments of the
tubes, reached in and grasped a plate terminal,
forgetting that the i joo-volt supply was still on.
"That particular set never worked again,"
states Mr. Langley laconically, "and it was some
time before I did." There was evidently noth-
ing wrong with his heart. After the completion
of the development work on the sets, he made
test flights with them from the air base at Nor-
folk, Virginia. " But none of these sets was ever
used in France," the designer adds, somewhat
sadly. The answer to that is that few of the air-
planes ever got to France either.
In 1920, the Radio Corporation of America
having been formed, the radio engineering and
manufacturing activities of the Aldene factory
were transferred to the General Electric Com-
pany's plant at Schenectady. Adam Stein Jr.
became Managing Engineer of the Radio De-
partment there, and Langley was assigned to
the Receiver Section, later to become the En-
gineer-in-Charge thereof. Practically all the
broadcast receivers turned out by the General
Electric Company have contained one or several
of Langley's inventions and design features.
Working with Messrs. Carpenter and Carlson,
Mr. Langley was responsible for the production
of the first Radiola super-heterodyne models,
incorporating the sealed "catacomb" construc-
tion and the divided cabinet. He spent seven
years at Schenectady, leaving for his present
executive position with the Crosley Company
on February i, 1927.
During the last three years, Mr. Langley has
been much interested in the work of the radio
manufacturers' associations. He was vice-chair-
man of the Radio Section of the Associated
Manufacturers of Electrical Supplies, and later,
when that body was merged with the National
Electrical Manufacturers Association, became
Chairman of the Committee on Section Activi-
ties in the Radio Division. He also served, in
1926, on the Standardization Committee of the
Institute of Radio Engineers.
With his years of experience in radio manu-
facturing and organization, and his wide ac-
quaintance among radio men, Mr. Langley be-
lieves that the next two years will witness re-
markable progress in the industry. He points
out that many lines of progress have been almost
completely blocked until the present season.
With patent difficulties largely resolved, notable
progress in standardization, adequate Federal
control of broadcasting, and the development of
exact methods of measurement and quantity
production, the economic stability of the in-
dustry should approach that of more settled
branches of business. Mr. Langley has contrib-
uted more than his share in the progress of
radio toward that goal.
ECEIVERS
THE "HIAWATHA"
An attractive six-tube receiver by Mohawk, Chicago.
As the chassis picture shows, there are six tubes. The
three tuned stages are adjusted by means of a single
tuning knob. The chassis depicted is standard in several
Mohawk receivers, which range in price from $67.50
to $275.00 for battery operation. For a. c. operation,
add $110.00 to the above prices. The retail price of the
"Hiawatha" is $165.00. It has a built-in pyramid form
loud speaker, for which very excellent reproducing
qualities are claimed
FOUR TUNED STAGES
Are incorporated in this six-tube receiver by Bremer-Tully.
The "Counterphase" 6-35, to give the receiver its exact name,
will delight the advocates of two-dial tuning, for the condensers
are arranged in two units of two, and are, therefore, controlled
by two knobs on the front panel. There are separate controls
for sharp tuning and volume. This new "Counterphase" re-
tails at $110.00. A console model sells for $165.00
'GRANADA" CONSOLE
Ry Electrical Research Laboratories ("Erla"),
of Chicago. The finish is of dark antique wal-
nut combined with birdseye maple. The
drawer front is of satin wood with maple
overlay. The chassis comprises the equip-
ment for four r.f. stages (three of which are
tuned) , detector, and two transformer-
coupled audio stages. Tuning is accomplished
by means of a single dial, and there is a built-
in loud speaker. Price $295.00. Furnished with
an a.c. converter system, all tubes, and an
output filter, price $395.00
BOSCH, MODEL 57
Here is an interesting receiver typical of the progress of recent years —
an example of the modern self-contained installation. The price, $440.00,
is not excessive when we consider that the receiver is designed for
socket-power operation, has a built-in loop, and also includes a loud
speaker of advanced design. This price is reduced to $340.00 if the
socket power feature is not desired. The single station selector, which
adjusts five separate variable capacities, is graduated in kilocycles
THE FADA 7
Another receiver employing four stages of r.f.,
but two tuning controls are used with this
model. A loop is supplied with the Fada 7 al-
though an outside antenna may be used suc-
cessfully. The loop fits into a special clamp on
the side of the cabinet. The two audio stages
are transformer -coupled. A special arrange-
ment in the detector circuit reduces the possi-
bilities of overloading. Price, $185.00
AMRAD'S THE "BERWICK"
A popular six-tube neutrodyne type circuit,
employing four tuned stages and single-control
tuning. As the chassis illustration shows, com-
plete shielding is featured. A cone loud speaker
is built into the "Berwick," which, partly due
to the special Amrad tone filter, gives remark-
ably good quality of reproduction. The price
is $195.00
227
How Reliable
Are Short
Waves?
RECENT EXPERIMENTS
of the General Electric
Company, of engineers
from other companies,
and of those interested in private re-
search, have resulted in an explanation
of many of the mysteries that have sur-
rounded the short waves. Everyone mar-
vels at the ease with which amateurs
communicate with fellow enthusiasts
over great distances with small input
powers. We have done it ourselves —
communicated and marveled both — and
great is the "kick" thereof. It is
undeniably thrilling to take from one's
lamp socket ob-cycle power of less than
one fifth that required to heat the aver-
age electric iron, and to feed it into a
comparatively simple system of apparatus
from which it emerges as radio-frequency
energy with which we actually ask a man
in South Africa how the weather is
there, all the time sitting quietly in
our den surrounded by unimposing gear.
When it is winter in New York it is
summer in South Africa, when day here,
it is night there, and so on. 1 1 is one of the
marvels of our time that two people in
the security of their homes but separated
by 7000 miles can transfer their thoughts
instantaneously and economically.
Just how good are these short waves?
How reliable is communication? How
many hours of the day, how many days
of the year, can we send messages via
short waves from New York to South
Africa?
The results of several investigations point to
the following facts which seem fairly well estab-
lished. Ten meters (30,000 kc.) is probably the
shortest useful wavelength. Below about 20
meters (15,000 kc.) the waves prefer to travel in
the daylight, and above that wavelength, night
time is the best. Below about 45 meters (6660
kc.) curious "skip distances" occur, resulting in
regions beyond which signals are heard but within
which they are inaudible. For example, on 15
meters (20,000 kc.) during daylight, transmission
is not practicable within a distance of 900 miles,
which increases to about 1000 miles at night,
although it is possible to transmit signals for
reception at points more distant than these
figures indicate. At 27 meters (11,000 kc.) the
daytime skip distance has been reported as 1000
miles and 450 miles at night, these distances
being about the same at 33 meters (0.086 kc.).
The General Electric experiments show that
the 32.79-meter wave is no good at all for short
distances. A power output of 500 watts on 65.16
meters (4500 kc.) will, however, transmit com-
mercial daytime signals up to 100 miles.
Short waves seem necessary for extremely long-
distance communication. During daytime, waves
of the order of 20 meters should be used ; waves
below about 45 meters are not much good for
short-distance work.
Night after night we have heard NAA on 37.5
meters pound away at a terrific rate, we have
listened to the Marconi beam stations on 26
rom
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meters, AGA at Nauen, Germany, FW in Paris,
and others, all bent on getting somewhere in a
hurry, and we wonder how soon it will be before
the band between 25 and 45 meters is as busy as
the long-wave channels. Amateurs in this coun-
try who have a channel 1000 kilocycles wide
around 40 meters have been blessed with an ex-
cellent assignment which at the time it was doled
out was thought to be more or less worthless.
More and more amateurs are going to 20 meters
and with low powers are accomplishing unheard
of records in broad daylight. They have not as
yet the feeling for this band and for conditions
existing there that they had for the 4O-meter
band, but it will come when they gain the wealth
of experience they have amassed on the longer
wavelength band.
INMOST radio work the mathe-
matics is fairly simple; the
difficulty comes when it is
necessary to put the mathe-
matical theory into practice. For example, the
following mathematics is that underlying the
theory of the input transformer for audio-
frequency amplifiers. The circuit about which
this theory is built up is given in Fig. i, and its
equivalent is shown in Fig. 2. In this mathema-
tics, N is the turn ratio of the transformer.
Es - NEp = Is Rg
Ep = HEg— Ip Rp
Es = N ([lEg - NU Rp)
IgRg = N ((JiEg — NlgRp)
I NjJiEg
Rg+ N'Rp
the Audio Trans-
former
NjJLEg
Differentiating this equation with respect to
N and solving for a maximum, it is found that:
N' = Rg/Rp
228
and substituting this into the equation
above for Es:
Es =
All of this assumes that the trans-
former is perfect, i.e., no d.c. resist-
ance, no magnetic leakage, infinite prim-
ary and secondary reactance. It shows
that under these conditions the voltage
delivered to the input of the tube is one
half that delivered to the previous tube
multiplied by the turns ratio of the
transformer and by the amplification
factor of the previous tube.
If the input impedance is one megohm,
i ,000,000 ohms, and the plate impedance
of the previous tube is 12,000 ohms, the
turn ratio will be equal to the square
root of the ratio between these two
quantities, viz:
v, :. 000,000
N = = 3 approximately
In order that a large percentage of the
a.c. voltage developed in the plate
circuit of the previous tube be available
across the primary of the input trans-
former, the impedance of this trans-
former must be high. If we want to
amplify well at 100 cycles, the input
impedance should be not less than 30,000
ohms which means that the primary
should have no less than 50 henries in-
ductance — which in turn explains why
transformers, good ones, cost money,
and why a skinny little affair with a
few sheets of iron in the core and a little wire
on the primary makes radio music sound "some-
thing fierce."
Furthermore, if the turn ratio is three, and the
inductance of a winding varies as the square of
the turn ratio, the secondary inductance must be
about 450 henries — and when anyone states that
the secondary of an audio transformer makes a
good output choke he neglects the fact that one
cannot wind up an inductance of 450 henries
without adding enough d.c. resistance to prevent
the last tube from getting any plate voltage at
all.
MATHEMATICS OF THE OUTPUT TRANSFORMER
THE mathematics of an output transformer
design is no more difficult than that of the
input transformer — and the answer is the same,
as the following rigamarole proves. The symbols
used in this discussion are the same as for the
input transformer. N is the turn ratio of the
transformer, and instead of Rg we use Rs.
=,_
Rs Rs
Ep = ;J.Eg— IpRp
Whence ,s = ^ J^Eg-ftf^
NVlEg
NjiKg
N'Rp +Rs YI (RpNM-Rs)
N
<3>
<o
o
<0
Rt
FIG. 2
JANUARY, 1928
"STRAYS" FROM THE LABORATORY
229
Differentiating this expression with respect to
N and solving for a maximum,
And Is ;
whence power in Rs = I| Rs
H-Eg'
8Rp
If the speaker Rs is in the plate circuit of the
power tube without the output transformer,,
and if the impedance Rs equals Rp the power
will be as indicated above, showing that the
transformer is indeed an impedance adjusting
device and that it is possible to secure maximum
power in a load impedance which is not equal to
the tube impedance provided the output trans-
former has the proper turn ratio.
A little consideration will show that if the
primary impedance of this transformer is equal
to the tube impedance and if the secondary im-
pedance is equal to — "matches," is the usual
word — the load impedance one half the voltage
existing in the plate circuit will be expended in
heating the plate. It is obvious, then, that the
primary impedance again should be several
times that of the tube impedance, but since the
final tube has a low impedance, the ux-iyi (cx-
371) type for example has an impedance of 2000
ohms, a manufacturer of transformers needs to
put nothing like the impedance in his output
transformer primary that he puts into an input
transformer. Likewise the secondary impedance
must be high compared with the load, or speaker.
As long as the turns ratio is proper, energy will
be transferred from the tube to the speaker with a
minimum loss, and for all practical purposes the
output transformer may be neglected in calcu-
lations.
SOME OF RADIO BROADCAST'S
High-Towered readers are technically in-
•Bimt clined, and must enjoy the
monthly battle of wits among
radio advertising writers whose "eulogies" appear
in many radio publications. We saw recently
a new loud speaker advertised which consisted of
a "tone column of new design; by means of a
scientifically designed tone distributing chamber
a forced crossing of sound waves is accomplished,
and a divisional tone chamber of unique design
segregates high and low tones, reproducing both
with equal facility." Bell Laboratories engineers
should take notice of this new scheme for attain-
ing perfect fidelity, and should forget all about
loud speakers which will look like a pure resist-
ance to a power tube at all frequencies. All that
is necessary is to segregate the low voice from
the high one and then re-combine them. Presto!
There is also a new antenna that promises
much, for, according to a widely circulated
advertisement, it meets the need of radio users,
whether for small or large sets. It has been thor-
oughly tested for over two years under all kinds
of conditions and on many kinds of sets. In
every set, it has proved its many advantages:
1. Easy to put up or take down.
2. Picks up waves in any direction because
it is round.
3. Proven more selective.
4. Greater volume.
5. Greater distance.
6. Helps eliminate static.
7. Small and compact.
8. Neat in appearance.
9. Low in cost — only $7.50.
What more could anyone want?
This kind of bunk is not only confined to the
advertising pages of the media in question,
sadly to recount. The following passages are
quoted from a recent article describing a new
and revolutionary receiver that anyone can build
for about twice as much as he would have to
pay for a well known and thoroughly engineered
set.
"Its volume is due to the high amplification
in the audio end of the circuit and to the fact
that two 71 tubes in push-pull are used in the
last stage."
Off hand this seems reasonable until one con-
siders that there are three audio tubes — which
furnish most of the amplification — and that
there are eight tubes which precede them! It
reminds us of the early days of radio when the
Laboratory had its hands full weeding out the
good apparatus from the poor. A receiver came
to Garden City equipped with thirteen tubes,
guaranteed to pick up any signal in any part of
the world at any time. The total plate current
of this super-receiver, including a power tube, was
ninemilliamperes. It seemed incredible — and was,
until we discovered that eight of the thirteen
tubes had no plate voltage on them. But let us
continue with this totally new receiver.
"With all that amplification and power hand-
ling capacity there will be undistorted volume
enough to make the welkin ring. But all of this
would be merely potential volume were it not
for the almost incomprehensible amplification
in the intermediate amplifier. It is here where
the weak signals from the remote stations are
pulled from infinitesmal levels and placed on the
plane of the signals from local stations. Both the
amplification and selectivity could be expressed
in numbers but they would be so large as to be
meaningless to the human intelligence."
There you are, and five more columns of it
for good measure!
THE NEW SCREENED GRID TUBE
The bulb of a "dead" ux-222 tube was broken
so that this photograph of the interior construc-
tion might be taken. The RADIO BROADCAST
Laboratory is expending considerable time ex-
perimenting with these tubes so that the infor-
mation contained in articles in these pages might
be backed up with actual experience. We can
promise readers some particularly fine articles
along such lines in the very near future
DURING recent months, the
^few Laboratory has received for
^Apparatus test the following apparatus:
Power units from Kellogg,
Wise McClung, Valley, Universal, Briggs and
Stratton, Boutin Electric Co., Sterling Mfg.
Co., and Grigsby Grunow; tubes from the
following tube plants, Arcturus, R. C. A., Cun-
ningham, Supertron, CeCo, Manhattan Electric
Supply Co., Connewey Laboratories, Zetka,
Cable Supply Co., Televocal, Van Home, De-
Forest, and Supercraft; audio transformers from
Modern, Silver-Marshall, Samson, Tyrman,
Sangamo, Amertran, G. W. Walker; the new
Eby sockets, a Muter double-impedance am-
plifier, a Pacent Phonovox electrical pick-up
unit, the excellent looking Abbey receiver manu-
factured by Splitdorf and already illustrated in
RADIO BROADCAST, a useful floor cord made by
Belden which enables one to place wires under
a rug without danger of tripping or of impairing
the appearance of the room — the wires may
carry house lighting current for a lamp, or loud
speaker wires; a complete assortment of Acme
Wire Co. Parvolt condensers; rheostats, etc.
from Carter; a complete push-pull amplifier and
B supply units from Samson, Thordarson, and
General Radio; resistances for stabilizing grid
circuits, for plate supply circuits, for center
taps on a.c. tube circuits, etc., from General
Radio, Electrad, Frost, Daven, Amsco, Gardner
and Hepburn, Aerovox; and coils from Precision
Coil Co.
Many other interesting pieces of apparatus
have been received, previous mention of which
has been precluded pending test and on account
of space limitations. Among the larger items are
Silver-Marshall's interesting Time Receiver, a
huge and much involved horn loud speaker from
Newcomb-Hawley, using a Baldwin Unit, and
known as a Console Grand Reproducer, a Peerless
loud speaker from the United Radio Corporation
of Rochester, and a Holmes Piano loud speaker
from the International Radio Corporation, of
Los Angeles. The Newcomb-Hawley loud
speaker has a very long air column secured by
giving the neck several convolutions about the
wide opening. The Peerless is an attractive loud
speaker with an excellent element. Both loud
speakers cover wide frequency ranges and go
down particularly well.
The Laboratory was especially interested to
receive one of the "tuned" impedance ampli-
fiers about which so much is heard, this one
delivered by Mr. Kenneth Harkness in person,
giving us the opportunity of meeting him for
the first time. Frequency curves are being pre-
pared on this amplifier, and will be ready soon.
Transformers for the new a.c. tubes were re-
ceived from Amertran, General Radio, Mayo-
lian, and Northern Manufacturing Company.
New rheostats came in from Frost, Centralab,
and Carter. Some large heavy-duty resistors from
the Electro-Motive Engineering Corporation
also made their appearance. Among the other
items are new Samson apparatus, loud speaker
units from the Balsa Wood Corporation, Engi-
neers Service Company, Baldwin, Vitalitone, and
Magnaphon Company, a series of new and prob-
ably very efficient inductances made by the
Precision Coil Company, a "Subantenna"
(is there any way of testing this antenna without
digging up the garden?), two sheets of beautifully
burnished copper for shielding, from C. G.
Hussey & Company, of Pittsburgh, condensers
from X-L Radio Laboratories, Electrad apparatus
and a fine looking White socket power unit from
Sioux City, Iowa.
oncomitants
THE AMPLION "GRAND"
A S PLEASING to the eye as to the ear
•** is this magnificent loud speaking
device by Amplion. Contrary to what one
might justly suppose upon first glance, the
"Grand" does not use a horn inconceivably
munificent in inches, but employs a com-
bination cone and sound board. The
"Grand" lists at $145.00. It is supplied with
a 20-foot cord. The walnut cabinet measures
34" x 33" x 18"
BY PACENT
HER E is a seven teen-
inch cone loud speaker
with several interesting fea-
tures. Its extreme rugged-
ness and responsiveness to
weak signals are features.
The manufacturer claims
that this cone has a thirty
per cent, greater frequency
coverage and sensi I i vi t y
than most of the popular
model cones on the market.
Price, $22.50
Is,
TO THE LEFT
A new power cone loud
speaker employing electro-
dynamic principles. Due to its
unique construction, great vol-
ume may be handled without
any possibility of rattling. An
external source of direct current
is necessary for operating this
instrument. Either the storage
battery or the electric light
mains may be employed for this,
depending upon which type of
loud speaker is used. If the
storage battery is employed, the
current drain will not exceed
that usually drawn by a 171
type tube. The price of the
** Aristocrat" is $85.00 for stor-
age battery operation or $90.00
for 110-voltd. c. operation
THE MAGNAVOX "ARISTOCRAT"
DESIGNED FOR HEAVY-DUTY WORK
rpHERE are four voltage taps on this new B supply device
-1 by National, three of which are adjustable. The detector
voltage is from 22 to 45; the r.f. voltage, from 50-75; and the
a.f. voltage from 90-135. The power-tube voltage tap delivers
180 volts. Price, with cord, switch, and plug, $40.00. Rectifier
tube, $5.00
230
of (rood Quality
EXPONENTIAL HORNS
A GOOD exponen tial horn is capable
of very excellent results so far as qual-
ity reproduction is concerned, and is excep-
tionally efficient. The Temple Console U>
the right employs a 75-inch exponential
air column, and is priced at $65.00. The
Temple Drum below also has an exponen-
tial air column and comes in two models,
using 54-inch and 75-inch air columns,
priced at $29.00 and $18.50 respectively
.
A NKW SOCKET-POWER DEVICE
TpOGETHER with a relay which automatically switches the
A house electric light supply to the B device illustrated, or
to a trickle charger, depending upon whether the set is in use
or not. These devices are by Slromberg-Carlson, of Kochester,
and retail at: H device. $63.00 (with tube); relay, $11.00
FOR THE PHONO-RADIO COMBINATION
THE Platter Cabinet Company, North Vernon,
Indiana, is responsible for this attractive cabinet
of walnut plyw<>od, in which space is provided for
a complete radio installation and a phonograph.
The price of the cabinet is $72.00. The same manu-
facturer will supply turntable, motor (electrical
or mechanical), radio receiver, electrical pick-up
device, and joud speakers of many patterns to fit
into the cabinet, if desired
231
THE GREBE "SYNCHROPHASE" SEVEN
The circuit diagram of this receiver is shown on the next page
How the "Synehr
rE REQUIRE a seven-tube receiver
with single tuning control to be sold
at a retail price of $ 13 5.00. Produce it."
Such, in effect, might have been the wording
of a memorandum from the board of directors of
A. H. Grebe to the engineers responsible for the
design of the " Synchrophase " Seven. Thereupon,
a tedious process of laboratory and mathematical
experiment sets in, for the "cut and try"
methods of "mediaeval" radio days are for-
gotten, since present broadcasting conditions
would make such procedure impracticable.
Being familiar with the congestion among
stations, the transmitting characteristics of the
broadcasting stations, and the power used by the
stations, the radio engineering department was
able to select the number of tubes to be used as
radio-frequency amplifiers, decide upon the
detector system, and arrive at a decision con-
cerning the number of stages of audio-frequency
amplification necessary to produce a satisfactory
receiver output signal. They were aware of the
operating channels used by broadcasting stations
in various localities, hence they could judge if
their tuning system would be capable of separat-
ing the stations and of providing radio reception
without a background of interference from other
stations.
This was, however, not all a matter of guess
work. Such perfectly engineered radio receivers
are first produced on paper, with the aid of
mathematics and the "slip stick" (a nick-name
for the slide rule). The amount of time put into
the design of radio receivers of modern times is
almost inconceivable when compared to that of
six or seven years ago.
After due deliberation, the decision of the
Grebe engineers was to employ four stages of
tuned radio-frequency amplification, a non-
regenerative detector, and two stages of trans-
former-coupled audio-frequency amplification.
The question then arose relative to the design
By John F. Rider
of the radio-frequency system. Should it be
shielded or unshielded? Development carried
out prior to this time resulted in the birth of
a new type of fieldless inductance — an induct-
ance which could be used in a multi-stage tuned
radio-frequency receiver without fear of coil
interaction. This coil, known as the "binocular"
inductance, was the brain child of P. D. Lowell,
and is the evolutionary development of the
toroidal winding. Since this coil is fieldless, inter-
stage shielding was unnecessary; two, three, or
four stages of unshielded tuned radio-frequency
amplification may, therefore, be used without
worrying about excessive regeneration. Elimi-
nate the coil fields and shielding is unnecessary,
since coil interaction will not take place. The
elimination of shielding means economy without
any sacrifice.
The function of shielding is also to preclude
direct coil pickup, but since the fieldless coil will
not pick up any energy, shielding is unnecessary
on this account. The binocular coil, therefore,
solved several problems in the design of the
"Synchrophase" Seven. The coil itself consists
of two solenoidal windings mounted closely
together with their axes parallel and with the
two windings connected in such a manner that
their electromagnetic fields are opposing each
other. This means that, if one coil starts to ra-
diate a magnetic field, the other coil simultane-
ously radiates a magnetic field of equal intensity
but of opposite phase or direction, and the two
fields combine and counterbalance each other.
The result of the- combined fields is zero.
Hence, no reaction between the tuned trans-
formers is evident.
The same phenomenon applies to the pickup
of waves by the transformers. A voltage intro-
duced in one coil is reacted upon by the voltage
introduced in the other coil by that passing
wave. The two induced voltages react upon each
other and the resulting induced voltage is zero.
232
Hence pickup of energy is not apparent. The
fact that these coils are fieldless permits of a
layout different from that possible when the
coils used have strong fields. Interaction of fields
is the greatest objection to the single-layer sole-
noid. It is a very efficient winding out possesses a
very strong field, and total shielding is impera-
tive in a receiver employing a number of single-
layer solenoid radio-frequency transformers.
The next problem was the actual design of the
binocular inductances. The mere selection of a
form of winding does not complete the design
problems of the tuned radio-frequency trans-
formers. Solid wire is conventional for the aver-
age tuned radio-frequency transformer. Is it
best for these coils? Does the form factor of the
average coil apply to this type of winding?
Can some other wire be used to greater advan-
tage? Here is room for research and experiment.
The first binocular coils were wound with
solid wire. Further experiments and calculations
by the engineering department proved conclu-
sively that "litz" wire improved the inductance-
resistance ratio to a large extent and as far as
practical results were concerned, coils wound
with "litz" wire could be made to have a more
uniform amplification curve over the broadcast
frequency spectrum, in addition to improving
the selectivity of the tuned circuit. Here again
we find a deviation from the conventional path.
"Litz" wire has frequently been frowned upon
as unsuited for high-frequency work. The de-
signers of the "Synchrophase" have overcome
the difficulties and are utilizing "litz" to good
advantage.
The occasion next arose for the development
of an original system to overcome a frequently
occurring fault with conventional tuned radio-
frequency amplifiers. It is of paramount im-
portance that the frequency response curve of
the radio-frequency system be substantially flat.
Furthermore it is desirable that the effects of the
JANUARY, 1928 HOW THE "SYNCHROPHASE" SEVEN WAS DEVELOPED
233
grid-filament capacity within the tube be so nulli-
fied that the purchaser can use whatever tubes he
may choose without fear of upsetting the tuned
circuit balance obtained in the factory when the
receiver was first tested. With many receivers
the neutralizing condenser (or condensers) has
to be readjusted whenever any changes
in the tubes are made. The frequency re-
sponse curve of the average tuned radio-fre-
quency amplifier shows maximum response on
some short wavelength (high frequency) with a
falling characteristic as the wavelength is in-
creased (frequency lowered). The system repre-
sented in Fig. i by the variable condenser d
and the two resistances, R\ and Rz, was devel-
oped and incorporated to attain the two objec-
tives mentioned at the beginning of this para-
graph. The action of these units is twofold.
First, they eliminate the effect of the grid-
filament tube capacity upon the tuned circuit,
particularly on the low settings of the tuning
condensers, in such manner that tubes may be
changed without affecting the original resonance
setting. Second, they control the voltage being
give sufficient sensitivity and selectivity. Fur-
thermore, the sideband suppression characteris-
tics of the radio-frequency system are known
and the introduction of a variable constant,
which would be encountered with a variable
regenerative detector, would upset the balance
between the radio and audio amplifiying sys-
tems.
THE AUDIO CHANNEL
THE audio amplifying system is closely asso-
ciated with the radio-frequency system; in
fact, it must be, for the reason that the frequency
characteristics of the audio-frequency amplifying
transformers are governed by the sideband
characteristics of the radio-frequency system.
If the sideband suppression of the upper audio
register is great in the radio-frequency ampli-
fier, the audio system must possess a certain
rising characteristic. The slope of the rise is
governed by the degree of suppression in the
radio-frequency amplifier. Hence the two sys-
tems are closely associated. Being familiar with
the sideband suppression in the radio-frequency
~ Gnd.
FIG. 1
Circuit diagram of the "Synchrophase" Seven
fed into the grid-filament circuit of the amplify-
ing tube, so that the radio-frequency voltage
fed into the tube is practically uniform over the
complete tuning scale and the frequency re-
sponse curve of the tuned system is sufficiently
flat. With this arrangement, and the inherent
lack of regeneration in the system, a high degree
of stability and amplification is afforded.
The four stages provide ample selectivity and
sensitivity and are designed to possess sideband
characteristics with minimized suppression
above 1000 cycles. This consideration is very
important, and the presence of excessive re-
generation would tend to nullify all the effects
of scientific design. But the properties of the
fieldless coil guard against this deterimental
effect. With sufficient spacing between the in-
ductances, the very small amount of external
field, which cannot be eliminated completely,
does no harm. Hence the regeneration present
is uniform over the scale and is at no time
sufficient to cause uncontrollable oscillation.
The detector system is the grid leak-condenser
arrangement, affording maximum signal sensi-
tivity and intensity. The compensating system
utilized in the radio-frequency stages, is also
resorted to in the detector input circuit, thus
permitting the use of any detector tube without
unbalancing the tuning system. A non-regenera-
tive detector was decided upon because the four
stages of tuned radio-frequency amplification
system, two audio stages are decided upon after
a study of the amplifying powers of the system;
these two stages possess sufficient magnifying
power to afford a satisfactory output. The over-
all response curve of the audio system is shown
in Fig. 2. The gain in transmission units is shown
on the ordinate and the frequencies are shown
on the abscissa. The curve is plotted on a loga-
rithmic scale.
Particular consideration was given to the
feminine speaking voice, the frequencies of
which are difficult to amplify, and to the over-
tones of the high-frequency producing musical
instruments. The result is that the transformers
were designed to function satisfactorily on audio
frequencies above 8000 cycles. This is easier said
than done. A great deal of work was entailed
before suitable transformers were produced.
In order to realize satisfactory amplification on
the upper audio register it was important to
reduce the distributed capacitance of the second-
ary winding. This was accomplished by the use
of three layers of insulation between each layer
of winding. The distributed capacity of the
secondary winding is approximately 18 micro-
microfarads. The importance of a low distributed
capacity can be appreciated when one realizes
that the higher it is, the more limited will be the
frequency range of the amplifying unit.
An example of vision, and a knowledge of the
buying public's whims and fancies, is displayed
in the inclusion of a device which permits tonal
flexibility. The problem arose during the process
of development when the sales staff mentioned
the fact that the aural fancy of the listener-in
was apt to vary over a wide range. Could not
some device be incorporated which would permit
variation of the tone of received speech or music,
so as to satisfy the individual tastes of the mul-
titude? Some fans prefer a preponderance of low
tones, while others are not so anxious about
these low frequencies. The engineers decided
that the best location for such a unit would be in
the audio amplifying system, but a continuously
variable change in the physical structure of the
audio-frequency transformers to produce differ-
ent response was impractical. Hence the "tone
color" unit, consisting of a number of fixed ca-
pacities which can be shunted across the second-
ary of the second-stage audio-frequency trans-
former to change its operating characteristic,
was originated. The "tone color" is controlled
by a knob on the front of the panel and, by its
manipulation, the listener is able to adjust the
tone to suit his own taste. The capacities in the
"tone color" vary from 0.00008 mfd. downwards.
THE PROCESS OF TESTING
CNG1NEERING and originality has made
«-< possible the manufacture of all the necessary
equipment, exclusive of the cabinets, in the
Grebe plant, at Richmond Hill, Long Island.
The manufacture and testing of the tuned
radio-frequency inductances is of especial in-
terest. The winding is spaced yet the winding
form is not grooved. This is made possible by
means of a grooved slider which carries the wire
as it is wound on the winding form. The grooves
on the slider space the wire, and the turns are
kept in place by means of a layer of clear lacquer
which is sprayed upon the coil before assembly.
Ingenuity in testing now manifests itself. The
wire, as mentioned before, is "litz," and it is
extremely important that all the turns remain
intact. If a single strand is broken it will result
in a steep rise in the radio-frequency resistance
of the wire, with consequent increase in losses,
and lower selectivity. The condition of the
finished coils is tested on a d.c. bridge, accurate
enough to show one broken strand. The total
resistance of all the strands is balanced against
a known resistance. One broken strand in the
"litz" cable will deflect the meter in the bridge,
in which case the coil is rejected. The satisfac-
tory coils' radio-frequency resistances are then
measured. The inductance value of a completed
coil should be 310 microhenries.
The condensers are matched on a capacity
bridge, each one being individually tested against
a standard. The condensers are then grouped
according to their respective capacities. A con-
trol is arranged which shows a variation of 7
micro-microfarads for the complete scale, and
extremely small variations are, therefore, de-
tectable. By means of this control it is also possi-
ble to determine increased effective resistance of
the condenser under test. The bridge is fed from
^S~
^
Primary Inductance 90 Henries
Secondary Inductance 500 Henna
0 100 400 1000 10,00
FREQUENCY
FIG. 2
The overall response curve of the
"Synchrophase" Seven audio channel
234
RADIO BROADCAST
JANUARY, 1928
a looo-cycle source and the output of the bridge
is connected to a single-stage audio amplifier,
thus increasing the sensitivity of the system.
The operator uses the headphone method of
adjusting for capacitance by finding the mini-
mum sound intensity. When the sound is min-
imum the capacity of the unknown is exactly
that of the standard. A condenser with high
losses does not permit of complete silence in the
phones, and is rejected.
The audio-frequency transformers are also
tested in an interesting manner. It is highly im-
portant to know the response of the transformers
to be. placed in the receiver, but it would be a
tedious procedure to plot a response curve for
each individual unit, hence each transformer is
compared with a standard on certain frequencies.
A tube oscillator, generating a 5OO-cycle note
and a 6ooo-cycle note, is connected to a standard
amplifier. The output of this amplifier is con-
nected to the transformer to be tested, and the
output of the transformer under test is connected
to a vacuum-tube voltmeter, the output circuit
meter of which gives visual deflections indicative
of the response of the transformer under test.
The circuit is so arranged that, by means of an
anti-capacity switch, the transformer under test
can be replaced by the standard and the deflec-
tions compared. By means of a switch, the oscilla-
tor can be adjusted to generate either the 500-
or the 6ooo-cycle signal. This signal is free of
harmonics and is constant at all times. The de-
flections with the standard transformer are
therefore constant.
The complete receiver undergoes several tests,
and the method of testing is also original and
novel. A buzzer-modulated master oscillator,
tuned to 200, 400, and 530 meters (i 500, 750, and
566 kc.) feeds a master antenna. The buzzer
modulation is accomplished by breaking the
plate voltage supply with the interruptions of the
buzzer. The operator testing the receiver (several
operators are testing at one time) has his own
antenna of standard inductance and capacitance
value. He first adjusts the receiver at 200 meters
by tuning it to resonance with the 2oo-meter
oscillator signal. The receiver output is then
noted by means of a tube voltmeter connected
to the output circuit of the receiver. After the
receiver is adjusted on 200 meters, adjustments
are made on 400 and 530 meters, and the second
harmonic of 530, which is 265 meters (i 130 kc.).
In this way each receiver is tested on four wave-
THE GREBE CONE LOUD SPEAKER
lengths. This is indeed a comprehensive test, for
it will bring to light any defects in design upon
any of the wavelengths within the range em-
ployed for broadcasting purposes. If the tube
voltmeter does not show standard output on all
four waves, the receiver is rejected for a re-
examination.
The problem of conductive coupling in the
receiver to adjacent leads was overcome by the
use of the chassis as the negative filament lead,
thus eliminating numerous long leads. The fila-
ment wiring in the receiver consists of only the
positive polarity wires. The negative lead is
formed by the chassis. The condensers are all
grounded upon the chassis.
The mechanical alignment is facilitated by
punching the complete chassis in one piece. It is
made out of aluminum and stamped out on a
6o-ton press. The chassis, after the stamping,
carries all the mounting holes and brackets, thus
assuring correct alignment. The receiver, from
start to finish, is carried from one operation to
another by means of a conveyer system approxi-
mately moo feet in length. This conveyer con-
sists of a belt or a roller as the occasion demands,
AN INTERIOR VIEW OF THE "SYNCHROPHASE" SEVEN
and the partially assembled receiver moves from
one operation to another until it finally reaches
the final department.
THE GREBE CONE
T~HE electrical development of the Grebe loud
' speaker is also of interest, particularly be-
cause this field of endeavor requires highly
trained engineering. The development of a loud-
speaker does not consist of the mere selection
of steel, iron, wire, and a paper cone. Let us con-
sider for a moment an important consideration
which the fan generally passes over very lightly.
T his is the angle of the apex of the cone, and the
size of the cone. The information relative to the
size of the cone will doubtless be of interest to
constructively inclined radio fans. According to
the engineer in charge of cone construction, their
experiments showed that a 20" cone was the best
compromise and that increases above this diam-
eter did not justify the additional space required.
Experiments showed that very little is gained by
using a cone of larger diameter. Reduction in
size, however, showed a material loss.
As to the angle of the apex, 20 degrees is also
the best compromise for efficiency and quality.
The greater the angle, the greater the efficiency
but the poorer the quality of reproduction. The
2o-degree angle was considered the best for
quality and efficiency. Many articles published
in this and other periodicals have stressed the
importance of a large value of inductance for
loud speaker windings in order to produce satis-
factory response on the low frequencies. With
this in mind, a value of 1.7 henries was selected
as the loud speaker coil inductance. The shape
of the armature is also an important considera-
tion, and by using an armature that is wide and
short, the lowest moment of inertia is obtained.
The selection of the material for the armature
also requires care and silicon steel was chosen
instead of Swedish iron, because the losses of
silicon steel are less on the higher audio register.
The difference between Swedish steel, iron, and
silicon steel is not appreciable on the lower audio
register but it approaches an appreciable value
on the higher audio frequencies.
The elimination of harmonics in the average
loud speaker is a paramount item because their
presence will not pecmit true reproduction. To
attain this result it is necessary to minimize
magnetic saturation.
The testing of the loud speaker is carried out
by first subjecting it to a series of audio fre-
quencies obtained from a beat note oscillator.
This beat note oscillator consists of two radio-
frequency oscillators adjusted in a manner which
permits the generation of a beat note; this note
is passed through several stages of audio-
frequency amplification and then into the loud
speaker. One of the radio-frequency oscillators,
is variable in tuning and the frequency of the
beat note is variable between 50 and, approxi-
mately, 20,000 cycles. This test will bring to
light any defects in the loud speaker mechanism
which would result in a rasping sound or a rattle
when it is placed into operation. Another test
consists of the reproduction of an organ record
played upon a talking machine and fed into the
loud speaker by means of an electric pick-up
and amplifier combination. The organ selection
has a wealth of low notes, and these are particu-
larly desired for testing purposes, since the
amplitude of these low frequencies is high. This
test will bring to light any defects in the place-
ment of the armature. Another test consists of
the application of the plate current of a 171 tube
through the windings of the loud speaker,
first in one direction and then in the other,
to test for magnetic saturation when it is in
operation.
AS IHh
RY TAUI DkKHfck
TECHNICAL problems presented in this
section in the past have consisted of
numerical problems requiring more or
less lengthy solutions, so that only one question
could be allowed to an issue. We shall vary these
occasionally by a series of questions requiring
only brief answers, like those below. The sub-
jects, while not strictly confined to the design
and operation of broadcast transmitters and as-
sociated apparatus, will have some connection
with those considerations of quality in repro-
duction which are of most interest to the profes-
sional broadcast technician.
QUESTION i. Why does sharp tuning tend to
drop out the high audio frequencies associated
with a carrier?
Answer. The audio energy of speech or music
exists in the side bands accompanying the car-
rier in question. If, for example, the carrier is
of the order of 600 kilocycles, a frequency within
the broadcast band, and the audio note being
transmitted is 5 kilocycles, the side bands will
have a frequency of 595 and 605 kilocycles. A
sharply tuned circuit resonant to 600 kilocycles
will include perhaps one kilocycle on either side,
and will discriminate to a greater and greater
degree against the higher audio frequencies,
which lie further out from the central or carrier
frequency. Hence the 595- and 6o5-kilocycle
currents, in the present example, may be lost
altogether, and with them the ^-kilocycle audio
note which they would yield on demodulation.
By this mechanism, called "side band cutting,"
the higher musical frequencies are likely to be
lost.
QUESTION 2. Why does slight detuning of a
sharply resonant circuit, with reference to the
carrier frequency, tend to reinforce the higher
notes contained in the modulation?
Answer. See Fig. 4, which has reference to the
same example used to illustrate the answer to
Question I. Now, however, the circuit has been
tuned so that the peak of the resonance curve
occurs at 602.5 kilocycles instead of at the carrier
frequency of 600.0 kilocycles. As a result, the
peak of receptivity, after demodulation, has
been shifted from currents of frequencies in the
neighborhood of zero cycles to currents in the
neighborhood of 2500 cycles per second. If, ow-
ing to the steepness of the resonance curve, the
cut-off characteristic of the circuit becomes seri-
ous one kilocycle to either side of the peak, as
assumed in the answer to Question i above, with
the peak set at 602.5 kilocycles the audio fre-
quencies up to 3.5 kilocycles are nevertheless in-
cluded in the received band. It will be seen that
through this mechanism a sharply tuned radio
frequency circuit may be used to some degree
as an equalizing or frequency correcting device
in reception. This observation may be checked
in practice. A similar phenomenon is found in
some super-heterodyne receivers.
QUESTION 3. What change in loudness is nor-
mally noticeable by the human ear?
Answer. A change of 3 TU is usually observed
in speech or music even by listeners who are not
expecting it. This corresponds to a change in
energy of 2:1. A practiced listener looking for a
change may detect differences of tha order of i
TU in a sustained note, without much difficulty.
This is equivalent to an energy change of about
25 per cent.
QUESTION 4. What size steps, in TU, would
you allow in a smooth gain control?
Answer. Since, according to the answer to
Question 3 above, a change of 3 TU is notice-
able, the maximum allowable step in a smooth
gain control is 2 TU.
QUESTION 5. What error do non-technical
observers invariably make in estimating rela-
tive loudness of sounds?
Answer. They underestimate radically. As is
well known, the human ear follows a logarith-
mic response characteristic, which is as much as
to say that a large increase or decrease in the
stimulating energy results in a slight change
in the loudness subjectively perceived. Or,
more definitely, multiplying the energy by a
fixed ratio results only in adding to the loudness
an increment proportional to the logarithm of
the energy ratio. This is expressed mathemati-
cally in the formula for the telephonic trans-
mission unit, which is a measure of subjective
loudness:
TU = 10 log Pi/P2
where PI and P2 are the powers corresponding
to the two telephone currents under comparison.
Non-technical listeners, being unaware that
hearing is a logarithmic process, usually apply to
sounds the standards of measurement and esti-
mating to which they are accustomed in dealing
with distances, for example. A broadcast listener,
comparing reception from two stations, one of
which is a stage of audio amplification above the
other, will say that the first station is "fifty per
cent, louder," or "one hundred per cent, louder."
Actually one a. f. stage may correspond to 20
TU, or a sound energy ratio of 100. In other
words, a non-technical listener is apt to speak of
an energy ratio of the order of 2:1 where the
actual figure is of the order of 100:1.
Commercial Technical Publications
ALONG catalogs and technical publica-
tions received we must mention the
September, 1927 issue of the General
Radio Experimenter, a four-page paper sent out
monthly to concerns and individuals on the mail-
ing list of the General Radio Company of Cam-
bridge, Massachusetts. [This publication may
be secured by our readers by filling out the
" Manufacturers' Booklet" coupon appearing
in the advertising section in this and other issues.
Booklet number 74. — Editor] Thi firm, as is
well known, specializes in communication lab-
oratory and measuring apparatus, such as
standards of inductance, resistance, and capa-
citance, oscillators, oscillographs, audibility
meters, bridges, artificial telephone lines, etc.
Its engineers have played no small part in re-
ducing radio designing to a respectably exact
235
science. The September, 1927 issue of the Experi-
menter is of special interest to broadcasters in
that it contains an article on " Design and Use
of Attenuation Networks," by Horatio W. Lam-
son. The subject was discussed, it may be re-
membered, in this department for September,
1927 (Pages 293-294). Mr. Lamson's paper
covers the same ground, in part, with the addi-
tion of a number of formulae and a detailed
description of the General Radio Company's
variable attenuation networks. Given, as in Fig.
i, a source of impedance Z and an absorbing
circuit or "sink" of the same impedance, joined
by an H-network as shown, with currents I0
and I leaving the source and entering the sink,
respectively, for a definite number of transmis-
sion units of attenuation N we may calculate
the arms X and Y from
Z k— i
X = - ( )
2 k + i
k» —
where k
or, in TU
k = 10 i/»° = Antilog »/
(0
(2)
(3)
(4)
If, as shown in Fig. 2, we make all five branches
of the H-network adjustable by steps, moving
five switch arms in unison to the proper switch
points through a single control, the character-
istic impedance Z of the network may be main-
tained constant to match the impedances to
either side, while the attenuation is varied in
steps. This is the principle of the Type 239 Vari-
able Attenuation Network supplied by the Gen-
eral Radio Company. The box is equipped with
two multiple switches. In the size which af-
fords a total attenuation of 55 TU, one decade
is calibrated in steps of 5 TU, and the other in
steps of 0.5 TU. Another size goes up to a total
of 22 TU, and in this case the steps are 2TU
and 0.2 TU. Characteristic impedances of 600
and 6000 ohms are carried in stock or built to
order. Some types are provided with a center
tap for the Y-branch, where a ground may be
applied.
A somewhat older type of variable pad sup-
plied by the same manufacturer is adjusted by
the addition or subtraction of fixed sections,
which are cut in or out by means of four-pole
double-throw switches, as shown in Fig. 3. This
is known as the Type 249. The manipulation
of this form is necessarily somewhat less con-
venient, but in many cases it serves the same
purpose and the cost is about half of the rotary
switch form. There are eight-section boxes af-
fording a total attenuation of 1 10 TU in steps of
i TU, and six-section boxes with a total of 63
(>-r\^^WAVVWrWYAS rWWWWVWrWrMAr — O
HMrWnAMr'WWVW] i
5J 4 3* 2J li 0*
Output
Input
FIG. 2
236
RADIO BROADCAST
JANUARY, 1928
m n
Input
Output
TU in the same steps. The same characteristic
impedances, 600 and 6000 ohms, are available.
As explained in the September, 1927, RADIO
BROADCAST discussion, the simpler T-networks
may be used in place of the H-type where a
balanced circuit is not essential. The General
Radio Company also supplies the sectional net-
works in the T-connection, at a somewhat lower
price, inasmuch as the number of coil-taps and
switch-arms required is less.
The Portrait of the Author
MR. FRANKLYN F. STRATFORD, who
embellishes these articles with clever
pictures, sometimes sketches my like-
ness for the customers, so that they may not
shoot the wrong man when they take offense
at my sooth-sayings. In so doing Mr. Stratford
has perpetrated a libel on me. I ask that in-
terested readers turn to the illustration in the ,
November, 1927 issue, over the quotation, "Let
the ghost call at my office." The picture includes
the ghost, myself, and part of the office. About
the ghost 1 say nothing; Mr. Stratford's idea of
a ghost is no doubt as good as anyone's. And my
own likeness is not bad. It is true that my nose
is depicted as about the size of Cyrano de Ber-
gerac's, and not as well-shaped, but so God
made me. My head has a contour not unlike
that of a truncated cone, in Mr. Stratford's
sketch, but such geometrical outlines are not
lacking in esthetic value, and it would be worst
if the cone were upside down. What I object to
is the office furniture, and particularly the desk.
The desk depicted seems about four feet wide.
I wish the world to know that my office boy sits
at such a desk. My own desk was made to order
in Circassian walnut, and cost $3000. The top is
a solid piece of Florentine marble, 150 square
feet in area. Nymphs and satyrs are painted on
the sides. When next Mr. Stratford draws my
desk let him take an extra column and do justice
to his subject.
Linguistic Observation
THE vilest French and German I have ever
heard — in the sense of execrable accent,
not of content, be it said — is on radio
broad -ast programs, and I refer to many large
stations as well as small ones, if you please. The
radio announcers, with a trifling number of ex-
ceptions, pronounce foreign languages like so
many high school freshmen. The better vaude-
ville circuits are vastly superior in this detail.
When a girl like Kitty Doner spills some French
before the assembled intelligentsia at the New
York Keith's 8ist Street, it is Parisian French
as you might hear it on the boulevards. But the
announcers drive any half-way educated listener
to thoughts of homicide whenever they have oc-
casion to pronounce a simple phrase like Danse
Russe or Wiener Blut. What ails the announcers
and their bosses? Don't they know any better?
Then let them go back to school. Or don't they
care? Then let them seek some business in which
they don't have to appear before the public.
Memoirs of a Radio Engineer: XXI
INSTEAD of going forward a few more
months in the recital of these memories,
at this point I wish to regress briefly in
order to include an incident which was omitted
in its proper place. It returns to my recollection
when I hear of some broadcast listener ending
his mortal existence by throwing a length of
antenna wire across a high tension line, or
through a fall from a roof. Such fatalities are
too infrequent to deserve mention, perhaps, in
a country which takes no account of some
100,000 deaths in four or five years through
automobile accidents, but the victims are just
as dead, although not killed in a popular man-
ner. I might have joined their number, thus
600 602.5 605
tREQUENCY
Kilocycles
FIG. 4
swelling the total slightly, but for luck. The time
was about 1914, when I was feeding a crystal
receiving set from a one-wire antenna about
four hundred feet long. So long was it, in fact,
that it crossed a city street. After some months
of fine reception, during which I was able to
boast to the other amateurs about the great
distances from the phones at which signals
might be heard at my house, the antenna yielded
to the elements one night, and in the morning it
was down. On the street which it crossed there
was an electric power line, the cross arms carry-
ing six or nine heavy rubber covered wires.
My copper strand now lay across these conduc-
tors. I went to the house at the end of the block
and looked up at the transmission line. It did not
appear dangerous, and I decided that it must be
a i lo-volt circuit, and that nothing much could
happen. However, I decided to be very prudent,
so 1 went below for a bamboo trout rod, made a
cast for my antenna wire, hooked it, and lifted
it off the transmission line. It fell back, however,
and I grasped it impatiently in my bare hands
and swung it clear. Nothing happened. What
could happen even if a boy radio operator got
his antenna tangled up with a I lo-volt line
covered with an eighth of an inch of rubber?
But the other day I passed along that block,
and, thirteen years older, looked up at the trans-
mission line, which was unchanged in equipment
and fittings, as far as I could judge. It is not a
no- volt line, and probably never was one. It
may be carrying its load at a tension of 2200
volts, or perhaps 4400. Either would have been
enough. Some people have luck. The insulation
on the wires was not frayed.
The Radioman's "Britannica"
DRAKE'S RADIO CYCLOPEDIA. By Harold P.
Manly. Published by Frederick J. Drake and
Company, Chicago. Price $6.00. Pages, about
800. Illustrations, 950.
MR. MANLY'S "Cyclopedia" is a com-
prehensive compilation of all the con-
ceivable information which a set builder
and designer needs for ready reference. The
reviewer could not, of course, read the entire
work in detail because that would require several
weeks, but many pages were critically examined.
The first impression gained is the completeness
with which the author covers his subject.
As an example of the wealth of detail on a
'particular subject, under the heading of " Re-
ceiver, Audio Amplifier for," constructor's cir-
cuit diagrams, showing the arrangement of parts,
wiring, outstanding performance qualities, and
specifications of components, are given for fifteen
types of audio amplifier systems, including three-
stage choke-coupled, three-stage transformer-
coupled, one transformer and two choke-coupled,
three-stage double impedance, one transformer
and one push-pull stage, two push-pull stages,
three resistance-coupled stages, one transformer
and three resistance stages with output choke,
two transformer stages with output transformer,
two transformer stages with parallel output
tubes, two transformer stages with potentiometer
control.
In the matter of receiving circuits, the follow-
ing types are described: Browning-Drake,
crystal, four-circuit, long-wave, loop, "N" cir-
cuit, neutrodyne, one-tube, regenerative, Rice,
Roberts, short-wave, single-circuit, single-control,
super-heterodyne (13 pages), super-regenerative,
and tuned radio-frequency.
A table, "Coil Design, Advantages and Disad-
vantages of Types of Coils," is an example of the
practical kind of information collected in a
manner suited to easy reference. This table lists
various elements of coil design, such as type of
winding, shape of winding, proportion of wind-
ing, wire insulation, wire size, material of winding
form, design of winding form, fastening of wind-
ing, material of supports and connections to
winding, and gives under each of these headings
three to six different practices which may be
followed. For example, under "Material of
Form," paraffined paper or cardboard, fibre and
"mud" dielectrics, dry paraffined wood, hard
rubber, phenol, bakelite, and glass are listed.
Under each of these design possibilities, the
characteristics of each type is given in the
simplest terms, "poor, fair, good, and best,"
for the following factors: Durability, most in-
ductance, least resistance, little distributed
capacity in small field. Thus, "type of winding,
(i) cylindrical, single wire, close wound," is de-
clared the "best" from the standpoint of durabil-
ity, most inductance, and least resistance, but
"poor" from the standpoint of less distributed
capacity and small field. Honeycombs, on the
other hand, are good from the standpoint of
durability, inductance, less distributed capacity,
and small field, but only fair from the resistance
standpoint. By the aid of the table, the designer
may select the type of winding form which best
suits his purpose.
In addition to covering constructional informa-
tion, due space is given to practical operation,
general theory, and design. Power supply for A,
B, and C potential, design of receivers with alter-
nating-current supply for filament lighting,
single-control, shielding, are some of the subjects
fully treated, indicating the volume to be up to
the minute.
One mysterious feature of the whole work is
that hardly a single line of credit is given for
sources of information and assistance. Not a
page in this book is numbered. The reviewer does
not believe, however, that a more satisfactory
addition to the experimenter's library, in any
one volume, can be made.
— E. H. F.
RADIO BROADCAST ADVERTISER
237
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for tubes to warm up. No difficulty in
controlling volume. No noise. No AC
hum. No crackling or fading of power.
Instead the same high standard of re-
ception to which you are accustomed.
In this method there is nothing ex-
perimental, nothing untried. It consists
of two of the most dependable products
in radio — a standard set and Balkite.
And if you should already own a radio
set, the cost of equipping it with Bal-
kite is only a fraction of the cost of a
new receiver.
By all means go to AC reception. Its
convenience is the greatest improve-
ment in radio. But be as
critical of an AC receiver
as you would of any
other. That your AC
receiver be a standard set
equipped with Balkite
electric "AB." Then it
will be as clear and faith-
ful in reproduction as
any receiver you can buy.
Two models, #64.50
and #74.50. Ask your
dealer. Fan-
steel Products
Co . , Inc. ,
North Chi-
cago, Illinois.
ite
ELECTRIC AB.
ns no l>attery~\>
RADIO BROADCAST ADVERTISER
flfAGNAYOX
Dynamic Power
Speaker for new
all-electric A-C Sets
HOOK it up like this sketch
because the 6 volt rectified
output of any standard trickle
charger or "A" rectifier will
energize the field of the Mag-
navox 6 volt Dynamic power
speaker unit.
Aristocrat Model speaker
(complete unit), illustrated
above, $85.
Beverly Model table type
complete, $65. Unit only,
(type R~4, 6 volt) $50. Fits
any standard cabinet.
Only the Dynamic type
speaker can bring out the full
qualities of reproduction de-
manded today.
Write for speaker bulletins
THE MAGNAVOX CO.
Oakland, California
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to
that time was printed.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. I to 88, can be secured from the Circulation Department,
Doubleday, Page & Company, Garden City, New York, for $1.00. Some readers have
asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any such errors do occur, a new Laboratory Sheet with the old
number will appear
— THE EDITOR.
No. 153 RADIO BROADCAST Laboratory Information Sheet JanuarYi 1928
Standard- and Constant-Frequency Stations
BROADCASTERS WITH ACCURATE FREQUENCIES
'T*HE Radio Service Bulletin, published monthly
1 by the Radio Division of the Department of
Commerce, Washington, District of Columbia,
contains a list of standard and constant frequency
broadcasting stations as determined by the Bureau
of Standards. This bureau makes measurements on
an average of about three times a month on the
transmissions of a small number of stations and as
a result of these tests data are published in the
Bulletin on those stations which have been found to
maintain a sufficiently constant frequency to be
useful as standards. These are known as "Standard
Frequency Stations." The list of "standard fre-
quency stations" is supplemented with a list of
"constant frequency stations." No regular tests
are made on these latter stations but each station
in the list employs a special device, such as a crystal,
to maintain its frequency accurately so that they
can be generally relied upon to maintain their cor-
rect frequency.
STANDARD FREQUENCY STATIONS
WBZ
KDKA
WBAL
900.00
950.00
1050.00
CONSTANT FREQUENCY STATIONS
Call Letters
WEAF
WRC
wjz
WGY
Frequency Kc.
610.00
640.00
660.00
790.00
Call Letters
WMAQ
WJAD
wcco
WTAM ]
WEAR J
WBBM
EGO
KTHS
WCAD
WJJD
WLS
WSM
WKAQ
KOA
KFAB
WBAA
WHK
WMBI
WABQ
WEBJ
KWUC
KFVS
Frequency Kc.
670
670
740
750
770
780
780
820
820
870
880
880
920
970
1100
1130
1140
1150
1170
1230
1340
No. 154
RADIO BROADCAST Laboratory Information Sheet
January, 1928
The 112-A and 171- A Type Tubes
OPERATING CHARACTERISTICS
volts. The UX-171-A (cx-371-A) must only be used
TWO new power tubes have recently become
available; they are designed especially for use
in the output of a receiver. These new tubes employ
an improved type of filament which gives high
emission at a filament current of 0.25 amperes at
5 volts. They are exactly similar to the older ux-1 12
and ux-1 71 type tubes with the exception that the
filament consumption is only half that of the older
types. The filament of the corresponding 112 and
in the last stage of a receiver, and a choke-condenser
combination or output transformer should be used
in the plate circuit to keep the plate current out
of the loud speaker.
The advantage of these new tubes is in their
greater efficiency. Under the same condition of plate
voltage they produce the same plate current as
the corresponding 0.5-ampere tubes j with only
half as much filament current.
171 type tubes is 0,5 amperes at 5 volts.
The other
These
tubes must not be substituted for the ux-
characteristics of
t hrsr new
tubes remai
i the same
112 (cx-
12 )or ux
-171 (cx-
71) types ir
a receiver
as those of the 0.5 ampere
filament tubes. These
without
changing
the values of fixed filament con-
characteristics are given below.
trol resih
lances or
rheostats
if they are used. Since
The UX-112-A
fcx-312-Al
may be sa
tisfactorilv
they tak
e the sai
ne filame
il currenl <
is a 201 -A
used as a detector, general
purpose tube, or as a
type tube, it follows the filament control
resistances
power tube in th
e last stau
e of a recei
ver. When
designed
for the 1
alter tubs
may be us
ed in con-
used as a detector, the plate voltage should be 45
junction with these new tubes.
TYPE
FILA-
MENT
VOLTS
FILA-
MENT
CURRENT
PLATE
VOLTAGE
NEGA-
TIVE
BIAS
PLATE
IMPED-
ANCE
AMP.
CON-
STANT
PLATE
CURRENT
OUTPUT
MILLI-
WATTS
UX-112-A
5
0.25
90
6
8800
8
2.5
40
(CX-312-A)
135
9
4800
6
120
157J
10.5
5500
8
195
UX-171-A
5
0.25
90
16.5
25(X)
3
10
130
(CX-371-A)
135
27
??00
16
330
180
40.5
2000
20
700
RADIO BROADCAST ADVERTISER
239
Just as the aao transformer, compared with all other
makt's, liives you the sense of Gihraltar-like sturdiness
and dependability truly in ;i class hy itself", so does its
performance far outclass that of other transformers.
The Finest Tone
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— and complete A. C. operation. Complete
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C-jiy and CX-J26 tubes — and at a cost cf
less than half what you'd pay for nearly
equivalent performance in a factory-built set.
Every one of the thousands who built
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And now the new and improved 1928 model
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TMITATED everywhere — never equalled — the S-M 220 audio transformer
-L stands out to'day as the finest for audio amplification that money can buy
just as it did when introduced a year and a half ago. The 220 has been copied
in one or more of its characteristics by every high-grade transformer put on
the market since then — in the rising low note or in 5000 cycle cut-off, features
first offered by S-M. That's proof that the principles the 220 introduced are
right — that the market is still trying to catch up with the leader.
Don't be misled by exaggerated claims — for it takes plenty of core and wire
to make a good transformer. The 220 has from 25 to 50 per cent more steel
and copper in its construction than any other transformer on the market. That
alone means the high primary impedance through which real bass note amplifi-
cation is made possible.
That's why S-M 22o"s and H2i's are specified in more popular receiver
designs — why they have outsold every other transformer in their price field.
That's why they're sold on an unconditional money-back guarantee to give
better quality than any other audio amplifying device available.
We could charge from 25 to 50 per cent more than we do, but at no price can you get a better
transformer. The 210 audio is $8.00, and the 221 output is $7.50. They are priced low, but,
you can't buy a better audio coupler at any price, for there's none better made.
The New 240 Audios
We can't make the 22o's cheaper but if you desire a transformer
somewhat lower in price, taking up a little less room, and with a
little less core and wire, the new 240 audio and 24 1 output trans-
formers are available — superior to most other transformers, and far
and away ahead of anything in their price field. They have the
same general characteristics as the famous 22o's and 22i's, but pro-
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They have the same 5000 cycle cut-off for which 22o's are famous,
eliminating the objectionable whistles and heterodyne squeals of
congested broadcasting. The 240 audio sells for $6.00 and the 241
output at $5.00. Hard to beat at any price, they are impossible to
equal at these prices. And — you can bring your old set up to the
rr.inute using them — they're small enough to fit in most anywhere.
328 Super Power Transformer
A heavy power transformer for either full wave or half wave
rectifiers — for UX-28i (or UX-2i6-B) rectifier tubes. Will furnish
480 volts at loo milliamperes of thoroughly filtered direct current
using two UX-28i tubes, the S-M 331 Unichoke, and only six
microfarads of filter condenser. This is power for a 210 push-pull
amplifier at full voltage and to furnish receiver B power as well.
Consists of two 550 volt secondaries, two 7! volt, 2j ampere fila-
rrent windings and one ij volt,. 2 ampere filament winding for
UX-226 tubes. Price $18.00.
SILVER-MARSHALL, Inc.
838-B West Jackson Blvd. Chicago, 111.
Only a few of the real S-M developments are listed here. io(f in
stamps will bring you more real information on power equipment, A. C.
operation, and other pertinent subjects than you can read in a week.
The A. C. Improved Shielded Six— a completely light socket operated hatteryless set using the new A. C.
tubes. It's illustrated above, with its complete dry ABC power unit— less th.m 7 inches squaie. Price, 630
A. C. receiver kit, $99.00, and 6?2A, ABC socket power kit, $34.50.
SILVER-MARSHALL, INC.
838-8 West Jackson Blvd., Chicago.
Please send me all data on S-M audio transformers, power
equipment, and new A.C. improved Shielded Six.
240
RADIO BROADCAST ADVERTISER
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The new improved Hammarlund'
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I R. O B El RJT S
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HAMMARLUND-ROBERTS, Inc.
1182 Broadway, Dept. A, New York
No. 155
RADIO BROADCAST Laboratory Information Sheet
Wave Traps
January, 1928
THREE CIRCUITS
THE trend of broadcasting, for sometime, has
been toward the use of high power, and this has
made the problem of selectivity a serious one for
many listeners located within a few miles of a high-
power broadcasting transmitter. When difficulty
is experienced in satisfactorily tuning-out such a
station, it will be advisable to incorporate a wave
trap in the antenna circuit. Wave traps are very
easily constructed and cost little. They consist of
any ordinary coil and a condenser, connected in
the antenna circuit, and adjusted to absorb a large
amount of the energy being received from the inter-
fering station. The traps may be connected in
several ways, as indicated on the diagram. The
arrangement shown at A will give most complete
elimination of the undesired signal but may also
cause a considerable decrease in volume of stations
operating on adjacent channels. The arrangement
shown at B is probably the most flexible manner in
which to connect a wave trap. If the coil is arranged
with several taps an adjustment can be arrived at
which gives most satisfactory results. Arrangement
C is only useful in case of mild interference. The
circuit tunes very sharply and will effectively elimi-
nate interference provided it is not too great.
In constructing a wave trap, coil L may consist
of 47 turns of No. 22 wire on a 3-inch diameter form
if the tuning condenser Ci has a capacity of
0.0005 mfd.; with a 0.00035 condenser coil L should
consist of 60 turns. With either size, coil Li may
consist of about 15 turns wound at the b end of the
secondary coil. With arrangement B taps should
be made at about every 10 turns.
No. 156 RADIO BROADCAST Laboratory Information Sheet
January, 1928
Wavelength-Frequency Conversion
A TABLE FOR THE BROADCASTING BAND
ON LABORATORY Sheet No. 157 is given a
wavelength-frequency conversion table cover-
ing the broadcasting band. Broadcasting is assigned
to channels 10 kc. apart on frequencies that are
divisible by 10. It is simple to use the table. If
we knew that some station was transmitting on
1000 kc. we can determine from the table the cor-
responding wavelength, which in this case is ap-
proximately 300 meters. The wavelength corre-
sponding to any given frequency can be determined
by dividing the frequency in kc. into 300,000.
A 10-kc. separation between broadcasting stations
is necessary to prevent bad interference between
two stations on adjacent channels. When a broad-
casting station is transmitting it actually uses a
band of frequencies (side bands) 10,000 cycles wide
— 5000 cycles either side of the "carrier" frequency.
The carrier frequency is the frequency assigned a
station by the Federal Radio Commission, but as
mentioned above, in the ordinary process of modula-
tion a frequency band 10,000 cycles wide is used.
When a station is transmitting it also radiates a
frequency exactly double its carrier frequency. The
additional wave is called the second harmonic, being
equal in frequency to the carrier frequency multi-
plied by two. Careful design and operation of the
transmitter will keep these harmonics small in
amplitude and this is essential if interference is to
be prevented. If a station transmits on, say, 600 kc.
and also radiates a strong second harmonic with a
frequency of 1200 kc., it will interfere with another
station transmitting on a carrier frequency of 1200
kc.
Any radio station might be considered to have
two ranges; first the broadcasting range, being the
distance area over which the program on the station
may be received satisfactorily and, secondly, the in-
terference range, being the area over which a station
causes interference due to the production of a
heterodyne whistle between its carrier and the
carrier of another station. The first range is much
smaller than the second and a station having a
service area of 100 miles will have an interference
range of probably about 1000 miles.
No. 157 RADIO BROADCAST Laboratory Information Sheet January, 1928
Table for Wavelength-Frequency Conversion
Kc. METERS
Kc. METERS
Kc. METERS
Kc. METERS
550 545. 1
560 535.4
570 526. 0
580 516.9
590 508. 2
800 374.8
810 370.2
820 365.6
830 361 . 2
840 356. 9
1,050 285.5
1,060 282.8
1,070 280.2
1,080 277.6
1,090 275.1
1,300 230.6
1,310 228.9
1,320 . 227.1
1,330 225.4
1,340 223.7
600 499.7
610 491.5
620 483.6
630 475.9
640 468. 5
850 352.7
860 348. 6
870 344.6
880 340. 7
890 336.9
1,100 272.6
1,110 270.1
1,120 267.7
1,130 265.3
1,140 263.0
1,350 222. 1
1,360 220.4
1.370 218.8
1,380 217.3
1,390 215.7
650 461.3
660 454.3
670 447.5
680 440. 9
690 434.5
900 333. 1
910 329. 5
920 325.9
930 322.4
940 319.0
1,150 260.7
1,160 258.5
1,170 256.3
1,180 254.1
1,190 252.0
,400 214.2
,410 212.6
,420 21 1 . 1
,430 209. 7
,440 208. 2
700 428. 3
710 422.3
720 416.4
730 410.7
740 405.2
950 315.6
960 312.3
970 309. 1
980 303.9
990 302.8
1,200 249.9
1,210 247.8
1,220 245.8
1,230 243.8
1,240 241.8
.450 206. 8
,460 205. 4
,470 204.0
,480 202.6
.490 201.2
750 399. 8
760 394.5
770 389. 4
780 384.4
790 379. 5
1,000 299.8
1,010 296.9
1,020 293.9
1,030 291.1
1,040 288.3
1,250 239.9
1,260 238.0
1,270 236.1
1,280 234.2
1,290 232.4
1,500 199.9
RADIO BROADCAST ADVERTISER
241
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HUM. Let the Karas A-C-Former Filament Supply, Type
12, replace your "A" Battery and charger. Will operate 8 I J-
voltType 226 or 326 Tubes, 2 2^-voltType 227 or 327 Tubes,
and 2 s-volt Type 177 Tubes at one time. Compact, power-
ful, sturdy and built the Karas Way — by precision methods.
Write for complete information about the new Karas A-C-
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KARAS ELECTRIC COMPANY
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Two Aids to
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MODERN
"B" Compact
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Fp improve your set or get the best results
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THE MODERN ELECTRIC MFG. CO.
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Scientific measurement
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RADIO BROADCAST ADVERTISER
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No. 158 RADIO BROADCAST Laboratory Information Sheet January, 1928
The Three-Tube Roberts Reflex
CIRCUIT CONSTANTS
'"PHERE have been many requests from readers
••• for further information on the Roberts 3-tube
receiver illustrated in the August, 1927 issue of
RADIO BROADCAST on page 2(h*. This receiver is a
reflex set consisting of a stage of r.f. amplification,
a regenerative detector, one stage of reflexed
transformer-coupled audio amplification, followed
by another straight audio stage. The circuit, which
was not given in the article mentioned above, and
which many readers have requested, is published
on Laboratory Sheet No. 159. The list of parts is
given below.
Li, La — R. F. transformer. L« may consist of 45
turns of No. 24 wire wound on a 3-inch
tube. Li should contain 40 turns of No. 24
wire with a tap at each 10 turns. Li should
be wound alongside the filament end of Lz.
Lj, Li, Ls — Interstage r.f. transformer. Ls and Li
have the same specifications as Li and L»
with the exception that Ls should be wound
with No. 26 or No. 28 wire and should only
be tapped at the exact center instead of at
every 10 turns. That end of Ls nearest the
grid end of Lt should connect to the plate
of the r.f. tube, the center tap connects to
transformer Ta, and the other end of Ls con-
nects to the neutralizing condenser. LB is a
movable tickler coil consisting of 20 turns of
No. 26 on a 1 \ inch tube.
Ti, Ts — Any good audio transformers.
T:t — Any good output transformer.
Ci, C:r— O.0005-mfd. variable condensers.
Si — Antenna tap switch.
S» — Filament switch.
Ji — Double-circuit interstage jack.
.!•_• Single-circuit jack.
V — Volume control, 50,000-ohm variable resistance
Ca — Neutralizing condenser, 0.000015 mfd.
C9 — Grid condenser, 0.00025 mfd.
Hs — 4-megohm grid leak.
Ri — 10-ohm rheostat.
R-i — 0.5-ampere fixed filament control resistance.
C4 — 0.001-mfd. fixed condenser.
Ca — 0.0001-mfd. fixed condenser.
C6 — 0.00025-mfd. fixed condenser.
Eleven binding posts
Three sockets
Hook-up wire
For best results a power tube should be used in
the last socket. If a 171 type tube is used with 180
volts on the plate, the C bias required is 40.5 volts.
When the receiver has been completed it should
be neutralized by tuning-in some station, adjusting
the tickler until the detector oscillates and a whistle
is heard and then varying the neutralizing condenser
until the whistle changes in pitch the least amount
(its loudness will change* considerably) as Ci is
varied.
No. 159 RADIO BROADCAST Laboratory Information Sheet January 1928
The Three-Tube Roberts Reflex
No. 160 RADIO BROADCAST Laboratory Information Sheet January, 1928
Fading
HOW IT MAY BE PLOTTED
f~\N THIS Laboratory Sheet is published a curve
^ showing how the signal strength from station
WGV varied over a period of about 10 minutes during
a fading test on this station made during the 'early
part of November.
Anyone can make these measurements. To make
fading measurements of this sort the only instru-
ment needed is a 1.5-or 2-mA. milliammeter. The
meter is connected in the B plus lead to the detector
tube; it will read about 1 mA. if the detector is a
201 -A type tube using a grid leak and condenser for
detection with 45 volts on the plate. When a signal
is tuned-in the meter deflection will decrease, the
amount of the decrease depending upon the strength
of the signals. If the meter deflection with the signal
tuned-in is subtracted from the meter deflection
when not receiving a signal, the difference will be
the amount the meter deflection has changed due
to the signal. If the normal plate current is 1 mA.
and the signal causes the values to decrease to 0.6
mA. then the deflection due to the signal is 0.4 mA.
If this value varies with time it indicates fading
and can be plotted as a curve, as shown on this
Sheet. An examination of this curve indicates that
at the start of the test the meter deflection due to
the signal was 0.5 mA. but that after about one
minute the signal strength quickly fell to 0.25 mA.
and then increased and decreased several times in
rapid succession.
0.1
34567
TIME IN MINUTES
RADIO BROADCAST ADVERTISER
245
Constant
Accuracy!
[TRUVOLT
An All-Wire
Variable
Voltage Control
Install Truvolt in the
B'Eliminator you are con'
structing and vary your
voltage exactly. A new
type wire variable high re'
sistance kept cool by its
greater radiation surface -
like an air cooled motor.
Develops but £ the tem-
perature of other resist-
ances of like size.; hence is
permanently accurate and
lasts indefinitely. Positive
metallic contact always
and 30 exact readings of
resistance.
Type
Resistance
Ohms
T'5 o to 500
T-io o to 1,000
T'2O O tO 2,OOO
T-5o o to 5,000
T-ioo o to 10,000
T-2OO O tO 2O,OOO
T-25O o to 25,000
T'5oo o to 50,000
Current
Milliamperes
224
158
112
71
50
35
. 32
22.5
Price $3.50 each
All rated at 25 watts.
At Your Dealers
Also a full line of Wire
Fixed Resistances
Write for free
Hook-up Circular
''This Is An
Eliminator Year"
Dept. 14B, 175 Varick Street
New York
ELECTRAD
LEA
Improved Reception
Get it with the
CARBORUNDUM
REG. U. S.PAT. OFF.
GRID LEAK
ONE certain way of getting better and clearer reception
is to slip a Carborundum Grid Leak into your set.
(& Things will quiet down instantly. Carborundum Grid
Leaks do not disintegrate — hence they are quiet. They
are solid, fixed, dense rods of Carborundum. They assure
an uninterrupted flow of current. They banish Grid
Leak noises.
<I Carborundum Grid Leaks are tested at the maximum
operating grid voltage, namely — 5 volts, and Resistors
at 90 volts.
From your dealer, or direct
Send for Hook-Up Booklet D-2
THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y.
CANADIAN CARBORUNDUM Co., LTD., NIAGARA FALLS, ONT.
Sales Offices and Warehouses in New York, Chicago, Boston, Philadelphia, Cleveland, Detroit
Cincinnati, Pittsburgh, Grand Rapids, Milwaukee
The Carborundum Co., Ltd., Manchester, Eng.
Deutsche Carborundum Werke, Dusseldorf, Ger.
V Carborundum !> the Reeisterol Trade Nw
^ oou Cubide. TblB True Mirk ia tbe cic
! uged 1>J The Carborundum f"nmr*nj for Sill.
IBive prupirtjr of Tbe Carburuadum Cump*uj.
RADIO PANELS
BAKELITE— HARD RUBBER
Cut, drilled and engraved to order. Send rough sketch
for estimate. Our complete Cataloe on Pant-Is, Tubes and
Rods — all of genuine ttukelite or Hard Rubber — mailed
on request-
STARRETT MFG. CO.
521 S. Green Street Chicago, III.
BROWNING-DRAKE BLUE PRINTS?
Write to
Radio Broadcast Magazine
Booklet Department
Garden City New York
$1.00 per set
Independent Radio Corporation
Manufacturers of
Precision Radio Apparatus
1516 Summer Street Philadelphia
111
T'l
•>•«
da on
.Write for my Big 1928 Radio Catalog
—just off the press. Thousands
marvelous bargains in nation-
ally advertised goods. All the
LATEST I ^ RADIOS and
equipment Lowestwhole-
All aboutlrouble finding?^
FREE Log and
Call Book and Cat-
alog. Get your copy to-""
day. Send postcard now!
American Auto & Radio Mfg.
HARRY SCHWARTZBUKa. PRRS.
Dipt. 123 American Radio flldg., Kansas City. Ml. 3 I
246
RADIO BROADCAST ADVERTISER
"RADIO BROADCASTS" DIRECTORY OF
MANUFACTURED RECEIVERS
1 A coupon will be found on page 258. All readers who desire additional
information on the receivers listed below need only insert the proper num-
bers in the coupon, mail it to the Service Department of RADIO BROADCAST,
and full details will be sent. New sets are listed in this space each month.
KEY TO TUBE ABBREVIATIONS
99 — 60-mA. filament (dry cell)
01-A — Storage battery 0.25 amps, filament
12 — Power tube (Storage battery)
71 — Power tube (Storage battery)
16-B — Half-wave rectifier tube
80 — Full-wave, high current rectifier
81 — Half-wave, high current rectifier
Hmu — High-Mu tube for resistance-coupled audio
20 — Power tube (dry cell)
10 — Power Tube (Storage battery)
00-A — Special detector
13 — Full-wave rectifier tube
26 — Low-voltage high-current a. c. tube
27 — Heater type a. c. tube
DIRECT CURRENT RECEIVERS
NO. 424. COLONIAL 26
Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One to
three dials. Volume control: antenna switch and poten-
tiometer across first audio. Watts required: 120. Con-
sole size: 34 x 38 inches. Headphone connections.
The filaments are connected in a series parallel arrange-
ment. Price $250 including power unit.
NO. 425. SUPERPOWER
Five tubes: All 01-A tubes. Multiplex circuit. Two
dials. Volume control: resistance in r. f. plate. Watts
required: 30. Antenna: loop or outside. Cabinet sizes:
table, 27 x 10 x 9 inches; console, 28 x 50 x 21.Prices:
table, $135 including power unit; console, $390 includ-
ing power unit and loud speaker.
A. C. OPERATED RECEIVERS,
NO. 508. ALL-AMERICAN 77, 88, AND 99
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Rice neutralized t. r. f. Single drum
tuning. Volume control: potentiometer in r. f. plate.
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,
25 x 38 x 18 inches; No. 99 console, 27{ x 43 x 20 inches.
Shielded. Output device. The filaments are supplied
by means of three small transformers. The plate supply
employs a gas-filled rectifier tube. Voltmeter in a. c.
supply line. Prices: No. 77, $150, including power unit;
No. 88, $210 including power unit; No. 99, $285 in-
cluding power unit and loud speaker.
NO. 509. ALL-AMERICAN "DUET"; "SEXTET"
Six tubes; 2 t. r. f. (99), detector (99), 3 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
"Duet," 23 x56x 165 inches; "Sextet," 22J x 13 J x 15J
inches. Shielded. Output device. The 99 filaments are
connected in series and supplied with rectified a. c.;
while 12 is supplied with raw a. c. The plate and fila-
ment supply uses gaseous rectifier tubes. Milliammeter
on power unit. Prices: "Duet," $160 including power
unit; "Sextet," $220 including power unit and loud
speaker.
NO. 511. ALL-AMERICAN 80, 90, AND 115
Five tubes; 2 t. r. f. (99), detector (99), 2 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
No. 80, 23i x 12} x 15 inches; No. 90, 37| x 12 x 121
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi-
vidually shielded. Output device. See No. 503 for
power supply. Prices: No. 80, $135 including power
unit; No. 90, $145 including power unit and compart-
ment; No. 115, $170 including power unit, compart-
ment, and loud speaker.
NO. 510. ALL-AMERICAN 7
Seven tubes; 3 t. r. f. (26), 1 untuned r. f. (26), detec-
tor (27), 2 transformer audio (26 and 71). Rice neutral-
ized t. r. f. One drum. Volume control: resistance in r. f.
plate. Cabinet sizes: "Sovereign" console, 30^ x 601
x 19 inches; "Lorraine" Hiboy, 25J x 53} x 17} inches;
"Forte" cabinet, 25{ x 13} x 17j inches. For filament
and plate supply: See No. 508. Prices: "Sovereign"
$460; "Lorraine'r$360; "Forte" $270. All prices include
power unit. First two include loud speaker.
NO. 401, AMRAD AC9
Six tubes; 3 t. r. f. (99), detector (99), 2 transformer
(99 and 12). Neutrodyne. Two dials. Volume control :
resistance across 1st audio. Watts consumed: 50. Cabi-
net size: 27 x 9 x 11 J inches. The 99 filaments are con-
nected in series and supplied with rectified a. c., while
the 12 is run on raw a. c. The power unit, requiring
two 16-B rectifiers, is separate and supplies A. B. and C
current. Price $142 including power unit.
NO. 402. AMRAD ACS
Five tubes. Same as No. 401 except one less r. f.
stage. Price $125 including power unit.
NO. 536. SOUTH BEND
Six tubes. One control. Sub-panel shielding. Binding
Posts. Antenna: outdoor. Prices: table, $130, Baby
Grand Console, ISldS.
NO. 537. WALBERT 26
Six tubes; five Kellogg a. c. tubes and one 71. Two
controls. Volume control: variable plate resistance.
Isofarad circuit. Output device. Battery cable. Semi-
shielded. Antenna: 50 to 75 feet. Cabinet size: 1OJ x
29J x 16i inches. Prices: $215; with tubes, $2.50
NO. 484. BOSWORTH, BS
Five tubes; 2. t. r. f. (26), detector (99), 2 transformer
audio (special a. c. tubes). T. r. f. circuit. Two dials.
Volume control: potentiometer. Cabinet size: 23 x 7
x 8 inches. Output device included. Price $175.
NO. 406. CLEARTONE 110
Five tubes; 2. t. r. f., detector, 2 transformer audio.
All tubes a. c. heater type. One or two dials. Volume
control: resistance in r. f. plate. Watts consumed: 40.
Cabinet size varies. The plate supply is built in the
receiver and requires one rectifier tube. Filament sup-
ply through step down transformers. Prices range from
$175 to $375 which includes 5 a. c. tubes and one recti-
fier tube.
NO. 407. COLONIAL 25
Six tubes; 2. t. r. f. (01-A), detector (99), 2 resistance
audio (99). 1 transformer audio (10). Balanced t. r. f.
circuit. One or three dials. Volume control: Antenna
switch and potentiometer on 1st audio. Watts con-
sumed: 100. Console size: 34 x 38 x 18 inches. Output
device. All tube filaments are operated on a. c. except
the detector which is supplied with rectified a. c. from
the plate supply. The rectifier employs two 16-b tubes.
Price $250 including built-in plate and filament supply.
NO. 507. CROSLEY 602 BANDBOX
Six tubes; 3. t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Neutrodyne circuit. One dial, Cabinet
size: 17i x 5} x 7| inches. The heaters for the a. c. tubes
and the 71 filament are supplied by windings in B unit
transformers available to operate either on 25 or 60
cycles. The plate current is supplied by means of
rectifier tube. Price $65 for set alone, power unit $60.
NO. 408. DAY-FAN "DE LUXE"
Six tubes; 3 t. r. f., detector, 2 transformer audio. All
01-A tubes. One dial. Volume control: potentiometer
across r. f. tubes. Watts consumed: 300. Console size:
30 x 40 x 20 inches. The filaments are connected in
series and supplied with d. c. from a motor-generator
set which also supplies B and C current. Output de-
vice. Price $350 including power unit.
NO. 409. DAYCRAFT 5
Five tubes; 2 t. r. f., detector, 2 transformer audio.
All a. c. heater tubes. Reflexed t. r. f. One dial. Volume
control: potentiometers in r. f. plate and 1st audio.
Watts consumed: 135. Console size: 34 x 36 x 14 inches.
Output device. The heaters are supplied by means of
a small transformer. A built-in rectifier supplies B
and C voltages. Price $170, less tubes. The following
have one more r. f. stage and are not reflexed; Day-
craft 6, $195; Dayrole, 6, $235; Dayfan 6, $110. All
prices less tubes.
NO. 469. FREED-EISEMANN NRII
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Volume control: potentiometer. Watts consumed: 150.
Cabinet size: 19} x 10 x 101 inches. Shielded. Output
device. A special power unit is included employing a
rectifier tube. Price $225 including NR-411 power unit.
. NO. 487. FRESHMAN 7F-AC
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Equaphase circuit. One dial. Volume
control: potentiometer across 1st audio. Console size:
24Jx 411 x 15 inches. Output device. The filaments and
heaters and B supply are all supplied by one power unit.
The plate supply requires one 80 rectifier tube. Price
$175 to $350, complete.
NO. 421. SOVEREIGN 238
Seven tubes of the a. c. heater type. Balanced t. r. f.
Two dials. Volume control: resistance across 2nd audio.
Watts consumed: 45. Console size: 37 x 52 x 15 inches.
The heaters are supplied by a small a. c. transformer,
while the plate is supplied by means of rectified a. c.
using a gaseous type rectifier. Price $325, including
power unit and tubes.
NO. 517. KELLOGG 510, 511, AND 512
Seven tubes; 4 t. r. f., detector, 2 transformer audio.
All Kellogg a. c. tubes. One control and special zone
switch. Balanced. Volume control: special. Output de-
vice. Shielded. Cable connection between power supply
unit and receiver. Antenna: 25 to 100 feet. Panel 7(3
x 27.; inches. Prices: Model 510 and 512, consoles, $495
complete. Model 511, consolette, $365 without loud
speaker.
NO. 496. SLEEPER ELECTRIC
Five tubes; four 99 tubes and one 71. Two controls.
Volume control: rheostat on r. f. Neutralized. Cable.
Output device. Power supply uses two 16-B tubes.
Antenna: 100 feet. Prices: Type 64, table, $160; Type
65, table, with built-in loud speaker, $175; Type 66,
table, $175; Type 67, console, $235; Type 78, console,
$265.
NO. 538. NEUTROWOUND MASTER ALLECTRIC
Six tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and two 71 in push-pull amplifier). The 01-A
tubes are in series, and are supplied from a 400-mA.
rectifier. Two drum controls. Volume control: variable
plate resistance. Output device. Shielded. Antenna:
50 to 100 feet. Price: .1360.
NO. 413. MARTI
Six tubes: 2 t. r. f., detector, 3 resistance audio. All
tubes a. c. heater type. Two dials. Volume control-
resistance in r. f. plate. Watts consumed: 38. Panel size
7 x 21 inches. The built-in plate supply employs one
16-B rectifier. The filaments are supplied by a small
transformer. Prices: table, $235 including tubes and
rectifier; console, $275 including tubes and rectifier;
console, $325 including tubes, rectifier, and loud
speaker.
NO. 417 RADIOLA 28
Eight tubes; live type 99 and one type 20. Drum
control. Super-heterodyne circuit. C-battery connec-
tions. Battery cable. Headphone connection. Antenna:
loop. Set may be operated from batteries or from the
power mains when used in conjunction with the model
104 loud speaker. Prices: $260 with tubes, battery
operation; $570 with model 104 loud speaker, a. c.
operation.
NO. 540 RADIOLA 30-A
Receiver characteristics same as No. 417 except that
type 71 power tube is used. This model is designed to
tamed in lower part ot cabinet. Jbither a short in
or long outside antenna may be used. Cabinet size:
42 Jx 29 x 17 J inches. Price: $495.
NO. 541. RADIOLA 32
This model combines receiver No. 417 with the model
104 loud speaker. The power unit uses two type 81
tubes and a type 10 power amplifier. Loop is completely
enclosed and is revolved by means of a dial on the panel.
Models for operation from a. c. or d. c. power mains.
Cabinet size: 52 x 72 x 17} inches. Price: $895.
NO. 539 RADIOLA 17
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 27). One control. Illuminated dial.
Built-in power supply using type 80 rectifier. Antenna:
100 feet. Cabinet size: 25f, x 7J x 8J. Price: $130
without accessories.
NO. 545. NEUTROWOUND, SUPER ALLECTRIC
Five tubes; 2 t. r. f. (99), detector (99), 2 audio (99
and 71). The 99 tubes are in series and are supplied from
an 85-mA. rectifier. Two drum controls. Volume con-
trol: variable plate resistance. Output device. Antenna:
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:
$150.
NO. 490. MOHAWK
Six tubes; 2 t. r. f., detector, 2 transformer audio. All
tubes a. c. heater type except 71 in last stage. One dial.
Volume control: rheostat on r. f. Watts consumed: 40.
Panel size: 12\ x 8« inches. Output device. The heaters
for the a. c. tubes and the 71 filament are supplied by
small transformers. The plate supply is of the built-in
type using a rectifier tube. Prices range from $65 to
$245.
NO. 522. CASE, 62B AND 62C
McCullough a. c. tubes. Drum control. Volume con-
trol; variable high resistance in audio system. C-battery
connections. Semi-shielded. Cable. Antenna: 100 feet.
Panel size: 7 x 21 inches. Prices: Model 62B, complete
with a. c. equipment, $185; Model 62 C, complete with
a. c. equipment, $235.
NO. 523. CASE, 92 A AND 92 C
McCullough a. c. tubes. Drum control. Inductive
volume control. Technidyne circuit. Shielded. Cable.
C-battery connections. Model 92 C contains output
device. Loop operated. Prices: Model 92 A, table, $350;
Model 92 C, console, $475.
BATTERY OPERATED RECEIVERS
NO. 542. PFANSTIEHL JUNIOR SIX
Six tubes: 3 t. r. f. (01-A), detector (01-A), 2 audio.
Pfanstiehl circuit. Volume control: variable resistance in
r. f. plate circuit. One dial. Shielded. Battery cable. C-
battery connections. Etched bronze panel. Antenna:
outdoor. Cabinet size: 9 x 20 x 8 inches. Price: $80, with-
out accessories.
NO. 512. ALL-AMERICAN 44, 45, AND 66
Six tubes; 3 t. r. f. (01-A, detector) 01-A, 2 trans-
former audio (01-A and 71). Rice neutralized t. r. f.
Drum control. Volume control: rheostat in r. f. Cabinet
sizes: No. 44, 21 x 10 x 8 inches; No. 55. 25 x 38 x 18
inches; No. 66, 27J x 43 x 20 inches. C-battery connec-
tions. Battery cable. Antenna: 75 to 125 feet. Prices:
No. 44, $70; No. 55, $125 including loud speaker; No.
66, $200 including loud speaker.
NO. 428. AMERICAN C6
Five tubes; 2 t. r. f. detector, 2 transformer audio.
All 01-A tubes. Semi balanced t. r. f. Three dials. Plate
current 15mA. Volume control: potentiometer. Cabinet
sizes: table, 20 x 8! x 10 inches; console, 36 x 40 x 17
inches. Partially shielded. Battery cable. C-battery
connections. Antenna: 125 feet. Prices: table, $30
console, $65 including loud speaker.
RADIO BROADCAST ADVERTISER
247
New AERO Circuits
For Either Battery
or A. C. Operation
The Improved Aero-Dyne 6, and the
Aero 7 — popular new circuits are
built around these marvelous coils
You Should Learn About Them Now!
Proper constants for A. C. operation of
the improved Aero-Dyne 6 and the Aero
Seven have been studied out. and these
excellent circuits are now adaptable to
either A. C. or battery operation. A. C.
blue prints are packed in foundation
units. They may also be obtained by
sending 25e for each direct to the factory.
AERO Universal Tuned Radio Frequency Kit
Especially designed for the Improved Aero-
Dyne 6. Kit consists of 4 twice-matched
units. Adaptable to 201-A, 199. 112, and the
new 240 and A. C. tubes. Tuning range be-
low 200 to above ">.">o meters.
This kit will make any circuit better in
selectivity, tone and range. Will eliminate
losses and give the greatest receiving effi-
ciency.
Code No. U- 16 (for .01105 Cond.) .. .$15.00
Code No. U-163 (for .00035 Cond.)... 15.00
AERO Seven Tuned Radio Frequency Kit
Kspi-cially designed for the Aero 7. Kit con-
>Kts of 3 twice-matched units. Coils are
wound on Bakelite skeleton forms, assuring
a 95% air di-electrie. Tuning range from
below 200 to above 550 meters. Adaptable
to 2H1-A. 199, 112, and the new 240 and
A. C. tubes.
Code No. U- 12 (for .0005 Cond.) .. .$12.00
Code No. U-123 (for .00035 Cond.)... 12.00
MITE— All AERO Universal Kits for use in
(inii-il radio frequency circuits have packed
in t-ni-ti mil with a fixed primary a tir'n-i-
matched calibration slip showing reading
at cadi fised primary AERO Universal Coil
at 250 inifl 300 Dieters; all having an ac-
rurati' inul similar ciililiratioit. He sure to
keep these slips. They're valuable if you de-
cide to add another R.F. Stage to your set.
A NEW SERVICE
\\ »• have arranged to furnish the homo sol builder
with complete Foundation Units for the above
named Circuits, drilled and engraved on Westing-
house Micarta. Detailed blue-prints for both
battery and A. C. operation and wiring diagram
for each circuit included with every foundation
unit free. Write for information and prirrs.
You should be able to get any of the above
Aero Coils and parts from your dealer. If
he should be out of stock order direct
from the factory.
AERO PRODUCTS, Inc.
1772 Wilson Ave. Dept. 109 Chicago, 111.
COOL
POWER
Samson Power IHock No. 210— The only block which will supply 500 volts
at 80 mils to two 210 tubes.
Powerize with Samson Units for Best Results
For new SAMSON Power Units insure the best there is in radio current supply by
1. Doing away with hum, motor boating and poor voltage regulation.
2. Remaining so cool after 24 hours continuous operation under full load that they will be well
within the 20° rise of temperature specified by the A. I. E. E.
3. Being designed to more than meet the specifications adopted by the National Board of Fire Underwriters.
4. Insuring safety against shock because of protected input and output terminals.
5. Insuring for all tubes the correct filament voltages specified by their manufacturers.
6. Compensating for lighting circuit voltage variation by the use of a special input plug and
terminal block to which is attached a six ft. flexible rubber-covered connecting cord and plug.
Our Power Units bulletin descriptive of these is free for the asking. In addition, our
construction bulletin on many different "B" Eliminators and Power Amplifiers
will be sent upon receipt of lOc. in stamps to cover the mailing cost.
\amson
Manufacturing Since 1882
Principal Office, CANTON, MASS.
lUaich VOP
fl, 6
or Uour
Jubes
//TUBES/
Could Talk!
They would tell you — that only at the
precise and definitely prescribed fila-
ment current, or temperature, can their
tonal qualities, clarity and sensitiveness
be brought out to the full. That "A"
battery current constantly varies accord-
ing to the age of the battery and state
of charge — and operation with too little
or too great current is certain death
to efficient tube performance — and too
quickly, of the tube itself. That only AMPERITE
can automatically supply and control this exact
current despite battery variation — as long as
sufficient current is to be had. That you should
never confuse AMPERITE with fixed filament
resistors which do not do the Amperite's job.
AMPERITE is sold by dealers everywhere. Price
81.10 mounted (in U. S. A.).
Write for FREE "Amperite Book" of the season's best circuit*
and latest construction data. Address Dept. K.ll-1
50 Franklin St., New York
Jhe "SELF-ADJUSTING" Rheostat
RADIO BROADCAST ADVERTISER
NO. 485. BOSWORTH B6
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Two dials. Volume control:
variable grid resistances. Battery cable. C-battery
connections. Antenna: 25 feet or longer. Cabinet size
15 x 7 x 8 inches. Price $75.
NO. 513. COUNTERPHASE SIX
Six tubes; 3 t. r. f. (01-A), detector (00- A), 2 trans-
former audio (01-A) and 12). Counterphase t. r. f. Two
dials. Plate current: 82 mA. Volume control: rheostat
on 2nd and 3rd r. f. Coils shielded. Battery cable. C-
battery connections. Antenna: 75 to 100 feet. Console
size: 18| x 40} x 155 inches. Prices: Model 35, table,
$110; Model 37, console, $175.
NO. 514. COUNTERPHASE EIGHT
Eight tubes; 4 t. r. f. (01-A) detector (00-A), 2 trans-
former audio (01-A and 12). Counterphase t. r. f. One
dial. Plate current: 40 mA. Volume control: rheostat
in 1st r. f. Copper stage shielding. Battery cable. C-bat-
tery connections. Antenna: 75 to 100 feet. Cabinet size:
30 x 125 x 16 inches. Prices: Model 12, table, $225;
Model 16, console, $335; Model 18, console, $365.
NO. 506. CROSLEY 601 BANDBOX
Six tubes; 3 t. r. f., detector, 2 transformer audio. All
01-A tubes. Neutrodyne. One dial. Plate current:
40 MA. Volume control: rheostat in r. f. Shielded.
Battery cable. C-battery connections. Antenna: 75 to
150 feet. Cabinet size: 17J x 5j x 7|. Price, $55.
NO. 434. DAY-FAN 6
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). One dial. Plate
current: 12 to 15 mA. Volume control: rheostat on r. f.
Shielded. Battery cable. C-battery connections. Output
device. Antenna: 50 to 120 feet. Cabinet sizes:Daycraft
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7. Prices:
Day-Fan 6, $110; Daycraft 6, $145 including loud
speaker; Day-Fan Jr. not available.
NO. 435. DAY-FAN 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), I resist-
ance audio (01-A), 2 transformer audio (01-A and 12
or 71). Plate current: 15 mA. Antenna: outside. Same
as No. 434. Price $115.
NO. 503. FADA SPECIAL
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 20 to 24 MA. Volume control:
rheostat on r. f. Coils shielded. Battery cable. C. -battery
connections. Headphone connection. Antenna: outdoor.
Cabinet size: 20 x 13J x 10} inches. Price $95.
NO. 504. FADA 7
Seven tubes; 4 t. r. f. (01-A), detector (01 -A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 43, A. Volume control: rheostat
on r. f. Completely shielded. Battery cable. C-battery
connections. Headphone connections. Output device.
Antenna: outdoor or loop. Cabinet sizes: table, 25} x
13} x 11 J inches; console, 29 - 50 x 17 inches. Prices:
table, $185; console, $285.
NO. 436. FEDERAL
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t. r. f. One
dial. Plate current: 20.7 mA. Volume control: rheostat
on r. f. Shielded. Battery cable. C-battery connections.
Antenna: loop. Made in 6 models. Price varies from
$250 to $1000 including loop.
NO. 505. FADA 8
Flight tubes. Same as No. 504 except for one extra
stage of audio and different cabinet. Prices: table, $300;
console, $400.
NO. 437. FERGUSON IDA
Seven tubes; 3 t. r. f. (01 -A), detector (01 -A), 3 audio
(01-A and 12 or 71). One dial. Plate current: 18 to 25
mA. Volume control: rheostat on two r. f. Shielded.
Battery cable. C-battery connections. Antenna: 100
feet. Cabinet size: 21* x 12 x 15 inches. Price $150.
NO. 438. FERGUSON 14
Ten tubes; 3 untuned r. f., 3 t. r. f. (01-A), detector
(01-A), 3 audio (01-A and 12 or 71). Special balanced
t. r. f. One dial. Plate current: 30 to 35mA. Volume con-
trol: rheostat in three r. f. Shielded. Battery cable, C-
battery connections. Antenna: loop. Cabinet size:
24 x 12 x 16 inches. Price $235, including loop.
NO. 439. FERGUSON 12
Six tubes; 2 t. r. f. (01-A), detector (01-A), 1 trans-
former audio (01-A), 2 resistance audio (01-A and 12
or 71). Two dials. Plate current: 18 to 25mA. Volume
control; rheostat on two r. f. Partially shielded. Battery
cable. C-battery connections. Antenna: 100 feet
Cabinet size: 225 x 10 x 12 inches. Price $85. Consolette
$145 including loud speaker.
NO. 440. FREED-EISEMANN NR-8 NR-9, AND
NR-66
Six tubes: 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. NR-8, two
dials; others one dial. Plate current: 30 mA. Volume
control: rheostat on r. f. NR-8 and 9: chassis type
shielding. NR-66, individual stage shielding. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet sizes: NR-8 and 9, 19! x 10 x KM inches; NR-66
20 x 101 x 12 inches. Prices: NR-8, $90; NR-9, S100;
NR-66, $125.
NO. 501. KING "CHEVALIER"
Six tubes. Same as No. 500. Coils completely shielded.
Panel size: 11 x 7 inches. Price, $210 including loud
speaker.
NO. 441. FREED-EISEMANN NR-77
Seven tubes; 4 t. r. f. (01 -A), detector (01 -A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Plate current: 35mA. Volume control: rheostat on r. f.
Shielding. Battery cable. C-battery connections.
Antenna: outside or loop. Cabinet size: 23 x 10^ x 13
inches. Price $175.
NO. 442. FREED-EISEMANN 800 AND 850
Eight tubes; 4 t. r. f. (01-A), detector (01-A), 1 trans-
former (01-A), 1 parallel audio (01-A or 71). Neutro-
dyne. One dial. Plate current: 35 mA. Volume control:
rheostat on r. f. Shielded. Battery cable. C-battery
connections. Output: two tubes in parallel or one power
tube may be used. Antenna: outside or loop. Cabinet
sizes: No. 800, 34 x 155 x 135 inches; No. 850, 36 x 65 x
17J. Prices not available.
NO. 444. GREBE MU-1
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t. r. f. One,
two, or three dials (operate singly or together). Plate
current: 30mA. Volume control: rheostat on r. f. Bi-
nocular coils. Binding posts. C-battery connections.
Antenna: 125 feet. Cabinet size: 225 x 9J x 13 inches.
Prices range from $95 to $320.
NO. 426. HOMER
Seven tubes; 4 t. r. f. (01-A) ; detector (01-A or OOA) ;
2 audio (01-A and 12 or 71). One knob tuning control.
Volume control: rotor control in antenna circuit. Plate
current: 22 to 25mA. "Technidyne" circuit. Completely
enclosed in aluminum box. Battery cable. C-battery
connections. Cabinet size, 84 x 19} x 9} inches. Chassis
size, 6f x 17x8 inches. Prices: Chassis only, $80. Table
cabinet, $95.
NO. 502. KENNEDY ROYAL 7. CONSOLETTE
Seven tubes; 4 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). One dial. Plate current:
42mA. Volume control: rheostat on two r. f. Special
r. f. coils. Battery cable. C-battery connections. Head-
phone connection. Antenna: outside or loop. Consotette
size: 365 x 355 x 19 inches. Price $220.
NO. 498. KING "CRUSADER"
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 20 mA. Volume control: rheostat on r. f.
Coils shielded. Battery cable. C-battery connections.
Antenna: outside. Panel: 11x7 inches. Price, $115.
NO. 499. KING "COMMANDER"
Six tubes; 3 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 25mA. Volume control: rheostat on r. f.
Completely shielded. Battery cable. C-battery con-
nections. Antenna: loop. Panel size: 12 x 8 inches. Price
$220 including loop.
NO. 429. KING COLE VII AND VIII
Seven tubes; 3 t. r. f., detector, 1 resistance audio, 2
transformer audio. All 01-A tubes. Model VIII has one
more stage t. r. f. (eight tubes). Model VII, two dials.
Model VIII, one dial. Plate current: 15 to 50 mA.
Volume control: primary shunt in r. f. Steel shielding.
Battery cable and binding posts. C-battery connections.
Output devices on some consoles. Antenna: 10 to 100
feet. Cabinet size: varies. Prices: Model VII, $80 to
$160; Model VIII, $100 to $300
NO. 500. KING "BARONET" AND "VIKING"
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 19mA. Volume control: rheostat in r. f.
Battery cable. C-battery connections. Antenna: out-
side. Panel size: 18x7 inches. Prices: "Baronet," $70;
"Viking," $140 including loud speaker.
NO. 489. MOHAWK
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 audio
(01-A and 71). One dial. Plate current: 40mA. Volume
control: rheostat on r. f. Battery cable. C-battery con-
nections. Output device. Antenna: 60 feet. Panel size:
125 x &l inches. Prices range from $65 to $245.
NO. 547. ATWATER KENT, MODEL 33
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71 or 12). One dial. Volume control: r. f. fila-
ment rheostat. C-battery connections. Battery cable.
Antenna: 100 feet. Steel panel. Cabinet size: 21 Jx 6f
6J inches. Price: $75, without accessories.
NO. 544. ATWATER KENT, MODEL 50
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 12 or 71). Volume control: r. f. filament rheo-
stat. C-battery connections. Battery cable. Special
bandpass . filter circuit with an untuned amplifier.
Cabinet size: 20J x 13 x T, inches. Price: $120.
NO. 452. ORIOLE 90
Five tubes; 2 t. r. f., detector, 2 transformer audio.
All 01-A tubes. "Trinum" circuit. Two dials. Plate
current: 18mA. Volume control: rheostat on r. f.
Battery cable. C-battery connections. Antenna: 50 to
100 feet. Cabinet size: 25} x 1 15 x 125 inches. Price $85.
Another model has 8 tubes, one dial, and is shielded.
Price, $185.
NO. 453. PARAGON
Six tubes; 2 t. r. f. (01-A), detector (01-A), 3 double
impedance audio (01-A and 71). One dial. Plate cur-
rent: -10 in A. Volume control: resistance in r. f. plate.
Shielded. Battery cable. C-battery connections. Out-
put device. Antenna: 100 feet. Console size: 20 x 45
x 17 inches. Price not determined.
NO. 543 RADIOLA 20
F^e tubes; 2 t. r. f. (99), detector (99), two trans-
former audio (99 and 20). Regenerative detector. Two
drum controls. C-battery connections. Battery cable.
Antenna: 100 feet. Price: $78 without accessories.
NO. 480. PFANSTIEHL 30 AND 302
Six tubes; 3 t. r. f. (01-A), detector (01-2A), trans-
former audio (01-A and 71). One dial. Plate current:
23 to 32 MA. Volume control: resistance in r. f. plate.
Shielded. Battery cable. C-battery connections. An-
tenna: outside. Panel size: 17* x 85 inches. Prices: No
30 cabinet, $105; No. 302 console, $185 including loud
speaker.
NO. 515. BROWNING-DRAKE 7-A
Seven tubes; 2 t. r. f. (Ol-A), detector (00-A), 3 audio
(Hmu, two 01-A, and 71). Illuminated drum control.
Volume control: rheostat on 1st r. f. Shielded. Neutral-
ized. C-battery connections. Battery Cable. Metal
panel. Output device. Antenna: 50-75 feet. Cabinet,
30 x 11 x 9 inches. Price, $145.
NO. 516. BROWNING-DRAKE 6-A
Six tubes; 1 t. r. f. (99), detector (OC^A), 3 audio
(Hmu, two 01-A and 71). Drum control with auxiliary
adjustment. Volume control: rheostat on r. f. Regenera-
tive detector. Shielded. Neutralized. C-battery connec-
tions. Battery cable. Antenna: 50-100 feet. Cabinet
25 x 11 x 9. Price $105.
NO. 518. KELLOGG "WAVE MASTER,"
504, 505, and 506.
Five tubes; 2 t. r. f., detector, 2 transformer audio.
One control and special zone switch. Volume control:
rheostat on r. f. C-battery connections. Binding posts.
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel-
7} x 25J inches. Prices: Model 504, table, $75, less
accessories. Model 505, table, $125 with loud speaker
Model 506, consolette, $135 with loud speaker.
NO. 519. KELLOGG, 507 AND 508
Six rubes, 3 t. r. f., detector, 2 transformer audio. One
control and special zone switch. Volume control: rheo-
stat on r. f. C-battery connections. Balanced. Shielded.
Binding posts and battery cable. Antenna: 70 feet
Cabinet size: Model 507, table, 30 x 13ix 14 inches.
Model 508, console, 84 x 18 x 54 inches. Prices- Model
507, $190 less accessories. Model 508, $320 with loud
speaker.
NO. 427. MURDOCK 7
Seven tubes; 3 t. r. f. (01-A), detector (01-A), 1 trans-
former and 2 resistance audio (two 01-A and 12 or 71).
One control. Volume control: rheostat on r. f. Coils
shielded. Neutralized. Battery cable. C-battery con-
nections. Complete metal case. Antenna: 100 feet.
Panel size: 9 x 23 inches. Price, not available.
NO. 520. BOSCH 57
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control calibrated in kc. Volume
control: rheostat on r. f. Shielded. Battery cable. C--
battery connections. Balanced. Output device. Built-in
loud speaker. Antenna: built-in loop or outside antenna.
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340
including enclosed loop and loud speaker.
NO. 521. BOSCH "CRUISER," 66 AND 76
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat
on r. f. Shielded. C-battery connections. Balanced
Battery cable. Antenna: 20 to 100 feet. Prices: Model
66, table, $93.50. Model 76, console, $175; with loud
speaker $195.
NO. 524. CASE, 61 A AND 61 C
T. r. f. Semi-shielded. Battery cable. Drum control.
Volume control: variable high resistance in audio sys-
tem. Plate current: 35mA. Antenna: 100 feet. Prices;
Model 61A, $85; Model 61 C, console, $135.
NO. 525. CASE, 90 A AND 90 C
Drum control. Inductive volume control. Technidyne
circuit. C-battery connections. Battery cable. Loop
operated. Model 90-C equipped with output device
Prices: Model 90 A, table, $225; Model 90 C, console,
S350.
NO. 526. ARBORPHONE 25
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat.
Shielded. Battery cable. Output device. C-battery con-
nections. Loftin-White circuit. Antenna: 75 feet. Panel:
71. x 15 inches, metal. Prices: Model 25, table, $125-
Model 252, $185; Model 253, $250; Model 255, combin-
ation phonograph and radio, $600.
NO. 527. ARBORPHONE 27
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
(01-A). Two controls. Volume control: rheostat. C-
battery connections. Binding posts. Antenna: 75 feet.
Prices: Model 27, $65; Model 271, $99.50; Model 2"2,
$125.
NO. 528. THE "CHIEF"
Seven tubes; six 01-A tubes and one power tube.
One control. Volume control: rheostat. C-battery con-
nection. Partial .shielding. Binding posts. Antenna:
outside. Cabinet size: 40 x 22 x 16 inches. Prices:
Complete with A power supply, $250; without acces-
sories, $150.
NO. 529. DIAMOND SPECIAL, SUPER SPECIAL,
AND BABY GRAND CONSOLE
Six tubes; all 01-A type. One control. Partial shield-
ing. C-battery connections. Volume control: rheostat.
Binding posts. Antenna: outdoor. Prices: Diamond
Special, $75; Super Special, $65; Baby Grand Console.
$110.
RADIO BROADCAST ADVERTISER
249
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A Complete Aerial Kit
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It is much easier to buy a
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with Beldenamel Aerial
Wire, Belden Lightning
Arrester, etc., than to pick
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Every item in the Belden
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perfect performance.
Insure yourself against aerial
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Aerial Kit
Iii the still of the Arctic Night
In the still of the Arctic night, broken
only by the occasional bark of a far-off
walrus, the Radio Operator cannot leave
his ship, frozen into the ice pack, and run
around the corner to the Radio Shack
for a new filter condenser to replace the
one that just blew out.
He has got to be sure when he starts
that his equipment is not going to give
out.
That is why Cliff Himoe took TOBE
Condensers with him on the Bowdoin
for the MacMillan Arctic Expedition.
Here is a Radio message just received
from the boat: The TOBE'S are up to the
mark!
"Your filter condenser standing up well on Bowdoin 's
transmitter, with no signs of trouble at continuous
2000 volts dc regards from the arctic."
Himoe WNP
The University-of-Michigan-Greenland Expedition is also equipped with
TOBE Condensers.
Make sure that your Radio Power Equipment includes TOBE Condensers.
TOBE Condensers cure condenser worries permanently and painlessly.
Send for Price List B-l
Tobe Deutschmann Company
s Cambridge Massachusetts /
WANTED!
Radio Dealers
PROFESSIONAL
Set Builders and Radio Fans
IN every community to introduce and become our
factory Representative on the newest, most rev-
olutionary radio development in the history of
the industry . . . The SUPER HILODYNE Circuit,
a radio circuit that is modern and independent.
See December issue of Radio News.
The SUPER HILODYNE is a new basic circuit
employing nine tubes. Its all around performance
will amaze you. You can help repeat Radio History
and make money by representing us in your com-
munity in your full or spare time. Write TO-DAY
for details. Dept. RB-128.
ALGONQUIN
245 Fifth Avenue
ELECTRIC
CO., INC.
New York City
250
RADIO BROADCAST ADVERTISER
No. 531. KOLSTER, 8A, SB, AND 8C
Eight tubes; 1 t. r. f. (01-A). detector (01-A). 3-audio
(two 01-A and one 12). One control. Volume control:
rheostat on r. f. Shielded. Battery cable. C-battery con-
nections. Model 8 A uses 50 to 75 foot antenna; model
8B contains output device and uses antenna or detach-
able loop; Model 8C contains output device and uses
antenna or built-in loop. -Prices: 8A, $185; 8B, $235;
8C, $375.
NO. 532. KOLSTER, 6D, 6G, AND 6H
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r. f . C-battery connections. Battery cable. Antenna :
50 to 75 feet. Model 6G contains output device and
built-in loud speaker; Model 6H contains built-in B
power unit and loud speaker. Prices: Model 6D, $80;
Model 6G, $165; Model 6H, $265.
NO. 533. SIMPLEX, SR 9 AND SR 10
Five tubes; 2 t. r. f. (01-A), detector (00-A), 2 audio
(01-A and 12). SR 9, three controls; SR 10, two con-
trols. Volume control ; rheostat. C-battery connections.
Battery cable. Headphone connection. Prices: SR 9,
table, $65; consolette, $95; console, $145. SR 10, table
$70; consolette, $95; console, $145.
NO. 534. SIMPLEX, SR 11
Six tubes; 3 t r. f. (01-A), detector (00-A), 2 audio
(01-A and 12). One control. Volume control: rheostat.
C-battery connections. Battery cable. Antenna: 100
feet. Prices; table, $70; consolette, $95; console, $145.
NO. 535. STANDARDYNE, MODEL X 27
Six tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
power tubes), one control. Volume control: rheostat
on r. f. C-battery connections. Binding posts. Antenna'
75 feet. Cabinet size: 9 x 9 x 19J inches. Prices: S 27,
549.50; S 950, console, with built-in loud speaker,
$99.50; S 600, console with built-in loud speaker,
$104.50.
NO. 481. PFANSTIEHL 32 AND 322
Seven tubes: 3 t. r. f. (01-A), detector (01-A), 3 audio
(01-A and 71). One dial. Plate current: 23 to 32 mA.
Volume control: resistance in r. f. plate. Shielded
Battery cable. C-battery connections. Output device.
Antenna: outside. Panel: 17f x 8S inches. Prices: No.
32 cabinet, $145; No. 322 console, $245 including loud
speaker.
NO. 433. ARBORPHONE
Five tubes; 2 t. r. f., detector, 2 transformer audio
All 01-A tubes. Two dials. Plate current: 16mA. Vol-
ume control: rheostat in r. f. and resistance in r. f. plate.
C-battery connections. Binding posts. Antenna: taps
for various lengths. Cabinet size: 24 x 9 x 10J inches.
Price: $65.
NO. 431. AUDIOLA 6
Six tubes; 3 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Drum control. Plate cur-
rent: 20mA. Volume control: resistance in r. f. plate
Stage shielding. Battery cable. C-battery connection.
Antenna: 50 to 100 feet. Cabinet size: 28J x 11 x 14i
inches. Price not established.
NO. 432. AUDIOLA 8
Eight tubes; 4 t. r. f. (01-A), detector (00-A), 1 trans-
former audio (01-A), push-pull audio (12 or 71). Bridge
balanced t. r. f. Drum control. Volume control: resis-
tance in r. f. plate. Stage shielding. Battery cable. C-
battery connections. Antenna: 10 to 100 feet. Cabinet
size: 28j x 11 x 14^ inches. Price not established.
NO. 542 RADIOLA 16
Six tubes; 3 t. r. f. (01-A), detector (01 A), 2 trans-
former audio (01-A and 112). One control. C-battery
connections. Battery cable. Antenna: outside. Cabinet
size: 16 x 8J x "i\ inches. Price: S69.50 without acces-
sories.
NO. 456. RADIOLA 20
Five tubes; 2 t. r. f. (99), detector (99), 2 transformer
audio (99 and 20). Balanced t. r. f. and regenerative de-
tector. Two dials. Volume control: regenerative.
Shielded. C-battery connections. Headphone connec-
tions. Antenna: 75 to 150 feet. Cabinet size: 19j x
Hi x 16 inches. Price $115 including all tubes.
NO. 457. RADIOLA 25
Six tubes; five type 99 and one type 20. Drum con-
trol. Super-heterodyne circuit. C-battery connections.
Battery cable. Headphone connections. Antenna: loop.
Set may be operated from batteries or from power mains
when used with model 104 loud speaker. Price; $165
with tubes, for battery operation. Apparatus for opera-
tion of set from the power mains can be purchased
separately.
NO. 493. SONORA F
Seven tubes; 4. t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Special balanced t. r. f.
Two dials. Plate current: 45mA. Volume control:
rheostat in r. f. Shielded. Battery cable. C-battery
connections. Output device. Antenna: loop. Console
size: 32 x 45j x 17 inches. Prices range from $350 to
$450 including loop and loud speaker.
NO. 494. SONORA E
Six tubes; 3 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Special balanced t. r. f.
Two dials. Plate current : 35 to 40mA. Volume control :
rheostat on r. f. Shielded Battery cable. C-battery
connections. Antenna: outside. Cabinet size: varies.
Prices: table $110; semi-console, $140; console, $240
including loud speaker.
NO. 530. KOLSTER, 7A AND 7B
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 12). One control. Volume control: rheostat
on r. f. Shielded. Battery cable. C-battery connections
Antenna: 50 to 75 feet. Prices: Model 7A, $125; Model
7B, with built-in loud speaker, $140.
NO. 495. SONORA D
Same as No. 494 except arrangement of tubes; 2
t. r. f., detector, 3 audio. Prices: table, $125; standard
console, $185; "DeLuxe" console, $225.
NO. 482. STEWART-WARNER 705 AND 710
Six tubes; 3 t. r. f., detector, 2 transformer audio.
All 01-A tubes. Balanced t. r. f. Two dials. Plate cur-
rent: 10 to 25mA. Volume control: resistance in r. f.
plate. Shielded. Battery cable. C-battery connections
Antenna: 80 feet. Cabinet sizes: No. 705 table, 26 j
x 11J x 1315 inches; No. 710 console, 29| x 42 x 17J
inches. Tentative prices: No. 705, $115; No. 710,
$265 including loud speaker.
NO. 483. STEWART-WARNER 525 AND 520
Same as No. 482 except no shielding. Cabinet sizes:
No. 525 table, 19J x 10 x 11 J inches; No. 520 console,
22J x 40 x 141J inches. Tentative prices: No. 525, $75;
No. 520, $117.50 including loud speaker.
NO. 459. STROMBERG-CARLSON 501 AND 502
Five tubes; 2 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two dials.
Plate current: 25 to 35mA. Volume control: Rheostat
on 1st r. f. Shielded Battery cable. C-battery connec-
tions. Headphone connections. Output device. Panel
voltmeter. Antenna: 60 to 100 feet. Cabinet sizes:
No. 501, 255 x 13 x 14 inches; No. 502, 28; S x 50,TS x 16|
inches. Prices: No. 501, $180; No. 502, $290.
NO. 460. STROMBERG-CARLSON 601 AND 602
Six tubes. Same as No. 549 except for extra t. r. f.
stage. Cabinet sizes: No. 601, 27,', x 16! x 14,3n inches;
No. 602, 28* x 51J x 19« inches. Prices: No. 601, $225;
No. 602, $330.
NO. 472. VOLOTONE VIII
Six tubes. Same as No. 471 with following exceptions;
2 t. r. i. stages. Three dials. Plate current: 2-mA.
Cabinet size: 26i x 8 x 12 inches. Price $140.
NO. 546. PARAGON "CONGRESS"
Six tubes; 2 t. r. f. (01-A), detector (01-A), 3 im-
pedance-coupled audio (two 01-A and 12 or 71). One
main control and three auxiliary adjustments. Volume
control: resistance in r. f. plate circuit. Plate current:
40 mA. C-battery connections. Tuned double-im-
pedance audio amplifier. Output device. R. F. coils are
shielded. Cable or binding posts. Cabinet size: 7x 18 x!9
inches. Price $90.00; without cabinet, $80.00.
New Formica Kit Panels
J^ECENT additions to the list of handsomely dec-
orated panels for famous kits include the Madi-
son Moore International One Spot (A. C.) E. T.
Flewellings Super Eight, and the new B*T Power
Six Electric Kit. There are also front and sub
panels for Karas (two dial) World's Record Super
Ten; Camfield Nine; Tyrman; Magnaformer, H. F.
L. Victoreen and many others.
These panels are sold by all leading jobbers
THE FORMICA INSULATION COMPANY
46 1 8 Spring Grove Avenue Cincinnati. Ohio
Any jobber or
dealer can get
Formica panels for you
ORMICA1
Made from Anhydrous Bakelite Desins
SHEETS TUBES -RODS
Formica has a
Complete Insulatir
Service for
manufacturers.
B
ELIMINATOR
VOLTMETER
Made for hard service but
always accurate and sensitive
Resistance, 1000 ohms per volt,
— for Radio service men, dealers
and manufacturers. Precision
d'Arsonval movement, 3/4 inch
scale, hand-calibrated. The
damping is very fine. Polished
base.
Ranges, 0-100
0-500 volts
Price #28.00
Write for booklet "Hoyt Meters
for Radio."
BURTON-ROGERS CO.
Sole Selling Agents
Boston Mass.
RADIO BROADCAST ADVERTISER
2.51
Selected for
Gooley Rayfoto
IT is significant that the S-M 220 audio trans-
former was selected before all others for the
Cooley Rayfoto telephoto apparatus. This
logical selection bears ouf past performance — •
for authority upon authority has made the
same selection until 22o's are used in more
popular receiver designs than any other trans-
former. Any number of unbiased laboratory
tests show the 220 to be supreme in the audio
field and the unofficial report of the testing
laboratory of the largest telephone manufac-
turer rates 22o's at the top of the list.
Remember, if it's real, true tone quality you
•want, you can pay out ten or twelve dollars
for an audio transformer but you can't possi-
bly get a better transformer than S-M 22o's
at $8.co each — for none better have ever been
made!
SILVER-MARSHALL, Inc.
838-B West Jackson Blvd. Chicago, 111.
Compiled exclusively for deal-
ers in radio sets, radio parts,
and for set builders. An
Amazing Catalog con-
taining the newest things
in the world of radio.
Unbeatable values in
Radio Parts, Kits
and Supplies of
National Fame.
A complete array
of Cabinets and
consoles, in all
latest styles, fin-
ishes and popular sizes
at Unmatched Prices.
The high quality of our prod-
ucts eliminates loss. Large
stocks offer you large selection.
Our speedy shipments insure your
customer'* good will and bigger profits for
you.
Silver Marshall Unipac in stock— all models
and types. Fully described and priced in our
catalog on page 64. Liberal discounts to the trade.
Immediate delivery.
Short Wave Section
Our catalog contains a section devoted to a show-
ing of the highest grade short wave receiving and
transmitting apparatus.
Also the finest electrical
appliances for use in the
home.
Shure Service means
sure profits. You can take
orders direct from our il-
lustrated list price catalog.
Whatever your radio
needs may be, you will find
them in our 1928 catalog.
Write for a copy TODAY.
SHURE RADIO COMPANY
:'. l.ll' Went Madison Street. Chicago. Ill,
ANNOUNCING
THE
BRACH RELAY
FOR THE
RAYFOTO RECEIVER
Approved by A. G. Cooley
Available Now, Write
L.S. BRACH Mfg. Corp.
IZ9 Sussex Ave. Newark, N. J.
AEROVOX products are ap-
proved by Austin G. Cooley
for his "RAY-FOTO" appa-
ratus
Faithful Service
The function of a power resistance
is to control voltage and current.—
accurately — permanently — silently.
AEROVOX PYROHMS used with
GOOD equipment make a BETTER
power unit.
AEROVOX PYROHMS are built
last — are used by more than 20 lead!
power unit manufacturers. — This is
conclusive evidence of their reliability-
accuracy —worthiness.
Made in all values of resistance
for continuous duty at 20, 40, 100 and
200 watts.
"•Bui/I 'Bf/Wr
70 Washington St., Brooklyn, N. Y.
AERO Corona Coil
Used in New
Cooley "Rayfoto"
Of course the new Cooley "Rayfoto" uses
an AERO Inductance Coil. This special
coil is designed to meet the exact speci-
fications of A. G. Cooley, whose "Ray-
foto" receiver so many experimenters will
build. For every inductance requirement
AERO Coils are proved best — by experts
and amateurs as well. Always specify
AERO Coils if you want the finest in
radio performance.
AERO PRODUCTS, Inc.
1722 Wilson Avenue
Chicago, III.
Cooley Ray-Foto
Printer Unit
The only available recorder
for this assembly
Machine Products, in close
* association with Austin G. Cooley,
inventor of the Cooley Ray-Foto Ma-
chine, is now manufacturing and ac-
cepting orders for the essential record-
ing apparatus required for the complete
assemble of this latest achievement in
the science of radio.
Write for details, prices, etc.
Presto Machine Products
Corp.
7O Washington Street
Brooklyn New York
for
COOLEY
"RAY-FOTO"
We have a modulation trans-
former conforming to the
specifications for the
COOLEY "RAY-FOTO"
Apparatus. The Price is
$950
Write us for details
National Company, Inc.
W. A. Ready, Pres.
Maiden Massachusetts
NATIONAL
Modulation Transformer
252
RADIO BROADCAST ADVERTISER
You'll like this
Distinctively Novel
Treatment of Radio
(OFF PRESS DECEMBER 1)
A POPULAR GUIDE
TO MODERN RADIO
By B. FRANCIS DASHIELL
of the U. S. Weather Bureau
Right up to the minute —
Clearexplanations of the basic
sciences involved in radio —
Discussions of apparatus and
equipment — special treat-
ment of weather effects—
101 diagrams; 8 full-page
plates —
The finest sort of Christ-
mas remembrance for radio
fandom.
Price $3.50
Clip this and mail with
remittance to
Williams & Wilkins Co.
Publishers of Scientific Books
Baltimore Maryland
Seventh Edition Just Off the Press
ROBISON'S MANUAL OF RADIO
TELEGRAPHY AND TELEPHONY
Completely Revised and Up-to-Date
Of the 6th edition of this book reviewed by QST
it was said this is perhaps
"The Best Radio Book That Ever
Came To This Desk"
The standard Navy book on radio originally prepared in
1907 by Lieutenant (last year Admiral and C-in-Cof U- S.
Fleet) S. S. Robison. The 6th edition and th^ present
edition revised by Commander S. C. Hooper, U. S. Navy,
late Radio Officer, U. S. Fleet.
Price $5.50 postpaid
(former edition sold for $8.00)
Address:
Secretary-Treasurer, U. S. Naval Institute
Annapolis, Md., U. S. A.
NEW PERPETUAL
RADIO
HANDBOOK
Loose-Leaf
Pocket Size
$3.50
POST PAID
COMPLETE WITH LEFAX 6-RING
FLEXIBLE POCKET BINDER
WRITE FOR FULL PARTICULARS ON
LOOSE-LEAF RADIO DATA SERVICE
LEFAX, INC., PHILADELPHIA, PA.
THIS RADIO CHRISTMAS
by
Z.eh Bouck
T IKE all people, I hate to brag. And I sin-
-L< cerely believe that there is no one in this
world who knows more about giving things
radio for Christmas than the writer. I have
had a radio laboratory for some ten years
now, to which manufacturers send samples of
their products. With the exception of an
occasional birthday, or a debt here and there,
this apparatus accumulates until around this
time of the year. And I'd give away a lot more
Christmas presents if radio manufacturers
only supplied green tissue paper and red
ribbons.
So it is most fitting that I should be telling
you how to spend your money on radio Christ-
mas presents — or perhaps it isn't. I find my-
self in somewhat the reverse situation of
Oscar Wilde's cynic who knew the price of
everything but the value of nothing. At any
rate, our ever-increasing horde of radio
burglars will find what I have to say of un-
equalified use.
From One Dollar Up
WE — or rather you — may start your pur-
chases from a dollar up. (Make sure you
do not start them with a dollar down. This
stretches Christmas out over too long a period
of time with rather fatal results to the Christ-
mas spirit.)
In the case of a radio Christmas present,
not everything within the various price ranges
can be considered. There are many parts
particularly designed for special circuits and
receivers, and unless you are aware that the
recipient is interested in this particular appa-
ratus you will do well to confine yourself, for
the greater part, to accessories.
One Dollar to Three Dollars
This class recommends itself to gifts among
the family — to brother, sister, cousins, aunts,
and all the rest sacred to Gilbert and Sullivan.
The following are really too useful for gifts:
One or two 01A type tubes
A loud speaker extension cord
A battery cable
A light socket antenna (for the gentle-
man with the loop set)
An antenna set
A set of 0.5, 1.0, 1.5, 2.0, 3.0, and 5.0-
megohm metallic grid leaks
At the very beginning we run into the in-
evitable book. The following are on our own
shelves:
FOR THE ENGINEER: Engineering Mathe-
matics, D. Van Nostrand and Company
FOR THE AMATEUR: The Radio Amateur's
Handbook, The American Radio Relay League,
Hartford, Connecticut, $1.00.
FOR THE AVERAGE FAN: The Outline of
Radio, by John V. L. Hogan, Little Brown
and Company, or How Radio Receivers Work,
by W. Van B. Roberts, published by RADIO
BROADCAST, Garden City, N. Y., $1.00
A subscription to The Bell Technical Journal
(195 Broadway, New York City) at $3.00
will be gratefully received by the engineer in
the family, and a subscription to QST (Amer-
ican Radio Relay League, Hartford, Conn.)
at $2.00 by the amateur or even broadcast fan.
Three Dollars to Five Dollars
As we go up a bit in price, the charity that
should begin at home evidences itself in gifts
outside the family — our purse strings loosen
and we splurge with:
Output filters
A set of five 1.0-mfd. bypass condensers
A telephone headset
A power tube
A filament relay
The following books for engineering folk:
Theory of Vibrating Systems and Sounds by
Crandall, S5.00. (D. Van Nostrand & Co.)
The Thermionic Vacuum Tube by H. J.
Van deBijI, (McGraw Hill), $5.00
A most acceptable and unique gift may be
effected by obtaining a copy of Radio Instru-
ments and Measurements from the Bureau of
Printing and Engraving, Government Print-
ing Office, Washington, for $.75 (no stamps)
and having it bound by Brentano's or some
similar establishment.
And a subscription to RADIO BROADCAST
is never out of place.
Five Dollars to Ten Dollars
A slide rule is always an acceptable present
to the engineering friend who possesses the
inevitable book, if-he hasn't a slide rule. Get
a Keuffel and Esser Polyphase Mannheim
ten-inch rule. Do not succumb to the seduc-
tive technicalities of various "duplex" and
"log log" designs. The engineer would thank
you, of course, for these last types, and use it,
perhaps, as a straight edge; but that's about
all.
You can always determine whether your
technical friend has the book you want to
give him or not. Just say to him, "I under-
stand that in hyperbolic space the character-
istic constant is negative, the degree of
negativity varying directly with the diver-
gence from Euclidean space. I want to check
up on this. Lend me your Crandall, or your
Morecroft or your Van de Bijl, will you?"
If he tells you he hasn't the book, you will
know he has it but doesn't want to loan it to
you.
The following are indispensable books:
The Manual of Radio Telegraphy and Tele-
phony, Admiral S. S. Robison, United States
Naval Institute, Annapolis, Md. $5.50
Principles of Radio Communication, J. H.
Morecroft, John Wiley and Sons, New York
City, $7.50 (and worth it!)
An electrical Engineering Handbook
Among parts and accessories, we have:
A QRS or Raytheon Rectifying tube
An output filter
A resistance-coupled amplifying kit
A filament control relay (to control your
power unit and A battery from the set's on-off
switch)
A tube rejuvenator
A Balsa Speaker kit
A loud speaker unit
Ten Dollars to Fifteen Dollars
The customary way to give Christmas gifts
is to establish the understanding that you do
not believe in the exchange of gifts — that you
are giving nothing except cards — and then
give presents anyway to make your friends
uncomfortable. We suggest the following in
the line of this expensive misanthropy:
An "A" supply filter such as the "A-Box"
A good trickle charger
^ l^t
A Balsa speaker kit
Fifteen Dollars to Twenty Dollars
We are fairly well above the usual engineer-
ing books, but you might try a set of Rabelais.
Boni and Liveright have a new limited edition
selling for $20.00
Then there are:
A complete set of "B" batteries (a really
fine present!)
A cone loud speaker
A set of good audio transformers
A - - kit
A standard high-rate charger
A Balsa speaker kit
Twenty Dollars to Twenty-Five Dollars
We may now leave on the price tags, and
suggest —
RADIO BROADCAST ADVERTISER
253
A cone loud speaker
A complete set of A-C tubes
An "A" battery and charger combination
A kit
A radio table (a good one).
Twenty-Five Dollars to Fifty Dollars
We now leave gifts to the family and
friends and consider presents for elevator boys,
postmen, janitors, ice-men and others requir-
ing special attention.
A very fine cone or Balsa speaker.
A well-designed "B" and "C" battery
eliminator.
A- -kit
From Fifty Dollars up
We started with gifts for the family, and
we conclude with the same. If there is a very
expensive bit of apparatus for which you
have long yearned — some deluxe speaker,
perhaps a Norden Hauck Super or a Radiola
Borgia model, or maybe a Wheatstone Bridge
or a Leeds & Northrup type K potenti-
ometer— why give it to the family for Christ-
mas.
And in closing let me advise you to do your
Christmas shopping early — early on the
morning of December twenty-fourth.
TO
'RADIO
DEALERS/
The R. B. Laboratory Inform'
ation Sheets have been appear-
ing in RADIO BROADCAST since
June, 1926. They are a regular
feature in each issue and they
cover a wide range of inform-
ation of value to the radio
experimenter and set builder.
We have just reprinted Lab.
Sheets Nos. i'88 from the
June, 1926, to April, 1927,
issues of RADIO BROADCAST.
They are arranged in numerical
order and are bound with a
suitable cover. They sell at
retail for one dollar a set.. Write
for dealers' prices. Address
your letter to
I
Circulation Dept.,
RADIO BROADCAST
Garden City, N. Y.
A HigH-POlVERED 10 -TUBE
MODEL FOR 1928
STANDARD ADMIRALTY MODEL
NORDEN-HAUCK
IMPROVED SUPER- 10
LICENSED UNDER HOGAN PATENT 1,014,002
"Highest Class ''Receiver in the World"
This new and advanced design brings to you all the luxury and performance you
could possibly desire in a radio receiver. Absolutely nothing has been omitted to
provide supreme reception — a new standard previously unknown.
The up-to-the-minute engineering principles found exclusively in the improved
Super-10 are comparable to the high compression head and super charger in an auto-
mobile engine.
In the Norden-Hauck Improved Super-10 you have
— Wonderful Selectivity
—Faithful Reproduction with any Degree of Volume
— Signals received at only one point
— Two major tuning controls for all wave lengths
— Wave band 200/550 meters (adaptable down to low waves and as high as
6000 meters with removable coils)
Material and workmanship conform to U. S. Navy specifications.
The improved Super-10 is sold complete as a manufactured receiver, or we are glad
to furnish blue prints and all engineering data for home construction.
Upon request, new attractive illustrated literature will be promptly mailed to you
without cost or obligation on your part.
Tear off and mail today
Your correspondence or inquiry
for further information is
cordially invited
Write direct to
NORDEN-HAUCK, INC.
ENGINEERS
"Builders of the Highest Class
Radio Apparatus in the World"
MARINE BLDG., PHILA., PA., U. S. A.
Cable: Norhauck
NORDEN-HAUCK, INC.
MARINE BLDG., PHILA., PA.
Gentlemen:
n Without obligation on my part send me complete
literature on the new improved Super-10.
D I enclose $2.00. for which send me, postpaid,
complete Blue Prints and operating instructions
for the new improved Super-10.
D I enclose $1 .00 for which send me Blue Prints of
the Model 500 B. C. Power Unit.
Name
Address. .
•-R. E.
YOU GET
Free Technical Advice by R. E. Lacault, E. E.
on Parts and Kits Purchased from Us
Let Him Help You Select the Best
Send for R. E. L. Handbook and Discount List
R. E. LACAULT
Radio Electric Laboratories
1931 Broadway New York City
Read Radio Broadcast
every month. You can't afford to miss an issue. Order
your copy from your Newsdealer or Radio Store. If
you wish to subscribe direct send $4.00 for one year
or JS6.0O for two years.
DOUBLEDAY, PAGE & COMPANY
Garden City, N. Y.
Learn the Code at Home With the Omnigraph
Morse and Wireless — taught at home in
half usual time <ind at trifling cost. Omni-
graph Automatic Transmitter will send,
on Sounder or Buzzer, unlimited messages,
any speed, just as expert operator would.
Adopted by U. S. Govt. and used by lead'
ing Universities, Colleges, Technical and
Telegraph Schools throughout U. S. Send 6c for dialog.
OMNIGRAPH MFG. CO., 1 3K, Hudson St., New York
O:
DIAL.
advanced circuit. AH
Bteel chassis totally shielf
Balanced parts of best quality.
Marvelous power and selectivity. Get*
" e long range stations as clear ana bell.
ledial UMM control. An unsurpassed vaine-
st one of our many mighty bargains.
FREE Log and Call Book
and Big N»w Catalog- just off the press. Full of
Radio Bargains. Send for your free copy now!
American Auto & Radio Mfg. Co.
Dtp!. 122 Arnericin Radio Blrig., Kansas City, Ma. 2
iy
RADIO
254
RADIO BROADCAST ADVERTISER
While your
neighbors are
cussin'the static
Your set, with its Dubilier Light-Socket
Aerial, is bringing the programs in smooth
as silk. It's a fact! This little aerial, which
you simply attach to the set and plug into
the nearest light socket, reduces both static
and interference to a marked degree. It
uses no current whatever and absolutely
eliminates the lightning hazard. Costs you
nothing to prove it, for the Dubilier Aerial
is sold by all good dealers on a 5-day,
money-back basis. If your dealer can't sup-
ply you, write direct to us. Price, $1.50.
Dubilier
LIGHT SOCKET AERIAL
// you're planning to build a paver-unit
make sure that the condenser blocks you intend
to use are built to withstand long hours of heavy-
duty service. Dubilier blocks have an excessive
high factor of safety and a "life" that makes
them by far the most economical to buy. Full
instructions enclosed with each block unit.
DUBILIER CONDENSER CORP.
4377 Bronx Blvd. New York, N. Y.
Dubilier
CONDENSERS
77. TUBES — A booklet for the heRinner who is interested
in vacuum tubes. A non-technical consideration of the
various elements in the tube as well as their position in the
receiver. CLEARTRON VACUUM TUBE COMPANY.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
91. VACUUM TUBES — A booklet giving the characteristics
and uses of various types of tubes. This booklet may be
obtained in English, Spanish, or Portuguese. DEFOREST
RADIO COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS — A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new 4OO-milliampere rectifier tube. CARTER RADIO
COMPANY.
97. HIGH-RESISTANCE VOLTMETERS — A folder giving in-
formation on how to use a high-resistance voltmeter,
special consideration being given the voltage measurement
of socket-power devices. WESTINGHOUSE ELECTRIC: A:
MANUFACTURING COMPANY.
102. RADIO POWER BULLETINS— (Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
103. A. C. TUBES — The design and operating character-
istics of a new a. c. tube. Five circuit diagrams show how
to convert well-known circuits. SOVEREIGN ELECTRIC &
MANUFACTURING COMPANY.
38. LOG SHEET — A list of broadcasting stations with
columns for marking down dial settings. U. S. L. RADIO,
INCORPORATED.
41. BABY RADIO TRANSMITTER OF QXH-QEK — Descrip-
tion and circuit diagrams of dry-cell operated transmitter.
BURGESS BATTERY COMPANY.
42. ARCTIC RADIO EQUIPMENT — Description and circuit
details of short-wave receiver and transmitter used in
Arctic exploration- BURGESS BATTERY COMPANY.
43. SHORT-WAVE RECEIVER OF QXH-QEK — Complete
directions for assembly and operation of the receiver.
BURGESS BATTERY COMPANY.
58. How TO SELECT A RECEIVER — A commonsense
booklet describing what a radio set is, and what you should
expect from it. in language that any one can understand.
DAY-FAN ELECTRIC COMPANY.
67. WEATHER FOR RADIO — A very interesting booklet
on the relationship between weather and radio reception,
with maps and data on forecasting the probable results
TAYLOR INSTRUMENT COMPANIES.
USE THIS BOOKLET COUPON
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, N. Y.
Please send me fat no expense) the following book-
lets indicated by numbers in the published list above:
, ,
I Name.
1 Address.
(Name)
(Street)
(City) (State)
ORDER BY NUMBER ONLY
I This coupon must accompany every request. RB 1-28
73. RADIO SIMPLIFIED — A non-technical booklet giving
pertinent data on various radio subjects. Of especial in-
terest to the beginner and set owner. CROSLEY RADIO COR-
PORATION.
74. THE EXPERIMENTER — A monthly publication which
gives technical facts, valuable tabKs, and pertinent informa-
tion on various radio subjects. Interesting to the experi-
menter and to the technical radio man. GENERAL RADIO
COMPANY.
76. RADIO INSTRUMENTS — A description of various
meters used in radio and ,-.ectrical circuits together with a
short discussion of their uses. JEWELL ELECTRICAL IN-
STRUMENT COMPANY.
78. ELECTRICAL TROUBLES — A pamphlet describing
the use of electrical testing instruments in automotive work
combined with a description of the cadmium test for stor-
age batteries. Of interest to the owner of storage batteries.
BURTON ROGERS COMPANY.
95. RESISTANCE DATA — Successive bulletins regarding
the use of resistors in various parts of the radio circuit.
INTERNATIONAL RESISTANCE COMPANY.
96. VACUUM TUBE TESTING — A booklet giving pertinent
data on how to test vacuum tubes with special reference to
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT
COMPANY.
98. COPPER SHIELDING — A booklet giving information
on the use of shielding in radio receivers, with notes and
diagrams showing how it may be applied practically. Of
special interest to the home constructor. THE COPPER AND
BRAS; RESEARCH ASSOCIATION.
99. RADIO CONVENIENCE OUTLETS — A folder giving
diagrams and specifications for installing loud speakers in
various locations at some distance from the receiving set.
YAXLEY MANUFACTURING COMPANY.
105. COILS — Excellent data on a radio-frequency coil
with constructional information on six broadcast receivers,
two short-wave receivers, and several transmitting circuits
AERO PRODUCTS COMPANY.
1 06. AUDIO TRANSFORMER — Data on a high-quality
audio transformer with circuits for use. Also useful data
on detector and amplifier tubes. SANGAMO ELECTRIC COM-
PANY.
107. VACUUM TUBES — Data on vacuum tubes with
facts about each. KEN-RADIO COMPANY.
108. VACUUM TUBES — Operating characteristics of an
a.c. tube with curves and circuit diagram for connection
in converting various receivers to a.c. operation with a
four-prong a.c. tube. ARCTURUS RADIO COMPANY..
109. RECEIVER CONSTRUCTION — Constructional data on
a six-tube receiver using restricted field coils. BODINE
ELECTRIC COMPANY.
Now That Everybody
Demands
Electrically-Operated
Radios!
Dongan is in Production
on All Types of
A. C. Tube Transformers
Six months ago Dongan en-
gineers were preparing for
the day when the industry
unanimously accepted com-
plete electrical operation of
receiving sets. For every new
tube brought forth, Dongan
designed the proper trans-
former or power unit.
To-day you can secure from
the production line Trans-
formers and Power Supply
Units for whatever type of
AC or ABC Tube you
have chosen. For Dongan
has been in production on
approved types for many
months.
Here is the Newest
No. 6515 Transformer for use
with 4 UX 226, 1 UY 227 A
C Tubes and 1 UX 171 Tube.
Together with a B Elimina-
tor, this new transformer
will convert old type set in-
to an efficiently operating
A C set.
$4.75 List
This is one of 14 types rang-
ing in price from $3.50 to
$8.00 for use with the new
types of A C Tubes.
Manufacturers
are invited to write for any kind of infor-
mation from our engineering department.
Fans — order from your dealer or send
check or money order to factory direct.
No. 5553
ABC
POWER UNIT
for UX 226,
UY227, UX
171, and UX
280 Tubes
$22 List
DONGAN ELECTRIC MFG. CO.
2991-3001 Franklin St., Detroit, Michigan
\TRANSFORMERSot MERIT (or FIFTEE, I YEARS ,
RADIO BROADCAST ADVERTISER
•2,55
1 10. RECFIVER CONSTRUCTION — Circuit diagram and
constructional information for building a five-tube set
usint; restricted field coils. BODINE ELECTRIC COMPANY.
lit. STORAGE BATTERY CARE — Booklet describing the
care and operation of the storage battery in the home.
MARKO STORAGE BATTERY COMPANY.
112. HEAVY-DUTY RESISTORS. Circuit calculations and
data on receiving and transmitting resistances for a variety
of uses, circuits for popular power supply circuits, d.c. resis-
tors for battery charging use. WARD LEONARD ELECTRIC
COMPANY.
1 13. CONE LOLTD SPEAKERS — Technical and practical in-
formation on electro-dynamic and permanent magnet type
cone loud speakers. THE MAGNAVOX COMPANY.
114. TUBE ADAPTERS — Concise information concerning
simplified methods of including various power tubes in
existing receivers. ALDEN MANUFACTURING COMPANY.
115. WHAT SET SHALL 1 BUILD? — Descriptive matter,
with illustrations, of fourteen popular receivers for the home
constructor. HERBERT H. FROST, INCORPORATED.
104. OSCILLATION CONTROL WITH THE "PHASATROL"—
Circuit diagrams, details for connection in circuit, and
specific operating suggestions for using the "Phasatrol"
as a balancing device to control oscillation. ELECTRAD,
INCORPORATED.
A KEY TO RECENT
RADIO ARTICLES
By E. G. SHALKHAUSER
THIS is the twenty-fifth installment of references
to articles which have appeared recently in var-
ious radio periodicals. Each separate reference
should be cut out and pasted on 4" x 6" cards for
filing, or pasted in a scrap book either alphabet-
ically or numerically. An outline of the Dewey
Decimal System (employed here) appeared last in
the January RADIO BROADCAST.
R4O2. SHORT-WAVE SYSTEMS. SHORT WAVES,
QST. Aug., 1927. Pp. 9-14. \-Meter
"The |-Meter Band Officially Opened," B. Phelps and
R. S. Kruse.
Detailed information on J-meter transmitting and re-
ceiving sets is presented. It is stated that tubes having the
XL filaments have a very short life at these frequencies,
best results being obtained from the old UV-2O2 tubes,
The antenna system, and the, methods used in determining
the length of the wave transmitted, are shown. The field
tests indicate the manner in which signals decrease in
strength and show the location of dead spots.
Ri32.i. AMPLIFYING ACTION: INDUCTIVE AMPLIFIERS,
COUPLING. Audio.
QST. Aug., 1927. Pp. 1 5-20.
" Better Audio Amplification for Short-Wave Receivers,"
L. W. Hatry.
The writer shows the practical use of more than one audio
stage of amplification for short-wave receivers. In order to
insure more uniform volume from headphones, whether
listening to foreign or domestic stations, a switching or a
shunt resistance system is described. The type of audio
transformer to be used depends greatly upon the type of
reception desired, a scheme being shown whereby an am-
plifier may be made either peaked or flat by using a tuned
rejector circuit.
6. RADIO TELEPHONE SETS
(ELECTRON-TUBE).
TRANSMITTER,
Short-Wave Crystal.
QST. Aug., 1927. Pp. 21-24.
"Cuban 6 XJ." F. H. Jones and H. P. Westman.
The construction and the tuning of a first-class phone
station operated on 20 meters, are outlined. A crystal,
having a natural period of 159.6 meters, controls the trans-
mitted frequency. The set consists of an oscillator and
three amplifiers. Instead of using the Heising constant-
current method of modulation, the series method of plate
modulation is employed with good results. A circuit diagram
and a list of parts are shown.
R2i3. HARMONIC METHODS. HARMONICS,
QST. Aug., 1927. Pp. 34-35. Determination of.
"The Identification of Radio- Frequency Harmonics,"
J. E. Waters.
A method of determining and identifying radio-frequency
harmonics when making measurements of radio- frequency
oscillations is outlined. Use is made of a standard wave-
meter, an oscillator, and a receiver.
Ri 13. TRANSMISSION PHENOMENA.
TRANSMISSION,
Sbort-Waoe.
nd Its Practical
Cm. TRANSMISSION PHENOM
QST. Aug., 1927. Pp. 36-42.
"Short-Wave Radio Transmission
Uses," C. W. Rice. (Continued.)
The variation of signal strength with distance is discussed,
taking into consideration the effect of multiple reflection.
In order to choose the proper wavelength to use for distant
transmission in summer daylight, a theoretical chart is
prepared, showing probable performance of different waves.
Conclusions drawn point to the following. Below 10 meters
distant communication is impossible; theplaneof polariza-
tion in the sky wave is no determining factor for energy
flux density and for ray paths; different waves give best
results between two given points; low-angle radiation is
best for long-distance work.
RiSi.yi. QUARTZ. QUARTZ.
RADIO BROADCAST. Sept., 1927. Pp. 271-273.
"Piezo-Electric Crystals," M. T. Dow.
The writer explains the use of quartz crystal oscillators
in the calibration of frequency meters. How to distinguish
between the harmonics that are heard when two oscillators
are in operation, is fully outlined. Photographs and circuit
diagrams illustrate the points in question.
"A" Batteries
"A" Battery Eliminators
Special Sockets
Noise
Hum
0
Leading radio engineers approve and
endorse the Sovereign Heater Type A-C
Tube. They know that A-C Tubes
give results that can be obtained in no
other manner.
Think — with A-C Tubes all you ever
will have to do is press a button — switch
on your set just as you switch on an
electric light. There's no bother with
"A" batteries or "A" battery elimina-
tors, or battery chargers, no noise, no
microphonics — nothing but pure, round,
undistorted tones.
Bring your set up-to-date. If your
dealer cannot supply you with Sover-
eign A-C Tubes for standard sockets,
write us. Special treatise with diagrams
free. Write
Sovereign Electric & Mfg. Company
127 No. Sangam»n St. Chicago, Illinois
Set Builders
and Amateur
Transmitters —
Here are your
Instruments!
D. C. and A. C. Panel Types in
flush style cases — Models 506,
and 517, 2"; and Models 301 and
476, 3j" sizes. A complete line
of Voltmeters, Ammeters and
Milliammeters, as well as
Thermo-Couple types, all uni-
form in appearance. Nothing on
the market can compare with
them in quality of workmanship
and electrical features.
It has required years to redesign
the famous Weston Standards
down to these small sizes and
offer them at such low prices
for such high quality. Improve
upon your old sets when build-
ing the new. Write for Circular
J — the new booklet which com-
pletely covers the Weston Radio
Line.
WESTON ELECTRICAL INSTRUMENT CORPORATION
179 Weston Ave. Newark, N. J.
WE WON
INSTRUMENTS
256
RADIO BROADCAST ADVERTISER
Micrometric
Control
for
Your Set!
The Volume Control Clarostat
now makes its bow. It's a little
fellow, compact, good looking, inex-
pensive, handy — just the thing for ap-
plying adjustable yet positive resistance
in various parts of the set. And it's a
genuine Clarostat through and through.
Control loud-speaker volume;
match transformers for best tone
quality; tune loud-speaker to your
taste; get maximum sensitivity out
r. f. and detector tubes; control regener-
ation micrometrically, especially on
short waves — all with Volume Control
Clarostat. And there are many other
ways now becoming popular, for im-
proving your set with micrometric re-
sistance control.
The Volume Control Clarostat has re-
sistance range of practically zero to
500,000 ohms in several turns of knob.
Ample current-carrying capacity for all
receiver applications. Holds its resist-
ance adjustment. Silent in operation.
Screw terminals. One-hole mounting.
And only $1.50 list.
mr^
ut of ^B
jener-
Iv on
VOLUME CONTROL
Of course you must continue to use the
larger Standard Clarostat for B-elim-
inator applications, and the giant
Power Clarostat for A-B-C power
units, line-voltage control, and
power amplifiers, as heretofore.
There's a Clarostat for every pur-
pose. Make sure, however, you
get a genuine Clarostat — look for
distinctive green box and name
CLAROSTAT stamped on nickel
shell. Don't be fooled!
Ask your dealer for literature on
Clarostats and how to improve your
radio set. Or write us direct
American Mechanical Laboratories
INCOKPOKATED
Special* tt* in Variable Kcsislitnt
285 N. Sixth Street
Brooklyn, N. Y.
R] 13- TRANSMISSION PHENOMENA. TRANSMISSION
Proc. I. R. £. June, 1927. Pp. 501-517. Short- Wave
"Some Practical Aspects of Short-Wave Operation at
High Power," H. E. Hallborg.
Propagation data on the frequency range of 3000 to
30,000 kilocycles are submitted. A correlation is shown be-
tween wave frequency and angle of projection of the wave
front. The effect of ionization on the angle of projection is
indicated. Some calculations are given of probable values of
attenuation constant.
The importance of frequency stabilization is discussed,
and three typical circuits for utilizing control crystals are
described. Features of the design and adjustment of a
2o-kw. power amplifier are also outlined. Antenna and
antenna feed systems are discussed, and graphical results ol
comparisons of various antenna types are given. The rela-
tive importance of static at short wavelengths is considered
The author's anticipation of the density of the short wave is
summarized.
R6i2. SHORT-WAVE STATIONS. STATIONS,
Proc. L R. E. June, 1927. Pp. 467-409. Short-Wave.
Short-Wave Commercial Long-Distance Communica-
tion," H. E. Hallborg, L. A. Briggs, and C. W. Harisell.
The development of short-wave communication by the
Radio Corporation of America is outlined. A summary of
short-wave installations, with call letters, wavelengths, and
services to which each installation is assigned, is submitted.
Traffic charts showing the diurnal and seasonal character-
istic of various wavelengths over typical circuits are also
shown. An outline of the technical problems inherent to the
development of tubes and transmitter circuits is discussed.
Methods are described for obtaining proper operation 01"
tubes and transmitters at these very short wavelengths.
The paper is illustrated with typical pictures and charts
showing transmitter development and traffic performance.
R8oo (512.82). COMPLEX VARIABLES. FUNCTIONS.
Proc. 1. R. E. June, 1927. Pp. 519-524.
"Maximization Methods for Functions of a Complex
Variable," V. B. Roberts.
The maxima and minima of a function of a real variable
are found by equating to zero the derivative of the function.
In the case of a function of a complex variable, however, the
derivative is a vector quantity, so that conditions may be
imposed upon its direction as well as upon its magnitude.
These various conditions lead to maxima and minima of the
various aspects of the function. Rules are developed for
setting up equations giving the various maximizing condi-
tions, and a simple example is given illustrative of the use
of the rule.
PHASE RELATIONS.
R24O. PHASE DIFFERENCE.
Radio, Aug., 1927. Pp. 2l-ff.
"Phase Relations in Radio," J. E. Anderson.
Of importance to radio experimenters is this discussion
on the effect of phase relation between current and voltage
in amplifier circuits. To illustrate the point, the phase con-
ditions in a 4-tube resistance-coupled amplifier are analyzed
in detail. Impedance- and audio-transformer coupled circuits
are also discussed and the points to be observed are men-
tioned.
R334- FOUR-ELECTRODE TUBES FOUR-ELECTRODE
Radio. Aug., 1927. P. 23-24. CHARACTERISTICS.
"The Static and Dynamic Characteristics of a Double-
Grid Vacuum Tube," H. R. Lubcke.
Static and dynamic characteristics of Van Home double-
grid vacuum tubes are graphed and discussed. It is noted
that (i) a change in characteristics accompanies a change
in frequency; (2) high plate voltages should be used because
of hi-mu characteristics; (3) the inner grid should have a
l-voltC bias and the outer grid a 3-volt Cbias; (4) the plate
impedance of the tube should match that of the transformer
primary in radio-frequency amplification.
R8oo. (530.) PHYSICS. ULTRA-VIOLET
RAYS.
RADIO BROADCAST. Sept., 1927. Pp. 263-265.
"A Discovery That Newton Missed," J. Stokley.
The history of ultra-violet rays, starting with the time of
Newton two centuries ago, continuing with their discovery
by Ritter, and ending with an explanation of their use made
to-day in medical sciences, is given.
RR356. TRANSFORMERS. TRANSFORMERS,
RADIO BROADCAST. Sept., 1927. Construction of
Pp. 274-278.
"Home-Constructing Transformers and Chokes for
Power-Supply Devices," H. S. Davis.
By means of charts and certain fundamental mathemati-
cal formulas, sufficient information may be obtained to de-
sign and construct power transformers and choke coils for
use in a.c. operated receivers. Of importance is said to be the
characteristics of secondary windings, i. e., voltage current
and power values, total turns in each winding, size and
amount of core and wire, etc.
R330. ELECTRON TUBES. ELECTRON TUBES,
RADIO BROADCAST. Sept., 1927. Pp. 284-285. New A. C.
"The New A. C. Tubes," Radio Broadcast, Laboratory
Staff.
Information and data on the operation of various a.c.
tubes now on the market show how these may vary in per-
formance. From the writers viewpoint, a.c. operated tubes
still belong in the experimental class.
Erratum.
AN ERROR occurred in the circuit diagram
•** of the "Shielded Six" receiver published
in the November, 1927, issue of RADIO BROAD-
CAST. The connection indicated between terminal
Mo. 6 of the third coil socket and the negative
terminal of the detector tube socket, should be
gnored. If this connection is made the C bat-
tery will be short-circuited and the detector will
operate very inefficiently.
RADIO PARTS
for 'Discriminating
J Set Builders °
Bradjminit A •
This fixed resistor is scientifically
treated to resist moisture. It is not
affected by temperature, moisture
or age. Provides the ideal resist-
ance for B-eliminator hookups re-
quiring fixed resistors of quality.
The re-
markable
accuracy
of t h e
Bradley-
ohm - E
has caused it to
become standard
equipment for accurate plate voltage
control onmanyleadingB-eliminators.
Use it -
L*c^«_»iiic aidjiuan-i ' ^
equipment for accurate plate voltage
'•""*'"! onmanyleadingB-eliminators.
on your power-unit hookups.
BradWleak
This vari-
able grid
leak pro-
vides the
precise
grid leak value for best results with
every tube.Try it on your set and no-
tice the greatly improved reception.
Bradjejcstat
The per-
fect fila-
ment con-
trol. Easily
installed in
place of rheo-
stats now in service. Gives noiseless,
stepless filament control for all tubes.
Use Bradleystats on your next set.
Electric Controlling Apparatus
M1LWAUKE E. X=^. WISCONSIN
RADIO BROADCAST ADVERTISER
257
Tone Control from
your Easy Chair
The New No. 3
* g x->
ModtfpluG
With 20 Feet of Cord
Just lounge in your easy chair, and let
the program come in smoothly modu-
lated as it changes in character. No
more jumping up to adjust the dials
every time the station changes from vo-
cal to orchestration. Simply tune with
your dials to maximum strength and
clarity of station, then from your easy
chair, with 20 feet of cord, use Modu-
plug No. 3 to smooth the reception
down to any degree of tone, without
changing the ratio of high and low notes.
Centralab Modu-Plug gives any degree
of volune from a whisper to maximum.
Can also be used to provide a very con-
venient method of connecting two speak-
ers in series at some distance from the
receiving set.
No 3, $3.00; Regidar Cord Type or Jack
Type, each $2.50. All mailed C. O. D.
Centralab Power Rheostat
This sturdy unit is a "knock-out" for
warp-proof, heat-proof performance in
socket power circuits. The heat-proof
characteristic permits continuous oper-
ation at temperatures of 482° F. and be-
yond. Special design and construction
assure this. The resistance wire is
wound on metal core, asbestos insulat-
ed. The wire is firmly held in position at
all times because the metal core will ex-
pand under heat in the same degree as
tlir wire. This provides a smooth act-
ing control under all conditions.
Smooth regulation is further insured by narrow
mistance strips. The narrow width gives small
resistance jumps per linn.
Compact 2" diameter: 1" behind panel. Single
bole mounting. BakeHteknob. ohms r>on. n:,u.
150, 50, 15, 6, 3, .2, .5— price. $1.25. Can also
be furnished as a potentiometer.
At dealer's, or C. O. D. Send postal for new circuit
literature. Tou need this ideal Power Rheostat.
Central Radio Laboratories
22 Keefc Ave., Milwaukee, Wis.
Gen
What Kit Shall I Buy?
HE list of kits herewith is printed as an exten-
sion of the scope of the Service Department of
RADIO BROADCAST. // is our purpose to list here
the technical data about kits on which information
is available. In some cases, the kit can be pur-
chased from your dealer complete; in others, the
descriptive booklet is supplied for a small charge
and the parts can be purchased as the buyer likes.
The Service Department will not undertake to
handle cash remittances for parts, but when the
coupon on page 258 is filled out, all the informa-
tion requested will be forwarded.
201. SC FOUR-TUBE RECEIVER — Single control. One
stage of tuned radio frequency, regenerative detector,
and two stages of transformer-coupled audio amplification.
Regeneration conirol is accomplished by means of a variable
resistor across the tickler coil. Standard parts; cost approxi-
mately $58.85.
202. SC-I1 FIVE-TUBE RECEIVER — Two stages of tuned
radio frequency, detector, and two stages of trans-
former-coupled audio. Two tuning controls Volume control
consists of potentiometer grid bias on r.f. tubes. Standard
parts cost approximately $60.35.
203. "H!-Q" KIT — A five-tube tuned radio-frequency set
having two radio stages, a detector, and two transformer-
coupled audio stages. A special method of coupling in the
i.f. stages tends to make the amplification more nearly equal
over the entire band. Price $63.05 without cabinet.
204. R. G. S. KIT — A four-tube inverse reflex circuit,
hav ng the equivalent of two tuned radio-frequency stages,
detector, and three audio stages. Two controls. Price $69.70
without cabinet.
205. PIERCE AIRO KIT — A six-tube single-dial receiver;
two stages of radio- frequency amplification, detector, and
three stages of resistance-coupled audio. Volume control
accomplished by variation of filament brilliancv of r.f.
tubes or by adjusting compensating condensers. Complete
chassis assembled but not wired costs $42.50.
206. H & H-T. R. F. ASSEMBLY — A five-tube set; three
tuning dials, two steps of radio frequency, detector, and 2
transformer-coupled audio stages. Complete except for base-
board, panel, screws, wires, and accessories. Price $30.00.
207. PREMIER FIVE-TUBE ENSEMBLE — Two stages of
tuned radio frequency, detector, and two steps of trans-
former coupled audio. Three dials. Parts assembled but
not wired. Price complete, except for cabinet, $35.00.
208. "QUADRAFORMER VI" — A six-tube set with two tun-
ing controls. Two stages of tuned radio frequency using
specially designed shielded coils, a detector, one stage of
transformer-coupled audio, and two stages of resistance-
coupled audio. Gain control by means of tapped primaries
on the r.f. transformers. Essential kit consists of three
shielded double-range "Quadraformer" coils, a selectivity
control, and an "Ampitrol," price $17.50. Complete parts
$70. 1 5.
209. GEN-RAL FIVE-TUBE SET — Two stages of tuned
radio frequency, detector, and two transformer-coupled
audio stages. Volume is controlled by a resistor in the plate
circuit of the r.f. tubes. Uses a special r.f. coil ("Duo-
Former") with figure eight winding. Parts mounted but
not wired, price $37.50.
210. BREMER-TULLY POWER-SIX — A six-tube, dual-
control set; three stages of neutralized tuned radio frequency,
detector, and two transformer-coupled audio stages. Re-
sistances in the grid circuit together with a phase shifting
arrangement are used to prevent oscillation. Volume control
accomplished by variation of B potential on r.f. tube.
Essential kit consists of four r.f. transformers, two dual
condensers, three small condensers, three choke coils, one
5OO,ooo-ohm resistor, three i soo-ohm resistors, and a set
of color charts and diagrams. Price $41.50.
212. INFRADYNE AMPLIFIER — A three-tube intermediate-
frequency . amplifier for the super-heterodyne and other
special receivers, tuned to 3490 kc. (86 meters). Price $25.00.
213. RADIO BROADCAST "LAB" RECEIVER — A four-tube
dual-control receiver with one stage of Rice neutralized
tuned-radio frequency, regenerative detector (capacity
controlled), and two stages of transformer-coupled audio.
Approximate price, $78.15.
214. LC-27 — A five-tube set with two stages of tuned-
radio .requency, a detector, and two stages of transformer-
coupled audio. Special coils and spec al means of neutralizing
are employed. Output device. Price $85. 20 without cabinet.
215. LOFTIN-WHITE — A five-tube set with two stages of
radio frequency, espec ally designed to give equal amplifica-
lion at all frequencies, a detector, and two stages of trans-
former-coupled audio. Two controls. Output device. Price
$85.10.
216. K.H.-27 — A six-tube receiver with two stages of
neutralized tuned radio frequency, a detector, three stages
of choke-coupled audio, and an output device. Two controls.
Price $86.00 without cabinet.
217. AERO SHORT-WAVE KIT — Three plug-in coils de-
signed to operate with a regenerative detector circuit and
having a frequency range of from 19,900102306 kc. (1510130
meters). Coils and plug only, price $12. 50.
218. DiAMOND-op-THE-AiR — A five-tube set having one
stage of tuned-radio frequency, a regenerative detector
one stage of transformer-coupled audio, and two stages of
resistance-coupled audio. Volume control through regenera-
tion. Two tuning dials.
2ig. NORDEN-HAUCK IMPROVED SUPER 10 — Ten tubes;
five stages of tuned radio frequency, detector, and four stages
of choke- and transformer-coupled audio frequency. Two
controls. Price £260.00.
220. BROWNING-DRAKE— Five tubes; one 5*age tuned
radio frequency (Rice neutralization), regenerative detector
(tickler control), three stages of audio (special combination
of resistance- and impedance-coupled audio). Two controls.
CelatsiteWire
A cable of fine, tinned copper
wires with non-inflammable
Celatsite insulation. Ideal for
sub-panel or point-to-point
wiring. Strips easily, solders
readily. Nine beautiful colors;
sold only in 23 ft. coils, in car-
tonscolored tomatchcontents.
Acme
Celatsite Wire
Tinned copper bus bar hook-
up wire with non-inflam-
mable Celatsite insulation, in
9 beautifu 1 colors. Strips .„.
easily, solders readily, won't ||
crack at bends. Sizes 14, 16,
18, 19; 30 inch lengths.
Spaghetti Tubing
Oil, moisture, acid proof; highly
dielectric- — used by leading engi-
neers. Nine colors, for wire sizes 12
to 18; 30 i nch 1 engths. (We also
make tinned bus bar, round and
square, in 2 and 2)2 ft. lengths.)
Stranded Enameled
Antenna
Best outdoor antenna
you can buy. Seven
strands of enameled
copper wire. Presents
maximum surface for
' reception, resists corrosion;
this greatly i mproves the
signal. Outside diameters equal to
sizes 14 and 16. (We also offer solid
and stranded bare, and stranded
tinned antenna.)
Loop Antenna Wire
Sixty strands of No. 38 bare copper
wire for flexibility, 5 strands of No.
36 phosphor bronze to prevent
stretching. Green or brown silk
covering; best loop wire possible to
make.
Battery Cable
A rayon-covered cable of
5,6,7,8 or 9 vari-colored
Flexible Celatsite wires
for connecting
butteries or
eliminator to ^
set. Plainly
tabbed; easy to connect. Gives set
an orderly appearance.
Send tor folder
THE ACME WIRE CO., Dept. B
New Haven, Conn.
ACM
IRE
MAKES BETTER RADIOj
258
RADIO BROADCAST ADVERTISER
HOWARD
1928, A. C. 6
Aluminum shielded all electric; R.
C. A. or Cunningham tubes. 425
volt amplifier. No batteries, Marvel-
ous tone, volume, distance and se-
lectivity. Complete $311.50.
Mlliciksalr Clectcic
Cools anb
i\oom 506
19 g>. Well* Street, Chicago, 311.
ELK/W
FREE RADIO
CATALOG
HAMILTON-CARR RADIO CORP.
711 West Lake St. Dep't. 376 Chicago, 111.
WHAT KIT SHALL I BUY? (Continued)
221. LR4 ULTRADYNE — Nine-tube super-heterodyne; one
stage of tuned radio frequency, one modulator, one oscillator,
three intermediate-frequency stages, detector, and two
transformer-coupled audio stages.
222. GREIFF MULTIPLEX — Four tubes (equivalent to six
tubes); one stage of tuned radio frequency, one stage of
transformer-coupled radio frequency, crystal detector, two
stages of transformer-coupled audio, and one stage of
impedance-coupled audio. Two controls. Price complete
parts, S;o.oo.
223. PHONOGRAPH AMPLIFIER — A five-tube amplifier de-
vice having an oscillator, a dectector, one stage of trans-
former-coupled audio, and two stages of impedance-coupled
audio. The phonograph signal is made to modulate the
oscillator in much the same manner as an incoming signal
from an antenna.
224. BROWNING-DRAKE — Five tubes; one stage tuned
radio frequency (with special neutralization system), re-
generative detector (tickler control), three stages of audio
(special combination of resistance and impedance-coupled
audio). Two controls.
225. AERO Shoit-WaveTransmitting Kit consists of inter-
changeable coils to be used in tuned-plate tuned grid circuit.
Kits of coils, two choke coils, and mountings, can be secured
for 20-40 meter band, 40-80 meter band, or 90-180 meter
band, for $1 2.00
USE THIS COUPON FOR KITS
I
RADIO BROADCAST SERVICE DEPARTMENT
Garden City, New York.
Please send me information about the following kits in- I
dicated by number:
Name.
Address
(Number)
(Street)
(City) (State)
ORDER BY NUMBER ONLY. This coupon must
accompany each order.
RBi-28
A New R. F. System
'THE DE FOREST Company, which from the
•I beginning has been one of the principal
opponents of the rapidly augmenting position
of the Radio Corporation in the radio patent
field, recently announced that Dr. George A.
Somersalo, a Finnish physicist, has developed a
new system of radio-frequency amplification
which does not conflict with the Alexanderson
tuned radio-frequency patent. This system de-
pends upon the use of a filter ahead of the
first radio stage, the radio-frequency amplifier
being untuned. The Alexanderson patent, how-
ever, is not the only one possessed by the Radio
Corporation of America and a great battle of
wits lies ahead for those who want to do entirely
without Radio Corporation licenses. No one
who has had extensive contact with the American
inventor, however, would venture to predict
that it cannoi be done.
USE THIS COUPON FOR COMPLETE SETS
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, New York.
Please send me information about the following manu-
factured receivers indicated by number;
Name. . .
Address
(Number) (Street)
(City) (Stale)
ORDER BY NUMBER ONLY
This coupon must accompany each order. RB 1-28
RADIO
DEALERS
Send for our catalog
illustrating the prod-
ucts of over 100
radio manufacturers.
WHOLESALE ONLY!
F. D. PITTS COMPANY
219-223 Columbus Ave.
BOSTON, MASS., U. S. A.
Established 1919
"that won't work on a
Your Next "B" Had Better Be the
BETTER-B
Type 7180
NATIONAL CO., Inc.
W. A. Ready, Pres.
Maiden Mass.
The UniqueRADIOTHRILLof receiving
Australia and Japan the same night was expe-
rienced September 11, 1927, by K. G. Ormi
ton. on a home-built Magnaformer 9-8 No
6, 1927, R. C. Anderson, on his HOME-BUILf '
Magn former 9-8 pulled in 1 New Zealand, 2
Australian. 2Japane.se and 61 lone distance
Western Hemisphere stations from the Atlan-
tic to Pacific— 6. 000 to 9, 000 miles on loud speaker vith a world
of volume. On hix h.-nx'-liuilt Maffiwfbrin«r&8J. M. Douglas
cut cleanly through the blanketing barrage of the numerous,
powerful lociil CmcrtNro stations and pulli-d in 32 out-of-town
stsitiunn without interference. Only a Maprmiformer 9-8 can
give you su.-h performance. It is witE.out question the
greatest Radio Set in the world. It brings -them in not
only from QoMt tpCout hut from Continent to Continent It
s NEW and decidedly DIFFERENT. -
fl tubes
clude
. .
all latest scientific developments. Performance truly phe-
sion on Engineers
nuim-nal. Has registered a profound impressio
and Technical Editor! everywhere. Hi-int- <'(.ri'-t:inil> lectured
in all radio magazines. In fame is sweeping the earth. Amaz-
ing fidelity of tone. Even brings out the full, round, boom-
boom of the bass drum entirely absent from other receivers.
Easily and quickly built at home or in any radio shop Simple
and easy to operate. Absolutely Ama/im: IVrtVc-hnn of Tone
Quality. Very hight-Ht. H:IMS i-iti.er R,;, -fiver. Dt-Hik-tn-.l for
of Custom Set Builders^ I-^ull »d«itl£: «xplaoation of CHU!
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267
// all the Radio sets I've "fooled"
with in my time were piled on top of
each other, they'd reach about half-
way to Mars. The trouble with me
was that I thought I knew so much
about Radio that 1 really didn't know
the first thing. I thought Radio was
a plaything — that was all 1 could
see in it for me.
I Thought Radio Was a Plaything
But Now My Eyes Are Opened, And
Tm Making Over $100 a Week!
$50 a week! Man alive, just one year ago
a salary that big would have been the height
of my ambition.
Twelve months ago I was scrimping along
on starvation wages, just barely making
both ends meet. It was the same old story —
a little job, a salary just as small as the job
— while I myself had been dragging along in
the rut so long I couldn't see over the sides.
If you'd told me a year ago that in twelve
months' time I would be making $100 and
more every week in the Radio business —
whew! I know I'd have thought you were
crazy. But that's the sort of money I'm pull-
ing down right now — and in the future I
expect even more. Why only today —
But I'm getting ahead of my story. I was
hard up a year ago because I was kidding
myself, that's all — not because I had to be.
I could have been holding then the same
sort of job I'm holding now, if I'd only been
wise to myself. If you've fooled around with
Radio, but never thought of it as a serious
business, maybe you're in just the same boat
I was. If so, you'll want to read how my
eyes were opened for me.
When broadcasting first became the rage,
several years ago, I first began my dabbing
with the new art of Radio. I was "nuts"
about the subject, like many thousands of
other fellows all over the country. And no
wonder! There's a fascination — something
that grabs hold of a fellow — about twirling
a little knob and suddenly listening to a
voice speaking a thousand miles away!
Twirling it a little more and listening to the
mysterious dots and dashes of steamers far
at sea. Even today I get a thrill from this
strange force. In those days, many times I
stayed up almost the whole night trying for
DX. Many times I missed supper because
I couldn't be dragged away from the latest
circuit I was trying out.
I never seemed to get very far with it,
though. I used to read the Radio magazines
and occasionally a Radio book, but I never
understood the subject very clearly, and lots
of things I didn't see through at all.
So, up to a year ago, I was just a dabbler
— I thought Radio was a plaything. I never
realized what an enormous, fast growing in-
dustry Radio had come to be — employing
thousands and thousands of trained men.
I usually stayed home in the evenings after
work, because I didn't make enough money
to go out very much. And generally during
the evening I'd tinker a little with Radio —
a set of my own or some friend's. I even
made a little spare change this way, which
helped a lot, but I didn't know enough to
go very far with such work.
And as for the idea that a splendid Radio
job might be mine, if I made a little effort
to prepare for it — such an idea never entered
my mind. When a friend suggested it to me
one year ago, I laughed at him.
"You're kidding me," I said.
"I'm not," he replied. "Take a look at
this ad."
He pointed to a page ad in a magazine,
an advertisement I'd seen many times but
just passed up without thinking, never
dreaming it applied to me. This time I read
the ad carefully. It told of many big oppor-
tunities for trained men to succeed in the
great new Radio field. With the advertise-
ment was a coupon offering a big free book
full of information. I sent the coupon in,
and in a few days received a handsome 64-
page book, printed in two colors, telling all
about the opportunities in the Radio field
and how a man can prepare quickly and
easily at home to take advantage of these
opportunities. Well, it was a revelation to
me. I read the book carefully, and when I
finished it I made my decision.
What's happened in the twelve months
since that day, as I've already told you,
seems almost like a dream to me now. For
ten of those twelve months, I've had a
Radio business of my own. At first, of
course, I started it as a little proposition
on the side, under the guidance of the Na-
tional Radio Institute, the outfit that gave
me my Radio training. It wasn't long be-
fore I was getting so much to do in the
Radio line that I quit my measly little cleri-
cal job, and devoted my full time to my
Radio business.
Since that time I've gone right on up,
always under the watchful guidance of my
friends at the National Radio Institute. They
would have given me just as much help, too,
if I had wanted to follow some other line
of Radio besides building my own retail
business — such as broadcasting, manufactur-
ing, experimenting, sea operating, or any one
of the score of lines they prepare you for.
And to think that until that day I sent for
their eye-opening book, I'd been wailing "I
never had a chance!"
Now I'm making, as I told you before,
over $100 a week. And I know the future
holds even more, for Radio is one of the
most progressive, fastest-growing businesses
in the world today. And it's work that I
like — work a man can get interested in.
Here's a real -tip. You may not be as bad
off as I was. But think it over — are you
satisfied? Are you making enough money,
at work that you like? Would you sign a
contract to stay where you are now for the
next ten years — making the same money? If
not, you'd better be doing something about
it instead of drifting.
This new Radio game is a live-wire field
of golden rewards. The work, in any of the
20 different lines of Radio, is fascinating,
absorbing, well paid. The National Radio
Institute — oldest and largest Radio home-
study school in the world — will train you
inexpensively in your own home to know
Radio from A to Z and to increase your
earnings in the Radio field.
Take another tip — No matter what your
plans are, no matter how much or how little
you know about Radio — clip the coupon be-
low and look their free book over. It is
filled with interesting facts, figures, and
photos, and the information it will give you
is worth a few minutes of anybody's time.
You will place yourself under no obligation
— the book is free, and is gladly sent to any-
one who wants to know about Radio. Just
address J. E. Smith, President, National Ra-
dio Institute, Dept 2O, Washington, D. C.
J. E. SMITH, President.
National Radio Institute,
Dept. 2O, Washington, D. C.
Dear Mr. Smith:
Please send me your 64-page free book, printed
in two colors, giving all information about the
opportunities in Radio and how I can learn quickly
and easily at home to take advantage of them. I
understand this request places me under no obliga-
tion, and that no salesman will call on me.
Name
Address
Town State
Occupation
RADIO BROADCAST
FEBRUARY, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XII, No. 4
Cover Design - - - - - From a Design by Harvey Hopkins Dunn
Frontispiece At the Rugby High-Power Station 270
The Eyes of a Future Air Liner "Anonymous" 271
A 45-kc. A. C. Super-Heterodyne Dormand S. Hill 274
The March of Radio - - - - An Editorial Interpretation 278
The Commission Improves Broadcasting Con-
ditions
Who Buys This Year's Radio Sets?
Rural Listeners Sewed by Re-Ailocations
Frequency Allocations of the International
Convention
New Commissioner Appointed
Inside the Radio Industry
R.iJio Industry Standards
News from Abroad
The Screened-Grid Tube - - The Laboratory Staff
Radio Folk You Should Know
(l). Walter Van B. Roberts
Drawing by Frantyyn F. Stratford
An A. C. Push-Pull Amplifier and B Supply
New Recordings by Radio Favorites
" Our Readers Suggest —
/. £. Coombes
Extending Loud Speaker Leads
The Cartridge Type Charger
The Glow Tube
Output Transformer Connections
A Simple Vernier Condenser
Some Reliable Radio Power-Supply Accessories
Why the Output Device? - Keith Henney
Operating Your Rayfoto Picture Receiver Austin G. Cooley
How the "NR-60" Was Engineered John F. Rider
Radio Receivers Representing A Wide Price Range -
Constant B-Device Output G. F. Lampfyn
A Fantasy on Sponsored Programs - - John Wallace
The Listeners* Point of View
F. ]. Fox and R. F. Shea
Matching R. F. Coils - - -
"Strays" from the Laboratory
New Tubes Mean Greater Economy
New Amateur Regulations
Technical Radio Problems for Broadcasters and Others
Don't Overwork the A Battery
Better Loud Speakers Are Here
As the Broadcaster Sees It
Death Among the Broadcasters
Carl Dreher
Antennas from 1913 to r
" Radio Broadcast's" Laboratory Information Sheets -
No. 161. Comparing the 112, 171, and 210
Type Tubes
No. 162. it2. 171, and 210 Tube Curves
No. 165. Audio Amplification
No. 166. Acoustics
No. r67- Resonant Circuits
No. iS8. The Ear
No. 163. Testing Receivers
No. 164. A Modulated Oscillator
Manufacturers' Booklets Available
" Radio Broadcast's" Directory of Manufactured Receivers •
What Kit Shall I Buy?
Short- Wave Notes - - - - - - •
282
286
287
289
291
294
296
299
J02
304
jc6
308
310
320
322
330
331
< AMO^G OTHER THINGS. . .
WASHINGTON is distinctly the center of radio interest
these days. One important conference which means
much to radio all over the world is barely concluded with the
closing of the International Radio Convention on November
25th when the Federal Radio Commission announces that pub-
lic hearings will be held in Washington about the middle of
January on the question of short-wave allocations. The thoughts
of everyone have turned toward the short waves, and the
Commission is very wise in holding hearings to enable some
sort of ordered development to take place in these many
vital channels now and in the years to come. Now in the short-
wave, channels are government, commercial, military, marine,
naval, and amateur services. And, in addition, these channels
contain some genuine experimental broadcasting stations and
many more stations operating under experimental licenses
which are broadcasting without any intelligent reason at all.
The Commission is to be praised for its foresight in throwing
this question open before it is too late.
THIS issue of RADIO BROADCAST contains articles of un-
doubted interest. " The Eyes of a Future Air Liner,"
for example, points out how radio can be applied to the present
problems of air navigation. " Anonymous" cloaks the iden-
tity of an authority on radio and aviation — a man who is better
qualified to write on these twin subjects than any one we know.
There has been much almost hysterical writing about the won-
derful possibilities of the screened-grid tube, recently an-
nounced, and precious little genuine information about actual
experiment with the possibilities of this very interesting tube.
The Laboratory Staff, in the article on page 282, presents actual
facts about what this tube can do, highly important to every
experimenter whose interests lie in this direction. . . . For the
first time, too, as far as we know, the facts about output de-
vices are related. From the story by Keith Henney on page 294
you can learn exactly what the different types are, what they
will do, and how best to use each type.
REGULAR broadcasting in the New York area of photo-
graphs sent by the Cooley Rayfoto system will be es-
tablished before this issue is in the hands of readers and, ac-
cordingly, we publish a story by the inventor, Austin Cooley,
presenting some additional technical information about the
receiver which is now available in parts form to every in-
terested constructor. Many readers write to request their
names be forwarded to the manufacturers of the essential prod-
ucts. Any reader who has not yet done so should address a
letter to the undersigned who will forward the request to the
companies concerned. Picture broadcasting is here and' we
prophesy that in the not too distant future great numbers of
experimenters will take this field for their own, completely
fascinated by it.
WE SHALL soon publish the descriptions of a remarkably
inexpensive receiver using the screened-grid tube, a new
receiver design by Glenn Browning, a technical description with
circuit diagrams and data on the Crosley " Bandbox" set,
and an interesting kit for an A-socket power supply which will
furnish enough A potential for ten quarter-ampere tubes.
— WILLIS KINGSLEY WING.
Doubleday, Doran &• Company.
MAGAZINES
COUNTRY LIFE
WORK D'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
SHORT STORIES
EDUCATIONAL REVIEW
LE PETIT 'OURNAL
RL Eco
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WEST WEEKLY
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OFFICERS
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Copyright, 19?8 in the United States, em/oimdland, Great Britain, Canada, and other countries by Doubleday, Doran & Company, Inc. All rights reserved.
TERMS: $4.00 a year; single copte* 35 cents.
RADIO BROADCAST ADVERTISER 269
DISTANCE
lends
ENCHANTMENT
When you buy or build a radio set make
sure that it has Copper Shielding. Where
long distance reception is desired Copper
Shielding is essential. It is a refinement
to your set that will enable you to hear
the programs of distant, stations much
more clearly.
Copper Shielded sets give:
BETTER RECEPTION
FINER SELECTIVITY
IMPROVED TONE QUALITY
By virtue of its easy working qualities and
its high conductivity Copper Shielding
is a decided improvement to any set.
COPPER CT- BRASS
RESEARCH ASSOCIATION
25 Broadway, New York
Write for your copy of this
book. There is no cost nor
obligation on your part.
§'
'
.
At the Rugby High-Power Station of the British Post Office
The antenna lead-in as seen from the interior of the transmitter house. This
station is one of the transmitters built in England by the British Marconi Com-
pany for the British Post Office, for communication with the Dominions. The
British transmitter for the transatlantic radio telephone circuit is located at Rugby
and the high-power radio telegraph transmitter is used for direct communication
with Australia
270
OUT OF TOUCH WITH TOE WORLD
One need not be a meteorologist, versed in the significance of the clouds,
to know what weather is ahead and below, after flying in the upper at-
mosphere for many hours. A simple application of modern scientific
principles will supply the information to pilots out of sight of the terrain
The Eyes of the Future Air Liner
CURING one of the ill-fated attempts
to fly to Hawaii this summer the short-
wave signals from the radio transmitter
aboard the plane were copied in New York.
Entire messages were easily received and the
progress of the flight followed by newspaper
reporters at the receiving stations, although the
power of the transmitter wasn't enough to
thoroughly warm up a curling iron.
It was a dramatic occurrence. Soon after the
pilot took his heavily-loaded, single-engine
plane off the runway and headed it westward
over an unmarked trail traveled by few,
cheerful messages came flashing back telling of
the progress of the flight. The confident jaunty
messages continued for some time. Then sud-
denly came warning of disaster. "We're in a
spin," was the startling and serious message.
The pilot was evidently able to momentarily
bring his ship out of the spin, and put it back on
an even keel. But not for long for the next mes-
sage announced that the plane was again in
a tailspin. And that was all, the last that was
ever heard from that plane. Undoubtedly, the
plane, loaded to the limit, was unstable. It could
not be held in level flight in a fog or clouds, and
stalled, with the resultant crash to the water
below. Radio told of the end.
Over 3000 miles away newspaper reporters
listening to these messages were impressed with
"Anonymous"
the distance of transmission. In certain New
York newspapers much was made over this feat
of short-wave transmission. Reading these
articles, one was ready to believe that something
phenomenal in radio communication had taken
place, and that the solution for problems of
aircraft radio could be readily found in the use of
short waves.
It is not believed that this is exactly so. Every
radio amateur knows what can be done with low
power on short waves. Bouncing his waves off a
reflecting medium which scientists have named
the Heaviside Layer, he is able to hop his
signals all over the globe. He might well be
something of a billiard player to properly angle
his da-dit-dit-das so as to drop them on a
friend's antenna perhaps on the other side of the
world. But the amateur found that there were
places, usually not so far away, where his waves
could not be received, and other places close to
him that reported considerable "fading." This
much is known about short-wave transmission.
But communication from plane to ground will
be useless if not reliable over the entire route
of flight. The "skip-effect" and the "fading"
characteristic of waves much shorter than 80
meters makes their use in aircraft communica-
tion of little value. For what good will be the
reception in San Francisco of a message sent
by a plane flying from New York to Chicago
271
when the message is intended for someone in
New York?
The "skip" distance, or immune zone, i«
known to vary with the wavelength, the time of
day, the time of year, the kind of antenna, and
the nature of structures surrounding the antenna.
There is a great deal to be learned about short-
wave transmission from an airplane before the
adoption of a definite near-short wave can
be decided upon. The low power required, the
simplified apparatus, the light weight, small
size, and cost of short-wave equipment tempts
one to jump at the proposition of equipping
commercial craft with these sets. But research
work in this connection must be exceedingly
thorough. This means that the period of research
must be extended to include all conditions as to
season, time of day, and kind of terrain flown
over, if work with short waves is to result in
anything conclusive.
Before such research is begun it would be well
to make a survey of the needs of commercial
aviation with regard to radio service. Let us
consider this point very briefly. First of all it
appears that radio can be put to at least two
very good uses on regular express and passenger
air lines. Some means of telling the pilot in
flight what is happening to the weather along
the route ahead of him as well as at his destina-
tion would seem to be very desirable. Equally
272
RADIO BROADCAST
FEBRUARY, 1928
desirable would be a means for tell-
ing the pilot when he was off his
course and to help him get on it
again. These two are the most im-
portant requirements at the present
time. Nothing need be invented to
provide this assistance to aerial
travel. It is but a question of appli-
cation of things now known.
To see just how the two kinds of
radio service mentioned might be
utilized, let us use our imagination
and picture an airway of the near
future.
We may start where the most
imagination is required and visit
New York's great municipal airport.
It is just dark and we have arrived
in plenty of time for a glance around
before we take the early evening
express plane for Chicago. There
are a number of planes on the "fly-
ing line." Busy mechanics are fuss-
ing around these while other me-
chanics and helpers push and wheel
planes into and out of the huge squat
hangars. Twinkling red, green, and
while lights outline the boundary of
the airdrome. The red lights indi-
cate obstacles; the green lights show
favorable approaches to the landing
area, while the white lights show
the general outline of the field. A
flood light illuminates like day much
of the landing area. Smaller lights
flood the hangars and the concrete
"aprons" between. A huge beacon
flashes from a low tower on one of
the hangars.
We approach the "flight office"
and here we see a busy official mark-
ing up on a bulletin board news of the movement
of "ships" on the various airways terminating
at New York. Another official is marking the
latest weather reports on a large weather map
of the United States. Here we also see posted
forecasts of the weather to be expected along the
different airways. We read with no feeling of
glee that on the route to Chicago we may expect
rain, and low clouds through the mountain
region, and somewhat higher clouds with
A SPERRY REVOLVING BEACON
This particular one was installed by the Department of Commerce
showers from Cleveland to Chicago. Anxiously
we go to inquire if in view of the weather pros-
pects the Chicago express will leave to-night.
We are assured that it will, and are advised to
go aboard soon, as the "take-off" will not be
delayed.
Aboard the big three-engined air liner we
soon find that most of the twenty seats in the
cabin are already occupied. We have seats
near the front fortunately, and can observe
through a doorway the controls and
instruments in the pilot's cabin.
The engines have been warmed
up and tested at full throttle and
now are idling, the metal propellers
turning over lazily, awaiting only the
will of the pilot. He is getting into
his seat and is talking to his me-
chanic in a seat at his side, when
an official comes aboard to converse
a moment with these members of
the "crew." We are being "cleared''
for Chicago. The official leaves, the
doors are secured and we are off.
The rumbling muffled roar settles
down into a droning beat as the
three engines are synchronized in
speed.
Below, the twinkling lights of
suburban towns glitter against the
black of night. Soon, however, we
leave the region of more thickly
clustered lights and then we are able
to pick up some of the rotating lights
of marker beacons which show the
way westward. They blaze a trail
all the way to our destination which
will be easy to follow if bad weather
is not encountered.
Our attention having been directed
so much below we failed to see the
mechanic reel out his trailing wire
antenna and tune the receiver
located in front of him. Now we
notice a small panel on the instru-
ment board, just below a compass
indicator. In this panel a small
white light is blinking slowly — on-
off, on-off, without a break. This is
evidently a signal. After a time we
notice other lights on this panel.
There are combinations of reds, greens, and
whites, that come on for a few seconds, change,
and then go out. More signals. The pilot and
mechanic evidence interest but do not seem
perturbed.
Looking out of the window at our side we see
but a gray black nothingness faintly lighted by
the illumination from the lighted cabin. We can
see nothing below, and we realize that we are in
clouds or fog. A large altimeter in the front wall
OFF FOR CHICAGO. THE NIGHT AIR MAIL LEAVES HADLEY FIELD, NEW JERSEY, BY THE AID
(FEBRUARY, 1928
THE EYES OF A FUTURE AIR LINER
273
HIGH-INTENSITY LANDING FIELD FLOOD LIGHTS
One of these Sperry lights will illuminate a 5O-acre field
of the cabin shows that we are 3200 feet above
sea level. We are in the clouds. If they continue
and we cannot fly beneath them and see the
trail of lights on the ground, how are we to find
our way? How will we know when it is safe to
come down again?
We will watch the little panel with the steadily
blinking white light and the peculiar combina-
tions of colored lights that come only occasion-
ally. As we watch, the white light blinks
unsteadily and then changes to green and flashes
regularly once more. We are off our course, to
the right, we are told by a passenger just behind
us. He has been over this route before and tells
us that when the green light flashes we are to the
right of the course. If it shows red, we are to the
left. When it is white we are exactly on our
course. The color combinations which we saw
appear for only a short time on the panel were
signals concerning the weather ahead. It was in
this way that the pilot knew that it was safe to
climb up into the clouds, and so avoid the storm
below, and yet steer clear of mountain peaks —
reefs in this ocean of air.
For hours we fly through the night, yet there
is no sensation of flying. That is because we are
unable to see anything but the dense fog of the
cloud bank through which we pass. Our feeling
is that our comfortable, lighted cabin is floating
in space. The vibration of the engines and the
muffled drone of the exhaust nearly lulls us to
sleep. We see the needle of the altimeter crawl
slowly up. Five thousand feet, six thousand; per-
haps the pilot seeks to climb above the cloud into
the moonlight which should be above. But no,
the altimeter now shows that we are descend-
ing a little. Evidently the cloud bank is very
thick, and it is not worth while to go above it.
We should be nearing our destination, that is
if these red and green and white lights have been
faithful to their trust. And the combinations of
colored lights, which now again are gleaming in
the dimness of the pilot's compartment. Have they
been unerring too? We shall soon know. The
engines have been throttled a little. The floor
of our cabin slopes forward and the needle of the
altimeter is dropping slowly. We are losing
altitude, and soon should burst through the
"ceiling" of cloud. Suddenly the gray black mass
which has engulfed us for hours is swept away.
Twinkling lights appear below showing towns
and lighted highways. Off to our left we see the
rotating beam of a marker beacon, and, some
little way ahead, another. We are on our course.
Ahead there is a great glow in the sky, and as we
draw nearer we realize that it is the light from a
large city reflected against the clouds.
Now we pick up a bright flashing red light. It
marks the airport of this city. Soon we are
circling over it, and can see the line of lighted
hangars and a brightly lighted letter "T" on
the ground. This is to indicate the direction of
the surface wind. We glide smoothly down,
circle once more, and come in to land. Leveling
off we float along hugging the ground and then
with a few gentle bumps and a short roll we come
to rest. To taxi up to the line in front of the flight
office, and disembark, requires but a moment.
We are in Chicago.
Radio has done its work. It told the pilot when
he was off his course, and how to get on it again.
It told him this and more, by very simple signals.
Signals he could see. It told him of storms ahead,
of cloud levels, and winds, and he was able to
fly over disturbed areas and dangerous areas,
and to come down safely at the proper time.
No uncomfortable head-phones in a helmet were
required, and it was not necessary that he know a
telegraph code.
Some, perhaps many, may think the picture
drawn is fantastic and only a dream. That re-
mains to be seen. As for the ability to fly in the
manner described, through clouds and fog, there
are ships and pilots in plenty equal to the task.
Let others apply things already known in the
radio art, and the radio aids to aerial navigation
which have been pictured will be a reality. Short
waves may ultimately be the medium whereby
this is accomplished, but considerable experiment
will be necessary before the vagaries of these
high frequencies will be fully understood.
© William E. Arthur & Co., Inc.
WERFUL FLOOD LIGHTS. THE MAIL WILL BE DELIVERED IN CHICAGO TOMORROW MORNING
RADIO BROADCAST Photograph
OBTAINING SOME DATA ON THE A. C SUPER-HETERODYNE IN THE "RADIO BROADCAST" LABORATORY
Whenever receivers are described constructionally in RADIO BROADCAST, they are invariably tested out in the magazine's laboratory first. Fre-
quently changes are recommended to the designers, and the technical staff does not give its O. K. unless the receiver comes up to expectations
A 45
» A. C* Super-Heterodyne
By DORMAND S. HILL
IN A season during which a bewildering array
of super-heterodyne receiver designs are
offered to the radio fan and home builder, it
is felt that, in presenting still another "super"
to the readers of RADIO BROADCAST, it would be
well to define, if possible, the relation of such
a receiver to other designs, and to point out just
why it was felt necessary that another entry
should be made in an already too crowded field.
The forty-five kilocycle socket-powered super-
heterodyne described here has as the greatest
argument in its favor the fact that, though it is
fully as sensitive and selective as the majority
of eight, nine, and ten-tube sets of its class, its
tuning controls are so simple that peak results
are always at the command of even the novice
operator, its tone quality is unusually good for
super-heterodynes and, possibly most important,
it derives all power from any sixty-cycle alter-
nating-current home light socket.
The set is entirely self-contained, power unit
and set being housed in a standard seven by
twenty-four inch cabinet, twelve inches deep.
The only external equipment required is a good
loop and a modern loud speaker. Since there is
not a single battery to run down, and as the
power unit is entirely dry, the servicing problem
becomes one of occasional tube replacements
only. The new a.c. tubes, which make possible
the socket powered super-heterodyne described
here, give promise of greater average life than
is experienced with five-volt battery-type tubes.
In view of the foregoing advantages — better
performance, excellent tone, and complete self-
contained light socket operation — it is felt that
the appeal of this super-heterodyne set should
be indeed great. There is another factor which
tremendously enhances the value of the receiver
— its low initial cost. The entire receiver and
power unit, constructed of the finest quality
parts throughout, will cost only about $145.00,
or, with a beautiful walnut cabinet, about $22.00
more. Thus, for less than $170.00 at list prices, the
radio fan, or even the novice, can build for him-
self a full socket-powered super-heterodyne and
obtain exceptional selectivity and sensitivity,
while the 45-kc. super-heterodyne rivals one-
dial sets in the simplicity of its tuning. Another
factor in the home-built set is the beauty of
finish of each individual part — a factor often
neglected in all but the most expensive factory-
built sets.
The forty-five kilocycle super-heterodyne
employs eight tubes in a new a.c. tube circuit,
carefully tried and tested. It possesses a great
factor of "hum safety" due to the generous use
of 0-327 (ux-22y) heater tubes instead of the
greater hum-producing cx-326 (ux-226) type
tubes. One c-327 type tube is used as a grid-
tuned oscillator, one in a conventional Rice re-
generative split loop first detector circuit, and
three more follow in a forty-five kilocycle inter-
mediate amplifier, which, in turn, works into a
c-327 second detector. Then follows a two-stage
low-frequency transformer-coupled amplifier em-
ploying a cx-326 (ux-226) first-stage tube, and
either a cx-i 12 (ux-i 12) or cx-37i (ux-i7i) out-
put tube with output transformer. The power
supply consists of the conventional B device
circuit using a cx-38o (ux-28o) thermionic
rectifier and a special filament heating trans-
former for all tubes. The power unit delivers
1.5, 2.5, and 5 volts a.c. and 200 to 220 volts
pure d.c. to the receiver A, B, and C circuits.
A description of the individual circuit sections
will help to provide a clear understanding of the
unusual simplicity of the set, and the ease with
which it may be built. On the front panel are
three knobs. Two of these control the two illum-
inated tuning drums affecting the o.ooo35-mfd.
variable condensers, one of the two tuning
the loop and the other tuning the oscillator,
both with high reduction vernier drives and well-
spaced 36o-degree scales, numbered o to 200.
In tuning, both dials tally approximately, sta-
tions being heard loudest at one point on the
loop drum and at two points on the oscillator
drum, although powerful local stations may be
274
heard at more than two points. The third knob,
a volume control, provides adjustment from
absolute zero to a full maximum. It is not critical
as to setting, but if turned too far to the right,
will cause the intermediate amplifier to block.
Looking down into the set from above, at the
left front is the plug-in oscillator coil, LI; behind
it is the oscillator tube socket, and to the coil's
right is the oscillator condenser, Q, and drum.
At the left rear are the loop and loud speaker
connection tip jacks; and at their right, along the
rear of the Micarta chassis, is the audio amplifier.
The latter consists, from left to right, of an out-
put transformer T3, the output tube, 33:1 ratio
audio transformer, T2, the cx-326 (ux-226) first-
stage tube, and then the first-stage 3:1 trans-
former, TI. The filament balancing resistors,
and R2, on the audio tube sockets, are clearly
visible. The frequency characteristic of the audio
amplifier is practically flat from 100 cycles to
over 5000 cycles, and then falls off for reasons to
be given later. The voltage gain of the audio
amplifier, with cx-326 (ux-226) and cx-ii2
(ux-i 12) tubes is about 400 overall.
Just in front of the output transformer, and
behind the first detector tube socket (second from
left), is the knob of the loop regeneration con-
denser, C3 in Fig. i. To the right are the four
forty-five kilocycle intermediate transformers,
Lj, LS, L4, LS, with the three amplifier and second
detector (at right) tube sockets in front of them.
At the center of the front panel is the loop tuning
drum and condenser, Ci. Between the two tuning
drums is the jooo-ohm volume-control potentio-
meter Rs, and on the sub-base also between tht
drums is a knob controlling the radio-frequency
amplifier C bias by means of the potentiometer,
RI. The first transformer, Lj, of the intermediate
amplifier is untuned; the next, La, is a tuned
stage (an XL o.oooj-mfd. Variodenser, Q, below
the chassis, with adjusting screw projecting up,
is used for tuning this filter). Then follows a
second untuned transformer, L4, and, at the right,
a second tuned transformer Lj, feeding the de-
FEBRUARY, 1928
A 45-KC. A.C. SUPER-HETERODYNE
275
POWER UNIT AND RECEIVER PROPER
In the event that the power unit is to be mounted elsewhere than
right beside the receiver, the front panel for the latter may be smaller
lector tube. This latter stage is tuned by means
of a fixed condenser, C6.
The power unit, consisting of a power trans-
former, T4, a condenser block, Ci2, filament
transformer, T6> and Clough selective filter choke,
U, with tube socket, and binding posts (and
resistor, RIO, below), is on a seven-by-twelve
inch chassis at the right of the set chassis, the
two being cross-connected by the use of Eby
binding posts as shown. An under-chassis view
shows the voltage dividing resistor, RIO, beneath
the power unit chassis, and other obvious parts
beneath the receiver chassis. The simplicity of
wiring is evident.
SELECTIVITY
THE selectivity of the set is quite good, and
allows of ten- to fifteen-kilocycle separation
of powerful local and weak out-of-town stations.
The frequency band passed is a good ten kilo-
2 Meg. R,
cycles wide in normal operation, thus providing
excellent tone quality with the audio channel
used. This audio channel, due to its cut-off above
5000 cycles, materially aids the apparent selectiv-
ity of the radio-frequency circuits; in fact, the
frequency characteristics of radio and audio cir-
cuits match very nicely.
An examination of the circuit indicates that all
grid returns are brought back to the common
B minus lead. First detector and oscillator are
operated with approximately forty-five volts
plate potential, and with zero grid potential;
the grid-circuit returns and heater tube cathodes
connect to the B minus lead. The three radio-
frequency amplifiers derive an adjustable C bias
from the 4OO-ohm potentiometer, RI, which is
connected between their cathodes and the B
minus lead (a voltage is developed by virtue of
the plate currents flowing through this resistor).
The best bias is one-half to one volt, and, once
set, varies automatically with changes in plate
voltage. The C bias resistor and the plate voltage
potentiometer are bypassed with i-mfd. con-
densers, Q and Cj, to prevent radio-frequency
coupling. Plate voltage on the radio-frequency
amplifier can be varied from zero to about ninety
volts, using the jooo-ohm potentiometer (volume
control knob), and generally about forty to
forty-five volts gives greatest volume and sen-
sitivity without amplifier oscillation. C bias for
the detector is obtained from a jooo-ohm resistor,
RS, between the B minus lead and the detector
cathode, shunted with a o.ooo5-mfd. bypass
condenser, Cg.
The C bias for the first audio stage is obtained
across a ijoo-ohm resistor, Re, between the B
minus lead and the center tap of a 64-ohm resistor,
RI, shunting the filament of the cx-326 (ux-226)
audio tube. C bias for the second audio tube is
similarly obtained by a aooo-ohm fixed resistor,
Rv, between B minus lead and the center tapof a
second 64-ohm balancing resistor, Rt, across
the last audio tube's filament. This 2ooo-ohm
resistor is bypassed with a i-mfd. condenser, Cg,
to improve low-frequency reproduction. For
safety, a 64-ohm resistor, Rs, connected across
the 23-volt heater circuits of the CX-J27 (ux-22y)
tubes, leads to plus 45 volts to prevent hum.
The plate voltage of the first audio stage is about
90 volts; the C bias should be 5 to 6 volts — cor-
rect for cx-326 (ux-226) tubes. The last audio
tube may be interchangeably a cx-i 12 (ux-i 12)
or a cx-371 (ux-iyi) type tube, the former for
greatest amplification, the latter for best quality
on strong signals. With a cx-112 (ux-H2) tube,
C bias is about 20 volts and the plate voltage
about 200 — a safe value and one at which the
performance of the 1 12 type tube is quite credit-
able. The C bias for a cx-37i (ux-iji) tube
would be about 38 volts, and the plate poten-
tial, about 170 volts — entirely satisfactory
values, and slightly below the tube's rated
maximum.
The construction of the set is quite simple,
involving the use of the followtti£f;parts. If the
exact values specified are used, all adjustments
for proper a.c. operation are automatic. Substitu-
tion may necessitate experiment:
B-
FIG. 1
The circuit diagram of the 45-kc. a.c. super-heterodyne
276
RADIO BROADCAST
PARTS LIST
Two Remler 100 Universal Drum Dials
Lj, Lt Remler 600 Interstage Trans-
formers
La, Lf Remler 610 Tuned Stage Trans-
formers
Q, Q Remler 638 type o.ooo35-Mfd.
Condensers, Variable
TI, T2 S-M 240 Audio Transformers
T3 S-M 241 Output Transformer
Six S-M 512 Five-prong Tube Sockets
Two S-M 5 1 1 Tube Sockets
One S-M 5 1 5 Coil Socket
Li S-M mA Coil
Two Pairs S-M 540 Mounting Brackets
C3 S-M 340 Midget Condenser
Cio Polymet o.oooij-Mfd. Condenser,
with Clips
Cj Polymet o.ooo2j-Mfd. Condenser
Cn Polymet o.oo2-Mfd. Condenser
C8 Polymet o.ooj-Mfd. Condenser
R» Polymet 2-Megohm Grid Leak
Q, CT, Cj Polymet i-Mfd. Bypass Con-
densers
Re Frost FIJOO Resistor
R? Frost F2OOO Resistor
Ri, R2, Rs Frost FT64 Resistors
Five Frost 253 Tip Jacks
Ra Frost 5Ooo-Ohm De Luxe Potentio-
meter
Rs Polymet jooo-Ohm Resistor
R< Frost 4oo-Ohm De Luxe Potentio-
meter
Ct XL Model G "Variodenser"
Sixteen Eby Binding Posts: (8-pIain,
2 B-, 2 B + Det., 2 B+Amp., 2 B +
Int.)
$9.00
12.00
10. OO
10. OO
12. OO
5.OO
4.50
I 00
1 OO
2 50
I .40
I.JO
45'
35
.40
.60
25
3.00
.50
5°
I.JO
•75
!.25
I .OO
1.25
1.50
2.40
Westinghouse Micarta Walnut Panel
7 x 24 x T36 inches
l Westinghouse Micarta Sub Panel
12 x 17 x A inches
FEBRUARY, 1928
POWER SUPPLY PARTS LIST
T< S-M 329 Power Transformer 9.00
Le S-M 331 "Unichoke" 8.00
Ts S-M 325 Filament Transformer 8.00
S-M 5 1 1 Tube Socket 50
Pair S-M 540 Mounting Brackets 70
Cn Polymet 14-Mfd. Condenser Block 9.50
RIO Ward-Leonard 659 Resistor 2 . 50
Westinghouse Micarta Power Unit
Base, 12 x 7 x t*, Inches 4.00
8 Eby binding posts: (4Plain, I B — ,
I B + Del., I B + Amp., I B + Int.) 1.20
TOTAL $43. 40
Panels can either be drilled, following the ap-
paratus layout of the photographs, or procured
drilled and engraved from any Micarta dealer.
The apparatus should be mounted on them after
careful study of the photographs, and in the
positions shown. One point to observe is that all
cathode leads from the 0-327 (uv-227) tubes
should be brought out below the chassis by one
of the socket mounting screws, as this is good
practice to follow wherever practicable.
In wiring the set and power unit, all 1.5-, 2.5-,
and j-volt a.c. leads should be twisted to localize
their fields. All grid and plate leads should be of
busbar, in spaghetti where necessary, as should
the leads to the tuning condensers, while all other
low-potential wiring should preferably be of
Kellogg switchboard wire. The leads from the
8.00 2.5-volt binding posts of the receiver to F posts
of the five-prong tube sockets are each composed
9.00 of two No. 14 tinned wires in parallel, for high
TOTAL $103 60 current-carrying capacity. All metal parts of the
set and power unit, such as transformer frames
or shells and condenser bank case should ground
to B minus. The drum dial frames, carrying the
dial lights, are taken care of through the lamp
wiring to the 5-volt a.c. circuit, which grounds
through the F2OOO C bias resistor, Rj.
TEST AND OPERATION
AFTER finishing the set and power unit, it
would be well to check voltages with a high-
resistance voltmeter (1000 ohms per volt). The
power unit not connected to the receiver should
show about 70 to 80 volts on the 45-volt tap;
120 to 130 on the go-volt tap; and 220 or more on
the high tap. Next, the power unit should be
connected to the receiver, no tubes being inserted
in the set, and voltages again checked (for short
circuits). All voltages should have fallen some-
what. The audio tubes should now be inserted
in the set and the loud speaker connected. A
strong hum evidences proper operation of the
audio channel if B and C voltages (as given pre-
viously) check out approximately. If posts Nos.
I and 2 of the first audio transformer are short-
circuited, the hum will fall to the actual operating
value; it should be so low as not to interfere
with reception at average speaking volume. If
the hum is stronger, ground the B minus post
to a water pipe. If the hum is still too high (and
it may be under unusual line or set assembly
conditions), the solution is to move the power
unit away from the set. If all cx-327 (ux-227)
-INT. IsilNT.
L3R3R4 I L2
L1
L5 3«D.INT.
2ND DEI I C1 1 14
R1
Isi.AUDIO
fCX-326)
LOOKING DOWN INTO THE CABINET OF THE A.C. SUPER-HETERODYNE
The various parts are lettered so that they may be easily identified by cross reference to Fig. I, on the previous page
I; FEBRUARY, 1928
A 45-KC. A.C. SUPER-HETERODYNE
277
THE COMPLETE RECEIVER AND POWER UNIT
It is here shown in an attractive looking cabinet, a prod-
uct of D. H. Fritts and Company, Chicago, Illinois
heater tubes are inserted, the hum pitch will vary
as the tubes warm up and, after a minute, will
decrease to the average operating value observed
with posts Nos. I and 2 of the first a.f. trans-
former shorted (this very low hum is always
experienced with cx-326 [ux-226] or other "raw
a.c." tubes.)
To operate the set, set the midget condenser
all out, connect a Bodine 1,350 or equivalent
good loop to the loop posts, and tune-in stations
with the two drums. Set the C bias potentiometer
to include f to J of its total resistance in circuit
which will give 3 to I volt negative bias on the
r.f. amplifiers. A good starting point would be
KDKA, tuned in at about 53 on the loop, and 46
or 58 on the oscillator, or WDAP, at 120 on the
loop and 103 or 130 on the oscillator. If the
volume knob is set as far as it will go to the left,
no signal will get through; advancing the knob
right up to the oscillation point (sometimes
called "spill-over," "plunk," or "squeal"
point) will increase volume. If the volume knob
is turned to the right of this point, only squeals
will be heard. Remember, no squeals should be
heard on the set, other than station heterodyne
squeals of substantially unvarying pitch. On a
short-wave station, the midget condenser should
be turned in slightly to increase sensitivity; if
turned in too far, only squeals will be heard —
bear this in mind. Once set, leave it alone, but in
the first case, be sure to set it on a 2io-or 220-
meter (1430 or 1360 kc.) station. The oscillator
coil rotor should generally be set at about a 45-
degree position. There are four of these points
in the full 36o-degree arc of rotation. Remember
that full i8o-degree rotation from any of these
points will cause either upper or lower oscillator
dial setting to give strongest signals on any
particular station. Therefore, set the rotor on a
weak 300- or 325-meter (looo-or g2o-kc.) station
to produce greatest volume with good selectivity
on either upper or lower oscillator dial setting,
then use whichever point (upper or lower) is
loudest, in tuning all other stations. On a weak
signal, adjust the XL Variodenser for strongest
signals and sharpest tuning of the oscillator dial.
TROU BLE-SHOOTING
D EM EMBER, if the set does not give as
^^- good results for sensitivity and selectivity
or tone as any other average eight- or nine-tube
"super," or seven- or eight-tube t.r.f. set, under
identical and simultaneous operating conditions,
it simply is not put together or operated in ac-
cordance with the foregoing paragraphs. There-
fore, look for your trouble in your own work.
The set should not squeal in operation; if it
does, incorrect operation is the cause — look to
midget condenser and volume control settings
more carefully.
Lack of sensitivity and selectivity should cause
careful readjustment of the XL condenser and
midget condenser, and a comparison against
some other set of known performance.
Hum should be checked as outlined for the a.f.
amplifier. If it tests out correctly, and there is
hum coming through the r.f. circuits, the trouble
is an open grid-circuit and most probably due to
poor or incorrect wiring. If loud hum is in the
audio amplifier (with first a.f. transformer
primary posts, Nos. i and 2, shorted) look for
defective wiring, open balancing resistor, or poor
tubes. Move the power unit several feet away
from the set when making this test.
In proper operation the receiver should give
good super-heterodyne performance, say, average
500- to 2Ooo-mile loud speaker range, on all good
stations, hum so low as not to be noticeable
through station announcements at average
speech volume, and absolutely dependable opera-
tion in the hands of a novice, with practically
no servicing problem — and all at an operating
cost of less than ten cents an hour.
C3 C6 C7 C9 R7 C4
R6 R5 C8
Mount"
Here
UNDERNEATH THE SUB-PANEL
Here again the parts have been lettered for easy reference. The grid bias resistance for the detector tube was being experi-
mented with at the time this picture was taken, and, therefore, its correct location has been indicated by means of dotted lines
IMt-AV.N AiVI) IIMrKHPKKTATIQN OK liKKKM I KADIO KVUM IN
The Commission Improves Broadcasting Conditions
THIS month we chronicle what
should be an improvement of a
most pleasing nature in the broad-
casting situation, the clearing of 25 of the
36 channels between 600 and 1000 kc.,
accomplished by the Federal Radio Com-
mission's General Order No. 18. Perhaps,
by the time these lines are published, the
entire 36 channels will be cleared. "Clear-
ing" means that in most cases many
stations operating on one channel have
been placed elsewhere and coast-to-coast
duplication of stations now obtains which
"clears" the channel for all practical
purposes.
But we thirst for even greater improve-
ment. Having tasted the gratification which
comes of the Commission's firm and com-
mendable action, we hope for more. Every
move in the direction of clearing channels
means larger audiences and, in conse-
quence, still better broadcasting.
With amazing strides in program de-
velopment and with a Federal Radio Com-
mission working for the best interests of
broadcasting, we hope that, sooner or later,
ideal reception conditions will be attained.
Indeed, the order clearing channels from
600 to 1000 kilocycles, truly a drastic
move, promises to bring good reception
not only to urban districts but to rural as
well, where radio is becoming the most
important and essential form of home en-
tertainment and education.
So many listeners who write us are unfair
in laying the blame for heterodyne whistles
upon the incompe-
tence of the Federal
Radio Commission.
The Commission is
not incompetent; it
is impotent. No five
men under the sun
could solve the pre-
sent broadcasting
tangle without hav-
ing undisputed
power to eliminate
stations from the
broadcasting band.
In spite of any
congressional decla-
ra tions that the
ether may be regu-
lated in the public
interest and that
none have vested
rights to use it, it is
quite generally as-
sumed that broad-
casting stations
have established
what amounts to vested rights in the
ether. Having invested capital and legally
conducted a public service, station owners
contend that they cannot be deprived
of the opportunity of continuing that
service without compensation. Be that
as it may — we contend that stations,
which had to wait for broadcasting licenses
until the regulatory powers of the Depart-
ment cf Commerce were nullified by un-
favorable court decision, have no right on
the air. If property confiscation is neces-
sary to secure good broadcasting, let us
find a way to confiscate worthless broad-
casting stations.
The elimination of two or three hundred
of the smaller stations, accomplished by a
board with confiscatory powers, need not
cost more than two or three million dollars,
really a small sum when the social and
economic importance of broadcasting and
the magnitude of the industry serving it
are considered.
We make a serious suggestion for a tax
on commercial broadcasting. We realize
that our numerous friends among broad-
casting station owners will regard us, for a
moment at least, as an enemy, seeking to
add another to their already numerous
burdens. A tax on commercial broadcasting
would, at first, certainly penalize the good
stations in favor of the bad. But a two
per cent, tax, spent solely upon compensat-
ing the owners of confiscated stations,
could bring radical improvements in
broadcasting, such that audiences would
© Henry Miller
THE FEDERAL RADIO COMMISSION
This view was taken a few days before the death of the Chairman, Admiral Bullard, who is third
from the left. Harold A Lafount, the new Commissioner appointed to succeed John F. Dillon, de-
ceased, is shown at the extreme right. Until a Chairman is chosen, Eugene O. Sykes is acting as Vice-
Chairman. From left to right: Sam Pickard, E. O. Sykes, W. H. G. Bullard, Carl H. Butman secre-
tary, O. H. Caldwell, H. A. Lafount
278
be enormously increased, with inevitably
augmented revenues to broadcasting sta-
tions and improved program standards.
Furthermore, the amount of tax paid
by stations would serve as an indisputable
guide to their value. Educational and
religious stations, now operating at con-
siderable losses, could charge the organiza-
tions sponsoring them, on an hourly basis,
an amount sufficient to cover their def-
icits and thus, having established revenue,
suffer no penalty for their non-commercial
status. A definite principle of compensa-
tion for station condemnation could be
established, based upon a year's com-
mercial revenue, plus the physical value of
its equipment. Three years of taxation of
commercial broadcasting and an honestly
administered and efficient condemnation
board would leave a strong broadcasting
structure, consisting only of the most
popular and successful stations, with the
weak sisters bought out at minimum cost,
and clear channels for the remaining. The
stations to continue would be selected not
only upon the basis of economic value but
upon a definite and scientifically organized
plan, taking into account power, service
area, and geographical location.
The ultimate effect of such a policy
would certainly double, triple, and four-
fold the value of commercial broadcasting
to program sponsors. Interference-free
reception and increased coverage would
inevitably result in program improvement.
The clear reception of a program on every
channel would three-
fold the usefulness
of the receiver and
increase program
choice, serving as
another incentive to
add to the listening
audience. The radio
industry would,
therefore, prosper by
the sale of more re-
CL-iving sets. On
every hand, for the
listener, station
owner, and manu-
facturer, there
would be greater
prosperity and
greater service.
We are indeed
aware that, at first
sight, to burden a
harassed broadcast-
ing industry, suffer-
ing from interfer-
ence and insufficient
FEBRUARY, 1928
TIME TO REPLACE YOUR RADIO SET?
279
revenue, is not likely to be popular among
the commercial broadcasters. Too often,
when taxation is suggested as a remedy,
the cure is worse than the disease.
The Commission, by its recent alloca-
tions, has clearly demonstrated that fewer
stations per channel means improved re-
ception. But it has made its progress by
virtually destroying almost two thirds of
the broadcasting frequencies in order to
make one third capable of performing
maximum service. Is it efficient utiliza-
tion of valuable ether channels to impair
two thirds of those available so that one
third may be of maximum service?
The only sensible ideal is to make every
channel useful to the utmost of its capacity.
Any channel, which serves as a graveyard
for ten, twenty, or thirty stations, rep-
resents the confiscation of a substantial
investment on the part of receiving set
owners. If we value the receiving sets in
service at $450,000,000 — and this is a
conservative estimate — broadcast listeners
have spent some $5,000,000 a channel.
Confiscating two thirds of the broadcast
band, by allotting it to chaos, represents a
loss of $300,000,000 to listeners.
Is the listener not entitled to free and
complete use of his apparatus, considering
that his collective investment is much
larger than that of the broadcasting sta-
tions? Broadcasters who wail about de-
stroyed investments are themselves guilty
of destruction a thousandfold greater than
that which they suffer.
If confiscation of property is necessary
to establish good broadcasting, let us give
the Federal Radio Commission full power
to condemn broadcasting stations and the
funds with which to purchase them. We
do not hesitate to condemn private prop-
erty in order to build improved highways,
a process which has made the automobile
business one of America's greatest and
most serviceable industries. Now let us
condemn private property in order to have
good highways of the ether. It will make
radio a truly great industry, serving every
American family and home.
Who Buys This Year's Radio Sets-1
THE replacement market will be
radio's most profitable sales field
this year. The listener who has had
experience and contact with radio is
readier to appreciate the advantages of
socket power operation and the greatly
improved tonal quality attained by this
year's better receiving sets. The radio
trade quite generally overlooks the replace-
ment market, although receivers of two,
three, four and five years ago are still
widely used. The automobile industry is
now subsisting very largely upon replace-
ments which reach a dollar total far in ex-
cess of new owner purchases.
To the radio industry, this is a new prob-
lem and the approach to the replacement
market requires fundamental changes in
sales and advertising methods. The indus-
try should seize upon its opportunity en-
thusiastically because three fourths of the
selling resistance has already been elimina-
ted by the set owner's previous experience.
He is ready to understand and appreciate
the significance of modern improvements,
with but a simple explanation, laid before
him where he is accustomed to absorb his
radio knowledge.
The replacement market has the fortu-
nateadvantage that those most enthusiastic
about radio are efficiently reached through
specialized mediums which appeal to the
more ardent and, consequently, more
responsive radio follower. The publications
in the radio field have a combined circula-
tion of nearly one million and, therefore,
reach the best one fifth or one sixth of the
entire replacement market. Those who pur-
chase radio consumer magazines are natur-
ally more interested in radio than those
who do not. They have followed radio for
several years at least, and are the most
likely to possess obsolete sets. This in-
valuable group is reached at a lower cost
than an equal number of prospects among
general magazine circulations. Popular
magazines, serving every class of society
instead of singling out especially fruitful
groups, reach an insignificantly small pro-
portion of already interested buyers and
persons sold on radio by actual experience.
A general magazine is fortunate if one out
of twenty of its readers have the slightest
interest in its radio advertising; every
reader of a radio magazine is a prospect
for a 1928 radio.
Since the general spirit of the better
radio magazines is no longer predominantly
technical, but covers all phases of the
radio science, art, personality, broadcast-
ing, as viewed behind the microphone and
heard before the speaker, progress in manu-
factured receivers, telephotography and
television, and numerous other fields of
wide appeal, circulations have changed in
character so that they include not only the
home constructor and radio engineer, but
the dealer and jobber, the wealthy and
ardent listener, and the most liberal pur-
chasers of radio equipment. The new situa-
tion offers a great opportunity to the manu-
facturer to sell his wares at minimum cost.
A prophet is without honor in his own
country and the radio manufacturer is
quite inclined to regard the radio en-
thusiast as a sort of demented crank who
has no influence upon the purchase of radio
sets. However, he readily admits, when
pinned down, that it was this very element
which built up his industry and that, in-
stead of being cranks, they are pioneers
and leaders. Of course, there are a few
manufacturers who cannot profitably ad-
dress themselves to this discriminating
and well-informed group, because they do
not make a product fit to offer to an expert
radio enthusiast. But, in general, the prod-
ucts of the radio industry have reached a
standard which makes them highly accept-
able to the man with some technical knowl-
edge and appealing to him is an asset
which means the sale of not only one but
usually a good many radio receiving sets.
Rural Radio Listeners Served by
Re-allocations
IN A statement issued by the Commis-
sion shortly after its clearing of the
6oo-to looo-kc. channels, it points out
that millions of listeners in remote com-
munities, presumably a good two thirds
-
|f
.
A BRITISH MARCONI SHORT-WAVE RECEIVING STATION
This receiving unit, located at Skegness, England, was built by the Marconi company for the British
Post Office and is used as the British end of the India and Australia service. The view above shows a
corner of the land line connections and high speed recording instruments. On the left are key and
sounder for communication with the transmitting station and Radio Central in London; next are two
sets of high-speed recorders with tape pullers and a Wheatstone transmitter for sending to the London
Central office
280
RADIO BROADCAST
FEBRUARY, 1928
of the radio audience, who have little or no
choice of local programs, are especially
benefited by the new allocations. It is this
group which leans most heavily upon
radio's utilitarian and entertainment serv-
ice. The Commission states that, although
the DX listener is served by these re-
allocations, its principal purpose is to make
radio more acceptable to the rural lis-
tener.
There is some criticism due to the fact
that the thirty or more stations which now
have clear channels are affiliated with one
or the other of the networks. Therefore, a
rural listener, going down the dials on a
clear night, would find only three programs
available to him, although he may tune-in
twenty of the stations. Ultimately, this
situation may be alleviated by the assign-
ment of all chain stations to a single chan-
nel. This is not feasible at this time because
of the great cost entailed in synchronizing
stations, a complete and extra wire net-
work being necessary to accomplish this,
and, furthermore, because the affiliated
stations do not receive their programs ex-
clusively from the chain source. The better
stations throughout the country have
affiliated themselves with chain organiza-
tions and it is therefore inevitable that they
should receive favored consideration in the
matter of being assigned clear channels.
Consequently, the Commission's action is
unavoidable and it cannot rightly be ac-
cused of favoritism.
Sooner or later, however, it will be
necessary to synchronize stations so that
the same channel will be used by all sta-
tions radiating a program. This will give
an added advantage to the rural listener
because he will derive signal energy, not
only from the nearest of the chain stations
to which he tunes, but the combined signal
energy from all the stations which energize
his set. The Blue Network, for example,
combined on a single channel by synchron-
ous broadcasting, would deliver an ade-
quate local service signal almost any-
where in the eastern part of the United
States.
It has been suggested that a single
synchronizing signal be broadcast from
which all stations are to derive the carrier
signal. Such a synchronizing signal would
have to be of a frequency low enough that
its harmonics would include every broad-
casting channel. Thus a io,ooo-cycle
synchronizing signal, radiated by modulat-
ing a high-frequency carrier, would be
received at every broadcasting station in
the country. Those assigned to a 5OO-kc.
frequency, for example, would, by means
of a harmonic producer, pick off the fiftieth
harmonic of the io,ooo-cycle synchronizing
signal. This would be sufficient to serve as
the carrier for the station. The 5ist har-
monic would provide the 5io-kc. signal
and so on throughout the broadcasting
band.
Although this process appears to be a
simple solution of the frequency stability
problem, it is, unfortunately, full of
technical pitfalls, sufficient to prevent its
immediate general utilization.
We are unable to build harmonic pro-
ducers of sufficient reliability to obtain the
selected harmonic with unfailing certainty.
Much investigation is necessary before
reliable harmonic producers to cover the
entire broadcast band would be available
so that they could be employed by the
usual broadcasting station technical staff.
The harmonic producer is still a laboratory
product, requiring the highest kind of en-
gineering talent to secure satisfactory
results.
Technical aids will certainly come to the
help of the broadcasting situation, but
they cannot be relied upon to give prompt
and substantial relief, in our present
knowledge of the radio art. The mills of
the gods and the laboratories of scientists
grind slowly, but, fortunately, they never
cease grinding.
Frequency Allocation Outstanding
Achievement of International Con-
ference
T REQUIRES a careful study of the
allocations adopted by the Interna-
tional Radio Telegraphic Conference
to appraise the labors of that body briefly
and it is premature to report on more than
its outstanding and obvious achievement,
the establishment of a complete schedule of
international wavelength allocations. In
examining this schedule, it must be borne
in mind that nations may permit any kind
of emission to any radio station under their
jurisdiction at any frequency, under the
sole condition that such emission does not
interfere with any other country. To sta-
tions, which, by their nature, are known to
be capable of causing material international
interference, the contracting parties agree
to assign frequencies in accordance with the
schedule which appears below.
The assignments made to amateurs rep-
resent a curtailment of their present wide
range of channels, although they have not
lost completely the right to any of their ac-
customed bands. Those bands, designated
as "amateur" without restriction or divi-
sion, are exclusive amateur bands and there-
fore available for international communica-
tion. As to the broadcasting bands, the
American standard has been adopted,
although a few channels in the i5O-kc.
region have been made available for Euro-
pean broadcasting. A number of small but
well distributed short-wave bands for
international links are also provided, which
take into account the possibilities of both
daylight and night transoceanic rebroad-
casting. The Conference, evidently, lis-
tened appreciatively to the advice of ex-
perts in selecting these short-wave bands.
10 to too kilocycles (30,000 to 3000 meters) — Point to point
service.
100 to 1 10 kilocycles (3000 to 2725 meters) — Point to point
and mobile service.
no to 125 kilocycles (2725 to 2400 meters) — Mobile.
125 to 150 kilocycles (2400 to 2000 meters) — Mobile, mari-
time service, general public correspondence only.
150 to 160, kilocycles (2000 to 1875 meters) — (a) Broadcast-
ing, (b) point to point, (c) mobile. Subject to agreement
as follows: All regions where broadcasting stations
now exist working below 300 kilocycles (above 1000
nwters) — Broadcasting) other regions, (b) point to
point, (c) mobile. Regional agreements will respect the
rights of one another in this band.
194 to 285 kilocycles (1550 to 1050 meters) — (a) Mobile,
(b) point to point, (c) broadcasting. Subject to regional
agreement as follows: Europe (a) Mobile (aircraft only),
(b) point to point (air services only), (c) point to point
(NGP) from 250 to 285 kilocycles (1200 to 1050 meters):
(a) broadcasting from 194 and 224 kilocycles, (155010
1340 meters); other regions: (a) Mobile, except com-
mercial ships, (b) point to point (aircraft only), (c) point
to point (NGP).
285 to 315 kilocycles (1050 to 950 meters)— Special (radio
beacons).
315 to 350 kilocycles (950 to 850 meters)— Mobile (aircraft
service only). See Note i.
350 to }6o kilocycles (850 to 830 meters)— Mobile (NGP).
360 to 300 kilocycles (830 to 770 meters)— (a) Special
(direction finding); (b) mobile, where it does not interfere
with direction finding.
390 to 460 kilocycles (770 to 650 meters) — Mobile.
460 to 485 kilocycles (650 to 620 meters) — Mobile, except
damped and radio telephone waves.
485 to 51; kilocycles (620 to 580 meters)— Mobile (distress
calling, &c). See Note 2.
515 to 550 kilocycles (580 to 545 meters) — Mobile (not open
to general public correspondence), except damped and
radio telephone waves.
-How Radio Channels Are Internationally Assigned-
550 to 1300 kilocycles (545 to 230 meters) — Broadcasting.
See Note 3.
1300 to 1500 kilocycles (230 to 200 meters) — (a) Broad-
casting, (b) mobile (on the frequency 1364 kilocycles
only, wave length 200 meters).
1500 to 1715 kilocycles (200 to 175 meters) — Mobile.
1715 to 2000 kilocycles (175 to 150 meters) — Mobile, fixed
and amateurs.
2000 to 2250 kilocycles (150 to 133 meters) — Mobile and
fixed.
2250 to 2750 kilocycles (i 33 to 109 meters) — Mobile
2750 to 28 50 kilocycles (109 to 105 meters) — Fixed stations.
2850 to 3500 kilocycles (105 to 85 meters) — Mobile and
fixed.
3500 to 4000 kilocycles (85 to 75 meters) — Mobile, fixed and
amateurs.
4000 to 5500 kilocycles (75 to 54 meters) — Mobile and
fixed.
5500 to 5700 kilocycles (54 to 52 meters) — Mobile.
5700 to 6000 kilocycles (52.7 to 50 meters)— Fixed.
6000 to 6150 kilocycles (50 to 48.8 meters) — Broadcasting.
6150 106675 kilocycles (48.8 to 45 meters) — Mobile.
6675 to 7000 kilocycles (45 to 42.8 meters) — Fixed.
7000 to 7300 kilocycles (42.8 to 41 meters) — Amateurs.
7300 to 8200 kilocycles (41 to 36.6. meters) — Fixed.
8200 to 8550 kilocycles (36.6 to 35.1 meters)— Mobile.
8550 to 8000 kilocycles (35.1 to 33.7 meters) — Mobile and
fixed.
8000 to 9500 kilocycles (33.7 to 31.6 meters) — Fixed.
9500 to 9600 kilocycles (31.6 to 31.2 meters) — Broadcast-
ing.
9600 to l l.ooo kilocycles (31.2 to 27.3 meters) — Fixed.
1,400 kilocycles (27.3 to 26.3 meters) — Mobile.
1,000 to
1,400 to
i. TOO to
casting.
1,900 to
2.300 to
1,700 kilocycles (26.3 to 25.6 meters)— Fixed.
1.900 kilocycles (25.6 to 25.2 meters) — Broad-
2,300 kilocycles (25.2 to 24.4 meters) — Fixed.
2,825 kilocycles (24.4 to 23.4 meters)— Mobile.
12,825 to 12,350 kilocycles (23.4 to 22.4 meters) — Mobile
and fixed.
12,350 to 14,000 kilocycles (22.4 to 21.4 meters) — Fixed.
14,000 to 14,400 kilocycles (21.4 to 20.8 meters) — Amateur.
14,400 to 15,100 kilocycles (20.8 to 19.85 meter?) — Fixed
(5,100 to l 5,350 kilocycles (19.85 to 19.55 meters) — Broad-
casting.
15,350 to 16,400 kilocycles (19.55 to 18.3 meters) — Fixed.
16,400 to 17,100 kilocycles (18.3 to 17.5 meters) — Mobije.
17,100 to 17,750 kilocycles (17.5 to 16.9 meters) — Mobile
and fixed.
17,750 to 17,800 kilocycles (16.9 to 16.85 meters) — Broad-
casting.
17,800 to 21,450 kilocycles (16.85 to 14 meters)— Fixed.
21.450 to 21,550 kilocycles (14 to 13.9 meters) — Broadcast-
ing.
21,550 to 22,300 kilocycles (13.910 13,45 meters) — Mobile.
22,300 to 23,000 kilocycles (13.45 to 13.1 meters) — Mobile
and fixed.
23.000 to 28,000 kilocycles (13.1 to 10.7 meters) — Not re-
served.
28.000 to 30,000 kilocycles (10.7 to 10 meters) — Not re-
served.
30,000 to 56,000 kilocycles (10 to 5.35 meters) — Not re-
served.
56,000 to 60,000 kilocycles (5.35 to 5 meters)— Amateurs
and experiments.
60 kilocycles (5 to o meters) — Not reserved. Note 1 — 3331
kilocycles (ooo meters) is the international aircraft calling
and listening frequency.
Note 2 — 500 kilocycles (600 meters) is the international
calling and distress frequency. It may be used for other
purposes when it will not interfere with calling.
Note 3 — Mobile services use the band 550 to 1300 kilo-
cycles (545 to 230 meters) on the condition that they do
not interfere with the services of any nation using this band
exclusively for radio telephone broadcasting.
Note — NGP means: Not for genera) public correspondence.
FEBRUARY,
WHAT THEY DO IN NEW ZEALAND
281
New Commissioner Appointed
N NOVEMBER 14, President
Coolidge announced the appoint-
ment of Harold A. Lafount of Utah
as a member of the Federal Radio Commis-
sion to fill the vacancy created by the
death of John F. Dillon. Mr. Lafount has
used a radio receiving set and therefore
approaches the problems of broadcast
regulation with a confidence equal to that
with which we would assume the command
of a battle fleet after a visit to a navy yard.
The new commissioner may prove to be the
dark horse who brings an ultimate victory
over confusion and we wish him every suc-
cess. But certainly, it has been amply
demonstrated that the Commission's prob-
lems are highly technical and that the
Commissioners are handicapped in their
work until they have, at great cost of time
and effort, learned the intricacies of broad-
casting.
Inside the Radio Industry
A CLASSIFICATION of questionnaires re-
*» turned by 3546 dealers, made by the
Electrical Equipment Division of the Depart-
ment of Commerce, indicates that 26 per cent,
are electrical supply dealers, 20 per cent, radio
dealers, 13! per cent, hardware dealers, 8J
per cent, dealers in musical instruments, and 6
per cent, automobile dealers, 5! per cent, bat-
tery and ignition supplies, 4j per cent, tires and
tire repair shops, and smaller percentages to
other classes. A total of 68 different varieties of
retail outlets is represented in the classification.
It is rather surprising to find the hardware re-
tailer so prominently represented and the music
dealer outlet so small in proportion to the
whole.
Another comprehensive statistical survey, to
be a quarterly investigation conducted by the
Department of Commerce, is an enumeration
of the stock of radio sets and their principal
accessories in dealers' and jobbers' hands. The
survey is national in scope and the first returns
are based upon 7718 filled-in questionnaires.
This number of dealers had 147,548 battery re-
ceiving sets on hand and 9548 socket powered
sets;ordinary speakers, 1 53,091 ; amplifier-speaker
units. 5018; B and C batteries, rated in 45
volt units, 525,441; storage A batteries, 77,148.
This makes an average of twenty battery-oper-
ated receiving sets and a little over one socket
power set per dealer, a healthy situation, con-
sidering that both dealers and jobbers are rep-
resented. Moving less than 150,000 battery-
operated sets at this season is not an abnormal
demand upon the public.
RADIO INDUSTRY STANDARDS
OUR persistent campaign for the adoption
of a single set of standards for the radio
industry has now come to an end because both
trade organizations have, at last, agreed to work
together in this one respect at least. This
move, however, is only the first step in our
program, which calls for complete unifica-
tion of the two trade associations. The present
step, respecting standards, brings this objective
nearer.
The Radio Manufacturers' Association and the
Radio Division of the N. E. M. A. have agreed
to review all manufacturing standards pertain-
ing to radio and will publish a single industry
standard. In cases of dispute, the American
Engineering Standards Committee will serve as
an arbitration board. The entire industry is to
be congratulated upon this outcome of the per-
sistent campaign which a few individuals have
waged quietly and persistently for many
months.
THE Radio Manufactuers' Association has
appointed a Patent Interchange Committee,
with A. J. Carter as its chairman, which is to
work out a patent pooling plan. It has obtained
the consulting services of Mr. C. C. Hanch,
who worked out the patent cross license system
for the automobile industry. We would suggest
that this worthy effort be combined with that
along similar lines being made by the Policies
Division of N. E. M. A. Without unification of
effort, both associations are wasting time and
cannot hope to accomplish anything of perman-
ent value.
THE Radio Corporation's quarterly state-
ment for the September quarter announces
a net profit of 54,141,355, its largest net operat-
ing profit for any quarter. Its earnings per share
were $2.80 and, for the same quarter a year ago,
NEWS FROM ABROAD
1* HE writer has had the privilege of talking to
Mr. J. M. Bingham, the Chief Engineer of
the New Zealand Broadcasting System, who is
visiting the United States in order to learn the
latest in broadcasting practice from American
engineers. As a matter of fact, the entire
broadcasting industry of the United States
might profitably visit New Zealand in order
to learn how to run radio broadcasting
successfully. No country has more efficient regu-
lation.
Broadcasting has been placed in the hands of a
single company by authority of the New Zealand
Parliament. This monopoly is supported by an
annual tax upon broadcast listeners. The pur-
chase of every receiving set and every part that
goes into a receiving set, down to the last bind-
ing post, is recorded by dealers. Government
agents have access to their books at all times.
No listener can escape the vigilant eyes of
government inspectors. The revenue thus gained
is divided between the broadcasting stations and
the Government, but not in the unsatisfactory
ratio which obtains in the British Isles. Eighty
per cent, or more of the broadcast tax collected
in New Zealand is actually spent in program
talent or the erection and maintenance of broad-
casting stations. No radio advertising or com-
mercial goodwill broadcasting is allowed or
necessary.
One would conclude that, under such an
efficient system, with its magic wand to over-
come any serious problems and vicissitudes,
broadcasting would thrive and grow. Its growth
has been steady but not startling. The number of
licensees, in a population of one and a quarter
million, is about twenty thousand. Four high
power broadcasting stations cover the four-
hundred-mile length of the country. There are
some dead areas, but prospective changes in
transmitter location will soon remedy these.
Interconnecting wire circuits are being de-
veloped but, as yet, there is virtually no chain
broadcasting. Naturally, with but four stations,
there are no frequency allocation difficulties.
There is no economic problem in meeting station
maintenance cost. There is little or no evasion of
listener tax. Altogether, it is the most efficient
broadcasting system in the world.
A DEPARTMENT of Commerce statement
advises that there are 685 broadcasters in
the United States and its territories; the total
in all nations, other than the United States, is
431. Of these, 196 are in Europe, 128 in North
America, outside of the United States, 52 in
South America, 18 in Asia, in Oceania 28, and
in Africa 9. The four most powerful broadcast-
ing stations in this country are WGY, 100,000
watts with 50,000 watts as its usual power; WEAF,
50,000 watts; KDKA, 50,000 watts; and wjz,
35,000 watts. In Russia, there are two 40,000
watt stations and one of 20,000 watts. The total
number of broadcasting stations in numerical
order are: Canada 59, Cuba 47, Russia 38,
Sweden 30, Australia and Germany 24 each,
Argentina 22, United Kingdom 20, France and
Mexico 18, Spain 15, Brazil 12, Chile 9, Fin-
land 7, England 6. There are four each in
Belgium, Czecho-Slovakia, Uruguay, India,
Netherlands, East Indies and New Zealand;
three in Italy, Poland, China, Japan and
South Africa, and smaller numbers in other
countries.
STATION 2 YA AT WELLINGTON, NEW ZEALAND
The New Zealanders have elegant scenery on which to mount their radio stations if this can
be taken as typical. 2 YA has 5000 watts power and is one of four stations serving the country
RADIO BROADCAST Photograph
USING 222 TYPE TUBES IN AN AUDIO AMPLIFIER
This is the conventional resistance-coupled amplifier using two screened-grid tubes and one 171 power
tube. The little cap on top of the tube is the signal grid connection. The values of resistance, etc.,
are given on Fig. 5
By The Laboratory Staff
THE new screened-grid tube, the ux-222 or
cx-}22, is designed to appeal to the more
experimentally inclined of the set con-
structing fraternity, and while it is comparatively
simple to build receivers to utilize some of the
advantage of these tubes, the great task comes
after the last wire is in place.
Contemporaries of RADIO BROADCAST have
devoted considerable space to this new tube and,
perhaps, are so keenly alive to its potentialities
that they have somewhat over-exaggerated its
possibilities so far as the average non-technical
set builder is concerned. The screened-grid tube
has been in the RADIO BROADCAST Laboratory
for several months now, and for a considera-
ble longer period of years in the research labor-
atories of the R.C.A. and the General Electric
Company. As a result of our experiments at
Garden City, we must still say that this is an
experimental tube, and that hard and fast rules
for quickly throwing together coils and con-
TABLE i
AMPLIFICATION
FACTOR
PLATE
IMPEDANCE
8
2000
12,000
'5
30
35
25,000
150,000
250,000
densers with screened-grid tubes to connect
them, are not yet possible.
Tubes available in the United States differ
considerably from those used in England, and
in our opinion suffer somewhat in comparison.
This is not due to their electrical characteristics
but, rather, due to the mechanical arrangement
which, in English tubes, seems to have been
worked out with more thought toward ease of use.
Readers interested in the tube may find Cap-
Iain H. J. Round's book, The Shielded Four-
Electrode Yalve, very helpful. It is published by
Bernard Jones Publications, Ltd., 58 Fetter
Lane, London, E.C-4, and the price is two shill-
ings and sixpence (a little over sixty cents).
Considerable time has been devoted in RADIO
BROADCAST Laboratory to determine how to use
these tubes in radio-frequency amplifiers. Before
discussing these experiments in detail, we will
indicate the advantages obtained through the
use of a 222 screened-grid tube instead of a
2OI-A type tube in a radio-frequency amplifier.
This involves delving somewhat into r.f. ampli-
fier theory to get an idea of how they work and
upon what their amplification depends.
When a 201 -A type tube is used in a radio-
frequency amplifier circuit (see Fig. i) in con-
junction with an ordinary r.f. transformer, the
amplification obtained will be a function of the
number of turns in the primary coil and its
coupling to the secondary coil. With either a very
few or a great many primary turns the amplifi-
cation will be low, but with some definite inter-
mediate number of turns the amplification will
become a maximum. Under such conditions
the amplification using a 201 -A tube will be
about 10 at 500 meters (600 kc.) and about
1 5 at 200 meters (i 500 kc.). In order to get even
this amplification from a 2OI-A type tube, a
carefully designed circuit is necessary, incorpor-
ating some method of neutralization to overcome
the effect of the capacity between the grid and
plate of the tube, which would otherwise cause
the circuit to break into self oscillation.
Somewhat greater amplification can be ob-
tained with an ordinary three-electrode tube if
the electrodes are so constructed and arranged as
to give the tube a higher amplification constant.
Such a tube is called a "high-mu" tube and
although such tubes have been used most fre-
quently in resistance-coupled audio amplifiers,
they may also be used in an r.f. amplifier. There
are, however, several reasons why their use in the
latter capacity is not advisable.
The amplification factor of a tube is entirely
under the control of the tube engineers, and tubes
can be built with little difficulty having constants
anywhere from 0.5 to 500. When the amplifica-
282
tion constant of a tube is increased in this man-
ner, however, the plate impedance also increases
and, in fact, increases approximately as the
square of the amplification constant, so that the
plate impedance increases much more rapidly
than the amplification constant. The table on
this page will give some idea of how the plate im-
pedance varies as the amplification factor is
changed.
Now, in order to obtain considerable gain from
a high-mu tube when it is used as a voltage
multiplier in an r.f. stage, it is necessary to have
a very high impedance load in the plate circuit,
so that transformer coupling with a step-up ratio
may not be practical. An ordinary high resistance
might be used were it not for the fact that it
would be shunted by the output and input ca-
pacities of those tubes preceding and following it.
These capacities across the load resistance
would limit the effective impedance of the load
in the plate circuit to a low figure, so that the
amplification will fall to a comparatively low
value. An effective way in which to obtain high
gain from a high-mu tube is through the use of a
tuned-plate amplifier (see Fig. 2 and compare it
with Fig. i). In such a circuit the output and
201- A
201-A
-J —
R.F. Transformer
FIG. I
A transformer is used to connect two tubes work,
ing as radio-frequency amplifiers. The number
of turns on the primary for maximum amplifica-
tion is controlled by the input and output im-
pedance of the tubes used. For a given set of
tubes and at a given frequency there is a number
of turns which will give maximum amplification
FEBRUARY, 1928
THE SCREENED-GRID TUBE
283
input capacities of the tube are in parallel with
the condenser which tunes the circuit and have
no effect other than to decrease slightly the
amount of capacity necessary in the variable
condenser in order to tune to any given wave-
length. At resonance the effective resistance as
measured across the two ends of a tuned circuit
is very high and the tuned plate type of amplifier
is therefore capable of producing an effective
high impedance in the plate circuit— a necessity
if high gain is to be obtained, as stated before.
The effective resistance at resonance of even a
good coil-condenser combination, when it is
connected into an amplifier, is, however, proba-
bly not more than 100,000 to 200,000 ohms.
When the effective resistance in the plate circuit
of a tuned plate r.f. amplifier is equal to the plate
impedance of the tube, the amplification ob-
tained is one half the mu of the tube. Thus, a
tuned circuit giving an effective resistance of
150,000 ohms, and used in conjunction with a
tube having an amplification constant of 30 and
a plate impedance of 150,000 ohms would pro-
duce an effective amplification of one half mu,
or 15. It should be evident that the limiting
factor preventing the attainment of much larger
values of amplification, is the large increase in
plate impedance that occurs when the amplifica-
tion constant is increased. What we want, ob-
viously, is a tube with a very high amplification
factor and as low a plate impedance as possible.
Such characteristics are not obtainable using an
ordinary three-electrode tube because, as indi-
cated previously, the plate impedance increases
much more rapidly than the amplification con-
stant. To obtain a high mu with a comparatively
low plate impedance, it is necessary to introduce
a fourth electrode into the tube. The effect of the
fourth electrode was explained in articles on the
four-electrode tube in the December, 1927, and
January, 1928, issues of RADIO BROADCAST, and
will not be repeated here except to point out
that this fourth electrode does give a very large
increase in the amplification constant without as
large an increase in plate impedance as would be
obtained with a three-electrode tube. Measure-
ments in the Laboratory indicate that the am-
plification constant of the 222 tube is about 200,
under certain conditions, and the plate imped-
ance is about 800,000 ohms. If an ordinary three-
electrode tube, such as a type 240 high-mu tube,
were to be constructed to have a mu of 200, the
plate impedance would be about five to seven
million ohms! A high value of amplification
constant with a comparatively low plate imped-
ance is one of the major characteristics and
advantages of the 222 screened-grid tube.
The amplification obtained from this tube is a
function of the mutual conductance of the circuit
and the impedance of the load in the plate circuit.
Owing to the fact that the impedance of the tube
is so high, higher than its load impedance, the
mutual conductance of the circuit is practically
equal to that of the tube. If the mutual conduc-
tance of the tube is assumed to be 3 50 micromhos
the amplification with various load impedances
can be obtained by multiplying the mutual con-
ductance in mhos by the load impedance. The
values have been calculated and appear in Table
2. For certain reasons, however, it is likely that
we can't get more than about 200,000 ohms in a
tuned circuit under operating conditions. If an
effective resistance of 200,000 ohms is connected
in the plate circuit of a 222 tube, then the am-
plification will be about 70 (see Table 2). Com-
pare this with the amplification of 10 to 15 ob-
tained with a 201-A type tube.
The 222 tube has another distinct advantage,
also important in the construction of high-gain
radio-frequency amplifiers. This second advan-
tage is that the effective grid to plate capacity
^
FIG. 2
If the plate impedance of the previous tube is
very high the entire input coil of the following
tube may be used to approach the maximum
amplification possible. This is true when the
screened-grid tube is used, for its plate impedance
is very high indeed, of the order of one half to
one megohm
of the tube is very small. It is this capacity which
causes an ordinary tube to oscillate when it is
used in an r.f. circuit. Theoretically, it is possible,
therefore, to use this new tube in an r.f. amplifier
without resorting to any scheme of neutralization
to prevent the tube from oscillating.
Some experiments have been made in the
Laboratory in an attempt to use these tubes in
an r.f. amplifier designed for operation over the
broadcast band. The circuit diagram is given
here in Fig. 3. The experiments indicated more
than anything else the difficulty of operating
these tubes in a circuit designed to give the
maximum amplification of which the tube is
capable. The experiments also indicate that the
tube can only be satisfactorily used in circuits
containing very complete shielding and very
complete filtering in the battery supply leads.
This is to be expected, for such shielding and
filtering is necessary in a good r.f. amplifier, using
201-A type tubes and, obviously, will be much
more essential in an amplifier using these new
tubes.
If the amplification of a circuit consisting of a
ux-222 tube followed by a tuned circuit is meas-
ured, it be will found, with a good coil, to average
about 30. The amount of gain obtained depends
upon the efficiency of the coils used and increases
as the coil is made better.
The first experiments were made with just
one stage of r.f. amplification using the 222 tube
followed by a detector, and even with very
complete filtering and with both of the circuits
shielded in aluminum cans the circuit would
oscillate on practically all wavelengths. The coils
used in the tuned circuits in this receiver were
those made by Silver-Marshall, Incorporated, and
it is probably true that, if poorer coils had been
used, the circuit would have been found stable in
operation. In fact, one ohm in series with the
tuned circuit at 500 meters (600 kc.) and four
ohms in series with the circuit at 200 meters
(i 500 kc.) was all that was necessary to make the
circuit stable. This additional resistance neces-
sary to prevent oscillation is not very great and
many coils would have even higher resistances,
than that of the combined Silver-Marshall coils
and resistances.
The same conditions of instability were, of
course, also experienced when the receiver was
changed over to use 222 tubes in two stages of
r.f. amplification. Again, even with good filtering
of the battery circuits, it was impossible to
TABLE 2
Effect of Coil Resistance
SERIES
RESISTANCE
OF
COIL
EFFECTIVE
RESISTANCE
AT
RESONANCE
FIGURE
OF
MERIT
AMPLIFICATION
Gm = 350
50
25
17.5
12.5
6.2
50,000
100,000
150,000
200,000
300,000
31.5
63.0
126
252
504
17.5
35
42.5
70
105
Conditions: Coil inductance 250 microhenries
Frequency, 1000 kc.
control the circuit, and it persisted in oscillating,
over the entire broadcast band. The circuit could
be stabilized by any of the "losser" methods.
In this particular receiver it is found that a resist-
ance of about looo ohms connected between the
grid and tuned input circuit would prevent the
tubes from oscillating. Also stabilization of the
amplifier is possible by tapping the plate on to a
portion of the output coil rather than connecting,
it to the top of the tuned circuit, but this method
of connection also results in a decrease of am-
plification. The photograph on page 284 shows
| Output
FIG. 3
Here is a two-stage screened-grid broadcast frequency amplifier hook-up. The stage shielding, and
the filtering in each plate- and screen-voltage lead must be very good, and leads to the control or
signal grid on top the tube must be short and often shielded. The leads connecting one stage to the
next should be run in copper tubing which is grounded. Even then it may be found difficult to "1--'J
down" the circuit
'hold
284
how the coil was tapped. Further experiments
will be conducted in the Laboratory to indicate
the comparative effect of these various methods
of stabilizing the circuit where they are necessary,
but the use of such methods of preventing oscil-
lation probably decrease the amplification that
can be obtained and it will be preferable to design
the receiver in such a manner as to give stable
operation without any stabilizing devices. It may
seem peculiar to the reader that so much diffi-
culty was experienced with oscillation in the r.f.
amplifier when one of the major purposes of the
tube was to give freedom from instability in r.f.
circuits. It should be realized, however, that the
tube gives a very high amplification and it is
necessary to develop new design features in re-
ceivers before these tubes can be utilized to best
advantage. When it is realized that very careful
design is required to produce stable high-gain
radio-frequency amplifiers using ZOI-A'S it should
be clear why even greater care is necessary when
a 222 tube is used, and perhaps four times the
amplification per stage is obtained. It is probable
that high-gain amplifiers that are perfectly stable
at high radio frequencies will be constructed, but
as yet we have not been able to do it in the
Laboratory. This should not be construed as a
statement to the effect that the possible gain is
not greater than that obtainable with 201 -A
type tubes, for it certainly is — considerably so,
but what we wish to infer is that circuits designed
to operate with the tube to its best advantage
are not available.
There are other problems than those con-
nected with gain and stability. That of securing
selectivity is probably even greater than that of
maintaining stability over a wide frequency
band. Owing to the greater amplification of all
signals, the apparent selectivity is poor. When
one has a two-stage broadcast frequency am-
plifier using screened-grid tubes giving three
times, to be conservative, the gain per stage of
2OI-A tubes, the problem of selectivity becomes
serious. The solution may be to decrease the
gain per stage or to use some type of filter circuit
at the input of the receiver capable of increasing
the selectivity.
USE IN AUDIO AMPLIFIERS
IN AUDIO-frequency amplifiers the difficulties
' are not so great, due to the fact that what
grid-plate capacity exists in the tube (it is of the
order of 0.025 mmfd.) cannot feed back such a
RADIO BROADCAST
FEBRUARY, 1928
2800
2600
2400
2200
2000
1800 ~
< 1600 -
o
3 1400-
1200
1000
800
600
400
200
100 1000 10000 100000
CYCLES
FIG. 4
When the total a.c. voltage appearing in the plate circuit of the last tube is divided by the input
voltage to the first tube, this kind of curve results. In each case the final tube was a 171, and various
combinations of high-mu tubes, screened grid tubes, and standard 2OI-A tubes were measured and
the results plotted as shown
RADIO BROADCAST
LABORATORY
Two CAT- S3! & One UX-171
Ik 12 mfd
AO <>180 O-40.5
-1.5 Tuo VX-SiO & One UX-171
~*TwoUX lo'-A orOn'cX-'tT'&'o^'ux-l" " "— "— ..'^
large voltage into the input as it can at higher
frequencies
The two uses of this tube have been pointed
out in previous articles. It may be used as a
screened-grid tube in which the grid-plate
capacity has been almost eliminated, or as a tube
in which the grids are reversed and one is used
mainly to reduce the space charge of the tube so
that we have a tube whose values of amplifi-
cation factor and impedance are much greater
than the best of our high-mu tubes, the plate-
grid capacity still being appreciable.
Experiments in the Laboratory indicate that
the space-charge application of the tube is a good
talking point but not much good in practice. If
one wants to use this new tube in a low-frequency
amplifier, which is where the space-charge tube
would be important, all that is necessary is to
use the screened-grid tube with proper values of
resistances, capacities, and voltages. A photo-
graph on page 282 shows a conventional three-
stage resistance amplifier used in the Laboratory
RADIO BROADCAST Photograph
AN AUTO-TRANSFORMER MAY BE USED
In place of the conventional two-winding transformer between tubes, an auto-transformer may be
used. This photograph shows how the proper place to tap the coil is determined in the Laboratory.
The amplification at each tap is measured and the best number of primary turns found
to obtain the data given in Fig. 4. Using
screened-grid tubes with 180 volts to the 0.25-
megohm resistors and 45 volts on the screen, a
flat characteristic was obtained from 60 to
10,000 cycles. The total voltage appearing in the
plate circuit, roughly three times that across
the looo-ohm resistance in its output, divided
by the input voltage, gave a ratio of 2200, _
which is almost three times that obtainable when
ux-240 high-mu tubes were used. Six volts were
obtained across the output resistance when the
input voltage was roughly five millivolts.
There is no catch in this amplifier, and for
anyone who wants a voltage gain of 2200, and
can use it, we recommend converting his old
resistance amplifier into one using the new tubes.
While the curve in Fig. 4 shows that some
amplification may be obtained at low radio
frequencies with resistance coupling, much
greater voltage step-up will be secured if tuned
plate circuits are used, just as we use them at
broadcast frequencies. Here the voltage gain
possible is a function of but two factors, the
mutual conductance of the circuit and the load
impedance. The mutual conductance of the
circuit is practically constant and equal to the
static mutual conductance of the tube. Neither
of these statements is true of ordinary tubes
in ordinary circuits.
Multiplying the two factors together gives
the maximum voltage gain to be expected, which
is approached but not reached in practice. With
a mutual conductance of 300 and a tuned circuit
with an effective impedance of 250,000 ohms, a
voltage step-up of 75 should be secured, and with
air-core coils, amplification as high as 200 in
the intermediate-frequency band has been re-
corded. When resistance coupling is used, the
familiar drop in amplification at high frequencies
is noted, due to the stray shunting capacities
as well as the output and input capacities which
tend to lower the effective impedance in the
plate circuit.
In the amplifier of Fig. 4 a voltage gain of
2200 was indicated when 222 type tubes were
used in the first and second stages. This is the
total a.c. voltage in the plate circuit of the last
tube divided by the input voltage. Figuring
that the power tube, 3171, contributes a voltage
amplification of 3, the two screened-grid tubes
FEBRUARY, 1928
2000
1500
10X30
500
100
Samson
CX-322 Symphonic UX-201-A
200 400 600 800
1000 1200 1400
CYCLES
FIG. 5
There is often some advantage in a highly peaked amplifier. These curves
were made with a Samson "Symphonic" transformer when used with a
screened-grid tube
contribute about 27 each. In the Laboratory a
single cx-322 (ux-222) fed into a ux-171 gave a
voltage stepup of 120, corresponding to what
may be expected from a three-stage resistance
amplifier when two 2OI-A tubes with a 171 are
used.
Off hand a voltage amplification of over 3000
with three tubes seems tremendous, but let us
consider two transformer-coupled stages plus
a final 171 amplifier. If the transformers have a
3:1 turn ratio, and the tubes have a mu of 8. the
total voltage amplification from plate circuit
of the last tube to input will be (3 x 8)2 x 3. which
gives 1730.
When transformers are used with the screened-
grid tube, the effect of a low primary inductance
transformer used with a low-impedance tube is
obtained. In other words, a good transformer
with a low-impedance tube gives a good
characteristic; a high-ratio transformer (low
primary inductance) with a high-impedance
tube gives a peaked characteristic; a good trans-
former with a high-impedance tube also gives
more amplification about the middle of the audio
band than it does at the two ends. Curves of a
Samson "Symphonic" transformer, which gives
flat amplification with a I2,ooo-ohm tube, are
shown in Fig. 5 and may indicate to code listeners
how they can confine the amplification to a
rather narrow band of audio frequencies. This
transformer naturally resonates at a rather low
frequency, and if the amateur or code listener
desires his amplifier to peak at a higher fre-
quency he should use a transformer with lower
primary inductance, say a 5-1 transformer.
THE SCREENED-GRID TUBE
These curves show a
discrimination of two to
one in voltage amplifi-
cation between 200 and
500 cycles, and a total
amplification of nearly
2000 under certain con-
ditions. In other words,
across 7500 ohms in the
output of a 201 -A type
tube, 8.85 volts were ob-
tained with an input of
3.5 millivolts. This is
vastly greater amplifi-
cation than amateurs
use to-day, and probably
far greater than they
need. The average short-
wave receiver with one
stage of audio, and fair
coupling to the antenna,
goes down to the noise
level, if the audio gain
is about 30 to 50. The
advantage of using more
audio amplification lies
in the fact that looser
coupling to the antenna
may be utilized, with
consequent decreased
radiation — with the us-
ual type of receiver — and
the fact that in good lo-
cations, where the noise
is far down compared to
weak signals, this ampli-
fier will enable the lis-
tener to hear practically
any radio-frequency dis-
turbance in the ether,
whether it is caused
by signals or otherwise.
The diagram of connec-
tions for this amplifier
are given in Fig. 5. If
still greater discrimination in favor of a cer-
tain small band of audio frequencies is desired
the screened-grid tube might be connected
to the detector output by means of a low-
inductance choke, say of two or three henries,
as shown in Fig. 6. This will be practically
a short-circuit on the low frequencies, and
will lower the voltage gain at all frequencies,
285
but there will be plenty left. The average tele-
phone receiver peaks very sharply between 700
and 1200 cycles and, combined with such a
circuit as has been used in the Laboratory,
should enable the listener to work through low-
frequency static noises. There is some question
among amateurs whether it is desirable to tune
their audio amplifiers, since so many "hams"
use low-frequency sources of plate supply for
their power tubes, many using raw a.c. and
others using self-rectifying circuits in which the
0.01 I
222
201-A
FIG. 6
If still greater discrimination against unwanted
audio signals is desired, this manner of connect-
ing the detector to the audio stage might be use-
ful. The low-impedance choke in the input short
circuits the low frequencies. The bypass con-
denser across the audio transformer secondary
shunts out the higher audio tones and leaves only
a narrow band around 1000 cycles
tone is rather low. It is probable that it is the
higher audio tones which should be eliminated
from a code amplifier by proper bypassing, for it
is these tones due to tube noise and other sources
that supply nothing to the amateur but, on the
other hand, tax his nervous energy.
The screened-grid tubes which have been
tested in the Laboratory are microphonic, and
in the transformer-coupled system shown in Fig.
6, some trouble was encountered in keeping
the amplifier from singing at the frequency
where it amplifies greatest, which was near the
mechanical resonant frequency of the elements
of the tube. In the resistance amplifier less
trouble was encountered, but it must be re-
membered that we are dealing with a large volt-
age amplification, which means that the likeli-
hood of trouble from every source is increased.
RADIO BROADCAST Photograph
AN EXPERIMENTAL SET-UP
This is the Laboratory's "brass box" receiver — one r.f. stage using a screened-grid tube, with acces-
sory apparatus, a detector, and a single stage of transformer-coupled audio amplification, are included.
Arrangements are made for using a 2OI-A type tube in place of the 222 type so that the increase in
amplification due to the new tube may be directly measured. The detector is calibrated and used as
a vacuum-tube voltmeter while the audio stage enables the experimenter to monitor what is going
on in the system
RADIO FOLK YOU SHOULD KNOW
WALTER VAN B. ROBERTS
Drawing by Franklyn F. Stratford
MR. ROBERTS is well known to readers of
RADIO BROADCAST as a frequent contribu-
tor to the magazine, and as the author of the
comprehensive and lucid " How Radio Receivers
Work" (Doubleday, Page & Co.). He is the in-
ventor of the Roberts receivers, combining cas-
cade radio-frequency amplification and regenera-
tion. Since 1924 he has been on the engineering
staff of the Radio Corporation of America, as
a receiver and patent specialist. Mr. Roberts
was an instructor in Physics and Electrical
Engineering at Princeton before assuming his
present position.
With some exceptions, among which the
Roberts receiver is noteworthy, new receiving
circuits christened with the name of the inventor
have been lacking both in originality and tech-
nical merit. The reason has generally been too
much publicity urge and not enough engineering
qualifications on the part of the begetter of the
great idea. Mr. Roberts is utterly lacking in
publicity itch, and very strong in engineering
background. From Princeton he has the follow-
ing degrees: B. S., A. M., E. E., and Ph. D.,
but he is so modest about them that few people
know he has them. The same applies to his schol-
astic honors in mathematics and physics— mem-
bership in Phi Beta Kappa, a medal for electrical
research, and several fellowships and scholar-
ships. A characteristic touch is the footnote
appended to the bibliography at the end of his
excellent little book, "How Radio Receivers
Work": "This Bibliography is recommended
to radio experimenters who really desire to in-
crease their technical knowledge." The book
itself is a very good summary, even under the
handicap of some degree of popularization, of
technical knowledge in the radio receiver field,
but this fact the author apparently declines to
recognize.
In May, 1917, Mr. Roberts enlisted in the
Signal Corps as a Master Signal Electrician, "a
high-sounding title ranking along with some of
the higher grades of sergeants, if I remember cor-
rectly," as he puts it. He soon returned to Prince-
ton to organize and run the Department of Sig-
nalling and Wireless in the School of Military
Aviation, an army ground school for aviators.
The object of the course was to inculcate the
several thousand men who took it with an ele-
mentary knowledge of radio theory and prac-
tice on the spark-set-and-crystal-detector level,
and to teach them to receive and send Morse at
low speed. The code students were taught to
print each letter separately as received, and
cautioned not to look at letters already recorded
for fear that they would be influenced in copying
what was to follow. "To this day," testifies Dr.
Roberts, " I copy code by writing letters sepa-
rately and get all 'balled up' if I try to see what
the message is about before it is all finished."
Evidently he found learning the code a very
painful process at first, as it is for most people.
A monograph could be written about the agon-
ized thoughts, amounting almost to hallucina-
tions, the disturbances of breathing, the invol-
untary lapses of attention during which the code
characters are heard while, in a sort of paralysis,
'T'HERE are many and important figures in the
•L radio world who are not especially well known
to readers of this magazine. We have read in great
detail of the lives and work of such men as Marconi,
Alexanderson, Deforest, Sarnoff, Crosley, Arm-
strong— to choose names at random — but there are
many others who are worthy of note and who are be-
hind the scenes. RADIO KROADCAST will, from time
to time, carry stories which will take the reader be-
hind the scenes a bit. A short article in our January
issue told something about Ralph H. Langley of the
Crosley Company. This article, devoted to Walter
Van B. Roberts, describes a man whose name is
known all over the world because of his circuit,
which was first described in this magazine for April,
1024. Mr. Roberts' activities are not especially well
known to our readers and the accompanying article
attempts to sketch some of his work.— THE EDITOR.
•M*
the mind refuses to decipher them, which af-
flict the learner, particularly when he is pushed
ahead too fast. As far as the intellectual factors
were involved, Dr. Roberts naturally had little
difficulty, and one of his feats, which proved
WALTER VAN B. ROBERTS
useful in convincing the men that their memory
of the code characters would improve with prac-
tice, was an ability to receive at ten words a
minute any new code made up of four-element
combinations of dots and dashes, after four
minutes of study.
Early in 1918, Mr. Roberts obtained a com-
mission as First Lieutenant in the Signal Corps,
and soon after he was transferred to the 2gth
Engineers Sound-Ranging Service. In this
branch of artillery practice microphones are
placed at about half-mile intervals in convenient
or possible places, depending on the terrain and
the nature of the gun fire as well as on the tech-
nical requirements of the method. A pair of wires
runs from each transmitter to a central station.
When an enemy gun fires, the sound, traveling
at only about 1200 feet per second, is received
first by the microphone nearest to it, and, after
an appreciable interval, by the next microphone,
and so on. These times are automatically re-
corded at the central station, and the location
of the gun follows after a few minutes of calcu-
lation. The big job is keeping the lines intact;
Mr. Roberts states that half the personnel of a
sound-ranging group is required for this purpose,
over a hundred breaks in the lines during a
night of heavy shelling being not uncommon.
He thinks that a small radio transmitter asso-
ciated with each microphone might be better •
than the wire links.
Mr. Roberts was a technical officer in the
sound-ranging dugouts from June to October,
1918, when he was retired to hospital "with an
excuse for getting a wound stripe," as he is
pleased to phrase it. However, valuable technical
officers were not sent back for bruised finger
nails, and we may surmise that Mr. Roberts did
not find his way to the rear alone, or under his
own means of locomotion. He did go to the front
alone, however, and by almost as painful a route.
It seems that he sailed for France as a casual
officer in charge of one hundred and twenty
crates of sound-ranging equipment, including,
storage batteries, carboys of acid, wire, and
special microphones responsive only to low-
frequency sounds. His first job was to keep his
one hundred and twenty crates together in the
unloading process. He succeeded, presumably
by exerting the forcefulness of a brigadier gen-
eral, which is difficult without the silver star.
With all the stuff in a freight car, Roberts added
his baggage and a can of corned beef, and finally
himself. He thus traveled in state to the freight
yards outside of Paris, where he remained two
days. He did not leave his freight car, because no
one knew when it would pull out, and he wished
urgently to be with it at that time. After a week
in the freight car, he finally got close enough to
the front to permit the equipment to be trans-
ferred to three trucks, which moved it into the
trenches under cover of darkness.
Before the war Dr. Roberts had one other job
—he worked on acoustic problems for the West-
ern Electric Company, at $12 per week. But he
says that this sum was more than he was worth.
Mr. Roberts is married, has two children, and
lives in Princeton, New Jersey.
286
RADIO BROADCAS
HERE ARE THE NECESSARY TUBES FOR THE UNIT DESCRIBED IN THIS ARTICLE
The metal disc is the size of a half dollar, and is shown to give some idea of the size of the tubes
An A* C* Push-Pull Amplifier and
By J. E. Coombes
•'holograph
THE introduction of a.c. tubes has greatly
simplified the construction of complete
receivers which derive all of their power
directly from the electric light mains. For those
of us who now have a tuner unit or a complete
receiver with an out-of-date audio amplifier, the
a.c. tube is a logical means whereby we can con-
struct a completely a.c. operated audio amplifier
that can be hitched on to the output of the de-
tector tube or to which we can connect an elec-
trical pick-up when we want to play phonograph
records. And, incidentally, we can design our
amplifier also to supply plate voltage to the
detector and r.f. tubes of the radio receiver
proper. Such a combination amplifier and B
supply device is illustrated in this article.
The device illustrated herewith includes a two-
stage transformer-coupled amplifier using a type
227 a.c. tube in the first stage, followed by two
type 210 tubes in a push-pull arrangement.
Plate potential for these tubes is obtained from
two 216-8 or 281 type tubes operating in a full-
wave rectifier circuit. Filament current for the
two 2 lo's is obtained from a filament winding on
the power transformer (Ti in Fig. i) and filament
current for the 227 a.c. tube is obtained from a
separate filament transformer, T2. The latter
transformer also contains a winding which can be
utilized to supply one or more r.f. tubes in the
radio receiver proper, thereby making the entire
set operate directly from the power mains.
We are assuming that 226 type a.c. tubes will be
used in the r.f. amplhier, and a 227 type tube for
the detector. The latter will be supplied by the
same transformer winding as the first audio stage.
The B power part of the amplifier contains a
glow tube to maintain the output voltages con-
stant independent of the load drawn by the
radio receiver.
Some readers may merely want to construct
the push-pull circuit and B supply rather than a
complete two-stage amplifier. For this reason
the circuit diagram has been divided into two
parts by a dotted line, the push-pull amplifier
and B supply being located to the left and the
first stage of audio amplification to the right.
Neglect the right-hand side of the diagram if
only the push-pull amplifier and B supply are to
be constructed, and connect the output of the
receiver proper to the terminals marked X-Y,
the new input posts. This latter unit (the
push-pull amplifier) will operate without any
appreciable hum alt hough a slight amount of hum
is noticeable during the silent periods in a pro-
B Supply
288
RADIO BROADCAST
FEBRUARY, 1928'
gram when using the complete two-stage am-
plifier.
Naturally this amplifier can handle considera-
ble volume. Volume, however, is not the main
objective any more than an 8o-mile-per-hour
automobile is expected to travel at top speed
through traffic. Like the automobile, however,
this heavy-duty power amplifier has the liberal
fund of reserve power essential to prevent over-
loading and thereby reproduce a radio program
with the least possible distortion.
The power transformer, TI, contains three
separate windings. One winding provides 550
volts either side of the center tap to supply a
full-wave rectifier system using two 216-8 or
281 type tubes. The latter tube, because of its
greater rating, will generally have somewhat
longer life than a 2 16-8 tube and will also give a
slightly greater output voltage. In addition to
the center-tapped high-voltage secondary, the
transformer also con tains two yj-volt windings to
supply filament current to the rectifiers and the
210 power amplifier tubes. The output of the
rectifier is fed into a filter system containing two
filter chokes, Li and L2, and three condenser
banks, Q, C2, C3. The high-voltage output,
(about 450 volts under load) of the filter is fed
directly to the plates of the ux-2io (cx-3io)
tubes.
All of the resistances necessary in the construc-
tion are contained in the Ward-Leonard Vitrohm
resistor kit, type No. 507-47. RI and R2 in the
diagram are two 5Ooo-ohm resistances contained
in the kit. RS is composed of a combination of
resistors. By using different values of resistance
at this point the amount of current drawn by the
glow tube is varied. Generally, it will be satis-
factory to have RS consist of the 3500-0(1171 and
i 5OO-ohm resistances in series, to give a total
resistance of 5000 ohms. However, when the
tuner unit consists of only a couple of tubes, say
a detector and one stage of r.f., this resistance
may be increased by connecting the 3ooo-ohm
resistance in serieswith the twomentioned above.
This combination will give a total resistance of
8000 ohms and this additional resistance will
decrease, somewhat, the current drain on the
filter system and the maximum possible voltage
is thereby delivered to the plate of the power
tube.
The C bias for the 227 type tube is obtained
from the voltage drop across the ijoo-ohm re-
sistance, Rt This resistance is bypassed with a
2-mfd. condenser. C bias for the 210 tubes is
obtained from the 75O-ohm resistance, R5, con-
nected to the center tap of the filament winding
supplying these tubes. A bypass across this re-
sistance is not necessary because there are no
audio-frequency currents flowing through it.
The following table shows how the total out-
put voltage of the rectifier-filter system varies
with current drawn from it:
D
C. CURRENT, i«A.
D. C. VOLTS
60
537-5
7°
So
00
515.0
487.5
462.5
TOO
440.0
1 10
427-5
120
4'7-5
In normal operation the 2io's take about 20
mA. each, the glow tube a maximum of 40 mA.,
the first audio stage requires a maximum of 5
mA., and if the detector and r.f. tubes take a
total of 10 mA., then the total load on the B
supply unit will be 95 mA. At these current
drains the output is about 450 volts and sub-
tracting about 30 or 35 volts which is lost in the
C bias resistance, there is left an effective voltage
of about 415 volts on the plates of the 210
tubes.
The complete amplifier, as the illustration
shows, was constructed on a baseboard, measur-
ing 9 x 24 inches, and most of the wiring can be
done under the baseboard by drilling holes
through the board directly beneath the terminals
on the various units and threading the leads
through. The filament leads to the 2io's and 227
should be twisted. No special kinks are necessary
in the construction and the circuit diagram and
illustration in this article should supply all the
necessary constructional hints.
To assemble the complete amplifier and B sup-
ply exactly as illustrated, the following parts are
necessary:
T! — Thordarson Power Transformer, T-2OO.8
LI, U — Thordarson Double Filter Choke,
T-2O99
T2 — Thordarson Filament Transformer, T-2445
T3 — Thordarson R-2oo Audio Transformer
T4 — Thordarson Push-Pull Input Transformer,
T-2408
T6— Thordarson Push-Pull Output Choke, T-
2420
Ci, Q — Acme Parvolt Filter Condensers, Series
B, 2-Mfd.
C3 — Acme Parvolt Filter Condenser, Series B,
4-Mfd.
C4 — Acme Parvolt Filter Condenser, Series A,
4-Mfd.
C5 — Two Acme i-Mfd. Parvolt Filter Con-
densers, Series A
C6 — Acme Parvolt Filter Condensers, Series A,
i-Mfd.
these resistances
are contained in the
Ward Leonard Vi-
trohm Resistor Kit,
R! — 5000 Ohms
R, — 5000 Ohms
R3 — 5000 to 8000 Ohms
(See Text)
R, — 1500 Ohms No. 507-47
R6 — 750 Ohms
R6 — General Radio Center Tapped Resistance
Five Benjamin Sockets, 4~Prong, No. 9040
One Benjamin Socket, 5-Prong, No. 9036
Seven Eby Binding Posts
THE REQUISITE TUBES
Two ux-2io Power Tubes
One ux-874 Glow Tube
Two ux-2i6-B Rectifier Tubes
One ux-227 A.C. Heater Type Tube
The power lead from TI can be plugged into an
extra receptacle which is in the end of the fila-
ment transformer, leaving one lead to be plugged
into the regular light socket. In operation, the
resistances will get quite warm and the regulator
tube should glow with a bluish or pinkish glow.
The input terminal connecting to the P post ol
the input transformer should connect to the
plate of the detector tube and the other input
lead should connect to the B + 45-volt terminal
on the B supply. If one side of the A battery is
not grounded, it should be.
It will be noted that R.C.A. terminology has
been resorted to throughout this article when
referring to tube types. Tubes exactly similai
to those bearing the R.C.A. stamp are supplied
' by Cunningham. The following table shows the
parallel types:
R. C. A.
Cunningham
ux — 226
cx — 326
UX — ;227
ex— 327
UX — 210
UX — 2l6-B
ux — 281
ux — 874
cx — 310
cx — 316-6
cx — 381
cx— 374
Many independent manufacturers are als<
supp'ying tubes the characteristics of which an
similar to or approximate very closely those o
the tubes specified in this article.
KM>IO UK. .MIC ,\si Photograph
THE COMPLETE PUSH-PULL AMPLIFIER AND B SUPPLY
cRecordings by
FAMOUS SYMPHONY CONDUCTORS
THE insert at the top, shows Nikolai Sokolotf.
conductor of the Cleveland Symphony, shown
in the large oval. Many records have been made
for Brunswick by the Cleveland orchestra. Henri
Verbrugghen is shown in the left-hand insert of
the lower group of three conductors, the center
one being Willem Mengelberg, and the right-hand
one Walter Damrosch. Verbrugghen is conductor of
the Minneapolis Symphony, heard over wcco;
Mengelberg now conducts the New York Phil-
harmonic, heard over WOR; Walter Damrosch, con-
ducting a large group of New York Symphony men,
is heard over wjz and chain each Saturday night.
The Cleveland orchestra broadcasts through WEAR
Recent Symphony Orchestra
Recordings
FEW records which have been recently
issued deserve special attention, particu-
larly because they are noteworthy achieve-
ments in recording. If you are not aware of
the vast improvement that has been made in this
art by the development of electrical recording,
play a record of the old method and compare
it with one of the new method. You will observe
the extended tone range, of the latter, in which
you will hear high and low notes which were lost
by the old system of recording. Of course that is
taking for granted that your own reproducing
apparatus is adequate. If you are still making
use of one of the pioneer phonographs, or an
antediluvian horn as your loud speaker, all
records will sound equally bad. But with good
equipment it won't require much imagination
to believe that you are in the hall with the orches-
tra itself instead of in your own home listening
to canned music.
One of the new records which would be par-
ticularly successful for this demonstration which
we suggest is the "1812" Overture of Tschai-
kowsky (Brunswick), in which the composer has
plumbed the musical depths with the resounding
tones of the tympani, then in the next breath
climbed to ecstatic heights with the strings. The
full orchestra is brought into play and not an
iota of color is lost by the recording of
this magnificent overture, which has been
played in masterly fashion by the Cleve-
land Orchestra under the direction of
Nikolai Sokoloff.
Nor are any of the delicate shadings lost in
the exquisite Dernier Sommeil de la l/ierge of
Massenet, as played for Brunswick by the Min-
neapolis Symphony under the baton of Henri
Verbrugghen. This lovely ecclesiastical music
contrasts strangely with the robust Coppelia
Ballet which appears on the reverse side of the
record. This delightful composition by Delibes
has as much swing to it as any present day dance
number you can think of and a melody as simple
as any jazz strain — and furthermore it is many
times as soul-satisfying.
Two more classical dance numbers are Johann
Strauss's Artist's Life and Tales From the Vienna
Woods (Brunswick). The interpretation of these
oft-heard waltzes by Willem Mengelberg, con-
ducting the New York Philharmonic Orchestra,
is to their usual rendition as a production of
Midsummer Night's Dream by Max Reinhardt
is to a high-school performance of the same
comedy.
Perhaps the most famous musical selection in
the world. is the Wedding March from Lohengrin.
Certain it is that a great many people, be they
married or single, know it and love to hear it
played. Certain it also is that most of them have
never heard it more beautifully interpreted, if as
beautifully, as it has been by the Cleveland Or-
chestra under the direction of Nikolai Sokoloff,
for Brunswick. This makes the usual rendition,
cloaked in romance and sentiment though it be,
289
seem stale by comparison. And the same may
also be said about the Prelude to Act 3 of Lohen-
grin, which selection is on the opposite side of
the Wedding March (Brunswick).
Another familiar number is the Song of India
by Rimsky-Korsakow. We once thought that
we never wanted to hear this again. That was
because a neighbor of ours — oh, years ago — had
just invested in a phonograph; and a few records,
very few! One of them was the Song of India
popularly recorded. The thrill of having a phono-
graph was evidently great, for the machine was
never silent. It was Spring and all windows were
open. Need we say more? But we find that this
record by the Cleveland Orchestra is something
else again. We can hear it with as much delight
as if it were entirely new to us. This same or-
chestra's version of Tschaikowsky's Sleeping
Beauty waltz is full of color and feeling and
contrasts vividly with the usual performance of
this favorite by hotel orchestras and bands,
whose treatment of it is seldom more than an
adequate reading of the notes (Brunswick).
On the next page we give a list of recent
electrically recorded symphony records.
Recent Popular Records
HAVING on various occasions thrown stones
in no uncertain fashion at popular music it
behooves us to explain ourselves before we pro-
ceed to review some of the popular records.
While we still contend that it wearies us in bulk,
we admit that we thoroughly enjoy it in small
doses. A little of it over the radio is an excellent
thing; and the same applies to the phonograph.
290
RADIO BROADCAST
FEBRUARY, 1928
But the dose must be moderate and we want it
palatable.
Though we can t seem to get away from the
stumbling block of a limited number of current
songs which we are forced to hear over and over
again, the better orchestras do their best to vary
the music as much as possible by the addition
of frills in studied orchestration. Those who or-
chestrate well can make good music out of
mediocre. Take for instance Good News and
Lucky in Love as played for Brunswick by Ben
Selvin and His Orchestra. Yes, those are the
same selections which we frowned on so severely
last month. But you would never know they
were the same! That is what Selvin orchestration
does for a piece. A little trimming here and there
by a steel guitar — and the trick is done. The re-
sult: a simply grand dance record!
This orchestra is versatile, too. In / Could
Waltf On Forever it makes the most of the
strings, the sax, and the piano. Even that moss-
grown favorite, Cheerie-Beerie-Bee, on the reverse,
takes on new life under Selvin treatment (Bruns-
wick).
Play-ground in the Sky from "Sidewalks of
New York," being a particularly good number
to start with, doesn't need much doctoring and
it has very wisely been simply treated by this
same orchestra. Incidentally, why haven't we
heard this selection oftener? It is swell! Wherever
You Are from the same show isn't as good but
the most has been made of it (Columbia).
The fourth record by this outfit is / Call You,
Sugar and Yes She Do (Brunswick). Again trick
orchestration. Selvin does this instrumental or-
namentation extremely well, making it fit into
the general scheme of things instead of letting it
stand out like the ball on the Paramount Build-
ing, as a lesser light would be apt to do. The
result is that the records are not ruined for
dancing but are improved.
Our old favorite, Ernie Golden, is a past mas-
ter at this art of orchestration. He rings the bell
again with All By My Ownsome and A Nigbt In
June, in which he introduces a steam caliope
effect which rs grand! We suggest that he get it
patented and use it as a musical trade mark
(Brunswick).
Don Voorhees has made four recordings on
three different discs for Columbia. These four
are: Rain, Baby's Blue, Highways Are Happy
Ways, and When the Morning Glories Wake
Up In The Morning. There is a sort of smooth
placidity about this orchestra by which you
can always identify it. It never gets excited,
it is uniformly good and yet it never seems to
climb quite to the topmost heights. However, it
has personality and that is a lot in these days.
We have named the records in the order in which
we rate them, the first being by far the best.
Listen to the saxophone.
On the opposite side of Baby's Blue is The
Calinda by the Radiolites. It is a very good
number with an irresistible swing. Not the least
attractive feature of the record is the vocal
chorus by Scrappy Lambert, of cough drop fame.
(Columbia).
The Radiolites are responsible for another
good dance record, There's A Cradle in Caroline
and Everybody Loves My Girl. Neither selection
is inspired but each moves along with a smooth
rhythm (Columbia).
A record that stands out from the rest is
Charmaine and Did You Mean It? by Abe Ly-
man's California Orchestra. Both numbers are
played with a restraint not often displayed by a
dance orchestra. Soft pedals and plaintively in-
sinuating rhythms are a relief after robust,
vigorous jazz (Brunswick).
If you have once heard Phil Ohman and Victor
Arden stroke, jingle, bang, and otherwise urge on
the ivories, you will look forward eagerly to
hearing them again. We have and did, and were
disappointed by their record for Brunswick,
There's Everything Nice About You and Mine.
Oh, yes, they are good numbers, well played,
but there is too much of the orchestra and too
little piano. You can always hear good orchestras
but there is only one Ohman and Arden.
Two more disappointments were records by
Ben Bernie and His Hotel Roosevelt Orchestra
and by Vincent Lopez and His Casa Lopez
Orchestra. By rights one can expect the best
from these two bands. But they both play as if
pay day were at least a month away. The records
are Miss Annabelle Lee and Swanee Shore by the
first outfit and Someday You'll Say "O. K." and
Just a Memory by the second. Both are Bruns-
wick.
Only moderately good are the rest: A Night in
June and Are You Happy by the Ipana Trouba-
dours (Columbia); Feelin' No Pain and Ida
Sweet as Apple Cider by Red Nichols and His
Five Pennies (Brunswick); Manhattan Mary and
Broadway, both numbers from "Manhattan
Mary," by Cass Hagan and His Park Central
Hotel Orchestra (Columbia); Like the Wandering
Minstrel and Molly M alone, from "The Merry
Malones," played by The Cavaliers (Columbia);
and No Wonder I'm Happy and Sing Me a Baby
Song by the George H. Green Trio (Columbia).
Taken all in all all these dance records that we
have reviewed form a good collection. Not one
of them is really poor.
If you are a devotee of Roxy you will welcome
three records played in the Roxy Theatre by
Lew White, the organist, Broken Hearted and
Just Like a Butterfly, When Day is Done and
Forgive Me, Underneath The Weeping Willow and
At Sundown (Brunswick all). It is all typical
movie organ music. Many people object to that
sort of thing but we like it when it is well done,
as this is. Our preference is for Underneath the
Weeping Willow and second choice is Broken
Hearted. Neither of these has a vocal chorus and
the rest have. Does a vocal chorus go with organ
music?
The male counterpart of Vaughn De Leath
seems to be Vernon Dalhart. He isn't as gushy,
for which let us be truly thankful, but the idea
is the same. He offers My Mother's Old Red Shawl
and Down On The Farm on a Brunswick record.
Billy Jones and Ernie Hare, the Happiness
Boys, again present us with a little vulgar singing
of a nice sort. Well, you know they aren't exactly
refined but they are good. This time they have
recorded You Can't Walk Back From An Aero-
plane and Who's That Pretty Baby? for Columbia.
Art Gillham, the Whispering Pianist, hands
out the typical vaudeville sob stuff, piano and
recitative, in Just Before You Broke My Heart
(Columbia). On the other side is / Love You But
I Don't Know Why which is moderate.
About the only thing to say about Roam On
My Little Gypsy Sweetheart and There's A Cradle
in Caroline as sung by the Goodrich Silvertown
Quartet is that they have been in better shows
than this (Columbia).
The same might be said of the Anglo-Persians
who play Call of the Desert on a Brunswick record.
But they redeem themselves by the selection on
the reverse side. Down South. We end on a note
of praise for the carpet riders.
New York Philharmonic Orchestra
•
Chicago Symphony Orchestra
St. Louis Symphony Orchestra
Cleveland Symphony Orchestra
Minneapolis Symphony Orchestra
New Electrical Symphony Orchestra Recordings
VICTORY BALL — Fantasy. Parts i and 2 . (Schelling) 1127 Victor
VICTORY BALL — Fantasy. Parts 3 and 4 (Schelling) 1128 Victor
ARTIST'S LIFE (Strauss) 50096 Brunswick
TALES FROM THE VIENNA WOODS (Strauss)
MARCHE SLAVE, Parts i and 2 (Tschaikowsky) 50072 Brunswick
MIDSUMMER NIGHT'S DREAM — Scherzo (Mendelssohn) 50074 Brunswick
MIDSUMMER NIGHT'S DREAM — Nocturne (Mendelssohn)
WINE, WOMAN AND SONG (Strauss) 6647 Victor
SOUTHERN ROSES (Strauss)
CARNIVAL OVERTURE, Parts i and 2 (Op. 92) (Dvorak) 6560 Victor
IN SPRINGTIME — Overture, Parts I and 2, Op. 36 (Goldmark) 6576 Victor
(i.) SERENADE (Volkmann, Op. 63.) (2.) Flight of Bee (Rimsky-Korsakow) 6579 Victor
VALSE TRISTE (Sibelius)
To A WATER LILY (MacDowell) . 1152 Victor
To A WILD ROSE (MacDowell)
COUNTRY DANCE, No. i (German) 9009 Victor
PASTORAL DANCE, No. 2 — Merrymaker's Dance, No. 3 (German)
FINGAL'S CAVE — OVERTURE, Parts j and 2 (Mendelssohn) 9013 Victor
BLUE DANUBE WALTZ (Strauss) 50052 Brunswick
TALES FROM VIENNA WOODS (Strauss)
DANSE MACABRE (Saint-Saens) 50089 Brunswick
MERRY WIVES OF WINDSOR OVERTURE (Nicolai)
FINLANDIA (Sibelius) 50053 Brunswick
SYMPHONY No. 2 (Brahms)
HUNGARIAN DANCE, No. 5, G MINOR (Brahms) 15092 Brunswick
VALSE TRISTE (Op. 44) (Sibelius)
SLAVONIC DANCE No. 3 (Dvorak) 15091 Brunswick
TRAUMEREI (Schumann)
1812 OVERTURE — PARTS i AND 2 (Tschaikowsky) 50090 Brunswick
LOHENGRIN: Prelude to Act 3 (Wagner) 15121 Brunswick
LOHENGRIN: Wedding Music (Wagner)
SLEEPING BEAUTY WALTZ Tschaikowsky 15120 Brunswick
SONG OF INDIA (Rimsky-Korsakow)
COPPELIA BALLET — Prelude and Mazurka (Delibes) 50087 Brunswick
DERNIER SOMMEII. DE LA VIERGE (Massenet)
DER FREISCHUTZ, OVERTURE, Parts i and 2 (Weber) 50088 Brunswick
MELODRAMA FROM " PICCILINO" (Guiraud) 15117 Brunswick
WAIATA Poi (Hill)
"Our Readers Suggest-
9 9
OUR Readers Suggest. . ." is a regular feature
of RADIO BROADCAST, made up of contri-
butions from our readers dealing with their experi-
ences in the use of manufactured radio apparatus.
Little "kinks," the result of experience, which give
improved operation, will be described bere. Regular
space rates will be paid for contributions accepted,
and these should be addressed to "The Complete
Set Editor," RADIO BROADCAST, Garden City, New
York. A special award of $10 will be paid each
month for the best contribution published. The
prife this month goes to Conrad Ederle, New York
City for bis suggestion entitled "Extending Loud
Speaker Leads."
— THE EDITOR.
Extending Loud Speaker Leads
IT IS often very desirable to place a loud
speaker some distance from the set in con-
junction with which it is operating. The
long leads, however, are somewhat bulky, and
are especially conspicuous when run along
the wood molding.
It was recently the writer's job to install a
loud speaker diametrically across the living room
from the receiver in such a manner as to merit
the approval of several discriminating family
critics. The method used to accomplish this task
may be of general assistance.
In the first place one of the two long leads
generally necessary was dispensed with. There
are two available grounds in our living room,
a radiator by the receiver, which is used for the
set ground, and gas logs in a fireplace, on the
mantel over which the loud speaker is mounted.
A connection from the loud speaker to the logs
was used as one wire, the other loud speaker
terminal being connected to the receiver as
shown by the dotted lines in Fig. i. As a matter
of experiment, the resistance of the ground cir-
cuit (i. e., the matter between the set ground
and the loud speaker ground) was determined,
and its value found to be 28 ohms. This is not,
indeed, very low, but, on the other hand, not
high enough to occasion an appreciable loss in
signal strength.
A No. 26 single white cotton-covered wire was
used as the conductor from the loud speaker to
the set. This wire was run inconspicuously along
the cream colored molding. However, the last
six feet, from the molding across the wall to the
loud speaker cord, was necessarily exposed.
The visibility of the exposed portion was reduced
materially by running the single wire down a
corner and gluing the wire in place rather than
using tacks. A drop of LePage's glue was placed
at one foot intervals along the wire. This was
allowed to become tacky before being pressed
against the wall. Talcum powder was blown
from the palm of the hand, while the glue was
still moist, effectively hiding the brown color,
and blending successfully with the buff tone of
the walls.
CONRAD EDERLE,
New York City.
STAFF COMMENT
AS MR. EDERLE observes, it is often
desirable to operate a loud speaker at some
distance from the receiver. The desirability of
this arrangement may be dictated by esthetic
or technical considerations. Some receivers,
notably those operating from loop antennas,
function best in a definite section cf a room.
When the cartridge type charger which has
recently appeared on the market is used, how-
ever, this scheme is no longer satisfactory. An
investigation made to learn why a battery
connected to the charger as shown in Fig. 28
seemed to lose its charge in a few days disclosed
the reason. An ammeter introduced into the
circuit to indicate the rate of charge showed
a slight negative reading when the a. c. power
was cut off. Further in-
vestigation disclosed a re-
verse current of approxi-
mately 180 milliamperes
passing continuously when
the transformer was dis-
connected from the power
line.
A double-pole double-
throw switch was included
in the circuit as shown
in Fig. aC. The battery
now retains its charge as
long as it did before the type
of charger was changed.
HERBERT J. HARRIES,
Gas logs ^ Pittsburgh, Pennsylvania
STAFF COMMENT
MEASUREMENTS in
the Laboratory on the
Showing how a single lead to the set, plus a ground connection, can be new tvPe National full-
used with either transformer or choke coil output device to operate wave charger, which em-
a loud speaker at some distance from the receiver ploys two cartridge reed-
• (Ground Filament il not
already connected to ground)
<^r Radiator
FIG. I
The same holds true with loud speakers when
careful consideration is given to acoustic effects.
Belden has produced a flat two-wire extension
cord which may be laid under a rug, providing
a very convenient form of inconspicuous wiring.
While the Belden arrangement was designed
ordinarily with the requirements of the i lo-volt
power line in mind, there is no reason why it
should not be adapted to a loud speaker output
circuit.
In using the ground return suggested by Mr.
Ederle, it is quite essential that an output
device be employed1 — either a choke coil arrange-
ment or a transformer. Unless one of these is
used, the high voltage to the plate of the output
tube will, in many cases, be shorted 'over to
ground. Both circuit arrangements are shown
in Fig. i.
The Cartridge Type Charger
MANY fans have the connections from
the storage A battery to the charger
arranged as shown in Fig. 2A, merely closing the
1 10 volts a. c. circuit whenever the battery needs
charging. This scheme is entirely satisfactory
when a bulb type charger is used, for the path
between the plate and the filament of the tube
becomes non-conducting when the filament
heating current is cut off and, therefore, no
discharge path through the charger is presented
to the A battery current.
291
No Discharge Path
Rectifier Cartridge
Fuse
t To Radio Set V
High-Resistance Discharge Path
(0 >
No Discharge Path
FIG. 2
Various methods of A battery charger connec-
tions. C shows a system of connections for a
cartridge rectifier
292
fiers, indicate that practically no current will
flow if the arrangement in Fig. 26 is employed,
suggesting that the switching is unnecessary.
We believe that the current Mr. Harries noted
was due to a defective cartridge. In such a case
the -switching arrangement might very well be
resorted to since a cartridge that is only slightly
defective will still give many hours service. The
switching arrangement shown in Fig. 2C may
be slightly improved by using a three-blade
switch, the extra contacts being used to control
the i lo-volt line to the charger. When the switch
is in the right-hand or charge position, the
charger will automatically be turned on.
The Glow Tube
THE use of the glow or regulator tube, such
as the ux-874 (cx"374) or the Raytheon
type R, effects a general improvement in socket
power circuits. The stability of the r. f. circuit is
sometimes improved, while the tendency to
"motorboat," and oscillation in the audio-
frequency amplifier is considerably reduced by
its use. The glow tube is connected between the
ninety-volt tap and the negative binding post
on the power supply unit and is so designed
that a practically constant potential is main-
tained across these posts regardless of the current
load.
The regulator tube was specified or furnished
To 180V. +
llx
To 90 V. +
To Neg."
,^-i-^. Socket lor
/ V glow Tube
'LJ'
T
FIG. 3
How to add a glow tube to any B supply device.
The addition of the glow tube will increase the
stability and all-around efficiency of the circuit.
with very few B supply devices, homebuilt or
ready made, previous to the present radio season.
The benefits of the glow tube can be obtained
with such power sources by connecting the tube
externally. The addition of the tube is a matter
of a few simple connections. Briefly, the glow
tube is connected between the ninety-volt tap
and negative, and an additional resistor, having
a value of three thousand ohms, is wired between
the high-voltage tap and the ninety-volt tap.
The regulator tube plugs into a standard ux
socket, the grid post on the socket being the
anode terminal of the tube and the negative
filament terminal the cathode. The anode should
always be wired to the ninety-volt post. The dia-
gram of connections is shown in Fig. 3.
HENRY LANDON,
Chicago, Illinois.
STAFF COMMENT
A REGULATOR tube should never be added
*» to any socket power set until it is deter-
mined whether the device will supply an addi-
tional drain of 30 milliamperes without an
excessive voltage drop.
RADIO BROADCAST
Output Transformer Connections
\A7HEN connecting up an output trans-
* former it may be noticed that the instru-
ment is usable for either the straight transformer
form of output or as a choke with condenser
bypass type (Fig. 4). The idea, when I tried it
out, proved to be quite successful and showed
some possible advantages for the arrange-
ment.
The tone quality, from the two jacks, was
different. The transformer coupling was more
mellow and softer and the impedance coupling
more brilliant in tone with the particular in-
Trans.
Output
2mfd.
Choke
Output
FIG. 4
An output arrangement making it possible to use
the transformer as a choke if desired
struments that I used. General tone fidelity
was good in both cases so one could select the
arrangement most pleasing at the time, or
match the reproduction from different loud
speakers to some extent.
The double output suggested the simultaneous
use of two reproducers and was tried using
Sparton and Baldwin loud speakers. Both
worked perfectly alone or together in either
position and neither reproducer seemed in any
case to reduce the volume obtained from the
other one alone.
J. B. HOFFMAN
Kewanee, Illinois.
STAFF COMMENT
\A R. HOFFMAN suggests a simple and
^"* practical method of connecting two loud
speakers with different characteristics to secure
a tonal combination more pleasing to the ear
than the more usual series connections— -always
providing, of course,
that the loud speakers
used have impedances Movable Plate
adapted to this particu-
lar arrangement. The
choke connection will, in
some cases, provide more
pleasing reproduction
than the transformer
system. Mr. Hoffman's
arrangement may be
used in conjunction with
the resistor controls sug-
gested for tandem
speaker operation in this
department last month.
The volume from the
individual loud speakers
is necessarily reduced
when two or more of
them are used but the
total volume from the re-
ceiver may be increased.
FEBRUARY, 1928
A Simple Vernier Condenser
WITH the present-day congestion of radio
traffic, any device that may facilitate
tuning is worthy of consideration. The writer
found that the construction of a simple vernier
condenser along the lines to be described im-
proved reception on his tuned r. f. receiver.
The vernier is connected across the main tuning
condensers in the receiver, and is employed in
securing that delicate adjustment so often
essential to quality reception.
The mechanical details of the device are
illustrated in the drawing, Fig. 5.
The base consists of a piece of spare panel
material, aj inches long by 2 inches wide. The
plates are cut from stiff copper sheets with a i J-
inch radius. The peak of the stator plate is cut away
for the shaft of the rotor. The fixed plate is fastened
to the base by small screws threaded to the panel,
or with nuts.
A long brass screw (See Fig. 5) provides the
shaft to the rotor, which is clamped between a
nut and the screw head. A shim or several
washers between the rotor plate and the panel,
space the two plates of the condenser from J to \
of an inch, depending upon the amount of tuning
desired.
The closer the plates are arranged together
the greater will be the variation. A lock-nut
and washer on the other side of the small panel
holds the shaft at the desired tension. A hard
rubber top of a binding post is used as a knob.
In the author's receiver the vernier condenser
is mounted on the main tuning panel, as shown
in the sketch.
L. B. ROBBINS,
Harwich, Massachusetts
STAFF COMMENT
THERE are many uses for a small variable
condenser of this type. Its possibilities as a
short-wave vernier, as a compensating condenser
across the main tuning capacities in a gang con-
denser, and as a neutralizing condenser in ca-
pacity stabilized circuits, are immediately
suggested. With the exception of such instances
where the vernier condenser is actually employed
for tuning, in which case constant adjustment
is necessary, it will be desirable to mount this
capacity adjuster on the sub-panel of the
receiver.
Pig-Tail
- Binding Post
Head
Panel
Constructional details of a useful vernier condenser
OME RELIABLE RADIO
POWER- SUPPLY ACCESSORIES
AN AUTOMATIC CONTROL
The purpose of this switch is to auto-
matically connect the a. c. power source
to either the A battery charger or the B
socket-power device, depending upon
whether the set is switched off or on.
It is a product of H-S-L Radio, In-
corporated, Niagara Kails, New York.
Price, $3.75
A AND B POWER
''PHIS Vesta power unit com-
^ bines a source of A current
with one of B current. Features are:
A Westinghouse rectifier is used;
built-in hydrometer; side windows
enable the state of charge and li-
quid level to be viewed; there is
an au toma tic rela y incorpora ted .
The B supply is ISO volts at either
40 or 60 mils. Price, 40 mils, $72.00;
60 mils, $77.00. The lower picture
shows the unit with case removed
AN "ALL AMERICAN" B DEVICE
T^HERK are four B taps on this unit— 45 volts,
-1 67 volt-s, 90 volts, and power tap. In addition,
the two knobs which may be seen on the front panel
are for adjusting the 45-volt and 67-volt outputs
to any desired amount for most satisfactory oper-
ation. There is also a " Hi-Lo" switch for increasing
or decreasing the voltage output in accordance
with the milliampere drain. The price of this unit,
in the 110 v., 50-60 cycle model, is $31.50. less tube
TOWER OF BOSTON
TS responsible for this ruggedly
A constructed B device. The out-
put is rated at 65 mi Hi amperes,
180 volte. There are five positive
B taps — detector, 67 vol ts, 90
volts, 135 volts, and 180 volts.
An automatic power control switch
is built in the unit. If a trickle
charger is used, this latter control
switch automatically switches it
in or out of circuit. Price, $32.50
A NEW A-SUPPLY DEVICE, BY GRIGSBY-GRUNOW-HINDS
IT IS here shown with the popular " Majestic" Super-B, in combination
with which it is particularly adaptable. This new "Majestic" A unit is
completely dry in construction, and uses no acids or liquids whatever. The
manufacturers claim that there is absolutely no hum in operation. The
maximum output of the " Majestic" A unit is 2i amperes at 60 volts, and
it lists at $39.50. The Super-B unit, incidentally, lists at $29.50 with tube.
The complete "Majestic" A-B supply therefore sells for $69.00
AN INEXPENSIVE B UNIT
"DY Modern, of Toledo. The maximum voltage output at 25
L* mils, is 185 volts, and at 30 mils., 175 volts. The Modern B
Compact lists at $26.50 without Raytheon tube. The voltage at
the power tube tap may be reduced by inserting a fixed resistor la
the fuse clips provided within the case
293
RADIO BROADCAST Photograph
IN SPITE of its apparent simplicity (it con-
sists of a core of iron, windings of copper
wire, and perhaps a paper condenser), an
"output device" performs several useful pur-
poses, aside from being the connecting link be-
tween one's loud speaker and a power amplifier.
In the first place it keeps the d.c. plate current
of the last amplifier tube from circulating
through the windings of the loud speaker and,
secondly, it may adjust matters when a loud
speaker and a tube are used whose respective
impedances do not "jibe."
From the standpoint of keeping d.c. from the
loud speaker, the output device is only neces-
sary when power tubes are used — when the plate
current is greater than ten milliamperes. From
the standpoint of fidelity the device is necessary
when the loud speaker impedance differs con-
siderably from that of the tube out of which it
works. In the latter case, only one kind of out-
put device, the output transformer, does any
good, the choke-condenser type serving no use-
ful purpose from the standpoint of fidelity unless
the choke has taps on it, when it becomes an auto
transformer, and not, strictly speaking, a choke.
What does it matter if the d. c. plate current
of the last tube in one's amplifier goes through
the loud speaker?
There are several effects. The power which
the loud speaker winding must dissipate as heat
may be found by multiplying the resistance of
the winding by the current squared through it.
If the loud speaker has a resistance of 1 500 ohms
and the final power tube is a 171 with a plate cur-
rent of 20 milliamperes (0.02 amps.), the power
lost is 0.6 watts, which may or may not be too
great for the winding todissipate in heat, depend-
ing upon whether the winding was made with this
thought in view. If the winding will not satisfac-
torily dissipate this heat (such will eventually be-
come evident by a burnt-out winding) the use of
an output device, of suitable electrical dimen-
sions, may be resorted to as a safety measure.
One fiftieth of an ampere (20 mils.) flowing
through the loud speaker which has a resistance
Why the Output Device?
By Keith Henney
Director of the Laboratory
of 1 500 ohms represents a voltage drop, obtained
by multiplying these two values together, of 30
volts, which must be subtracted from the ter-
minal voltage of the plate supply source to cal-
culate what voltage is actually on the plate of
the final tube. If the B battery consists of four
standard blocks we should have 180 volts and
accordingly we place a C bias on the 171 type
tube of 40.5, but since there are 30 volts drop in
the loud speaker winding, the actual plate volt-
age is only i 50, and 40.5 volts C bias is, therefore,
too great. The use of an output device in which
the voltage drop is lower than through the loud
speaker is to be recommended in such a case.
When d.c. flows through the winding of the
loud speaker, the armature, the little lever that
moves in accordance with voice-frequency cur-
rents and imparts its message to the loud speaker
diaphragm, is pulled from its neutral position
with respect to the winding, and is much more
liable to strike the pole pieces of the magnet
under strong signals. In other words, the arma-
ture is working under a permanent bias which
is neither necessary nor desirable; it forces the
armature to work under a hardship that is easily
removed by means of the output device.
Some types of output devices have the addi-
tional advantage that they remove d.c. plate
voltages from the loud speaker tips with the re-
sult that these tips or any part of the loud
speaker mechanism or the output jack or ter-
minals may be touched while the "juice" is on
without danger of shock. No output device,
however, will protect one from being shocked
by the loud speaker voltages produced by strong
signals. What one hears as kettle drums — or
static — is the result of very strong sudden volt-
ages across the loud speaker after they have been
translated into sound by the loud speaker dia-
phragm.
Output devices, then, are used to:
(i.) Keep d.c. from the loud speaker winding.
(2.) Prevent serious loss in plate voltage.
(3.) Prevent heating of the loud speaker wind-
ing due to power loss there.
(4.) Prevent placing a mechanical bias on the
loud speaker armature.
(5.) Adjust serious impedance differences and,
therefore, improve fidelity.
AND SOME OUTPUT DEVICES:
(6.) Keep the loud speaker terminals at low d.c.
potentials preventing shock or burn.
As mentioned previously, there are two types
of output devices, or loud speaker filters, as they
are sometimes called. There is the true trans-
former, with two windings, of copper wire in-
sulated from each other and wound on an iron
core which is insulated from the windings; and
there is the choke and condenser combination.
The transformer, by its very nature, keeps the
d.c. from the loud speaker and d.c. voltages
from the terminals. It has the added advantage
that, by proper design, differences in imped-
ance which may exist between the loud speaker
and the power tube may be adjusted.
The choke-condenser combination consists of
a high-inductance copper coil of many turns on
an iron core — and the condenser. If the choke is
tapped, impedance differences may be adjusted,
but for purposes of discussion, it then becomes a
transformer, although the two windings are not
insulated from each other but possess a certain
part of the copper wire in common. This com-
bination of a coil and a condenser may be con-
nected into the power tube circuit in two ways,
one of which is better than the other. The trans-
former may be connected in only one way, which
corresponds to the poorer of the condenser-choke
connections.
FEBRUARY, 1928
WHY THE OUTPUT DEVICE?
295
The output transformer is illustrated
in Fig. i. The d.c. resistance of the pri-
mary should be low so that little plate
voltage is lost; the a.c. impedances of
both windings should be high so that
most of the a.c. voltage developed by in-
coming signals will appear across the
loud speaker winding and not be lost on
the tube's impedance. The d.c. voltage
lost is again the product of the current
and the resistance, so that every time one
milliampere flows through 100 ohms,
a tenth of a volt is prevented from
reaching the plate. If the tube requires 20 milli-
amperes and the resistance is 500 ohms (a typi-
cal case) we have lost 10 volts.
The transformer has one disadvantage in that
all of the voice-frequency currents must return
to the filament of the last tube through the com-
mon impedance of the plate supply apparatus,
as shown in Fig. I. Unless this impedance is
small, either inherently or unless it be reduced
by proper bypassing, the amplifier is liable to
"sing," or to cause poor reproduction from
otherwise good apparatus, due to audio-fre-
quency regeneration.
Two condenser-choke combinations are il-
lustrated in Fig. 2. The resistance of the choke
must be small, for the same reason that it must
be small in any case — to prevent plate-voltage
loss; the inductance must be high at rather large
values of d.c. current, and the condenser must
— HMfc-
FIG. 2
shows the result, 32 per cent, of the current which
should flow through the loud speaker being lost.
The condenser which is in series with the loud
speaker must take its share of the voice currents
which are circulating in this circuit, and for that
reason its impedance, compared to that of the
loud speaker, must be small.
METHODS OF CONNECTION
IF THE condenser-choke arrangement is con-
* nected as in B Fig. 2, all of the a.c. currents
in the plate circuit of the last tube return to the
filament directly. This connection has the added
advantage that neither of the loud speaker ter-
minals are at high d.c. potential with respect to
ground. One side connects directly to A minus,
which is at ground potential, while the other
connects to the condenser and is insulated from
the high potential. If the condenser breaks down
used without impedance adjustment
with a 4OOO-ohm, or even higher
impedance, loud speaker. But if two
5000-ohm tubes are used in a push-pull
circuit so that the resultant impedance
is doubled to 10,000 ohms, and one
considers a loud speaker whose im-
pedance at 100 cycles is 1000 ohms,
trouble will occur.
Here we need a transformer. If the
primary and secondary individual im-
pedances are high compared with the
impedances of the tube and loud
speaker, and provided a good core with good
coupling is used, there will be little voltage loss,
and practically the entire a.c. voltage on the
plate of the last tube will be transferred to the
loud speaker, the magnitude depending upon
the turn ratio of the transformer, of course.
The trouble mentioned above will not be
loss of power due to improper impedance match-
ing so much as distortion due to another cause.
All tubes have a plate current plate voltage
characteristic that is somewhat curved. This
curve produces additional frequencies when in-
coming signals produce large values of a.c. plate
current. If, however, a large impedance is placed
in the plate circuit, changes in grid voltage, due
to large signals, produce a smaller proportionate
change in a.c. plate current, and the character-
istic is straightened out. Mathematics shows that
when the imoedance of the load is twice that of
JmW.
1600"- 21*1011
FIG. 3
FIG. 4
be large. The equivalent circuit is shown in Fig.
3. Here is a source of voltage, a series imped-
ance representing the plate resistance of the
tube, a shunt impedance representing the choke,
and a series impedance representing the conden-
ser, and another impedance representing the
loud speaker. The shunt impedance is a bypass
for the audio frequencies and naturally must be
large compared to the remainder of the circuit,
i.e., the series impedance of the loud speaker
ind the condenser.
. Let us take a definite example. We shall con-
sider a 171 type tube with an internal imped-
ance of 2000 ohms, a shunt choke of 25 henries, a
condenser of 4 mfd., and a 2ooo-ohm loud
speaker. This latter figure represents the im-
pedance of the loud speaker at some audio fre-
quency, say too cycles, and has little to do with
its d.c. resistance. At this frequency the choke
has an impedance of 15,700 ohms, representing
a loss of 6.0 per cent., and the condenser has an
impedance of 400 ohms representing a loss of
9.0 per cent., with the result that all but 15 per
cent, of the voice-frequency currents flow
through the loud speaker, compared to the case
in which neither condenser or choke were used
when there is no loss. The 1 5 per cent, loss will
be hardly detectable to the human ear. The
impedances of the condenser and choke are most
important at low frequencies.
Let us consider another case, this time choosing
a loud speaker which has an impedance of 1000
ohms at 100 cycles, a tube with an output im-
pedance of 5000 ohms, a choke of 10 henries, and
a i.o-mfd. condenser series impedance. Fig. 4
the B-battery voltage will be put across the
loud speaker, therefore a good condenser must
be used — one capable of withstanding not only
the voltage of the plate supply without punctur-
ing but the added voltages produced across it
by the audio frequencies, which, however, will
be small if its capacity is large. In A of Fig. 2
one of the loud speaker terminals is "hot" since
it is connected to the positive side of the plate
supply, which is high above ground potential.
In this case nothing happens if the condenser
breaks down except that the plate current will
divide between the loud speaker and the choke,
most of it still going through the 'latter because
of its lower d.c. resistance. The voltages across
the condenser in this case are lower than in B
of Fig. 2 since there is no steady voltage due to
the plate supply but only the audio-frequency
voltages, and these will be small owing to the
low impedance of the condenser.
The absolute values of the inductance and the
capacity may be varied within certain limits
depending upon the tubes and the loud speaker
used. With a 2ooo-ohm tube and a 4OOO-ohm
loud speaker, 20 henries is plenty and a capacity
of 4.0 mfd. is correct.
Since the effect on audio frequencies of both
the choke and the condenser may be neglected,
if proper values of each are used, the loud speaker
looks directly into the plate circuit of the power
tube, and as far as a.c. currents go, might just
as well be connected there. This is perfectly
proper provided the impedances of the tube and
loud speaker do not differ too widely. For ex-
ample, a 2ooo-ohm or a jooo-ohm tube may be
the tube, the greatest amount of undistorted
power will be secured from the tube. At low fre-
quencies the impedance of most loud speakers
is very low, so that the tube's characteristic is
curved, and loud low-frequency signals produce
a rattle or rumble that is objectionable. For this
reason, the loud speaker should not match the
tube in impedance, but should have a greater
impedance, and if this is not possible, a trans-
former must be used which makes the loud
speaker look like a higher impedance to the
tube. This may be done by using a step-up trans-
former, looking from the loud speaker to the
tube, so that the impedance of the former is
stepped-up or increased as far as the latter is
concerned.
Such is the story of loud speaker filters, or out-
put devices. With power tubes in the plate circuit,
when there are over ten milliamperes flowing, they
are useful in protecting the loud speaker; when
low-impedance speakers are used with high-
impedance tube circuits, they are desirable. Unless
the plate current is such that the loud-speaker
armature is sadly biassed and rattling against
the pole pieces of the magnets, it is doubtful if
the average listener can tell the actual differ-
ence in fidelity whether the device is used or not.
If a condenser-choke combination is used the
loud speaker should be connected to the nega-
tive filament lead or the center tap of an a.c.
operated power tube. Connected thus, the owner
of the loud speaker will be protected from d.c.
shocks, although he can get a severe jolt by hold-
ing to the speaker terminals when a kettle drum
operator gives his instrument a good "whack."
THE RAYFOTO RECORDER
This photograph illustrates a final model of the recorder. The pictures are recorded on
paper wrapped around the drum. This unit is des.gned to fitover the turnl^
piece of
Your
Pictore Receiver
THERE are several details concerning the
Rayfoto printer and Rayfoto recorder
which were not discussed in the article in
the December RADIO BROADCAST; a knowledge
of these is not necessary in order to construct the
printer although necessary to obtain most satis-
factory results. In this article we will use several
terms that have not been used in preceding ar-
ticles but which will serve to differentiate be-
tween the various units of the Rayfoto apparatus.
A description of these terms, with a brief ex-
planation of the function of the various parts
which they define, will be found in the table of
definitions on this page.
Readers of this series of articles will recall the
description given in the November article of the
Rayfoto relay and its function. This relay is
operated by the plate-current increase
produced in the amplifier tube of the
printer by the synchronizing signal. There
is a natural tendency, however, for the
relay contacts to vibrate for a very short
time after they first close. This causes
irregular operation of the trip magnet
which the relay controls, and the irregu-
lar operation in turn produces uneven
synchronizing which causes jagged effects
in the received picture.
To prevent this irregular action of tne
relay it was necessary to arrange the
circuit so that when the relay contacts
closed they would lock tightly together.
The most important part of this lock-
ing circuit is a resistance, R2 in the cir-
cuit diagram published on page 297.
When the relay, R4, closes, due to the
synchronizing impulse, it causes current
to flow through the trip magnet coil and
hence through resistance R2 to minus B.
The current through R2 produces a volt-
age drop across the resistance of such
polarity as to decrease the negative bias on
the grid of the amplifier tube. This causes
By Austin G. Cooley
the plate current to increase a comparatively
large amount, and this plate current, flowing
through the coils of the relay, R,, makes it lock
fast and prevents the contacts from vibrating.
As soon as the armature on the trip magnet re-
leases the drum, the contacts on the trip magnet
close and thereby short-circuit the relay so that
it is out of the circuit while the drum is making
a revolution.
The locking resistance should be adjusted so
that the plate current of the amplifier tube, as
read at jack J,, is about 15 milliamperes when
the relay and trip magnet contacts are closed.
There is always a certain amount of sparking
at the contacts but this causes no harm unless
the spark is sufficiently intense to cause an arc
after the contacts have opened. This is remedied
-Table of Definitions™ •• * • -
Printer: A two-tube unit consisting of a one-stage
audio-frequency amplifier and an oscillator. The Ray-
foto signals from the radio receiver are amplified in
the audio amplifier the output of which is impressed on
the Rayfoto modulation transformer which, in turn
modulates the oscillator. The output of the oscillator
produces the corona discharge which prints the picture.
Recorder: The mechanical unit for attachment to a
phonograph turntable, and consisting of a drum on
which a piece of photographic paper is wrapped, a
clutch system, and a trip magnet for use in obtaining
synchronism.
Relay: This relay is operated by the synchronizing
impulse and when the contacts on the relay close, the
trip magnet operates and releases the drum on the
Rayfoto recorder.
Lap: The interval between the time that the drum
on the Rayfoto recorder completes a revolution and
the time that the synchronizing impulse is received
I he recorder lap was explained fully in the November
1927, RADIO BROADCAST.
Static Slip: The operation of the Rayfoto relay by a
static impulse instead of by the regular synchronizing
impulse.
296
by increasing the gap between contacts when
they are open.
The contacts should be kept clean although
there is nothing to be gained by excessive filing
and cleaning. Cleaning the contacts about once
a month with a piece of cloth is all that is
necessary.
Reliable operation of the synchronizing system
is impossible if there are excessive set noises.
Such noises can often be traced to noisy batteries
or poor connections. Make no attempt to receive
Rayfoto pictures until such noises are cleared
out. This does not imply that perfect receptive
conditions are necessary for picture reception
but considerable extraneous noise is not conduc-
ive to success.
The photographic paper that has been found
most satisfactory is Azo No. 2 semi-matt
or semi-gloss, singleweight, size 5x7
inches. The room in which the pictures '
are received must be somewhat darkened
and a test can be made to determine if
the room is dark enough by placing a
piece of paper on the drum, allowing it
to remain there about five minutes, and
then developing it. If, in the developer
solution, it turns gray or black in about
30 seconds there is too much light in the
room, and the room will have to be
darkened in some way. Of course, in the
evening, no difficulties will be experienced
and it will generally be found safe to
operate the Rayfoto receiver without any
shading at a distance of about ten feet
or more from a forty-watt electric
light.
In wrapping the piece of photographic
paper around the drum for this test be
sure that the emulsion side is on the out-
side. The side of the paper with the
emulsion on can be determined by biting
a piece of the paper with your front
teeth. That side of the paper with the
FEBRUARY, 1928
OPERATING YOUR RAYFOTO PICTURE RECEIVER
297
emulsion will take the impression of the teeth or
will stick to the teeth.
After experience has been gained in the opera-
tion of the system, No. 4 Azo paper can be used
and it will be found that this paper can stand
more light without being affected. When No. 4
paper is used a greater discharge of corona is
necessary than with No. 2. If the signal strength
is low so that not much corona is available, it will
be best to use No. i paper, which is more sensi-
tive.
In making preliminary tests it is a good idea
to let the printer operate on broadcast signals
and, after a run has been made, to develop the
paper for about thirty seconds and determine
if the corona discharge from the strong signals is
sufficient to print out black.
Be sure to wrap the paper around the drum in
the right direction, which is opposite to the direc-
tion of rotation of the drum. If the paper is
wrapped in the wrong direction the corona
needle will catch under the edge of the paper and
pull it up.
The speed of the drum at the transmitter has
been standardized at 100 revolutions per minute
and, therefore, the speed of the drum on the
Rayfoto recorder should be near 106 revolutions
per minute in order to obtain the correct lap.
Adjust the speed of the drum to this value by
letting the drum revolve for a minute with the
trip magnet armature down, counting the num-
ber of revolutions.
If the Rayfoto recorder unit is examined it will
be found that the arm which carries the corona
needle will slide along the machined shaft
located at the rear of the device. If the arm does
not move along the shaft very easily, it should be
oiled. At no time should the shaft be touched
"with emery paper or sandpaper. The shaft may
be cleaned if necessary by mixing a little Gold
Dust powder with some lubricating oil and wip-
ing off the shaft.
To adjust the Rayfoto receiver to operate
through static, it is necessary to first adjust the
relay and corona discharge. Tune exactly to the
station transmitting the pictures. Reduce the
signal in the printer by the gain control to a
point where the relay just ceases to operate on
the synchronizing impulse. Determine whether
there is sufficient corona by examining the dis-
charge from the needle point. There should be
quite a noticeable discharge. A piece of Azo
paper should, of course, be on the drum when
any test of corona discharge is being made and
if there is not sufficient corona for making a
fairly black mark from the strong signals, in-
crease the spring tension on the relay, then boost
up the gain until the relay just starts to operate.
Check again to see if the corona discharge is
sufficient. If not, repeat until a fair discharge is
obtained. When working through static, it may
be necessary to work with a discharge much
lower than normal. Consequently, the print will
be weaker, unless a more sensitive paper, such as
Azo No. i is substituted for that generally used,
to make up for the reduced corona.
In making the above adjustment, the drum
may be held in such a position that the stop-shoe
does not strike the push rod by revolving the
drum half a turn. The discharge made by the
synchronizing signal may then be observed.
If it is difficult to obtain sufficient control of
the relay by the spring adjustment, the gap
between the armature and pole tip may be in-
creased by adjusting the contacts.
After these adjustments have been made,
tune the radio receiver to a frequency about
fifteen kc. above or below the frequency of the
picture transmitting station. If the relay oper-
ates more than once a second from the static
noises, the experimenter might as well turn in
RADIO BROADCAST Photograph
THE RAYFOTO RELAY
A close-up of the relay. It is this relay, actuated by the synchron-
izing signal, that causes the drum of the recorder to be released,
every revolution, at exactly the correct moment
and give up the idea of picture reception for
the rest of that night. If the relay does not oper-
ate from static noises, the gain should be in-
creased to a point where it just commences to
operate; then reduce the gain a small amount.
Thus you find the critical point of maximum
permissible gain without static tripping the syn-
chronizing relay. After this has been done, tune
back to the picture signal and check to see that
the gain has not been increased too much.
The next thing to do is to adjust the speed of
the recorder. The speed should be such that the
recorder lap is as small as is consistent with
regular operation of the trip magnet.
CHECKING PERFORMANCE OF
THE EQUIPMENT
THE November RADIO
BROADCAST gives some of
the essential information on
the subject of blurring and
detail. It may be well to
mention here one or two
things the experimenter may
check if he experiences
trouble. In many cases, the
following simple checks will
solve the difficulty.
First, be certain of the
connections to the modulation
transformer, makingsure that
the proper terminals are used,
because this has an important
bearing on the operation of
the entire system. The pri-
mary terminals are No. I
and No. 2. No. I should go
to the plate of the input
amplifier tube and No. 2 to
the meter jack and then to
the battery supply. No. 3 of
the secondary should be con-
nected to the plate of the
oscillator through the r. f.
choke and No. 4 goes to the
meter jack and then to the
booster voltage supply.
Also the connections to
the primary of the audio transformer in the
printer should be reversed to determine which
arrangement gives most satisfactory operation.
If there is a large recorder lap, that is, if the
receiving drum has sufficient lead to arrive at
the end of the revolution considerably ahead of
the converter drum, the relay will be connected
in the circuit for a longer period than necessary.
Should some static of strong intensity be re-
ceived during the lap, the drum will be released
ahead of the synchronizing impulse. Such jumps,
due to static operation of the relay, are known
as static slips.
The possibility of these static slips decreases
I RAYFOTO ' ,
->t*" RECORDER -*|
so
- c
B-
Jl
!>8 09 610
B+ B+ B+
A.F. Osc., Relay
Booster
FIG. I
The circuit diagram of the Kayfoto printer unit. The connections between this unit and the Rayfoto
recorder are indicated. Constructional information on the printer was given in the December issue
of RADIO BROADCAST. The Recorder unit cannot be home constructed but may be purchased as a
complete unit
298
RADIO BROADCAST
FEBRUARY, 1928
as the lap is reduced. Careful adjustment of
phonograph motor speed is suggested to main-
tain a minimum lap. If, however, the speed is
matched too closely, there is no lap. The trip
magnet then operates as the stop shoe strikes the
push rod. Such operation is very unstable and
produces very jagged pictures.
If the recorder speed is reduced so that it is
slightly slower than that of the convenor, the
recorder drum will not reach the end of the revo-
lution in time to receive the synchronizing im-
pulse. The relay will then operate on the im-
pulse of the next revolution, or, if there are
strong picture signals, during the revolution, and
the result will be no picture at all or one that is
very badly distorted.
After a little experience, the experimenter will
be able to tell from the sound of the recorder
whether the lap is correct. Sometimes streaks
occur in the Rayfoto pictures because the oscil-
lator tube ceases to function for a moment. Such
a streak appears in the Rayfoto picture printed
on page 216 of the January RADIO BROADCAST.
This frequently occurs when the oscillator is
tuned to give the maximum amount of corona.
To avoid these streaks, detune slightly with the
variable condenser across the oscillator coil.
A higher resistance in the grid circuit also tends
to reduce the possibilities of streaks.
Streaks are also caused by poor connections
and by detuning of the radio receiver by hand
or body capacity. For this reason, it is desirable
to have a well-shielded receiver.
At present, pictures with fairly strong con-
trast are being transmitted so that good Rayfoto
prints may be made with the average haphazard
adjustment of the printer. Some may find that
they are getting a little too much corona on the
minimum signals and that the intermediate
shades are produced as blacks. Correction for the
minimum signal can be best accomplished by
reducing the booster voltage. The difference
between the intermediate shades and blacks
can easily be increased by reducing the gain and
then allowing a little more time for development
of the picture. When reducing the gain, it may
be necessary to reduce the spring tension on the
relay.
From the foregoing it should be obvious that
some skill is required to secure the best possible
results. Poor pictures are a matter of poor ad-
RADIU BKUAIHAST Photograph
THE RECORDER IN PLACE
The photograph illustrates how the Rayfoto recorder
is mounted over the turntable of a phonograph
justment of motor speed, amplifier gain, stop-
start mechanism. Good pictures are a credit to
the experimenter who receives them. In picture
reception, the amateur has one advantage over
the fan who contents himself with mere audio
reception. He obtains permanent and irrefutable
evidence of his success — a catalogue of his prog-
ress throughout the development of what will
some day be a widely practised science and art —
the reception of high-grade pictures in the home.
PARTS FOR A RAYFOTO PICTURE RECEIVER
CERTAIN parts for use in a Rayfoto receiver
^— ' have been especially designed for the pur-
pose and therefore possess the essential char-
THE RAYFOTO PRINTER UNIT
The parts for the unit, containing the amplifier and oscillator circuits, can be purchased and then
d together as indicated in the photograph. The circuit diagram is given in Fig. I . At the left is the
Rayfoto corona coil. The transformer at the extreme right is the Rayfoto amplifying transformer and
at its left is the Rayfoto modulation transformer. The Rayfoto relay can be seen mounted on the panel
acteristics for good results. They have been
designed to take care of the present requirements
of the system and will also be satisfactory for
use as the system may be gradually developed.
These special parts, made under the Rayfoto
trade mark, are listed below:
LI — Rayfoto Corona Coil
Ti — Rayfoto Amplifying Transformer
T2 — Rayfoto Modulation Transformer
RI — Rayfoto Relay
Rayfoto Printer Unit
The remainder of the parts necessary to con-
struct a picture receiver are given below. Any
standard parts conforming with the specifica-
tions given below may be satisfactorily used.
Ri — Variable Resistance for Gain Control
R2 — 2OO-Ohm Variable Resistance Capable of
Carrying 100 Mils.
Ra — 12-Ohm Filament Rheostat, o.j-Ampere
Capacity
Ca — o.i-Mfd. Fixed Condenser
RI — o.oi-Megohm Grid Leak and Mounting
Ci, Ct — o.oooj-Mfd. Fixed Condensers
Ci — o.oooj-Mfd. Variable Condenser
L2 — Radio-Frequency Choke Coil
Sj — Filament Switch
Sj — Push Button Switch
Ji. J?. Js — Double-Contact Short-Circuiting
Jacks
Rt— 4-Ohm Filament Ballast Resistance
Telephone Plug
Milliammeter, 0-25 Milliampere Scale
Two Sockets
Fourteen Binding Posts
Panel
Panel Brackets
The designating letters preceding the parts
given in the above list refer to the lettering on
the circuit diagram given on page 297 of this
article. Readers interested in constructing a
Rayfoto picture receiver and desiring further
information regarding the necessary parts may
obtain this data by writing to RADIO BROADCAST
magazine.
THE FREED-EISEMANN "NR-6o" ELECTRIC RECEIVER
How the "NR*60" was Engineered
I ^^ ENTLEMEN, we need a new electric re-
(I -ir ceiver, designed for a.c. tubes and
^»-** equipped with B supply. The receiver
must be a single-control set to retail at $150.
The above is the sum and substance of a mes-
sage delivered to the engineering department
of the Freed Eisemann Corporation and is the
reason for the birth of the "NR-6o receiver."
The electrical development of this receiver
will prove of intense interest to the radio fra-
ternity at large, because it covers a subject very
much in the public eye at present.
One can readily see that the problem placed
before the engineering department of this organ-
ization differs greatly from that usually con-
fronting the average research staff. The request
was not for a d.c. receiver, but one designed for
use with tubes utilizing raw a.c. upon the fila-
ments and also a B supply unit. Hence we have
four requirements. First is the receiver circuit it-
self, which constitutes a problem replete with
many obstacles, particularly so in this day of com-
petition. Secondly, the use of a.c. tubes means the
provision in the design of the receiver for the
elimination of the 6o-cycle hum in the filament
supply. Thirdly, the design of the power trans-
former which will supply all the filament voltages
and the a.c. for the plate voltage, later to be recti-
fied by the rectifying tube, is a problem not to be
scoffed at. Fourth, is the coordination of all
By John F. Rider
the parts to. produce a satisfactory all-electric
receiver. The latter is more easily said than done,
as can be attested by many fans.
Let us follow in the order mentioned above
and watch the progress of the electrical develop-
ment. Six tubes are to be used in the receiver.
The receiver is to be operated with an outdoor
antenna. A certain amount of selectivity is there-
fore necessary. Considering the status of broad-
casting at the present, and the possibility of in-
creased power at the transmitters, provision for
satisfactory selectivity must be incorporated in
the event that more stations go on the air,
station wavelengths are reallocated, or trans-
mitter power is increased. This necessitates that
at least three tuned stages be used. Furthermore,
the manufacturer specifies a certain antenna
length, which, however, is not always obtainable.
To assure satisfactory sensitivity in the event
that a short antenna is used, three stages of
tuned radio-frequency amplification are decided
upon. Such decision, however, can be made only
after the gain or amplification per stage has been
determined mathematically and checked empiri-
cally.
In order to permit this determination, a large
number of different types of tuned radio-
frequency transformers must be first designed
on paper and then constructed for experimental
purposes. This experimental work is of para-
299
mount importance during the development of a
radio receiver. The variance in types of the
different experimental tuned radio-frequency
transformers is found in the type of wire used,
the diameters of the winding form, the spacing
of the individual turns, the placement of the
primary with respect to the secondary, the ratio
of inductance to capacity on different wave-
lengths, the length of the winding form, and
many other intricate details. Comparison in a
mathematical manner is not sufficient, because
phenomena encountered in practice can not be
included in the calculations. Hence both
mathematical and experimental determinations
are necessary.
The actual experimental work of measuring
the gain per stage for various radio-frequency
amplifying systems is a tedious, detailed pro-
cedure. The tuned radio-frequency transformer
to be measured is coupled to a tube. A known
radio-frequency voltage is fed into the input cir-
cuit of this tube. The output of the tuned radio-
frequency transformer is then measured at var-
ious broadcast wavelengths by means of a
vacuum-tube voltmeter. A comparison of the
output voltage values of the various radio-
frequency transformers is a direct indication of
their merit.
After a large number of tests of various forms
of inductances, and with the realization that a
300
special system of neutralization was available
in addition to the fact that individual shielding
was permissible, the staff decided to utilize what
is considered to be the most efficient form of
inductance, the single-layer solenoid with spaced
winding. With this decision the design of the
three tuned stages was complete, but what
about the antenna system? Should this be un-
tuned, and of the conventional system? The
consensus of opinion was to deviate from the
conventional and to utilize a tuned antenna
circuit. The sensitivity of the complete system
would be greater, the receiver output would be
greater and, in addition, the frequency response
characteristic of the complete r.f. system would
be better. Last but not least, the tuned an-
tenna system could be designed so that single-
control would be satisfactory, regardless of the
length of the antenna employed.
This started another series of investigations,
and after a period of time, the variometer tuned
type of input was selected. This arrangement
possessed several salient features. First, it per-
mits unicontrol. Second it provides greater gain
or amplification as the wavelength is increased.
This property is inherent in inductively tuned
circuits and is diametrically opposite to the
phenomena in capacitatively tuned circuits.
This is due to the increase of impedance of
inductively tuned circuits with increase in wave-
length. The action of the variometer-tuned
antenna-input circuit by increasing the gain on
the upper wavelengths of the normal broadcast
spectrum would tend to compensate the falling
characteristic of the other stages. This type of
tuned antenna input circuit affords a much
greater signal voltage to the grid filament cir-
cuit of the first r.f. tube. As a matter of fact the
difference between such a tuned system, Fig.
lA, and the conventional untuned antenna,
Fig. i B, is of the order of 3 to I in favor of the
former arrangement (system A).
By the use of a small series capacity, con-
nected between the antenna and the grid input
terminal of the first tube, the variance in an-
tenna capacity when different lengths of antenna
are used, is practically nullified, and the tuned
system is to all intents and purposes, isolated.
This means that the setting of the variometer
dial will remain constant regardless of the length
or type of antenna used.
Stability of the radio-frequency system was
the next point of interest. Being in possession
of a Hazeltine license, neutralization of this form
for the radio-frequency stages was an immediate
decision. Having designed the inductances and
knowing the operating characteristics, the con-
ventional Hazeltine system was selected. This
system utilizes a voltage transfer of reversed
phase from one grid circuit to the preceding
grid circuit. The value of the feed-back voltage
is governed by the design of the secondary of
the tuned radio-frequency transformer and is
the voltage across a certain portion of this
RADIO BROADCAST
FIG. I
winding. The voltage is obtained by tapping
the secondary winding at a predetermined point.
With respect to shielding, the decision to
shield individual stages by enclosing the tube,
coil, and condenser in a can, was immediate. The
choice, however, of the shielding material, re-
quired some consideration. Electrical conduc-
tivity and economy are the two important
factors. After considering these two points the
selection was aluminum.
The experimental work carried out upon the
tuned radio-frequency transformers influenced
the selection of the type of winding. Now arose
the problem of producing "matched" induc-
tances. Accuracy is very important in all single-
control units. To overcome slight discrepancies,
such as would be occasioned by one or two turns
more or less on the coils, each tuned radio-
frequency transformer is equipped with a copper
vane located at one end of the main inductance.
Manipulation of these vanes permits accurate
variation of the inductance of the windings,
thus facilitating "matching" of the condenser-
inductance combinations, and the tuned circuits.
Summarizing the radio-frequency amplifying
system we have the following: A tuned antenna
input, complete individual shielding, three
stages of tuned radio-frequency amplification,
complete neutralization, and single tuning con-
trol. The maximum capacity values of each
tuning condenser is 0.00032 mfd. The shape of
the tuning condenser plates affords a modified
straight frequency-line variation.
DETECTOR AND AUDIO SYSTEMS
NOW for the detector and audio systems.
Utmost sensitivity is desired, hence the grid
leak-condenser system of detection is employed.
As to the audio system, the choice must be
FEBRUARY, 1928'
made consistent with three factors, economy, j
results, and knowledge. Only two tubes are]
available for audio amplification. The best way
of obtaining sufficient volume is by means of
transformer coupling, and since extensive re-
search work has been carried on to design and ]
produce an excellent audio-frequency trans- i
former, the decision to use transformer coupling
was natural. That the research work along this
line was of high calibre is shown by reference to
Fig. 2. This curve shows the operating character-
istic of the audio transformer. It is a 3 to i
coupling unit, without a pronounced peak on the
higher audio frequencies, a characteristic seldom
found with the average audio-frequency trans-
former. The elimination of a sharp peak at some
frequency between 3000 and 10,000 cycles is due
to scientific coil design and minimization of
leakage reactance.
The next problem was the selection of a means
of coupling the output tube to the loud speaker.
Some coupling medium is necessary because of
the heavy output plate current occasioned by the
necessity of using a power tube in the output
stage. Passing the heavy plate current through
the loud speaker windings would injure them,
in addition to the possibility of reducing the
magnetic strength of the magnets in the event
that the polarity of the loud speaker is reversed
with respect to the polarity of the plate battery.
The design of a coupling unit was imperative.
A transformer of very good design was de-
veloped, and its frequency operating character-
istic when used with a 171 type tube is shown in
the accompanying curve, Fig. 3, at the bottom
of this page.
Now arose the problem of volume control.
Much work was done along this line; as a matter
of fact, this work could not be avoided, since
the method of controlling receiver signal output
with a d.c. receiver is not wholly satisfactory
when applied to a.c. receivers. After an ex-
tended period the system shown in the wiring
diagram on page .301 was selected as being most
effective. This is a variable high resistance shunt-
ing the tuned input circuit
This arrangement provides a means of adjust-
ing the receiver output by controlling the signal
voltage passing into the first radio-frequency
amplifier. This arrangement proved satisfactory
because it does not display an effect upon the
sideband characteristics of the radio-frequency
amplifier, nor does it manifest any variation in
the degree of neutralization. Yet the control of
volume is perfect.
THE TUBES USED
UNDER the existing circumstances, the
tubes selected were the RCA 226 and 227,
with a 171 in the output, or the equivalent
Cunningham 326 and 327 with a 371 in the out-
put. The operating characteristics of these tubes
are practically identical to that of the regular d.c
filament tubes, hence the design of the associ-
V
^ — ' J ~" "" ^
S
Audio Transformer with
' 201- A tube.Ep
mffvk
10
100 1000
FREQUENCY, CYCLES PER SECOND
FIG. 2
10.000
Frequency Characteristics of
^"^^
Output Transformer and
171 Tube-Ep-135 Eg* "27
^^s^
too looo
FREQUENCY, CYOES PER SECOND
FIG. 3
10.000
FEBRUARY, 1928
HOW THE "NR-60" WAS ENGINEERED
301
CIRCUIT DIAGRAM OF THE "NR-6o"
ated apparatus did not require special pre-
cautions. The 226 type of tube was selected for
the three stages of radio-frequency amplification
and for the first audio stage. The 227 heater type
of tube was selected for the non-regenerative
detector and the 171 was used as the output tube.
A precaution required in the receiver was that
twisted cables be used and that they be isolated
so that transfer of the Go-cycle hum was mini-
mized. That the arrangement was effective is
demonstrated by the satisfactory operation of
the receiver, despite the fact that the audio-
frequency transformers have satisfactory re-
sponse on 60 cycles. Were the filament wiring in a
position to cause hum due to induction, this
hum would be heard with regularity in the loud
speaker.
The use of a c. tubes necessitates a mid-tap
for each amplifying system. Experience proved
that a variable potentiometer shunting each
tube filament circuit was a better means of
obtaining an accurate electrical balance than
the use of a mid-tapped transformer winding.
The use of such a mid-tap requires a separate
grid bias for each amplifying system. This grid
bias is obtained from the B supply.
The design of the B supply unit and the A
supply unit was an interesting problem. Let us
consider the power unit as a whole. The power
pack supplies all the voltages required for fila-
ments, grids, and plates. It is complete in itself
encompassing the B device, the A supply, and the
output transformer. A study of the wiring dia-
gram of the power supply on this page shows an
arrangement which can be followed to excellent
advantage by many manufacturers of power
transformers and by others interested in a.c.
tubes of the type mentioned herein. The 226
tubes are rated at 1.5 volts and 1.05 amperes
and the 227 is rated at 2.5 volts and 1.75 amperes.
The voltage is low and the current is high. If
a large number of these tubes are fed through
one cable and from one source of supply, that is.
from one winding, the total amount of current
will reach a fairly high value and any small
resistance in the circuit will cause an appreciable
voltage drop. To minimize this effect each system
of amplification is equipped with a separate
filament winding, supplying energy to the tubes
in that system. This arrangement also elimi-
nates the necessity of inserting various values of
resistances to supply the correct voltages, were
one single winding used. For example, the
maximum filament winding voltage is 5 volts, for
the 171 tube. The 227 requires 2.5 volts and the
226 requires 1.5 volts. All of these voltages could
be supplied from one ;-volt winding of proper
capacity. But the insertion of the necessary
resistances for reducing the 5 volts to the correct
value for the other tubes would increase the cost
of manufacture and would be less efficient. The
method used was found much more efficient and,
therefore, adopted. An accurate mid-tap is
made possible for the radio-frequency and the
first audio-frequency tubes by the use of a po-
tentiometer. Furthermore, each filament circuit
consists of a pair of twisted cables. The 227 de-
tector tube receives a plate voltage of 45 volts
from the B unit. By employing filament windings
which provide the required filament voltages, all
filament controls are eliminated.
The design of the B device was cause for
considerable thought. Should it be a half-wave
rectifier or a full-wave rectifier? Each possessed
certain advantages. The half-wave rectifier is
simpler, but the full-wave rectifier affords cer-
tain technical and practical advantages. In the
first place the frequency of the charging voltage
applied to the condensers of the filter system
is 120 cycles with a full-wave rectifier and as
such the action of the condenser is better; the
reactance of the condensers is lower. The filter-
ing action improves as the frequency of the hum
to be eliminated increases. In addition, the cur-
rent capacity of the unit is doubled. Where a
half-wave rectifier would permit 65 mils.,
a full-wave rectifier would permit 130 mils, at
the same voltage. Hence, by using the full-wave
rectifier, sufficient current is provided at high
voltages.
To eliminate any possible hum due to induc-
tion from the power device to the receiver, the
complete unit is housed in a shield. The con-
densers used in the B device are, in turn, housed
in an individual can within the main can. Both
cans are grounded to the common ground termi-
nal and the main can is at ground potential.
One side of the main line is connected to
ground through a o. i-mfd. condenser, thus by-
passing to ground any radio-frequency energy in
the power line.
The design of a receiver is not limited solely to
the choice and pattern of the individual com-
ponents of the receiver. Complete test of the
combined parts may show that they are not
satisfactory when used together.
The method of testing the radio-frequency
transformers applies to the method of testing the
gain or amplifying power of the complete radio-
frequency amplifier.
The audio-frequency transformers are also
tested with vacuum-tube voltmeters. Each trans-
former is tested on three frequencies and a
definite output must be obtained before the
transformer is passed.
A vacuum-tube voltmeter is employed when
balancing out the hum in the receiver and by
means of the meter reading the value of the
existing ripple is ascertained.
After the receiver is assembled ready for the
first complete test, it is placed into a test rack.
The source of energy supply for this test comes
from a crystal-controlled master oscillator cir-
cuit tuned to a fixed frequency of 600 kilocycles.
This type of oscillator also supplies testing
frequencies which are multiples of the fixed
frequency. These multiple frequencies are the
harmonics generated by the crystal-controlled
tube. The tuned circuits in the receiver are
adjusted to 600 kilocycles and are brought to
resonance by means of the copper vanes associ-
ated with the inductances. Then the receiver
is tuned to the second harmonic of 600 kilo-
cycles, which is 1200 kilocycles, approximately
250 meters. It is then adjusted to perfect reso-
nance by means of balancing condensers on the
shortest wavelength within the broadcast band.
Attachment Plug
(Wl
>2.5 V.-
\A
V
1 §.
OJ <U
!•-
< ™
±^
—
—
— -
o
Fil.
O
Del.
Fil
Gnd. ~
THE POWER SUPPLY OF THE "NR-6o"
O
2nd.
A.F.
RADIO
RECEIVERS
REPRESENTING
A WIDE PRICE
RANGE
SPLITDORF'S "BUCKINGHAM"
Designed to blend in with the surroundings of a
home decorated in the English style, the period of
this cabinet work dates back some four hundred
years. The "Buckingham" is a six-tube receiver
employing three r.f. stages, tuning being accom-
plished by an attractive rose shaped knob which may
be seen in the center of the receiver. A complete
A, B, C power unit is housed within t In- cabinet.
Behind the cane center panel in the upper part of
the chest is the "Maestro Cone Tone" reproducer.
The list price of the "Buckingham" is $800.00
complete
THE FERGUSON "HOMER"
Compactness is expressed in this new receiver by
J. B. Ferguson. Housed within an exceptionally
attractive little cabinet is this seven-tube receiver,
employing four r.f. stages, two only of which are
tuned, and two audio stages. A single illuminated
dial accomplishes the tuning, and there is also a
volume-control handle on the panel. Control of
volume is obtained by means of variable plate
coupling. The audio channel makes use of General
Radio transformers. The "Homer" lists at $95.00
as illustrated. Chassis only, $80.00
302
'T'HE advent of the more expensive,
J- more luxurious, receiver, is not to
be heralded as something new, al-
though developments along this line
have been very marked of late. Ever
since its swaddling clothes days radio
has been represented in a surpris-
ingly wide range of prices. That a cer-
tain manufacturer charges ten times
as much for one receiver as for another
using the same circuit and number of
tubes, need not deter the man of mod-
est means from investing in the least
expensive model. Frequently the chas-
sis in both models is identical, the
extra cost being due to refinements of
cabinet work, the inclusion of a com-
plete power-supply unit and also,
perhaps, a built-in loud speaker
A LOOP RECEIVER
This is the "Ortho-sonic" F40 receiver, by Federal
of Buffalo. The circuit makes use of seven tubes in
a carefully balanced and shielded circuit. The loud
speaker, which is built in and concealed by a silk
screen and hand-carved grille, is said to be capable
of beautiful tone. The loop may be seen mounted
equip.
inlay and hand carving. Price, without tubes or
accessories, $450.00
THE "CRUSADER"
Hy King, also of Huffalo. Many interesting features
distinguish this receiver. Special attention, for ex-
ample, has been paid to it-s design that the use of a
H-supply device will not complicate mattera. There
are two r.f. stages and three audio stages, the latter
employing a combination of transformer and double-
impedance coupling. The three variable tuning
condensers are adjusted by means of a single k nob.
but there is an auxiliary knob for the first stage so
that exact resonance may be obtained. The "Cru-
sader" is completely shielded. The cabinet will fit
in with either mahogany or walnut, home furnishings
particularly well. Price, without accessories, $115.00
L
303
No. 1 29
RADIO BROADCAST Laboratory Information Sheet
October, 1927
The Type 874 Glow Tube
HOW IT FUNCTIONS
'T'HE type 874 tube is a special voltage regulator
1 designed for use in B power units to maintain
the voltages, supplied by the unit, constant. An
ordinary B power unit operated without a glow tube
has a comparatively poor regulation, i.e., the volt-
age changes considerably with changes in the
amount of current being drawn from the unit. It
would obviously be of decided advantage if this
voltage could be made to remain practically con-
stant at all loads. The power unit could then be used
with any receiver irrespective of the amount of
current being drawn by it (within reason) with the
knowledge that the actual voltages designated on
the binding posts of the B device were being sup-
plied. How the glow tube functions to maintain the
voltage constant may be understood by reference
to the curve A. This curve is plotted by measuring
the voltage across the glow tube with various load
currents and it should be noted that the voltage
across the tube is practically 90 at all loads up to
more than 40 mA. In ordinary operation, when
there is no current being drawn from the 90-volt
tap, the glow tube current is about 45 milliamperes.
Then, if current is drawn for a receiver from the
90-volt tap, which would ordinarily cause the volt-
age to go down, the current through the glow tube
automatically decreases, providing for the current
required by the set. The voltage thereby is main-
tained at exactly 90.
Curve B illustrates the curve of output voltage
that might be obtained from a B power unit not
using a glow tube. At no load the voltage is 123.
while at a load of 10 mA. the voltage drops to 90.
If, however, the receiver requires 20 milliamperes,
the actual voltage available would be only 60 volts.
"0 10 20 30 40 50 60 70 80 90 100
I, LOAD CURRENT IN mA.
A "NUT-SHELL" EXPLANATION OF GLOW TUBE OPERATION
The functions of a well-known type of regulator tube were fully described on Laboratory Sheet
No. 129, which is reprinted above. The principles underlying the performance of the Raytheon R
tube, illustrated below, are somewhat different to those of the 874 type tube
Constant
By G. F. Lampkin
THE most obvious problem in the con-
struction of a B device is that of filtering
— of reducing the hum to a negligible
value. In some power units, especially those made
during the last few years, so much attention was
paid to this problem that another problem, not
so apparent, but fully as important, was some-
what neglected. This latter problem is one of
voltage regulation — the changing of the B device
output voltage when the output current is varied.
A cut and dried definition states that voltage
regulation of an electrical device is the rise in
voltage when full load is thrown off the device,
expressed as a percentage of the full-load voltage.
The regulation of ordinary electrical apparatus
is seldom greater than ten per cent. The regula-
tion of some B power units runs above 100 per
cent.
If a 9o-volt set of B batteries be connected to a
receiver, it may be known with reasonable cer-
tainty that the voltage applied to the receiver is
90, whether there are one or six tubes being
supplied. If a B device is connected to a receiver
and the device has poor regulation, the voltage
Input
FIG. I
GLOW TUBE CONSTRUCTION
The use of a glow tube in B power units
is becoming increasingly popular. The
Raytheon one here shown is very efficient.
It was described at length in the October,
1927, RADIO BROADCAST
may be 150 when supplying one tube but less
than half that figure when supplying six. If the
experimenter has available a high-resistance
voltmeter suitable for the measurement of the
output voltages of a B power unit, the voltages
may be checked while the power unit is con-
nected to the receiver to make certain that the
voltages supplied to the set are correct. Some
power units are equipped with variable resistance
units so that the correct voltage may be obtained
304
by the proper adjustment of them. Without a
high-resistance voltmeter it is difficult to adjust
accurately the voltages of a B supply unit,
containing variable resistances to control the
voltage. However, if the variable resistances are
loosened so that the resistance is as high as possi-
ble and are then gradually tightened until the
receiver operates satisfactorily, it is possible to
adjust the voltages with fair accuracy. There is a
danger of shortening the lives of the tubes in the
receiver if the resistances are tightened beyond
that point which gives satisfactory reception.
Under some circumstances the variation of the
d.c. voltage with the load current introduces
another disadvantage in that it tends to cause
audio distortion. When the loud speaker is con-
nected as indicated in Fig. I, the plate current
delivered by the power unit supplying the entire
receiver may have a swing of ten milliamperes
when a loud low note is being amplified. A re-
ceiver that would give such a signal might draw
a total load of about thirty milliamperes and the
plate current swing will, therefore, form an ap-
Power Tube
FIG. 2
FEBRUARY, 1928
CONSTANT B DEVICE OUTPUT
305
Rectifier--'
Regulation
%
Overall Regulation Curve - '
Approximate Overall Reg.---
Transformer Resistance = 38 ohms
Filter Resistance = 655 ohms
Rectifier Resistance = 1587 ohms
15 20 25 30
D.C. OUTPUT CURRENT, mA.
FIG. 3
preciable part of the total load so that the B
device voltage will also vary. When the plate
current increases, due to the signal, the B device
voltage drops and tends to nullify the change;
similarly, when the plate current decreases the
voltage goes up and again tends to nullify the
change. The regulation of the device would thus
tend to cut off both the positive and negative
peaks of the signal. The filter condenser at the
output of the B device can take care of the plate
current swings to some extent by charging and
discharging on the negative and positive swings
respectively. The effect of the condenser in this
function is dependent on the frequency, however,
and at low frequencies it does not exercise control
to any great extent over the output voltage.
When the loud speaker is connected as in Fig.
2, distortion due to a variable load on the power
unit is prevented because all the a.c. currents
must flow around through the loud speaker and
back to the filament and hence do not go through
the power supply. As a result, the current
drawn through the choke Lfrom the power supply
is practically constant and the load on the power
140
120
100
u
|
ri 80
/
^360-1
5/im Loa
i
„,.*.
/;
20- Oil m
Load
0
t-
z>
Q_
5 60
0
o
a
40
20
(
,'
««••—
,.—
1,07-Ohm Load
) 1 2 3 4 56
CAPACITY, MFD.
FIG. 4
15 20 25 30
LOAD CURRENT IN MILLIAMPERES
FIG. 5
unit does not vary appreciably with the signal.
The regulation of a B device is caused by the
internal impedances of the three units that make
up the device — the transformer, the rectifier,
and the filter. As the current drawn from the
device increases, the internal voltage drops also
increase and the result is that the output voltage
becomes less. A graph of the output voltage of a
typical B device for different values of current is
shown in Fig. 3. Such a graph is called a regula-
tion curve. It is nearly a straight line and for
purposes of simplification it may be replaced by
one such as the lowest straight line of the group.
The vertical distance between this line and the
upper horizontal line, which represents the no-
load voltage, is the internal voltage drop for any
given current value. The drop at 50 milliamperes
load is 144-30, or 114 volts. Dividing voltage
by current, .JiJ, gives the value of total internal
resistance as 2280 ohms. This resistance is partly
hypothetical, for it represents the overall value
from a.c. input to d.c. output. It might be called
the "equivalent" internal resistance.
That part of the regulation which is due to the
transformer is comparatively negligible. The
secondary voltage of the transformer dropped
from 116 to 114.5 when the output current was
changed from o to 50 milliamperes; this corre-
sponds to a regulation of 1.3 per cent., and an
equivalent internal resistance of 38 ohms. The
regulation due to the filter is dependent chiefly
on the resistance of the filter chokes, and on the
capacity of the first filter condenser, i.e., the one
immediately after the rectifier. The curves of
Fig. 4 show what effect the size of the first con-
denser has on the output voltage. At light loads,
high-resistance, the voltage goes up sharply,
then flattens out, as the capacity is increased.
For any load, the voltage curve is flat at a value
of 4 microfarads. This is a more or less standard
value, so the contribution of the first condenser to
the filter regulation may be neglected, and only
the resistance of the chokes considered. This
resistance can be measured with d.c., and was in
this case 655 ohms. The equivalent resistance
of the rectifier, is, by subtraction, 2280 -
(655 + 38) = 1587 ohms. Thus, for this particu-
lar B device, the rectifier constituted the major
cause of regulation. The individual curves of
transformer, rectifier, and filter regulation shown
give a good idea as to how the voltage drops are
distributed. The total of the distances from the
no-load-voltage line to these three curves gives
the approximate overall regulation curve.
The problem of
producing power
units with good
regulation is im-
portant. As a re-
sult several meth-
ods are at present
in vogue whereby
power units can be
constructed with
comparatively
good regulation.
The use of a glow
tube in the output
circuit of a power
unit will cause the
regulation of the
unit to be excell-
entovertheentire
range of useful
load. A group of
curves taken on a
power unit utiliz-
ing a glow tube
are given in Fig.
5. Also it has been
found that by
decreasing the total resistance across the out-
put of the power unit the regulation can be im-
proved. When the total resistance R, Fig. 6, is
reduced, the currents circulating through it,
which represent a loss, are increased, but if the
power unit has available sufficient capacity, this
loss of current is advisable because it improves
the regulation of the entire unit.
From
Filter
System —
I
f
I
•y
I
n '
Output
Voltages
R<
|
?l
f
I
+ I
i
n '
?
A 1
^-* ^j
FIG. 6
The Listeners' Point of View
By JOHN WALLACE
THIS is station KWOK broadcasting on a
wavelength of four yards and six inches
by authority of the Federal Boxing Com-
mission. Station KWOK is loaned and saturated
by the McSwif Stomach Pump Company and
the Quebec Liquor Commission, Chicago Branch,
and is situated on top of the Division Street
gas holder, holder of high-grade gas. Every
Wednesday evening at this time a program of
detrimental music is brought to you by buggy
from New York through the courtesy of Ham-
stein, Hoffstein, Snickelby, and Snootch, manu-
facturers of taxi cabs, doll cabs, bottle caps, and
cogs, KWOK, Where Everybody's Sappy. Please
stand by for the Eastern pronouncer.
This is WOOP, New York, broadcasting by spe-
cial license of the city pound with a frequency
that is positively dismaying. Every Monday
evening at this time our facilities are engaged
by the HofTstein, Hammerstein, Snigelby and
Scrooch Company, manufacturers of high grade
taxi caps, doll cats, bottle cogs and coops, pre-
senting the " Hof-hac-snack-co Hour" through
WOOP together with 43 other stations, four pre-
cincts, three wards, and the juice of one lime.
Stand by please while yout local station idem-
nifies itself.
This is KWOK, Chica-
This is WOOP New Yo- (just to give the boys
in the switch yard a chance to do their stuff.)
This is KWOK
'Taint, it's WOOP
Tis
Taint
'Tis (O dear, this could go on forever, but at
this point both stations join hands in a circle
and the girls choose partners.)
You're on your back in the studios of WOOP
the key station of the Duodecimal System. I will
now tip the microphone over on Mr. Gregory
Swallop advertising manager for the Hatstein,
Hemstein, Hockelby and Pooch Company who
will renounce the program. Mr. Swallop.
Good evening folks. Well once again the
"Hic-haec-hoc-co Hour" is with you and 1
know how happy you are to hear from us and I
LESTER PALMER
Chief announcer and program director of sta-
tion wow, at Omaha
just know you are going to enjoy our program.
I also know the color of your eyes — yes I do,
take those handles down! — and how high up
is, and the date of the second coming, and oh
lots of other things. Seven days is an awfully
long time to wait, isn't it, my ducks? Why of the
17,586,864,203 letters we received during the
week 117 were from listeners who died because
they couldn't wait. Ha, ha, they must have had
jobs in a cafeteria! Ha, ha. Well. I will have my
little joke. Well I know you are anxious to hear
the program so I will not delay you any longer
except to divulge to you that this hour of enter-
tainment is donated to you gratis as a Christmas
present, free, through the munificence of Messers
-^hhh! Come over closer— HINKLESTEIN,
HOCKELSTEIN, SNOOPELB Y and SNATCH.
Don't tell! This high grade firm was foundered
in 1898 and has been engaged for forty years
in the manufacture of high grade taxi backs, doll
craps, bottled cats, and bogs. Our taxi backs are
equipped within and without with equillibrated
non-actinic colloidal stradilators and sometimes
with metaspheroid double-trussed oscillators — a
reassuring thing to know, my doves, in case of
eggs. Hinc-hoc-sno-co Brand Bottled Cats may
be obtained at any grocery store, your money
back if the color frays. Our bogs are shipped
direct to you from the boggery, untouched by
human hand.
Were you Mr. Listener, and you Mrs. Lis-
tener too, ever caught in the rain without a
taxi cab? You got soaked didn't you? And if
you'd of hired a cab you'd of got soaked too,
wouldn't you? You should own your own. So I
will now present to you the Old Soak who with
his White Mule will spirit you away this evening
to the Never-never Lands, there to hear lovely
strains of music of foreign crimes, rendered for
you by the Lard-Werks orchestra. Here take it
you bum!
Hello folksch, thisich me. An afore we gawan
wisha program thorchestra sgonna play for you
our musical trade mark the Funeral March so
that whenevah you heah it, wherevah you may
be, you may remembah the lovely, "Hing-hang-
snig-co Hours" and recall that one of our bogs
in your back yard means immediate death for
your neighbors' chickens.
Orchestra plays Chopin's Funeral March
. . . and as the last strains softly strain o'er
the distant strains we vault lightly from the
saddle of good old Black Beauty while the car-
riage boy informs us that we bring to you to-
night a pogrom of Hebrew heirs collected for
you by our research department in the pictur-
esque pathways of Palestine and Palisades Park.
And now if you will extinguish your lights, turn
off that damned radio, relax, returning to the
squatting position at the count of five, we will
enter the tonneau of the Brox Bros. Travelling
Crane and — wissht! — We find ourselves on a
sunny slope in Spain whilst from the half open
door of a little tepee in the very shadow of
Popocatapetl we hear the gentle warble of the
Swiss Marine Band crooning plaintively to its
young that lovely lullaby "On the Road to Man-
dalay-hay."
Orchestra plays the Prelude in C Sharp Minor.
306
Boom! Boom! Boom! Three crashing chords on the
piccolos followed by some thin tweedling sounds,
four policemen and a cat.
This is WOOP — We Own Our Pants — broad-
casting the Himpstein, Hinchbein, Snogerty
and Snike program. Stand by please for your
local anaesthetic.
This is KWOK broadcasting on a wa —
(WOOF'S switchman wins this chukker by sev-
enteen words, receiving in award two kewpie
dolls and a ham.)
This is WOOP my dears, Old Soak speaking.
Our sturdy steed seems to have gone back to
pasture and rubbing our eyes we find ourselves
on a Kansas farm! Well I swan! And so now the
boys are going to play for you a new derange-
ment of that lovely piece by Saahnt Saahns
called "The Swan." This is the first time to our
knowledge that a female child under the age of
fourteen has ever been choked to death over
the radio and is presented to you by special
arrangement with the composer. Saahnt Saahns
was born in Moravia in 1792. He was the son
of a sea cook and a bridge keeper's daughter.
His great grandfather on the maternal side
invented the poodle by interbreeding dachs-
hunds and cotton batting so it is not surprising
that the age of three found the gifted young
Saahnt conducting his own works in the Ruhr
district. There were no bond houses in that day
so he decided to become a musician. He never
got around to this, however, and in 1632 his
unclad body was found in the Thames. Morti-
cians discovered three measures of rye in his
stomach and nineteen measures of music ta-
tooed on the elevation nearest London Bridge.
Thus was this immoral melody given to the
world, which will now be played for you by Gilles
de Rais on the flute. Mr. de Rais is the greatest
living flautist. He was the first man to flaut
across the English Channel. For your interest,
his flute is a genuine Strad and is valued at
$17.98 an inch except in leap year one cent more.
Mr. de Rais will be accompanied by Miss Elva
Orkney on the night boat. The Swan. . . .
BOB HALL OF KOIL
Mr. Hall is chief announcer, studio director,
baritone soloist, " Uncle Josh" and director
"Little White Church on the Hill" at this middle
western station
FEBRUARY, 1928
HAIL! A GOOD RADIO "TALK"
307
Orchestra plays Tschaikowsky's Nutcracker Suite.
. . . and as this lovely Air for the G String con-
cludes we discover that our old faithful White
Mule has stumbled over the last bar and must
be shot. (Three sobs followed by a cannon shot
and screams of protest from the loud speaker).
But hopping blithely on the bullet we find our-
selves suddenly conveyed to Alsatia. "I'll Say
She Does" will be the next number by the
dance orchestra.
Orchestra plays Tschaikowsky's Nutcracker Suite.
And now folks, before this " Squawk-squack-
co Hour" comes to a close we want to tell you
about the elegant booklet we have prepared
just for you. It is printed on decollete vellum in
an edition strictly limited to four million
copies, each one signed in six places by the
authors, Hipstein, Hopstein, Spiggoty and
Speck, manufacturers of waxey tacks, boot
jacks, model gats and fogs. It contains not only
a copy of the Constitution, multiplication tables
up to ten, a list of contributors to the Yale
alumni fund of 1876, the population of the prin-
cipal cities of Denmark and the Lives of the
Saints, but also such valuable information as
" Eighty-nine Appetizing Ways to Serve Coddled
Bats," "How to Re-cog Your Baby," and "How
To Make Attractive Lamp Shades, Bird Baths,
ind Pen Wipers Out of Old Taxi Backs." Write
us and tell us how much you enjoyed our pro-
gram and how it has brought cheer into your life
— or leave out all that but anyway give us your
name and address and the addresses of twenty
of your friends who you think would also be in-
terested in high-grade blueing. And now we
conclude our program with the "Squawk-
squack-co March."
Orchestra plays Tschaikowsky's Nutcracker Suite
This is WOOP. The program you have just
heard was handed to you on a silver platter as
the joint offering of Santa Glaus, the Celestial
Powers, and Hamstein, Hoffstein, Snickelby and
Snootch, manufacturers of ... hey, Joe, what
the hell do those buzzards make anyhow?
The Possibilities of the Radio
"Talk"
WE WERE pretty nearly won back to
radio "talks" the other night after
having at one time sworn off them for
life. We happened to tune-in wjz at 6 P.M.
Central Time on a Tuesday and heard a Mr.
Frank Dole holding forth on the Airedale. Mr.
Dole's weekly dog talk, it seems, has been a regu-
lar wjz feature for many years. He is known as
an expert on dog life and is kennel editor of the
New York Herald-Tribune.
However, we didn't know all this when we
accidentally stumbled across his program and it
had to survive or be tuned-out on its own mer-
its. Our speaker was violating all the rules in the
little hand book on elocution. He was dropping
the "g's" on words ending in "ing" and mis-
pronouncing some others. His speech could
certainly not be described as fluent and was de-
cidedly lacking in that first requisite of elocution
— polish. Furthermore, he occasionally got
tangled up in his words and would have to start
a sentence over again. Some times, even, he
paused — an infamous procedure in radio de-
livery, wasting the station's good time like that!
And along toward the end of his dissertation
he waxed sentimental — an oratorical device we
heartily abhor. But that's not all: to cap the
climax he terminated his talk with some per-
sonal messages to friends of his in the old home
town in Maine!
Certainly a sufficiently lengthy catalogue of
faults to damn any speaker — in the face of which
we stoutly maintain that the talk was one of the
best we have ever heard on the radio.
Mr. Dole succeeded in that oft talked of, but
seldom demonstrated, stunt, to wit: putting
across personality. He spoke exactly as he would
have if you had cornered him on the street
and asked him to tell you something about Aire-
dales. Each one of the "faults" enumerated
above contributed to this impression of infor-
mality and the net effect was convincing — he
sounded as if he did know something about Aire-
dales. Your average radio speaker, given the same
material, would have made it sound as if he had
just looked up the subject in the Encyclopedia
Britannica.
Which last remark sums up the general run
of radio talks. Almost invariably they give the
impression of having been dug out of some book
for the occasion. The listener's reaction to such a
FRANK DOLE
Kennel Editor of the New York Herald-Tribune
who is regularly heard through wjz speaking on
dogs, a subject which he handles remarkably well
delivery is invariably this — "why not look it
up in a book myself? it's easier to read than to
listen to," click!, and the would-be talker is
switched off. The speaker has to add something
to the words if they're to mean any more than
the same stuff printed. Mr. Dole's addition to
his mere subject matter was his indubitable love
for dogs, which stuck out all through his disser-
tation. His was no speech performed for the sole
purpose of filling out a fifteen minute radio pro-
gram. He likes dogs, likes to talk about them
and wants other people to like them. His interest
in his subject was contagious and we suspect
that he may even number non-dog owners in
his audience.
Given other speakers with similar qualities
of delivery and we don't know but that we would
alter our opinions concerning the merits of the
radio talk. If we could be assured that enough
untutored speakers could be obtained, who
would talk naturally and not dress their material
up for the microphone, we would suggest an
admirable series of radio talks — let some metro-
politan station schedule a series of weekly ten
minute talks, promising a new speaker, an au-
thority on his subject, each week. Then as speak-
ers get head waiters, bakers, subway guards,
mounted policemen, customs inspectors, window
demonstrators, flag pole painters, information
clerks, pan handlers, bell hops, ribbon clerks,
bootleggers — or any others of the numerous
people whose work gives them a unique slant on
humanity, and with whom the average man
doesn't ordinarily have an opportunity to be
clubby. Let them tell the inside dope on their
business in their own words.
Of course it would first be necessary for the
director of that program to interview the pros-
pective speakers to ascertain whether or no their
garrulities would be interesting. He could ques-
tion them in the course of an hour's interview
about entertaining and intimate sidelights on
their trade. During the course of the conversa-
tion he could keep a topical record of the inter-
esting things that came up. Then the speaker
could be furnished with this brief list of remind-
ers, perhaps only five or ten sentences long, and
told to go ahead and talk until his ten minutes
were up.
The series would succeed or fail according to
its convincingness. Absolutely no editing, other
than by the method suggested above, could be
indulged in, and the speaker would have to be
encouraged to talk in his every day language.
Any faking of material, or permission of exagger-
ations for the purpose of putting "punch" in
the talk, would defeat its own end. The listeners
— a suspicious lot — would immediately decide
that the "confessions" were faked in their en-
tirety and delivered by some actor-announcer.
But if the thing were honestly done it would
be honestly convincing. Suppose a window
washer, inexperienced at formulating his ideas,
got "microphone fright" before his speech was
two minutes under way, and the program had
to be filled out with piano music — the catas-
trophe would only serve to build up the prestige
of the whole series.
INTERESTING news from France, trans-
lated by ourself at the cost of much labor
1 and consulting of dictionaries, for your
delectation:
Acting upon the Radio Broadcasting decree
issued on December 31, 1926, the constitution
of a new organization, the "Radio-Diffusion
Francaise," is being prepared by the qualified
representatives of literary and artistic groups,
of radio manufacturers and dealers, of the press,
and of various associations interested in the de-
velopment of radio.
The "Radio-Diffusion Francaise" proposes
to act upon the suggestions and orders of the
statute established by the government by bring-
ing about broadcasts of such quality and in-
terest as will be worthy of French thought,
technique, and art.
Under the auspices of the " Radio- Diffusion
Francaise, " a complete broadcast of the perfor-
mance of "La Traviata" at the National Opera
House was transmitted by station Radio-Paris,
with full power, on January 26, 1927. The opera
was offered to the listeners by the "Grands
Magasins du Printemps." (The which, as you
know, is a department store in Paris).
AN EW day time schedule has been inaugur-
ated by WJR. It is called the Musical Mati-
nee program and lasts from 12:45 to 2 o'clock
every day except Sunday. Dance music is al-
ternated with concert music, and occasionally a
solist is added. Dance music is by Charles
Fitzgerald and his Rhythm Kings, and light
concert numbers by Jean Goldkette's Petite
Symphony Orchestra.
MATCHING
R. F. COILS
By
F. J. FOX and R. F. SHEA
Engineering Dept., American Bosch Magneto Corporation
THE CRYSTAL-CONTROLLED MASTER OSCILLATOR
See Fig. 2 for the circuit diagram
THE trend toward simplicity of operation
as manifest in the design of radio receivers
during the last few years has rendered
necessary a rapid development in the technique
of production testing. During the time when
single-control receivers were unknown, there
was less necessity for precision test methods.
It was desirable that the coils and tuning con-
densers be identical in order that the dials might
read alike, but considerable tolerance could be
allowed without affecting the efficiency of the
receiver. It is quite evident that this cannot be
permitted with modern receivers, where as many
as five or six tuned circuits are coupled together
and controlled from one central drive. In this
case any appreciable departure from uniformity
will reduce the efficiency of the receiver and,
consequently, it becomes very necessary to
develop and maintain elaborate inspection
equipment in order to insure absolute uniformity
of all the component parts of the tuned circuits.
In this article it is our purpose to analyze the
various means of testing and matching radio-
frequency inductances.
Most of the methods of testing inductances at
radio frequencies involve some variation of the
well-known resonant circuit, wherein the coil
to be tested is used in combination with a cali-
brated condenser as a wave trap. This wave trap
may be attached to some sort of detector circuit
or else it may be incorporated in an oscillator
circuit. If the former is used, an oscillator must
be used to supply power, so, as a rule, it is more
economical to make the tuned circuit part of
the oscillator circuit.
The type of apparatus to be designed for this
purpose is determined by several considerations.
If the test set-up is to be used for matching coils,
50 Turns No. 26 D.C.C.,2* Dia
— 1
<
a
| \
1
Y--
°
Quartz
o
1 ,
Crystal
0
-6V
its frequency must be fixed and the tuning of the
wave trap condenser must not change the power
or the frequency of the oscillator. The apparatus
must be designed for all possible accuracy
consistent with quantity production, and, above
all, it must be reliable and fool-proof. The accur-
acy required depends on whether the coils are to
be sorted and then matched, or whether they are
to be passed or rejected. If a small receiver using
not more than three coils is being built, it is
advisable to match coils. If, however, a large
set is being manufactured, it is too expensive an
operation to match five or six coils. In this case
500 mmfd.
FIG. 2
The master oscillator circuit
with quartz crystal control
LG 20 Turns Lp 50 Turns
No.24 D.C.C on 2%"Tubing
FIG. 1
A setup developed for matching coils
it will be found more advisable to hold the coils
within a certain percentage variation from a
standard, this allowable variation being as much
as can be tolerated without serious loss in re-
ceiver performance.
In Fig. i is shown a coil test set-up which was
developed for the purpose of matching coils. This
set-up utilizes a Hartley oscillator in connection
with a wave trap circuit. Lg and Lp are the grid
and plate coils respectively and Ci is the main
tuning condenser. The oscillator may be set at a
frequency of about 1000 kc. A resistance of ten
ohms is placed in series with the grid coil and the
wave trap circuit is shunted across this resist-
ance. The wave trap consists of a thermo-
galvanometer in series with the coil to be tested,
and a variable condenser, C», of such a size that
308
it will tune the coil to 1000 kc. Across the con-
denser is a vernier, Cs, of approximately 30
mmfd. capacity, and this vernier will indicate
the amount that the test coil deviates from
standard. The variable condenser, C>, is so
adjusted that the galvanometer will give a
maximum reading when the vernier is set at 1 5
mmfd. or, let us say, a dial reading of 50, the
standard coil being connected at X. If, now,
a coil to be tested is placed across X it will
usually necessitate a readjustment of the vernier
in order to obtain a maximum galvanometer
deflection. The amount of this deviation is an
indication of the deviation of the coil's induct-
ance from standard. Coils which give vernier
readings between 40 and 60 on the dial may be
passed since the deviation is, roughly, only plus
or minus i per cent. By passing all coils coming
within the limits and rejecting any which fall
outside we can hold coils to as great a degree of
uniformity as desired. Or if the coils are to be
matched, they are labeled with the reading of the
vernier and sorted, all coils bearing the same
number being identical.
MATCHING THE TESTING DEVICE
WH 1 LE the above system is extremely useful
when small quantities of coils are being
tested, it has several disadvantages when applied
to quantity production. Chief among these is the
difficulty of exactly duplicating two such testing
devices. If coil matching is desired, we cannot
match coils tested on one set-up with those tested
on another set-up.
To overcome this disadvantage, a coil-testing
method has been worked out with which it is pos-
sible to duplicate measuring set-ups and in this
way handle a large volume with a minimum of
expense and a maximum of efficiency.
This improved system employs a constant-
frequency master oscillator and a number of
auxiliary oscillators. The last-mentioned oscil-
lators incorporate the test circuits. The master
oscillator maintains the test frequency of 1000
kc. and all the other oscillators are adjusted
to this frequency by means of a detector loosely
coupled to each oscillator.
Fig. 2 shows a wiring diagram of the master
oscillator using a quartz crystal for frequency
control. The crystal is connected between the
grid and filament of a vacuum tube and is
shunted by a grid leak. The plate circuit is tuned
by means of a, coil and condenser in parallel, and
the circuit will oscillate when the natural period
FEBRUARY, 1928
MATCHING R. F. COILS
309
C, 30 mmfd.
C3 30 mmfd.
TEST COIL
1620T
No.24D.C.Ci
LP50T
FIG. 3
The circuit of the auxiliary oscillator. A
detector circuit is loosely coupled to it
of the crystal is found. A 5-miIliampere d. c.
meter is connected in the plate supply circuit
and this serves to indicate the condition for
maximum oscillation. When oscillation begins,
the plate current decreases, and maximum
oscillation corresponds to minimum plate cur-
rent. It will be found best to operate with the
tuning condenser set for a slightly lower capacity
than that for best oscillation in order that
oscillation will start when the switch is turned
on. Crystals having an accuracy of rs of i
per cent, may be obtained from the General
Radio Company. Since only constant frequency
is required, the crystals need not be ground
accurately to any particular frequency, and
hence may be obtained at a lower price.
The wiring diagram for the auxiliary oscillator
is shown in Fig. 3. The oscillator is the same as
that shown in Fig. i with the addition of a 30-
mfd. vernier condenser, C4, across the main
tuning condenser, Ci, so that the latter may be
set and locked and C4 used to adjust this oscilla-
tor to the same frequency as that of the master.
Loosely coupled to the auxiliary oscillator is
a detector circuit consisting of a coil and con-
denser and a vacuum-tube detector. A pair of
headphones is connected in the plate circuit.
The auxiliary oscillator is tuned to the frequency
of the master by the heterodyne or beat note
method. In other words, the vernier is turned
until the beat note heard in the headphones is
lowered to "zero beat." The test circuit is placed
across the ten-ohm resistance in the grid circuit
in the same manner as shown in Fig. i. This
test circuit has the main condenser, d, and the
vernier condenser, Cs, as before, the large main
condenser being used to set the standard coil
reading for maximum meter deflection when the
vernier is set at mid-scale. The vernier condenser,
Cs, is the only piece of equipment that has to be
matched in each oscillator set-up. To facilitate
this, the condenser is made of heavy plates with
extra large spacing, and each condenser is
measured on a capacity bridge before being used.
This is necessary in order that coils tested on one
set-up can be used with coils giving the same
reading on another set-up.
A saving of one test set-up may be accom-
plished by adding to the crystal oscillator a coil
test circuit. This is done by inserting a resistance
in the plate or tuned circuit and shunting the
wave trap circuit across it, as shown in Fig. 4.
It is seen that the crystal oscillator is unchanged
except for the introduction of the measuring
circuit. This test circuit is identical with those
used in the previously described oscillators with
the exception that it is in the plate circuit instead
of the grid circuit of the oscillator.
TEST PROCEDURE
IN USING this arrange-
1 ment the following pro-
cedure is employed. The
crystal oscillator is set to
a stable operating condi-
tion as described previ-
ously. A standard coil is
now connected at X and
the tuning condenser, d,
is adjusted until maximum
current flows in the test
circuit when the vernier
condenser, C3, is set at
mid-scale. Limits are set
on either side of the
vernier mid-scale by in-
serting coils which are
known to be plus or minus
the desired amount in
inductance.~Tfrere are a
number of ways by which
a standard may be obtained. A number of coils
may be made in experimental production, and
these may be measured on an inductance bridge.
One of these is used which is representative of
the average. Another method is to run a large
number of coils through the coil tester and pick
201-A
kilocycles. Thus, if the test coil has an inductance
of 200 microhenrys and if the test frequency is
looo kc., the capacity required is'
i ,000,000,000
0.0395 X 1,000,000 X 200
= 127 Mmfd
L070T.
A 150 mmfd. condenser will, therefore, easily
serve the purpose.
A photograph of the crystal-controlled oscil-
lator described above accompanies this article.
The test coil may be seen in the test position.
The eyelets on each end of the coil serve as
coil terminals and these are also used to make
contact with the tips provided on the test setup.
The adjusting condensers are placed inside in
order to prevent the operators from tampering
with them. The dial on the panel controls the
vernier, C3. The limits are either marked on
the dial or they may be posted near the
operator.
A photograph of an auxiliary oscillator and
detector combination is also shown, in this
case the main adjusting condensers are inside
the case. The vernier, Ct, used for frequency
setting, may be adjusted by means of a screw
driver from the outside. The detector coil is on
the right-hand side and is placed about eight
inches from the oscillator coil so that the coup-
_ £350 mmfd.
7T 125A.CV
10O
*T
C2
yTest
Coil
D.C.
C3
FIG. 4
A saving of one test setup is possible by combining the latter with the crystal oscillator
out a coil which is equal to the average. The
choosing of limits is a difficult problem. It is
possible to set up a radio-frequency amplifier
and try coils which are plus or minus standard
inductance and vary these limits until the radio-
frequency gain is affected appreciably. These
coils can then be placed in the tester and the
maximum allowable limits determined. It is
also possible to compute the limits which may
be allowed and from this obtain the capacity
variation which will tune these coils to resonance
and thus obtain the allowable limits in terms of
the vernier condenser capacity. Another and less
accurate method is to choose limits from a study
of the tests of a large number of coils. I n this case
the smallest limits possible, consistent with
quantity production, may be selected.
All auxiliary oscillators are brought to the
same frequency as that of the standard by the
"beat frequency" method as described above.
The oscillators are checked as frequently as
possible, say every few hours.
The size of the tuning condenser (Q in the
diagrams) necessary to bring the test coil to
resonance will of course depend on the test
frequency and the inductance of the coil to be
tested. The proper value of Qi can be easily
computed from the following equation:
ling is small. The dial on the panel is for the
vernier, Cs.
The system described in this article has been in
operation in a well-known laboratory for some
time and has given very excellent results.
Ci
1,000,000,000
0.0395 P L
where C is in mmfd., L in microhenrys, and f in
THE AUXILIARY OSCILLATOR AND
DETECTOR
The circuit diagram of this unit is shown in Fig. 3
New Tubes
Mean Greater
Economy
THE ARRIVAL on
the open market of
power tubes of the 1 12
and 171 types (the
CX-37I-A, ux-112-A, and
•cx-3 1 2-A and
ux-iyi-A) which require but one-quarter
ampere, half of the original filament
current, is another step in the evolution
of the vacuum tube. Now we hear rumors
of new general purpose tubes of the 2OI-A
type which will consume but one-eighth
ampere, half the present tube's require-
ments, again reducing the power required
by filaments to the low value of 5.25 watts
for the average six-tube receiver. Years
ago we used tubes which ate up our
batteries to the tune of more than one
ampere each — but in those days we did
not have six-tube sets — and the new
tubes, present and promised, mark one
more step in a continual advance toward
•economy.
The 1 12-A type of tube, which is a
quarter-ampere semi-power tube, has an
amplification factor of 8 and an imped-
ance of 5000 ohms, similar to the 210
power tube except that one cannot use
plate voltages as high. This semi-power
tube, in our opinion, is a tube which
should be used more generally than is
the 171 or lyi-A tube. Two of them in
parallel will deliver as much undistorted
power as a 171 type on one-third the input
a.c. voltage and with slightly less plate
current drain from one's batteries. This
business of requiring adequate volume
with smaller input voltages is import-
ant to one who dwells over 100 miles from
powerful stations. Here more voltage am-
plification is needed to bring signals to the
volume level desired and, since the 171 type of
tube with its low mu is essentially a local sta-
tion power tube, that is, it requires large input
signals, its advantage over the 112 type is not
always apparent.
Two i I2's in parallel, which is a better com-
ibination than push-pull when choke-coupled to
the average low-impedance loud speaker, can be
•operated from B batteries economically. A single
171 tube with only 135 volts on the plate draws
as much from the B batteries as two I iz'sin paral-
lel with 1 57 volts on the plate and requires more
than twice the input voltage to deliver less power
•output. In other words, weaker signals will de-
liver the volume required when 1 12 type tubes
are employed.
The screened-grid tube is another step toward
economy. Its filament operates from 3.3 volts
.and requires 0.132 amperes — the same filament
as is used in the old and, we must say, rather
poor, 120 type tubes — and delivers roughly three
times the voltage amplification at high fre-
quencies as the 2io-A type of tube. Probably as
many stages of amplification as we are accus-
tomed to in r.f. circuits will be required with the
screened grid tube to furnish sufficient selectivity,
but the resultant input to the detector will be
much greater than when our present general-
purpose tubes are used.
ONE OF THE most fre-
quent complaints made to
radio service men sounds like
this: "My radio seems to be
all right when I first turn it on, but then fades
•out. What is wrong?" This is invariably prefaced
•with the statement that all batteries are in good
condition, i.e., that new B batteries are in use
and that the A battery has been newly charged.
What is wrong? The answer in nearly every
case is that the storage battery is run down, and
rom
that if it is thoroughly charged trouble will dis-
appear like dew in the morning. People using
trickle chargers apparently fail to understand
or appreciate the fallibility of all things mechan-
ical or electrical. Over the week end, they work
the radio for hours at a time giving it little chance
to recharge from the trickle charger, until the
little booster cannot hold up its end of the bar-
gain longer. The battery is down and nearly out,
the signals fade after a few minutes of the pro-
gram, and the only thing left to do is to cart the
battery to the nearest service station.
WE TAKE considerable
pleasure in announcing that
the loud speaker situation
seems to be improving rapidly.
For years we knew of no loud speaker that could
be compared to the W.E. 54O-AW, or the larger
W.E. cones, either in sensitivity or in tonal range
or in what we might call "intelligibility." This
latter term is taken from telephone practice
to mean the ability to distinguish the various
instruments of an orchestra — when listening to
it from a given loud speaker — or to recognize
various consonants such as d, b, t, s, when spoken
singly and without context, or to recognize the
identity of an announcer. Many loud speakers
convey sounds to us in a comparatively decent
fashion, it seems, but when we try to distinguish
the piano from a banjo, or to pick out the wood
winds from the violins, we realize that something
is wrong. All of the instruments seem "blended"
together; we cannot distinguish one from another.
We wonder how many loud speakers have been
sold because the salesman, or the advertising
told how carefully the loud speaker had been de-
signed so that a proper "blending" had resulted?
We have listened to two cone speakers re-
cently which will give the 54O-AW a close race —
the Fada 415-6 and the B.B.L. Both of these are
rather large cones, of about 24 inches diameter,
and both are remarkably good. As a matter of
fact they are so good that we have decided to
310
call upon all of the loud speaker manu-
facturers to send their instruments into
the Laboratory, and to get to the bottom
of the present loud speaker situation.
And speaking of loud speakers, it is our
opinion that improving the loud speaker
will spell trouble for the designers, manu-
facturers, and owners of a.c. sets. With
a Balsa loud speaker which we operate
with a Western Electric 54O-AW unit
out of a single 171 tube with about 160
volts on the plate, the average a.c. set
is too noisy for pleasure although on
other loud speakers the hum is inaudible.
In other words, the a.c. tube either
marks the limit of loud speaker develop-
ment, or the newer and better loud
speakers will force a.c. tubes to deliver
signals unruffled by a.c. hum. We hope
the latter, for the average loud speaker
of to-day is less than five per cent, effici-
ent, considering the entire audio band
to be passed. Which prompts us to ask
Mr. Burke, writing in the General Radio
Experimenter, what he means when he
states that most of the power delivered
to a loud speaker by a power tube is
transformed into sound waves and radi-
ated. The average power radiated by man
talking is about ten microwatts, and yet
to get the same degree of loudness, we
shove into the loud speaker 500 milliwatts
of so-called undistorted power.
NEWSPAPERS credit
the Radio Commis-
sion with following the
advice of the A. R. R. L.
in removing from the so-called 8o-meter band
the many amateur 'phone stations now existing,
and opening up the 20-meter band for radiophone
communication. In addition, the amateurs have
from 1580 to 2000 kc. (150 to 190 meters) and a
nice fat band between 56,000 and 64,000 kc.
for communication by 'phone. This sounds fine
until one realizes that the lower-frequency band
has always been open for amateur 'phones- —
except when they caused disturbance to broad-
cast listeners, when they could not be operated
until late at night — and the higher frequencies
are in the so-called 5-meter band which is prob-
ably no good for code and worse for voice. The
8o-meter band disturbed no B.C.L.'s, and was
high enough up the wavelength scale that fairly
good quality of speech could be transmitted.
But let us hasten to admit that we have had
radiophone apparatus working in the Laboratory
on as low as 3 meters and that with 20 watts
input we were able to hear the ticking of a watch
held near the microphone as far away as one
mile. We didn't experiment over greater dis-
tances.
The new international regulations, probably
in effect by 1929, narrow the so-called 4O-meter
band, but leave the other bands about as before.
In this 4O-meter band all of the amateurs of the
world who once could be found from 30 to 50
meters will be shoved, and instead of listening for
South America and South Africa on 27.5 to 33
meters and England and France above our Amer-
ican band, we may find them mixed up with 8's
and g's which are so numerous in this country.
We shall be thankful for one thing when these
new regulations go into effect — they will auto-
matically remove from the amateur bands the
many high-power commercial stations, such as
FW in France and several in Germany, which
clutter up amateur communications that seem
futile to commercial interests, and yet which
paved the way into a band that will in ten years
carry the bulk of the world's communication.
AS THE BROADCASTER SEES IT
Technical Radio Problems for Broadcasters and Others
LUEST1ON i: What is usually wrong with
a loud speaker of which it is said: "It
sounds all right on music, but not as
good on speech?" How may the characteristics
of the monitoring loud speaker affect the output
of a broadcasting station?
ANSWER: The fault in such a case is usually
loss of the high frequencies, causing speech to
sound muffled, and even unintelligible if the cut-
off point is low enough. In reality the defect is
equally present in musical reproduction, but
most people are more sensitive to this particular
defect in speech. A loud speaker which cuts off
on the high end at about 3000 cycles will sound
manifestly "tubby" on speech to almost any
observer, but many listeners tolerate it readily
for music, some even praising the result as "mel-
low."
The ideal condition for judging the quality of
a broadcasting station would naturally be to
have the apparatus, including the monitoring
equipment, flat over the whole audio band, and
to have the same condition hold for the receiv-
ing sets. The broadcast operators could then be
assured that the listeners would hear every-
thing just as it was heard at the station. Under
existing conditions, with many types of receiv-
ers and loud speakers in use, the best course for
the broadcasting station to follow is the same as
if all the receivers were good. Its own monitoring
equipment, including the loud speaker, should
respond impartially over a band between, say,
100 and 5000 cycles. If the loud speaker at the
station is "drummy," or "down" in high frequen-
cies, the operators may tend to over-emphasize
this portion of the band in microphone placing,
equalization of lines, etc. If, on the contrary, the
station loud speaker is "tinny," or relatively lack-
ing in low notes, there may be a preponderance of
bass in the station's output without the opera-
tors being aware of the fact. While such effects
may benefit some listeners whose receiving appa-
ratus requires acoustic correction, it will result
in distorted reproduction in both the good re-
'ceivers-and those which have the opposite fault
relative to the monitoring circuits at the trans-
mitter. Thus the characteristics of the station
loud speakers are often an important element in
the fidelity of reproduction attained.
QUESTION 2: What amount of energy is re-
quired for effective loud speaker operation under
the usual listening conditions?
ANSWER: A well designed cone loud speaker re-
quires a telephonic level of plus 10 TU. This is
roughly the maximum distortionless output of a
tube of the 120 power type. Such a tube will de-
liver no milliwatts of undistorted output. On
the basis of zero level equalling 10 milliwatts,
and calculating from the formula for conversion
from energy units into TU, which has been cited
so often in this department that it need not be
repeated, this corresponds to plus 10.4 TU.
For broadcast transmitter monitoring it is prefer-
able to use a tube affording more margin, say up
to plus 15 TU (the 171 type or equivalent).
On the other hand, if the loud speaker is im-
proved in sensitivity 100 milliwatts of audio
energy may be ample for its operation.
QUESTION 3: Why does a loud speaker sound
"tinny" (lacking in bass tones) when the volume
is decreased below the comfortable listening
level?
ANSWER: The same effect occurs with natural
sources of sound when the volume reaching the
ear is decreased. The cause is found in the ear
rather than in the source of sound. The ear is
much more sensitive to relatively high-pitched
sounds (say between 1000 and 4000 cycles) than
to bass notes. For example, while the threshold
of hearing in the favorable middle portion of the
audio range, say at 1000 cycles, may be around
minus 60 TU, at 100 cycles it may be no lower
than minus 20 TU. When the volume is de-
creased the bass notes drop below the auditory
threshold, so that the ear no longer responds to
them, long before the treble disappears and all
audition ceases. This phenomenon explains the
effect observed. In some cases there may be
contributing causes in the loud speaker mechan-
ism.
Death Among the Broadcasters
TOO often we have had occasion, in this
department, to discuss recent electrical
fatalities among broadcast technicians
and ways of avoiding such accidents in the fu-
ture. It is admittedly impossible to render work
with high-tension currents perfectly safe, and
there will always remain an irreducible mini-
mum of unavoidable mishaps. A transformer
may break down without warning, admitting
high voltage to a circuit where no one expects it,
lightning surges may take place, psychological
lapses sometimes upset the most carefully
planned precautions. A fatal casualty in the last
class occurred recently at the Daventry station
of the British Broadcasting Company. The'man
killed was W. E. Miller, a Maintenance Engi-
neer. The B. B. C. gives the following account
in its announcement:
"Mr. Miller threw in a high-tension switch in
3"
connection with the apparatus at 5 CB and a few
minutes later was observed to lean over a guard
rail apparently with the object of making an
adjustment which should not have been under-
taken with the switch on."
The death of Mr. Miller is stated to be the first
in the five years of operation of the B. B. C.
The question in such a case is whether me-
chanical precautions can be elaborated to a
point where a man will be protected against his
own temporary unawareness of danger. In other
words, must a sharp distinction be made between
accidents due to circuit breakdowns and the
like, and psychological failures resulting in death
or serious injury? Knowledge of circuits appears
in some cases to be no protection at all. As 1
have pointed out in previous articles on the sub-
jects, some of the men, or rather boys, working
on broadcast transmitters are altogether too
young for dangerous jobs, but older men, it must
be admitted, are sometimes no more fortunate.
What, then, can be done to establish safety by
machinery?
One device is to enclose all the high-voltage
apparatus in a grounded cage with special doors.
The doors may be opened by turning a wheel
which cuts off the high tension inside the cage
and grounds the plate circuits. The wheel
cannot be turned back while the door is open.
This comes close to being an absolute safeguard
when only one man is involved. He cannot get
into the dangerous portion of the station with-
out cutting off the current. If another operator
is involved, however, it may happen that one
man is working on the apparatus while another,
unaware of the fact, closes the door, locks it
with the wheel, and burns up the operator in-
side the cage. A red tag system will obviate this,
if it is faithfully followed — but where there is
an "if," someone will get killed some day.
A similar device consists of circuit inter-
rupters on doors in panels giving access to tubes
from the front of the panel. When the door is
opened, for replacement of a tube, or observa-
tion, the plate supply to that tube is cut off. But
it is sometimes almost imperative to allow a man
to observe the operation of the set, from a point
behind the panel, while the circuits are ener-
gized. If that man starts to touch the equip-
ment, he is on his way to the undertaker. Or,
if he leans over a guard rail, as Mr. Miller did,
he invites immediate death in the same way.
Such a guard rail, it may be pointed out, has
scarcely more than a symbolical value.
There are, in sum, two schools of design,
working on opposite fundamental assumptions.
One group contends that the best thing is to
312
leave the high-tension circuits open and accus-
tom the operators to keeping away from them.
If they realize fully, it is argued, that only their
own care stands between them and death, they
will be careful. The other group carries out the
design on the assumption that human beings are
irremediably fallible and must be safeguarded
by forethought operating through mechanical
devices. Probably one system fits some men best
while others are safer under the opposite scheme.
But unfortunately we do not select personnel
on the basis of temperament in such details,
nor do we possess adequate psychological data
which would enable us to
control accidents by such
means.
It is in this general direc-
tion that I would suggest
study and thought. Person-
ally I am not convinced of
the superiority of either of
the design systems outlined
above. There is no doubt
that much can be done with
mechanical safety devices.
One has only to consider
the low ratio of accidents in
a well conducted vacuum-
tube factory to realize that.
With highly dangerous po-
tentials distributed through
such a plant, and most of
the workers on the forty-
cents-an-hour level, it is pos-
sible practically to eliminate
accidents by careful safety
engineering and attention to
orderly procedure and clean-
liness. Nevertheless, with
highly-trained technical per-
sonnel the margin of safety
may be as great at the end
of a hooked stick, even with
the live parts of the set ac-
cessible, if a special effort is
made to control the psycho-
logical factors. At army avia-
tion fields the pilots are fre-
quently under the scrutiny
of surgeons who are expected
to detect anomalies of sight
and hearing, chronic fatigue,
and emotional disorders in
time to prevent avoidable
accidents. The engineer in
charge of a broadcast trans-
mitter should watch his men
in somewhat the same way.
Usually he is in a position to
know when anyone on the
staff is in some personal diffi-
culty which might interfere
with his ability to keep out of danger. Psychiatrists
can cite cases where men working in factories have
injured themselves as a result of lack of normal
coordination clearly traceable to domestic
troubles and other emotional disturbances. In a
broadcasting station the part of wisdom would be
to detach a man in such a condition from trans-
mitter duty and place him temporarily in the
control room or wherever he would be safe.
But, aside from such acute cases, preventive
measures of a psychological nature may also
be applied at intervals. After the monthly resus-
citation drill for members of the staff a discus-
sion may be started on accidents which have
occurred in the experience of the men, and how
they might have been prevented. This will direct
attention to the problem and may in a measure
preclude the contemptuous familiarity with the
apparatus into which technicians are apt to fall
RADIO BROADCAST
after nothing has happened for a period. There
is no danger of making radio men morbidly con-
scious of such danger as exists. Their faults are
in the opposite direction; they are not afraid
enough. Yearly medical examinations, with
special attention to the condition of the heart,
are very desirable, in that a man with a sound
heart who is caught on a high-tension circuit
usually has a good chance for his life if he is
released quickly, whereas a cardiac case is snuffed
out in the first few seconds. To compel or al-
low men to work excessively long hours is plain
criminality on the part of the employer.
HOW ULTRA-VIOLET RAYS AID PHOTOGRAPHY
Ultra-violet photomicrographic apparatus in use at the Bell Telephone Laboratories,
New York. The lenses of the apparatus are of quartz and the ultra-violet rays are
furnished from an arc light using rods of cadmium or magnesium instead of carbons.
A system of quartz prisms, in front of the lamp house, permits the operator to "tune-in"
on one particu'ar frequency of the invisible rays
Antennas from 191310 1927
B
ACK in 1913, when I was just getting out
of preparatory school, the Marconi Com-
pany was engaged in erecting a series of
transmitting and receiving stations for trans-
oceanic communication. The receiving stations
on the Atlantic seaboard were located at Chat-
ham, Massachusetts, and Belmar, New Jersey.
At each of these points the placid skyline of the
countryside was broken by a string of four-
hundred foot iron masts, mounted on cement
emplacements, and guyed to anchorages in the
surrounding fields. Much money went into those
hollow masts — and never came out again. Within
a year the development of the vacuum tube had
reached a point where an amplifier, fed from an
antenna of moderate height, would produce as
readable a signal from over the ocean as the
FEBRUARY, 192:
mile-long antenna strung on four-hundred foe
masts. The four-hundred footers were take
down and stored away. When, four years late:
I viewed the cement blocks still set in the eartl
I reflected with amusement that the engineei
of the Marconi Company had been bad propr
ets, and, with the superficial confidence of
young man, I probably thought I could hav
done better had I stood in their shoes whe
the decision was to be made.
In 1923, ten years after that die was cast,
left the Riverhead transatlantic receiving sta
tion of the Radio Corporation of America, hav
ing served my time as a re
ceiving engineer. The wav
antenna at Riverhead,
type developed by Haroli
H. Beverage, stretched t
the southwest over miles o
Long Island sand, througi
forests of scrub pine, am
oak, almost to the sea. I
did its stretching on thirty
foot telephone poles. It wa
a good antenna, one whicl
was kind to European sig
nals and not at all kind t<
the static which came fron
the opposite direction. Man;
more such antennas hav
been built since that time
on the same sort of poles
When I left Riverhead, ha(
anyone told me that trans
oceanic receiving antenna
would ever be built other
wise, I should have ex
pressed polite doubts. Mac
my informant added tha
steel towers would rise ir
Riverhead almost as higl
as the Marconi masts ai
Belmar, before I returnee
to the town, I should hav<
expressed doubts not nearl>
as polite. Had he statec
finally that there would b(
five of them, with ninety-
foot cross arms at the top,
I should have taken him,
I am afraid, for a harmless
lunatic whose aberration
led him to imagine towe.s
instead of the more usual
pink elephants or snakes.
Another four and one-
half years flit past. The
short-wave explorations of
the ether (if you care to as-
sume one) begin, and soon
reach formidable portions.
A short-wave receiving
system is developed in which vertical antenna
wires hang from steel crossarms which, curi-
ously, are supported by steel towers three hun-
dred feet high, while at the other ends of the
crossarms reflector wires sweep gracefully to the
earth. The wave antennas are still at Riyerhead,
combined and phased for even greater efficiency,
and even more inconspicuous, for five of the
three-hundred foot towers have come to keep
them company. The fact that none of us ex-
pected them did not keep them from coming.
They obeyed a different sort of logic than that
which ground out conclusions in our brains.
They followed the innate logic of invisible os-
cillations propagated through space and the
laws of the materials which men use in com-
municating over the distances separating one
continent from another. And so, for the moment,
they stand proudly over the scrub pine woods.
RADIO BROADCAST ADVERTISER
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Name
Address
314
RADIO BROADCAST ADVERTISER
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ACM
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MAKES BETTER RADIO
The Radio Broadcast
SHEETS
"TpHE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
*• magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to
that time was printed.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. i to 88, can be secured from the Circulation Department,
Doubleday, Doran & Company, Inc., Garden City, New York, for $1.00. Some readers
have asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any such errors do occur, a new Laboratory Sheet with the old
number will appear.
— THE EDITOR.
No. 161 RADIO BROADCAST Laboratory Information Sheet February, 1928
Comparing the 112, 171, and 210 Type Tubes
THEIR RESPECTIVE OUTPUTS
r\N LABORATORY SHEET No. 162 are shown
*"* three aurves that indicate an interesting re-
lation between the three most common types of
power tubes, i.e., the 112, 171, and 210 types. The
curves indicate the relation between the power out-
put of the tubes and the value of the signal voltage
impressed on the grid. The plate impedance and
amplification constants of the 112 and 210 type
tubes are practically identical and, therefore, the
curves for these two tubes coincide from zero up
to that point corresponding to the maximum output
power of the 112, which is approximately 195 milli-
watts, or 0.195 watts.
If a vertical line is drawn at any point on the
curve, for example, at A, the points at which this
line crosses the various curves will indicate the
power output obtained from the particular tube
associated with the curve being examined. In this
particular case, line A, drawn at the point corre-
sponding to a signal voltage on the grid of 15 volts
indicates that, with this value of signal voltage,
the power output of a 210 tube with 425 volts on
the plate is approximately 0.34 watts. The power
output of a 171 at the same point is approximately
0.1 'watts. The maximum grid voltage that can be
impressed on a 112 without resultant output dis-
tortion is about 10.5 volts and, therefore, a 112
tube cannot be used if the signal input voltage is
greater than this value. At B we have drawn
another line corresponding to a signal on the grid
of 8 volts. Here we find that the power output of a
112 is approximately 0.1 watts and the power out-
put of a 171 about 0.04 watts. It is therefore evident
that at low values of input voltage a 112 tube is
capable of putting more power into the loud speaker
than is a 171. If the signal voltage, however, is in
excess of 10} volts, the 112 cannot be used and the
chbice then lies between the 210 and the 171. The
curves indicate that the 210 will give much more
power output than a 171 but it should be realized
that much greater plate voltages are necessary on
the 210 than on the 171. With 180 volts on the plate
the 171 can deliver approximately 740 milliwatts of
power, but 250 volts on the plate of the 210 will
only permit this tube to handle signal voltages up
to 18 volts and the maximum output power will
be only 460 milliwatts. From these data the follow-
ing conclusions can be arrived at:
(1.) For input signals on the grid of the power
tube of 10 volts or less the 112 tube will deliver
the most power to the loud speaker.
(2.) When more power output is required and only
moderate plate voltages are available (not in excess
of 200 volts) a 171 is capable of giving greater
output than can be obtained from a 210 under simi-
lar conditions of plate voltage.
(3.) Where high plate voltages around 400 volts
are available the 210 should be used and under the
same input signal it will give approximately 2J
times as much power as can be obtained from a 171.
No. 162 RADIO BROADCAST Laboratory Information Sheet February, 1928
112, 171, and 210 Tube Curves
1.6
1
1
1
|A
s
1.2
51 n
1
RADIO BROADCAST
LABORATORY
s'(m VMS)
1
EL
t—
1
1
s
1
1
s
(/«7vU^^
^s'
^+
t^fg
£^~-H —
0 10 20 30 40
PEAK SIGNAL VOLTAGE ON GRID OF TUBE
These curves indicate how the power output of
the 112, 171, and 210 type tubes varies with differ-
ent va ues of signal voltage on the grid of the tube.
The significance of these curves is explained in de-
tail on Laboratory Sheet No. 161.
RADIO BROADCAST ADVERTISER
315
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Both sets of plates are entirely in-
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The drum is 15 inches in circum-
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RADIO BROADCAST ADVERTISER
Centralab
Radiohm RX 100
A new taper of resistance specifically
to control volume of receivers using
the new AC tubes. A variable resist-
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tubes without destroying the delicate
balance of voltage for efficient oper-
ation.
Centralab RX 100
Radiohm, with
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and smooth, noise-
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the R. F. stages,
does not affect the
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potentials, insur-
ing balance and
eliminating a source of AC hum.
In "super" circuits, the most satisfactory
volume control is obtained by inserting
the RX 100 in the grid of the intermediate
frequency that is not sharply tuned.
Also a 50 ohm Centralab Power Rheostat inserted
in the primary of the transformer will compensate
for any line fluctuation — increasing life of tubes
and holding entire circuit at the point of best
operating efficiency.
Centralab
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A new improved positive voltage control
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Other products of Centralab are
Radiohms, Modulators, Potentio-
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describes them all. Write for it.
No. 163
RADIO BROADCAST Laboratory Information Sheet February, 1928
Testing Receivers
USING THE MODULATED OSCILLATOR
THE accurate determination of the characteristics
of a radio receiver requires a careful laboratory
test, but it is possible to construct comparatively
simple apparatus of much practical value for the
testing and repairing of receivers. The instrument
that will enable us to make such tests is the modu-
lated-oscillator. From a modulated oscillator we can
obtain an audio-frequency tone which can be fed
into the input of the audio amplifier in a radio re-
ceiver and the functioning of the audio amplifier
thus checked, or by turning on both r.f. and a.f.
oscillators we can obtain a modulated wave which
can be used to test both the r.f. and a.f. circuits.
The circuit diagram of a modulated-oscillator
will be found on Laboratory Sheet No. 164. The
following paragraphs will explain how to use the
instrument for testing receivers.
(1.) Audio Amplifiers
Place all the tubes in and connect all the batteries
to the amplifier. Do not place the detector tube in
its socket. Connect the plate terminal of the de-
tector tube socket to audio output terminal No. 1
on the modulated oscillator. Connect both the B +
detector lead on this receiver and terminal No. 2
on the modulated oscillator to B — on the receiver.
Turn on the receiver and audio circuit of the modu-
lated oscillator and adjust potentiometer P to
give an output of medium intensity from a loud
speaker connected to the output of the audio
amplifier. A defect in the amplifier is indicated if
the output is low or distorted or both.
(2.) Radio- Frequency Amplifiers.
A test of the r.f. amplifier of a receiver is accom-
plished by first placing all the tubes in the receiver
and connecting all the batteries, and then winding
about two turns of insulated wire around the coil
on the oscillator, connecting the other end of this
wire to the antenna post on the receiver. The
oscillator should be located about ten feet away from
the receiver. If the a.f. and r.f. tubes in the modu-
lated oscillator are turned on and the receiver's
tuning circuits adjusted to resonance, an audio-
frequency tone should be audible in the output.
Since the a.f. amplifier in the receiver was tested
previously, any defect in the operation of the re-
ceiver must be located in the r.f. amplifier or de-
tector circuit.
No. 164 RADIO BROADCAST Laboratory Information Sheet February, 1928
A Modulated-Oscillator
R.F. Oscillator 0.0012 mfd. 11 A.F. Oscillator
All the constants of the apparatus used in the
instrument are given on the diagram. Some in-
formation on the use of this instrument will be
found on Laboratory Sheet No. 163. The frequency
of the audio-frequency oscillations can be varied by
using various values of capacity across the push-
pull transformer.
No. 165
RADIO BROADCAST Laboratory Information Sheet February, 1928
Audio Amplification
GENERAL CONSIDERATIONS
AN AUDIO system can be considered satis-
factory if it amplifies the signals impressed on
its input sufficiently to operate adequately a loud
speaker and does so without distorting the signals
to an extent sufficient to become apparent in the
output of the loud speaker. Such performance can
only be realized when the amplifier has been cor-
rectly designed and is operated properly.
The overall frequency characteristic of an ampli-
fier is frequently quite dissimilar to the characteris-
tic of a single stage. This is especially true of trans-
former- or impedance-coupled amplifiers and is
probably due. in most cases, to coupling in the plate
supply. Regenerative effects are thereby introduced
into the circuit, which may produce considerable
changes in the frequency characteristic of the audio
system. Such effects are also present, at times, in
resistance-coupled amplifiers and generally cause
such an amplifier to "motor-boat."
The solution of such difficulties is.either to design
the amplifier so that with the regenerative effect
present the system has a flat characteristic or to
design two units to have a flat characteristic and
then arrange the circuit so carefully that regenera-
tive effects will not be present. This necessitates
feeding all the grid and plate circuits through resist-
ances or choke coils and bypassing all the circuits
with condensers.
Some recent audio transformers are designed to
have a fairly sharp cut-off at about 5000 cycles to
reduce the effect of various extraneous sounds,
such as tube noise, high-frequency heterodyne
whistles, etc., which are composed mostly of fre-
quencies above 5000 cycles. Frequencies above
this value add little to the quality of the speech or
music and can therefore be eliminated without in-
troducing noticeable distortion. It is doubtful
whether the majority of broadcasting stations them-
selves transmit notes of more than 5000 cycles in
frequency.
Also many amplifiers have a tendency to oscillate
at very high audio frequencies and sometimes at
supersonic frequencies. If the amplifier is designed,
however, to give little or no amplification to fre-
quencies much above 5000 cycles, this tendency of
the amplifier to oscillate will be nullified.
RADIO BROADCAST ADVERTISER
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This transformer is more than a protec-
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General Radio
Quality Apparatus
THE apparatus manufactured by the General Radio Com-
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Laboratory instrument and part is guaranteed, and in
many cases they represent the result of years of develop-
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tories. It has been the aim of this Company to contribute
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Low loss condenser design has re-
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Type 334-F 500 MMF Panel
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Type 334-H 500 MMF Panel
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Type 334-N 350 MMF Panel
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Type 334-P 350 MMF Panel
mounting with gear $5.00
Type 334-K 250 MMF Panel
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Type 334-M 250 MMF Panel
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Type 445 Plate Supply and
Grid Bias Unit
The General Radio Type 445 Plate Supply has been designed to
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combination of voltages from 0-180 may be obtained. An adjust-
able grid bias voltage from 0-50 is also available for use on the
power tube of the amplifier.
The Type 445 Plate Supply is designed for use on 105 to 125 volt
A. C. lines (50-60 cycles) and uses the UX 280 or CX 380 rectifier tube.
This unit is licensed by the Radio Corporation of America for Radio
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UX-280 or CX-380 Rectifier tube . . . 5.00
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318
RADIO BROADCAST ADVERTISER
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No. 166 RADIO BROADCAST Laboratory Information Sheet February, 1928
Acoustics
DAMPING AND REVERBERATION
THE quality of reproduction from any loud
speaker depends to a considerable extent upon
the room in which it is used and upon the room's
furnishings. The reason why the room and its
furnishings influence the output of the sound gener-
ator, whether it be a piano, phonograph, or a loud
speaker, is not difficult to understand, and will be
explained briefly here.
In an average room the sounds from a piano, for
example, are somewhat damped by the hangings,
carpets, furniture, etc., so that they decrease to
inaudibility quite rapidly. When the furniture,
rugs, etc. , are removed and the piano is permitted to
stand on the bare boards, the sounds from it will be
prolonged and the music will become jumbled,
especially when playing forte. This effect is due to
the absence of the furniture, which normally acts
as a damping agent, and also due to the fact that the
piano is resting directly on the floor so that the latter
acts to increase the effective area of the sound board.
The sounds produced by the piano when it is in direct
contact with the floor will be somewhat louder than
usual, indicating increased efficiency.
Under any given room conditions the rate at
which a sound dies away is the same whether the
sound at its beginning is loud or soft. However,
the time taken for the sound to become inaudible
depends upon the loudness of the original sound and,
of course, the louder the sound, the longer it will
take to decrease in volume to a point where it is
inaudible. In a room containing furnishings that
cause considerable damping, we may, therefore,
play much louder than in an unfurnished room,
without causing any excessive blurring.
A room can be too completely damped, when the
playing will sound "dead." A certain amount of
blurring or intermingling of succeeding chords is
considered good, for it adds coloration to the music.
The importance of these matters in relation to the
design of the studios in broadcasting stations is
evident. The correct amount of damping must be
obtained to prevent deadening the music (too much
damping) or to obviate difficulties due to reverber-
ation (too little damping.)
No. 167 RADIO BROADCAST Laboratory Information Sheet February, 1928
Resonant Circuits
GAIN AND SELECTIVITY
'T'HE current at resonance in a tuned circuit is
* equal to the voltage induced in the circuit di-
vided by the total resistance of the circuit. The
actual capacity of the condenser or the inductance
of the coil used in the circuit do not enter into the
calculation once the induced voltage and the
resistance are known. The voltage across the
coil in the circuit is equal to a
constant times the current times
the inductance of the coil and,
the voltage is, therefore, larger
the greater the inductance of
the coil. Since a vacuum tube is
a voltage rather than a current
operated device, it might appear
that best results, i.e., greatest
amplification, would be ob-
tained by making the coil very
large. When we increase the in-
ductance of a coil by adding to
the number of turns, however,
we also increase the resistance
and the increase in resistance
nullifies to some extent the ad-
vantage gained through the use
of a larger coil.
The selectivity of a tuned stage in a receiver de-
pends upon the series resistance of the circuit;
with low-resistance circuits the selectivity is good
while with high-resistance circuits the selectivity is
poor. The curves on this Sheet indicate the effect of
resistance in the tuned circuit. Curve 1 shows the
characteristic of a very low-resistance tuned circuit
and curve 2 a comparatively high-resistance circuit.
Since practically all of the resistance in a tuned
circuit is in the coil, it follows
that carefully constructed, fairly
"low-loss" coils should be used
in a radio-frequency circuit.
A coil can be made so good
as to cut "side-bands," how-
ever, and thereby distort the
received signal head-band sup-
pression results in the loss of the
high audio frequencies in the
modulated wave.
If the ratio of the inductive
reactance of the coil (6.28 times
the frequency times the induc-
tance of the coil) to the radio-
frequency resistance of the coil
at the same frequency is made
much more than 250, distortion
of the "side-bands" results.
No. 168 RADIO BROADCAST Laboratory Information Sheet February, 1928
The Ear
ITS CHARACTERISTICS
rPHE characteristics of the human ear have been
•«• determined and investigated by many different
scientists, and some of these characteristics are
given below:
(a.) There is a minimum sound intensity below
which the ear cannot detect any sounds. A curve
was published on Laboratory Sheet No. 109, in-
dicating how this minimum audible intensity varied
with frequency.
(b.) There is a maximum intensity of sound above
which the auditory sensation is one of pain rather
than sound. The intensity and its variation with
frequency was also explained on Lab Sheet No. 109,
(c.) There is a lower limit of the pitch of a sound
below which the ear will not respond. This lower
limit is about 20 cycles.
(d.) There is an upper limit to the pitch of a sound
above which the ear will not respond. The upper
limit is about 20,000 cycles.
(e.) The car can distinguish between about
300,000 separate sensations of sound.
(f.) The ear can respond to pressure changes be-
tween the pressure required to produce a minimum
audible sound and a pressure 100 million times
greater. These two pressures correspond to an
energy ratio of 10,000 trillion.
(g.) The ear can distinguish between the loud-
ness of various sounds. At low levels of sound in-
tensity a change of about 25 per cent, is necessary
to be distinguishable. At greater intensities a
change of 10 per cent, in loudness is detectable by
the ear.
(h.) The ear can distinguish between the pitch of
various sounds. At medium frequencies a change in
frequency of about 0.3 per cent, can be detected;
at low frequencies a change of about 1 per cent, is
necessary.
A knowledge of these characteristics is useful to
Ihe student interested in problems of sound repro-
duction.
RADIO BROADCAST ADVERTISER
319
SUPERIOR PARTS
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MILWAUKEE. WISCONSIN
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You can build the "Hi-Q SIX" yourself
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FLOBER.TS
-HtQ*SIX-
HAMMARLUND-ROBERTS Inc., Dept. A, 1182 Broadway, New York
•Associate Manufacturers-
RADIO BROADCAST ADVERTISER
Use an
indoor Aeria
for
GreaterSdediviwT
In large cities, near
the big radio sta-
tions, selectivity is
a difficult problem.
An indoor aerial
sharpens the tun-
ing or any radio
receiver without
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programs received from local
broadcasting stations. Fur-
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special lightning protection.
Belden Indoor Aerial Wire is
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easily concealed around pic-
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Belden Manufacturing Co.
*:*iz-A S. Western Ave., Chicago
For sale at leading Radio Deal-
en in distinctive Belden cartons.
Ideal for making loop antenna for
superheterodyne sets.
Indoor Aerial Wire
cy ^
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
DE/4DERS may obtain any of the booklets listed below by use~
*^- ing the coupon printed on page 328. Order by number only.
\. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS — A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-
TION— Circuit diagrams and discussion. ALL-AMERICAN
RADIO CORPORATION.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
1 1. RESISTANCE COUPLING — Resistors and their ap-
plication to audio amplification, with circuit diagrams.
DEJUR PRODUCTS COMPANY.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
1 5. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE CONDENSERS — A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their application to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
17. BAKELITE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
19. POWER SUPPLY — A discussion on power supply with
particular reference to lamp-socket operation. Theory
and constructional data for building power supply devices.
ACME APPARATUS COMPANY.
20. AUDIO AMPLIFICATION — A booklet containing data
on audio amplification together with hints for the construc-
tor. ALL AMERICAN RADIO CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE-
METER — Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
positions in the circuit where audio-frequency chokes may
be used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio-frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED,
51. SHORT-WAVE RECEIVER — Constructional data on a
receiver which, by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY — A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL. INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA — Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. RESISTANCE COUPLING^— A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION.
62. RADIO-FREQUENCY AMPLIFICATION — Constructional
details of a five-tube receiver using a special design of radio-
frequency transformer. CAMFIELD RADIO MFG. COMPANY.
63. FIVE-TUBE RECEIVER — Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
64. AMPLIFICATION WITHOUT DISTORTION — Data and
curves illustrating the use of various methods of amplifica-
tion. ACME APPARATUS COMPANY.
66. SUPER-HETERODYNE — Constructional details of a
seven-tube set. G. C. EVANS COMPANY.
70. IMPROVING THE AUDIO AMPLIFIER — Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used.
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM — A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY.
80. FIVE-TUBE RECEIVER — Data are given for the con-
struction of a five-tube tuned radio-frequency receiver.
Complete instructions, list of parts, circuit diagram, and
template are given. ALL-AMERICAN RADIO CORPORATION.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
82. SlX-TUBB RECEIVER — A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams.
and templates for the construction and assembly of sockel
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Pane! layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequenc>
transformers of special design. KARAS ELECTRIC COMPANY
85. FILTER — Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A sockel
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimenta
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blue print and necessarv
data, for building an eight-tube receiver. THE GEORGE \V
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER — Data and blue print:
are given on the construction of a short-wave transmitter
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES
90. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification art
given. ALDEN MANUFACTURING COMPANY.
93. B-SOCKET POWER — A booklet giving constructional
details of a socket-power device using either the B H or 3 1 3
type rectifier. NATIONAL COMPANY, INCORPORATED.
94. POWER AMPLIFIER — Constructional data and wiring
diagrams of a power amplifier combined with a B-suppl>
unit are given. NATIONAL COMPANY, INCORPORATED.
ipo. A, B, AND C SOCKET-POWER SUPPLY — A booklel
giving data on the construction and operation of a socket
power supply using the new high-current rectifier tube,
THE Q. R. S. Music COMPANY.
101. USING CHOKES — A folder with circuit diagrams ol
the more popular circuits showing where choke coils ma>
be placed to produce better results. SAMSON ELECTRIC
COMPANY.
22. A PRIMER OF ELECTRICITY — Fundamentals oi
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
25. ELECTROLYTIC RECTIFIER — Technical data on a new
type of rectifier, with operating curves. KODEL RADIO
CORPORATION.
26. DRY CELLS FOR TRANSMITTERS — Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS— Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE — Battery life curves with general
curves on tube characteristics. BURGESS BATTERY COM-
PANY.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
31. FUNCTIONS OF THE LOUD SPEAKER — A short, non-
technical general article on loud speakers. AMPLION COR-
PORATION OF AMERICA.
32. METERS FOR RADIO_ — A catalogue of meters used in
radio, with connecting diagrams. BURTON-ROGERS COM-
PANY.
33. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. WHY RADIO Is BETTER WITH BATTERY POWER — Ad-
vice on what dry cell battery to use; their application to
radio, with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR — Information on the care of
vacuum tubes, with notes on how and when they should be
reactivated. THE STERLING MANUFACTURING COMPANY.
69. VACUUM TUBES— A booklet giving the characteris-
tics of the various tube types with a short description of
where they may be used in the circuit. RADIO CORPORA-
TION OF AMERICA.
77. TUBES — A booklet for the beginner who is interested
in vacuum tubes. A non-technical consideration of the
various elements in the tube as well as their position in the
receiver. CLEARTRON VACUUM TUBE COMPANY.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
91. VACUUM TUBES — A booklet giving the characteristics
and uses of various types of tubes. This booklet may be
obtained in English, Spanish, or Portuguese. DEFOREST
RADIO COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS— A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new 4Oo-milliampere rectifier tube. CARTER RADIO
COMPANY.
97. HIGH-RESISTANCE VOLTMETERS — A folder giving in-
formation on how to use a high-resistance voltmeter,
special consideration being given the voltage measurement
of socket-power devices. WESTINGHOUSE ELECTRIC &
MANUFACTURING COMPANY.
1 02. RADIO POWER BULLETINS — Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
(Continued on t>aee 128)
RADIO BROADCAST ADVERTISER
321
THE
"IMPROVED ARISTOCRAT"
MODEL RECEIVER
was built around
SICKLES COILS
You can expect to duplicate the exceptional re-
sults only with the same
SICKLES COILS
These are the same standard high quality ac-
curately calibrated coils which have had no
superior during the past five years. Specially
designed for the
LYNCH IMPROVED ARISTOCRAT
COIL COMBINATION No. 28, $4.50
There are Sickles Diamond Weave Coils
for all Leading Circuits.
The F. W. Sickles Co.
132 Union Street
SPRINGFIELD, MASS.
No
N
No
No
No
COIL PRICES
30 Shielded Transformer .... $2.00 each
24 Browning-Drake ............ 7.50 Set
ISA Roberts Circuit ........... 8.00 "
25 Aristocrat Circuit .......... 8.00 "
28 Lynch Aristocrat ........... 4.50 "
PLUS.'
^
I
Poly met Block
Condensers
The foremost Power Unit Manu-
facturers, as well as Radio Fans,
who know, all use Polymet Block
Condensers. Why ? Because they
have stood the test of time and
use — their rugged construction
and high voltage capacity are the
Power Unit Builder's guarantee
against break-down and grief.
At All Dealers
Write for complete information regarding Polymet
Condensers and Catalog of all Poly met
Radio Essentials.
POLYMET MANUFACTURING CORP.
589 Broadway, New York City
POLYMET
The latest and most
complete radio test-
ing instrument
Pattern No. 137
A.C.andD. C. Radio
Set Analyzer
Does Your Dealer
Serve You Right?
Are you, as a set owner, getting the very best service on your radio set from your
dealer or is he trying to get by with inferior equipment.
Service these days need not involve any guess methods for the Jewell Electrical In-
strument Company, who pioneered radio testing equipment, has made radio servicing positive
and satisfying. Jewell equipment is found in every dealer's store and new instruments are
produced as the need dictates.
A new Jewell Set Analyzer is now available to dealers who desire a service instru-
ment that will solve the new service problems coming with the increasing use of A. C. operated
radio sets and sets using the new A. C. tubes. It is the last word in radio testing equipment.
It Will Make A. C. Tests On-
Four and five prong A. C. tubes, Kellogg A. C.
tubes, line voltage, filament and charger trans-
former voltage and filament voltage on A. C. tubes
or on tubes operated in series.
It Will Make D. C. Tests On—
All D. C. tubes, A-batteries or A-eliminators, B-
batteries or B-eliminators, total plate current or
current per tube, grid voltage, transformers and
circuit continuity tests.
The complete Radio Set Analyzer weighs only six and one-half pounds and comes
equipped with adapters and test leads. It is complete in every way.
Make sure that your dealer uses reliable and accurate instruments when servicing
your set, and write us for a copy of our radio instrument catalogue, which shows many fine
instruments for set owners.
Jewell Electrical Instrument Co.
1650 Walnut St., Chicago
"28 Years Making Good Instruments"
ELKAY
RADIO
INTERFERENCE FILTERS
Take out noises in your radio caused
by motors and household appliances.
Requires NO attention. Over 1000
now in use.
Size No. i for small motors, $10
Up to 1-4 h. p.
Size No. 2 for larger equipment $15
Up to y h. p. (& 220 volts
Write for Price List
TOBE DEUTSCHMANN CO.
\ CAMBRIDGE, MASS. /*
RADIO BROADCAST ADVERTISER
"RADIO BROADCASTS" DIRECTORY OF
MANUFACTURED RECEIVERS
<J A coupon will be found on page 331. All readers who desire additional
information on the receivers listed below need only insert the proper num-
bers in the coupon, mail it to the Service Department of RADIO BROADCAST,
and full details will be sent. New sets are listed in this space each month.
KEY TO TUBE ABBREVIATIONS
99— 60-mA. filament (dry cell)
01-A — Storage battery 0.25 amps, filament
12 — Power tube (Storage battery)
71 — Power tube (Storage battery)
16-B — Half-wave rectifier tube
80 — Full-wave, high current rectifier
81 — Half-wave, high current rectifier
Hmu — High-Mu tube for resistance-coupled audio
2O^Power tube (dry cell)
10 — Power Tube (Storage battery)
00-A — Special detector
13 — Full-wave rectifier tube
26 — Low-voltage high-current a. c. tube
27 — Heater type a. c. tube
DIRECT CURRENT RECEIVERS
NO. 424. COLONIAL 26
Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One to
three dials. Volume control: antenna switch and poten-
tiometer across first audio. Watts required: 120. Con-
sole size: 34 x 38 inches. Headphone connections.
The filaments are connected in a series parallel arrange-
ment. Price $250 including power unit.
NO. 425. SUPERPOWER
Five tubes: All 01-A tubes. Multiplex circuit. Two
dials. Volume control: resistance in r. f. plate. Watts
required: 30. Antenna: loop or outside. Cabinet sizes:
table, 27 x 10 x 9 inches: console, 28 x 50 x 21.Prices:
table, $135 including power unit; console, $390 includ-
ing power unit and loud speaker.
A. C. OPERATED RECEIVERS
NO. 508. ALL-AMERICAN 77, 88, AND 99
Six tubes; 3 t. r. f . (26), detector (27), 2 transformer
audio (26 and 71). Rice neutralized t. r. f. Single drum
tuning Volume control: potentiometer in r. f. plate.
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,
25 x 38 x 18 inches; No. 99 console, 27} x 43 x 20 inches.
Shielded. Output device. The filaments are supplied
by means of three small transformers. The plate supply
employs a gas-filled rectifier tube. Voltmeter in a. c.
supply line. Prices: No. 77, $150, including power unit;
No. 88, $210 including power unit; No. 99, $285 in-
cluding power unit and loud speaker.
NO. 509. ALL-AMERICAN "DUET"; "SEXTET"
Six tubes; 2 t. r. f. (99), detector (99), 3 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
"Duet," 23 x 56 x 16i inches; "Sextet,"22J x 13} x 155
inches. Shielded. Output device. The 99 filaments are
connected in series and supplied with rectified a. c.;
while 12 is supplied with raw a. c. The plate and fila-
ment supply uses gaseous rectifier tubes. Milliammeter
on power unit. Prices: " Duet," $160 including power
unit; "Sextet," $220 including power unit and loud
NO. 511. ALL-AMERICAN 80, 90, AND 115
Five tubes; 2 t. r. f. (99), detector (99), 2 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
No. 80, 23i x 12} x 15 inches; No. 90, 37} x 12 x 12}
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi-
vidually shielded. Output device. See No. 509 for
power supply. Prices: No. 80, $135 including power
unit; No. 90, $145 including power unit and compart-
ment; No. 115, $170 including power unit, compart-
ment, and loud speaker.
NO. 510. ALL-AMERICAN 7
Seven tubes; 3 t. r. f. (26), 1 untuned r. f. (26), detec-
tor (27), 2 transformer audio (26 and 71). Rice neutral-
ized t. r. f . One drum. Volume control : resistance in r. f .
plate. Cabinet sizes: "Sovereign" console, 30} x 601
x 19 inches; "Lorraine" Hiboy, 25} x 53| x 17} inches;
"Forte" cabinet, 25i x 131 x 17) inches. For filament
and plate supply: See No. 508. Prices: "Sovereign"
$460; "Lorraine $360; "Forte" $270. All prices include
power unit. First two include loud speaker.
NO. 401, AMRAD ACS
Six tubes; 3 t. r. f. (99), detector (99), 2 transformer
(99 and 12). Neutrodyne. Two dials. Volume control:
resistance across 1st audio. Watts consumed: 50. Cabi-
net size: 27 x 9 x 11} inches. The 99 filaments are con-
nected in series and supplied with rectified a. c., while
the 12 is run on raw a. c. The power unit, requiring
two 16-B rectifiers, is separate and supplies A. B. and C
current. Price $142 including power unit.
NO. 402. AMRAD ACS
Five tubes. Same as No. 401 except one less r. f.
stage. Price $125 including power unit.
NO. 536. SOUTH BEND
Six tubes. One control. Sub-panel shielding. Binding
Posts. Antenna: outdoor. Prices: table, $130, Baby
Grand Console, $195.
NO. 537. WALBERT 26
Six tubes; five Kellogg a. c. tubes and one 71. Two
•xmtrols. Volume control: variable plate resistance,
isofarad circuit. Output device. Battery cable, Semi-
shielded. Antenna: 50 to 75 feet. Cabinet size: 10} x
29} x 16} inches. Prices: $215; with tubes, $2.50
NO. 484. BOSWORTH, B5
Five tubes; 2. t. r. f. (26), detector (99), 2 transformer
audio (special a. c. tubes). T. r. f. circuit. Two dials.
Volume control: potentiometer. Cabinet size: 23 x 7
x 8 inches. Output device included. Price $175.
NO. 406. CLEARTONE 110
Five tubes; 2. t. r. f., detector, 2 transformer audio.
All tubes a. c. heater type. One or two dials. Volume
control: resistance in r. f. plate. Watts consumed: 40.
Cabinet size varies. The plate supply is built in the
receiver and requires one rectifier tube. Filament sup-
ply through step down transformers. Prices range from
$175 to $375 which includes 5 a. c. tubes and one recti-
fier tube.
NO. 407. COLONIAL 25
Six tubes; 2. t. r. f. (01-A), detector (99), 2 resistance
audio (99). 1 transformer audio (10). Balanced t. r. f.
circuit. One or three dials. Volume control: Antenna
switch and potentiometer on 1st audio. Watts con-
sumed: 100. Console size: 34 x 38 x 18 inches. Output
device. All tube filaments are operated on a. c. except
the detector which is supplied with rectified a. c. from
the plate supply. The rectifier employs two 16-b tubes.
Price $250 including built-in plate and filament supply.
NO. 507. CROSLEY 602 BANDBOX
Six tubes; 3. t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Neutrodyne circuit. One dial, Cabinet
size: 17} x 5} x 7f inches. The heaters for the a. c. tubes
and the 71 filament are supplied by windings in B unit
transformers available to operate either on 25 or 60
cycles. The plate current is supplied by means of
rectifier tube. Price $65 for set alone, power unit $60.
NO. 408. DAY-FAN "DE LUXE"
Six tubes; 3 t. r. f., detector, 2 transformer audio. All
01-A tubes. One dial. Volume control: potentiometer
across r. f. tubes. Watts consumed: 300. Console size:
30 x 40 x 20 inches. The filaments are connected in
series and supplied with d. c. from a motor-generator
set which also supplies B and C current. Output de-
vice. Price $350 including power unit.
NO. 409. DAYCRAFT 5
Five tubes; 2 t. r. f., detector, 2 transformer audio.
All a. c. heater tubes. Refiexed t. r. f. One dial. Volume
control: potentiometers in r. f. plate and 1st audio.
Watts consumed: 135. Console size: 34 x 36 x 14 inches.
Output device. The heaters are supplied by means of
a small transformer. A built-in rectifier supplies B
and C voltages. Price $170, less tubes. The following
have one more r. f. stage and are not reflexed; Day-
craft 6, $195; Dayrole, 6, $235; Dayfan 6, $110. All
prices less tubes.
NO. 469. FREED-EISEMANN NRII
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Volume control: potentiometer. Watts consumed: 150.
Cabinet size: 19} x 10 x 10 J inches. Shielded. Output
device. A special power unit is included employing a
rectifier tube. Price $225 including NR-411 power unit.
NO. 487. FRESHMAN 7F-AC
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Equaphase circuit. One dial. Volume
control: potentiometer across 1st audio. Console size:
24} x 41 }x 15 inches. Output device. The filaments and
heaters and B supply are all supplied by one power unit.
The plate supply requires one 80 rectifier tube. Price
$175 to $350, complete.
NO. 421. SOVEREIGN 238
Seven tubes of the a. c. heater type. Balanced t. r. f
Two dials. Volume control: resistance across 2nd audio
Watts consumed: 45. Console size: 37 x 52 x 15 inches
The heaters are supplied by a small a. c. transformer
while the plate is supplied by means of rectified a. c,
using a gaseous type rectifier. Price $325, including
power unit and tubes.
NO. 517. KELLOGG 510, 511, AND 512
Seven tubes; 4 t. r. f., detector, 2 transformer audio.
All Kellogg a. c. tubes. One control and special zone
switch. Balanced. Volume control: special. Output de-
vice. Shielded. Cable connection between power supply
unit and receiver. Antenna: 25 to 100 feet. Panel 7\%
x 27} inches. Prices: Model 510 and 512, consoles, $495
complete. Model 511, consolette, $365 without loud
NO. 496. SLEEPER ELECTRIC
Five tubes; four 99 tubes and one 71. Two controls.
Volume control: rheostat on r. f. Neutralized. Cable.
Output device. Power supply uses two 16-B tubes.
Antenna: 100 feet. Prices: Type 64, table, $160; Type
65, table, with built-in loud speaker, $175; Type 66,
table, $175; Type 67, console, $235; Type 78, console,
$265.
NO. 538. NEUTROWOUND,MASTER ALLECTRIC
Six tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and two 71 in push-pull amplifier). The 01-A
tubes are in series, and are supplied from a 400-mA.
rectifier. Two drum controls. Volume control: variable
plate resistance. Output device. Shielded. Antenna:
50 to 100 feet. Price: $360.
NO. 413. MARTI
Six tubes: 2 t. r. f., detector, 3 resistance audio. All
tubes a. c. heater type. Two dials. Volume control-
resistance in r. f. plate. Watts consumed: 38. Panel size
7 x 21 inches. The built-in plate supply employs one
16-B rectifier. The filaments are supplied by a small
transformer. Prices: table, $235 including tubes and
rectifier; console, $275 including tubes and rectifier;
console, $325 including tubes, rectifier, and loud
speaker.
NO. 417 RADIOLA 28
Eight tubes; five type 99 and one type 20. Drum
control. Super-heterodyne circuit. C-battery connec-
tions. Battery cable. Headphone connection. Antenna:
loop. Set may be operated from batteries or from the
power mains when used in conjunction with the model
104 loud speaker. Prices: $260 with tubes, battery
operation; $570 with model 104 loud speaker, a. c.
operation.
NO. 540 RADIOLA 30-A
Receiver characteristics same as No. 417 except that
type 71 power tube is used. This model is designed to
operate on either a. c. or d. c. from the power mains.
The combination rectifier — power — amplifier unit uses
two type 81 tubes. Model 100-A loud speaker is con-
tained in lower part of cabinet. Either a short indoor
or long outside antenna may be used. Cabinet size:
42} x 29 x 17J inches. Price: $495.
NO. 541. RADIOLA 32
This model combines receiver No. 417 with the model
104 loud speaker. The power unit uses two type 81
tubes and a type 10 power amplifier. Loop is completely
enclosed and is revolved by means of a dial on the panel.
Models for operation from a. c. or d. c. power mains.
Cabinet size: 52 x 72 x 17J inches. Price: $895.
NO. 539 RADIOLA 17
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 27). One control. Illuminated dial.
Built-in power supply using type 80 rectifier. Antenna'
100 feet. Cabinet size: 25f, x 7J x 8}. Price: $130
without accessories.
NO. 545. NEUTROWOUND, SUPER ALLECTRIC
Five tubes; 2 t. r. f. (99), detector (99), 2 audio (99
and 71). The 99 tubes are in series and are supplied from
an 85-mA. rectifier. Two drum controls. Volume con-
trol: variable plate resistance. Output device. Antenna:
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:
$150.
NO. 490. MOHAWK
Six tubes; 2 t. r. f., detector, 2 transformer audio. All
tubes a. c. heater type except 71 in last stage. One dial.
Volume control: rheostat on r. f. Watts consumed: 40.
Panel size: 12J x 8| inches. Output device. The heaters
for the a. c. tubes and the 71 filament are supplied by
small transformers. The plate supply is of the built-in
type using a rectifier tube. Prices range from $65 to
$245.
NO. 522. CASE, 62B AND 62C
McCullough a. c. tubes. Drum control. Volume con-
trol; variable high resistance in audio system. C-battery
connections. Semi-shielded. Cable. Antenna: 100 feet.
Panel size: 7 x 21 inches. Prices: Model 62B, complete
with a. c. equipment, $185; Model 62 C, complete with
a. c. equipment, $235.
NO. 523. CASE, 92 A AND 92 C
McCullough a. c. tubes. Drum control. Inductive
volume control. Technidyne circuit. Shielded. Cable.
C-battery connections. Model 92 C contains output
device. Loop operated. Prices: Model 92 A, table, $350;
Model 92 C, console, $475.
BATTERY OPERATED RECEIVERS
NO. 542. PFANSTIEHL JUNIOR SIX
Six tubes: 3 t. r. f. (01-A), detector (01-A), 2 audio.
Pfanstiehl circuit. Volume control : variable resistance in
r. f. plate circuit. One dial. Shielded. Battery cable. C-
battery connections. Etched bronze panel. Antenna:
outdoor. Cabinet size: 9 x 20 x 8 inches. Price: $80, with-
out accessories.
NO. 512. ALL-AMERICAN 44, 45, AND 66
Six tubes; 3 t. r. f. (01-A, detector) 01-A, 2 trans-
former audio (01-A and 71). Rice neutralized t. r. f.
Drum control. Volume control: rheostat in r. f. Cabinet
sizes: No. 44, 21 x 10 x 8 inches; No. 55, 25 x 38 x 18
inches; No. 66, 27} x 43 x 20 inches. C-battery connec-
tions. Battery cable. Antenna: 75 to 125 feet. Prices:
No. 44, $70; No. 55, $125 including loud speaker; No.
66, $200 including loud speaker.
NO. 428. AMERICAN C6
Five tubes; 2 t. r. f. detector, 2 transformer audio.
All 01-A tubes. Semi balanced t. r. f. Three dials. Platr
current 15mA. Volume control: potentiometer. Cabinet
sizes: table, 20 x 8J x 10 inches; console, 36 x 40 x 17
inches. Partially shielded. Battery cable. C-batterjr
connections. Antenna: 125 feet. Prices: table, $30
console, $65 including loud speaker.
T T r» •
[ HowtoBijiild an A- Power Unit
T ''
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335
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For Further Information Address
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Mail Coupon for Two Valuable
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If you will fill out and mail coupon below we will send
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improved
musical performance
210 Power Amplifier
and Plate Supply
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up to these present standards of reception by building this
Thordarson 210 Power Amplifier and B Supply.
Easy to build. Every effort has been made to make assembly
as simple as possible. The metal baseboard is equipped with
all sockets and binding posts mounted. All necessary screws,
nuts and hook-up wire are furnished complete; simple pictorial
diagrams are supplied. You can assemble this unit in an hour.
Simple to install. No changes in receiver wiring are necessary.
This amplifier can be attached to set in a moment.
Economical to operate. Highly efficient and cool in operation.
Consumes less current than a common 50 watt lamp.
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RADIO BROADCAST
MARCH, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory Contributing Editor
Vol. XII, No. 5
Cover Design ..... From a Design by Harvey Hopkins Dunn
Frontispiece A Short' Wave Transmitter for Imperial Broadcasting 338
University Offerings in Radio Education * <• - Carl Dreher 339
An A.C. Browning'Drake Receiver - - Glenn H. Browning 343
The March of Radio
What Is the True Broadcasting Situation?
Does Monopoly Rule the Commission?
The Growing Political Pressure on the Com'
mission
Limitations to the Use of High'Frequency
Channels
An Editorial Interpretation 346
The First Rayfoto Transmission
Two Stations Cannot Occupy the Same Ether
Space
Will the Radio Industry Do It Again?
The Month in Radio
I AMONG OTHER THINGS. . .
THE many radio experimenters who are looking forward
to a college course to lead them farther in their chosen field
will find this month's leading article, by Carl Dreher, of con-
siderable value. Mr. Dreher's story on radio instruction in
colleges and universities is not exhaustive and there are many
other colleges which have courses of value to the student who
plans eventually to go into radio work. The article does, how-
ever, answer many of the general questions most frequently
asked us in correspondence.
A New A Power Unit - - - - Ralph Barclay 350
"Strays" from the Laboratory 351
Poorly-Designed Amplifiers Into What Impedance Should the Tube Work?
Quartz Transmitting Tubes Audio Transformer Measurements
Quiet A.C. Sets
An Interview with J. V. L. Hogan - - - - Edgar H. Felix 353
A Four'Tube Screened'Grid Receiver - - - - McMurdo Silver 355
Some New Loud Speakers and Sets - - - 358
The Armchair Engineer - - - - - - - Keith Henney 360
CJRM, Pioneer Picture Broadcasting Station - Edgar H. Felix 362
"Our Readers Suggest— - - - 363
A Distortion Indicator A.C. Tube Operation Without Rewiring
"Motor-boating"
The Listeners' Point of View - John Wallace 365
If You Like Good Music, Listen This Way For Program Directors Only
As the Broadcaster Sees It ' - Carl Dreher 367
How a Famous Artist Broadcasts Speech Constants
Note for Lexicographers Catalogs and Commercial Publications
The A. C. "Bandbox" - John F. Rider 369
Loud Speakers and Power Equipment - - 373
Designing an R.F. Amplifier ----- - Sylvan Harris 376
Suppressing Radio Interference - A. T. Lawton 379
"Radio Broadcast's" Laboratory Information Sheets 384
No. 169 Data on the ux-an (CX-JM) No. 173 The Regulator Tube
No. 170 Selectivity and Sensitivity No. 174 Grid Bias
No. 171 The cj-jia (ui-na) and cx-j7i No. 175 Filter Choke Coils
(ux-i7i) No. 176 How the Plate Circuit Affects the
No. 171 A Simple Wavemeter Grid Circuit
"Radio Broadcast's" Directory of Manufactured Receivers - - - 388
Manufacturer's Booklets Available - - - 392
What Kit Shall I Buy 393 ' j
Book Review: - - - - Carl Dreher 394
Principles of Radio Communication: J. H. Morecroft
The contents of this magazine is indexed in The Readers' Guide
to Periodical Literature, which is on file at all public libraries.
THIS issue contains a great deal of interesting material for
the experimenter and home constructor as well as some
pages of especial importance to the many who are connected
with the business of selling radio apparatus. The description of
the Crosley "Bandbox" receiver is one example; Sylvan Harris'
article describing the Stewart Warner receiver is another. The
interesting illustrations in the full pages of radio set and ac-
cessory pictures form a useful guide to interesting new prod-
ucts. The description of the a.c. Browning-Drake set shows this
popular tuning unit combined with an excellent amplifier unit
working on the push-pull principle. Thus far, we have described
the Samson push-pull amplifier and B-supply, the Thordarson
push-pull amplifier and B-supply, and in this issue reference is
made to the AmerTran push-pull amplifier. Each of these devices
will give the user excellent audio quality when combined with a
good loud speaker. The Knapp A-Power unit, described
on page 550, should appeal to many home-constructors be-
cause of its performance and price. And on page 355 and
following, a remarkably, inexpensive screened-grid receiver is
discussed.
"pOR those who like to discuss the design and performance
•L of amplifiers, the leading article in our technical editorial
section, "Strays from the Laboratory," will provide plenty of
material for discussion. Keith Henney, who writes this depart-
ment, will be pleased to hear from those of our readers who have
ideas on the matter. On page 352, the average characteristics of
the 126 and 127 type tubes are presented.
READERS who are interested in receiving additional in-
formation from the makers of the Cooley Rayfoto appa-
ratus may send their names to the undersigned who will forward
them. The April RADIO BROADCAST will contain a long-awaited
article on the RADIO BROADCAST "Lab" circuit, a description
of an interesting short-wave phone and code transmitter, and a
wealth of other interesting constructional material.
THE Laboratory Data Sheets, which have been one of the
most popular features of RADIO BROADCAST since they
first appeared in our June, 1926, issue, are the work of Howard
E. Rhodes of the technical staff of RADIO BROADCAST Labora-
tory. Of necessity they cannot be signed, but so many have
written us in complimentary terms of them that we feel that
' the many readers who have expressed interest in this regular
feature should know to whom they are due. The first eighty
eight Data Sheets, by the way, are available in bound form
from the Circulation Department of Doubleday, Doran and
Company, Inc., and sell for one dollar.
—WILLIS KINGSLEY WING.
Doubleday, Doran Or Company,
MAGAZINES
COUNTRY LIFE
WORLD'S WORK
GARDEN & HOME BUILDER
RADIO BROADCAST
SHORT STORIES
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OFFICERS
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S. A. EVERITT, Wee-President
RUSSELL DOUBLEDAY, Secretary
JOHN J. HESSIAN, Treasurer
LILLIAN A COMSTOCK, Asst. Secretary
L. J. McNAUGHTON, Asst. Treasurer
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Copyright, 1928, in the United State*, Newfoundland, Great Britain, Canada, and other countries by Doubleday, Doran
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RADIO BROADCAST ADVERTISER
337
VITROHM RESISTORS IN EVERY INDUSTRY IN EVERY LAND
u
5000 ohm, tapped center, Vitrohm
grid leak for transmitting circuits
of 1000 watts or less. This resistor
is used frequently in airplane
transmitters. It is priced at $2.80.
— switch on, sir —
Wr
Vitrohm Resistors
^ for radio
t Vitrohm Resistors are
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tecting both the wire and
terminal contacts with
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This process has been used
by Ward Leonard Electric
Co. for more than 36 years.
IT Circular 507 , describing
Vitrohm Radio Resistors,
and "Vitrohm News" will
be sent you without charge
upon request.
ITH the drop of his arm, the pilot signifies that
he is ready to take his ship of the air to her own element.
A few years ago, that roar of motor and short dash across
the field meant the loss of all contact with the ground,
until the flight was ended.
Tod'ay, radio maintains constant communication between
airplane and ground. The pilot, or navigator, receives
and gives instructions; learns of changing conditions, and
is able to protect better airplane and cargo.
It is interesting to know that Vitrohm Resistors are
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In the air, on and under the sea, at the poles, in every
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WARD LEONARD ELECTRIC CO.
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38-32-33-1
A Short-Wave Transmitter for Imperial Broadcasting
ANIMATED by the success of other European countries in this field, the
•*»- British Broadcasting Corporation finally permitted itself to fall victim to
short-wave broadcasting. The purpose of 5 SW is to unite the radio audiences of
the far-flung corners of the British Empire, and reports so far received would
indicate that quite a large degree of success is being met with in this effort.
The wavelength of 5 SW is 24 meters (12,500 kc.) and it may be heard well in
this country. With the exception of Saturdays and Sundays (when the schedule
is irregular), 5 SW broadcast* daily from 7:30 to 8:30 A. M. E. S. T., and from
2:00 t« 7:00 p. M. E. S. T. The power is 20 kw. The transmitter is at present
erected in the experimental laboratories of the Marconi Company at Chelms-
ford, some thirty miles from London. The apparatus consists of two panels of a
Marconi short-wave beam transmitter (shown in the foreground) with the
addition of three modulating panels, which may be discerned faintly in the
background
338
WHERE ELECTRIC COMMUNICATION ENGINEERING MAY BE STUDIED
Students at work in the Cruft Memorial Laboratory, Harvard University.
Professor G. W. Pierce is Rumford professor of physics there. In the ar-
ticle below he tells what courses are available at Harvard for the radio man
N'
fOT infrequently readers address this mag-
azine with questions regarding univer-
sity training in radio. They are inter-
ested in such matters as entrance requirements
at various institutions, courses offered, pre-
requisites, and the practical value of the train-
ing available. As a rule the questions come, not
from the usual group from which college stu-
dents are drawn, but from young men who feel
the need for adding to their knowledge but lack
formal preparation. Secondary school graduates,
and those who have been fortunate in securing
college preparatory education at the usual age,
generally are familiar with the educational
system beyond this point, but many others have
only the vaguest ideas about the procedure of
technical study in institutions. They imagine,
in some cases, that all universities admit stu-
dents to certain courses of interest to them,
regardless of aptitude or previous training on the
part of the student. Actually there is a wide
range of flexibility among technical colleges,
some offering a wealth of extension courses, with
little scrutiny of the applicant's credentials,
while others have rigid entrance qualifications,
no extension courses, and, in a number of in-
stances, no electives and no variations in the
curriculum. The relation of radio engineering to
the more fundamental divisions of technology
is also frequently misapprehended, the impor-
tance of radio being naturally exaggerated in
the minds of some of its devotees. All this has
made it appear worth while to conduct an in-
quiry into the subject of university training in
radio communication, with a view to supplying
information regarding conditions in representa-
tive institutions, and also to make clear the rela-
tion of university training in radio to other forms
of study of the subject.
Letters were written to the professors of Elec-
trical Engineering at ten institutions, with re-
quests for answers to the following questions:
By Carl Dreher
(i.)What communication and radio engineer-
ing courses are given as required or elective
studies in the electrical engineering division?
(2.) Does your institution offer any extension
courses in communication or radio engineering,
and, if so, what are the entrance requirements
for such specialized work?
Nine out of the ten institutions addressed
replied, giving the information sought. Of course
a choice of ten universities and technical schools,
among several hundred, is not sufficient for com-
© Bachrach
J. H. MORECROFT
Professor of Electrical Engineering, Columbia
University, New York City: "1 do not recom-
mend that a man specialize too much while he
is at college"
339
prehensive conclusions, but it does serve to show
the general trend of higher education in radio.
Colleges known to be interested in the radio
field were rather favored, although not exclu-
sively, and there was some attempt at territorial
distribution.
The answer of Prof. J. H. Morecroft at Co-
lumbia University is well worth quoting, inas-
much as it represents one reasoned policy in
higher technical education:
" Both Professor Slichter and I have always
felt that it is extremely foolish for a young man
to specialize on a specific branch of engineering
work before he is well aware of his aptitude and
of the opportunities awaiting him in any special
field, and naturally the courses at Columbia are
laid out in accordance with this idea.
"The very large companies which are always
ready to take any men whom we regard as well
fitted for research work have this same idea with
regard to specialization. Our largest communi-
cation company, for example, does not desire to
have men trained in specialized communication
theory and practice. Their representatives have
always expressed to me their desire for men who
are trained rather in the general fields of science
and engineering than those who have attempted
to specialize in some certain phase of the work.
"Whereas the fundamental principles of com-
munication, including radio, are given to all of
our electrical engineering students, there is no
special arrangement of courses for those who
might desire to specialize in radio. In the senior
year the electrical engineering students at
Columbia are allowed to take more than half
of their work from a list of elective subjects and
at this time of course a man desiring to do so
can pick out most of his work in the communica-
tion field.
" I myself do not recognize radio engineering
as being apart from telephone engineering or
other similar types and do not recommend that
340
RADIO "BROADCAST
MARCH, 1928
a man specialize too much while he is at college.
When he starts to work he will have to specialize
to earn his living and will get but little oppor-
tunity to carry on studies outside of those re-
quired by his daily tasks, so that it seems foolish
for him to give up the opportunity for broad
training while at college."
Tfiese views of Professor Morecroft's are an
authoritative statement of what might be called
the broad-training policy in engineering educa-
tion, which in my own opinion, is the best thing
for those who fortunately have the time and
money to take advantage of it. Columbia does,
however, offer an extension course, "Electrical
Engineering eg-io- Radio Communication, "which
"is not intended for those who are already fa-
miliar with radio theory and practice but rather
for those who have had no training in this par-
ticular field, and is so designed that anyone who
has had the equivalent of an ordinary high
school course will be able to do the work satis-
factorily." The class meets twice a week for an
aggregate of three hours. The admission require-
ments for Columbia University Extension stu-
dents are very elastic. For "mature students
whose chief interest lies outside the Univer-
sity and who have leisure to pursue only a few
courses in the late afternoon or at night . . . the
sole condition is that they show their ability to
pursue the work with profit." In practice this
amounts to satisfying the instructor or a super-
vising professor that one has some background
in the subject and an earnest desire to learn more
of it. In past years Columbia has given some ex-
cellent advanced extension courses in vacuum-
tube theory and other branches.
Professor Morecroft is one of the most promi-
nent of American radio engineers, and a past
president of the Institute of Radio Engineers.
Dr. G. W. Pierce likewise ranks among the high-
est radio technicians, and is similarly a past
president of the Institute. Nevertheless Harvard
University, where Professor Pierce is Rumford
Professor of Physics and Director of the Cruft
Memorial Laboratory, pursues a policy differing
from that of Columbia, in that Harvard offers a
" Programme of Study in Electric Communica-
tion Engineering," and confers the degree of
" Bachelor of Science in Communication Engi-
AT HARVARD UNIVERSITY
The Cruft Memorial Laboratory
neering" upon candidates who complete the
four-year course satisfactorily. The course is
substantially one in electrical engineering, with
specialization beginning in the third year. Of
the eight courses listed in that year four are
radio, or, broadly, communication subjects
(" Electric Oscillations and Their Application
to Radiotelegraphy and Radiotelephony; Elec-
tric Oscillations, Electric Waves, and Radio-
Frequency Measurements; Electron Tubes —
Amplifiers, Detectors, and Oscillators; Electron
A WELL-EQUIPPED LABORATORY
A view of the electrical-engineering laboratory of the Rennsselaer Polytechnic Institute, Troy,
New York. R. P. I. offers special and graduate work in communfcation to qualified students
Tubes, Advanced Course"). The other courses
in the third year are in electrical engineering and
mathematics. In the fourth year there are five
communication subjects and four courses in
electrical engineering.
Harvard University also offers work in com-
munication engineering to graduate students
and on occasion confers the degrees of "Master
of Science" and " Doctor of Science in Com-
munication Engineering." The admission re-
quirements in all cases are high. In the case of
the four-year course leading to the bachelor's
degree the entrance requirements are the same
as for admittance to the Freshman Class of Har-
vard College, the academic elements being sub-
stantially those provided by a first-class high
school or preparatory training.
The Massachusetts Institute of Technology
answered the questionnaire through Prof. Ed-
ward L. Bowles. In the regula'r electrical engineer-
ing course intended for students who seek train-
ing in electrical power engineering, two optional
one-term courses, "Principles of Radio Com-
munication" and "Principles of Wire Commu-
nication," are available. Students who desire to
specialize in electrical communication, after
taking the regular E. E. course for two years,
may register for the " Electrical Communica-
tion Option" at the beginning of the junior year.
This option "embraces work covering wire
telephony, carrier telephony and radio tele-
phony, also wire telegraphy, carrier telegraphy,
and radio telegraphy. The properties and en-
gineering applications of electron tubes are also
included." During the third year only one spe-
cific communication course, "Electrical Com-
munications, Principles," appears, but there are
other modifications in the work, such as the addi-
tion of a course in vector analysis, the omission
of a course in heat engineering which appears
in the regular E. E. outline, etc. In the fourth
year there is marked specialization In commu-
nication and electro-magnetic theory. Inciden-
tally, a one-term Senior course in "Sound, Speech,
and Audition" is included. The degree is that
of "Bachelor of Science." M. I. T. also offers a
number of limited-attendance five-year "co-
operative courses in electrical engineering"
which, for the first two years, are the same as
the regular E. E. course, while for the last three
years, the student's time is equally divided be-
tween instruction at the Institute and work
in industrial plants. "Option 3," in Communica-
tions, is arranged in co-operation with the Bell
Telephone Laboratories in New York City.
These co-operative courses lead to the degree
of " Bachelor of Science" after four years, and
"Master of Science" after five years. Admission
to the Institute is by examination. There are no
extension courses.
At Stevens Institute, Hoboken, N. J., where
the Department of Electrical Engineering is
headed by Prof. Frank C. Stockwell, succeeding
no less a radio man than L. A. Hazeltine, no
special attention is paid to communication train-
ing. Stevens offers only a single course, leading
to the degree of " Mechanical Engineer," and has
no electives in any engineering subject. Exten-
sion courses are unknown, nor does Stevens ac-
commodate special students. However, as part
of the regular work in electrical engineering, a
certain amount of radio engineering is pre-
scribed for all students, including laboratory
exercises and class room practice.
Undergraduate students at Rensselaer Poly-
technic Institute, working for their E. E. de-
grees, after the usual grounding in mathematics
and physics, followed by general electrical en-
gineering courses, receive a communication en-
gineering course in the last seven weeks of the
senior year. The following subjects are presented
MARCH, i9a8
UNIVERSITY OFFERINGS IN RADIO EDUCATION
341
in the order named: "Telephone transmitters;
telephone receivers; transformation of medium-
frequency alternating currents and electromotive
forces; resistance, inductance, and capacitance
in medium-frequency alternating-current cir-
cuits; distribution of current and electromotive
force over telephone lines; electrical filters, trans-
mission line impedance, and equivalent net-
works; fundamental telephone and telegraph
circuits; telephone transmission and its measure-
ment; telephone and telegraph systems and
telephone service; vacuum tubes and their ap-
plication; telephone repeaters and public ad-
dress systems; multiplex or carrier current tele-
phony; radio telephony and telegraphy; inter-
ference and cross-talk."
Rensselaer men seeking the B. S. in Physics
are required to take a general course in electrical
engineering covering the production, transmis-
sion, and utilization of electrical energy for
light, power, and communication purposes. In
the junior year these students have a seven-
week course in radio communication. The topics
are as follows: "Underlying electrical theory;
properties of oscillatory circuits; antenna sys-
tems and radiation; damped and undamped wave
radio telegraphy; general properties of the three-
electrode vacuum tube; the three-electrode vac-
uum tube as detector, amplifier, oscillator, and
modulator; radio telephony."
R. P. I. offers special and graduate work in
communication engineering to qualified students.
Applicants who have acquired the physics and
mathematics covered in the first and second
years at Rensselaer, or in equivalent courses else-
where, may be admitted to a special course in
radio communication whereby practically the
entire third year is devoted to laboratory and
theoretical study of radio. "We do not advise
students to take this special course unless they
know positively that .they are going to enter
some branch of the radio industry at the com-
pletion of their course," writes Prof. W. J.
Williams, who supplied all the information re-
garding communication training at R. P. I.
It would appear that this special course is in the
line of definitely vocational training in radio
engineering for men who have the requisite
grounding in the general engineering field, in-
cluding, necessarily, considerable mathematics
and physics. Two one-year graduate commu-
nication courses are also given in alternate years.
One covers wire communication and general
electric circuit theory. The other is in radio com-
munication and advanced electromagnetic the-
ory. About twelve hours of work a week are
required. The content of these courses is vari-
able, the effort being to keep the subject matter
up to date. This work is necessarily limited to
students who have the E. E. or B. S. in Physics
from Rensselaer, or equivalent degrees from
some other institution.
At the Polytechnic Institute of Brooklyn, on
the basis of Prof. Erich Hausmann's reply, four
subjects are given as required studies in the
curriculum leading to the degree of Electrical
Engineer. These are "Telegraphy" (two hours
per week of class work in the second semester
of the Junior year); "Telephony" (two hours
per week of class work in the first semester of the
Senior year); "Radio Communication" (two
hours per week of class work in the second semes-
ter of the Senior year); "Communication Lab-
oratory" (three hours per week of laboratory
work in the second semester of the Senior year).
The course in radio communication is described
as "A practical and theoretical course on the
generation of radio oscillations of the sustained
and decadent types, damping of wave trains,
resonance of single and coupled circuits, plotting
of reactance diagrams and resonance curves
reception of electric waves, the use of vacuum
tubes as amplifiers, detectors and oscillators,
the forms of antennas, and the design of com-
mercial forms of radio telegraphic and tel-
ephonic apparatus. Prerequisite, Alternating
Current Circuits. "The "Communications Labor-
atory" work covers operation of telephone, tele-
graph, and fire alarm installations, tests of char-
acteristics of spark, arc, and tube oscillation
generators, measurements of such quantities
as coupling coefficient and decrement, etc.
The four courses outlined above are also given
in the Evening Session of the Polytechnic, the
first three during one year and the fourth during
the following year, alternating. The prerequisites
are "Electricity and Magnetism," "Direct-
Current Machines," and "Calculus," For "Tele-
phony," "Alternating Current Circuits" is an
additional prerequisite, and the three class
room courses must precede the "Communica-
tion Laboratory" course. "A few years ago,"
writes Professor Hausmann, "an elementary
evening course in radio was given which did
not require a knowledge of calculus: while this
course has not been offered for several years,
there is no reason why it should not be given
ate students who have completed the fourth
year electrical courses, as well as to other
students with similar qualifications.
(3.) A combination lecture and laboratory
course on . the theory of transmission circuits,
intended to occupy about one third of the
student's working time for ten weeks. The
subject matter includes the theory of long-
distance power and telephone circuits, waves
on transmission lines, theory and design of
simple and composite wave filters. Probably
half of this course applies directly to tele-
phone communication problems. It is open to
electrical engineering graduate students in
full standing.
(4.) Another graduate course with the same
prerequisites is about fifty per cent, concerned
with communication problems, such as skin
effect, transient oscillations, theory of tele-
phone receivers and loud speakers, and har-
monics, the treatment being of an advanced
mathematical nature. There are two lectures
a week for ten weeks.
All these courses are given by Professor
Terman, who is in charge of communication
and analytical work at Stanford University.
The University of Wisconsin, with its College
of Electrical Engineering located at Madison,
ELECTRICAL ENGINEERING BUILDING, UNIVERSITY OF MINNESOTA
The communication laboratories of this fine building occupy the third floor. The University
has an experimental radio station and, like R. P. I., operates a broadcasting station
again. What do you think of the demand for
such a brief course, say of 1 5 lectures?" The best
way to gauge the demand is to propound the ques-
tion and to invite any readers who are interested
to communicate with Professor Hausmann. The
writer believes that there is a sufficient demand
for such a course to warrant offering it again.
Stanford University in California, while offer-
ing no extension work of any kind, lists four
communication engineering courses described by
Prof. Frederick Emmons Terman as follows:
(i.) Lecture course in principles of radio
communication. Three lectures a week for ten
weeks, open to seniors who have taken the
regular electrical course, and to graduate
students.
(2.) Laboratory course in radio measure-
ments. Two lectures and one afternoon in
laboratory per week for ten weeks. Reports
are required. The experiments consist of
bridge measurement of vacuum-tube amplifi-
cation factors, dynamic plate resistance, etc.;
radio-frequency resistance; resonance curves;
detectors; audio-frequency transformer char-
acteristics; adjustment of vacuum-tube
oscillators, etc. This course is open to gradu-
cannot be said to neglect the field of communica-
tion engineering. Four resident elective courses
in "Radio Telegraphy"; "Electric Amplifiers
and Oscillators"; "Radio Circuit Analysis and
Design " ; and "Telephony and Telegraphy," are
provided. The first is substantially the "applica-
tion of alternating-current theory to radio-
problems and measurements," accompanied
by laboratory work. The second includes,
"analytical study of the properties of amplifier
and oscillator circuits and of the characteristics
of tri-electrode thermionic amplifiers," like-
wise with laboratory sessions. " Radio Circuit
Analysis and Design" is described as "a con-
tinuation of the above courses, treating such
topics as amplifiers and their design, operation of
oscillators in parallel, design of oscillators, modu-
lation and demodulation, and analysis and design
of radio transmitting and receiving sets." The
theory of instruments and lines is treated under
"Telephony and Telegraphy," laboratory work
being included. The above are all one-semester
courses. Other courses bearing on communication
problems are also available for graduate stu-
dents, such as "Advanced Theory of Electric
342
RADIO BROADCAST
MARCH, 1928
Circuits" and "Seminar in Electric
Circuit Theory." The content of
both of these courses is largely in
the field of transient and high-
frequency phenomena, behavior of
networks, etc.
A number of correspondence
courses in communication work are
included in the bulletin "Courses in
Electrical Engineering" issued by
the University Extension Division
of the University of Wisconsin.
Course 318, "Principles of the Tele-
phone" is given in three parts:
"Subscriber's Apparatus," "Cen-
tral Office Equipment," "Aerial
and Underground Construction."
The instruction fee for the first part
is $6, with ten assignments in this
portion. "This course," according
to the catalogue, "includes study
of the laws underlying speech, trans-
mission, of the instruments, switch-
boards, and other apparatus in an
exchange, and of the laying, testing,
and maintaining in good condition of
the circuits outside the exchange."
Course 329, "Principles of Radiotelegraphy "
treats the standard topics in twenty assign-
ments, for an instruction fee of $12. An under-
standing of trigonometry is stated to be essen-
tial. An evening course on "Theory of Radio
Circuits" is also being given in Milwaukee
under the auspices of the Extension Division.
This is an engineering course, open to "graduates
of scientific courses of college grade or men of
equivalent training," and may carry credit for
degrees. It provides "a quantitative treatment
of radio circuit theory" and aims to demonstrate
"the dependence of radio circuit theory upon
fundamental electric theory." The fee is §10
for the course of eighteen sittings. Four other
radio courses are given by the Extension Divi-
sion in Milwaukee, these being designed for
amateurs, so that the treatment is more popular
and elementary.
The Professor of Electrical Engineering at
the University of Wisconsin, Edward Bennett,
is a well-known radio engineer and has con-
© Harvard Crimson
IN THE CRUFT MEMORIAL LABORATORY, HARVARD UNIVERSITY
The picture shows a group of students making
measurements during one of the courses
tributed extensively to the literature of the
subject.
For the University of Minnesota, C. M.
Jansky, Jr., Associate Professor, Radio Engi-
neering, writes as follows, after referring to his
paper, "Collegiate Training for the Radio
Engineering Field" in The Proceedings of the
Institute of Radio Engineers for August, 1926:
"Collegiate work in the field of radio engi-
neering is given in the Department of Electrical
Engineering of the University of Minnesota.
Students desiring to specialize in communication
engineering in general, or radio engineering in
particular, take their work in this department.
Upon completing the four years' work they
receive the degree of ' Bachelor of Science in
Electrical Engineering,' and upon completing
an additional year of graduate work they receive
the degree of ' Master of Science in Electrical
Engineering.' The student gets his first course
in the communication field in his junior year.
He gets a year's course in radio engineering
devoted
research
A CORNER OF ONE OF THE COLUMBIA UNIVERSITY LABORATORIES
Making measurements on a resistance-coupled audio amplifier in the Hartley Laboratory
in the senior year. Where men are
specializing in radio, 1 select such
elective courses as will be of particu-
lar value to them, such as 'Transient
Electrical Phenomena' and 'Differ-
ential Equations.'
"This year the Electrical De-
partment has approximately 80
senior students, about 40 of whom are
registered in radio engineering. Not
all of these 40 will, however, be-
come radio engineers, as many of
them will go into other fields of
electrical engineering.
"We are obtaining an increasing
number of post-graduate students
who are specializing in radio com-
munication. These students, in
addition to advanced courses in el-
ectrical engineering, take advanced
courses in physics and mathema-
tics. Where possible, 1 recommend
the fifth year.
" I believe our building and equip-
ment excel that of the majority of
institutions. We have approximately
7000 square feet of floor space
to communication laboratories and
rooms. In addition, we operate an
experimental radio station and a broadcasting
station."
The above summaries of communication engi-
neering training which is offered at nine centers
of higher learning afford a view of some of the
main trends in the field. At some institutions
there is little interest in communication engi-
neering except as a part of general electrical
engineering. The philosophy underlying this
attitude is that industry is so highly specialized
that it is hopeless to give a man more than the
broad fundamentals at school, and that if this is
accomplished, he will make his way after he gets
into business by the addition of his common
sense and the training provided by the job
itself. Some of the large communication concerns,
in fact, set up schools of their own for the
engineers on the staff, evidently with the
thought that the technological content of their
particular jobs cannot be secured in any outside
school. Many colleges, on the other hand, teach
the theory and some of the practice of telegraphy
and telephony, by wire and radio, to qualified
students of junior and senior grade. Still others
go further and, in addition to such studies,
offer popular extension courses, correspondence
study, and the like. If there is a demand for
vocational study, for example, in a neighbor-
hood, the local university is probably better
qualified to fill the need than some prima-
rily commercial institution. Study, even if it is
not of the most scholarly sort, is not apt to do
anyone harm, and it may do good, as long as it
is not allowed to interfere with the rigorous and
inexorably thorough training which makes a real
engineer. Again, it may be argued that commun-
ication engineering courses deal with funda-
mentals just as much as the older power
engineering subjects, that nowadays a vacuum
tube is as important a machine as a dynamo.
Different courses are for different people, we
may conclude. If a man has the intellectual
equipment, the money, and the time required for
a thorough study of the subject he intends to
make his lifework, by all means let him spend
four or six years preparing himself. Let him
specialize only after he has mastered the funda-
mentals. But if at some time a man wants to
learn something special in a superficial way, no
harm is done, provided he knows what he is
getting, and does not take it for more than what
it is.
HOW THE COMPLETED TWO-TUBE TUNER LOOKS
The five knobs, from left to right, are: "On-Off" switch, trimmer con-
denser (Cs), main tuning control, volume control, regeneration control
An A. C
t If 'HE Browning-Drake circuit has been
I popular for a number of years, due, prob-
•^ ably, to the fact that the set is very easy
to build and operate, sufficiently sensitive to re-
ceive most distant stations which are above the
noise level, and selective enough to cope with
present broadcasting conditions, except when
located in extremely congested regions. The sen-
sitivity of the set is primarily due to the tuned
r.f. transformer which Dr. Drake and the
writer developed a number of years ago at Cruft
Laboratory, Harvard University. Also, the
antenna tuning system, which is a conductively
coupled one, gives more signal strength than any
the writer has tested so far. This is especially
true when operating the set with a short an-
tenna.
The electrical engineering in the Browning-
Drake receiver has been changed very little
during the last three years, though minor im-
provements have been incorporated from time
to time. With the introduction of a.c. tubes and
the popularity of so-called single control re-
ceivers, however, it seems particularly advisable
at the present time to change the mechanical
layout of the receiver and add any refinements
in the electrical design which constant work on
the circuit have indicated as worthy of recom-
mendation.
As most radio constructors know, the Browning
Drake circuit consists of one stage of tuned r.f.
amplification with some type of neutralization,
coupled to a regenerative detector. Any form of
audio amplification may be used with this tuning
arrangement, but, of course, the audio amplifier
determines to a large extent the quality of the
received signals.
This article deals essentially with the new two-
tube receiver unit, employing a.c. tubes and
making use of single control, and we will not go
into detail about the audio channel. In passing,
it might, however, be mentioned that the
Browning-Drake Corporation supplies a foun-
dation kit for a five-tube receiver, which includes
the necessary sub-panel for the mounting of
whatever audio equipment is used, and a larger
By Glenn H. Browning
base panel than that used in the two-tube tuner
unit described here.
After experimenting for some time with a.c.
tubes two cx-327 (ux-227) tubes were chosen for
the tuner unit. With a tuner constructed according
to the instructions in this article, and used with
a three-stage amplifier also wired for a.c. tubes,
there is very little audible ob-cycle hum in the
loud speaker. Sometimes it is necessary to experi-
ment with the voltages used and also with the
tubes in order to get the best combination, other-
wise there may be some hum in the loud speaker,
and the quality would be impaired
The nucleus of the Browning-Drake set de-
scribed here is what might be called a single
drum control unit; it consists of a single illumi-
nated drum type dial driving two variable
condensers. The necessary coils for the two-tube
tuner are also an integral part of the drum
unit. As antennas differ a great deal, it is advis-
able to put a small condenser in parallel with the
first tuning condenser in such fashion that it
may be controlled from the front panel, and
variations in antenna length thus compensated.
In actual tuning, this condenser is used as a
minor control. In Fig. i, the diagram of the
complete tuner unit, this condenser is indicated
as C3.
As will be noted, a slightly different system of
neutralization than has heretofore been used is
employed; also parallel plate-voltage feed for
the r.f. tube is featured. The parallel feed, which
consists of an r.f. choke coil in series with the r.f.
B-battery lead, together with a o.j-mfd. con-
denser, keeps all r.f. current from entering the
B supply, and forces this current to go through
FIG. 1
This diagram gives the complete connections for the two-tube tuner unit. Manufacturers of a. c.
tubes of the heater type state that less hum will be evidenced if the heater is biased with respect to
the cathode. This bias may be plus or minus, depending upon which gives the better results
343
344
RADIO BROADCAST
MARCH, 1928
THE NUCLEUS OF THE BROWNING-DRAKE A. C. TUNER
It is known as the single drum control, and comprises (refer to fig. i, page
343) Ci, C2, Li, La, L , regeneration coil, and the receptacle for the pilot light
the 0.5 mfd. condenser and the primary of the
r.f. transformer. Neutralization is then accom-
plished by means of a few extra turns, L3, on the
r.f. transformer, the end of which is connected
through a neutralizing condenser, C4, to the grid
of the tube. In practice, it is necessary to have
the stator plates of the neutralizing condenser
connected to the grid of the first tube rather than
the rotor plates. It is found that a tube with a
much larger capacity between grid and plate can
be tolerated by the use of the above-mentioned
system of neutralization.
When the set builder is located in a very con-
gested region and there are a number of local
broadcasting stations within a radius of three or
four miles from the receiver, shielding is to be
recommended, and a complete shield for the
Browning-Drake receiver will probably be
commercially available soon. Such shielding
eliminates all pick-up by coils and the wiring of
the set, and adds materially to the selectivity of
the receiver when it is used under the above
conditions. Where the set builder is located in
the country or suburbs, shielding is unneces-
sary.
The parts necessary for the construction of
the single-control a.c. Browning-Drake tuner
unit are listed below:
LIST OF PARTS
Official Browning-Drake Single Drum
Control Kit comprising Ci, Ci, Li, Lz,
La, the regeneration coil and pilot light
socket $26.00
Official Browning-Drake Type T-2
Foundation Unit consisting of West-
inghouse Micarta drilled and en-
graved front panel, base panel com-
plete with mounting hardware. Also
miscellaneous machine screws, nuts,
and wire 13 . 50
LI Browning-Drake Radio-Frequency
Choke 2 . oo
d Browning-Drake 135-Mmfd. Trim-
mer Condenser 2.50
€4 Browning-Drake 3O-Mmfd. Neu-
tralizing Condenser 1.75
Yaxley Filament Switch No 10 B-D .60
Cs Tobe o.5-Mfd. Moulded Condenser .90
RI Tobe 8-Meg. Grid Leak ... .75
Ce, Cy "Tinytobe" Condensers (o.ooi
and 0.00007 Mfd.) .80
Cs Mica Fixed Condenser (o.oooiMfd.) .75
Five Eby Binding Posts (Ant., Gnd.,
B + Amp., B + Det., B— ) . . .75
One Set of Shields (Optional) . . . 8.00
R. Clarostat 2.25
Rs Browning-Drake Center-Tapped
Resistor .60
Two Benjamin Five Contact A-C
Sockets 2.40
One Flashlight Lamp (2.5 Volt) . . .10
TOTAL .
BROWNING-DRAKE
CORPORATION
A REAR VIEW OF THE COMPLETE TWO-TUBE UNIT FOR D. C. OPERATION
After the parts are mounted on the drilled and engraved panel it is a simple matter to complete the wiring. The use
of the single drum control unit greatly helps matters. This layout is similar to that employed in the a. c. model
MARCH, i9a8
AN A. C. BROWNING-DRAKE RECEIVER
CONSTRUCTION OF THE RECEIVER
THE receiver is very easy to build
and for most set builders detailed
constructional information is un-
necessary. The leads running to the
B supply and filament supply for the
a.c. tubes are placed underneath the
sub-panel, while the high-potential
leads, which carry r.f. current, are
placed above the sub-panel. These
high-potential leads comprise:
The connection from the stator
plate of the first tuning condenser
to the grid of the first tube; the
plate of the first tube through the
o.j-mfd. condenser, and from the
o.5-mfd. condenser to the primary of
the r.f. transformer; the neutralizing
lead, which comes from one end of
the secondary of the r.f. transformer
to the rotor plates of the neutralizing
condenser. Of course, the connec-
tions between the grid leak, grid con-
denser, and the grid itself, should be
as short as possible. These are the
most important connections in the set, and they
should be run as directly as possible and kept
away from other connections
In connecting the A supply of the tubes,
twisted pairs must be run from the power supply
to their filaments. This is extremely important
for if the wires are not carefully twisted to-
gether, a.c. hum may be noticeable. Also, the
power apparatus, which should consist of a good
B supply device and the necessary transformer
for lighting the filaments of the tubes (the latter
being either incorporated as a part of the B
supply or as a separate transformer), must be
kept several feet away from the receiver; other-
wise there might be some 6o-cycle voltage in-
duced in the audio circuit of the radio set.
As will be noted in Fig. I, a Clarostat inserted
in the B plus lead of the r.f. tube is used for
volume control. This the writer has found quite
satisfactory as long as the parallel feed shown
in the diagram is used. Some experimenting will
be necessary on the C battery bias for the r.f.
tube, as the voltage may vary between ij and
45, according to the individual characteristics of
the tube used.
BALANCING AND OPERATION OF THE RECEIVER
WHEN the set has been connected up ac-
cording to the instructions given, and
attached to the power supply (note: the filaments
of the 0-327 [uY-227] tubes take about 45 sec-
onds to a minute to heat up sufficiently for
satisfactory operation), it is ready to balance.
Turning the tickler coil in one direction or the
other should throw the second circuit into oscil-
lation. This condition may be determined by
placing the finger on the stator plates of the
second tuning condenser, whereupon a distinct
"click" or "plop" will be heard in the loud
speaker. Then turn back the ticker coil until
the circuit just goes out of oscillation. If the
set is improperly balanced, turning the trimmer
condenser slightly will throw the circuit into
oscillation again, which state can be determined
as before. The neutralizing condenser then can be
varied by means of a wooden or bakelite screw-
driver until turning the antenna trimmer has no
effect whatever on oscillations produced in the
second circuit.
There is another method which will give al-
most the exact point of neutralization. Tune-in a
local station, remove one of the leads going to
the C battery of the r.f. tube and, by careful re-
tuning, the local station can in all probabilities
be heard. Set the neutralizing condenser so that
a minimum amount of signal is heard. This point
AN AMERTRAN PUSH-PULL AMPLIFIER
As mentioned on this page, it is a two-stage push-pull affair, provision
being made for the use of either a 2OI-A type tube or an a. c. type tube
in the first audio stage
on the neutralizing condenser is almost the
correct one, and the test given above can then be
applied for the exact point. It will be found that
neutralization is quite critical. Of course, when
neutralizing, the Clarostat should be turned
up as far as it will easily go (in a clock-wise
direction.)
In operation, the a.c. Browning-Drake is
exactly like previous models. The tickler coil
may be turned up to a point where the set is
just oscillating and the dial rotated, whereupon
a station will be indicated by a whistle. Set the
dial where the whistle is lowest in pitch and turn
back the tickler coil and adjust the antenna
trimmer condenser until the signal is plainly
heard. Readjustments of the drum dial will then
probably be advantageous.
AUDIO-AMPLIFIER SUGGESTIONS
AS HAS already been mentioned, the choice
of an audio amplifier is left entirely to the
constructor. There are several amplifier units
and plate supply units now on the market which
have very good characteristics, and it is believed
that the combination of such apparatus with
the two-tube tuner unit described here will pro-
PUSH-PULL AMPLIFIER
Det. PI
345
vide the user with as simple and
as effective a receiver as he may
need.
As an example of the type of
audio-frequency amplifier and power
supply that can be constructed and
which will work very satisfactorily
with the two-tube tuner, there is
shown in Fig. 2 the circuit diagram
of a combined push-pull amplifier
and power unit which may be made
from Amertran parts.
The amplifier is a two-stage trans-
former-coupled affair, designed to
use in the first stage a 0-327 (uv-227)
type a.c. tube. The other two
sockets in the amplifier are for the
power tubes. Tubes of the cx-jyi
(ux-iyi) orcx-3io (ux-2io) may be
used in conjunction with either a type
271 (for 171 tubes) or a type 152
(for 210 tubes) Amertran push-pull
output transformer. With a push-pull
amplifier similar to that shown here,
the comparatively large amount of
undistorted power necessary for high-quality
reproduction, can be obtained.
Completely assembled power amplifiers and
A, B, C supply units can also be obtained from
the Amertran Company. The amplifiers, when
combined with the power units, result in a circuit
differing slightly from that given in Fig. 2, in
that they are designed to use either a CX-3O1-A
(ux-2oi-A) or a 0-327 (uv-227) type tube in the
first stage, and cx-37i (ux-i7i) or cx-3io (ux-
210) type tubes in the push-pull stage.
The type 2AP-1O amplifier is designed for cx-
310 (ux-2io) type output tubes while the type
2AP-7I is for cx-371 (ux-i7i) type tubes. Both
of these amplifiers are the same in external ap-
pearance. The necessary Amertran power unit
will furnish complete A, B, and C power to the
push-pull amplifier and to all the other a.c. tubes
used in the receiver proper.
The complete type 2AP amplifier (either type)
lists at $60, without tubes. A set of Amertran
push-pull transformers, which might be used in
the home-construction of a power amplifier, can
be purchased for $30. The Amertran power
supply (the A, B, C Hi-Power Box) lists at
$95.00.
POWER SUPPLY
FIG. 2
The circuit diagram of an amplifier which may be used with
the two-tube tuner unit. It is made with Amertran parts
THI- MARCH OK RADIO
NKW.S AND IN rKUPUKTATIQN OF CiiUUFNT UADIQ KVt-.N I \S
What Is the True Broadcasting Situation?
WHENEVER we see the name of
Senator Howell of Nebraska in
print, our eyes blaze, because we
consider him to be the man who, single
handed, did more to obstruct the proper
administration of radio during the last nine
months than any other Senator. During
the closing days of the last session of Con-
gress, his was the only dissenting vote
raised to a unanimous consent agreement
to vote an appropriation for the mainte-
nance of the Federal Radio Commission.
Thereby deprived of an appropriation,
the Federal Radio Commission has been
most seriously embarrassed in its labors.
Its effectiveness has been crippled because
a petulant Senator chose to throw a monkey
wrench at the radio listeners of America.
The Commission can issue orders to broad-
casting stations, but has no means what-
ever of finding out whether those orders
are complied with. When its members
travel, they advance the money out of their
own pockets.
1 nstead of a staff of expert observers with
high-grade measuring instruments, the
Commission has had nothing to guide it
but the reports of the public, the com-
plaints of station owners and the protests
of politicians, advancing the fatuous claims
of every broadcasting station represented
in their particular constituencies, regard-
less of the public interest. The Commission
has not been able to employ consulting
experts in order to evaluate the numerous
panaceas offered it in the direction of fre-
quency stabilization, synchronization of
stations, and to determine quantitatively
the exact minimum spacing which may pre-
vail among stations of various power com-
binations without heterodyning within
their service areas.
Consequently, when we saw Senator
Howell's name in a dispatch from Wash-
ington, we expected bad news for radio.
The Senator, we find, is now engaged in a
war with the ghost of monopoly, which he
finds skulking behind every microphone
radiating chain programs. He wants a
Congressional investigation, perhaps as a
vehicle of publicity, perhaps for some other
purpose. He may suspect that Mr. Ayles-
worth, president of the N. B. C, once
' bought a lunch for a Federal Radio Com-
missioner or that George McClelland, vice-
president of the same company, sent a bas-
ket of apples from his Queens fruit ranch
to Sam Pickard. Whatever he finds will
be sensational and well phrased for news-
paper publication. To save time, we offer
the proposed Committee's findings even
before the hearings are arranged:
Does Monopoly Rule the Commis-
sion?
THE Federal Radio Commission, at this
writing, has cleared twenty-five channels
and picked the best stations in the country
to utilize them. Naturally, these stations,
since they have been well selected, are the
ones which offer the greatest variety and
the best type of program. Such programs
are not available in every hamlet from
which a Congressman comes, but are cen-
tered at the musical and artistic centers of
the United States. From such centers, a
company, the odious and monopolistic
National Broadcasting Company, has of-
fered a wire service to which independently
owned broadcasting stations have sub-
scribed, making superior programs avail-
able to them. This service has been con-
ducted at a tremendous loss, met out of
the treasuries of receiving set and acces-
sory manufacturers so that their customers
would derive pleasing entertainment as a
result of their purchases and therefore con-
tinue to patronize them.
Utilizing the chain programs has made
the subscribing stations superior in pro-
gram value to those which must rely for
their programs on the Squeedunk church
choir and the piano-playing professor at
a roadside speakeasy. And so, by selecting
good stations for good channels, the Fed-
eral Radio Commission has become guilty
of inflicting the Red, Blue, and Columbia
chain programs upon practically all the
AT THE INSTITUTE OF RADIO ENGINEERS
The old president and the new. On the left,
Ralph Bown, president for 1927, greets Dr. Alfred
N. Goldsmith who has been chosen to lead the
Institute for 1928. Doctor Bown is a radio en-
gineer for the American Telephone & Telegraph
Company and Doctor Goldsmith is chief broad-
casting engineer of the Radio Corporation of
America as well as one of the board of consulting
engineers of the National Broadcasting Company
346
channels in the cleared band. This is the
situation which Senator Howell will un-
cover, perhaps by spending a few hundred
thousand dollars of the Government's
money to do so.
We recognize, without the aid of a Con-
gressional investigation, that this situa-
tion is not an ideal one. It would be much
more desirable if only four or five leading
stations on each chain, widely separated at
such points as New York, Chicago, Den-
ver, and New Orleans, for example, should
be given clear channels so that long-dis-
tance listeners who are not within the serv-
ice range of other stations on the chain
can secure them via a cleared route.
The rest of the chain stations should also
have good channels so that they can be
heard throughout their service area with-
out an annoying heterodyne. This require-
ment, however, does not call for a nation-
ally clear channel, but merely one which is
free of excessive congestion. The claimed
service range of chain stations, as expressed
in their prospectuses, on the basis of which
they sell radio advertising, clearly indi-
cates that nationally clear channels are
not contemplated by them nor is national
service attempted by all or any of their
stations.
But certainly such stations as wjz,
WEAF, WOR, WGY, and WGN are worthy of
a nationally clear channel. Allowing five
clear channels to each of the three chains
would account for only fifteen of the
twenty-five clear channels. The remainder
should be reserved for some of the better
stations, offering high grade programs from
local sources, for example, WPG, Atlantic
City, WBBM, Chicago, wcco, Minneapolis,
and WHAM, Rochester. These latter two do
use chain programs but the excellence of
their local programs ranks them high
indeed.
We understand that wcco, recognizing
that chain programs are available from so
many points and are therefore needed
only locally, has decided to distribute its
chain programs through a smaller Minneap-
olis station, which covers only the local
Minneapolis-St. Paul area. The programs
of wcco will be almost entirely from local
program sources, such as their famous
symphony orchestra and other individual
and distinctive programs, thus contribut-
ing to the variety of programs offered
listeners near and far. This policy should
be encouraged by offering such stations
clear channels, thereby increasing program
variety.
The long-distance listener, remote from
the local service area of any broadcasting
MARCH, 1928 BROADCASTING DOES NOT BELONG ON SHORT WAVES
347
station, and that includes sixty or seventy
per cent, of the radio audience, is not served
if, with twenty-five cleared channels, he
can hear but three different programs.
Under those circumstances, there is no
necessity for clearing such a large number
of channels. Each clear channel means that
three or four higher frequency channels
must be more seriously congested. I f greater
program variety for the rural listener is
not gained by additional channel clearing,
it will soon cease. But, if there are suffi-
cient independent stations, originating their
own high-grade programs, or more chains,
then the clearing process can continue even to
the point where we have only clear channels
with either independent or chain stations
serving them and local channels forlow-
and medium-power stations.
At the present time, there is a monopoly
of good program service, attained by sub-
scription to the three chain programs — the
Columbia and the Red and Blue Networks
of the National Broadcasting system. This
monopoly has been won by good service
and by public tolerance. It is hard to name
ten or fifteen independent stations truly
worthy of cleared channels; the writer
confesses he knows of but four, WPG,
wcco, WHAM, and WBBM, the latter more
because of its good carrying qualities than
because of any especially good programs.
Of these, two use chain programs, but to
a limited extent. The Commission would
not for a moment hesitate to assign clear
channels to good independent stations, but
most broadcasting stations are hopelessly
mediocre. The broadcasting band is much
larger than is required to accommodate the
good stations of the country. Southern
politicians cry discrimination, but they
cannot name five stations having program
standards sufficiently high to attract con-
sistent audiences outside their local service
areas.
The Growing Political Pressure on
the Commission
IN CONGRESS, the evaluation of a
*• station is measured by the amount of
pressure which the station owner can
bring upon his particular Senator and Con-
gressman. A Congressman can readily be
induced to raise a large howl about the
most puny, insignificant, puerile, useless,
annoying, broadcasting station on earth.
He can wax eloquent before the Federal
Radio Commission and praise alleged serv-
ices which he has never heard of except
from the owners of the stations claiming to
render them, an eloquence usually entirely
unwarranted. Never would such an alleged
statesman ask a local station owner to
modify his demands for increased power or
a clearer channel in the slightest iota in
deference to the national situation and to
aid in securing uniformly good broadcasting
conditions all over the country.
We visited one of the most annoying and
obnoxious stations in New Jersey which
spreads a blanket of odoriferous advertis-
ing throughout the northern part of the
state. This station owner was able to show
us a pile of letters which he had obtained
by solicitation from his Senators and Con-
gressmen, commending its service, although
they had probably never listened to it
voluntarily. These legislators urge the Fed-
eral Radio Commission to give that station
special consideration over other stations
in the metropolitan area of New York,
simply because it means political support
next time elections come around.
Our prophecy, made before the Radio
Act was written, that placing broadcast-
ing regulation in the hands of a Commission
at the mercy of Congress would simply
make political lobbying the criterion by
which broadcasting rights are distributed,
may, unfortunately, be fulfilled. The Com-
mission has done its best to educate or to
disregard the politicians, but troth courses
have their difficulties. If the Commission
does not heed the politicians and their
local needs and impossible requests, it is
bound to suffer chastisement by failure to
secure confirmation of its members, by
curtailing of its appropriations or by
special legislation requiring recognition of
principles incompatible with good alloca-
tion but favoring station owners above the
listening public.
Limitations to the Use of High-
Frequency Channels
\A/E HAVE already mentioned the
* ' problem of selective fading on short-
wave channels, which causes varying
audio-frequency distortion, but there are
a number of other points, equally po-
tent, which must be considered when ap-
praising the value of the short-wave region
for broadcasting purposes. If the number
of broadcasting stations on high-frequency
channels continues to increase, the short-
wave DX audience will show continued
growth. Any great increase in the number
of radio receivers working on the short
waves will render these waves useless for
radio telephone reception because only a
radiating regenerative receiver can be
made to work on these waves. No sets have
yet been built successfully which do not
oscillate at the high frequencies, although
the new ux-222 tube promises to make
short-wave neutrodynes and super-hetero-
dynes practical. With the receivers now
available, however, tuning is so critical
that the most skilful operator cannot avoid
radiating whistles when tuning-in a sta-
tion. Consequently, wide-spread listening
will make the short waves even more dis-
turbing than the broadcasting channels
were during the oscillating receiver days
of 1922 and 1923.
A channel utilized on short waves is inter-
national in scope, almost regardless of the
amount of power used. Even a fifty-watt
station, broadcasting on short waves, re-
quires an internationally exclusive channel.
Therefore, there are a maximum of 2700
channels in the entire world between 10
and 200 meters (30,000 and 1500 kc.),
of which the United States might justly
claim perhaps 250 for all purposes. Already
the band between 25 and 50 meters (12,000
and 6000 kc.), is completely filled with sta-
tions and there are few blank spots in the
remaining channels. Hence, instead of a
vast unused ether territory, as those sug-
gesting a broadcasting band seem to con-
sider it, the high-frequency territory will
soon have a congestion problem of its own.
The needs of broadcasting and the needs
of the radio listener can be adequately met
by a well allocated layout of broadcasting
stations confined to the present broadcast-
I
RADIO ON CANADIAN TRAINS
Many of the crack trains of the Canadian National Railways are equipped with radio receivers to
entertain passengers on long daylight runs. The sets were especially designed for this service. Loop
operation is not used, every set receiving its energy from a low antenna on the car
348
RADIO BROADCAST
MARCH, 1928
ing band. Such an allocation can provide
ample program choice, equitable service
for all parts of the country, and sufficient
long-distance reception to meet the needs
of the public for years to come. The present
band is the only one ideally suited to broad-
cast transmission and reception. Stable,
non-radiating receivers which can select
stations ten kc. apart are easily made.
Neither of these features can now be em-
bodied in sets working on the high-fre-
quency band. Below 25 meters (12,000 kc.)
channels for radio telephony must be sep-
arated by 75 to 100 kc. because we do not
yet know how to avoid cross talk with closer
spacing.
A further difficulty is introduced by vary-
ing hour to hour transmission qualities of
the high frequencies, which requires chang-
ing of the frequency of a station every few
hours if it is to give reliable service between
any two points. Short-wave, transatlantic
telegraph communication stations need
three and four channels in order to main-
tain satisfactory twenty-four hour service
between two points on opposite sides of
the Atlantic.
More important than any of these objec-
tions to the use of high frequencies for gen-
eral broadcasting, however, are the needs
of the world for short-wave, radio tele-
graph communication networks. The high
frequencies are extremely prolific in tele-
graph channels. For speech and music,
a frequency space ten kc. wide is required
but, in a band of this width, fifty short
wave transmitters could be accommo-
dated.
This is assuming, of course, that means
of establishing perfect frequency stability
has been discovered so that a high-fre-
quency station might stay exactly on its
channel. While there would be a maximum
of 2700 broadcasting channels in the ether
space from 30,000,000 to 1,500,000 kc. or
200 down to 10 meters, there are actually
about 275,000 potential telegraph chan-
nels.
The needs for these channels are liter-
ally enormous. Already they are extensively
used in high-frequency beam transmission
across oceans and even to the opposite side
of the earth. They are needed for trans-
mitting news to large numbers of news-
papers by syndicate news services. They
will be needed for the tens of thousands of
aircraft transmitters which will fill the
skies within a decade or so and which will
depend upon radio for weather information
and for the safety of the lives of the passen-
gers. Navigation companies, railroads, bus
systems, police and fire systems, and forest
and water patrols, will require these chan-
nels in increasing numbers. Then there are
a host of private communication systems
in contemplation where the use of high-
frequency radio service will effect tremen-
dous economies and savings which will be
reflected in the cost of goods purchased by
the public. Department store chains, busi-
nesses having factory branches at widely
distributed points, ranch owners who have
to communicate with employees fifty and
a hundred miles away, lumber operators,
packers and shippers, and numerous other
services can use short waves and use them
effectively.
There is need for ship beacons, fire and
signal systems, aircraft service, aircraft
beacons, landing field radio beacons, and
a host of other services which dwarf ra-
dio broadcasting into insignificance so far
as social and economic importance is
concerned.
As radio listeners and as those partici-
pating in a large and prosperous radio indus-
try, we are inclined to exaggerate the
importance of broadcasting. The most im-
portant service which radio renders is in
promoting the safety of the lives of those
at sea. Radio has saved thousands of lives
annually by bringing aid to ships in dis-
tress. The ships of the air are not as staunch
as ships at sea, and radio is much more vital
to their safety. Ether congestion will add
material problems to the expansion of
aerial navigation.
The clamor for short-wave communica-
tion in order to soothe the feelings of broad-
casting station owners must cease. We have
learned the lesson of conservation of forests
and now go to great effort to replenish the
trees which have been so ruthlessly cut.
Once they are assigned to a service, there
is no way of planting new ether channels.
The mistakes of to-day are not easily recti-
fied to-morrow.
The broadcasting stations, which go on
short waves for any reason other than
serious research or to effect the rebroad-
casting of special international events, are
doing so in order that they may claim to
advertisers that they cover the civilized
world. Without doubt, going down on
short waves will bring responses from
foreign countries. If all the letters received
by all the short-wave broadcasters were
put in a heap, it would be found that there
are three men in South Africa, about ten
in Argentina, and about thirty in Aus-
tralia and New Zealand who are the sources
of seventy-five per cent, of all of these let-
ters. These short-wave transmitting outfits,
for which so much publicity value is
claimed, are serving audiences of very
small numbers.
Broadcasting on the regular channels, it
may be claimed, started in the same modest
way, serving only small numbers. But it
had the opportunity to grow because the
medium was suited to good transmission
and reception. That consideration does not
apply to high-frequency broadcasting. It
has DX fascination but not esthetic value.
As a means of distributing goodwill pro-
grams, the short waves are useless because
the musical reproduction is not sufficiently
good to please the listener. Those who lis-
ten to radio for the entertainment will pre-
fer the stabler low-frequency broadcasting
band.
May the publicity-seeking gentlemen
who solve the broadcasting problem by
newspaper interviews cease misleading the
public about the possibilities of short-
wave broadcasting!
The First Rayfoto Transmission
THE backers of Austin G. Cooley are ex-
hibiting pleasing conservatism in going for-
ward with their Cooley Rayfoto transmis-
sions. Instead of accepting the numerous offers
to broadcast through every station which
invites them to the microphone, they are still
quietly conducting tests with the aid of quali-
fied experimenters. Some twenty picture record-
ers are in the hands of experienced set builders
and they are making radio pictures, sent oc-
casionally during the early morning hours
through WOR, of L. Bamberger & Co. Newark,
New Jersey. If these twenty experimenters are
successful in securing reliable and satisfactory
pictures without special instruction or experi-
ence with the Cooley Rayfoto apparatus, more
recorders will be distributed until the reliabil-
ity of the apparatus is fully established. The
equipment will not be offered to the general
public until it has been fully tested by typical
users to their entire satisfaction.
Mr. Cooley's representatives are being flooded
with inquiries both from broadcasting stations
and from experimenters who desire to purchase
the apparatus. Phonograph records for trans-
mission and testing, and the complete equip-
ment, will be distributed as soon as existing
receivers have been fully tested. The recorder
at RADIO BROADCAST Laboratory has been very
satisfactory.
Two Stations Cannot Occupy the
Same Ether Space
ANEW YORK Times headline proclaims
that Dr. Lee DeForest has dis-
covered room for 500,000 broadcasting
stations. It is most irritating to read such mis-
leading statements because they afford an ex-
cuse for not dealing with broadcasting conditions
as they exist in the present. The remedies of to-
morrow do not alleviate the problem of to-day.
Scrutiny of Doctor DeForest's remarks shows
that the usually accurate Times misinterpreted
what he said. He merely stated that there are
some 6000 channels, with lo-kc. separation,
between 200 and I o meters ( 1 500 and 30,000 kc.)
and that perhaps 500,000 radio-telegraph sta-
tions could be disposed upon these frequencies
if the double-heterodyne method of transmis-
sion, requiring the use of low-frequency super-
audible, master oscillators, were employed.
Doctor DeForest also suggests that the same
system might be utilized in the broadcasting
band. Such a course would necessitate the com-
plete scrapping of all transmitting and receiving
equipment and add a delicate manipulation
somewhat beyond the skill of the average lis-
tener, to the tuning process. The remedy would
cost a billion dollars — or what you will — and
would not even accommodate all our present
stations.
Between loand aoometers — considered a radio
Utopia by experts in publicity and politics, there
are 27,500,000 cycles, or 27,500 kilocycles, of
frequency space. At lo-kc. separation, which is
necessary for ordinary radio telephony, there are
2750 broadcasting channels for distribution
among all the nations of the world. Some twenty
of these are already used by stations broadcast-
ing on this band as well as their regular longer-
wave channels some of which boast that they
are broadcasting "to the civilized world"
through their short-wave stations.
This is a misconception because the only
persons who listen to broadcasting on the short
waves now are DX cranks. No civilized person
would seek musical entertainment on these short
waves because of the existing audio-frequency
MARCH, 1928
WILL RECEIVERS BE "REVOLUTIONIZED" AGAIN?
349
distortion for which no one has found a cure.
Programs are quite distinguishable at enormous
distances but they appeal to musical tastes about
as much as a five-legged calf appeals to a stock
breeder. To suggest relief from broadcasting
congestion by pointing to the numerous high
frequencies is as practical as offering the vast
Arctic spaces to the overcrowded populations
of India.
The problems of the broadcasting situation are
extremely complicated. Experts have no easy
remedies to offer. With the unwearying persist-
ence of Cato, we repeat that excess broadcast-
ing stations must be eliminated. The rights of
the listener and the property rights of the broad-
caster are in conflict. No one, not even the broad-
casting station owner, at least when speaking
for publication, denies that the listeners' rights
are paramount. Therefore, the question centers
on how great are the rights of the broadcasting
stations involved because the broadcasting sta-
tion owner must make sacrifices so that the lis-
tener may hear undisturbed programs.
The National Association of Broadcasters
estimates that the total investment in broad-
casting stations, as computed on March i, 1927,
is 519,283,000. These figures were probably
obtained in answer to a questionnaire and are
therefore the broadcasters' own valuation of
themselves. We are inclined to regard the figure
as a good guess. The one hundred leading stations
are probably the larger part of this investment.
That leaves only about ten million dollars of
disputed rights involved, of which only half need
be confiscated to bring good broadcasting. If
that problem is too great for the master minds
in Congress to solve, we had better employ some
foreign broadcasting experts.
Will the Radio Industry Do It
Again?
\ A/1TH great secrecy, a score of manufac-
* * turers are designing new radio sets to
utilize the experimental ux-222 (cx-j22)
tube. This tube is virtually a laboratory
product, the much heralded double-grid type
tube, having four elements. Everything points
to a repetition of the radio industry's annual
suicide because undoubtedly one manufacturer
or another will soon startle the world with the
statement that he has a set using this great tube
which will make all rivals and predecessors ob-
solete. Then will follow the usual race and a score
of manufacturers will announce new ux-222 sets,
and all their previous models, some of them
hardly perfected by experience, will go into the
discard. In this way, the radio industry forces
itself into a seasonal state and adopts new
methods and types before the old ones are
hardly introduced. The way in which the a.c.
set was heralded completely ruined the business
in battery sets. Everything points to a repe-
tition of precedents, that the a.c. sets will be
rendered obsolescent by the new ux-222 tube.
There is no sense whatever in this procedure.
There is no reason for stopping the manufacture
of touring cars and sedans because the roadster
is popular. On the contrary, development should
be pursued on all types because all have their
particular and distinctive fields of service.
The annual destruction of last season's stocks
by the vainglorious announcements of next
season's improvements has forced the radio in-
dustry to concentrate its production during
only four months of the year and to maintain
its factories in virtual idleness during the re-
maining eight months of the year. Manufac-
turers do not dare to accumulate stock in excess
of the immediate demands and the result of
hand to mouth manufacture has been to re-
duce the quality and grade of workmen who can
be attracted to the industry. Look at the ad-
vertising now current, and observe that the
a.c. set has in no way reduced the simplicity,
the tonal quality, or the usefulness of the battery-
powered set.
The first radio set manufacturer who promises
the public a revolution in radio next year by
his ux-222 tube set should be squelched by the
radio trade. He is paving the way to wreck the
values of existing stocks of a.c. sets. The in-
dustry should determine, from now on, to make
its announcements of new styles and types mod-
est and in true perspective with the facts, and
leave revolutions to Mexican bandits.
The Month In Radio
THE Secretary of the Navy's annual report
states that 119,337 vessels were furnished
267,486 bearings by the Navy Radio Compass
Service. The savings to other government de-
partments by the use of the naval radio com-
munications service amounted to about a million
dollars.
IN A report on beam and directional short-
' wave radio telegraphy, issued by the Trans-
portation Division of the Department of
Commerce, V. Stanley Shute points out the ad-
vantage of the American beam system over the
British. The American beam antenna requires
only ordinary telegraph poles while the Marconi
system uses expensive and complex steel masts.
Another feature of the American antenna sys-
tem is that provision is made for the melting of
ice, overcoming serious difficulties in winter
transmission. This feature is impossible with
the Marconi beam. Other advantages, common
to both systems of beam transmission, is the
possibility of high-speed transmission, economy
of power, and stability of the received signal.
Mr. Merlin Aylesworth, in his New Year
statement, informs us that the Red, Blue, and
Pacific Coast networks, during 1927, spent ap-
proximately six million dollars in program pres-
entation, of which over two million was for talent
on sponsored programs, presented by some fifty
American concerns. The Company itself spent
a half a million dollars for its own sustaining
programs. Wire cost, involving 10,270 miles of
regularly used circuits, was in excess of $1,350,-
ooo. I f I Our attention is frequently called to
the verbose claims made by Norman Baker, op-
erating direct-advertising station KTNT. He writes
listeners that "his is the only station in America
that is dedicated to the farm, labor, and general
public's problems, which we will always fight
for against powerful interests. Do you realize
that advertising by radio, cuts overhead ex-
penses so low, that merchandise can be sold at
prices meaning from twenty-five to fifty per
cent, saving to you?"
We have examined some of these prices, for
example, the claim that Mr. Baker is selling
"tires, far below others, in fact we sell 12,000
miles guaranteed tires as low as others ask for
8000 miles tires." Specifically, the 30 x 333 over-
size cord, clincher tire, guaranteed for 12,000
miles, sells for $7.70 through KTNT'S radio em-
porium. The corresponding Sears, Roebuck, tire
sells for $7.75, making the possible saving less
than one per cent. Can this be called a sub-
stantial saving?
There is no law protecting the listener against
untruthful statements in radio advertising, al-
though firms, subjected to unfair competition,
may invoke the aid of legal protection on that
ground. fit Station 3 LO of Melbourne, Aus-
tralia, has begun to transmit on 36 meters, and
has been reported in many parts of the world.
The station's organization has made applica-
tion to install a number of relay stations with a
view to making its programs available to all
parts of the Australian continent. f I I The
Mackay interests will erect a short-wave trans-
atlantic radio station on Long Island to supple-
ment their Commercial Cable Company's sub-
marine cable service. The progress which has
been made in short-wave radio telegraph com-
munication makes it unlikely that any more
cables will be laid in the ocean.
AT THE BUREAU OF STANDARDS
The illustration shows a field set-up for comparing "coil antennas," more familiarly known as loops
A HOME-CONSTRUCTED A SUPPLY
A view of the A power unit described in this article.
It is here shown with the metal cover removed
A New A Power Unit
By Ralph Barclay
THE convenience and desirability of a
radio receiver that requires no attention
other than to turn it on and off, is ob-
vious, and to produce such a receiver has been
the aim of set designers for the last few years.
The problem has now been more less sur-
mounted and it is possible to-day to purchase
many receivers which are completely a.c. oper-
ated.
The design of apparatus for use in conjunction
with existing battery-operated receivers to ob-
tain socket power operation has also been satis-
factorily solved, and preceding articles in RADIO
BROADCAST have described many B power units
and A power units which will give socket power
operation of a receiver designed originally for
use with batteries. These preceding articles have,
however, described completely manufactured
units, while it is the purpose of the present article
to give the characteristics of the Knapp A power
unit, parts for which can be obtained for home
assembly.
The characteristics of the Knapp A power
unit are as follows:
(a.) It can be used to supply A power di-
rectly from the light socket, to any receiver
using up to about ten 2OI-A type tubes or com-
bination of tubes drawing an equivalent amount
of filament current. No changes at all are neces-
sary in the receiver, the two leads from the
unit merely being connected to the A plus
and A minus terminals on the set.
(b.) The hum audible in the loud
speaker when the tube filaments in
the receiver are supplied from the
power unit is so low as not to inter-
fere at all with reception.
(c.) The cost of operation is very
low — about 25 cents per month if the
receiver is an ordinary five-tube set,
in use an average of four hours a day.
(d.) The cost of a complete kit of
parts from which the A power unit
may be constructed is $22. 50.
(e.) The device requires no main-
tenance attention other than to turn
it on and off.
The circuit diagram of the de-
vice is given in Fig. i . The trans-
former, T, steps down the line
voltage to the correct value, the various taps on
the secondary being used to adjust the output
voltage. The taps are all numbered and the
movable contact should be clipped onto a low-
numbered tap if the receiver is a small one; if
the receiver contains a large number of tubes,
the clip should be placed on a high-numbered
tap. The two condensers, Ci and Ci designed
especially for use in this A power unit, and the
filter choke coils, LI and LZ, combine to make the
final output of the unit free from hum. Ci has
a capacity of about 1000 to 1500 mfd. and Ci
has a capacity of between 1500 and 2000 mfd.
It is the design of these condensers, in which
compactness combined with high capacity is
embodied, that makes possible the A device
described here. The choke coils each have an in-
ductance of about o.i henry, a resistance of 3
ohms, and a current-carrying capacity of ap-
proximately 3 amps. The rectifier, R, is a dry
metallic one and the particular unit used in this
power unit contains sixteen pairs of electrodes
arranged in a bridge circuit to give full-wave
rectification. At times, when the power is first
turned on, the rectifier will spark over but this
does not injure it in any way for the device is
self-healing, a characteristic not found gener-
ally in rectifiers of this type. The rectifier has a
life, according to its manufacturers, generally
in excess of 1000 hours. It is held in place by
several clamping screws and can easily be re-
^J '
r
Li
Rectifier
* 000
• ••
c,
•
L, A^A ^ — n«_
FIG. I
A circuit diagram of the home-constructed A supply
350
placed when necessary. A new rectifier can be
obtained for $6.00.
A complete kit from which the power unit can
be constructed should contain the following parts:
T — Transformer
Rectifier Unit
Ci, C2 — Special High-Capacity Condensers
Li, Lj — Choke Coils
Drilled Base Plate (Copper-Plated Steel)
Drilled Top Plate (Brown Bakelite with Studs
in Place)
Contact Plate (With Mounting Bracket)
H & H Toggle Switch
Drilled Baseboard
Metal Cover
A. C. Line Attachment Cord with Plugs
Output Cord for Connecting to Set with Polar-
ized Plug
Complete Instructions for Assembly and Oper-
ation
Necessary Nuts, Screws, Clamps, etc.
The constructional data supplied with the kit
of parts are very complete and with their aid,
the building of the unit may easily be accom-
plished in an hour or two. The baseboard is all
drilled and the first job is to fasten all the parts
to it. The unit may next be wired with any or-
dinary kind of rubber-covered wire.
In order that it may operate most satisfac-
torily, it is essential that either the A plus or A
minus be grounded. In most receivers one side
of the filament circuit is grounded but in those
cases where this is not true, it will
be necessary to connect a ground
between the A minus, preferably,
and the regular ground post on
the receiver.
Light socket operation of a radio
receiver is, therefore, a simple mat-
ter using a Knapp A power unit
and good B power unit. The Knapp
A power unit is supplied with an ex-
tra plug into which the supply lead
for the B power circuit may be con-
nected, and the entire installation is
then controlled from the single power
lead on the A power unit, and turning
on your receiver becomes a matter
of merely pushing a plug in a light
socket receptacle.
IN THE Laboratory at
foorly-Designed the present moment is
Amplifiers an a.c. receiver with
a well-known name
which uses a three-stage audio amplifier,
two stages being resistance-coupled and
one transformer-coupled. Although the
power tube, a 171 type, draws no measur-
able grid current, and although the plate
. current of this tube is constant as meas-
ured by a d.c. meter, the quality is bad;
something seems to overload. What is
wrong?
The transformer couples the detector
to the amplifier while resistance-capacity
units connect together the remaining
amplifier stages. There is no C bias on
either of the resistance-coupled tubes
(this seems to be standard practice,
although one has difficulty in understand-
ing why). To load up the final tube, 40
volts are required on its grid. Since the
next-to-the-last tube is coupled to this
power tube by a resistance-capacity unit,
there is no voltage gain except that due
to the tube. In other words, the next-to-
the-last tube must have 40 volts a.c. in
its plate circuit, necessitating about 5
volts a.c. on its grid, if the amplification
factor of the tube is 8, which is correct
for a 226 type tube. Five volts a.c. on the
grid of a tube which has no C bias will cause
severe overloading, and when a voltmeter
is placed from the plate of this tube to
the negative filament, the needle jumps
violently. The voltage between negative
filament and the plate battery side of the
resistor shows a voltage which is found constant
at 175 volts.
When the next-to-the-last tube overloads,
considerable d.c. plate current is generated. This
plate current generated in the tube, due to over-
loading, is opposite in direction to the no-signal
plate current and the voltage drop across the
coupling resistor due to this decrease in plate
current reduces the voltage drop across the
resistor due to the no-signal current. This allows
more plate voltage to be impressed on the tube,
so that the plate voltage varies from a steady
no-signal value of 25 to 50 on the modulation
peaks.
Now let us suppose that the transformer is
used to couple the second stage of the amplifier
to the power tube, which still requires 40 volts
a.c. on its grid. The turn ratio is 3 so that across
its primary are required 40 -^ 3, or 13.3 volts
which, divided by 8, the mu of the tube, gives
1.67, which is the grid a.c. voltage which the
next-to-the-last tube requires. If no C bias is
used, much less severe overloading will occur
than if 5 volts appear here, and in a fair loud
speaker it is true to say that no loss in quality
will be noticeable.
The answer is naturally to use C bias on all
tubes, but if this cannot be done, the trans-
former should be used last in the chain. This is a
better plan for another reason — that of using as
high an impedance as possible in the plate circuit
of the detector.
The plate resistors are each of 100,000 ohms
value, and for a transformer to have that im-
pedance at 60 cycles — which is as low a frequency
as anyone need worry about — its primary must
have 160 henries inductance!
This amplifier is clearly a case of poor engineer-
ing, and a small amount of pencil and slide rule
work would have shown the designers of this
receiver what could have been expected before
they had even bult one up and put it on the
laboratory bench and tested it with expensive
instruments.
Slfartz
'Transmitting
Tubes
FROM time to time we read,
and are mildly amused, about
the new glass substitutes
which admit ultra violet into
our homes — even in large cities where there is
practically no ultra violet because of smoke.
During the early development of the General
Electric's fused quartz, which transmits 92 per
cent, of all radiation, from ultra violet to heat,
General Elec. Co.
A SLAB OF FUSED QUARTZ
The writing would not be legible through a
piece of ordinary glass of equal thickness
351
we had the pleasure of working with Dr.
Berry of the General Electric Company
and the Harvard Cancer Commission, on
some uses of this beautifully transparent
glass.
Fused quartz has another important
quality in addition to its transparency to
ultra violet. This is its coefficient of ex-
pansion which is so low that it is pos-
sible to grind telescope lenses of quartz
without the many hours of slow work
necessary when our best lens glass is
used. Under the heat produced by the
grinding process the quartz expands so
little that there is no danger of crack-
ing, and it is possible to grind the lens to
the desired dimensions with less regard
to internal mechanical stress.
One of the great difficulties with high-
power transmitting tubes lies in the heat
generated, which must be dissipated with-
out danger to the glassware. Water-cooled
tubes mark one step in the develop-
ment of safe high-power tubes; another
may be the use of fused quartz, as is
being done experimentally in England.
We remember a demonstration in a
motion picture projection room where
glass condensing lenses are used which
get very hot and which occasionally
crack because of the severe mechanical
stress in the glass. A pair of lenses had
been made — large pieces of convex
quartz carefully ground and polished —
•r and were taken to the motion picture
house for test. They worked beautifully,
of course, and after the show it was
necessary to remove the lenses and take them
back to the laboratory.
This would have meant a delay of appreciable
time for them to cool if they had been made from
glass, but despite the operator's disclaiming any
responsibility (the quartz lenses were worth
their weight in gold) the lenses were removed,
thrown into a pail of water, and within a very
few moments they were sufficiently cool to be
removed to the laboratory.
While there is no prospect that there will be
any need to cool a loo-kw. tube as quickly as
this, or that anyone would want to carry such
a tube around, hot or cold, a tube that is im-
pervious to temperature changes will relieve
engineers from one worry at least.
Fused quartz is wonderfully transparent; one
can read a paper through a yard of it; it expands
but little under application of heat and, as a
matter of fact, is difficult to heat because the
radiation passes through it without being ab-
sorbed. It has another characteristic — it is fright-
fully expensive.
SOME interesting tests have
SuietA. C. been made by the manu-
Sets facturers of Kuprox, one of
the dry rectifiers, on using a
combination of rectifier and a.c. tubes. In every
case the audibility of hum emanating from the
receiver was decreased by the use of partially
filtered a.c. on the filaments.
One receiver was a standard five-tube set
using McCullough a.c. tubes. With d.c. through-
out, the audibility of hum — the origin of which
was unknown — was 2; with a.c. on the heaters of
these tubes, the hum rose to 250 audibility units,
and dropped to 46 when the Kuprox rectifier
and a single choke coil was used to rectify and
partially filter the a.c. Another receiver was a
well-known product requiring no batteries. With
d.c. on the filaments and a socket power device
for supplying the plate current, the hum was
from 1 20 to 150 units as measured on a General
352
RADIO BROADCAST
MARCH, 1928
Radio audibility meter. When the special a.c.
converter supplied by the manufacturer fur-
nished power for the filaments, the hum increased
to looo units, but dropped to from 90 to 120
when the Kuprox was added.
While we do not agree with the manufacturers
that Kuprox is "the most important discovery in
radio since the first three-element vacuum tube
was successfully used", and cannot agree with
advertising writers of a.c. sets who state that
there is absolutely no hum from their sets, if a
Kuprox unit, or other rectifier, and a choke
coil, will enable one to use a.c. tubes without
appreciable hum, we are willing to advise our
friends to go in for a.c. receivers.
At the present moment it is difficult to sub-
scribe whole-heartedly
to the apparent craze
for a.c. sets. Without
a doubt the ultimate
receiver will require no
attention, will be fool-
proof, and will operate
from any lamp socket,
but at the present mo-
ment we are not con-
vinced that we should
junk our storage bat-
tery and charger outfit,
which is perfectly quiet
and which requires an
expenditure of about
eight minutes a week
to put on and take off
the charger, for a new-
fangled receiver that
can be neglected as
soon as it is plugged
into a socket.
While on the ques-
tion of a.c. operation,
we might give the fol-
lowing data on Radio
Corporation of Amer-
ica a.c. tubes, which come from the Technical
and Test Department of that concern, and are
average data of a great many measurements:
MEASUREMENTS MADE WITH D.C. FILAMENT SUPPLY
UX-226
Ef = 1.5 v.; EC = -9.0 v.; Ep = 135 v.
Plate Impedance 8000 Ohms
Amplification Factor 8.2
Mutual Conductance % . 1050 Micromhos
Filament Current , . .' . . . . l .05 Amperes
Plate Current 5.2 mA.
maximum output of power will be absorbed when
the effective resistances of the source and the
load are equal and when the reactances are equal
but opposite in sign. Under these conditions the
power absorbed will be the voltage squared
divided by four times the effective resistance of
the source.
In other words, to supply power the numerical
value of the impedances must be equal — to use
the usual semi-technical language.
If a tube is to be used as a voltage multiplier,
say in a resistance-coupled amplifier, greater
amplification will result if the load resistance is
several times that of the tube resistance. In a
transformer-coupled amplifier, the impedance
which the tube looks into — the effective imped-
Transformer
^Measurements
100
500 1000
CYCLES
UY-227
Ef = 2.5 v.; EC = -6.0 v.; Ep
Plate Impedance 9810 Ohms
Amplification Factor 8.9
Mutual Conductance 907 Micromhos
Filament Current 1.75 Amperes
Plate Current 3.1 mA.
Into What Im-
pedance Should
the Tube Work?
CONSIDERABLEuncer-
tainty seems to exist in the
minds of popular writers
as to whether the impedance
into which a tube works should be equal to that
of the tube or several times greater. The answer
is that it all depends.
If any source supplies power to a load, the
A CIRCUIT USED FOR TRANSFORMER MEASUREMENTS
In the Laboratory the voltage appearing across the secondary of a new type A Sangamo audio
transformer was measured with this set up with a constant d.c. flowing through the primary and
a constant a.c. voltage impressed upon the primary. The resultant curve is also shown here
ance of the primary of the transformer, — should
be several times the impedance of the tube at the
lowest audio frequency which it is desirable to
transmit. At the higher frequencies a combina-
tion of effects takes place to maintain the amplifi-
cation more or less flat. With a good transformer,
that is, one which has a very high primary im-
pedance, and a high impedance tube, the am-
plification will still be peaked. This is the price
one pays for amplification — loss in fidelity. If it
were possible to make a tube whose impedance
would be low and still have a high amplification
factor, it would be possible to use good trans-
formers and have high amplification and a high
degree of fidelity. Or, if it were possible to build
10:1 ratio audio transformers which would not
"go resonant" and otherwise cause trouble at
audio frequencies, we should have high gain and
high fidelity — but here again we are in difficult
water.
This impedance matching problem prompts
one reader to ask if it is wise to add resistance to
a tube plate circuit in case we desire the tube to
work into a resistance several times the internal
impedance of the tube and if the load impedance
is not this great. A concrete example will illus-
trate the question. Suppose we have a io,ooo-ohm
90 v.
tube and a io,ooo-ohm load. Since greatest
amplification will result if the load has, say
30,000 ohms impedance, shall we add 20,000 ohms
to the plate circuit? The answer is no, unless the
voltage across the entire 30,000 ohms is made
use of, and not that across the !o,ooo-ohm load
alone. If the additional 20,000 ohms can be in-
cluded in the load, somewhat greater voltage
amplification will result.
THE LABORATORY has re-
cently had the pleasure of
measuring, according to the
N. E. M. A. standard method
already described in these columns, the voltage
appearing across the secondary of the new San-
gamo Type A audio
transformer when a
constant d.c. current
flowed through the pri-
mary, and when a con-
stant a.c. voltage was
impressed upon the
primary in series with
1 1,000 ohms. The cir-
cuit is given on this
page as well as a curve
representing the result
of the measurement,
which should be in-
teresting to all pur-
suers of fidelity in re-
production.
As mentioned be-
fore, we do not believe
measurements, such as
this, on single trans-
formers without ac-
cessory tubes and com-
mon impedance which
always exist in a stand-
ard two-stage ampli-
fier, mean a great deal,
because we have
found in practice that the curve obtained by
measuring the voltage across an output resist-
ance of a two-stage amplifier may differ alto-
gether from what one obtains by measuring
a single stage only. This should not be taken to
indicate that a two-stage amplifier using San-
gamo Type A transformers would not be as good
as is indicated in our curve — it might be better.
It all depends upon the care taken in the con-
struction and the amount and kind of feedback
existing in the circuits.
A single Silver-Marshall type 220 audio trans-
former falls off badly above 3000 cycles when
measured singly, while a two-stage amplifier
using these transformers is perfectly good up
to 5000 cycles, the additional amplification at
these higher audio tones being due to regener-
ation. Many two-stage amplifiers will howl or
sing at the higher audio frequencies if sufficient
impedance exists in the common negative plate-
battery lead. This difficulty is easy to remedy,
usually, and necessitates the use of a 2-mfd.
condenser across the B batteries, or socket power
device. The transformers used in such amplifiers
usually have a rising characteristic when meas-
ured singly, as was done in the Laboratory to
measure the Sangamo transformer.
5000
AN EARLY PICTURE OF MR. HOGAN
He is here shown using the first audion ever made, at which time he was DeForest's Laboratory assistant
By Edgar H. Felix
fO INDUSTRY is more clearly the pro-
duct of inventive ingenuity than radio.
If necessity is the mother of invention,
radio must take after its paternal parent — crea-
tive imagination. It has grown to its imposing
importance, not by virtue of necessity, but by
discovering for itself a new field — the bringing
of entertainment into the home.
"It is my belief" says John V. L. Hogan,
pioneer radio engineer and technical authority,
"that a vital and fundamental change has taken
place in the spirit of the industry. Instead of a
competition of ingenuity, the majority of manu-
facturers are now content to copy the designs of a
few leaders who shape the trend from season to
season."
Mr. Hogan is qualified to speak of the spirit
of the radio industry because he has been inti-
mately associated with the progress of that in-
dustry for more than twenty years. Shortly after
Marconi had sent his famous first signal across
the Atlantic in 1901, Hogan, then a boy in his
teens, witnessed a demonstration of wireless
telegraphy at the University of Wisconsin. Two
years later, he spent a summer at San Juan,
Porto Rico, most of it within the four walls of
the radio station there. As it has with so many
after him, radio made short work of its victim,
imbuing him with its incurable fascination. From
then on, radio has been his principal interest in
life. He did not lose time in associating himself
with the best minds in the art.
During 1906 and 1907, Hogan worked as De-
Forest's laboratory assistant and, in that capac-
ity, used the first audion ever made. After his
association with DeForest, he continued his
studies at Yale University, specializing in
mathematics and physics. But, before his work
was completed, Reginald Fessenden, recognizing
his natural ability for conducting experimental
work, employed him to assist with his experi-
ments at Brant Rock, Massachusetts. Here,
in 1909, the Arlington Naval Station transmitter
was designed, assembled, and tested. Mr.
Hogan's association with Fessenden extended
over a period of many years.
After completion of the Arlington transmitter
and its acceptance by the United States Govern-
ment, Fessenden and his National Electric Sig-
nalling Company transferred their activities
to Bush Terminal in Brooklyn. Hogan became
chief research engineer and later manager of the
company.
In the laboratory, operated under his direction,
the basic principles for continuous-wave trans-
mission were formulated by Fessenden. The first
successful, high-frequency alternator was built
for Fessenden at the General Electric Labora-
tories. E. F. W. Alexanderson, already distin-
J. V. L. HOGAN
353
guished by his achievements in electric railway
locomotive design, was assigned to the problem
and successfully built and later perfected the
high-frequency alternator. These were fruitful
periods of research, both in transmission and re-
ception. Hogan is credited with many inventions,
perhaps the most important of which is the de-
tector heterodyne which he described in the
Proceedings of the Institute of Radio Engineers
in 1913. He was a founder and later became presi-
dent of that body.
Fessenden is the inventor of the heterodyne
principle. In its original reduction to practice,
two windings in the telephone receiver were
used, one to carry the incoming detector signal
and the other to superimpose the local high-
frequency oscillations. Hogan's invention is the
method of combining the incoming signal with
the local heterodyne signal before detection by
an electrical rectifier. Owing to the square law
action of the detector, enormous increases in
sensitiveness are attained, accounting largely for
the effectiveness of the regenerative and super-
heterodyne systems. He was also the first to dis-
close the advantages of single control, so widely
applied in broadcast reception, even before the
various tuning circuits of receiving sets followed
any law of regular and equalized progression.
Identified so closely with the early growth of
radio, Hogan is now recognized as a leader in the
patent and engineering fields. His views on the
patent situation of to-day and the causes under-
lying its complexity are founded on the best
possible authority.
"Contrasting with the early tendency toward
extraordinary ingenuity," said Mr. Hogan, in
answer to the writers' request that he amplify the
statement which opened the interview, "the
radio industry has largely adopted the habit and
practice of copying the designs developed by
354
RADIO BROADCAST
MARCH, 1928
the leaders of the industry. For example, the
most widely used modern radio receiver, almost
a standard design for the entire radio industry, is
the alternating-current, tuned radio-frequency
set, employing no batteries, self-contained with
all the necessary power supply, and using a
single-control tuning system.
" Following so closely the same design princi-
ples, practically all makers use the same in-
ventions, covered by the same patents. With
such a formidable array of patents, some ad-
judicated and some not, the decisions of the
courts are bound to have salutary results upon
the economic situation in the radio industry. As
an example of the effect of only a single patent,
the recent adjudication of the Alexanderson
tuned radio-frequency patent was sufficient
incentive to more than twenty of the leading
manufacturers of the industry to obtain licenses
from the Radio Corporation of America, which
holds the right to issue licenses under this patent.
If future adjudications continue favorable to
the Radio Corporation, these licensees will not
suffer any great changes in their status. But sup-
pose that the Latour, the later Hazeltine, the
Lowell and Dunmore patents, and some of the
other patents whose scope and validity are not
yet tested in the courts, should be adjudicated
in favor of their holders, there may be another
set of substantial royalties to pay. The holders
of patents applying to vacuum tubes, such as
the thoriated filament, pure electron discharge,
and the magnesium keeper, may collect large
penalties from independent tube manufacturers
who have so far disregarded them.
"The radio industry has problems still ahead
of it," continued Mr. Hogan, "although there is
no doubt that they do not mean its destruction
or its paralysis. Their existence is due to a very
fundamental weakness in the present conduct of
most manufacturers in the field, namely, the
tendency to stereotype and imitate.
"The radio industry has not always been prone
to follow the designs of its pioneers, but showed
independent inventiveness on the part of many
individuals. Marconi, in the early days, held a
patent on the insulated, grounded antenna. In-
stead of waiting for the adjudication of that pat-
ent, or entirely disregarding it, rival inventors
worked out means so that they would not have
to use the Marconi antenna system, by devising
the loop type of aerial for instance.
" In the field of detectors, after the coherer and
the magnetic detectors had been invented, the
manufacturers in the field simply developed
other forms of detector. The electrolytic of
Fessenden, the crystal detector, and the three-
element vacuum tube of DeForest, each a valu-
able contribution to the industry, were invented
to improve service and, at the same time, their
manufacturers and users were practically cleared
of infringement of existing patents. Thus patents,
instead of serving as a constricting and re-
straining influence, were the stimulus to making
some of the most important inventions in the
radio art.
"Only three sensible courses are open to those
who find patents apparently covering devices
which they desire to make or actually do make,"
said Mr. Hogan. "They are either pay, or fight,
or don't use. The second of these is often hazard-
ous. Many members of the radio industry elect
a still more hazardous course — to use without
paying until patents are adjudicated. Naturally,
these are likely to have to pay dearly in the end.
Many of those who fight do so in the spirit that
patents are a danger and a menace, to be fought
and destroyed, though this is obviously not a
sound position. When forced to do so, they pay
reluctantly because there is no other course
open to them, rather than encouraging in-
ventions and utilizing them legitimately and
without restriction. The alternative of develop-
ing new means so as to avoid infringement is the
one least used, although it is the course that
would contribute most to the progress of radio."
Mr. Hogan cited specific instances of unad-
judicated patents which are almost universally
used by the industry and which manufacturers
are seemingly making no effort to circumvent by
THE FIRST PRACTICAL HIGH-FREQUENCY ALTERNATOR
It was built for Fessenden at the General Electric Laboratories, by E. F. W. Alexander-
son. The latter is now in the public eye on account of his television experiments
developing substitute or improved means. He
even snowed how, in the field of broadcast trans-
mission, the tendency is to endeavor to make the
best of conditions as they are instead of attempt-
ing seriously to develop and put into use new
means and methods.
Mr. Hogan has had exceptional opportunities
in studying transmission phenomena. Fessenden
was one of the first to build a successful radio tele-
phone transmitter, having established a record of
several hundred miles' range as early as 1906.
When the Arlington transmitter was still in-
stalled at Brant Rock, prior to its acceptance by
the Navy, a most comprehensive series of tests,
the first extensive study of radio transmission
phenomena, were made with its aid. Data as to
attainable range, with various powers, at all
hours, were collected aboard the U. S. S. Birming*
bam. Out of this mass of data, the historic and
useful Austin-Cohen formula was worked out.
Hogan was intimately concerned with these
tests, being in entire charge of the Brant Rock
end. With such pioneer study of transmission
phenomena as a foundation and the many sub-
sequent years of research and contact, his sug-
gestions as to the most effective way to attack the
present broadcasting problem are worthy of most
profound consideration.
"The limitations of our ether channels are
almost as definite and specific as familiar laws of
physics," Mr. Hogan stated to the writer. "The
number of solid bodies of a certain size that can
be fitted into a room of certain dimensions is
readily calculated and no one attempts to deny
the operation of the law which determines it.
In the available ether, likewise, there are just so
many broadcasting channels, each of which can
accommodate just so many stations of a certain
power. There is no evading this law. If we squeeze
more programs than fit in our ether space, the
programs are certain to be damaged.
"The number of stations which can be ac-
commodated in the broadcasting band is directly
a factor of their power. Either we maintain many
stations comfortably in the band by reducing
their power, or we increase their power and re-
duce the number of stations. If we exceed the
capacity of the ether, as we are doing at the mo-
ment, we have confusion. There is no successful
evading of technical laws upon which the capac-
ity of the ether is founded, unless we establish
new laws by making new discoveries. As in patent
tangles, so in ether tangles, inventions may cut
the Gordian knot.
"To continue to increase the number and the
power of stations on the air, we must attain such
objectives as perfect synchronization of carriers
and their modulation, limitation of carrier range
to the area actually served by programs, or
modulation of the carrier in a new way which
narrows the band occupied by a fully modulated
carrier. None of these things is impossible, but
how much more energy is spent by broadcasters
in clamoring to stay on the air than in developing
the means which will make room for them on the
air.
"Founded, as the radio industry is, upon in-
genuity and invention, the work of the research
laboratory is still its most valuable asset and is
still the only really effective gateway to the solu-
tion of its problems. Mere imitation is fatal to its
growth and to its economic future. To-day, for
every dollar spent on research, hundreds of
dollars are spent on imitation. The crying need
of the industry is research and originality, the
employment of engineering genius and con-
tinuous technical growth. With proper concen-
tration on these factors, patent difficulties will
be mitigated and the fullest potentialities of the
industry and its field of service will be devel-
oped."
RADIO BROADCAST Photograph
THIS IS HOW THE COMPLETED RECEIVER LOOKS
It fits into any standard cabinet that will take a 7 x 18 inch panel
A Four-Tube ScreenedUGrid Receiver
THE four-tube all-wave receiver described
herewith represents what is probably the
most profitable application to a radio re-
ceiver of the new screened-grid tube, from a
performance per dollar per tube standpoint.
The new screened-grid tubes, offered, as they
have been, by the tube makers with little or no
actual practical operating data, present most at-
tractive possibilities to the experimentally in-
clined by virtue of the increased amplification
that they theoretically make possible. The ap-
plication of one of these tubes in the four-tube
all-wave receiver described here provides a re-
ceiver of high sensitivity, selectivity, and general
worth, and the methods of utilizing the ux-222
(cx-jaa) tube should be of considerable interest
to the experimentally inclined in view of the
dearth of practical operating information; a num-
ber of misconceptions concerning the ux-222
tubes have already arisen in the minds of many
radio fans.
The receiver pictured in the accompanying
illustrations employs one ux-222 tube in a tuned
r.f. amplifier stage with conventional trans-
former coupling between this tube and the de-
tector, despite popular belief that the ux-222
tube should work with tuned impedance cou-
pling. The detector is made regenerative by the
use of a fixed tickler winding, with regeneration
controlled by a midget variable condenser. The
two-stage audio amplifier, employing two large-
core heavy 3:1 ratio transformers, provides a
practically flat curve from below 100 cycles to
over 5000 cycles. The measure of the receiver's
By McMurdo Silver
true worth is its performance compared against
other sets. Operated in a steel building in Chicago
with a forty-foot wire hanging out of a window
for an antenna, a model set brought in stations
within a range of 1000 to 1500 miles on the loud
speaker, while KFI, in Los Angeles, was faintly
heard on the loud speaker through local inter-
ference. A couple of popular one-dial factory
sets on the same table refused to "step out" at
all. The four-tube receiver was moved to a
CT"A//.S article describes a four-tube receiver which
is notable chiefly because of its economy— all
the parts listing for a total of $46.75. This feature
alone should attract many a home constructor and
professional set b uilder. As the author states in the
article, the use of the screened-grid tube increases
the voltage to the detector, from a distant station,
about twice compared to that delivered by a 2OI-A
type tube. This gain is not all that the new shielded-
grid tube is capable of producing, but is about all
that is possible in a single stage and with the re-
quisite degree of selectivity. This is a distinct gain,
and is desirable, and is due to the new tube alone,
but the home constructor should not expect a doit-
Ming of voltage before the detector to work miracu-
lous results on extreme DX; it means, simply, that
louder signals will be received without the bother of
neutralising apparatus or tricky adjustments.
The receiver delivers excellent tone quality.
— THE EDITOR
355
Chicago suburb, where it brought in stations on
the East and West coasts with ample loud
speaker volume, pulling in some fifty stations in
one evening on a fifty-foot antenna. Yet the parts
for the whole set cost less than $50.00.
In developing the set, experiments were started
on the basis of individually shielded stages for the
r.f. amplifier and detector, using tuned im-
pedance coupling as recommended in the ux-222
data sheets. It was immediately found that,
while quite high amplification could be obtained,
varying from 20 per stage at 550 meters (545 kc.)
to about 55 per stage at 200 meters (1500 kc.),
the amplifier was far too broad for practical use!
Using the optimum value of coupling between
r.f. amplifier and detector, the selectivity was
even worse, though the amplification increased.
All this was previously predicted by mathe-
matical analyses of the system, which experi-
ments simply served to confirm. Tuned imped-
ance coupling was then abandoned, and a
standard tuned r.f. transformer employed, hav-
ing a secondary coil equivalent to the coil previ-
ously employed in the tuned impedance amplifier
circuit. This transformer was provided with ad-
justable values of primary coupling, and a series
of amplification measurements were made at
different wavelengths, the different primary
sizes providing varying degrees of selectivity.
Some representative amplification curves are re-
produced in Fig. i. The final transformer se-
lected employs ninety turns of No. 20 plain
enamelled wire wound on a threaded moulded
bakelite form, with turns spaced to provide low
356
RADIO BROADCAST
MARCH, 1928
r.f. resistance, this coil being tuned by a 0.00035-
mfd. variable condenser to cover the wavelength
band from 200 to 550 meters (1500 to 545 kc.).
The primary consists of 55 turns of No. 32
d.s.c. wire wound on a i^-inch tube slipped in-
side the secondary form, the primary winding
being at the filament end of the secondary. The
actual amplification obtained with this coil and
a ux-222 tube is shown on the accompanying
curves, varying from 11 at 550 meters to 35 at
200 meters for the stage. This value is very low as
compared to the mu of the ux-222 tube (about
250) but it is about all that can be realized
without adversely affecting the selectivity.
Actually, the figure of merit for the ux-222 tube
is only about twice that of a ux-2oi-A, despite
its misleadingly high amplification factor, so
that it is entirely proper that the actual amplifi-
cation obtained in practice from the ux-222 tube
should only be about double that of a ux-2oi-A
tube, at substantially equal values of selectivity.
As stated, throwing selectivity to the winds, the
gain could be almost redoubled — an impossible
condition in practice.
At this point, conclusions arrived at on the
laboratory bench were checked experimentally,
and it was found that shielding was not necessary
or even helpful in the four-tube circuit, provid-
ing the coils were spaced about twelve inches
apart, as has been done in the final receiver lay-
out. Precautions were taken to keep coupling be-
tween the r.f. amplifier and the detector circuits
at a minimum by proper bypassing, but even
with shielding it was found that "motor-boating"
was experienced when the detector was ad-
justed for critical regeneration. An analysis of the
ux-222 tube's action indicated that this was due
to changes in screen grid current reacting on the
detector, and vice versa, through the coupling
of the B battery. This was eliminated by an r.f.
choke in the screen grid lead. The operation then
became entirely stable, and the results obtained
in tests were quite gratifying.
The physical aspects of the set are well illus-
trated in the photographs. On the attractively
decorated walnut-finished metal front panel are
mounted the vernier drum dials controlling the
two o.ooo35-mfd. tuning condensers, which are
of the modified straight frequency-line — straight
wavelength-line — type. These drums read nearly
alike in operation, log definitely for any station
90 Turns 26 Enamel
2" Diam. 214" Long
200
250
300
350 400
WAVELENGTH
450
550
FIG. I
heard, and are provided with small lamp brackets
for illumination. Between them is the 0.00075-
mfd. midget condenser controlling regeneration,
and below it the jo-ohm rheostat controlling the
filament voltage of the ux-222 tube to regulate
volume. Attached to the rheostat is an auto-
matic "On-Off" switch turning the set on or off
at will.
The a.f. amplifier is unusual in that it employs
ux-112-A (cx-312-x) type tubes in both the first
and second stages. The first stage operates at 135
volts plate potential, with 45 volts C bias. These
values insure good handling capacity and a low
plate impedance, favoring good bass-note re-
production. The second stage should have from
135 to 1 80 volts of B battery with 9 to 12 volts
of C bias. At the higher value, the undistorted
power output is nearly 300 milliwatts, a respecta-
ble value. Of course, a ux-iyi (cx-3yi) tube
could be used with greater undistorted power
output, but in this case an output device should
be used. The total current consumption of the
whole set is about i 5 milliamperes, a very low
value even for battery operation.
The simplicity of the front panel is in keeping
with the general design of the receiver, which is
simple in the extreme. All parts not on the panel
are mounted on the wood sub-base. The antenna
coil and coil socket are at the left end, and the
r.f. transformer and its socket at the right end
The schematic diagram of the four-tube receiver which uses a screened-grid r.f. tube
MARCH, 1928
A FOUR-TUBE SCREENED-GRID RECEIVER
357
A CLOSE-UP OF THE FRONT PANEL
of the base. On the baseboard beneath the varia-
ble condensers are fastened the i.o-mfd. bypass
condensers. The positions of all other parts is
clearly illustrated in the photographs.
The actual parts used in the set are listed be-
low, and due to the possible complexities that
might arise on account of the ux-222 tube, it
would be well not to substitute other parts for
those specified, particularly as the wavelength
ranges might also be affected were parts of the
oscillating circuits changed in any way.
LIST OF PARTS
Li — S-M niA 190-550 Meter Antenna
Coil $ 2.50
Li — S-M 11480 190-550 Meter R.F.
Transformer 2.50
Two S-M 515 Universal Interchange-
able Coil Sockets 2.00
Ls, U — S-M 275 Chokes .... 1.80
TI, T2 — S-M 240 Audio Transformers. 12.00
Ci, Ci — S-M 320 o.ooo75-Mfd. Vari-
able Condensers 6 . 50
Ca — S-M 342 o.oooo75-Mfd. Midget
Condenser 1 . 50
Q — Sangamo o.oooi5-Mfd. Condenser .40
CB. Ce — Fast i-Mfd. Condensers . . 1.80
Ri — Polymet 5-Megohm Grid Leak . .25
Ro — Carter IR5O-S 5O-Ohm Switch
Rheostat 1 . 50
R3 — Carter Hi i-Ohm Resistance . . .25
Rt — Carter H 1 5 1 5-Ohm Resistance . .25
Polymet Grid Leak Mount .... .50
Ten Fahnestock Connection Clips . . .50
Four S-M 51 1 Tube Sockets . . . 2.00
Two S-M 805 Illuminated Vernier
Drum Dials 6.00
7 x i~xi Inch Wood Baseboard with
Hardware l . 50
Van Doom 7 x 18 Inch Decorated
Metal Panel 3.00
TOTAL $46.7;
The assembly of the set is very simple. The
condensers are first mounted on the dial brackets,
the drums attached, and the brackets fastened
on behind the front panel, which also carries the
dial windows and the small dial lamp brackets.
The rear of the panel should be scraped to insure
good contact between the panel and dial brackets
and the same precaution should be observed in
mounting the midget condenser so that its shaft
bushing makes good contact with the panel. The
switch rheostat should be thoroughly insulated
from the metal panel by means of two extruded
fibre washers.
All parts mounted on the base are screwed
down as shown, taking care that terminal 3 of
the antenna coil socket is to the right, and post
3 of the detector coil socket (r.f. transformer)
is to the left. The positions of these sockets,
audio transformers, etc., should be exactly as
shown, all being screwed down using roundhead
No. 6 wood screws from f inch to 1 1 inches (for
the r.f. chokes) long.
The wiring is simple, and clearly illustrated in
the schematic diagram, Fig. 2 in which all instru-
ments represented by symbols, carry exactly the
same numbers and markings in the diagram as
they do physically. All grid and plate leads are of
bus-bar, in spaghetti where necessary, while all
low-potential battery wiring is grouped along the
center of the base, and is of flexible hook-up wire.
After all wiring is done, the central group is
cabled, or laced, using waxed shoemaker's
thread. The Fahnestock clips are used for bat-
tery connections.
Testing and operating the set is very easy, and
involves the use of standard accessories as listed
below:
Two UX-H2-A (cx-3i2-A) Tubes
One UX-2OI-A (cx-3Oi-A) Tube
One ux-222 (cx-322) Screened-Grid Tube
One Western Electric Cone Loud Speaker
One 6-Volt A Battery
Three (or Four) 4;-Volt Heavy-Duty B Batteries
Two 4j-Volt C Batteries
With the batteries connected and tubes in
place, the rheostat should be turned full on,
which will give 3.3 volts to the ux-222 tube
under average conditions. With the midget con-
denser all in, the right-hand tuning dial should
be rotated until a squeal is heard (every squeal is
a station). The squeal should be tuned-in loudest
by proper adjustment of the left-hand and right-
hand drums. If the midget condenser is then
DET.
turned out slowly, the squeal
will disappear and the station
program be heard. Volume
may be controlled by the
knob, adjusting R2. In tuning
for local stations, the regenera-
tion- condenser can be left set
about one quarter in (far
enough out so that no squeals
are heard), but in tuning for
distant stations it should al-
ways be turned in far enough
to make the detector oscil-
late, and stations first picked
up as a squeal, and then
cleared up by turning the
regeneration condenser out
slowly to cut out the squeal
and get the program. The
set is most sensitive, the
operator will find, with the
regeneration condenser just
barely out of the squealing condition.
The rotor in the antenna coil may be adjusted
with the fingers to give greatest sharpness of
tuning on the left-hand tuning dial. When set
at right angles to the coil form, greatest selectiv-
ity and least volume will be obtained.
By using a 1 1 1 D antenna coil and a 1 140 r.f.
transformer in the coil sockets, the set will tune
from 500 to 1500 meters (600-200 kc.). A inE
and a I I4E coil will go from 1400 to 3000 meters
(215-100 kc.). To operate below 200 meters
(1500 kc.), the screened-grid r.f. amplifier is cut
out entirely and the antenna connected to post 3 of
the detector coil socket through a 0.0000-2 5-mfd.
variable midget coupling condenser, such as
the S-M 340. With this connection, using the
right-hand condenser dial only to tune the re-
generative detector, the three-tube set will tune
from 70 to 210 meters (4285-1430 kc.), with a
1146 coil, from 30 to 75 meters (10,000 to 4000
kc.), with a i I4C coil; and down to about 18
meters (16,660 kc.) if the stator winding of an-
other S-M 1 14C coil is cut down to four turns.
It is not desirable to use the ux-222 r.f. amplifier
stage below 200 meters, the three-tube portion
of the set being amply sensitive for all short-
wave reception.
It will be necessary to shunt the regener-
ation condenser with a fixed capacity of about
o.oooi mfd. to cause oscillation at the frequencies
below the broadcast band.
Of course, suitable A or B power devices may
be used with the set, glow-tube equipped B units
being most satisfactory.
FUSE CUP FOR
UX-222 TUBE
/ ~ f t I f f ~ Vy~
UT.A.F. BtAMP. Bt05 B+45 CAMP C-4& At A- L.S. ANT.
B-
Ct
GND.
SHOWING THE ARRANGEMENT OF APPARATUS ON THE BASEBOARD
RADIO BROADCAST
ome
oud
'THE richness of its selected woods instantly dis-
-1 linguistics this beautiful Bosch receiver (shown to
the left) from the commonplace. The model 87 is a
seven-tube table type receiver having four stages of
balanced radio- frequency amplification, a detector,
and two transformer-coupled audio stages. Exceptional
selectivity is possible, while provision is made for very
exact and gradual control of volume. Needless to say,
there is but a single dial for station selecting, and this
is graduated in kilocycles. Engineering features make
the receiver adaptable for all forms of power supply,
while there is a switch on the front panel which not
only controls the power for the tubes, but automatically
turns on or shuts off the battery charger, B supply
device, and all other power equipment. The model 87
is priced at $195.00
A NOTHER unique loud
j*- speaker by Amplion — the
"Shield." The unusual lines and
artistic appeal of the "Shield"
lend charm to whatever sur-
roundings it may be required
to form a part of. The cabinet
construction is entirely new in
radio reproducer construction.
The new-process embossed wal-
nut panelling is attractively
curved, and combines a grille
front and back. The cone has a
diameter of 16J inches. Height.
22 inches. The Amplion
"Shield" retails at $67.50
A NEWCOMER to the
•**• ranks of the electric set is
depicted above — in the form of
the Roister 6J table type re-
ceiver. The new a. c. tubes make
possible the 6J, which is a
six-tube receiver employing
three r. f. stages, and having
built-in power equipment. AH
that is necessary to start the
set operating is to insert the
tubes, connect a loud speaker,
antenna, and ground (or loop),
and plug in to a light socket.
Tuning is accomplished by
means of a single control. The
6J retails at $250.00
MARCH, 1928
and
A BEAUTIFUL example of what Federal, Buffalo,
•*»• is offering — the E45-60 "Ortho-sonic." While
the price ($460.00) of the model shown is a little high
for the average man's purse, it is worth while to
remember that Federal has an equally attractive
five-tube table model for only $100.00. The picture
shows a completely a. c. operated six-tube receiver
with a built-in loud speaker. Tuning is accomplished
by means of a single knob, and the graduated scale
is illuminated to facilitate tuning. Its remarkable
selectivity is a feature claimed for the E45— 60, but
this is not obtained at the expense of tone quality.
The height is 54£ inches, the depth is 17 i inches, and
the width is 30J inches. The cabinet is an original
design in figured walnut with overlay of fiddle-back
mahogany. The knobs and pendants are burnished.
'T'HE new Atwater Kent
-*- a. c. receiver is shown
in the illustration above. It
is indeed a remarkable piece
of engineering — a complete
radio installation, with the
exception of the loud
speaker— in a metal cabinet
7J inches high and 17 J
inches long. The apportion-
ing of the six tubes is as fol-
lows: Three r. f. stages, de-
tector, two transformer-
coupled audio stages. Single
control tuning is featured,
and the built-in power unit
is shielded from the rest of
the receiver. Absolutely no
batteries are necessary for
operation. The price of the
Model 37 Atwater Kent
a. c. receiver is $88.00
A WELCOME newcomer
to the loud speaker
field is pictured to the left.
It is the "Air Chrome," a
product of the Air-Chrome
Studios, Irving ton, New
Jersey. Tests in RADIO
B ROAD CAST Laboratory
have shown this loud
speaker to be capable of
exceptional tone reproduc-
tion, while its efficiency is
claimed by the manufactur-
ers to exceed that of the
best cones on the market.
The "Air-Chrome" is not a
cone loud speaker although
in appearance it somewhat
resembles one. The console
model shown retails at
$65.00, there being a choice
of design in so far as the
tapestry front covering is
concerned . The loud
speaker without cabinet is
priced at #25.00
359
Armchair Engineer
Keith Hermey
Director of the Laboratory
TO THE RIGHT
This illustration shows a corner of the RADIO BROAD-
CAST Laboratory. As the accompanying article explains,
it is not necessary to have a laboratory or costly in-
struments at ones disposal U) conduct interesting radio
experiments. A piece of paper, a pencil, and a slide rule
are sufficient to enable one to learn a lot about the design
and operation of radio circuits, etc.
THERE are several interesting and perhaps
instructive investigations of receiver de-
sign that one may explore without a
laboratory full of expensive apparatus. A slide
rule, a pencil, and some paper, are all that are
necessary.
For example, let us consider a conventional
two-stage transformer-coupled audio amplifier
with an output device to protect the loud speaker
from the d.c. plate current of the last tube. There
are two methods of connecting the loud speaker
to this amplifier, as shown in Figs, i and 2. The
turn ratio of the first audio transformer let us
suppose to be Ti, and that of the second to be T2;
(AI and u.2 are the amplification factors of the
first and second tubes respectively. The detector
of this set-up also secures its plate current from
a common source, represented by the box at the
left. In the first case the loud speaker is connected
to the negative lead of the final amplifier tube.
Now let us suppose that a looo-cycle note comes
into this system producing an a.c. voltage of 50
across the output choke, which, if it is very good
indeed, will have an inductance of 40 henries,
or an impedance at 1000 cycles of about 250,000
ohms. If the loud speaker has an impedance of
only 4000 ohms at this frequency, most of the a.c.
current will flow through the loud speaker, as is
desired. This 50 volts across the choke is arbitra-
rily chosen, and the absolute value does not mat-
ter for our present discussion. Fifty volts is
probably higher than is encountered in practice.
Fifty volts across the 250,000 ohms impedance
of the choke will send through it a current of
about 0.2 milliamperes which, to return to the
filament of the last tube, must go through the
B battery leads, through the 2-mfd. con-
denser across the plate supply unit, and
thence to the filament. The 2-mfd. bypass con-
Ill 111
[III
denser has an impedance of about 80 ohms at
looo cycles (this may be found by reference to
laboratory sheet No. 127, in the September,
1927, RADIO BROADCAST) and the voltage across
it, obtained by multiplying the impedance by
the current, is roughly 0.016 volts, most of which
is impressed across the primary winding of the
first audio transformer because of its high im-
pedance compared to the plate impedance of the
tube. This tone will go through the amplifier,
and will be amplified accordingly, and if there
are an odd number of stages securing plate volt-
age from this common source, say a detector and
two audio stages, and if the transformer prima-
ries are "poled" correctly, the final voltage ap-
pearing across the output choke will not only be
amplified but will be in phase with the original
voltage.
The problem is to find out how strong this
voltage becomes by going through the amplifier.
If the transformers are 3:1 each and the first
tube has an amplification factor of 8, and the
final tube (an ux-iyi orcx-jyi) an amplification
factor of 3, the maximum amplification will be
the product of these factors, or 3 x 3 x 8 x 3, or
roughly 200. In the plate circuit this voltage will
divide, part being lost on the 2ooo-ohm plate
impedance of the output tube and part appearing
across the 4Ooo-ohm output impedance (choke
and loud speaker). As a matter of fact two-thirds
of the voltage will appear across the choke so
RADIO BROADCAST Photograph
that the voltage finally appearing there will be
0.016 x 200 x f, or about 2.1. In other words, the
original 50 volts which appeared across the out-
put choke have returned in phase but have been
decreased to 2.1 volts.
Now let us consider Fig. 2. Here all a.c.
components in the plate circuit of the last tube
must go through the plate supply before they can
return to the filament of the power tube. The
impedance of the choke is lowered by the shunt
impedance of the loud speaker, say to 4000 ohms,
and if the same 50 volts appears across this load
impedance the a.c. current through it will be
50/4000 or 12.5 milliamperes, which will pro-
duce a voltage of I ,o across the 2-mfd. condenser,
and this finally appears as i.o x 200 x f, or 135,
volts. Since this "feedback" voltage is greater
than the original voltage, and may be in phase
with it, an endless chain results and the amplifier
turns itself into an excellent oscillator, singing
at some frequency determined by the constants
of the circuit, usually at the point where the
maximum amplification of the audio transform-
ers takes place, say about 5000 cycles.
This is exactly what happens in an oscillator;
part of the output is fed back to the input so that
it is amplified through the tube and again im-
pressed across the output.
In the amplifier under discussion the feed-back
is caused by the impedance of the plate supply
unit which is common to all of the amplifier
stages. If the bypass condenser is increased
(which decreases the total impedance) the tend-
ency to oscillate becomes less, since the feed-
back voltage impressed upon the input to the
amplifier decreases with decrease in common im-
pedance. In the Laboratory, a high-quality two-
stage transformer-coupled amplifier with detec-
tor getting its plate supply from the same source
as the amplifier sang terrifically when a resistance
of 37 ohms was inserted in the negative B battery
lead when the loud speaker was connected di-
rectly across the output choke-condenser com-
bination. With one side of the loud speaker con-
nected to the filament, a total of 670 ohms in the
negative B lead could be tolerated before the
amplifier sang.
Bypassing the common resistance with a
2-mfd. capacity, the tolerance in common im-
pedance was increased, so that with the loud
speaker across the output choke, 200 ohms did
MARCH, 1928
not cause singing, and in the other case 2000
ohms could be tolerated.
This investigation indicates that, when a
condenser-choke output device is used, the loud
speaker should connect directly to the negative
A, or to the filament center tap if a.c. operated,
of the last tube. U'hen an output transformer is
used, corresponding to the case where the loud
speaker is connected across the output device,
and all of the a.c. components of the plate cir-
cuit must go through the plate supply, a large
bypass capacity should be used. This is necessary
when B batteries or plate-supply units are used,
for the latter have a rather large a.c. impedance
at all times, and the former have considerable a.c.
impedance when they have been used for some
time.
Now continuing our investigation, let us look
at this two-stage amplifier again. Let us suppose
that at some frequency the loud speaker repre-
sents a load to the last tube which takes as much
power as a pure resistance equal to twice the
impedance of the tube. This is an assumption
easily satisfied, and since tube experts in Eng-
land, and of the General Electric Company in
America, have shown that the maximum un-
distorted output will be attained under these
conditions, we shall start off on the right foot at
least.
If the loud speaker impedance is twice that of
the tube, f of the total a.c. voltage appearing in
the plate cicuit will be impressed across it.
Now the maximum voltage amplification of
the amplifier, which we shall call A, is as follows,
when T represents the turn ratio of the trans-
formersand[j. theamplifkation factor of the tubes:
A = Ti x HI x Ti x |A2
and since two-thirds of this appears across the
loud speaker, the voltage across the latter is:
Ei.s. = J x A x Ed
where Ed is the a.c. voltage available across the
primary of the first audio transformer.
Actually the loud speaker voltage will be less
than this figure, since the full transformer ratio,
and amplification factor of the tube, cannot be
realized, but good design will make it possible to
approach this maximum voltage amplification.
Now, looking at a booklet on tubes, we note
the maximum undistorted power output of a 171
type tube is 700 milliwatts, that the amplification
factor is 3, and that the plate impedance is 2000
ohms. Then at the frequency chosen, the loud
speaker impedance will look like 4000 ohms re-
sistance to the tube, and since the power, W0,
into it is:
Wo = I'Z = (£!.«.)»
—
or El.s. = v'Wo x Z = 1/0.7 x 4000 = 53 volts r.m.s.
where Z = loud speaker impedance, E|.s. = volt-
age across loud speaker, and I = current through
loud speaker, we see that there must be 53 volts
r.m.s. across the loud speaker to put 0.7 watts
into it, and since this is but two-thirds of the
total a.c. voltage in the plate circuit of the last
tube, the total is f x 53, or 79. 5 volts.
Since the amplification factor of this tube is
3. 79-5 •*• 3 = 26.5 r.m.s. or 37.4 peak volts
(since peak volts equals 1.41 times r.m.s. volts)
which must appear on the grid of the power tube,
so that when the booklet states that the grid
bias should be 40.5 it shows that our calculations
are not far wrong.
Now let us use a ux-2Oi-A(cx-3Oi-A) type tube
as the first amplifier and two 3:1 transformers
and calculate:
A =3x8x3x3 = 316
which shows that the maximum voltage am-
THE ARMCHAIR ENGINEER
plification of the amplifier, from input to the
first transformer to the plate circuit of the final
tube, will be 216, and since we need 79.5 volts
in the output tube plate circuit the voltage neces-
sary across the primary of the first audio trans-
former will be:
79.5 -^ 216 = 0.368 = Ed
This, then, is the voltage which the detector
must supply to the input of the audio amplifier.
Now in place of thelow-mu low-impedance tube
in the output or power stage let us use a ux-2io
(cx-3io), which has a mu of 8 and an impedance
of 5000 ohms, or a ux-i 12 (cx-312) which has the
same characteristics. In this case we must use a
step-down output transformer of 1.58 turns
ratio (1/10,000*4000) so that our 4Ooo-ohm
loud speaker will look like 10,000 ohms to the
power tube. Of course the same voltage will be
necessary across the loud speaker to deliver 700
milliwatts to it, i.e., 79.5, which, multiplied by
1.58, the turn ratio of the output transformer,
gives 125 as the voltage which must appear in
the plate circuit of the final tube.
In this case, however, the voltage amplification
of the amplifier is increased to:
3x8x3x8 = 575
and the detector output must be:
125 -f- 575, or 0.218
and the input peak volts to the last tube must be:
1 25 -j- 8 = 22, approximately
This calculation shows that the detector must
deliver only 0.218 volts compared to 0.368 when
Detector
361
(cx-3io) tube is substituted for a ux-i7i (ex-
370-
There is one more point which our computa-
tion may bring out — the reason why such high
voltages are necessary for the plates of ux-2io
(cx-3io) type tubes. If 40 volts C bias is used
on a ux-171 (cx-37i) type tube, 180 plate volts
are needed. This figure may be calculated by
multiplying 40 by 3, the mu of the tube, and by
what we may call a factor of safety of 1.5, or
40 x 3 x 1.5 = 180. Now, when we use a ux-2io
(cx-3 10) tube with a C bias of 22 the calculations
say 22 x 8 x 1.5 = 263 volts. If, however, the
detector delivers 0.368 volts the C bias on the
last tube must be 37.5 volts which, in turn, de-
mands a plate voltage of 8 x 37.5 x 1.5 = 450,
and there you are.
Our little investigation into amplifier problems
has not taken us from our armchair, and all we
have needed to determine several interesting
facts is a pencil, some paper, and if we possess
one, a slide rule. We have learned that output
devices, if choke-condenser affairs, should be so
connected that the a.c. plate currents return
directly to the filament of the last tube, and that
if we use an output transformer, or if the a.c.
currents do not return directly to the filament,
we must bypass as heavily as we can afford the
common impedance of the plate supply.
We have learned that we can estimate the
maximum voltage amplification of an amplifier
by multiplying the turn ratios of the transformers
and the amplification constants of the tubes
together, and that for distortionless amplification
the loud speaker should have roughly twice the
impedance of the tube. Under these conditions
the voltage across the loud speaker is two-thirds
of the total a.c. plate voltage in the plate circuit
FIG. 2
a 171 type tube is used to furnish the same
amount of power, 700 milliwatts, to the loud
speaker. If, however, the detector can deliver to
the input of the amplifier 0.368 volts without
distortion, due to detector overloading, the
power put into the loud speaker will be:
Wo = (Ed x A x j)« = 1.4 watts
10,000
In other words the 210 type output tube will
deliver exactly twice the power to the loud
speaker as is obtained when a low-mu low-
impedance tube is used. This difference is entirely
due to the higher amplification factor of the tube.
The results of this simple comparison between
output tubes are several. In the first place it
means that the detector tube can be worked with
lower input voltages, the r.f. amplifier need not
be "geared up" so high, weaker stations may
"load up" the amplifier, and it shows in some
measure why more volume results when a ux-2io
of the last tube, and the detector output required
may be calculated by dividing the a.c. voltage
in the last tube's plate circuit by the amplifica-
tion of the amplifier.
We have learned that a high-mu tube in the
final stage of an audio amplifier delivers con-
siderably more power, and requires considerably
smaller input voltages to deliver the same power,
compared to a low-mu tube. We have learned
why such high plate voltages are required on
power amplifiers using tubes with high values of
amplification factor. Throughout this armchair
investigation we have had to make certain as-
sumptions that will make a "hard-boiled"
engineer smile. We know but little of how a
loud speaker looks to a tube, we have not both-
ered with vector voltages, we have not tried to
be mathematically exact. But we have shown
that with a slide rule, a pencil, and some paper
we can delve into the subject of receiver and
amplifier design.
CJRM,
Pioneer Picture
Broadcasting
Station
By Edgar H. Felix
TO THE RIGHT
The illustration shows Mr. D. R. P. Coates, manager
of CJRM, with his picture transmitting apparatus
THE series of articles in RADIO
BROADCAST describing the Cooley
Rayfoto system, have brought to
its editors a surprising number of letters
from experimenters who have already
worked with telephotography of one kind
or another. These, together with the thou-
sands of letters, from those who plan to
build Cooley recorders, make it appear
quite certain that there will soon be a
definite new experimental field — the mak-
ing of radio pictures in the home. Indeed,
we know of quite a number of Cooley
outfits already in operation, even though,
as we write, broadcasting is only spasmodic.
Perhaps the most interesting broadcast-
ing experiment which has come to light is
that of CJRM, of Moose Jaw, Saskatchewan,
of which Mr. D. R. P. Coates is manager.
An active Radio Picture Club, formed un-
der his leadership, is already in existence,
and a group of ardent workers are busy
improving their existing picture reception
apparatus. The Radio Picture Club is
installing a Cooley picture receiving system
but, in the meanwhile, is working with a
somewhat more crude, picture system.
The transmitting apparatus, built by
Mr. Coates, is a remarkable example of
resourcefulness, for the facilities available
are very limited. The transmitter is made
with a cylindrical record phonograph as its
basis. A copper plate is mounted on the
drum, taking the place of the conventional
record. On the copper plate, the picture to
be sent is pasted in silhouette or outline
form. A stylus passes over the copper drum
and completes the circuit for an audio-
frequency "howler," the output of which is
used to modulate the transmitting carrier.
A synchronizing signal, using the stop-
start system, also used in the Cooley re-
ceiver, serves to re-check the synchroniza-
tion at the beginning of each revolution.
Reception is simply a reverse of the
transmitting process. A stylus makes a
continuous black line by pressing on carbon
paper laid over a sheet of white paper,
on a revolving cylinder. When the "howler"
signal comes in, the stylus is lifted, thus
giving a positive silhouette. Nothing sim-
pler than this system can be imagined, but
Mr. Coates tells us it was widely used by
the Germans during the War for transmit-
ting military information.
Owing to the fluctuations in drum speed,
the synchronization is not good. The dif-
ficulty lies in the fact that the phonograph
motor is brought to a full stop by the
synchronizing system and it does not al-
ways resume speed at the same rate when
released by the synchronizing control.
Naturally, the Radio Picture Club looks
forward to the receipt of its Cooley re-
corder equipment because that will over-
come these difficulties. An ingenious clutch
and locking arrangement makes good syn-
chronization easy with the Cooley system,
and it is independent of the operation of
the phonograph motor. The Cooley stop-
start system, and the mechanical unit which
is a part of it, is so built that the load on
the phonograph motor does not change
when the light aluminum drum is stopped
at the end of each revolution by the stop-
start mechanism. A clutch allows the motor
and the turntable to continue revolving,
so that there is little or no speed variation.
A PREDICTION
IT IS pleasing to see such enterprise in
far-away western Canada. A rather
interesting point in Mr. Coates' letter is his
point of view with regard to the broad-
casting of pictures:
"The present position of the radio pic-
ture art reminds me very much of the posi-
tion of radio seven or eight years ago. 1
believe that we shall find amateurs dabbling
in it for a while and that this will gradually
evolve until receiving apparatus is im-
proved and popularized. If we are to follow
the line that was taken by broadcasting,
we must go ahead and put pictures on the
air, no matter how simple and elementary,
so that people will be encouraged to build
apparatus for the purpose of reproducing
the pictures. The fact that there is no one
around here yet able to reproduce the pic-
362
•
\
£
h
tures does not deter me at all, because I
remember broadcasting years ago when our
audience was very limited indeed. If we
had waited for a big audience before going
ahead with broadcasting, we would not be
very far advanced at the present time."
Not only do we find that American sta-
tions have a similar point of view, but in-
quiries have come from broadcasting sys-
tems, even as far distant as New Zealand,
desiring to put Cooley pictures on the air
so as to give experimenters an opportunity
to develop the picture receiving art.
Mr. Coates is the originator of a system
of broadcasting "pictures" of the constel-
lations as an aid to the study of astronomy
He terms these "stellagraphs." The Stella-
graphs were broadcast by cooperation with
a local newspaper which printed a graph
paper suitably marked up so that any posi-
tion on the paper could be given by two
reference numbers. A third number in the
code indicated the intensity of the star so
that a lecturer on astronomy could enable
his radio listener to illustrate and draw
out the principal constellations of which he
was speaking.
The precedent set by Mr. Coates, in
suggesting the formation of a radio picture
club, is one which should be encouraged.
An individual experimenter may hesitate
to spend a hundred or a hundred and fifty
dollars to go into picture experimentation,
but, if five or six club together, the in-
dividual cost is small and the experimenters
have the benefit of their combined facilities
and ingenuity. The Cooley system is suf-
ficiently well developed that it can hardly
be termed a hazardous experiment and the
amount of special equipment required is
not particularly great. We have been ad-
vised that a number of substantial prizes
will soon be offered for the best Cooley
picture reception, through the courtesy of a
large radio manufacturer who believes in
the future of picture transmission and re-
ception. Naturally, the leaders and pioneers
who have the greatest experience, are the
most likely to be successful in such a con-
test.
"Our Readers Suggest
OUR Readers Suggest. . ." is a regular feature
of RADIO BROADCAST, made up of contri-
butions from our readers dealing with their experi-
ences in the use of manufactured radio apparatus.
Little, "kinks, " the result of experience, which give
improved operation, will be described here. Regular
space rates will be paid for contributions accepted,
and these should be addressed to "The Complete
Set Editor," RADIO BROADCAST, Garden City, New
York. A special award of $10 will be paid each
month for the best contribution published. The
pri^e this month goes to Fred Madsen, Chicago,
Illinois, for his suggestion entitled "A.C. Tube
Operation Without Rewiring"
— THE EDITOR.
A Distortion Indicator
THE average loud speaker is blamed for a
multitude of sins which really should be laid
at the door of other parts of the receiving
circuit. It is not generally understood that a rattle
almost identical with the mechanical rattle of an
overloaded loud speaker can be caused by a
distorting amplifier. The sound of the strain,
depending upon the extent of distortion, repro-
duces in a manner quite deceiving to other than
experts, all the various forms of blasting ex-
perienced in faulty loud speakers.
If you are experiencing difficulties of this
nature, it would be well to investigate the char-
acteristics of your amplifier before discarding
your loud speaker as defective. The procedure is
simple, as the following illustrations indicate.
A milliameter capable of carrying the current
to the power tube (a zero-to-25 milliamperes
meter is about right) can be inserted in the plate
circuit of any tube, providing a fairly reliable
indication as to whether or not that particular
tube is introducing distortion. The circuit is
shown in Fig. I.
Any deflection on the meter scale with incom-
ing signals is evidence that the tube in the plate
circuit of which it is included is rectifying, ;'. e.,
distorting. This distortion can be eliminated by
proper biasing. If the needle kicks down, more C
battery should be used. If the needle kicks up,
the C potential should be lowered. If the C bias
,is correctly adjusted no movement whatever
should be noticed in the needle when a signal
of moderate strength is being received. Any
movement, up or down, indicates distortion,
and the C battery should be adjusted in an
endeavor to stabilize the needle.
Quite naturally, every tube has a maximum
distortionless output with a given plate voltage,
and when this limit is exceeded by applying too
powerful a signal to the grid, rectification and
distortion will result, regardless of the grid bias.
; It will be at a minimum, however, if the grid
i battery is correctly adjusted. If more than a
. slight flicker of the needle is indicated at the
; desired volume, a higher plate voltage or a
, power tube of greater handling capacity should
be employed.
The correct biasing of every tube in the
audio-frequency amplifier can be effected in this
manner. As the grid swing applied to other
than the last or power amplifier stage is relatively
small, however, a rough adjustment (that is the
application of approximately the bias recom-
mended by the tube manufacturer for the plate
voltage used) will be sufficient in these preceding
stages.
PHILIP RILEY
Cincinnati, Ohio.
STAFF COMMENT
MR. RILEY'S distortion indicator is of
particular utility when the plate voltage
is obtained from a B power-supply device. The
voltage supplied by such an arrangement varies
with the load, and it is always more or less
indeterminant. The correct bias changes with
variations in plate potential, so an arbitrarily
designated bias voltage rarely affords the
maximum distortionless output.
Still more undistorted power can often be
obtained from a given amplifier-loud speaker
combination by the use of an output device
A.F. Tube
(usually power)
Oc (Variable)
FIG. I
A simple hook-up to indicate distortion
connected between the loud speaker and the
power tube, because the relatively high d. c.
resistance of the loud speaker lowers the actual
voltage on the plate of the tube, and the use of an
output device therefore results in a greater po-
tential being applied to the plate. The loud
speaker should never be placed directly in the
plate circuit when there is a current of more than
10 mils, flowing. Aside from the relatively power-
ful current surges, which may damage the
delicate windings, the steady direct current
tends to draw the armature toward one of the
pole pieces, causing the mechanism to hit
and rattle on loud signals. There are several
commercial output devices which may be in-
stantly connected between loud speaker and
power tube. Such filters are manufactured by the
National Company, Silver-Marshall, Muter,
Ferranti, General Radio. Samson, and Federal, etc.
363
"Motor-boating"
I HAVE a seven-tube set which employs
*• one stage of resistance-coupled audio am-
plification and I have been trying for some time
to find a B supply device that would not "motor-
boat," but without success. It was quite costly
to operate the set with a 171 power tube with
B batteries so I conceived the idea of using a
combination of B battery and B device. It is
well known that the r. f. stages and the power
tube take most of the B current, so I use the
B device on those taps and the battery on the
resistance coupled tap. This arrangement is very
satisfactory and is giving fine results. The drain
on the B battery is small, hardly noticeable in
fact, while the B device operates the tubes
drawing the heavy current. Fig. 2 tells the
story. The negative of both B supplies are
common.
C. R. YARGER
Shenandoah, Iowa.
STAFF COMMENT
THE method suggested by Mr. Yarger hits
directly at the very source of " motor-boating,"
i. e., a common B supply circuit through which
coupling may be effected. The arrangement
suggested by our correspondent will probably
be effective in the most violent cases of "motor-
boating."
Unfortunately, the purpose of B battery
elimination is more or less defeated in this
scheme. The current drain on the B battery is, as
Mr. Yarger points out, nevertheless very slight.
The connection of. an Amrad Mershon electro-
lytic condenser across the high-voltage and
negative terminals of the power supply of a
motor-boating receiver, will, in the majority of
cases, be equally effective in eliminating this
disturbance.
A glow tube, connected according to the
directions given in "Our Readers Suggest" for
February 1928, is also effective.
To Resistance
Coupled Stages
FIG. 2
A simple way of eliminating "motor-boating"
in all circuits. The troublesome circuit is fed
from a separate plate source
364
RADIO BROADCAST
MARCH, 1928
A. C. Tube Operation Without
Rewiring
IN THE November, 1927, issue of RADIO
BROADCAST, "Our Readers Suggest" depart-
ment gave directions for the rewiring of a
standard radio-frequency receiver and an
Atwater Kent 35 for the use of Arcturus alternat-
ing-current tubes.
This rewiring necessitated changes in the
filament and radio-frequency circuits of such
nature that many comparatively experienced
fans would hesitate to make. It is extremely
difficult to gain access to the wiring of many
commercial receivers, and some enthusiasts,
adept with the soldering iron and pliers, are
reluctant to tamper with a ready-made job.
1 have an Atwater Kent 35 receiver which I
desired to adapt for a. c. operation without
touching the actual wiring of the receiver. I
succeeded in doing this along the lines suggested
in Fig. 3, and in the accompanying photograph,
Arcturus a. c. tubes, which are of special con-
struction, being used for the purpose. The
arrangement, briefly, requires the sawing off of
the two heater prongs from the a. c. tube bases
and soldering lugs in their places, to which the
heater connections are made.
The mechanical changes are clearly illustrated
in the photograph. Though the prongs are
sawed off at the bottom of the base, sufficient
metal remains for firm soldering of the lugs.
The prongs should be carefully tinned before the
lugs are soldered to them in order to insure
perfect connection with the heater leads. See
that the leads from the elements within the tube
are not sawn off when the prongs are removed.
They should be firmly soldered to the remaining
prong stubs.
The original sockets in the receiver hold the
tubes with sufficient rigidity by means of the
plate and grid prongs, which remain unchanged.
Flexible Braidite is recommended for use in the
rewiring of the heater circuits. This can be
obtained in different colors facilitating con-
sistent heater connections. The same side of
every heater (as determined by their relation-
ship to the pin on the tube base) should be
connected together throughout the circuit.
Looking at the bottom of the base with the
pin toward you, the left-hand prong is filament
plus on a d. c. tube. On the Arcturus a. c. type
tube it is a combined heater and cathode con-
nection. It is good practice to wire these prongs
with red Braidite, using black for the other
heater leads. Both leads should be twisted, as
shown in the photograph. A separate wire is
brought out from the cathode of the detector
tube to which B minus, C plus, and D minus
WITH HEATER PRONGS REMOVED
An accompaning contribution explains how the
Atwater Kent model 35 receiver may be arranged
for a.c. tube operation. The main mechanical
change requires that the two heater prongs be
sawed off and replaced with soldering lugs
are connected. The expression "D" refers to
the special biasing battery necessary for the
detector tube, the grid of which is made
positive. The fundamental diagram is shown
in Fig. 3.
An Electrad Royalty 2OO,ooo-ohm resistor,
shown, in Fig. 3, in dotted lines, must be
FIG. 3
Adapting the Atwater Kent Model 35 receiver for a.c. tube operation without making any major
changes to the wiring of the receiver itself. The detector grid leak return is broken at X, and brought
down, according to the dotted line, to the special " D" plus lead. Dotted lines also show the position
of the volume control. The wiring below shows the external wiring to the heaters of the tubes.
Posts Nos. I, 2, and 3 are short-circuited, and no connections whatever are made to them
connected across the secondary of the first
audio-frequency transformer where it func-
tions as a volume control. This volume con-
trol is mounted externally. The only change
actually made in the receiver itself was a slight
alteration in the detector grid circuit. The grid
leak was removed and a piece of heavy wrap-
ping paper inserted in the prong toward the
back of the receiver. A small piece of cop-
per foil, to which a flexible lead was sol-
dered, was laid on top of the wrapping paper
so that no connection was made to the prong.
The copper foil, however, makes contact with
the cap of the grid leak when inserted. This
lead was brought out along with the other
wires and marked "D" plus 4.5 volts. This opera-
tion automatically opens the connection between
the grid leak and the center of a resistance which
exists across the filament of the detector in this
model of the Atwater Kent receiver.
The tubes were placed in the sockets and
the set was ready for operation.
Minus 1.5 volts of C battery were connected
to the ground post and minus 22.5 volts of C
battery were connected to the power tube. If it
is possible to tap off between 4.5 to 9 volts
on your first B battery or from the B supply
device, the D plus lead from the detector grid
leak may be lead directly to such a tap, otherwise
it will be necessary to insert a 4.5-volt battery,
plus to the grid leak and negative to the B
minus.
A plate potential of 90 volts is applied to the
plates of the radio-frequency and first audio
tubes and 180 volts to the plate of the power
tube. Arcturus type A-C 28 tubes are used in the
first radio-frequency amplifier and in the first
audio amplifier. An Arcturus detector type A-C
26 tube is employed in the detector socket
and a power tube type A-C 30 in the power stage.
The A plus and A minus leads from the original
Atwater Kent receiver are short circuited.
Fifteen volts a. c. is applied across the twisted
heater wires. This is obtained from an Ives type
225 step-down transformer.
The arrangement as applied here can be
adapted to practically any circuit with very few
changes.
FRED MADSEN
Chicago, Illinois.
STAFF COMMENT
THE arrangements suggested by Mr. Madsen
are quite practical. As he suggests, there are
doubtless many instances where the "harness"
system is preferable to actual set changes.
Commercial "harnesses," which are very
similar to the arrangement described, are being
placed upon the market to adapt various
receivers to different types of a. c. tubes.
In some receivers the prongs of the tube
are inserted in metal eyelet holes which protrude
a fraction of an inch or more above the sur-
face of the sub-panel. The presence of these
eyelets, which are connected electrically to
some part of the circuit, will make the receiver
inoperative unless care is taken to see that the
sawed off prongs or the soldering lugs do not
touch them. This is easily accomplished by the
use of a pasteboard disk cut to size and punched
with two holes to pass the grid and plate prongs.
In some instances it will be more desirable to
control volume by means of a zero to 500,000
ohm Electrad Royalty or Centralab resistor
connected across the radio-frequency secondary
preceding the detector tube. Not all variable
resistors of the required ohmic value will work
in this arrangement due to the relatively high
capacity of several makes.
The Listener's Point of View
IF YOU LIKE
E HAVE utilized this department be-
fore, in fact as recently as last January,
to make tearful entreaties to the radio
lords to furnish more straight instrumental
music. If we may be said to have any platform,
that is its principal plank.
In one of these articles we advanced the point
that listening to symphonic music via the radio
has at least one distinct advantage over listening
to the same in a symphony hall, namely: the
orchestra cannot be seen. With none of the
modesty proper to the father of an idea we aver
that the point is an excellent one and well worth
dragging out again.
The universal custom of lighting up concert
halls with a dazzling effulgence of electric light
has about as much to recommend it as would the
equipping of art galleries with a fire siren and a
ship's bell beside each picture. It is our occasional
custom to attend the Friday afternoon concerts
of the Chicago Symphony Orchestra, frequented
presumably, by the very cream of Chicago's
music lovers. Here, as elsewhere, the blaze of
light system prevails. In the course of the con-
cert, a surprisingly large proportion of the audi-
ence may be observed to be taking advantage of
this lavish pyrotechnical display in any one of
three ways: (a) reading their programs, (b) em-
broidering, (c) sitting on the edge of their chairs
better to watch the conductor. Anyone who can
thus disport himself before Brahms or Beethoven,
or even Tschaikowsky, and then later claim that
he "heard" the music is either a physiological
phenomenon or a prevaricator.To follow honestly
the development of a piece of music requires so
high a degree of concentration that it is absurd
to imagine that an attention divided between the
eye and the ear is sufficient. We have essayed the
more or less successful subterfuge of slumping
down in the seat with one or the other hand
before the eyes, but this lays us open to the
suspicion of our neighbors that we are (a) a silly
fellow feigning intense absorption, (b) asleep.
Extinguishing the lights would solve the problem,
but this the persons who run concert halls will
not do.
To attack the reading of program during a
concert is a ticklish proposition. It is "done"
by our very best people. Tell them they are
demonstrating their ignorance of music by so
doing and they will look at you aghast.
It is perfectly possible to look at, and enjoy,
a picture without knowing a thing about the
painter's life, in fact without even knowing who
painted it. This is done constantly, even by
connoisseurs. Music, a purer art than painting,
is even more independent of its composer and
he may be even more easily ignored.
Or it may be protested with still more vigor
that "you have to watch the conductor really to
'feel' the music unfolding!" This likewise is
pishposh. The gesticulations of the conductor,
however graceful or dramatic they may be, have
little to do with the music as music. They exist
for the purely technical purpose of evoking the
proper sounds at the proper time, and the tech-
nique of putting the thing across is no more your
business than would be the trade name of the
pigments your artist used in his painting.
Perhaps we seem to wax too wroth and to be
making a mountain out of a mole hill in our
vehemence against optical assimilation of music.
By JOHN WALLACE
But our fury is aroused by the fact that the peo-
ple who so insult good music in the concert halls
are supposedly the very topmost strata of music
lovers — the highbrows, no less! If the highbrows
of the nation don't know how to listen to serious
music what about the masses?
It would seem, perhaps, that the case we are
making out for proper concert listening is no
very happy one, and that we would place it on
the same tedious and exacting plane as listening
to a class-room lecture on philosophy or astron-
omy. This is not entirely true. Certainly we have
to concentrate just as much — a symphony by
Brahms has just as much meat in it as any four
chapters from Kant's Critique — but the concen-
tration can. be entirely effortless.
Herein, as we have said before, lies the ad-
vantage of radio. Given a good receiver and a
symphony orchestra properly "picked up" and
transmitted and you are all set for a concert
EUNICE WYNN OF KFWB
Miss Wynn is a regular artist of the Hollywood
station of Warner Brothers, KFWB. Cute songs,
she sings, according to the station
which may nine times out of ten be more en-
joyable than one in a mazda-equipped concert
hall. You can don your slippers, turn off the
lights and park in an easy chair— three separate
counts wherein "second hand" radio has it over
the first hand thing: With your own private
stage thus set you are in an ideal position really
to "hear" the music with a fullest possible
realization of what it really has in it.
A popular delusion exists that music should
caress the listener and lull him into a pleasant
state of lethargy, and that he need do nothing
but just "set" and let the vague tides of sound
wash over him soothingly. The answer to this is
age old: the artist can go only half way.
The reward for going half way is the surpris-
ing discovery that there are tasty bon-bons
waiting at the half-way point whose existence
was never even suspected.
Now our point is that it is easier for the neo-
phyte to cultivate an understanding of serious
music by listening to it on the radio than by
going to concert halls — simply because he can
do it with less distraction.
Devious and many are the ways suggested for
learning "how to appreciate music." Most of
365
them involve too much work (they are the best
ones). Others go in too much for the technical
and intellectual, which after all is only half the
content of music at most. We are going to sug-
gest a short-cut method — one which requires no
preparatory work at all.
HOW TO LISTEN TO GOOD MUSIC
FAOUBTLESS this system of learning how to
*-^ follow music has been suggested before —
though we have not run across it. It may be ob-
jected to as an unscientific method, as an unin-
tellectual method — in short as a too strictly
emotional method. But it is, a practical method.
Sit yourself before the receiving set in the
afore-mentioned slippered condition when there
is some first rate symphonic orchestra program
going on (we hope you can find one!). Turn off
the lights and the oil burner and otherwise ex-
clude all conceivable distractions and then con-
centrate on the sound issuing from the loud
speaker as though you were entombed in a mine
waiting for the faint ring of a distant pick ax.
Or strain your ears as though you were trying at
three in the morning for 2LO. Things will im-
mediately begin to happen. Surprising things. A
host of sounds will begin to emerge that were
formerly just lost in the shuffle. Pick out one of
the thinnest and feeblest of these sounds and
follow it through the maze like a bloodhound
pursuing little Eliza through the forest. Keep on
its trail and see what it does — and what some
of the big bullying noises do to it. Then for a
change pick out some little transitory tune —
perhaps only five notes long — wait for it like a
cat before a mousehole. Presently it will appear
again, perhaps in a different key or on a different
instrument, or even disguised with false whiskers.
But you will recognize it, and with a glee quite
equal to that of the cat when the mouse finally
emerges from its burrow.
Next try listening to two tunes — or two instru-
ments— at once. Watch how the two tunes sneak
along side by side, some times drawing together
and shaking hands; other times running off on by-
paths and making faces at each other. Watch
them intertwine and overlap and disappear and
emerge again with a new suit and their hair
combed on the other side. Search out some little
insignificant orchestral effect that seems to be
buried obscurely away at the bottom of the heap
of noises. Watch it while it pussy-foots around
the corner and gets itself a drink. Watch it start
to swell and swagger and toss its hat around.
Presently the snifter does its stuff and it is strut-
ting around bombastically. Before you know it,
it is running the whole works, the other noises
fleeing, terrified, to shelter.
In such wise, listening to the symphony or-
chestra becomes a grand game with yourself
just as much a participant as the orchestra. It
has much in common with football: there are
long end-runs and fake plays and intercepted
passes and trick formations; there is team work
and tripping, signalling, and shifts, even "time
out" where a rest occurs in the music. And both
the football game and the symphony are divided
into quarters.
The analogy to football is not quite complete.
What happens in a football game is largely sub-
ject to chance (as we found out just before we
swore off betting last season). But what happens
366
RADIO BROADCAST
MARCH, 1928
in a symphony, far from resulting from chance,
results from perfect organization.
Herein our proposed method of learning how to
listen fails. It will not reveal to you the organiza-
tion of the music. That would be asking too much.
However, the method we suggest will at least
demonstrate to a listener that music is not simply
a blur of sound, and will enable him to recognize
the elements out of which music is organized.
This will be a first step. Furthermore it will be
fun — which is the only excuse music has for ex-
istence anyway.
For Program Directors Only
WRITES Paul Hale Bruske, of Detroit:
My friend Jimmie is blessed with one
of those urbane baritone voices that
pleasantly vibrate so many loud speakers in the
sun rooms and front parlors of our broad land.
Yes! He's a radio announcer. More than that,
he's also a program director. On his shoulders
rests the responsibility of seeking, interviewing,
choosing, auditioning, hiring, scheduling and re-
jecting various features of alleged entertainment
and enlightenment. His station is a good one.
Jimmie does little if any seeking for talent.
He does a microscopical amount of hiring. At
interviewing he shines. His waiting room is usu-
ally full of folks who believe they have a Mission
and a Message. Male and female — blondes and
brunettes — old and young — artists and artistes
— they are all grist for Jimmie's mill. Auditions
occupy a good share of his day. He always takes
the name, address and telephone number, and
gives them a sweet promise to let them know.
One might think that, with all this wealth of
willing workers on call, the programs from
Jimmie's station would be replete with variety,
and fertile in surprise, as the theatrical notices
say. Such is not the result. Far from it. Tune-in
on him any evening and here is what you are
pretty sure to get: —
6:00 — 7:00 — Dinner concert from the
Herculaneum Room of a good hotel. Gwan to
Bed dope for the kiddies.
7:00—8:00 — News Bulletins, Hot Stuff for
Farmers, Organ Recital from a Cinema
Palace.
8:00 — 9:00 (Commercially Tainted Hour)
— Somebody's Antiseptic Carolers in solos,
duets and quartet numbers. Somebody's
Realestate Minstrels in comic songs and
dialog.
9:00 — 10:00 p. M. — (Big Station Feature);
— Baby Grand Philharmonic Orchestra in
classical and semi-classical numbers, with
guest artist soprano or tenor.
10:00 p. M. and on: — Jazz Bedlam from
some cabaret or night club.
On Sundays, Jimmie broadcasts church serv-
ices. In midsummers, he gives us band concerts
from the parks. He occasionally hands us a sport-
ing event. He has a weekly silent night. More
so than seems usually the case, Jimmie enjoys
quite a free hand. His boss is rich, a radio bug
and has no personal propaganda to get over —
not enough, at any rate, to make it obnoxious.
Some months ago I began to razz Jimmie a bit
on the striking lack of originality in his programs.
He insisted that he was every bit as good as his
competition, and I had to admit it. With him, it
was purely a matter of beating competition on
one common ground. Jimmie's rut was too deep.
He couldn't see over the top.
But one day I got a barb under his hide. Per-
haps the boss had just asked about the applause
letters. For Jimmie turned on me defiantly.
"What would you do if you were in my
place?" he challenged.
That was surely a quick pass of the celebrated
buck but, after all my raillery, I couldn't dodge.
"Well," 1 stalled, "I'd first try to analyze a
bit. Here you are, competing for public attention
with from four to forty other stations, depending
on reception conditions. You want folks to be
tuning you in and then letting the dials alone for
a while. You want them to think of you when
they think of radio — to talk about your station
and your programs. You want more applause
letters. You'd even prefer knocks to the present
silence. You crave personal glory. You could
endure a bigger check in your pay envelope."
"Yes! And how?"
"Shut up; I'm analyzing.
"The main offering of all radio stations is
music. On thatyou've goneabout the logical limit.
Vocally, instrumentally and in combination, you
fellows have probably tried about all the tricks
there are. I doubt if there is any new musical
dodge which would create more than a ripple of
interest. And what we want is a tidal wave.
"But there are at least two channels of ap-
proach to your dear invisible audience. The one
that isn't music is speech. Let us admit, therefore,
that the method you will use in getting folks to
talking about your station is the spoken word."
"No chance!" yelled Jimmie. "The dullest
thing that comes over the air is a speech. The
minute one starts here, I can just feel the people
tuning-out. There are only three kinds of radio
speeches. There's politics. There's platitudes.
And there's propaganda. Each is worse than the
other. I'd like to pass a rule that would abso-
lutely prohibit all speeches from this station.
" Why you've no comprehension of the speech-
ifierswe turn down right now," Jimmiecontinued.
"There isn't a public official in town who doesn't
think he'd be the hit of the season, if he could
only get on the air. Every convention that comes
here tries to get time for its Grand High Cocka-
lorum. The ladies with pet charities can't under-
stand why we don't put them on oftener. The
boy scouts litter up the place with officers that
have a message. Speeches? Take a swift jump
into the lake!"
"Wait a minute Jimmie," I begged. "Don't
get me as any friend of your three P's. They're
even more terrible than you say. But there must
be such a thing as interesting talk. The news-
papers get it."
Jimmie picked a fresh edition from his desk.
Clear across the front, in glaring 72-point,
screamed the legend, "MRS. BANCROFT
WEEPS ON STAND."
It was just the current divorce case and not
much of a case at that — no shooting, no violence
of any kind, hardly any real scandal. But both
parties were socially prominent. The gentleman
was rich. The lady alleged he was cruel and
neglectful. The children also socially prominent,
took sides. The case was good food for tea-table
gossip, so the papers were playing it strong.
Jimmie and I looked at the headline. It seemed
suggestive.
"She weeps, Jimmie," I said. "And the people
read about it. Wouldn't it be better if they could
really hear her weep?
" If you could schedule her to weep into your
mike to-night, would they tune-in?"
"You're whoopin' they would," admitted
Jimmie.
"Then go get her," i insisted. "Tell her she's
got a Mission. Explain that what's happened to
her is only a sample of what's happening to
thousands of other women. Get her to tell these
others what to do. Let her put her case to the
whole world, with her own voice and freed from
any cross-examination or other rules of any kind.
I'll bet she'd jump at the chance. Give those
listeners of yours something worth listening to."
"Gosh!" commented Jimmie.
"Then next night, give the same privilege to
Mr. Bancroft. Let him talk to the husbands.
Have him tell what a real life partner should do.
Let him say anything within reason about these
wives who spend their days in clubs, and don't
have time to cook a dinner for the family. Play
him as the outraged American husband, and let
him counsel others who feel bad with him. Then
let the household arguments rage. Every time
the case is mentioned, folks will think of your
station and wonder what next."
"Well, that's a good question. What next?"
" Next will come the poor boob who's just been
sentenced to life in the hoosegow for murder of
his sweetie's friend husband. Give him a last
chance to say farewell to the world. What a cinch
it will be for you to write his speech! To-night,
he's a man and has a name. To-morrow night, and
until he dies, he's nothing but a number. And
who's to blame? The woman, of course! And then
the moral. AH this in his own voice, with the hand-
cuffs rattling every time he turns a page.
"Gruesome? Sure, but will they listen?
"As for me, Jimmie, I've always had a longing
to know just what happens at a hospital during a
good, major operation on the human torso.
I'd rather hear you describe such a thing than
get your fresh-from-the-ringside word picture
of a good prize fight. That's only a sample of
what you can do when you once get your mind
on really interesting topics. But let that pass.
"Watch the front pages. They're the best bet.
Grab those features hot, give 'em a good, moral,
uplifting line of talk, rehearse 'em, and turn 'em
loose with their own voices to give us listeners
honest-to-goodness heart throbs in the raw.
If you're too busy to add this department's duties
to those you carry now, hire Pat Montgomery,
our old city editor, and put it up to him. Yellow
up — and that only means make your stuff
interesting."
Jimmie had been getting more pop-eyed with
every word. Temporarily, at least, 1 had him sold.
But he cooled off just as quickly. Eventually he
admitted that there was something in this idea
and promised he'd think it over.
"But no murderers! And no gory operations,
either," he declared. "Something controversial,
maybe. That's perhaps the secret of making
speech interesting. And I may be able to do some-
thing with decent celebrities of the day."
A few days later, Jimmie's station announced
the first controversial event. It was a debate.
On one side was the mayor. Opposed was one of
his appointees who had the courage to think for
himself. The debate itself wasn't so much. But
before it started, right in Jimmie's studio, the
mayor fired the appointee, and the latter an-
nounced the fact in his address. Jimmie's station
got a lot of good publicity, and he was greatly
elated.
For several weeks thereafter I was out of touch
with Jimmie and with radio. Back in town again
I bumped into Jimmie.
"I'll bet I've been missing some hot stuff," I
remarked. Jimmie looked blank. Actually I had
to remind him of the big idea.
"Oh! We've got something a lot better than
that," he boasted. "We've joined a big chain
and get our programs right from New York."
And then he went on to tell how much better his
chain was, on every count, as compared to the
others.
However, comma, there are other stations and
other cities. Every city has a newspaper, and
that newspaper must have a front page. Some-
where, I doggedly insist, there will bob up a
program director with the necessary nerve to
watch that front page and do what every success-
ful newspaper does — get circulation by being in-
teresting.
AS !Hh R
SThR .S
BY C:AKI DKFHFR
How a Famous Artist Broadcasts
THE scene is in the large "B" studio
of the National Broadcasting Com-
pany at the building on Fifth
Avenue in New York City. The room,
thirty-six by fifty-two feet, and two stories
in height, holds an orchestra of sixty-five
men recruited from the New York Phil-
harmonic, with Fritz Busch conducting.
The musicians are all in evening dress;
their white shirt-fronts gleam in the light
streaming down from six giant electroliers.
It is a General Motors hour on a Monday
night, a somewhat formal occasion, as
broadcast features go. About a hundred
spectators are grouped around the or-
chestra, most of the ladies seated, the men
standing. I lean against the wall, an idle
spectator for the moment, interested, even
so, in the effect of the presence of this
good-sized crowd on the acoustic charac-
teristics of the room. A concert manager
stands on one side of me, and a very famous
baritone on the other. We are all looking
toward Fritz Busch, who stands, with his
baton upraised, in an attitude of command-
ing tenseness, and at another man who faces
the microphones a few feet to one side of
the conductor. This man is of a notably
handsome and virile aspect; his body is
that of an athlete; his features might be
those of an intelligent and sensitive busi-
ness man, but at the same time something
of the actor and artist is easily discernible.
His head is about three feet from one of the
microphones of a double set-up. He stands
with his legs well apart and his arms
folded across a broad chest. This is John
Charles Thomas, the tenor. He is about to
sing an aria from Verdi's "The Masked
Ball." Interested in the outward manifesta-
tions of his technique, I watch the artist
carefully.
Fritz Busch now swings his arm down-
ward with an emphatic gesture, and the or-
chestra begins to play the introductory
bars. As the moment for his first note ap-
proaches, Thomas raises his left hand and
cups it behind his ear. He does this in
order better to hear the tones as they
! reach the microphone, for a man hears
his own voice both through the air and
through the bones of his head, while others
hear him only through the air. His other
arm the singer holds across his chest in a
rather cramped position, which does not
concern him, for he is singing with only
moderate volume and does not, for the
present, require the full capacity of his
lungs. Nevertheless, he is ready for exer-
tion, he has his coat off, and incidentally
he is not, like most of the others in the
room, in evening dress, but wears a business
suit and a blue shirt with soft collar.
He rounds his lips carefully for the notes
and sways a little in time with the music.
His attitude is one of mingled nonchalance
and the greatest circumspection. On the
one hand you see a man with every natural
advantage for his part, with a reputation
made early and securely based on experi-
ence; and yet this same man realizes that to
sing beautifully is never easy, and that it is
only too easy to deviate from the pitch, if
only a little, or to falter in the time, if only
for a fraction of a second, or to mar a phrase
with a breath that is only a little awkwardly
drawn. So, seen in one aspect, John Charles
Thomas sings effortlessly, and from an-
other angle, he is working as hard as any
man in any trade cares to work. The ex-
pression of his face changes, sometimes in
consonance with the music, but at times,
because he is singing more for the audience
which cannot sec him than for the hundred
Interesting Highlights this Month
— How John Charles Thomas Performs Be-
hind the Microphone.
—Matters Which Make Life Hard for the
Broadcaster.
— Where to Get New Information on Human
Speech Constants.
— Sources of Helpful Printed Information
from Manufacturers.
spectators, he seems frankly to use his facial
muscles to aid his larynx. And again, when
a note does not suit him precisely, he frowns
critically, engrossed in his own private
world of tonal creation. As Thomas
maneuvers through a difficult succession
of transitions, the concert manager nods
approvingly, while the baritone on my
right, when I glance at him, is watching
the singer with critical professional admira-
tion.
The aria is nearing its end. As he ap-
proaches the forte passage at the close,
Mr. Thomas moves his right arm down
from his chest and lets out something near
his full volume. He is much too good a
microphone performer to go all the way; it
is interesting to see how nicely, without
knowing a transmission unit from a kilo-
cycle, he unconsciously compresses his
volume range within approximately the
4O-TU-width allowable in radio tele-
phone transmission, leaving the control
operator little to do. Having had con-
siderable experience singing for the radio
and phonograph, and, presumably, having
heard the performances of others in the
same mediums, this artist has adjusted his
367
technique, when he sings for the air, to the
requirements of that particular machinery.
Therein you see one of the reasons for his
success. The difference between the artist
who goes well over the air and the one
who is a flop in the broadcast field is as
often one of adaptive intelligence as a mat-
ter of voice characteristics. That adaptive
intelligence may be intuitive rather than
quantitative, but the results are the same,
whether reached through the vocal feeling
of the artist or the calculations of the
engineer — better, in fact, when the artist
does the editing himself. So, at his climax,
Mr. Thomas roars formidably, but not so
recklessly as to cause consternation at BeH-
more, where the transmitter technicians
are keeping an eye on the modulation
peaks. Nor does he walk into the micro-
phone; he gestures somewhat with his free
right hand, but his feet remain rooted to
the spot where he originally took up his
position.
The last fine notes ring out, and for a
second the artist stands, still in his part,
looking somberly at the microphone, as
if, behind its unrevealing diaphragm, he
saw, across hill and plain and river, on
farms and in cities, the several hundred
thousand of his countrymen whom he has
held entranced for those few minutes. Then,
turning, he smiles broadly at the conductor,
and, as the announcer speaks his lines,
Thomas walks off-stage, or what amounts
to off-stage in a broadcast studio, puts on
his coat with a gesture curiously reminis-
cent of a football player struggling into his
blanket as he retires to the sidelines, and
looks over his next song before he is once
more called before the transmitters.
Note for Lexicographers
IN THE December, 1927 issue, under
the heading "Radio As An Electro-
Medical Cure-All" we recounted the
claims of a quack imbued with the convic-
tion that he is curing the assorted ailments
of the populace by saturating them with
his own brand of radio waves. The word
"stob" occurred several times in the
healer's description of his paraphernalia,
and, failing to find it in my Webster's
Collegiate, a very good dictionary for its
size, I was at a loss as to its meaning,
except that the context indicated that it
was some sort of metal ground stake. Mr.
H. G. Reading of Franklin, Pennsylvania,
clarifies the subject in the following com-
munication:
"Thinking it queer that there could
possibly be a word 'not in the (New
Standard) Dictionary,' I looked for 'stob'
368
RADIO BROADCAST
MARCH, 1928
and find it having several meanings, one of
which is 'a long steel wedge' used in coal
mines. Doubtless the Doctor wielded the
pick for a living at one time."
Mr. Reading's conjecture may possibly
have hit the mark. If so, the electronic
magic worker in question abandoned a
socially laudable profession. We may hope
that his adventures in the healing arts,
having led him to the conclusion that he
can remedy the lesions of a man a mile
away by modulating the output of his
battery-operated radio transmitter with the
stutterings of his "oscilloclast," will end
by putting him to work with a pick again,
although perhaps not in a coal mine.
Speech Constants
ON PAGES 753-754 of Morecroft's
Principles of Radio Communica-
tion (Second Edition), published
by John Wiley & Sons, Inc., there is a use-
ful summary of the results of the research
work on speech carried on in telephonic
laboratories during the past decade. Most
of the figures have already been given in
this department in the past, but Morecroft
adds one or two new ones gleaned from his
reading.
(1) The frequencies encountered in human
speech are within the range of 100 to 6000
complete vibrations per second.
(2) The energy contained in speech is
carried almost completely by frequencies
below 500 but the quality and intelligibility
of speech is determined very largely by the
frequencies higher than 500.
(•)) The average power output of the
average normal voice is about 75 ergs per
second or 7.5 microwatts.
(4) The average male voice exerts a pres-
sure of about 10 dynes per square centimeter
at a distance 3 centimeters from the mouth
of the speaker.
(5) The human ear can detect sounds, at a
frequency of about 1000 cycles, if the sound
pressure is as low as o.ooi dyne per square
centimeter. If the pressure exceeds about
looo dynes per square centimeter at this fre-
quency, the ear is practically paralyzed in so
far as sound is concerned and the sensation
is one of feeling rather than hearing.
(6) The ratio of peak power in the voice
(accented syllable) to average may be 200 to
i. Thus an average voice of 10 microwatts
shows peaks of 2000 microwatts.
Professor Morecroft gives references to
two articles in the Bell System Technical
Journal which have not been specifically
mentioned in 'this department. One is the
article on "Speech, Power and Energy" in
the October, 1925 issue of the Journal; the
other is a paper on speech analysis by
Harvey Fletcher in the July, 1925 issue of
the same publication. Both discussions
are of direct interest to broadcast techni-
cians.
Catalogs and Commercial Publica-
tions
THE number of commercial publica-
tions of interest to broadcasters is
increasing. Three may be mentioned
this month. The Sales Department of the
Radio Corporation of America (233 Broad-
way, New York City, with district offices in
Chicago and San Francisco) is distributing
to its dealers a leaflet entitled Average
Characteristics of Receiving Radiotrons.
[This leaflet, listed as No. 69 in our " Manu-
facturers' Booklets Available List, appear-
ing in the back pages of this magazine,
may be secured by our readers by using the
coupon indicated. — Editor.] Some of the
tubes described, such as the ux-2io (7.5
watts oscillator rating) are used in the
lower power stages of broadcast speech
amplifiers, while others are commonly em-
ployed in field equipment. The tubes are
classified as "Detectors and Amplifiers";
"Power Amplifiers"; "Rectifiers" and
"Miscellaneous." The data given is, first,
general physical and electrical information,
such as the type of base, outside dimen-
sions, special circuit requirements, possible
filament supplies, voltages, and currents.
For detection purposes the proper grid
return, grid leak, "B" voltage, and plate
current are specified. Under "Amplifica-
tion," for various plate and corresponding
bias voltages, the plate current, a.c. plate
resistance, mutual conductance, voltage
amplification factor, and maximum undis-
torted output in milliwatts, are included.
The alternating current filament and a.c.
heater type radiotrons are listed, and the
whole list is a useful page to be added to the
broadcast engineer's notebook.
J. E. Jenkins & S. E. Adair of 1500
North Dearborn Parkway, Chicago, have
issued their Bulletin No. 4, dealing with a
"Complete Input System" installed at the
1927 Chicago Radio Show. This equipment
was used during the entire week of the
show, feeding a network of some thirteen
of the local broadcasting stations, and a
public address system the output of which
supplied 22 eighteen-inch cone speakers in
the Coliseum. The "Broadcast Amplifier"
portion of the apparatus was mounted on a
frame 72 inches high by 25 inches wide,
which supported the following units:
meter panel; a monitor panel, employing a
W. E. 205-8 or R. C. A. ux-2io tube to feed
a loud speaker; an output level indicator; a
three-stage broadcast amplifier; a micro-
phone mixing panel; and a telephone jack
panel for the broadcast pairs and order
wires. The amplifier was the "Type A"
described in Jenkins & Adair's Bulletin lA,
comprising two stages of amplification
using W. E. IO2-E or R. C. A. ux-240
tubes, and an output stage for a 2O5-E
or ux-2io. A 35O,ooo-ohm wire-wound
gain control afforded 11 values of amplifica-
tion, with equal TU-increments. The 500
ohm output of the amplifier was connected
to the level indicator, the monitor ampli-
fier, and the jacks for the outgoing broad-
cast pairs. The maximum undistorted out-
put available is stated to be 0.8 watt, on a
plate voltage of 135 for the small tubes
and 350 for the output stage, secured from
heavy-duty dry batteries.
The power amplifier portion of the
equipment was mounted on a frame only 19
inches wide, but the same height as the
broadcast frame (72"). Current was sup-
plied from a generator capable of giving
150 milliamperes at 1200 volts and 10
amperes at 12 volts for the plates and
filaments, respectively, of the power tubes,
which consisted of two fifty-waiters in a
push-pull circuit. The actual plate po-
tential was 1000 volts, and separate grid
bias batteries enabled each tube to be ad-
justed to draw 60 milliamperes. Each tube
also had a o-ioo milliammeter in the plate
circuit, and a quarter-ampere fuse. The
push-pull amplifier was fed from a 5-watt
stage, which in turn received part of the
output of the three-stage broadcast ampli-
fier previously described. A level indicator
panel for the P. A. system was also in-
cluded in this frame, the input being
directly connected to the output of the
large amplifier with a high resistance in
series to reduce the voltage. This instru-
ment gave a check on the volume of the
loud speakers, incidentally showing up ir-
regularities in the 3000 feet of line connect-
ing up the loud speakers. The broadcast
and P. A. frames, set up with a desk be-
tween them, made a neat lay-out. All the
parts used in building the units with the
exception of such items as tube sockets,
etc., were manufactured by J. E. Jenkins &
S. E. Adair.
A more elaborate publication is Samson
Broadcast Amplifier Units, issued by the
Samson Electric Company, of Canton,
Mass. This is a pamphlet of 24 eight-and-
one-half-by-ten pages describing Samson
parts for broadcast amplifiers and as-
sociated equipment, and incidentally going
quite deeply into design considerations.
It is not intended for general distribution,
but may be obtained free of charge by
broadcasters writing for it on their letter-
heads. Microphone-to-tube transformers
arc first described, with some advice re-
garding connections and care of carbon
microphones. There appears to be an error
on page 5, where the d.c. of a 2OO-ohm
microphone is given as 200 milliamperes
per button, instead of 20. The difference
is serious! Following there is a discussion
of multiple microphone (mixer) operation,
but the pamphlet argues that "this practice
(using more than one transmitter for pick-
up) should be avoided unless it is impera-
tive." The point is highly debatable, but at
any rate, as the Samson people sell mixer
transformers, it is refreshing to see them
state what they believe to be true, regard-
less of a little economic advantage. Tube-
to-line and line-to-tube transformers, as
well as other matching devices, interstage
impedances and transformers are described
in following pages. The discussion of im-
pedance relations in audio circuits, direct
current design considerations, and the use
of center-tap connections, including de-
vices for obtaining a center tap electrically
where the actual winding midpoint is
unavailable, is quite thorough. The last
seven pages are devoted to "General Con-
siderations"— Interference Level, Gain,
Volume Control, Attenuation Networks or
Pads, and Pad Design. The Samson Elec-
tric Company's engineers have turned out
a valuable publication.
The A. C
A SHORT time ago, the writer had occasion
to visit a friend who maintains a hunting
lodge in the Berkshires — in the north-
western part of Connecticut. We spent the day
in a virgin forest, chopping trees and hauling
timber, for the stock of wood fuel required to
heat the lodge had to be replenished. There were
five of us at the camp and, at the day's end, after
our evening meal, we would gather around the
fire and listen to the radio.
Say what you will of the radio in the city, the
welcome cheer which it imparted to us up in the
woods created a deep impression in our minds.
To the woodsman habitually isolated many
miles from the city it must indeed be a blessing.
Imagine the interior of a rough shack, snowflakes
beating against the window panes which are al-
most hidden by sweeping drifts of snow, a merci-
less wind screaming through the tree tops, and a
temperature of "three above" outside. The
stillness within the shack is broken by the crack-
ling of the blazing log fire, and by the deep
breathing of the woodsman inhabitant, who sits
deep in thought — a few well worn books his only
companions. His nearest neighbor may be miles
away; it would be useless to try and reach
him during the several days the storm rages.
And what a different state of affairs exists at
this neighbor's. Outwardly there is little to
choose between the two shacks. They are both
lost in the depths of the snow. Each has its blaz-
ing open fire of logs, and in each lives a solitary
woodsman. But there is also a radio in the
second one, and what a transformation it has
wrought. Were you to knock at the door for
shelter, you might enter to the strains of a
Strauss waltz, a Berlin melody, or perhaps even,
By JOHN F. RIDER
some politician may be monopolizing the atten-
tion of the blustering fellow who admits you.
He'll discuss the Waldorf Astoria orchestra as if
he were accustomed to dine there and listen to it
almost every day, and will talk with you of Mr.
Coolidge's choices almost before the President
even chooses. Or he'll demonstrate how Gene got
in the winning punch, compare Damrosch's
rendition of Beethoven's "Fifth" with Mengel-
berg's, talk of the merits of the four-wheel
brakes on Dodge Brothers "Fastest Four," and
match the "Silver Slipper" orchestra with that
of the "Twin Oaks." No, he's never been to New
York. He was born up in the woods Rarely sees
an automobile. Yes, lots of the men now have
radios up here. Don't need them in the summer.
Too much to do outside, and plenty of people
around, anyhow. No, neighbor Joe hasn't got
one. He's an iconoclast (a word he picked up on
the radio). Never knows what's going on in the
big cities. He himself wouldn't be without a
radio.
THE "BANDBOX"
1" HE receiver that we used at the lodge in the
*• Berkshires was a Crosley " Bandbox."
Reception was good, volume adequate, and the
quality of reproduction, excellent. After listening
to a concert from Springfield, we tuned-in wcv,
with the usual result — periodical fading. This
phenomenon provoked a discourse by one of the
party — Jones, a medical man. He knew all about
receivers, although medicine was his forte.
His was an analytical mind, and he had grasped
the fundamentals of radio. It was simple. He
was an old timer. His interest dated back since
the day WOR commenced operations.
369
The discussion finally centred upon the re-
ceiver at hand. He was the radio authority. The
receiver seemed to work well, but . Yes, it
was selective, but . The volume was good,
but . Well, he had a ten-tube receiver at
home, which he had constructed; it comprised
five stages of tuned radio-frequency amplification,
push-pull audio amplification, a variable grid
leak, etc., etc. In sum and substance, it was a
"wow." He hoped that some day we would
have the opportunity to listen to his pet re-
ceiver!
At this point the writer timidly explained his
connection with the radio industry. Fine — Just
the man he was looking for. Could I explain to
him wherein the Crosley differed from any other
receiver? Would 1 point out to him the engineer-
ing features of the " Bandbox?" How could
this receiver be a scientific receiver, and still sell
at its low price? As far as he could see, all manu-
factured receivers were alike; he would never
buy a finished product anyhow. Would I tell
him something about the new a. c. operated
"Bandbox," which is fundamentally similar, so
far as the circuit constants are concerned, to the
battery-operated "Bandbox" we were using up
in the Berkshires?
The fact that highly scientific design and
highly scientific production were absolutely
necessary to produce a successful inexpensive
receiver never entered his mind. He overlooked
the fact completely that an accurate study must
be made before even the apportioning of the
tubes is made, or before the engineering staff
can decide upon how many stages of radio-
frequency amplification should be employed
The fact that the receiver is sold at a low price
370
RADIO BROADCAST
MARCH, 1928
cannot influence the staff to make haphazard
decisions. In this particular instance, I told him,
the selection of three stages of radio-frequency
amplification was a compromise of the sales
division and the engineering staff to produce and
sell a radio receiver at a reasonable cost for a
given amount of radio-frequency amplification
and stability. That is to say, calculations were
made to determine how much radio-frequency
amplification was necessary to provide a certain
amount of sensitivity, with a reasonable stability
factor. After a study of the sensitivity factor,
selectivity was the next consideration. Would
the three stages which afford sufficient sensitivity
be selective enough? This could be determined
mathematically, but it was also determined ex-
perimentally. This determination is extremely
important in the design of a radio receiver. A
low sales price and a high degree of efficiency
will immediately "make" a receiver, but low
sales price will not compensate deficiency in
design.
In view of the demand for single-control re-
ceivers, there was much discussion as to what
arrangement could be used in the " Bandbox"
to permit efficient single tuning control. The
receiver has but one major tuning control, and
in order to accomplish this, it was necessary to
incorporate into the design of the receiver, a
circuit arrangement which provided for the
different electrical characteristics of various
antennas. This was essential in order that true
single control be obtained, otherwise a vernier
control would be necessary for the input circuit.
Under normal conditions, different antennas,
with different electrical constants of capacity and
inductance, would alter the setting of the first
tuning condenser. In the a. c. "Bandbox" the
antenna stage has been left untuned. The remain-
ing stages are tuned, and are isolated from the
antenna stage. Hence the settings of the tuning
condensers remain uniform regardless of the
height or length of the antenna used. A radio-
frequency choke is connected across the grid-
filament circuit of the first tube. The antenna
and ground are connected across the choke,
and the action of this latter is to cause the radio-
frequency signals induced in the antenna circuit
to be impressed across the grid-filament circuit
of the tube. The choke must be one with very
900
800
700
2 600
<
£500
§400
•z
5300
s
200
100
1500 1400 1300 1200 1100 1000 900
FREQUENCY IN KILOCYCLES
FIG. I
800
700
600
little distributed capacity, since inherent capac-
ity would afford an easy path for the radio-
frequency signals to ground. By reducing the
effect of the choke, the magnitude of the signal
applied across the grid-filament circuit of the
first radio-frequency tube can be reduced, hence
the Crosley engineering department immedi-
ately visualized an excellent volume control.
This is found in the variable resistance which
shunts the radio-frequency choke in the antenna
circuit. This resistance is non-inductive, free of
capacity and, when varied, reduces the imped-
ance of the choke. By reducing the impadance
of the choke, its effect is reduced, and the signal
input is decreased. Thus we have a volume con-
trol, which does not display any effect upon the
selectivity of the receiver.
Receivers which oscillate and at the same
time perhaps radiate an interfering signal,
are not very popular, hence the radio-frequency
stages are neutralized — by means of the Hazel-
tine system. The manner of neutralization gives
the system an excellent radio-frequency amplify-
ing characteristic, and helps overcome the usual
falling characteristic on the longer wavelengths.
Fig. I shows the radio-frequency response curve
of the system. This graph is graduated from 200
meters (1500 kilocycles) to 545 meters (650
kilocycles). The maximum difference is about 25
per cent., and the minimum point of sensitivity
is around 320 meters. The amplification rises on
both sides of this point. The maximum gain is
found at 200 meters, but even at this frequency,
it is not a sharp peak. At no place on the curve is
there a sharp peak or depression. Contrary to
usual design, the amplification increases as the
wavelength setting is increased above 320
meters (940 kc.), the low amplification point of
the system. At 350 meters (545 kc.) the differ-
ence between its level and the maximum is ap-
proximately 16 per cent. These differences are
small, and are not noticeable in actual operation.
The radio-frequency transformers are single-
layer solenoids with bifilar primary windings;
that is to say, they have two primary windings.
One winding is the regular primary and the other
small winding is the inductance utilized in the
neutralizing system. The inductance value of
the secondary of these transformers is 190
microhenries and the capacity of the tuning con-
densers is approximately 430 micro-microfarads
(0.00043 mfd.). The excellent radio-frequency
response characteristic is attributable to a very
large extent to the design of the primary wind-
ing of each radio-frequency transformer, its
position with respect to the secondary winding,
and to the coil utilized in the neutralizing
system. A close study of the wiring diagram.
FIG. 2
The circuit diagram of the a.c. "Bandbox" showing the power unit connected for operation
MARCH, 1928
THE A. C. "BANDBOX"
371
40
£39
38
537
36
Audio-Frequency Characteristic
100
1000
10,000
FREQUENCY IN CYCLES
FIG. 3
Fig. 2, will bring to light the fact that this sys-
tem is different- from the conventional split-
primary neutralizing arrangements. It is just
these little differences which make for the vari-
ances in design, and necessitate extensive re-
search, in order that the final result be meritori-
ous and worthy of recognition.
An examination of the receiver shows thorough
and complete shielding of all the units, including
condensers, coils, and transformers. This is a
sound piece of engineering, since it practically
isolates the receiver from all external influences.
Very often, a. c. operation with the power
supply unit adjacent to a receiver utilizing
unshielded transformers results in the induction
of an interfering hum from the power equipment
into the receiver audio-frequency transformers.
Shielding the units eliminates all possibility of
external interfering influences. Sheet iron,
cadmium plated, is used as the shield for the
condensers, of which shield the chassis also forms
a part. Copper cans are used for the shielding of
the radio-frequency transformers. These shields
facilitate elimination of coil interaction and
external influences, and also tend to increase
stability. By selection of copper shields, the
design of the coils, and placement of these latter
with respect to the shields, the effect of the shield
upon the radio-frequency transformer is kept at
a very low value, so much so, that its detrimental
effects are negligible so far as sensitivity and
selectivity are concerned.
THE AUDIO SYSTEM
\ A/ITH respect to the audio system, two
V * stages of transformer coupling are utilized
and the operating curve is shown in Fig. 3.
A study of the curve shows a variation of less
than one half of a transmission unit through a fre-
quency spectrum of from 60 to 10,000 cycles. At
first glance, one is apt to imagine an operating
characteristic very much akin to the majority
of two-stage audio units. Upon closer observa-
tion, however, the small variation becomes ap-
parent. The gain of the audio channel is low, but
with the amplifying powers of the radio-fre-
quency system, the combination affords a very
satisfactory overall response. The absence of a
definite peak on some audio frequency shows the
result of careful study of the leakage reactance
factor in transformer design.
A study of the curve shows an overall fre-
quency range of from 60 to 10,000 cycles, with
about equal amplification on 60 and 10,000
cycles. The curve rises between 60 and 900
cycles, is fairly flat between QOO and 3000 cycles,
falls gradually to 8000 cycles, and then drops
abruptly between 8000 and 10,000 cycles.
OTHER FEATURES
DEING, at the time of my sojourn in the
*-) Berkshires, conversant with the features of
the a. c. operated " Bandbox," the writer was
able to communicate all the above information to
THE POWER UNIT
Its compactness is evidenced by
the photograph on page 369
Jones, whose mind, strangely enough, was gradu-
ally allowing itself to be changed to look upon
the manufactured receiver in more favorable
light.
By this time the other members of the group
had evinced interest. Some had read the adver-
tisements describing the receiver, and com-
menced hurling questions: "What were the
accuminators?" "Were there any other interest-
ing features?" The appearance of the accumina-
tor controls deceived the "expert." He was cer-
tain that they were resistances or potentiometers,
by means of which the grid bias voltages were
altered. He was much surprised to hear that
they were small vernier condensers, one in shunt
with the third radio-frequency stage input tuning
condenser and the other in shunt with the de-
tector tuning condenser. These are visible in the
wiring diagram and their function is to permit
more accurate tuning.
The chassis is of jV' iron and is grounded so
that all ground connections of the receiver may
be attached to it. The radio-frequency trans-
formers used in the receiver are tested on radio-
frequency bridges to within 2 per cent, and are
matched with condensers which are also tested
at radio frequencies. No coil or condenser con-
bination of a set of three varies more than i
per cent, from the rated values. In other words,
the coils and condensers are sorted into groups
and are matched so that the resonance points
are identical in the various tuned stages. The
grid returns for the untuned and tuned stages
are at ground potential and obtain the various
bias voltages through resistances, which carry
the plate current. The voltage drop across these
resistances is utilized as the grid bias.
The tubes in the three stages of racfio-fre-
quency amplification of the a. c. " Bandbox" are
of thecx-326 (ux-226) type, and this tube is also
used for the first audio stage. The detector is
30-327 (uY-22y) and the output audio tube is a
cx-371 (ux-iyi).
The electrical balance in the various filament
circuits is obtained by means of mid-tapped resis-
tances connected across the filaments, instead
of resorting to the use of mid-tapped trans-
formers. The plate voltage applied to the radio-
frequency tubes and also the first audio tube is
90 volts. The go-volt lead also connects to a
2o,ooo-ohm resistance in the set, and is thus
dropped to supply the required detector plate
voltage. In other words, only two positive plate-
voltage leads are available from the unit supply-
ing the receiver. These are the i8o-volt lead for
the power tube and the 9o-volt lead for the
fsr.
A REAR VIEW OF THE "BANDBOX" CHASSIS
372
other tubes. A separate 45-volt lead is not pro-
vided in the manner usually employed. The
power unit also has a negative grid bias 4O-volt
lead, and the regular B minus lead. The re-
sistances which supply the radio-frequency and
detector tubes with grid bias are in series with
the B minus.
All of the cx-326 type tubes are connected in
parallel and are fed from individual low-voltage
filament windings. The midpoint in the filament
circuit is obtained by means of a 2o-ohm mid-
tapped resistance in shunt with this filament
circuit. A mid-point is not required in the fila-
ment circuit of the 0-327 tube since it is of the
heater type. The mid-point for the 171 tube
filament circuit is obtained by means of a
loo-ohm mid-tapped resistance. The filament
heating transformer in the power unit supplies
three distinct voltages from three distinct wind-
ings. These are for the i.5-volt tube, the 2.5-voIt
tube, and the 5-volt tube. The cx-326 tubes re-
quire 1.5 volts at 1.05 amperes for normal fila-
ment operation. The 0-327 requires 2.5 volts
at 1.05 amperes, and the cx-37i requires 5 volts
at 0.5 ampere.
The " Merola" connection indicated on Fig. 2
is the contact point for a phonograph pick-up
unit, should it be used. " Merola" is the trade
name for a pick-up made by Crosley.
THE POWER UNIT
THE power unit differs in several respects
from the conventional. It is obtainable in
two forms, the first being suitable for a 6o-cycle
supply and the second for a 25-cycle supply. The
latter may also be used for 60 cycles.
A ux-28o type full-wave rectifying tube is
employed, as can be seen in Fig. 4. A well-
designed two-section filter is employed and the
chokes are of m henries inductance each, and
have a high current rating. This is important,
since filtration is improved when the choke is
operating below the maximum current rating.
The condensers in the filter network are of
lo-mfd. each, three being used in the form of a
single Mershon condenser. The voltage reduc-
ing resistance has a total resistance of 5000
ohms, tapped at 1525 ohms. With 280 volts in-
put across the two anodes of the rectifying tube,
the total voltage across the output is 220 volts.
The rectified voltage is, therefore, sufficient to
supply the required negative bias of 40 volts.
The transformer contained in the power unit has
six individual windings. The primary is tapped
for low and high line voltage. The rectifier tube
filament voltage is obtained from one secondary
RADIO BROADCAST
MARCH, 1928
Plug
FIG. 4
The circuit diagram of the power supply unit of the a.c. "Bandbox"
I
-, ----- Power Converter -------- >!•< — Set --------------- »•
B+180 Red
1
f
T> ~\~
1
1
84 <
voits :
t '
i 1525 Q
^ B+90 White '
220
Volts
90 :
Volts •
I '*
S 3475Q |
).C. Rectified
* _'
' . <
by Power
B- Brown
4 1
Converter-Tube
B+lst2nd3rd_
Radio.lst Audio
'B+Detector
2010-00 B-and Ctlst,2nd,3rd_;
Radio.lst Audio
st.2nd.3rd Radio _<N_
B-«nd Det. Grid §
C- 1st Audio,
B-2nd Audio
-C-40, Green
5L|_
w ?
-2nd Audio ¥»
FIG. 5
This diagram shows how the grid voltages are obtained
winding, the rectifier plate voltage from an-
other, while a winding of 2.8 volts is used to
supply the 2. 5-volt filament of the detector tube.
WHAT THE "BANDBOX" LOOKS LIKE WITH THE CABINET REMOVED
The excess voltage is an
excellent feature because
it provides for a reason-
able voltage drop in the
receiver filament circuit.
This phase of a. c. tube
operation has been the
cause of the greatest
amount of annoyance.
With the high current
consumption of low-
voltage tubes, the volt-
age drop in the average
receiver circuit, when
five or six tubes are
used, is sufficient to re-
duce the available fila-
ment voltage to a value
below the requirements
of the vacuum tubes. The
current drain of six or
eight cx-326 or 0-327
tubes is quite high, and
even a small amount of
resistance in the feed line will cause an appreci-
able voltage drop.
The voltage output of the winding of the
power transformer which supplies the i.j-volt
tubes is rated at 2.4 volts, and the voltage out-
put of the winding which supplies the 5-volt
power tube is 5.2 volts.
An idea of how the various grid bias voltages
are obtained can be gleaned by a study of the
wiring diagram of the receiver Fig. 2, and Fig. 5.
The three resistances which produce the C bias
voltages for the various tubes are shown in both
drawings. The main wiring diagram shows the
actual position of these resistances, as located in
the receiver. The small wiring diagram, on the
other hand, shows a much simpler arrangement,
such as would be found were these resistances
located in the power unit. The first 55-ohm
resistance results in a voltage drop of 3 volts.
This is the bias applied to the three radio-fre-
quency amplifiers and to the detector grid.
The next jj-ohm resistance, in series with the
first, produces a voltage drop of 6 volts, which is
applied to the grid of the first audio-frequency
tube. The 54O-ohm resistance produces the
voltage drop of 40 volts required for the second
audio tube, which, in this case, is a cx-37i
Interesting
,\peake
rs
and
THE FADA 22" CONE
ALTHOUGH this picture illustrates only the
table model, the 22" cone is obtainable also
in pedestal form at $50.00, and for hunting on the
wall at $25.00. The table model shown lists at
$35.00. Fada also has a 17" cone whieh retails (the
table pattern) for $25.00
THE BOSCH A UNIT
V\7"HICH has been designed to supply A current
* ' to a receiver employing from four to ten tubes.
The unit makes use of a Tungar rectifier tube. The
price of this A supply is $58.00, and it is produced
by the American Bosch Magneto Corporation,
Springfield. Massachusetts
Equipment
IF YOU HAVE AN ATWATER KENT
RECEIVER
"Y"OU will find this At water Kent B supply
•1 especially suitable for use in conjunction
with it. The B supply may, however, be used
with other receivers. It delivers up to 135
volts, and is for sets consuming not more than
40 mils. An automatic relay is incorporated
within the unit, and there is a receptacle in the
front for trickle charger plug. Price $39.00
A NEW DYNAMIC LOUD SPEAKER
T^HE movable coil principle is featured in this attrac-
* tive new loud speaker, which retails at only $65.00.
Two of its connections go to the A battery, but a min-
imum of current is consumed. The loud speaker (with
step-down transformer) without cabinet retails at
$47.50. Jensen Radio Manufacturing Company, Oak-
lain!. California
TWO MAGNAVOX LOUD SPEAKERS
'T'HE popular R-4 unit is shown to the left. It is a moving coil electro-
-*• dynamic loud speaker retailing for $50.00. It should be used in conjunction
with a baffleboard. The model to the right lists at $120.00. In addition to being
a loud speaker, it also combines a B supply unit and power amplifier. A 210
type tube is used for the latter, while a 216 type tube is employed as the rectifier
A NEW WESTERN ELECTRIC CONE
''THE Western Electric 540 AW cone loud speaker has been the standard
-•- of comparison for so long that considerable interest is bound to follow the
announcement of a new cone by this company. The 560 AW, as this new in-
strument is known, is a 25" cone, and it lists at $35.00. The decoration in red
and dark brown, is more striking than that on the 540 AW
373
rE ARE celebrating the four-month
birthday of this department by climb-
ing out of our rompers and taking a big
step. Henceforth we shall aim to be a guide to all
the best phonograph records. You cannot read
all the books published each year in order to
choose the best volumes, so you consult book re-
views and guides. Neither can you while away
the hours in your favorite music store listening
to the new — and old — offerings of the very
active phonograph companies. When you buy
records the chances are you act on the advice of
the music salesman, or take the word of a friend,
or if you happen to be on the mailing list of a
music store, you check over the catalogue and
select the most likely sounding titles. Any one
of these methods is precarious and the element
of chance is large in each.
When this department was mapped out in the
editorial mind, the word went forth that these
two pages were to be devoted to a general re-
view of phonograph records which had been
produced by artists who were familiar to lis-
teners-in as broadcast performers. Now we will
extend the field to include the records of all
artists whether or not they play the dual role.
Some of the recordings will be briefly reviewed,
others will merely be mentioned, and each
month there will be a list of records which we
consider well worth hearing, and buying, if the
spirit moveth.
WHAT HAVH WE HERE?
AFTER inspecting the current supply of
records we find that it contains the follow-
ing ingredients: The usual popular vocal numbers
by the usual popular vocal artists; an array of
good dance numbers with one outstanding suc-
cess, Dream Kisses', several old favorites rendered
superbly by such distinguished artists as Sophie
Braslau, John Charles Thomas, Charles Hackett,
and Maria Kurenko;
seven minutes of very
beautiful choral singing
by the Metropolitan
Opera Chorus; and an
album of Rimsky-Korsa-
kov music, of which,
more anon. These ingre-
dients have been highly
seasoned with the senti-
ment which, we are
led to believe by song
writers, song singers,
and phonograph com-
panies, the public cries
for, and they have been
expertly mixed, and sifted, spread on the discs
by the new electrical recording method, and
served hot to the public, for prices ranging from
seventy-five cents to ten dollars. Taken as a
whole there can be no question of the general
excellence of the output. Our chief complaint is
that it is too sweet for our taste. Is our taste
vat?
Don't Miss These
Scheherazade Suiti (Rimsky-Korsakov) played by the
Philadelphia Orchestra under Leopold Stokowski (Victor).
Cavalleria Rusticana-Gli Aranci Oletfano and Immeggiamo
II Signor (Mascagni) sung by the Metropolitan Opera
Chorus, with Orchestra (Victor).
Rigoletto: La Donna E Mobile (Verdi) and Cavalleria Rusli-
cana: Siciliana (Mascagni) sung by Charles Hackett
(Columbia).
Liebestraum (Lizt) and Sbeep and Goat Walkin' To Pasture
and Gigue (Bach) played by Percy Grainger (Columbia).
Among My Souvenirs and Washboard Blues played by Paul
Whiteman and His Concert Orchestra (Victor).
Dream Kisses and Among My Soui-enirs played by the
Ipana Troubadours and Ben Selvin respectively (Columbia).
My Lady and Two Loving Arms played by Cass Hagan
and His Park Central Orchestra and The Cavaliers res-
pectively (Columbia).
A Shady Tree and There Ain't No Land Like Dixieland To
Me played by Ernie Golden and His Hotel McAlpin Or-
chestra (Brunswick).
Back Wbere the Daisies Grow and Lonely in a Crowd played
by the Park Lane Orchestra (Brunswick).
Liliue and Hanobano Hanalei by the South Sea Islanders
(Columbia).
peculiar or are there others who do not clamor
for sentiment as the pervading flavor in their
musical diet? Would they, too, like a little
humor in their daily slice of song?
More or Less Classic
Cavalleria Rusticana — Gli Aranci Ole^ano and
Cavalleria Rusticana — Inneggiamo II Signor.
By Metropolitan Opera Chorus with Orchestra.
(Victor). An expert recording of two of the
374
Short Reviews of Recent Releases by
Victor, Brunswick, and Columbia—
A List of Some New Record Albums
—Rimsky - Korsakov's Scheherazade
Suite Obtainable in Complete Form
most melodious of the choruses of Mascagni's
opera, sung with great beauty and restraint.
(a) Sheep' and Goat Walkin to trie Pasture
(Guion), (b) Gigue from First Partita (Bach),
and Liebestraum (Liszt). By Percy Grainger
(Columbia). Here is variety itself: a humorous
tale, a lively jig, and a romance all on the same
record, and each feelingly interpreted by this
master pianist.
Hungarian Dance No. i (Brahms-Joachim)
and Slavonic Dance No. 2, in E minor, (Dvorak-
Kreisler). By Toscha Seidel (Columbia). Two
lusty dances played with too mechanical vehe-
mence to suit us.
Lucrefia Borgia: Brindisi (Donizetti) and
Come to Me 0 Beloved\ (Bassani-Malipiero). By
Sophie Braslau (Columbia). We prefer the rol-
licking joyousness of the drinking song to the
heavy solemnity of the cantata but that is a
matter of opinion. The rich contralto voice of
this artist handles both expertly.
Love's Old Sweet Song (Molloy) and The Sweet-
est Story Ever Told (Stults). By Sophie Braslau
(Columbia). Miss Braslau digs way down in the
bag and brings up some of the old tricks. But
she sings beautifully.
Rigoletto: La Donna c Mobile (Verdi) and Caval-
leria Rusticana: Siciliana (Mascagni) by Charles
Hackett (Columbia). So convincingly does this
glorious tenor sing Verdi's surprise number that
one is almost ready to agree that woman is
fickle! Well, were it necessary, we would agree
to anything for the privilege of listening to
Hackett's singing.
Coq D'Or.. Hymn to the Sun (Rimsky-
Korsakov) and Song of India (Rimsky-Korsakov)
By Maria Kurenko (Columbia). We would like
the first selection better were it minus a few
coloratura frills. As for the S. of I. we said what
we had to say about that years ago. However,
it is beautifully sung.
Smiling Eyes and Roses of Picardy. By John
Charles Thomas (Brunswick). Why turn this fine
baritone voice loose on such shop-worn ballads
as these?
"Popular"
Among My Souvenirs and Washboard Blues
by Paul Whiteman and his Concert Orchestra
(Victor). Whiteman at his unique best. You
can't dance to these but who wants to? It's music
worth hearing.
Dream Kisses by the Ipana Troubadours
(Columbia). At last we have something different
in dance numbers! A soothing, insinuating
rhythm built for dancing and played for dancing
MARCH, 1928
NEW RECORDS
375
Interesting Record Albums
Beethoven-. Symphony No. p, in D minor (Choral) ALBERT COATES AND SYMPHONY ORCHESTRA factor
Beethoven: Concerto in D major, yiolin FRITZ KREISI.ER AND STATE OPERA ORCHESTRA,
BERLIN Victor
Brahms: Symphony No. i, in C minor LEOPOLD STOKOWSKI AND PHILADELPHIA ORCHES-
TRA Pictor
Schubert: Symphony No. 8, in B minor (Un- LEOPOLD STOKOWSKI AND PHILADELPHIA ORCHES-
finishcd) TRA
Tschaikowsky: Casse Noisette (Nutcracker Suite) LEOPOLD STOKOWSKI AND PHILADELPHIA ORCHES-
TRA
Chopin: Sonata in B minor, for Pianoforte. Opus 58 PERCY GRAINGER
Brahms: Sonata in A major, Opus 100. Violin and TOSCHA SEIDEL AND ARTHUR LOESSER
Piano
Ravel: Ma Mire I'Oye (Mother Goose) Suite for WAL'TER DAMROSCH AND NEW YORK SYMPHONY
Orchestra ORCHESTRA
Dvorak: Symphony No. 5. "From the New World" SIR HAMILTON HARTY AND HA LI. £ ORCHESTRA
Berlioz: Symphonte Fantastique, Opus 14 FELIX WEINCARTNER AND LONDON SYMPHONY
«ORCH ESTRA Colu mbia
Beethoven: Symphony No. 5, in C minor WILHELM FURTWAENGLER AND PHILHARMONIC
ORCHESTRA. BERLIN
Beethoven: Symphony No. 7, in A major RICHARD STRAUSS AND THE ORCHESTRA OF THE
STATE OPERA, BERLIN Brunswick
Hande!: Concerto for Organ and Orchestra No. 4 WALTER FISCHER OF THE BERLIN CATHEDRAL
(Op. 4) WITH ORCHESTRA
Mozart: Jupiter Symphony, No. 41 Opus 55; RICHARD STRAUSS AND ORCHESTRA OF THE STATE
OPERA, B
Victor
Columbia
Columbia
Columbia
Columbia
Brunswick
Brunswick
Brunswick
Richard Strauss: Kin Heldfnleben
I_/J-CKA, UHKLIN Brunswick
RICHARD STRAUSS AND THE ORCHESTRA OF THE
STATE OPERA, BERLIN Brunswick
The records in the above groups are to be had only in.album form. The list is by no means complete but serves to
indicate a few of the most interesting complete recordings which are available. The Rimsky-Korsakov Schehera-
%ade Suite (Victor) is reviewed elsewhere on this page.
by S. C. Lanin's Toothpaste Boys. On the reverse
is Among My Souvenirs. Ben Selvin makes as
good a dance record out of this as Whiteman
did a set piece.
A Shady Tree and There Ain't No Land Like
Dixieland To Me by Ernie Golden and His Hotel
McAlpin Orchestra (Brunswick). Two more hot
numbers from the orchestra under the direction
of the gent who has musical "it."
Yep! 'Long About June and Blue Baby by Ray
Miller and His Hotel Gibson Orchestra (Bruns-
wick). The first is a lively down-east-barn-dance
sort of number that will make your feet very
restless; the second, only another dance tune.
Both smoothly played by this excellent Cincin-
nati orchestra.
Back Where the Daisies Grow and Lonely in a
Crowd by the Park Lane Orchestra (Bruns-
wick). After hearing these two numbers you will
add the P. L. to your list of best orchestras.
Ooh! Maybe It's You and Shaking the Blues
Away by Ben Selvin (Brunswick). Not quite up
to the Selvin mark but you won't want to sit
still to either number.
Barbara and There's a Cradle in Caroline by
Ben Bernie and H. R. Orchestra (Brunswick).
Just another disappointment.
Together We 7"n>0and that'll You Do by Isham
Jones Orchestra (Brunswick). Isham has cer-
tainly been in seclusion long enough to have dug
up better numbers than these for his return en-
gagement.
My Lady by Cass Hagan and His Park Central
Orchestra. Simply swell! Two Loving Arms by the
Cavaliers. A grand waltz. (Columbia).
Are You Happy? and Kiss and Make Up by
Vincent Lopez and His Casa Lopez Orchestra
(Brunswick). Answering the question: No more
so than if we'd never heard this record.
Together We Two by Fred Rich and His Hotel
Astor Orchestra. (Columbia). Only moderate.
Baby Feel Go Fitter Patter by Harry Reser's
Syncopators. Won't you give just a little some-
thing for a decent funeral?
Where Is My Meyer? by Eddie Thomas' Col-
legians (Columbia). A good nonsense song from
the Chau-ce Souris sung by Frank Harris with an
orchestral background and a little yodeling for
good measure. Clementine by Don Voorhees
and His Orchestra is only fair.
A Lane in Spain and There Must Be Somebody
Else by Van and Schenck (Columbia). A very
good vocal duet aided by guitar and piano.
Watching the World do By by Ford and Glenn
(Columbia). Why shouldn't it? This isn't enough
to stop for. Are You Thinking of Me To-night?
by Elliott Shaw. Insomnia must be prevalent
among song writers.
There's a Cradle in Caroline and /'// Be Lonely
by Frank Bessinger and Ed Smalle (Brunswick).
Good sentimental singing.
I'm Coming, Virginia and Just a Memory by
the Singing Sophomores (Columbia). Leaves us
cold.
Twiddlin My Thumbs and The Pal You Left At
Home by the Whispering Pianist (Columbia).
Good rubber wasted on tripe.
Liliue and Hanohano Hanalei by the South
Sea Islanders (Columbia). Good Hawaiian
music magnificently played.
My Blue Heaven and The Song is Ended by
Jesse Crawford (Victor). If you know anyone
who wields a better movie organ than the organ-
ist at the Paramount Palace we would like to
hear of him. Jesse Crawford is at his very best
on these records.
Are You Lonesome To-night? and Under the
Moon by Lew White (Brunswick). But the
Roxy organist isn't far behind.
Estrellita and Mi Viejo Amor by Godfrey
Ludlow (Brunswick). Good violin solos by the
well-known staff artist of the National Broad-
casting Company.
A COMPLETE SYMPHONY
Scheherazade — Symphonic Suite (Rimsky-Kor-
sakow). By Leopold Stokowski and the Phila-
delphia Orchestra. Complete on five double-
faced Victor records.
When the Russian composer Rimsky-Kor-
sakov called this music the Scheherazade Suilt
he did not mean to imply that he was telling
musical word for spoken word,
the story of the Sultan Schahriar,
who so distrusted women that he
vowed to put each of his wives to
death after the first nuptial night;
and of Scheherazade, the Sultana,
who caused him to forsake his
vow by entertaining him with
fascinating tales for one thousand
and one nights, at the end of
which time it is to be presumed
that he had regained his faith in
women. Rimsky-Korsakov merely
used the title as a hint to his
listeners that the suite was "an
Oriental narrative of some numer-
ous and varied fairy tale wonders," told by some
one person to her stern husband.
Take the hint of leave it. If you take it you
can easily pick out the voice of the stern husband
with which the first movement, The Sea and
the Vessel of Sinbad, opens. It is a bold phrase
played in unison by the trombone, the tuba,
horns, woodwinds, and strings in their lower
range. Then the sweet, timid voice of Schehera-
zade, in the high trembling notes of the violin,
with the harp in the background. Then we hear
the long roll of the sea translated into music by
the violins. Now and then the lapping of the
waves on the vessel. In the second movement,
The Tale of the Prince Kalender, you can cer-
tainly identify the figure of the fakir prince in
the now sad, now comic, notes of the bassoon;
and there is no mistaking the wild violent dance
of the Orient in which brasses, woodwinds, tuba,
trombone, bassoon, and strings combine. The
third movement tells a love story of The Young
Prince and the Young Princess. The romance is
plainly indicated in the simple tender melodies.
And lastly there is The Festival at Bagdad, music
full of the color and sinuous rhythm of the East.
Queer minglings of sounds, seductive strains,
call to mind beautiful veiled maidens, snake-
charmers, swaying camels, spicy odors, per-
fumes of the Orient. Then suddenly we swing
back again to the sea, this time not the calm,
rolling sea of the first movement but a turbulent,
treacherous sea, in which the vessel of Sinbad
finally sinks, after a mighty crash on the rocks.
And as the waters close over the ship the voice
of the Sultan, now subdued, tells us that the
tale is over and he is pleased, and the Sultana
goes back to the opening theme of the strings
for her finale.
Beautiful music, rich, colorful, varied — deal-
ing with weird and wonderful events but always
essentially human. Played by a master or-
chestra directed by a master hand — a feast
to suit the palate of the most discriminating
of music lovers.
!
[
RADIO BROADCAST Photograph
A RECEIVER EMBODYING NEW R. F. PRINCIPLES
This six-tube Stewart- Warner receiver employs the features of r.f. design which are described in this article
Designing an R.
By Sylvan Harris
PERHAPS the most important problem
that remains in connection with the
design of radio receivers is that of con-
trolling regeneration and the tendency toward
self-oscillation. The patent situation in the radio
industry to-day accentuates the importance of
this matter, but aside from this, and considering
only the technical aspect of the problem, there
are certain important points concerning which
the layman's ignorance is appalling and on which
many engineers are doubtful. The most impor-
tant of these is, perhaps, the magnitude of the
amplification which a radio-frequency amplifier
can furnish under the most favorable conditions.
This problem will not be discussed here; it will
suffice for the present to state that the greatest
amplification that a radio-frequency amplifier,
having regeneration, will furnish, is determined
by the electrical characteristics of the circuits,
and takes place when the decrease in amplitude
of the feed-back current from stage to stage be-
comes less than equal to the natural amplifica-
tion in the opposite direction. That is, a voltage
established in the plate circuit of the last ampli-
fier (r.f.) tube, is decreased in each stage looking
in a direction toward the input of the amplifier.
In the opposite direction we have the signal
voltage passing from stage to stage, but being
amplified at each step. When the decrease in
amplitude in the direction of feed-back becomes
small enough, oscillations are established, and
it is at the instant that these oscillations are
established that the greatest amplification is
obtained.
The maximum possible amplification that can
0 10 20 30 40 50 60 70 80 90 100
PERFORMANCE. PER CENT
FIG. I
376
be obtained from the system under given con-
ditions can be computed. A method of making
this computation was shown some time ago by
Dr. A. W. Hull, in his paper on the shielded-
grid tube in the Physical Review.
It can be shown that, using the usual tubes,
and under the usual average circuit conditions,
it is not possible to obtain a gain per stage of
more than about loor thereabouts, in the broad-
casting spectrum, assuming reasonable values for
the circuit elements and the 2O1-A type tube
characteristics. Furthermore, the amplification
naturally drops off as the frequency increases be-
cause of several complicated tube and circuit
factors. The amplification we are referring to is
the maximum amplification obtainable, keeping
the adjustments such that the system is always
on the verge of oscillation.
This brings to our attention a particular phase
of the problem, »jf., that of keeping the overall
gain of the amplifier constant over the broad-
casting frequency range. Since the amplification
is naturally greater at lower frequencies than at
higher, the only way in which to make it uniform
is to operate very close to the point of oscillation
at high frequencies, and not so close at low fre-
quencies. On account of difficulties encountered
due to the stabilizing elements (grid resistors,
etc.), we have many sets which operate well at
MARCH, 1928
DESIGNING AN R. F. AMPLIFIER
377
300 meters but are "dead" at 500 meters, and
many of which are rather "wild" below 300
meters.
On the other hand, due to absorption in metal
panels, additional attenuation introduced by
neutralizing condensers, etc., we often encounter
the condition where the set is "dead" at the
higher frequencies also. Of course, these terms
are merely relative; it is clear that under any
circumstances the design of the receiver, espe-
cially when it is intended for production in large
quantities, must provide for sufficient tolerance
in this matter of operating close to the oscillation
point.
Another point which is of paramount im-
portance, especially as regards the production of
radio receivers in large quantities, is that of the
relation between the performance of a receiver
and its cost. Let us call the "performance" of
our ideal receiver 100 per cent, and the perform-
ance of the receiver which will not work at all,
o per cent. As regards the cost, let us say we can
build a receiver whose performance is zero per
cent, for practically nothing. On the ether hand,
as we improve the performance of our receiver in
uniform steps, the cost mounts up and up at an
ever-increasing rate, until it would cost an in-
finite amount to produce the ideal receiver
operating at a performance of 100 per cent. The
relation between the performance and the cost of
a receiver is probably an exponential one, and
may be something like the curve of Fig. i. Thus,
we can design and build a receiver having a "per-
formance" of 60 per cent, at a reasonable cost,
but when we attempt to improve the performance
by 10 per cent, more, we drive the cost way up.
Of course, the curve of Fig. I is purely qualita-
tive; it is intended merely to illustrate the idea.
The receiver described in these articles has
been designed with these ideas in mind; at the
same time it must be remembered that there are
certain circuit arrangements which are more
flexible than others, making it possible to build a
better receiver at the same cost, so that actually
Fig. I should be a family of curves, each curve
applying to a different type of receiver. As to
the merits of the receiver to be described here,
it will be well to leave these to the judgment of
the reader rather than run the risk of laying one-
self open to criticism.
It is well known that the presence of inductive
reactance in the plate circuit of a radio-frequency
amplifier tube results in regeneration. Further-
more, if that reactance exceeds a certain critical
value, oscillations will be established in that
stage, and further, the critical value varies with
the frequency. Many different methods have
been tried for keeping this reactance below the
critical value, such as varying the coupling in the
resonance transformers simultaneously with the
tuning condenser. The method used in this circuit
is unusual as applied to r.f. amplifiers, although a
similar arrangement has been used for controlling
regenerative detectors.
Fig. 2 illustrates the fundamental idea of the
R.F.
Choke (
FIG. 2
circuit. The coil L and the condenser C constitute
the tuned input circuit. In the plate circuit of the
tube there is the usual primary coil of a resonance
transformer, Lo. This inductance Lo is of such
value that the circuits would ordinarily oscillate;
in other words, Lo is greater than the critical
positive value.
In order to stop the oscillations the condenser
Co is introduced in series with Lo; the condensive
reactance furnished by Co is negative in sign, so
that the net positive reactance in the plate cir-
cuit of the tube is reduced, depending upon the
value of the capacity of Co.
It is clear that the net reactance can be made
almost anything we desire by this means. We
may so proportion Lo and Co that Xo may be
positive and greater than the critical value, equal
to or slightly less than the critical value, or, we
may even make Xo equal to zero, or make it
negative. When Xo is positive and greater than
the critical value, the circuits will oscillate; under
any other condition it will not oscillate. The spe-
cial case where Xo equals zero is known as the
"zero reactance plate circuit," and will be dis-
cussed later on. The case where Xo is negative
(or capacitive) is not of interest here, for under
such conditions the circuit becomes very in-
efficient, due to the absorption of power at the
input of the tube. These conditions have been
discussed by J. M. Miller in Circular No. 351
Bureau of Standards.
It would evidently be very cumbersome to
operate two condensers in each stage of the radio-
frequency amplifier, a three-stage amplifier re-
quiring seven condensers, three "twins" and
one "single." The obvious thing to do, therefore,
is to operate them all together. The problem re-
mains then, to so proportion the inductance and
capacity in the plate circuits so that when Co
is varied at the same rate as C (the tuning con-
denser) the net plate circuit reactance will be
slightly below the critical value at all frequencies.
The first problem in the design was, therefore,
to determine whether C and Co could be varied
at the same rate; this amounts to the same thing
as determining whether the plates in the two
condensers could have the same shape. In order
to determine this, as well as to determine other
things that were to follow, a system of measuring
the amplification or "gain" per stage was set up,
a description of which was presented by the
writer in The Proceedings of the I.R.E., July, 1927.
The complete circuit of the receiver is shown
in Fig. 3. Each stage is completely shielded,
originally in copper cans, but later in aluminum
cans. A laboratory set-up was made, in con-
junction with the measuring system mentioned
above, "single" condensers being used in the
receiver, with leads coming out of the cans to
which separate plate condensers were connected.
Each condenser was individually controlled.
With a constant-frequency signal impressed on
the input of the receiver, the condensers in the
plate circuits of the r.f. tubes were gradually and
simultaneously increased from zero upwards, in
steps, their capacities being always kept the
same, and measurements of the gain were taken
at each step.
At a high frequency, say 1500 kilocycles, a
curve similar to that marked fi in Fig. 4 was
obtained. At the upper limit of the curve the
circuits broke into oscillation. Having completed
this curve, a similar curve was obtained for a
slightly lower frequency, say 1750 kilocycles,
illustrated by curve fj of Fig. 4. So, a family of
curves was obtained, each curve for a different
frequency; sufficient curves were obtained so that
the operation over the entire broadcasting range
of frequency could be studied.
It will be noted that there is an inflection in
each of these curves near the upper limit where
oscillations begin. Above the point where the
inflection begins the system is very critical, so
it was evident that the greatest gain per stage
that could be utilized with safety at any given
frequency is at this point. In Fig. 4, therefore,
the points a, b, c, d, represent the greatest
amplification that can be obtained with the par-
ticular tubes, coils, etc. Through these points a
curve can be drawn, marked AB, from which
can be taken values to plot a curve of Co against
the frequency, or against C, which is the infor-
mation which was required. It was found that on
plotting Co against C, the curve obtained was
very nearly linear, indicating that it was per-
SINGLE CONTROL
B+R.F and
1st AF
B+ Power
Amp.
FIG. 3
378
RADIO BROADCAST
MARCH, 1928
fectly feasible to vary Co at the same rate as C,
and that the two condensers may have plates of
the same shape and may be driven by the same
dial.
It is evidently desirable to have the same shape
plates in the two condensers, in the interests of
economy as well as simplicity. It was also found
that with the given coils, the capacity required in
the plate circuit (represented by the points a, b,
c, d, of Fig. 4) at various frequencies was very
ff.Jf.
CAPACITY OF PLATE CIRCUIT CONDENSER
FIG. 4
close to that required in the tuning condenser C
at each frequency. This relation can be ad-
justed at will, by simply changing the design of
the resonance transformer; it was thought
advisable, however, to keep both sections of
the "twin" condenser the same, as this would
facilitate factory inspection, permitting the
inspection of both sections, by the same oper-
ator and on the same testing "jigs."
Upon setting up a model of the receiver, it was
found, that, whereas the amplification was con-
siderable at lower frequencies, it dropped off
very rapidly as the higher frequencies were ap-
proached. This was very noticeable when the
receiver was tried "on the air;" the ability of the
receiver to "perform" at wavelengths shorter
than about 350 meters was practically nil.
The problem then remained to increase the sensi-
tivity of the receiver at the shorter wavelengths,
leaving the sensitivity at the longer wavelengths
the same.
The means used for doing this is, as far as the
writer is aware, a new one; it is new, not in the
sense that it has never been used before, but in
the sense that it has been done intentionally and
with a definite purpose. There is plenty of coil
capacity in plenty of receivers, but as far as
the writer has been able to find out, no one has
heretofore attempted to put this coil capacity to
a good use.
Up to this point in the work the primary coils
of the resonance transformer were wound in a
single layer at one end of the secondary, sep-
arated from the secondary by about one-quarter
of an inch. The idea occurred that by introducing
a slight amount of capacity coupling in the reson-
ance transformers, in addition to the magnetic
coupling, the regeneration at the higher fre-
quencies would be slightly increased, and the
desired increase in amplification would be there-
by attained.
Consequently, the primary coil of one of the
resonance transformers (that preceding the de-
tector) was wound on a short tube and slipped
inside the secondary. When tuned to a short
wavelength (or high frequency), the response of
the receiver would gradually increase as this
primary is moved up into the secondary further
and further, until oscillations begin. This point
is located, and the primary coil is then fixed in
place slightly below it. Besides the advantage
gained by increasing the amplification at the
higher frequencies and thus solving the greatest
problem which was encountered, there is an
additional and important advantage gained by
making the primary adjustable at the factory.
It is possible by this means to insure uniform
production of receivers with regard to sensi-
tivity.
The effect can be explained qualitatively by
means of Fig. 5. The curve AB is supposed to
represent the amplification curve of a stage of
the r.f. amplifier before the coil capacity has been
introduced. On introducing the coil capacity the
curve rises at the right-hand side, resulting in the
curve AC. On the first trial a considerable de-
pression was found in the curve at a frequency of
about 850 kilocycles. It was found, however, that
by properly adjusting the self-inductance of the
primary as well as its location within the second-
ary, this depression could be made to disappear
almost, and the amplification was thus made
practically uniform over the entire broadcasting
spectrum.
The resulting receiver proved to be very sensi-
tive and selective. No difficulty was experienced
in separating the local broadcasting stations in
either New York or Chicago, and it was possible
in many cases to even tune-in stations between
the locals.
There are several other additional features of
this receiver which are worthy of mention. One
of these is the location of a separate filament re-
sistor in the negative lead of each tube filament
of the r.f. amplifier.
By this means a negative bias is placed on each
grid, with the resu't that the receiver is very eco-
nomical with respect to the B supply. The maxi-
mum plate current is about 27 milliamperes,
and on receiving local concerts, sufficient volume
for ordinary sized homes is obtained with the
volume control "just on," and the set drawing
only about 10 milliamperes. This latter state-
ment holds also when receiving some powerful
stations at fair distances.
Another feature of the receiver is the C battery
detector. This type of detector was used instead
of the grid leak-grid condenser type on account
of its ability to rectify more powerful signals be-
fore overloading occurs. It also cuts down the
costs by eliminating the grid condenser and leak,
and necessary inspection were they used. The
difference in sensitivity between the two types of
detectors is of secondary importance in this re-
ceiver on account of the great sensitivity of the
r.f. amplifier.
The input stage of the amplifier is tuned by a
"single" condenser, and, in addition to this, has a
portion of the secondary winding cf the antenna
transformer variable. There are also three taps
on the primary or antenna coil, so that by means
of the taps and variable portion of the secondary,
the input stage is made very efficient. The con-
stants of this stage, however, are so chosen that
no matter on which of the three points the switch
may be set, it is not possible to "pass over" any
except the very weakest signals when varying
the condensers.
Another feature of the receiver is the absence
of bypass condensers in the r.f. amplifier. The
only place where a bypass condenser is used is in
shunting the primary of the first audio trans-
former. The general wiring of the receiver makes
it unnecessary to use them, the only avenue of
exit for the r.f. currents outside of the grid and
C
FREQUENCY
FIG. 5
plate leads being the B supply lead, which is
blocked by an effective r.f. choke coil.
The greater part of the wiring is in the metal
of the receiver — the aluminum cans and base.
The ground accommodates the A minus, B minus,
and C plus, making the entire wiring job a very
simple one indeed. A "matched unit" construc-
tion is used, the four cans and their contents
being identical in many respects. The first stage
differs from the rest only in the coil and single
condenser, and the fourth can (the detector
stage) differs only in having an individual fila-
ment control. This was deemed necessary, or at
least desirable, on account of the varying charac-
teristics of electron tubes. But when once this
rheostat is set for a particular tube, there is no
further necessity of adjusting it.
The mechanical arrangement of the receiver
is also novel. The separate cans are easily re-
movable, for servicing purposes, by simply
loosening the screws on the backs of the cans
which hold the terminal lugs fastened on to the
four or five leads connecting to the can. All the
battery supply leads are cabled along the rear
of the set outside the cans. Likewise the audio
amplifier, of the transformer type, is removable
as a unit, in the same manner. There are four
"twin" condensers and one "single" condenser
in the receiver, all of which are driven by the
same mechanism. To facilitate the "matching"
of condensers while the lids cf the cans are in
place, the front steel panel on which the con-
densers are mounted is slotted, so that the stators
of the condensers can be rotated through a small
angle and then clamped in place.
The great sensitivity of the receiver described
here is due to several things; first the primary
self-inductance is a little greater and the coupling
is slightly closer than in the usual resonance
transformer employed in r.f. amplifiers. Further-
more, it is possible to adjust, and to maintain the
adjustment closer to the oscillation point than is
usually the case. Next, there is the reduction of
grid losses due to the grid bias on each r.f. ampli-
fier tube, and finally there is the tuned input
stage.
Suppressing Radio Interference
Some Recently Investigated Sources of Interference — Trouble from High-Tension Lines and
Distribution Systems — Qeneral Hints on the Location of Sources, the Arrangement of a Patrol
Car, and the Receiver to Use — Procedure in Patrol Work and the Many Misleading Clues
rHEN we consider that a little spark,
say one-sixty-fourth of an inch long,
can cause severe radio interference, it
becomes obvious that almost any piece of elec-
trical apparatus in ordinary commercial use is
a potential source of trouble. This does not mean
that all electrical accessories do actually give
rise to disturbances. On the contrary; consid-
ering the expansion of the electrical industry
and the universal use of electrical equipment, we
may well marvel that the noise level of the
average city is so low.
When looking around for the possible cause of
interference, however, nothing in the electrical
line should be overlooked. It may help a little
if we detail some of the sources located recently
in following up interference complaints: —
( i.) Printing office linotype motor; normal
operation, no fault. Cleared up by method
(a) Fig. i.
( 2.) Clippers in barber shop. Normal. Cleared
up by method (a) Fig. i
( 3.) Same source as above. Abnormal — com-
mutator grooved. Used method (c) Fig. i
( 4.) Cream tester in dairy plant. Normal.
Used (a) Fig. I
( 5.) Battery charger, vibrating reed type.
A i-mfd. condenser across contacts elimi-
nated trouble.
( 6.) Same source as above — different manu-
facture. Required method (a) Fig. i
( 7.) Refrigerator, home type artificial refrigera-
ation. Used method (a) Fig. I
( 8.) Battery Charger, rotary rectifier. Obstinate
case. Used method (c) Fig. I
( 9.) Woolen mill, static neutralizer. Defective
plug connection. Repaired.
(10.) Brass foundry, lighting wires crossed and
sparking, concealed. Confusing, as cor-
responded with vibration of large motor
which was shaking floor. Motor supply cut
abruptly but radio interference died gradu-
ally with slowing down of motor giving clue
to the trouble, which was located and
fixed.
(n.) Voltage regulator in a power station.
Case still pending.
(12.) Chattering circuit breaker in power plant
operated by thermocouple. Breaker re-
adjusted and interference disappeared.
(13.) Washing machine motor, defective. Re-
paired.
(14.) Thermostat, mounted on wall subject to
abnormal vibration. Bad clicking radio
interference. Changed location of thermo-
stat to solid wall.
(15.) Constant-current transformer in power
station. Case pending.
(16.) Noisy grid leak in complainant's radio set.
Referred to service man.
(17.) Elevator in apartment house. Under in-
vestigation.
(18.) Bakery oven. Thermostats to regulate heat
and operate gas lighting jump sparks.
Case pending.
Many other cases of interference reported in
the same period had their origin in apparatus al-
ready discussed in previous sections while
an additional number arose from defects on
power lines, all of which were located and
rectified.
By A. T. Lawton
HIGH-TENSION LINES
IN THIS category we include primary distribu-
tion systems operating on from thirty thou-
sand to one hundred and ten thousand volts a.c.
We must frankly admit that the data on in-
terference from this source are far from complete.
Difficulties of a practical nature are responsible.
Thirty or more towns may be served by say, a
UNDER the title "Suppressing Radio Inter-
ference" the author has printed three previous
articles in this series, all of which deal, in an en-
lightening and comprehensive fashion, with the
different forms of interference with which the radio
listener may have to cope. Each article in the series
is complete in itself, and should be read by all
radio men whether they are troubled by man-made
static or not. Mr. Lawton' s articles cover a period
of two and a half years' research made in more
than i jo different cities. The first article appeared
in the September, 1927, RADIO BROADCAST, and
dealt with interference caused by oil-burning
furnaces, electro-medical therapeutic apparatus,
X-Ray equipment, and dental motors. The Novem-
ber article dealt with interference from motion pic-
ture theatres, telephone exchanges, arc lamps, in-
candescent street lamps, flour mills, factory belts,
electric warming pads, and precipitators. In the
January, 1928, RADIO BROADCAST, the following
sources of interference were dealt with: Farm
lighting plants, railway signals, land line telegraph
and stock tickers, radio receivers, and electric
street railways. The present article is of especial
interest to radio clubs and organisations contem-
plating the construction and operation of interfer-
ence locating equipment.
— THE EDITOR.
i io,ooo-volt three-phase system and to cut this
line the required number of times for test pur-
poses is out of the question since all towns de-
pending on it for electric power would be inter-
fered with to a prohibitive extent.
Also, when suspicion to any piece of apparatus
in connection with such a line arises and arrange-
(a)
(b)
Choke Coil
> 1
2 Ground
Q.
Q.
13
CO
ments can be made to have it investigated at a
close range, the line must, of course, be cut prior
to detail inspection. Complications enter;
foreign matter, deposited at such points as to be a
possible cause of the trouble, is burned up by the
surge produced on cutting the line. The investiga-
tor, not noting any apparent defect, and no spit-
ting of current being possible for an audio check,
often removes the source of the trouble uncon-
sciously.
Where several possible sources are observed
all must be rectified at once in order to get the
line back in operation as quickly as possible,
so even if elimination of interference is secured
the exact source is not definitely established.
Piece-meal elimination is a theoretical idea —
desirable from a scientific standpoint but im-
practical.
It is probable that a slightly leaky insulator on
a iio,ooo-volt line will cause radio interference
though certain observations point to the con-
trary. For instance, a six-petticoat suspension
insulator which was spitting vigorously over
three petticoats caused absolutely no radio
interference on a three-tube regenerative re-
ceiver located thirty feet distant. Possibly this
caused a disturbance farther out on the line but
other disturbances at the same points compli-
cated the determinations.
If a high-tension conductor on a pin insulator
is not fastened down securely, audible hissing is
usually the result, but it gives rise to no radio
interference. Two defective wall bushings on a
I2,ooo-volt line showed considerable spitting,
which gave an audible noise, but there was no
indication of radio interference on a "patrol"
receiver in the vicinity. Out on the line half a
mile or so it was impossible to tell whether these
constituted material sources or not; if anything,
the "mushy" noise usually associated with high-
tension lines was slightly augmented.
We must not assume that because a line, d.c.
or a.c., produces audible noise, it necessarily
gives a corresponding radio interference. Take
the case of a d.c. line operated at 700 volts and
carrying thirty thousand amperes. The "lines"
(C)
,-Chokes
a.
o g.
3? co
,° "^
1-mfd. Condensers 0.5-mfd. Condensers
0.5-mfd. Condensers
Choke Coil Data : Approx. 70 Turns
No. 14 D.C.C. Wire . Hardwood Bobbin
Measurements- a ifcb-)ffc-i£4t-4?e-L'
--J
FIG.
379
380
RADIO BROADCAST
MARCH, 1928
in this case were composed of several hundreds
of wires or, rather, rods, bound together at in-
tervals and were mechanically noisy but varia-
tions of this heavy current caused no radio
disturbance.
When two separate conductors are used as one
on a high-tension line, running close together and
attached to the same insulators, there will likely
be audible hissing although the voltage at any
given point is equal on both wires. Prevailing in-
terference could not be definitely associated with
lines of this nature.
It is worth noting that the smelting arcs fed by
the thirty-thousand ampere d.c. line referred to
above do not set up any serious disturbance be-
yond about one hundred yards. Even within this
distance we are inclined to think that some of the
interference noted on test had its origin in as-
sociated apparatus because in the near vicinity
of three a.c. arcs, operating on 22,000 amperes,
reception from station WGY, 300 miles distant,
was possible with the receiver within 60 feet of
the arcs.
The charging of h.t. lightning arresters sets up
heavy interference. Charging is done twice daily
as a rule, each operation requiring only a few
seconds. Where there are many sub-stations in a
restricted area it is usual to arrange to have the
arresters charged at 2 A.M. and 2 P.M. instead of
during the more significant broadcasting hours.
Thick snow falling between the horn gaps is
pretty sure to cause considerable snapping and
the interference, being vigorous, is propagated for
miles.
Surprising as it may seem, the normal inter-
ference field of a i io,ooo-volt a.c. line has much
in common with a 6oo-volt d.c. trolley feeder.
Within fifty or sixty feet of either, reception is
doubtful, but an abrupt cut occurs here, and
a few feet farther away normal reception is
possible, a condition which would seem to in-
dicate magnetic coupling rather than a pick-up
through direct radiation.
A.C. lines of fifty-thousand volts or so can, of
course, set up currents of very high potential in
parallel systems. We know that enough energy
is transferred by induction to the overhead
ground wire of a ioo,ooo-volt line to supply
lighting power to small communities, and ad-
• vantage is taken of this in many localities for the
purpose mentioned. It is obvious then, that
where h.t. lines and part of the city distribution
system run parallel at close range, any irregular-
ity of the high-tension line will transfer a vigorous
surge to the city system — a surge of sufficient
initial amplitude to carry it all over the dis-
tribution and create widespread interference.
The source in a case of this nature was recently
located seventeen and a half miles from the
town affected.
It has been noted in a few cases, that h.t.
systems having telephone lines on the same poles
or towers appear to be the greater offenders.
Further research is required here and must be
carried out with the full cooperation of the line
engineers and their qualified assistants. All
h.t. switches are not set with a cycle counter al-
though they really should be, and any investiga-
tor who happens to be touching bare metal
parts of the parallel line telephone installation
when the h.t. line is cut will probably have good
reason for remembering the incident.
In the case of noisy h.t. lines we do not know
of one exception to the following: In sub-zero
weather, interference is very bad; in mild
weather, it is slight; in rainy weather, when all
the insulators and cross arms are dripping wet, it
is practically nil. Offhand, we are inclined
to believe that this notorious trouble originates,
not at any one specific point, but is the result of
thousands of small brush discharges all over the
system. Incidentally, we hope that we are wrong;
the outlook for elimination is indeed poor if our
diagnosis happens to be correct.
DISTRIBUTION SYSTEMS
JUST what percentage of a city's total inter-
•' ference originates on the local distribution
system is a difficult question. One thing is cer-
tain; any interference occurring here is serious
because of its proximity to the broadcast listener
and its wide range. One loose primary cutout on
a 22oo-volt line can propagate severe interference
for two miles in one direction and every wire
running parallel picks up the disturbance by
induction and spreads it all over the district.
Now there are two primary cutouts used in con-
nection with every transformer, except in the
case of banked units, and if there are three
hundred transformers in the city we have roughly
six hundred potential sources of trouble from
this agency alone.
Primary cutout interference represents about
seventy-five or eighty per cent, of the total
trouble caused by power lines in any city at
any time. We should remember that this means
no material loss of energy to the power com-
pany; such faults will not necessarily affect
power consumption or even cause the house
lights to flicker. For the sake of the good will of
the public, however, it is in the interest of the
operating company to give this particular
accessory careful attention.
Interference from this source takes the form of
a hard buzzing. It may be steady or intermittent;
gusts of wind shaking the pole may start or stop
it and heavy trucks passing along the road will
do the same thing. Several cutouts buzzing in-
termittently will give the effect of wireless
telegraph transmission and is easily confused
by persons unfamiliar with the code.
A systematic check with a radio receiver
should be made of such sources at least twice
yearly. In one city, 146 transformers were
checked and 41 loose cutouts giving rise to radio
interference, were found. In another city the
relative figures were higher.
The next fault, in the order of frequency of oc-
currence, is that of primary leads (22oo-volt)
spitting to the transformer case, guy wires, or
crossarm braces. Severe buzzing results in the
first case — practically the same characteristics as
primary cutout interference — and it doesn't mat-
ter whether the transformer is grounded or not.
Spitting to an insulated guy wire gives rise to
a heavy clicking interference rather than buzzing.
Where the primary lead is scraping on a brace the
disturbance is not unlike that produced by the
home type violet-ray machine but may, under
varying conditions, take a different form.
Tree grounds are next in order. The intermit-
tent "zip" from this source is very annoying.
Even a little green twig waving on a bare 2200-
volt feeder can set up enough "chirping" to
bother reception. Tree trimming is the obvious
remedy here but property rights, etc., come up,
and much difficulty is often experienced in
getting action. It might be as well for tree owners
to reflect on the fact that copper has a bad effect
on tree growth and if a copper spike be driven in
the base of a healthy tree the tree will perish.
Chemical analysis of branches, grooved and
burned by 22oo-volt lines, showed a deposit of
copper, not only at the point of contact, but
also a short distance either way, just as though
the sap were absorbing this fine deposit and
spreading it through the tree system.
Interference from the next source, loose splices,
is not common. When such faults are present
they give rise to heavy clicking. Ge'nerally speak-
ing, poor splices or connections are the result of
winter jobs, done in zero weather when the line-
man's lot is no sinecure.
1 1 is not usual to find cracked or leaky bushings
in transformers. There are instances, of course —
a few bad ones — but they are rare. Also, in a
thousand odd transformers checked, only one
had loose inside connections, and there were
three of them in the one transformer. This
particular source wiped out reception in two ad-
joining towns.
LOCATION OF SOURCES
WHILE access to a properly equipped radio
patrol car is desirable, much good work in
the location of sources of radio interference has
been done with an ordinary loop receiver and
standard automobile.
In order to get an idea of the area covered by
any given interference, it is usual to telephone
various radio fans throughout the city and find
out if interference coinciding in time and char-
acter with your own case prevails at the distant
points. The distant observer should bring his
loud speaker near the house telephone so that
you may be able to check the noise from his set
and your own at the same time. Another method
is for the various observers to keep a log of the
characteristics and periods of activity of the
trouble under investigation. Synchronized
watches should be used here.
Knowing the general location, use is then made
of a loop receiver carried around in an automo-
bile. Any good super-heterodyne or radio-
frequency receiver with a volume control is
suitable.
Once in a great while some use may be made of
the directional properties of the loop; for the
present, disregard this feature for it is mis-
leading.
Prop the loop in a fixed position, not too close
to the side of the car, and drive around the
affected district. At some point where the inter-
ference is strong, cut down the volume control
so that the noise is just audible. Then repeat the
patrol. It is probable that another point will be
found where the noise comes up slightly; cut
down the volume control further and keep
lowering it at every increase in the intensity of
the disturbance until there are only one or two
points on the patrol route where the noise is
audible.
An inspection is then made, watching out for
garage battery chargers, transformer cutouts,
chiropractors' offices, etc., etc. If the trouble
seems to be in any way connected with the
lighting or distribution system it should be re-
ferred to the power company for action.
The foregoing gives a general idea of the
method followed in running down radio disturb-
ances. In view, however, of the growing interest
and activity along this line, it might be of help to
those organizing patrols on a large scale if we go
into a little more detail.
THE car should be a six-cylinder one; com-
plicated interference requires that the re-
ceiver volume control be cut down until the dis-
turbance is a mere whisper and any mechan-
ical rumbling noise is a detriment to the
patrol.
The car body, above the waist line anyway,
should be of wood, facilitating inside loop re-
ception. Metal bodies shield an inside loop and
weaken the signals in addition to distorting the
wave direction.
Measures are taken to prevent the ignition
interference unduly affecting reception. No
standard method, applicable to all cars, can be
MARCH, 1928
SUPPRESSING RADIO INTERFERENCE
381
recommended, but one of the following methods,
or a combination of them, should be effective:
(i.) A one-microfarad condenser across the bat-
tery circuit; attach one side to the ammeter
terminal and the other under any convenient
nut in contact with the chassis. Paint or
enamel causing imperfect contact should be
scraped away.
(2.) Duplication of method (i.) except that con-
nection is made at the coil primary instead
of at the ammeter.
().) Seventy-five turn choke coil, enclosed in a
metal box, inserted in the lead from the dash
switch to the coil primary.
(4.) Complete box screen of fine mesh wire gauze
over cylinder head clamped around engine
block arid covering spark plugs, distributor,
and ignition cables. Removable side gate is
fitted giving access to the enclosed parts.
Where trouble is experienced from the gen-
erator a one-half or one-microfarad condenser
from the positive brush to the chassis will help,
and if the tail light cable is carrying a surge
another condenser will be required here.
All low-tension wiring should be of armored
cable but copper braid over the high-tension
leads, while it clears up the interference, is ob-
jectionable since it tends to founder the spark
energy.
It is not desirable to wipe out the ignition
click completely; leave a slight trace of it to act
as a pilot signal for the receiver.
The layout of interior fittings, i.e., desk, cup-
boards, etc., will depend on the size of the car
and the scope of the patrol. Convenient racks for
record books, etc., should be fitted; it is very
necessary to have a place for everything and
equally necessary that the interior of such a car
be kept, at all times, in first-class order.
THE RECEIVER
COR official patrols, a good stable super-
» heterodyne receiver is desirable. We specify
stable because so many "supers" burst into oscil-
lation under the conditions of patrol — especially
near high-tension lines. I n this case the " mushy "
note of oscillation and the normal h.t. interfer-
ence are almost identical, and accurate determi-
nations are not possible.
Any make of tube known to be microphonic
should be ruled out without further consider-
ation. It is not necessary to take the precaution
of mounting the sockets on rubber. A volume
control of some nature is essential but throwing
the set out of tune to accomplish this is not
recommended.
The loop is mounted on a swivel base, allowing
at least ninety-degree rotation and the three
leads to the set should be sewn in a flat strap
leaving a distance of three-eighths or half an
inch between each wire. A storage A battery and
dry cell B batteries are connected to a receptacle
which is fixed permanently at some convenient
point on the desk front. The corresponding plug
and cable is, of course, attached to the "super."
A neat box containing spare A and B batteries
should also be carried, and should be fitted with
a receptacle similar to the desk one.
Where metal body cars are used the loop is
mounted outside, on the car roof, the handle for
rotation coming down through a special weather-
proof fitting.
It is obvious that in the course of extended
patrol the receiver will get some rough usage so
it is important that very careful attention be
paid to all connections and steps taken to make
the equipment as rugged as possible. Nothing
can be more exasperating than to have this gear
fail at a critical moment when tests involving
much prearrangement are being carried out.
Condenser bearings must be set up fairly fright
so that vibration of the car does not alter the
tuning. Mechanically unbalanced condensers,
mounted in a vertical plane, which move ever
so little through jolting of the car, can throw a
patrol into complete chaos. Frequent observation
of the filament ammeter is important; a slight
drop in filament current after the first intensity
observations have been made can cause consider-
able confusion.
Inclusion of a loud speaker in the equipment is
not recommended since this instrument tends to
suppress the finer characteristics, harmonics and
overtones, of specific interferences, rendering de-
termination of their origin more difficult. Head-
phones, exclusively, are used on standard
patrols.
PATROL WORK
C UCCESSFUL patrol work is largely a matter
*J of experience. Given a suitable car and the
necessary receiving equipment, the beginner is
apt to become discouraged at his failure to secure
immediate results — a condition which will pro-
bably last until he learns some of the wiles of the
elusive interference and knows the pitfalls to
avoid.
In the first place, the directional properties of
the loop are practically valueless in city work; its
plane for maximum sensitivity will, in every
case, be parallel to the adjacent street wiring and
instead of pointing toward the source, may
point in any direction away from it. There is
just one circumstance in which a rotating loop
can be of value and it is simply to cover this one
condition that we recommend the swivel base.
If the patrol is parked at the corner of in-
tersecting streets where distribution wiring runs,
say, north and south on one street and east and
west on the other, it is sometimes an advantage
to know on which set of wires the interference is
stronger. The loop may be turned through ninety
degrees while the car is parked directly under
the intersection of the wires and a determination
arrived at. The system showing the greater dis-
turbance is then followed up.
It is popularly supposed that, at its source,
interference is very loud, and that its intensity
tapers gradually to zero as we move away. This
is only partly correct. As a matter of fact, one
often finds that actually at the source, interfer-
ence is much weaker than, say, fifty feet away.
Suppose, however, we start patrol in the vicinity
of a source where the noise is very loud. On
moving away, say, 250 feet, the disturbance falls
to zero; at 500 feet it is up again very strong.
At 750 feet it has died again; at 1000 feet it
comes up, and so on for a mile or more of straight
patrol. We can see that this trouble is a case of
forced oscillations creating standing waves on
the distribution system and the varying intensi-
ties plotted out take the general form of a sine
curve.
In contrast to the sine curve, however, suc-
cessive "bumps" or peaks of intensity will be
slightly weaker than the preceding one, that
is, when we are moving away from the source.
The reverse is true when we approach the source
from a distance.
By cutting down the volume control to bare
audibility in the vicinity of the heavy bumps
it is possible to narrow down the trouble to a
small area, since nothing will be heard where only
a slight bump prevails. The audibility control
should have a knob and pointer rather than a
dial; it is desirable to be able to switch on to full
volume at intervals but we must know, accurate-
ly, the original setting to which to revert. Failure
to note this renders comparisons with previous
observations inaccurate.
Now, in the course of this patrol, certain com-
plications will probably enter. We are assuming
that the disturbance is strongest near the source
— if not directly at the source — and, naturally,
are watchful for the strongest "bump." In
ordinary reception, say, from some broadcasting
station, a difference of half a mile or so in dis-
tance between the station and receiver makes
very little difference in signal strength. A few
feet, however, can make a big difference in the
intensity of radio interference being guided by
city wiring; simply moving the patrol set over
to the other side of the street may make as much
WHERE RADIO COMPETES WITH THE WASHING
The owner of these tenements in Long Island City, New York, does not permit construction of
antennas on the roof, with the result that a forest of back yard poles at crazy angles support the
necessary antennas. Interference from improperly operated receivers is frequently acute in such con-
gested areas
382
RADIO BROADCAST
MARCH, 1928
as 40 per cent, reduction or increase as the case
may be. For this reason it is desirable always to
keep the same distance from the curb when pa-
trolling, so far as this is possible, and occasional
observations should be made to see that the line
is still on the same side of the street being
patrolled. If it has crossed over at an unob-
served point and continued on, on the other
side of the street, misleading checks may result.
Every wire, directly connected or not, in the
vicinity of a vigorous source of radio inter-
ference, will pick up the disturbance and radiate
it in different directions; trolley wires, being
much nearer the loop than the power wires, will
give a heavy indication even when the trouble
is not in any way connected with the car system.
Service wires running low across the street will
also produce a false peak and, incidentally, give
a bogus direction if directional properties of the
loop are being counted upon.
Potheads and pole ground wires are notorious
misleaders of the unwary. At these points the
overhead wiring is brought right down to us and
we will get a heavy bump of the noise when pass-
ing the pothead or ground wire although the
source may be half a mile or more away. The
bump here may even be stronger, so far as effect
on the receiver is concerned, than at its loudest
point near the source.
In the affected area, nearly every street corner
or intersection registers a number of confusing
bumps. This is due to abrupt physical changes in
the circuits, free radiation probably, since high-
frequency surges dislike going around sharp
corners.
A rise in the disturbance intensity will be
noted at each transformer passed during patrol
but when the car is running over an iron bridge
with side supporting girders, interference will
drop practically to zero although the source
may be nearby. A peak will be registered at dead
ends and circuit stops also, whether the wires are
alive or not. Dead wiring is just as effective in
propagating radio interference as live wiring and
under certain circumstances the actual source
may be on a system which is not energized except
by induction from some other line. If a dead cir-
cuit having on it a partial ground, parallels a
high-tension line, the voltage induced in the
former is sufficient to cause a spit-over at
the imperfect contact, resulting in severe dis-
turbance.
Where complicated interference is being in-
vestigated on streets on which electric cars are
run, much time will be saved by carrying out the
work between the hours of i A.M. and 5 A.M.
In fact, these are the best hours for radio patrol
work up to the point of location to a given pole
or residence. Daylight inspection is then neces-
sary. During the early morning hours street car
activity is at a minimum and traffic conditions
are ideal for concentrated patrol.
One thing to be religiously avoided is any
tendency to jump at hasty conclusions; an in-
vestigator cannot be too careful on this point.
Literally hundreds of reasons, each with a story
behind it, can be cited to show how very neces-
sary it is for the patrol man to attack his problem
wrth a perfectly open mind. One example se-
lected at random, may be of interest. Reception
over a fairly wide area in a certain town was
being spoiled by a strong buzzing interference.
The "buzzes" came at one-second intervals and
kept up for days at a time, stopping for a few
hours or a day, as the case might be, and then
starting off again. It was narrowed down to two
buildings — a large factory and an electrical
power plant. Generator interference close to the
plant swamped the disturbance being investi-
gated, but it was learned here that the "static
ground detector" on the factory supply lines
(2200 v.) showed an intermittent ground on one
phase. The factory electrician had checked every-
thing in detail and insisted there were no grounds
on his end of the business; the power company
did likewise. Service was not impaired in the
least but still the radio interference corresponded
exactly with the swinging of the ground in-
dicator, and such a ground on the 22oo-volt sys-
tem would account for our trouble.
We might say that there was absolutely no
reason whatever for suspecting this meter; it
was a standard instrument made by a very re-
liable firm. Nevertheless one of the condensers
in it had broken down and constituted the
source from which our radio interference orig-
inated. The trouble was eliminated with des-
patch.
It must be obvious from what has been said
that the location of the source of any given dis-
turbance is not always an easy matter. The work
is doubly difficult in the case of intermittent in-
terference or that which periodically alters its
intensity. Where several sources are active at
the same time, the resultant confusion de-
mands close concentration on the part of the
investigator.
On all standard patrols a five- or six-pound
sledge hammer is carried. If the characteristics
of the interference indicate power line trouble,
patrol is carried out until the source is confined
to half a block or less on one street. Then the
suspected poles are tapped with the sledge and
any loose connection of any nature whatever
will immediately show up on the patrol receiver,
usually as a violent buzzing. Loose primary cut-
outs, defective lightning arresters, partial
grounds, bad splices — all show up definitely and
at once.
Care is taken not to hit the pole too hard; an
inexperienced investigator can cause damage
here. If looking for loose splices, the pole should
be tapped in the plane of the overhead wiring
since right-angle tapping does not always send
the vibration along the wires. A moderate tap
in the plane of the wiring will show up defective
splices five poles distant.
Literally, thousands of transformer poles have
been checked in this way and we know of only
three instances in which the method failed. In
these instances the cutouts were jammed me-
chanically solid and could not vibrate but at the
same time they were making poor electrical con-
nection. Such cases are extremely rare, the point
is worth noting however, in view of a possible
recurrence.
Poles giving an indication of severe interfer-
ence on the first tap are not jarred a second time,
since the loose cutouts are liable to fall and dis-
rupt the service.
When a lineman is setting up loose cutouts it
is desirable to check with the sledge hammer and
radio set, tapping the pole while the lineman is
still aloft. A cutout in proper order for lighting or
power purposes may, at the same time, be a
source of radio interference because of some ap-
parently insignificant internal sparking.
We might say, in passing, that a good many
faults have been found in perfectly new line
accessories and constructions; new installations
are checked just as carefully as old construc-
tions.
COMPLAINT RECORDS
THE method of handling complaints, adopted
by public utility companies and other
organizations engaged in radio interference elim-
ination work, varies according to the services per-
formed and the area covered. The questionnaire
system finds favor in certain quarters. Its ap-
plication, however, is limited, and where work
is being carried out on a large scale the ques-
tionnaire is worse than useless.
Details of the recording system for taking care
of nationwide patrols with which the author is
associated would serve no useful purpose here;
it may be remarked, however, that the central
authority diagnoses every complaint, and, on
the information given, endeavors to fix its
source. If this can be done, appropriate remedial
measures are recommended; if not, the nearest
patrol car is ordered to the location and trained
experts take over the case, reporting to the divi-
sion headquarters on completion of the work.
Here, the information is classified and re-
corded together with other data relative to the
particular location, i.e., previous cases cleared
up, specific sources, general noise level, local
patrol facilities, radio clubs, etc., etc. In this
way a fairly accurate check is kept on the general
interference situation, which facilitates the lay-
ing out of future patrol work for the staffs en-
gaged.
In reviewing the radio situation generally and
from direct contact with thousands of broadcast
listeners, we are forced to the conclusion that the
greatest need in the radio game to-day is
a concentrated and determined effort to rid
every town and city of all preventable interfer-
ence.
The suppression of every source is a practical
impossibility, but it is obvious that the noise
level of any given centre can be considerably
reduced. Much work along this line has been
done by different private corporations and vari-
ous governments, and we hope that the day is
not far distant when every city will have its
specially equipped radio patrol car to run down
interfering disturbances and give radio the
chance that it deserves.
RADIO BROADCAST ADVERTISER
.'583
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When next you purchase a set, kit
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RADIO BROADCAST ADVERTISER
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The Radio Broadcast
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose alvays to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to
that time was printed.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. i to 88, can be secured from the Circulation Department,
Doubleday, Doran & Company, Inc., Garden City, New York, for jji.oo. Some readers
have asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any such errors do occur, a new Laboratory Sheet with the old
number will appear.
— THE EDITOR.
No. 169
RADIO BROADCAST Laboratory Information Sheet
Data on the UX-222 (CX-322)
March, 1928
CONSTRUCTION
"THE new UX-222 (cx-322) screened-grid tube
•*• is designed especially for use as a radio-fre-
quency amplifier and when used as such it is capable
of giving greater amplification than can be obtained
from other tubes. A receiver using these tubes
does not have to be neutralized. This Laboratory
Sheet gives details regarding its construction.
The arrangement of the ele-
ments as we look down on a ux-
222 (cx-322) tube is indicated in .- —
the drawing on this Sheet. At
the center is the filament, A,
consisting of a single straight
wire. Surrounding the filament
is the control or signal grid, B.
The plate, D, is located be-
tween C and E, which are two
comparatively, coarse " screen
grids." The filament terminals,
the plate terminal, and the extra
grid terminal (grids C and E are
connected together inside the
tube), are brought down to a
standard four-prong base. The
signal grid, B, is connected to a
small brass cap on top of the
tube.
\
\
The amplification constant of this new tube is of
the order of 200 to 300, the mutual conductance is
about 300 micromhos, and its plate impedance is
around one megohm. These values will vary widely,
depending upon the voltages. The amplification of
the tube in an r. f. circuit may average about three
times that possible with a 201-A type tube. Three
times as much amplification in the r.f. stage is equiv-
alent to 81 times as much power in the loud speaker.
When'a 201-A type tube is used
as an r. f. amplifier there is a
strong tendency for it to oscil-
late, due to feed-back through
the grid-plate capacity. The
plate of the ux-222 (cx-322) is
shielded from the signal grid by
the screen grid C-E, and the
tendency toward oscillation due
to feed-back through the tube
is practically nullified.
The general characteristics of
the tube, and the correct volt-
ages to employ when it is used
as an r. f. amplifier, are given
below:
Filament Volts 3.3
Plate Voltage 90 to 135
Screen-Grid Voltage +45
Signal Grid Bias - 1 to-1.5 volts
No. 170
RADIO BROADCAST Laboratory Information Sheet
Selectivity and Sensitivity
March, 1928
, DESIRABLE CHARACTERISTICS
'"PHE ideal receiver should be as selective as is
•*• possible; that is, it should receive a channel of
frequencies 10,000 cyctes wide (or only 5000 cycles
wide in the case of single side-band transmission)
equally well, but should not receive other frequen-
cies at all. A receiver for reception of broadcast
programs cannot be made any more selective than
this without impairing the quality of reproduction.
When a receiver is this selective, it will offer a bar-
rier to all frequencies except those lying in the chan-
nel to which it is tuned.
The ideal receiver should not need to be any
more sensitive than is necessary to amplify inter-
fering noises to more than tolerable loudness under
conditions of least interference. When the inter-
ference is greater, the sensitivity should be cut
down to keep these noises from becoming objection-
ably loud. In summertime the interfering radio
waves manufactured by nature are generally the
strongest.
Assuming that an ideal radio receiver is available,
there is only one way left (other than the invention
of a static eliminator or reducer) to reduce inter-
ference to any further extent and thereby increase
the distance over which satisfactory reception is
possible. This second method of reducing interfer-
ence is through the use of increased power at the
transmitting station. If the signa! strength at any
given location is increased, the ratio between the
signal and the static is thereby increased and re-
ception in this way made freer of interfering noises.
Just as in the case of land wire telephony, however,
we will probably never be able to put enough power
into the ether to give good transmission across the
continent in spite of bad interference.
In so far as sensitivity and selectivity are con-
cerned, the super-heterodyne type of receiver is
probably the most desirable. These characteristics
in a receiver of this type depend, however, in large
measure on the design of the intermediate-frequency
amplifier. This amplifier can be designed only to
amplify a very narrow band of frequencies (a good
design for reception of code signals), or, by the use of
band-pass filters, the equal amplification of a band of
frequencies can be accomplished (a satisfactory de-
sign for the reception of ordinary broadcast signals) .
RADIO BROADCAST ADVERTISER
385
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MANUFACTUREI
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Keep Your Filaments
Under Control
Better filament control means more uniform reception.
The guess method of setting the filament rheostat doesn't
tell you when the tubes are being burned too high or too
low. Neither can a filament rheostat be set accurately
by the brightness of the radio tube or by the volume of Pattern No. I3S
reception. Panel Mounting Voltmeter
The Jewell pattern No. 135 Voltmeter is the ideal radio instrument for use in accurate fila-
ament control. It tells at a glance the exact voltage being applied to the filament at that
time. The movement is of the D'Arsonval moving coil type with silvered parts and silver
etched dial, and with a pointer equipped with a zero adjuster. The case is two inches in
diameter and black enameled.
The instrument is easy to mount and is connected as shown in the diagram.
Write for description form No. 776.
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RADIO BROADCAST ADVERTISER
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WISCONSIN'
No. 171 RADIO BROADCAST Laboratory Information Sheet March, 1928
The CX-312 (UX-112) and CX-371 (UX-171)
FURTHER COMPARISONS
two types of power tubes best adapted for
A medium B voltages are the cx-312 (ux-112)
and the cx-371 (ux-171). The former tube, in-
troduced first, came into immediate favor, and for
a time was more popular than the cx-371 (ux-171).
This initial preference was due to several factors,
the most important ones being, first, the fact that
the voltages required by this type were identical
with those required by type cx-301-A (ux-201-A)
tubes, and therefore, the tube could be substituted
without battery changes. Secondly the horn type
loud speaker, generally more sensitive than the
cone loud speaker, was still popular, and there was
less necessity for the greater power output given
by the cx-371 (ux-171). A third factor was the mis-
apprehension about battery voltages, many not
realizing that although the cx-371 could be used to
best advantage at the maximum voltage of 180
volts, the quality of reproduction was equally good
at 135 volts, and the volume ample for average
home service,
During the current season the standing of the
two tubes is rapidly being reversed, the cx-371 (ux-
171) assuming the leadership, partly because of the
large number of new receivers for which the tube is
specified, and partly because of better facilities
for using the tube to its best advantages. As im-
provements in audio amplification and in loud
speaker design are made, the advantage of using this
type of tube becomes increasingly apparent. The
higher frequencies are usually reproduced satis-
factorily by any type of output tube, but to secure
full undistorted reproduction of low frequencies,
or the bass notes, a tube having low internal resis-
tance, such as the cx-371 (ux-171), is required.
In installing the cx-371 (ux-171), the first pre-
caution with which the user has to become familiar
is the use of a high grid biasing, or C, battery volt-
age— from 16-J to 40^ volts, depending upon the
B voltage used. With "general-purpose tubes, which
the power tubes replaced, the use of a C battery
was to a large extent optional with the user, al-
though the fact that better quality was obtained
with this battery was generally recognized.
Laboratory Sheets Nos. 161 and 162 gave some in-
teresting data and curves on the type 112 and 171
tubes. The 210 type tube was also covered in these
latter sheets.
No. 172
RADIO BROADCAST Laboratory Information Sheet
A Simple Wavemeter
March, 1928
CONSTRUCTION AND CALIBRATION
A WAVEMETER is a very useful asset to the
** laboratory of any radio experimenter. A coil of
wire and a condenser, connected together properly,
are all that is required to make this instrument.
The circuit diagram of a wavemeter is given on
the curve published herewith. It is evident from the
diagram that the coil is simply connected across
the condenser. The coil should preferably be a
solenoid wound on a piece of tubing so that it will
be able to withstand some abuse without any
alteration in its inductance, and should have suffi-
cient number of turns to cover the frequency band it
is to be used on.
The construction of the wavemeter presents no
problems. The method of calibrating it and plotting
a calibration curve may, however, require some
explanation. The procedure is as follows:
(1.) Set the wavemeter at a distance of about
two feet from your radio receiver.
(2.) Take the lead from the antenna and wrap
one turn around the coil of the wavemeter and
then run the antenna lead over to the regular
antenna post on your receiver.
(3.) Turn on the receiver and tune-in the
signals of some station. Now slowly revolve the
dial on the wavemeter and at some point on the
dial the signal output of the receiver will de-
crease. Note the reading on the wavemeter con-
denser dial which cuts out the signal most com-
pletely. Make the same test on some other stations.
(4.) Now draw the curve, using the data ob-
tained, in a manner similar to that indicated on
this Laboratory Sheet. The wavelengths, or fre-
quencies, on which the various stations are trans-
mitting can, of course, be obtained from any list
of broadcasting stations.
Such a wavemeter aids materially in the identi-
fication of stations heard on a receiver which is not
calibrated.
600
0 10 20 30 40 50 60 70' 80 90100
CONDENSER DIAL
No. 173
RADIO BROADCAST Laboratory Information Sheet
The Regulator Tube
March, 1928
WHY IT IS USED
'"PHE voltage regulator tube, or glow tube, as it is
•*- sometimes called, has found rather wide use in
the design of B power units, making them capable
of delivering a voltage output that is practically
constant over a wide range of load. The output of a
power unit not using a glow tube will, of course,
vary with the load, although the magnitude of this
variation may be held to comparatively low values
by good design. A power unit supplying an output
voltage that does not depend upon the load may be
used with practically any receiver with a knowledge
that the voltage actually delivered to the receiver
will be correct. Constant voltage output is, how-
ever, only one of the advantages accruing from the
use of a regulator tube.
The action of the tube in holding the voltage of
the output circuit constant serves also to eliminate
the small ripples which may be present as a result
of incomplete filtering, and this action makes possi-
ble a reduction in the capacity, and therefore the
expense, of the final filter condenser. In fact, the
tube, when in operation, has many properties in
common with a large iixed condenser. One of these
properties is extremely low a. c. impedance which,
when combined with its instantaneous response as a
voltage regulator, entirely eliminates the annoying
"motor-boating" effect which generally results
when an attempt is made to use one of the ordinary
B power units with many forms of amplifiers.
The fact that the regulator tube keeps the output
voltage constant also permits the safe use of con-
densers of a lower voltage rating than would be
permissible if the tube were not used. The rating of
the condensers used in an ordinary power circuit
is fixed by the maximum values of voltage that
they must handle. The voltage output of some units,
at no load, rises to comparatively high values and
the condensers must therefore have a rating suffi-
cient to withstand these voltages. The output voltage
of a power unit with a regulator tube is limited,
even at no load, to values only slightly above rated
voltage and, therefore, the condensers are not
called upon to withstand voltages greater than the
rated output of the unit.
RADIO BROADCAST ADVERTISER
387
174 RADIO BROADCAST Laboratory Information Sheet
Grid Bias
March, 1928
WHY IT IS USED
'T'HERE are apparently many, as indicated by
1 letters to the Laboratory, who still feel that the
major reason for using C bias on a tube is to reduce
the plate current. Although negative bias on the
grid of a tube does decrease the plate current, this is
not really the most important reason for its use.
C bias is used primarily to reduce distortion
and make the tube operate more efficiently. In an
ordinary receiver, C bias is most important in the
audio-frequency amplifier and we will, therefore,
discuss on this Laboratory Sheet the effect of using
various values of C bias on the grid of a tube.
The curves A, B, C, and D indicate the distortion
of signals which results when too little or too much
bias is used. Curve A represents the voltage on the
grid of the tube. Curve B shows how the plate cur-
rent of the tube varies if the bias on the tube is cor-
rect. It should be noted thai the
form of this curve is the same
as curve A, indicating that there
is no distortion being created by
the tube. If too little bias is used,
the positive halves of the input
voltage wave will cause the grid
to become positive when the
grid draws current, and the posi-
tive peaks are then cut off as
indicated at C. If the bias is too
great the tube operates on the
lower bend of its characteristic
and this causes the negative half of the signal to be
flattened out, as shown in curve D. To prevent
distortion, therefore, the proper C bias must be
used.
It is especially important that the bias on the
last tube be correct, for this tube must handle the
greatest amount of signal current and will, there-
fore, overload and distort most easily. As a matter
of information the correct bias for a 112 or 171 type
tube is given below:
TUBE
112
171
PLATE VOLTS
( 90
•{135
(137
( 90
•(135
(ISO
C BIAS
6.0
9.0
10.5
16.5
27.0
40.5
A
Negative
No. 175
RADIO BROADCAST Laboratory Information Sheet
March, 1928
Filter Choke Coils
EFFECT OF AIR GAP
TF THE filter circuit of a B power unit is to elimi-
A nate satisfactorily all hum, it is essential that the
filter choke coils have sufficient inductance under
actual operating conditions. The value of the induc-
tance of a choke coil as measured without any direct
current flowing through it will differ from the value
obtained with direct current, so all measurements
on choke coils should, therefore, be made with d. c.
flowing in the winding.
When direct current flows through a filter coil it
produces a certain amount of magnetic flux, or
"lines of force," in the core. This fiux tends to
saturate the core of the choke and, when this occurs,
the unit will no longer function satisfactorily in
eliminating the hum.
Manufacturers are always willing to supply data
on the maximum amount of d. c. current their filter
choke coil can handle and this value should not be
exceeded in practice.
When the filter coil is constructed, the core may
be clamped tightly together or a small air-gap
may be left. As the current capacity rating of the
coil is increased, the air-gap should be increased
also, and this tends to prevent magnetic saturation.
The group of curves on this Sheet show this effect.
The conditions under which they were obtained are
given below:
T — No air gap
A— -Average air gap
B — Air gap at one end, 0.01 inches
C— Air gap at both ends, 0.005 inches each
D — Air gap at both ends, 0.0075 inches each
E — Air gap at both ends. 0.01 inches each
If the d. c. current is to be 10 milliamperes,
construction type T is best, while type C is best at
a current of 30 milliamperes, or if the current through
the choke is to be 55 milliamperes, type E should be
used.
100
"0 5 10 15 20 25 30 35 40 45 50 55
MILUAMPSD.C.
No. 176 RADIO BROADCAST Laboratory Information Sheet March, 1928
How the Plate Circuit Affects the Grid Circuit
REVERSE ACTION capacity between the grid and the plate, RP the
plate filament resistance, Cp the plate-filament
capacity, and L the load impedance. Probably the
most important of the capacities shown is the grid-
plate capacity, Ci, for it is this capacity which
permits the grid circuit to be affected by what
goes on in the plate circuit. In radio- frequency
amplifiers it is this capacity which causes the tube
to oscillate.
The diagram at (B) should give some idea of the
complexity of the network represented by a tube,
and the action of this network of resistances, con-
densers, and inductances must be understood if the
action of a tube in any particular circuit is to be
accurately foretold. J. M. Millen, in Scientific
Paper of the Bureau of Standards No, 351, carefully
and completely determined the dependence of the
input circuit of a tube upon the output circuit.
TN WORKING with tubes, we normally consider
*• that the plate circuit iscontrolled by the grid and
that there is no reverse action. This, however, is not
strictly true, for the plate circuit does affect the grid
circuit in two ways.
In the first place the plate acts as a grid with
respect to the regular grid in the tube and large
variations in plate voltage have the same effect with
respect to the grid as has slightly varying the grid
voltage. The reverse effect is generally not ap-
preciable so long as the grid is held negative, as is
the case in an amplifier. The reverse effect is im-
portant in oscillator circuits, however, where the
grid is not always negative. In making an accurate
analysis of the action of an oscillator, it would
be necessary to consider this effect.
The second manner in which
the grid.is controlled by the plate
is through the grid-plate capac-
ity of the tube. At (A) in the dia-
gram on this Sheet, we have in-
dicated the circuit of an ordinary
r. f. amplifier and at (B) is shown
the equivalent circuit with the
inter-electrode resistances and
capacities indicated. Rg is the
grid-filament resistance of the
tube, Cg the grid-to-filament
capacity, Ci the inter-electrode
(B)
Whether it's bat-
tery or A-C Tubes
—BE MASTER
of Your Set!
T) ADIO can be a pleasure or a curse,
-*-^- depending upon whether you run
your radio set or your radio set runs
you. An uncontrolled radio set is like an
automobile without steering wheel and
throttle — except that the latter soon kills
outright, whereas the former causes a
slow, lingering, painful death to the
owner and others.
\^ET nothing is simpler than the con-
•*• trol of your set, whether equipped
with A-C or battery tubes. In the case
of either type of tubes, just connect a
VOLUME CONTROL
across antenna and ground binding
posts of your set. Now you have dis-
tortionless control that gives you any-
thing from full output to mere whisper
— from dance music for shuffling feet to
soft background for dinner conversation.
All for $1.50, and instantly applicable to
any receiver.
Again you must control your power
supply for A-C as well as battery type
tubes. In the case of A-C tubes, you must
compensate for line voltage fluctuations.
This is essential for best results. Much
of the hum with A-C tubes is due to im-
proper operating voltage. In the case of
all B-power supply devices, you must also
compensate for line voltage changes. The
solution here is a Power Clarostat (25-
500 ohm range) con-
nected in primary
circuit of power
transformer. You can
instantly adjust A-C
tube filaments or
heaters, B and C
voltages, all at one
time. Applicable to
any set or radio
power unit. And all
for #3.50.
\A/ RITE us for data on how to improve your
* radio, whether A-C or battery operated. And
whin you buy CLAROSTATS, ke sure you get Ike
genuine, distinguished by familiar green kox and
name Clarostat stamped on nickeled shell. Accept
no substitutesl
AMERICAN MECHANICAL
LABS. Inc.
Specialists in
Variable Resistors
285 No. 6th St. Brooklyn, N. Y.
388
RADIO BROADCAST ADVERTISER
"RADIO BROADCASTS" DIRECTORY OF
MANUFACTURED RECEIVERS
<J A coupon will be found on page 395. All readers who desire additional
information on the receivers listed below need only insert the proper num-
bers in the coupon, mail it to the Service Department of RADIO BROADCAST,
and full details will be sent. New sets are listed in this space each month.
KEY TO TUBE ABBREVIATIONS
99 — 60-mA. filament (dry cell)
01 -A — Storage battery 0.25 amps, filament
12 — Power tube (Storage battery)
71 — Power tube (Storage battery)
16-B— Half-wave rectifier tube
80 — Full-wave, high current rectifier
81 — Half-wave, high current rectifier
Hmu — High-Mu tube for resistance-coupled audio
20 — Power tube (dry cell)
10 — Power Tube (Storage battery)
00-A — Special detector
13 — Full-wave rectifier tube
26 — Low-voltage high-current a. c. tube
27 — Heater type a. c. tube
DIRECT CURRENT RECEIVERS
NO. 424. COLONIAL 26
Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One to
three dials. Volume control : antenna switch and poten-
tiometer across first audio. Watts required: 120. Con-
sole size: 34 x 38 inches. Headphone connections.
The filaments are connected in a series parallel arrange-
ment. Price $250 including power unit.
NO. 42S. SUPERPOWER
Five tubes: All 01-A tubes. Multiplex circuit. Two
dials. Volume control: resistance in r. f. plate. Watts
required: 30. Antenna: loop or outside. Cabinet sizes:
table, 27 x 10 x 9 inches; console, 28 x 50 x 21. Prices:
table, $135 including power unit; console, $390 includ-
ing power unit and loud speaker.
A. C. OPERATED RECEIVERS
NO. 508. ALL-AMERICAN 77, 88, AND 99
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Rice neutralized t. r. f. Single drum
tuning. Volume control: potentiometer in r. f. plate.
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy,
25 x 38 x 18 inches; No. 99 console, 27} x 43 x 20 inches.
Shielded. Output device. The filaments are supplied
by means of three small transformers. The plate supply
employs a gas-filled rectifier tube. Voltmeter in a. c.
supply line. Prices: No. 77, $150, including power unit;
No. 88, $210 including power unit; No. 99, $285 in-
cluding power unit and loud speaker.
NO. 509. ALL-AMERICAN "DUET"; "SEXTET"
Six tubes; 2 t. r. f. (99), detector (99), 3 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
"Duet," 23 x 56 x 16} inches; "Sextet,"22i x 13} x 15}
inches. Shielded. Output device. The 99 filaments are
connected in series and supplied with rectified a. c.;
while 12 is supplied with raw a. c. The plate and fila-
ment supply uses gaseous rectifier tubes. Milliammeter
on power unit. Prices: "Duet," $160 including power
unit; "Sextet," $220 including power unit and loud
speaker.
NO. 511. ALL-AMERICAN so, so, AND us
Five tubes; 2 t. r. f. (99), detector (99), 2 transformer
audio (99 and 12). Rice neutralized t. r. f. Two dials.
Volume control: resistance in r. f. plate. Cabinet sizes:
No. 80, 23i x 12J x 15 inches; No. 90, 37* x 12 x 12}
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi-
vidually shielded. Output device. See No. 509 for
power supply. Prices: No. 80, $135 including power
unit; No. 90, $145 including power unit and compart-
ment; No. 115, $170 including power unit, compart-
ment, and loud speaker.
NO. 510. ALL-AMERICAN 7
Seven tubes; 3 t. r. f. (26), 1 untuned r. f. (26), detec-
tor (27), 2 transformer audio (26 and 71). Rice neutral-
ized t. r. f. One drum. Volume control: resistance in r. f.
plate. Cabinet sizes: "Sovereign" console, 30} x 60J
x 19 inches; "Lorraine" Hiboy, 25} x 53} x 17J inches;
"Forte" cabinet, 25J x 13} x 17i inches. For filament
and plate supply: See No. 508. Prices: "Sovereign"
$460; "Lorraine $360; " Forte" $270. All prices include
power unit. First two include loud speaker.
NO. 536. SOUTH BEND
Six tubes. One control. Sub-panel shielding. Binding
Posts. Antenna: outdoor. Prices: table, $130, Baby
Grand Console, $195.
NO. 537. WALBERT 26
Six tubes; five Kellogg a. c. tubes and one 71. Two
controls. Volume control: variable plate resistance.
Isofarad circuit. Output device. Battery cable, Semi-
shielded. Antenna: 50 to 75 feet. Cabinet size: 10} x
29} x 16j inches. Prices: $215; with tubes, $250.
NO. 522. CASE, 62B AND 62C
McCulIough a. c. tubes. Drum control. Volume con-
trol; variable high resistance in audio system. C-battery
connections. Semi-shielded. Cable. Antenna: 100 feet.
Panel size: 7 x 21 inches. Prices: Model 62B, complete
with a. c. equipment, $185; Model 62 C, complete with
a. c. equipment, $235.
NO. 523. CASE, 92 A AND 92 C
McCulIough a. c. tubes. Drum control. Inductive
volume control. Technidyne circuit. Shielded. Cable.
C-battery connections. Model 92 C contains output
device. Loop operated. Prices: Model 92 A, table, $350;
Model 92 C, console, $475.
NO. 484. BOSWORTH, B5
Five tubes; 2. t. r. f. (26), detector (99), 2 transformer
audio (special a. c. tubes). T. r. f. circuit. Two dials.
Volume control: potentiometer. Cabinet size: 23 x 7
x 8 inches. Output device included. Price $175.
NO. 406. CLEARTONE 110
Five tubes; 2. t. r. f., detector, 2 transformer audio.
All tubes a. c. heater type. One or two dials. Volume
control: resistance in r. f. plate. Watts consumed: 40.
Cabinet size varies. The plate supply is built in the
receiver and requires one rectifier tube. Filament sup-
ply through step down transformers. Prices range from
$175 to $375 which includes 5 a. c. tubes and one recti-
fier tube.
NO. 407. COLONIAL 25
Six tubes; 2. t. r. f. (01-A), detector (99), 2 resistance
audio (99). 1 transformer audio (10). Balanced t. r. f.
circuit. One or three dials. Volume control: Antenna
switch and potentiometer on 1st audio. Watts con-
sumed: 100. Console size: 34 x 38 x 18 inches. Output
device. All tube filaments are operated on a. c. except
the detector which is supplied with rectified a. c. from
the plate supply. The rectifier employs two 16-b tubes.
Price $250 including built-in plate and filament supply.
NO. 507. CROSLEY 602 BANDBOX
Six tubes; 3. t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Neutrodyne circuit. One dial, Cabinet
size: 17} x 5} x 7f inches. The heaters f9r the a. c. tubes
and the 71 filament are supplied by windings in B unit
transformers available to operate either on 25 or 60
cycles. The plate current is supplied by means of
rectifier tube. Price $65 for set alone, power unit $60.
NO. 408. DAY-FAN "DE LUXE"
Six tubes; 3 t. r. f., detector, 2 transformer audio. All
01-A tubes. One dial. Volume control: potentiometer
across r. f. tubes. Watts consumed: 300. Console size:
30 x 40 x 20 inches. The filaments are connected in
series and supplied with d. c. from a motor-generator
set which also supplies B and C current. Output de-
vice. Price $350 including power unit.
NO. 409. DAYCRAFT 5
Five tubes; 2 t. r. f., detector, 2 transformer audio.
All a. c. heater tubes. Reflexed t. r. f. One dial. Volume
control: potentiometers in r. f. plate and 1st audio.
Watts consumed: 135. Console size: 34 x 36 x 14 inches.
Output device. The heaters are supplied by means of
a small transformer. A built-in rectifier supplies B
and C voltages. Price $170, less tubes. The following
have one more r. f. stage and are not reflexed; Day-
craft 6, $195; Dayrole, 6, $235; Dayfan 6, $110. All
prices less tubes.
NO. 469. FREED-EISEMANN NRII
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Volume control: potentiometer. Watts consumed- 150
Cabinet size: 19} x 10 x 10} inches. Shielded. Output
device. A special power unit is included employing a
rectifier tube. Price $225 including NR-411 power unit.
NO. 487. FRESHMAN 7F-AC
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 71). Equaphase circuit. One dial. Volume
control: potentiometer across 1st audio. Console size:
24} x 41} x 15 inches. Output device. The filaments and
heaters and B supply are all supplied by one power unit.
The plate supply requires one 80 rectifier tube. Price
$175 to $350, complete.
NO. 421. SOVEREIGN 238
Seven tubes of the a. c. heater type. Balanced t. r. f.
Two dials. Volume control: resistance across 2nd audio.
Watts consumed: 45. Console size: 37 x 52 x 15 inches.
The heaters are supplied by a small a. c. transformer,
while the plate is supplied by means of rectified a. c.
using a gaseous type rectifier. Price $325, including
power unit and tubes.
NO. 517. KELLOGG 510, 511, AND 512
Seven tubes; 4 t. r. f., detector, 2 transformer audio.
All Kellogg a. c. tubes. One control and special zone
switch. Balanced. Volume control: special. Output de-
vice. Shielded. Cable connection between power supply
unit and receiver. Antenna: 25 to 100 feet. Panel 7(g
x 27} inches. Prices: Model 510 and 512, consoles, $495
complete. Model 511, consolette, $365 without loud
speaker.
NO. 496. SLEEPER ELECTRIC
Five tubes; four 99 tubes and one 71. Two controls.
Volume control: rheostat on r. f. Neutralized. Cable.
Output device. Power supply uses two 16-B tubes.
Antenna: 100 feet. Prices: Type 64, table, $160; Type
65, table, with built-in loud speaker, $175; Type 66,
table, $175; Type 67, console, $235; Type 78, console,
$265.
NO. 538. NEUTROWOUND, MASTER ALLECTRIC
Six tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and two 71 in push-pull amplifier). The 01-A
tubes are in series, and are supplied from a 400-mA.
rectifier. Two drum controls. Volume control: variable
plate resistance. Output device. Shielded. Antenna:
50 to 100 feet. Price: $360.
NO. 413. MARTI
Six tubes: 2 t. r. f., detector, 3 resistance audio. All
tubes a. c. heater type. Two dials. Volume control-
resistance in r. f. plate. Watts consumed: 38. Panel size
7 x 21 inches. The built-in plate supply employs one
16-B rectifier. The filaments are supplied by a small
transformer. Prices: table, $235 including tubes and
rectifier; console, $275 including tubes and rectifier;
console, $325 including tubes, rectifier, and loud
speaker.
NO. 417. RADIOLA 28
Eight tubes; five type 99 and one type 20. Drum
control. Super-heterodyne circuit. C-battery connec-
tions. Battery cable. Headphone connection. Antenna:
loop. Set may be operated from batteries or from the
power mains when used in conjunction with the model
104 loud speaker. Prices: $260 with tubes, battery
operation; $570 with model 104 loud speaker, a. c.
operation.
NO. 540. RADIOLA 30-A
Receiver characteristics same as No. 417 except that
type 71 power tube is used. This model is designed to
operate on either a. c. or d. c. from the power mains.
The combination rectifier — power — amplifier unit uses
two type 81 tubes. Model 100-A loud speaker is con-
tained in lower part of cabinet. Either a short indoor
or long outside antenna may be used. Cabinet size:
42} x 29 x 17» inches. Price: $495.
NO. 541. RADIOLA 32
This model combines receiver No. 417 with the model
104 loud speaker. The power unit uses two type 81
tubes and a type 10 power amplifier. Loop is completely
enclosed and is revolved by means of a dial on the panel.
Models for operation from a. c. or d. c. power mains
Cabinet size: 52 x 72 x 17} inches. Price: $895.
NO. 539. RADIOLA 17
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer
audio (26 and 27). One control. Illuminated dial.
Built-in power supply using type 80 rectifier. Antenna:
100 feet. Cabinet size: 25,°,, x 7j x 8J. Price: $130
without accessories.
NO. 545. NEUTROWOUND, SUPER ALLECTRIC
Five tubes; 2 t. r. f. (99), detector (99), 2 audio (99
and 71). The 99 tubes are in series and are supplied from
an 85-mA. rectifier. Two drum controls. Volume con-
trol: variable plate resistance. Output device. Antenna:
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price:
$150.
NO. 490. MOHAWK
Six tubes; 2 t. r. f., detector, 2 transformer audio. All
tubes a. c. heater type except 71 in last stage. One dial.
Volume control: rheostat on r. f. Watts consumed: 40.
Panel size: 12} x 8j inches. Output device. The heaters
for the a. c. tubes and the 71 filament are supplied by
small transformers. The plate supply is of the built-in
type using a rectifier tube. Prices range from $65 to
NO. 411. HERBERT LECTRO 120
Five tubes; 2 t.r.f. (99), detector (99), 2 transformer
audio (99 and 71). Three dials. Volume control: rheo-
stat in primary of a.c. transformer. Watts required:
45. Cabinet size: 32 x 10 x 12 inches. The 99 filaments
are connected in series, supplied with rectified a. c.,
while the 71 is run on raw a. c. The power unit uses a
Q. R. S. rectifier tube. Price $120.
NO. 412. HERBERT LECTRO 200
Six tubes; 2 t.r.f. (99), detector (99), 1 transformer
audio (99), 1 push-pull audio (71). One dial. Volume
control: rheostat in primary of a. c. transformer.
Watts consumed: 60. Cabinet size: 20 x 12 x 12 inches.
Filaments connected same as above. Completely
shielded. Output device. Price $200.
BATTERY OPERATED RECEIVERS
NO. 542. PFANSTIEHL JUNIOR SIX
Six tubes: 3 t. r. f. (01-A), detector (01-A), 2 audio.
Pfanstiehl circuit. Volume control : variable resistance in
r. f. plate circuit. One dial. Shielded. Battery cable. C-
battery connections. Etched bronze panel. Antenna:
outdoor. Cabinet size: 9 x 20 x 8 inches. Price: $80, with-
out accessories.
NO. 512. ALL-AMERICAN 44, 45, AND 66
Six tubes; 3 t. r. f. (01-A, detector) 01-A, 2 trans-
former audio (OI-A and 71). Rice neutralized t. r. f.
Drum control. Volume control: rheostat in r. f. Cabinet
sizes: No. 44, 21 x 10 x 8 inches; No. 55, 25 x 38 x 18
inches; No. 66, 27J x 43 x 20 inches. C-battery connec-
tions. Battery cable. Antenna: 75 to 125 feet. Prices:
No. 44. $70; No. 55, $125 including loud speaker; No.
66, $200 including loud speaker.
NO. 410. LARCOFLEX 73
Seven tubes; 4 t.r.f. (Ol-A), detector (01-A), 2 trans-
former audio (01-A and 71). T.r.f. circuit. One dial.
Volume control: resistance in r.f. plate. Console size
30 x 42 x 20 inches. Completely shielded. Built-in A, B
and C supply. Price $215.
RADIO BROADCAST ADVERTISER
389
Slight Cost
— m a Few Moments
Your Set can be A C-Operated
There is a Dongan A C Transformer
designed specifically for each of the
approved A C Tubes
—for instance
here is
No. 6512
A remark-
ably well-de-
signed and
sturdy A C
Transformer, mounted in a crystalized lacquered
case, equipped with lamp cord and plug outlet
for B-Eliminator, also tap for control switch.
Operated with 4 UX 226, i UY 227 and i UX
171 R C A Tubes. $5.75 list
Then you can have exactly the same transformer
without plug outlet and control switch tap—
No. 6515 for $4-75 list
Ranging in price from $3.50 to $5.25, there are
10 other A C Transformers, operating with the
approved A C Tubes.
Send check or money order if your
dealer cannot supply you.
Custom Set Builders
Write for our special proposition to
Custom Set Manufacturers
DONGAN ELECTRIC MFG. CO.
2991-3001 Franklin St. Detroit, Michigan
TRANSFORMERS °F MERIT for FIFTEEN YEARS
1ARTEB
READY?
OF COURSE!
CARTER
Adapter Harness
for converting battery sets to
A. C. Tube Operation
Without any structural or wiring
change in the set. Change can be
made in a few minutes. Complete,
eliminates "C" batteries.
Write for illustrated folder
giving full information.
70
60
SO
40
30
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4- i:
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1 ' —
HE YB OAR.O of PIANO
YOUR receiver deserves an AIR-CHROME speaker.
The "balanced tension" principle, governing the oper-
ation of this speaker, is a new engineering development
... It means the full realization of the brilliance of
broadcast selections. . . . ALL MUSICAL IN-
STRUMENTS ARE WITHIN ITS RANGE.
Speakers at $15.00, $20.00, $25.00, and $65.00
Order from us or your dealer. If your dealer can-
not supply, send us his name. . . .
Write for descriptive literature
168 Coit Street
PEAKER
Irvington, N. J.
New Aero Circuits
for Either Battery or A. C. Operation
Proper constants for A. C. operation of the Im-
proved Aero-Dyne 6 and the Aero Seven have been
studied out, and these excellent circuits are now
adaptable to either A. C. or battery operation. A. C.
blue prints are packed in foundation units. They
may also be obtained by sending 250 for each direct
to the factory.
Aero Universal
Tuned Radio Frequency Kit
Especially designed for the Improved Aero-Dyne 6.
Kit consists of 4 twice-matched units. Adaptable to
2OI-A, 199, 112, and the new 240 and A. C. Tubes.
Tuning range below 200 to above 550 meters.
Code No. U-16 (for .0005 Cond.) $15.00
Code No. U-163 (for .00035 Cond.) 15.00
Aero Seven
Tuned Radio Frequency Kit
Especially designed for the Aero 7. Kit consists
of 3 twice- mate bed units. Coils are wound on Bake-
lite skeleton forms, assuring a 95 per cent, air dielec-
tric. Tuning range from below 200 to above 550
meters. Adaptable to 2io-A, 199, 112, and the new
240 and A. C. Tubes.
Code No. U-12 (for .0005 Cond.) . . .$12.00
Code No. U-123 (for .00035 Cond.) 12.00
You should be able to get any of the above
Aero Coils and parts front your dealer.
If he should be out of stock order
direct from the factory.
AERO PRODUCTS, INC.
1772 Wilson Ave. Dept. 109 Chicago, HI.
fiMPERITE
IValch Dog
ofljour
jubcs
Insuring* Tube
Efficiency^
AMPERITE alone gives utmost
life and performance from tubes.
Because AMPERITE alone keeps
the filament voltage, or tempera-
ture, constant, despite " A" battery
variations. Particularly needed
with Battery Eliminators. Simpli-
fies wiring and panel design. Elim-
inates hand rheostats and guessing.
Proved for 6 years. Entirely diffe-
rent from fixed filament resistors.
There is no alternative. Insist on
\ AMPERITE. Price «1.IO with
~\ mounting (inU.S.A.).Atalldealers.
Write for FREE "Amperite Book" of
season's best circuits and latest con*
^l struction data, to Dept. KB-:: •
^ 03@&*(tial! Gotnpntty J
m 50 FRANKLIN ST., NEW YORK "
JVMPERITE
*^E± RE<3 »_/ S F--ATT OFF
Dfe: "SELF-ADJUSTING"/./^..//^
390
RADIO BROADCAST ADVERTISER
NO. 485. BOSWORTH B6
Five tubes, 2 t. r. f. (01 -A), detector (01 -A), 2 trans-
former audio (01-A and 71). Two dials. Volume control:
variable grid resistances. Battery cable. C-battery
connections. Antenna: 25 feet or longer. Cabinet size
15 x 7 x 8 inches. Price $75.
NO. 513. COUNTERPHASE SIX
Six tubes; 3 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A) and 12). Counterphase t. r. f. Two
dials. Plate current: 32 mA. Volume control: rheostat
on 2nd and 3rd r. f. Coils shielded. Battery cable. C-
battery connections. Antenna: 75 to 100 feet. Console
size: 18| x 40J x 15J inches. Prices: Model 35, table,
$110; Model 37, console, $175.
NO. 514. COUNTERPHASE EIGHT
Eight tubes; 4 t. r. f. (01-A) detector (00-A), 2 trans-
former audio (01-A and 12). Counterphase t. r. f. One
dial. Plate current: 40 mA. Volume control: rheostat
in 1st r. f. Copper stage shielding. Battery cable. C-bat-
tery connections. Antenna: 75 to 100 feet. Cabinet size:
30 x 12{ x 16 inches. Prices: Model 12, table, $225;
Model 16, console, $335; Model 18, console, $365.
NO. 506. CROSLEY 601 BANDBOX
Six tubes; 3 t. r. f., detector, 2 transformer audio. All
01-A tubes. Neutrodyne. One dial. Plate current:
40 mA. Volume control: rheostat in r. f. Shielded.
Battery cable. C-battery connections. Antenna: 75 to
150 feet. Cabinet size: 17J x 5i x 7|. Price, $55.
NO. 434. DAY-FAN 6
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). One dial. Plate
current: 12 to 15 mA. Volume control: rheostat on r. f.
Shielded. Battery cable. C-battery connections. Output
device. Antenna: 50 to 120 feet. Cabinet sizes :Daycraft
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7. Prices:
Day-Fan 6, $110; Daycraft 6, $145 including loud
speaker; Day-Fan Jr. not available.
NO. 435. DAY-FAN 7
Seven tubes; 3 t.r.f. (01-A), detector (01-A), I resist-
ance audio (01-A), 2 transformer audio (01-A and 12
or 71). Plate current: 15 mA. Antenna: outside. Same
as No. 434. Price $115.
NO. 503. FADA SPECIAL
Six tubes; 3 t. r. i. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 20 to 24 mA. Volume control:
rheostat on r. f . Coils shielded. Battery cable. C. -battery
connections. Headphone connection. Antenna: outdoor.
Cabinet size: 20 x 13! x 10J inches. Price $95.
NO. 504. FADA 7
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. Two drum
control. Plate current: 43, A. Volume control: rheostat
on r. f. Completely shielded. Battery cable. C-battery
connections. Headphone connections. Output device.
Antenna: outdoor or loop. Cabinet sizes: table, 25J x
13} x 11 j inches; console, 29 x 50 x 17 inches. Prices:
table, $185; console, $285.
NO. 436. FEDERAL
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t. r. f. One
dial. Plate current: 20.7 mA. Volume control: rheostat
on r. f. Shielded. Battery cable. C-battery connections.
Antenna: loop. Made in 6 models. Price varies from
$250 to $1000 including loop.
NO. 505. FADA 8
Eight tubes. Same as No. 504 except for one extra
stage of audio and different cabinet. Prices: table, $300;
console, $400.
NO. 437. FERGUSON 10A
Seven tubes; 3 t. r. f. (01-A), detector (01-A), Saudio
(01-A and 12 or 71). One dial. Plate current: 18 to 25
mA. Volume control: rheostat on two r. f. Shielded.
• Battery cable. C-battery connections. Antenna: 100
feet. Cabinet size: 21J x 12 x 15 inches. Price $150.
NO. 438. FERGUSON 14
Ten tubes; 3 untuned r. f., 3 t. r. f. (01-A), detector
(01-A), 3 audio (01-A and 12 or 71). Special balanced
t. r. f. One dial. Plate current: 30 to35mA. Volume con-
trol: rheostat in three r. f. Shielded. Battery cable, C-
battery connections. Antenna: loop. Cabinet size:
24 x 12 x 16 inches. Price $235, including loop.
NO. 439. FERGUSON 12
Six tubes; 2 t. r. f. (01-A), detector (01-A), 1 trans-
former audio (01-A), 2 resistance audio (01-A and 12
or 71). Two dials. Plate current: 18 to 25mA. Volume
control; rheostat on two r. f. Partially shielded. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet size: 22i x 10 x 12 inches. Price $85. Consolette
$145 including loud speaker.
NO. 440. FREED-EISEMANN NR-8 NR-9, AND
NR-66
Six tubes: 3 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. NR-8, two
dials; others one dial. Plate current: 30 mA. Volume
control: rheostat on r. f. NR-8 and 9: chassis type
shielding. NR-66, individual stage shielding. Battery
cable. C-battery connections. Antenna: 100 feet.
Cabinet sizes: NR-8 and 9, 19J x 10 x 10! inches; NR-66
20 x 10i x 12 inches. Prices: NR-8, $90; NR-9, $100;
NR-66, $125.
NO. 501. KING "CHEVALIER"
Six tubes. Same as No. 500. Coils completely shielded.
Panel size: 11 x 7 inches. Price, $210 including loud
speaker.
NO. 441. FREED-EISEMANN NR-77
Seven tubes; 4 t. r. f. (01 -A), detector (01-A), 2 trans-
former audio (01-A and 71). Neutrodyne. One dial.
Plate current: 35mA. Volume control: rheostat on r. f.
Shielding. Battery cable. C-battery connections.
Antenna: outside or loop. Cabinet size: 23 x 10^ x 13
inches. Price $175.
NO. 442. FREED-EISEMANN 800 AND 850
Eight tubes; 4 t. r. f. (01-A), detector (01-A), 1 trans-
former (01-A), 1 parallel audio (01-A or 71). Neutro-
dyne. One dial. Plate current: 35 mA. Volume control:
rheostat on r. f. Shielded. Battery cable. C-battery
connections. Output: two tubes in parallel or one power
tube may be used. Antenna: outside or loop. Cabinet
sizes: No. 800, 34 x 151 x 135 inches; No. 850, 36 x 65 x
17j. Prices not available.
NO. 444. GREBE MU-1
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 trans-
former audio (01-A and 12 or 71). Balanced t. r. f. One,
two, or three dials (operate singly or together). Plate
current: 30mA. Volume control: rheostat on r. f. Bi-
nocular coils. Binding posts. C-battery connections.
Antenna: 125 feet. Cabinet size: 22J x 9i x 13 inches.
Prices range from $95 to $320.
NO. 426. HOMER
Seven tubes; 4 t. r. f. (01-A); detector (01-A or OOA);
2 audio (01-A and 12 or 71). One knob tuning control.
Volume control: rotor control in antenna circuit. Plate
current: 22 to 25mA. "Technidyne" circuit. Completely
enclosed in aluminum box. Battery cable. C-battery
connections. Cabinet size, 8J x 19j x 9^ inches. Chassis
size, 6J x 17 x 8 inches. Prices: Chassis only, $80. Table
cabinet, $95.
NO. 502. KENNEDY ROYAL 7. CONSOLETTE
Seven tubes; 4 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). One dial. Plate current:
42mA. Volume control: rheostat on two r. f. Special
r. f. coils. Battery cable. C-battery connections. Head-
phone connection. Antenna : outside or loop. Consolette
size: 36J x 355 x 19 inches. Price $220.
NO. 498. KING "CRUSADER"
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 20 mA. Volume control: rheostat on r. f.
Coils shielded. Battery cable. C-battery connections.
Antenna: outside, Panel: 11x7 inches. Price, $115.
NO. 499. KING "COMMANDER"
Six tubes; 3 t. r. f. (01-A), detector (00-A), 2 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 25mA. Volume control: rheostat on r. f.
Completely shielded. Battery cable. C-battery con-
nections. Antenna: loop. Panel size: 12 x 8 inches. Price
$220 including loop.
NO. 429. KING COLE VII AND VIII
Seven tubes; 3 t. r. f., detector, 1 resistance audio, 2
transformer audio. All 01-A tubes. Model VIII has one
more stage t. r. f. (eight tubes). Model VII, two dials.
Model VIII, one dial. Plate current: 15 to 50 mA.
Volume control: primary shunt in r. f. Steel shielding.
Battery cable and binding posts. C-battery connections.
Output devices on some consoles. Antenna: 10 to 100
feet. Cabinet size: varies. Prices: Model VII, $80 to
$160; Model VIII, $100 to $300.
NO. 500. KING "BARONET" AND "VIKING"
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 trans-
former audio (01-A and 71). Balanced t. r. f. One dial.
Plate current: 19mA. Volume control: rheostat in r. f.
Battery cable. C-battery connections. Antenna: out-
side. Panel size: 18 x 7 inches. Prices: "Baronet," $70;
"Viking," $140 including loud speaker.
NO. 489. MOHAWK
Six tubes; 2 t. r. f. (01-A), detector (00-A), 3 audio
(01-A and 71). One dial. Plate current: 40mA. Volume
control : rheostat on r. f . Battery cable. C-battery con-
nections. Output device. Antenna: 60 feet. Panel size:
12J x 8| inches. Prices range from $65 to $245.
NO. 547. ATWATER KENT, MODEL 33
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71 or 12). One dial. Volume control: r. f. fila-
ment rheostat. C-battery connections. Battery cable.
Antenna: 100 feet. Steel panel. Cabinet size: 21 |x 6J
6i inches. Price: $75, without accessories.
NO. 544. ATWATER KENT, MODEL 50
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 12 or 71). Volume control: r. f. filament rheo-
stat. C-battery connections. Battery cable. Special
bandpass filter circuit with an untuned amplifier.
Cabinet size: 20J x 13 x 7J inches. Price: $120.
NO. 452. ORIOLE 90
Five tubes; 2 t. r. f., detector, 2 transformer audio.
All 01-A tubes. "Trinum" circuit. Two dials. Plate
current: 18mA. Volume control: rheostat on r. f.
Battery cable. C-battery connections. Antenna: 50 to
100 feet. Cabinet size: 25J x 11$ x 12j inches. Price $85.
Another model has 8 tubes, one dial, and is shielded.
Price, $185.
NO. 453. PARAGON
Six tubes; 2 t. r. f. (01-A), detector (01-A), 3 double
impedance audio (01-A and 71). One dial. Plate cur-
rent: 40 mA. Volume control: resistance in r. f. plate.
Shielded. Battery cable. C-battery connections. Out-
put device. Antenna: 100 feet. Console size: 20 x 45
x 17 inches. Price not determined.
NO. 543 RADIOLA 20
Five tubes; 2 t. r. f. (99), detector (99), two trans-
former audio (99 and 20) . Regenerative detector. Two
drum controls. C-battery connections. Battery cable.
Antenna: 100 feet. Price: $78 without accessories.
NO. 480. PFANSTIEHL 30 AND 302
Six tubes; 3 t. r. f. (01-A), detector (01-2A), trans-
former audio (01-A and 71). One dial. Plate current:
23 to 32 m A. Volume control : resistance in r. f. plate.
Shielded. Battery cable. C-battery connections. An-
tenna: outside. Panel size: 17J x 8} inches. Prices: No.
30 cabinet, $105; No. 302 console, $185 including loud
speaker.
NO. 515. BROWNING-DRAKE 7-A
Seven tubes; 2 t. r. f. (01-A), detector (00-A), 3 audio
(Hmu, two 01-A, and 71). Illuminated drum control
Volume control: rheostat on 1st r. f. Shielded. Neutral'
ized. C-battery connections. Battery Cable. Metal
panel. Output device. Antenna: 50-75 feet. Cabinet,
30 x 11 x 9 inches. Price, $145.
NO. 516. BROWNING-DRAKE 6-A
Six tubes; 1 t. r. f. (99), detector (00-A), 3 audio
(Hmu, two 01-A and 71). Drum control with auxiliary
adjustment. Volume control: rheostat on r. f. Regenera-
tive detector. Shielded. Neutralized. C-battery connec-
tions. Battery cable. Antenna: 50-100 feet. Cabinet,
25 x 11 x 9. Price $105.
NO. 518. KELLOGG "WAVE MASTER,"
504, 505, and 506.
Five tubes; 2 t. r. f., detector, 2 transformer audio.
One control and special zone switch. Volume control:
rheostat on r. f. C-battery connections. Binding posts
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel:
75 x 25;5 inches. Prices: Model 504, table, $75, less
accessories. Model 505, table, $125 with loud speaker.
Model 506, consolette, $135 with loud speaker.
NO. 519. KELLOGG, 507 AND 508
Six tubes, 3 t. r. f., detector, 2 transformer audio. One
control and special zone switch. Volume control: rheo-
stat on r. f. C-battery connections. Balanced. Shielded.
Binding posts and battery cable. Antenna: 70 feet.
Cabinet size: Model 507, table, 30 x 13j x 14 inches
Model 508, console, 34 x 18 x 54 inches. Prices: Model
507, $190 less accessories. Model 508, $320 with loud
speaker.
NO. 427. MURDOCK 7
Seven tubes; 3 t. r. f. (01-A), detector (01-A), 1 trans-
former and 2 resistance audio (two 01-A and 12 or 71).
One control. Volume control: rheostat on r. f. Coils
shielded. Neutralized. Battery cable. C-battery con-
nections. Complete metal case. Antenna: 100 feet.
Panel size: 9 x 23 inches. Price, not available.
NO. 520. BOSCH 57
Seven tubes; 4 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control calibrated in kc. Volume
control: rheostat on r. f. Shielded. Battery cable. C-
battery connections. Balanced. Output device. Built-in
loud speaker. Antenna: built-in loop or outside antenna,
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340
including enclosed loop and loud speaker.
NO. 521. BOSCH "CRUISER," 66 AND 76
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat
on r. f. Shielded. C-battery connections. Balanced.
Battery cable. Antenna: 20 to 100 feet. Prices: Model
66, table, $99.50. Model 76, console, $175; with loud
speaker $195.
NO. 524. CASE, 61 A AND 61 C
T. r. f. Semi-shielded. Battery cable. Drum control.
Volume control: variable high resistance in audio sys-
tem. Plate current: 35mA. Antenna: 100 feet. Prices:
Model 61A, $85; Model 61 C, console, $135.
NO. 525. CASE, 90 A AND 90 C
Drum control. Inductive volume control. Technidyne
circuit. C-battery connections. Battery cable. Loop
operated. Model 90-C equipped with output device.
Prices: Model 90 A, table, $225; Model 90 C, console,
$350.
NO. 526. ARBORPHONE 25
Six tubes; 3 t. r. f. (01-A), detector (01-A), 2 audio
(01-A and 71). One control. Volume control: rheostat.
Shielded. Battery cable. Output device. C-battery con-
nections. Loftin-White circuit. Antenna: 75 feet. Panel:
75 x 15 inches, metal. Prices: Model 25, table. $125;
Model 252, $185; Model 253, $250; Model 255, combin-
ation phonograph and radio, $600.
NO. 527. ARBORPHONE 27
Five tubes; 2 t. r. f. (01-A), detector (01-A), 2 audio
(01-A). Two controls. Volume control: rheostat. C-
battery connections. Binding posts. Antenna: 75 feet.
Prices: Model 27, $65; Model 271, $99.50; Model 272.
$125.
NO. 528. THE "CHIEF"
Seven tubes; six 01-A tubes and one power tube
One control. Volume control: rheostat. C-battery con-
nection. Partial shielding. Binding posts. Antenna,
outside. Cabinet size: 40 x 22 x 16 inches. Prices.
Complete with A power supply, $250; without acces
series, $150.
NO. 529. DIAMOND SPECIAL, SUPER SPECIAL.
AND BABY GRAND CONSOLE
Six tubes; all 01-A type. One control. Partial shield-
ing. C-battery connections. Volume control: rheostat.
Binding posts. Antenna: outdoor. Prices: Diamond
Special, $75; Super Special, $65; Baby Grand Console,
$110.
RADIO BROADCAST ADVERTISER
391
Engineering ^Pamphlet on
B Power Supply
and Amplifier Design
Here is a new i2-page book, 85" by
n", containing blueprints of the
circuits, photographs and full lists of
parts for the construction of all of
the newest and most modern Power
Amplifiers and Power Supplies. The
latest development of Samson, Gen-
eral Radio, Silver-Marshall, Thor-
darson, National Co., Acme, etc.,
for high quality, high power audio
reproduction. Invaluable for all
set builders and home constructors
of radio. Send for it today.
Tobe Deutschmann Co.
Cambridge, Mass. •
Gentlemen: Please send me your new
book, "TOBE B POWER SUPPLY
and AMPLIFIER DESIGN." Enclosed
please find 250.
Name
Address.
Convert your set to A. C. with
the NEW Karas A-C-FORMER.
Easy to do — No rewiring.
YOU now can have A. C. operation of
your present battery-operated receiver
by using the New Karas A-C-Former Fila-
ment Supply and the Carter Adapter Cable
Harness now available. You can then use
the new A. C. Tubes and enjoy the marvel-
ous reception they afford — get distant sta-
tions with tremendous volume — be forever free from
battery operation. Kasy to convert your set. No
rewiring. Simply remove present tubes, insert Carter
Adapter Cable Harness, attach end of harness to
Karas A-C-Former, and put in new A. C. Tubes.
Anyone can do it in a few minutes. Mail coupon to-
day for full information on how to convert your set.
KARAS ELECTRIC CO.
4032-C North Rockwell St.
Chicago
KtlliS M.I i i l;n CO.
ICI:ILM North Rorkodl Ht., Chicago
Send m« complete details on how I can convei
my tube receiver lo A. C.
Addresa ..
City
SANGAMO
MICA. CONDENSERS
UNAFFECTED
I / u\\\
by
When thehumidity hovers around 100,
the components of your radio receiver
are subjected to the equivalent of a
water bath!
You can make certain, at least, that
the fixed condensers in the circuit will
not alter in capacity or efficiency under
these conditions.
Use Sangamo Mica Condensers — they
are permanently protected from all' at-
mospheric action by a solid sheathing
of pure bakelite!
SANGAMO ELECTRIC COMPANY
Springfield Illinois
\EKNCH /
Book on Resistance 25<f
Why not subscribe to Radio
Broadcast ? By the year
only $4.00; or two years,
$6.00, saving $2.40. Send
direct to Doubleday, Doran
& Company, Inc., Garden
City, New York.
ACME
WIRE CO.
LATSIT
for RADIO
WIRING
Flexible stranded Celatsite is i
composed of fine, tinned cop- H
per wires with non-inflammable jj
Celatsite covering in 9 bright
colors. Strips clean, solders : •
readily. Sold only in 25' coils, in cartons colored :"]
to match contents. Solid Celatsite has same col- B
ored covering, but over bus har wire.
ACME SOLID CELATSITE is a tinned copper 1
bus bar hook-up wire with non-inflammable Celat- 1
site insulation, in nine colors. Sizes, 14, 16, 18, H
19, 30" lengths. Write for folder. The Acme «
Wire Co., Dept. B, New Haven, Conn.
llllllllllllilllMIIHlllllllilllli ' mm^
DISTANCE
lends
ENCHANT.
MENT
"WFTHEN you buy
** a radio set im
' or build
a radio set make sure
that it has Copper Shield-
ing. Where long distance
reception is desired Cop-
per Shielding is essential.
It is a refinement to your
set that will enable you to
hear the programs of dis-
tant stations much more
clearly.
Copper Shielded sets give:
BETTER RECEPTION
FINER SELECTIVITY
IMPROVED TONE QUALITY
By virtue of its easy work-
ing qualities and its
high conductivity Copper
Shielding is a decided im-
provement to any set.
COPPER & BRASS
RESEARCH ASSOCIATION
25 Broadway, New York
Write for your copy of this book. There
if no cost nor obligation on your part.
392
RADIO BROADCAST ADVERTISER
Achieve
SUCCESS
in Radio
New course gives finest
instruction obtainable
You Can Learn at Home!
Good pay from the start,
rapid advancement, and phe-
nomenal success — a life pro-
fession of fascinating brain-
work— that is what Radio
holds for the man who knows
his subject thoroughly. Since
1909 Radio Institute of
America has trained thou-
sands to become successful
in the many branches of Ra-
dio. Are you going to plod
along at a thirty-five dollar a week job
when REAL MONEY is waiting for you
in radio?
New Course Finest Ever
Prominent radio men have en-
thusiastically greeted RIA's
new course as the most com-
plete and up-to-date offered
today. All this first -quality
equipment is furnished FREE
WITH THE COURSE-parts
for making many practical
radio circuits and the Peerless
Signagraph for code instruc-
tion.
R.L DUNCAN,
Director.
Radio Institute
of America and
author of
several volumes
in radio.
RIA backed by RCA, G-E
and Westinghouse
You get all the benefits of instruction conducted
by RCA and sponsored by RCA's associates, G-E
and Westinghouse. Our employment department
is at the service of graduates.
Study at Home!
Moreover you can STUDY AT
HOME— when you please and as
long as you please.
This new booklet describing the
course is just off the press. If you
want to learn more about the well
paying positions in this fascinating
profession send the coupon now
for your copy.
RADIO INSTITUTE OF AMERICA
Dept. E-3 326 Broadway, New York City
RADIO INSTITUTE OF AMERICA. Dept. E-3
326 Broadway, New York City
Dear Mr. Duncan :
Please send me your new catalog. I want to
know more about your new radio course.
Name...
Address .
A Varied List of Books Pertaining to Radio and Allied
Subjects Obtainable Free With the Accompanying Coupon
D EIDERS may obtain any of the booklets listed below by use-
**• ing the coupon printed on page jgj. Order by number only.
1. FILAMENT CONTROL — Problems of filament supply,
voltage regulation, and effect on various circuits. RADIALL
COMPANY.
2. HARD RUBBER PANELS — Characteristics and proper-
ties of hard rubber as used in radio, with suggestions on
how to "work" it. B. F. GOODRICH RUBBER COMPANY.
3. TRANSFORMERS — A booklet giving data on input and
output transformers. PACENT ELECTRIC COMPANY.
5. CARBORUNDUM IN RADIO — A book giving pertinent
data on the crystal as used for detection, with hook-ups,
and a section giving information on the use of resistors.
THE CARBORUNDUM COMPANY.
7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA-
TION— Circuit diagrams and discussion. ALL-AMERICAN
RADIO CORPORATION.
9. VOLUME CONTROL — A leaflet showing circuits for
distortionless control of volume. CENTRAL RADIO LABORA-
TORIES.
10. VARIABLE RESISTANCE — As used in various circuits.
CENTRAL RADIO LABORATORIES.
1 1 . RESISTANCE COUPLING — Resistors and their ap-
plication to audio amplification, with circuit diagrams.
DEjuR PRODUCTS COMPANY.
12. DISTORTION AND WHAT CAUSES IT — Hook-ups of
resistance-coupled amplifiers with standard circuits. ALLEN-
BRADLEY COMPANY.
15. B-ELIMINATOR AND POWER AMPLIFIER — Instruc-
tions for assembly and operation using Raytheon tube.
GENERAL RADIO COMPANY.
153. B-EtlMlNATOR AND PoWER AMPLIFIER — InstHJC-
tions for assembly and operation using an R. C. A. rectifier.
GENERAL RADIO COMPANY.
16. VARIABLE CONDENSERS — A description of the func-
tions and characteristics of variable condensers with curves
and specifications for their application to complete receivers.
ALLEN D. CARDWELL MANUFACTURING COMPANY.
17. BAKELITE — A description of various uses of bakelite
in radio, its manufacture, and its properties. BAKELITE
CORPORATION.
io. POWER SUPPLY — A discussion on power supply with
particular reference to lamp-socket operation. Theory
and constructional data for building power supply devices.
ACME APPARATUS COMPANY.
20. AUDIO AMPLIFICATION — A booklet containing data
on audio amplification together with hints for the construc-
tor. ALL AMERICAN RADIO CORPORATION.
21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE-
METER — Constructional data and application. BURGESS
BATTERY COMPANY.
46. AUDIO-FREQUENCY CHOKES — A pamphlet showing
positions in the circuit where audio-frequency chokes may
be used. SAMSON ELECTRIC COMPANY.
47. RADIO-FREQUENCY CHOKES — Circuit diagrams il-
lustrating the use of chokes to keep out radio-frequency
currents from definite points. SAMSON ELECTRIC COMPANY.
48. TRANSFORMER AND IMPEDANCE DATA — Tables giving
the mechanical and electrical characteristics of transformers
and impedances, together with a short description of their
use in the circuit. SAMSON ELECTRIC COMPANY.
49. BYPASS CONDENSERS — A description of the manu-
facture of bypass and filter condensers. LESLIE F. MUTER
COMPANY.
50. AUDIO MANUAL — Fifty questions which are often
asked regarding audio amplification, and their answers.
AMERTRAN SALES COMPANY, INCORPORATED.
51. SHORT-WAVE RECEIVER — Constructional data on a
receiver which, by the substitution of various coils, may be
made to tune from a frequency of 16,660 kc. (18 meters) to
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED.
52. AUDIO QUALITY — A booklet dealing with audio-fre-
quency amplification of various kinds and the application
to well-known circuits. SILVER-MARSHALL. INCORPORATED.
56. VARIABLE CONDENSERS — A bulletin giving an
analysis of various condensers together with their charac-
teristics. GENERAL RADIO COMPANY.
57. FILTER DATA — Facts about the filtering of direct
current supplied by means of motor-generator outfits used
with transmitters. ELECTRIC SPECIALTY COMPANY.
59. R ESISTANCE COUPLING — A booklet giving some
general information on the subject of radio and the applica-
tion of resistors to a circuit. DAVEN RADIO CORPORATION.
62. RADIO-FREQUENCY AMPLIFICATION — Constructional
details of a five-tube receiver using a special design of radio-
frequency transformer. CAMFIELD RADIO MFG. COMPANY.
63. FIVE-TUBE RECEIVER — Constructional data on
building a receiver. AERO PRODUCTS, INCORPORATED.
64. AMPLIFICATION WITHOUT DISTORTION — Data and
curves illustrating the use of various methods of amplifica-
tion. ACME APPARATUS COMPANY.
66. SUPER-HETERODYNE — Constructional details of a
seven-tube set. G. C. EVANS COMPANY.
70. IMPROVING THE AUDIO AMPLIFIER — Data on the
characteristics of audio transformers, with a circuit diagram
showing where chokes, resistors, and condensers can be used,
AMERICAN TRANSFORMER COMPANY.
72. PLATE SUPPLY SYSTEM — A wiring diagram and lay-
out plan for a plate supply system to be used with a power
amplifier. Complete directions for wiring are given. AMER-
TRAN SALES COMPANY.
80. FIVE-TUBE RECEIVER — Data are given for the con-
struction of a five-tube tuned radio-frequency receiver.
Complete instructions, list of parts, circuit diagram, and
template are given. ALL-AMERICAN RADIO CORPORATION.
81. BETTER TUNING — A booklet giving much general in-
formation on the subject of radio reception with specific il-
lustrations. Primarily for the non-technical home construc-
tor. BREMER-TULLY MANUFACTURING COMPANY.
82. SIX-TUBE RECEIVER — A booklet containing photo-
graphs, instructions, and diagrams for building a six-tube
shielded receiver. SILVER-MARSHALL, INCORPORATED.
83. SOCKET POWER DEVICE — A list of parts, diagrams,
and templates for the construction and assembly of socket
power devices. JEFFERSON ELECTRIC MANUFACTURING COM-
PANY.
84. FIVE-TUBE EQUAMATIC — Panel layout, circuit dia-
grams, and instructions for building a five-tube receiver, to-
gether with data on the operation of tuned radio-frequency
transformers of special design. KARAS ELECTRIC COMPANY.
85. FILTER — Data on a high-capacity electrolytic con-
denser used in filter circuits in connection with A socket
power supply units, are given in a pamphlet. THE ABOX
COMPANY.
86. SHORT-WAVE RECEIVER — A booklet containing data
on a short-wave receiver as constructed for experimental
purposes. THE ALLEN D. CARDWELL MANUFACTURING
CORPORATION.
88. SUPER-HETERODYNE CONSTRUCTION — A booklet giv-
ing full instructions, together with a blue print and necessary
data, for building an eight-tube receiver. THE GEORGE W.
WALKER COMPANY.
89. SHORT-WAVE TRANSMITTER — Data and blue prints
are given on the construction of a short-wave transmitter,
together with operating instructions, methods of keying, and
other pertinent data. RADIO ENGINEERING LABORATORIES.
oo. IMPEDANCE AMPLIFICATION — The theory and practice
of a special type of dual-impedance audio amplification are
given. ALDEN MANUFACTURING COMPANY.
93. B-SocKET POWER — A booklet giving constructional
details of a socket-power device using either the BH or 313
type rectifier. NATIONAL COMPANY, INCORPORATED.
94. POWER AMPLIFIER — Constructional data and wiring
diagrams of a power amplifier combined with a B-supply
unit are given. NATIONAL COMPANY, INCORPORATED.
ipo. A, B, AND C SOCKET-POWER SUPPLY — A booklet
giving data on the construction and operation of a socket
power supply using the new high-current rectifier tube.
THE Q. R. S. Music COMPANY.
101. USING CHOKES — A folder with circuit diagrams of
the more popular circuits showing where choke coils may
be placed to produce better results. SAMSON ELECTRIC
COMPANY. •
22. A PRIMER OF ELECTRICITY — Fundamentals of
electricity with special reference to the application of dry
cells to radio and other uses. Constructional data on buzzers,
automatic switches, alarms, etc. NATIONAL CARBON COM-
PANY.
23. AUTOMATIC RELAY CONNECTIONS — A data sheet
showing how a relay may be used to control A and B cir-
cuits. YAXLEY MANUFACTURING COMPANY.
25. ELECTROLYTIC RECTIFIER — Technical data on a new
type of rectifier, with operating curves. KODEL RADIO
CORPORATION.
26. DRY CELLS FOR TRANSMITTERS — Actual tests
given, well illustrated with curves showing exactly what
may be expected of this type of B power. BURGESS BATTERY
COMPANY.
27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS-
MITTERS— Characteristic curves and data on discharge tests.
BURGESS BATTERY COMPANY.
28. B BATTERY LIFE — Battery life curves with general
curves on tube characteristics. BURGESS BATTERY COM-
PANY.
30. TUBE CHARACTERISTICS — A data sheet giving con-
stants of tubes. C. E. MANUFACTURING COMPANY.
32. METERS FOR RADIO — A catalogue of meters used in
radio, with diagrams. BURTON-ROGERS COMPANY.
33. SWITCHBOARD AND PORTABLE METERS — A booklet
giving dimensions, specifications, and shunts used with
various meters. BURTON-ROGERS COMPANY.
35. STORAGE BATTERY OPERATION — An illustrated
booklet on the care and operation of the storage battery.
GENERAL LEAD BATTERIES COMPANY.
36. CHARGING A AND B BATTERIES — Various ways of
connecting up batteries for charging purposes. WESTING-
HOUSE UNION BATTERY COMPANY.
37. WHY RADIO Is BETTER WITH BATTERY POWER — Ad-
vice on what dry cell battery to use; their application to
radio, with wiring diagrams. NATIONAL CARBON COMPANY.
53. TUBE REACTIVATOR — Information on the care of
vacuum tubes, with notes on how and when tbey should be
reactivated. THE STF.RLING MANUFACTURING COMPANY.
69. VACUUM TUBES — A booklet giving the characteris-
tics of the various tube types with a short description of
where they may be used in the circuit. RADIO CORPORA-
TION OF AMERICA.
77. TUBES — A booklet for the beginner who is interested
in vacuum tubes. A non-technical consideration of the
various elements in the tube as well as their position in the
receiver. CLEARTRON VACUUM TUBE COMPANY.
87. TUBE TESTER — A complete description of how to
build and how to operate a tube tester. BURTON-ROGERS
COMPANY.
91. VACUUM TUBES — A booklet giving the characteristics
and uses of various types of tubes. This booklet may be
obtained in English, Spanish, or Portuguese. DEFOREST
RADIO COMPANY.
92. RESISTORS FOR A. C. OPERATED RECEIVERS — A
booklet giving circuit suggestions for building a. c. operated
receivers, together with a diagram of the circuit used with
the new 4OO-miIliampere rectifier tube. CARTER RADIO
COMPANY.
97. HIGH-RESISTANCE VOLTMETERS — A folder giving in-
formation on how to use a high-resistance voltmeter,
special consideration being given the voltage measurement
of socket-power devices. WESTINGHOUSE ELECTRIC &
MANUFACTURING COMPANY.
1 02. RADIO POWER BULLETINS — Circuit diagrams, theory
constants, and trouble-shooting hints for units employing
the BH or B rectifier tubes. RAYTHEON MANUFACTURING
COMPANY.
103. A. C. TUBES — The design and operating character-
istics of a new a. c. tube. Five circuit diagrams show how
to convert well-known circuits. SOVEREIGN ELECTRIC &
MANUFACTURING COMPANY.
(Continued on page 393)
RADIO BROADCAST ADVERTISER
393
41. BABY RADIO TRANSMITTER OF QXH-QEK — Descrip-
tion and circuit diagrams of dry-cell operated transmitter.
BURGESS BATTERY COMPANY.
42. ARCTIC RADIO EQUIPMENT — Description and circuit
details of short-wave receiver and transmitter used in
Arctic exploration. BURGESS BATTERY COMPANY.
58. How TO SELECT A RECEIVER— A commonsense
booklet describing what a radio set is, and what you should
expect from it, in language that any one can understand.
DAY-FAN ELECTRIC COMPANY.
67. WEATHER FOR RADIO — A very interesting booklet
on the relationship between weather and radio reception,
with maps and data on forecasting the probable results.
TAYLOR INSTRUMENT COMPANIES.
73. RADIO SIMPLIFIED — A non-technical booklet giving
pertinent data on various radio subjects. Of especial in-
terest to the beginner and set owner. CROSLEY RADIO COR-
PORATION.
74. THE EXPERIMENTER — A monthly publication which
gives technical facts, valuable tables, and pertinent informa-
tion on various radio subjects. Interesting to the experi-
menter and to the technical radio man. GENERAL RADIO
COMPANY.
76. RADIO INSTRUMENTS— A description of various
meters used in radio and electrical circuits together with a
short discussion of their uses. JEWELL ELECTRICAL IN-
STRUMENT COMPANY.
06. VACUUM TUBE TESTING — A booklet giving pertinent
data on how to test vacuum tubes with special reference to
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT
COMPANY.
98. COPPER SHIELDING — A booklet giving information
on the use of shielding in radio receivers, with notes and
diagrams showing how it may be applied practically. Of
special interest to the home constructor. THE COPPER AND
BRASS RESEARCH ASSOCIATION.
99. RADIO CONVENIENCE OUTLETS — A folder giving
diagrams and specifications for installing loud speakers in
various locations at some distance from the receiving set.
YAXLEY MANUFACTURING COMPANY.
105. COILS^— Excellent data on a radio- frequency coil
with constructional information on six broadcast receivers,
two short-wave receivers, and several transmitting circuits.
AERO PRODUCTS COMPANY.
106. AUDIO TRANSFORMER— Data on a high-quality
audio transformer with circuits for use. Also useful data oh
detector and amplifier tubes. SANGAMO ELECTRIC COMPANY.
107. VACUUM TUBES — Data on vacuum tubes with
facts about each. KEN-RADIO COMPANY.
108. VACUUM TUBES— Operating characteristics of an
a.c. tube with curves and circuit diagram for connection
in converting various receivers to a.c. operation with a
four-prong a.c. tube. ARCTURUS RADIO COMPANY..
109. RECEIVER CONSTRUCTION — Constructional data on
a six-tube receiver using restricted field coils. BODINE
ELECTRIC COMPANY.
1 10. RECEIVER CONSTRUCTION — Circuit diagram and
constructional information for building a five- tube set
using restricted field coils. BODINE ELECTRIC COMPANY.
in. STORAGE BATTERY CARE — Booklet describing the
care and operation of the storage battery in the home.
MARKO STORAGE BATTERY COMPANY.
112. HEAVY-DUTY RESISTORS — Circuit calculations and
data on receiving and transmitting resistances for a variety
of uses, diagrams for popular power supply circuits, d.c. resis-
tors for battery charging use. WARD LEONARD ELECTRIC
COMPANY.
1 13. CONE LOUD SPEAKERS — Technical and practical in-
formation on electro-dynamic and permanent magnet type
cone loud speakers. THE MAGNAVOX COMPANY.
1 14. TUBE ADAPTERS — Concise information concerning
simpjified methods of including various power tubes in
existing receivers. ALDEN MANUFACTURING COMPANY.
115. WHAT SET SHALL I BUILD?— Descriptive matter,
with illustrations, of fourteen popular receivers for the home
constructor. HERBERT H. FROST, INCORPORATED.
104. OSCILLATION CONTROL WITH THE "PHASATROL"—
Circuit diagrams, details for connection in circuit, and
specific operating suggestions for using the "Phasatrol"
as a balancing device to control oscillation. ELECTRAD,
INCORPORATED.
116. USING A B POWER UNIT— A comprehensive book-
let detailing the use of a B power unit. Tables of voltages —
both B and C — are shown. There is a chapter on trouble
shooting. MODERN ELECTRIC MFG. Co.
117. BEST RESULTS FROM RADIO TUBES— The chapters
are entitled: "RadioTubes," "Power Tubes," "Super De-
tector Tubes," "A. C. Tubes," "Rectifier Tubes," and
Installation." GOLD SEAL ELECTRICAL Co.
118. RADIO INSTRUMENTS. CIRCULAR "J"— A descriptive
manual on the use of measuring instruments for every radio
circuit requirement. A complete listing of models for trans-
mitters, receivers, set servicing, and power unit control.
WESTON ELECTRICAL INSTRUMENT CORPORATION.
119. THE NEW LOFTIN WHITE CIRCUIT — A twenty-four
page booklet explaining the principles and application of
this popular circuit. CONSOLIDATED RADIO CORPORATION.
120. THE RESEARCH WORKER — A monthly bulletin of in-
terest to the home constructor. A typical feature article
describes the construction of a special audio amplifier —
AEROVOX WIRELESS CORPORATION.
USE THIS BOOKLET COUPON
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, N. Y.
Please send me fat no expense) the following book-
lets indicated by numbers in the published list above:
Name
Address
(Number)
(Street)
(City) (State)
ORDER BY NUMBER ONLY
jThis coupon must accompany every request. RB 3-28
What Kit Shall I Buy?
HE list of kits herewith is printed as an exten-
sion of the scope of the Service Department of
RADIO BROADCAST. It is our purpose to list here
the technical data about kits on which information
is available. In some cases, the kit can he pur-
chased from your dealer complete; in others, the
descriptive booklet is supplied for a small charge
and the parts can he purchased as the buyer likes.
The Service Department will not undertake to
handle cash remittances for parts, but when the
coupon on page )<)<j is filled out, all the informa-
tion requested will be forwarded.
201. SC FOUR-TUBE RECEIVER — Single control. One
stage of tuned radio frequency, regenerative detector,
and two stages of transformer-coupled audio amplification.
Regeneration control is accomplished by means of a variable
resistor across the tickler coil. Standard parts; cost approxi-
mately $58.85.
202. SC-II FIVE-TUBE RECEIVER — Two stages of tuned
radio frequency, detector, and two stages of trans-
former-coupled audio. Two tuning control*. Volume control
consists of potentiometer grid bias on r.f. tubes. Standard
parts cost approximately $60.35.
203. "HI-Q" KIT — A five-tube tuned radio-frequency set
having two radio stages, a detector, and two transformer-
coupled audio stages. A special method of coupling in the
r.f. stages tends to make the amplification more nearly equal
over the entire band. Price $63.05 without cabinet.
204. R. G. S. KIT — A four-tube inverse reflex circuit,
having the equivalent of two tuned radio- frequency stages,
detector, and three audio stages. Two controls. Price $69.70
without cabinet.
205. PIERCE AIRO KIT — A six-tube single-dial receiver;
two stages of radio-frequency amplification, detector, and
three stages of resistance-coupled audio. Volume control
accomplished by variation of filament brilliancy of r.f.
tubes or by adjusting compensating condensers. Complete
chassis assembled but not wired costs $42.50.
206. H & H-T. R. F. ASSEMBLY — A five-tube set; three
tuning dials, two steps of radio frequency, detector, and 2
transformer-coupled audio stages. Complete except for base-
board, panel, screws, wires, and accessories. Price $30.00.
207. PREMIER FIVE-TUBE ENSEMBLE — Two stages of
tuned radio frequency, detector, and two steps of trans-
former-coupled audio. Three dials. Parts assembled but
not wired. Price complete, except for cabinet, $35.00.
208. "QUADRAFORMER VI" — A six-tube set with two tun-
ing controls. Two stages of tuned radio frequency using
specially designed shielded coils, a detector, one stage of
transformer-coupled audio, and two stages of resistance-
coupled audio. Gain control by means of tapped primaries
on the r.f. transformers. Essential kit consists of three
shielded double-range "Quadraformer" coils, a selectivity
control, and an "Ampitrol," price $17.50. Complete parts
$70. i 5.
209. GEN-RAL FIVE-TUBE SET — Two stages of tuned
radio frequency, detector, and two transformer-coupled
audio stages. Volume is controlled by a resistor in the plate
circuit of the r.f. tubes. Uses a special r.f. coil ("Duo-
Former") with figure eight winding. Parts mounted but
not wired, price $37.50.
210. BREMER-TULLY POWER-SIX— A six-tube, dual-
control set ; three stages of neutralized tuned radio frequency,
detector, and two transformer-coupled audio stages. Re-
sistances in the grid circuit together with a phase shifting
arrangement are used to prevent oscillation. Volume control
accomplished by variation of B potential on r.f. tube.
Essential kit consists of four r.f. transformers, two dual
condensers, three small condensers, three choke coils, one
5oo,ooo-ohm resistor, three Ijoo-onin resistors, and a set
of color charts and diagrams. Price $41.50.
212. INFRADYNE AMPLIFIER — A three-tube intermediate-
frequency amplifier for the super-heterodyne and other
special receivers, tuned to 3490 kc. (86 meters). Price $25.00.
213. RADIO BROADCAST "LAB" RECEIVER — A four-tube
dual-control receiver with one stage of Rice neutralized
tuned-radio frequency, regenerative detector (capacity
controlled), and two stages of transformer-coupled audio.
Approximate price, $78.15.
214. LC-27 — A five-tube set with two stages of tuned-
radio frequency, a detector, and two stages of transformer-
coupled audio. Special coils and special means of neutralizing
are employed. Output device. Price $85.2owithout cabinet.
215. LOFTIN-WHITE — A five-tube set with two stages of
radio frequency, especially designed to give equal amplifica-
tion at all frequencies, a detector, and two stages of trans-
former-coupled audio. Two controls. Output device Price
$85.10.
216. K.H.-27 — A six-tube receiver with two stages of
neutralized tuned radio frequency, a detector, three stages
of choke-coupled audio, and an output device. Two controls.
Price $86.00 without cabinet.
217. AERO SHORT-WAVE KIT — Three plug-in coils de-
signed to operate with a regenerative detector circuit and
having a frequency range of from 19, 090 to 2306 kc. (1510130
meters). Coils and plug only, price $12. 50.
218. DiAMOND-op-THE-AiR — A five-tube set having one
stage of tuned-radio frequency, a regenerative detector,
one stage of transformer-coupled audio, and two stages of
resistance-coupled audio. Volume control through regenera-
tion. Two tuning dials.
219. NORDEN-HAUCK IMPROVED SUPER 10 — Ten tubes;
five stages of tuned radio frequency, detector, and four stages
of choke- and transformer-coupled audio frequency. Two
controls. Price $260.00.
220. BROWNING-DRAKE — Five tubes: one s»age tuned
radio frequency (Rice neutralization), regenerative detector
(tickler control), three stages of audio (special combination
of resistance- and impedance-coupled audio). Two controls
electrify your set
the easy practical
Knapp way----
r The Kit completely assembled with ">
•J- metal cover in place. Operates on "y
V 105-120 volts AC, 50 to 60 cycles.*'
Hnam) A Powfu Mil
No expensive short lived AC Tubes, no
troublesome re-wiring, no annoying hum.
Increase instead of decrease the efficiency
of your set, no waiting... the Knapp "A"
Power gives you music instantly at the
snap of a switch.
This absolutely dry "A" Power is not in
any way a battery combination ... not
something to add to your battery ... it
is the most efficient "A" Battery Elimina-
tor ever designed. It supplies unfailing
"A" current to any set using 201-A or 6
volt tubes.
Magic Silence
So silent is Knapp "A" Power, that you
can place a pair of head phones directly
across the output and not be able to detect
a hum. This is made possible by the
efficient Knapp filter system, consisting of
2 oversized chokes and 2 condensers of 1500
microfarads each. A new discovery makes
these amazing capacities possible in the
small space of 2x2x8 inches I
Absolutely Dry
There is not a drop of moisture in this absolutely dry
unit. The condensers are baked so that not a drop of
moisture remains. The unique, fully patented, solid,
full-wave rectifier is absolutely dry. No water ... no
acid ... no alkali ...no tubes... no electrolytic
action. Nothing to get out of order. Nothing that
needs attention.
Assemble In Hall an Hoar
The Knapp "A" Power Kit is so easily assembled,
that within half an hour after you receive it, YOU can
have it in operation. The parts seem to fall in place,
No drilling and very little soldering. Everything
supplied, even to the screws, wire, drilled base-board
and metal cover. It is so complete, that even a plug
is supplied BO that a "B" Eliminator may be operated
from the same switch. We have never seen snch
simple instructions.
Big Profits lor
Set Builders
Our president, Mr. David W.
Knapp, is offering the set
builders of America, for a
limited time only, a money-
saving, profit-making plan
which is unique in the annals
of radio. Send the coupon
today, before it is too late.
Knapp Electric Corporation
Port Chester, N. Y.
MR. DAVID W. KNAPP, Pres.
Knapp Electric Corporation
331 Fox Island Road,
Port Chester, N.Y.
Send me complete information regarding the Knapp
"A" Power Kit and your special discount to Set
Builders.
Name
Address
RADIO BROADCAST ADVERTISER
IN A HUDDLE?
Yes!— But it's not a
Football Signal
They're looking at the
NEW WESTON
TRIPLE-RANGE
A. C. VOLTMETER
for measuring theA.C. supply and
tube voltages in connection with
A. C. RECEIVERS
Model
150/8/4 volts
THIS new A. C. portable voltmeter —
the latest addition to the famous
Weston line of Radio Instruments — has
been eagerly awaited by the entire fra-
ternity of radio interests, experimenter
and set owner alike. With the advent
of the new A. C. receivers, everywhere
one heard the question — "What kind
of an instrument do we need now?"
And here it is, an exquisite design,
typically Weston in construction and
performance. The highest quality, yet
moderately priced. See your dealer and
place your order now. Get in ahead
of that inevitable rush when Weston an-
nounces a new development.
WESTON ELECTRICAL INSTRUMENT
CORPORATION
179 Frelinghuysen Ave. Newark, N. J.
WESTON
RADIO
INSTRUMENTS
PRINCIPLES OF RADIO COMMUNICATION. By
J. H. Morecroft. Second Edition. Published by
John Wiley & Sons, Incorporated, New York.
Pages, looi. Illustrations, 831. Price, $7.50.
M
'ORrXROF T has gone into a second edi-
tion. The revised volume calls for a sup-
plementary review, for after the lapse
of six years (the first edition was issued in 1921)
much that was important is slipping into desue-
tude, and technological fancies have become
engineering realities. The ordinary engineer,
called on to review Morecroft's monumental
work, is placed somewhat in the position of a
parish priest ordered to review the Bible. It is
safe, however, to quote Professor Morecroft
himself in his outline of the changes made in the
new edition:
The new material incorporated in this edition
so increased the size that it was thought advisa-
ble to delete much of the first edition. A consider-
able part of the chapter on Spark Telegraphy
has been taken out, therefore, and two chapters
of the earlier edition have been deleted. The
chapter on radio measurements, and that on
experiments, have been omitted.
Notable additions to the older edition occur in
Chapters II, IV, VIII, and X. In Chapter II
many new data on coils and condensers at radio
frequencies are given. In Chapter IV, dealing
with the general features of radio transmission,
new material on field strength measurements,
reflection and absorption, fading, short-wave
propagation, etc., has been introduced. In Chap-
ter VIII (radio telephony) a great deal of ma-
terial on voice analysis has been added; the per-
formance of loud-speaking telephones, frequency
control by crystals, etc., has been discussed. In
Chapter X, dealing with amplifiers, the question
of distortionless amplification has been thor-
oughly dealt with, some of the material being
given for the first time. The questions of radio-
frequency amplification, balanced circuits, push-
pull arrangements, etc., have been explained.
Principles of Radio Communication is a com-
prehensive textbook of radio engineering. The
author, a Professor of Electrical Engineering at
Columbia University, and a Past President of
the Institute of Radio Engineers, is one of the
outstanding opponents of guesswork in radio
technology. When the publishers in their circular
describing the book refer to it as the "most
complete, accurate, and authoritative book on
radio available" they are simply telling the
truth. But in justice to the author, who has put a
considerable number of years into this job, it
should be stated that when the publishers con-
tinue: " — for Designers, Engineers, Service
Men, Distributors, Dealers, Salesmen, Teachers,
Students, Operators, Set Owners," they talk
like hasheesh addicts. I hope that Wiley sells
as many copies of Morecroft as the publisher of
Durant's Story of Philosophy has managed
to dispose of, to his own and his client's en-
richment, but I feel bound to warn Distrib-
utors, Dealers, Salesmen, and Set Owners that,
with negligible exceptions in their ranks, the
only portions of Principles of Radio Communica-
tion which they can hope to understand are the
articles and prepositions. Not that it is an
excessively abstruse work; any student of
mathematics through the calculus can follow the
demonstrations, and any student of radio en-
gineering can read the whole thousand pages
with vast profit. But it is a work in radio en-
gineering. Its precise virtue is that dealers,
salesmen, and the generality of set owners will
not understand it.
How radio has grown! Here is a book of a
thousand six-by-nine pages, and yet it is largely
an outline of principles. If you consulted it for
the actual design of a line equalizer or a lo-TU
Free 1928 Radio Guide
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Name
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TO
'RADIO
DEALERS/
The R. B. Laboratory Informa-
tion Sheets have been appear*
ing in RADIO BROADCAST since
June, 1926. They are a regular
feature in each issue and they
cover a wide range of infor-
mation of value to the radio
experimenter and set builder.
We have just reprinted Lab.
Sheets Nos. 1-88 from the
June, 1926, to April, 1927,
issues of RADIO BROADCAST.
They are arranged in numerical
order and are bound with a
suitable cover. They sell at
retail for one dollar a set. Write
for dealers' prices. Address
your letter to
Circulation Dept.,
RADIO BROADCAST
Garden City,
N. Y.
RADIO BROADCAST ADVERTISER
395
pad, you would not find either device even
mentioned. The author makes no bones about
this. "As in the previous edition," he writes in
the new preface, "no pretense is made that the
book is a treatise on radio practice; in general,
only the principles involved in the operation of
radio apparatus have received attention. What-
ever radio apparatus is discussed is dealt with
only to illustrate those principles the text is in-
tended to elucidate." But those principles, by
diagram, mathematical and physical analysis,
oscillogram, and every other resource of tech-
nical instruction, it does clarify. The chapter on
vacuum tubes alone runs to 240 pages, a book in
itself, and after you have mastered it you know
something about tubes. You may burn out the
next one you put into a socket anyway, but at
least you will not concoct any idiotic theories
about it. If you believe that there is a dividing
line between principles and practice, and that
life is too short to include both, you will, of
course, find no use for such a course as Morecroft
offers. You had best go out and sell bonds, in that
case. But if you are a radio engineer, or want to
become one in the only genuine sense of the
word, then Morecroft's textbook will be worth
more than $7.50 to you.
In a work of this size there are inevitably
sections over which other engineers may disagree
with the author. The treatment of " Elimination
of Strays," pages 340-343, may be cited. In Fig.
1 6, "one of the early attempts to eliminate
'strays,'" ascribed to De Groot, is shown. This
scheme is a neutralization system — one antenna
tuned to the desired signal, the other aperiodic,
etc. It will not work, which Professor Morecroft
knows as well as anyone, but he does not tell the
reader that the scheme is worthless, and why.
The ingenious and useful wave antenna of
Beverage, Rice, and Kellogg, which deserves
mention in this section if anything does, is
omitted without a word. Roy A. Weagant's name
is twice misspelled. But such defects, which might
be serious in a lesser work, are overshadowed by
the high virtues of Morecroft's imposing con-
tribution to radio science. CARL DREHER.
USE THIS COUPON FOR KITS
RADIO BROADCAST SERVICE DEPARTMENT
Garden City, New York.
Please send me information about the following kits in-
dicated by number:
Name. . .
Address
(Number)
(Street)
(City) (State)
ORDER BY NUMBER ONLY. This coupon must
accompany each order.
RB 3-28
USE THIS COUPON FOR COMPLETE SETS
RADIO BROADCAST SERVICE DEPARTMENT
RADIO BROADCAST, Garden City, New York.
Please send me information about the following manu-
factured receivers indicated by number;
Name . . .
Address
(Number) (Street)
(City) (Stale)
ORDER BY NUMBER ONLY
This coupon must accompany each order. RB 3-28
A. C.
OPERATION
Type 440-A Transformer
Price J10.00
The Type 44O-A Transformer illustrated is designed for use on 105-125 V
(50-60 cycle) A. C. and is rated at 65 watts. The following voltages and
currents are available.
2 Volts 10 Amperes
3-5 " 5 "
S " 2-5 "
7-5 " 2 "
The use of this transformer together with the new A. C. tubes and a
dependable plate supply unit such as the General Radio type 445 Plate Supply
and grid Bias unit makes the conversion of a battery operated receiver into one
operated from the light socket very simple. If you do not care to undertake
this change yourself go to your community set builder. He is well qualified to
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GENERAL RADIO Co.
Manufacturers of Radio and Electrical Laboratory Apparatus
30 STATE STREET CAMBRIDGE, MASS.
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396
RADIO BROADCAST ADVERTISER
The radio leadership of 1928
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RADIO BROADCAST
APRIL, 1928
WILLIS KINGSLEY WING, Editor
KEITH HENNEY EDGAR H. FELIX
Director of the Laboratory
.
Contributing Editor
Vol. XII, No. 6
<»
guj^rzj^i s
Cover Design - - From a Design by Harvey Hop\ins Dunn
\
402
403
406
410
413
414
416
419
421
423
427
429
433
434
436
438
440
441
443
446 i
Tk-.riL'p «-^ Yl/T^V 1 f * , ' * Fr/iwris C~jnu) &vnith
Picture Broadcasting Becomes a Practical The Commission Retreats
Reality The Blue Laws of Radio
Possibilities of Still Picture Broadcasting Here and There
The Shrinking Short-Wave Spectrum
A Short'Wave Phone and C. W. Transmitter Kendall Clough
Electrification Without A. C. Tubes - - Lewis B. Hagerman
How Radio Developments Have Improved Recording and Re'
Radio Mu»t Be Made a Necessity
Our Readers Suggest
Testing an Audio Amplifier Phonograph Pick-up Switch
Sources of Power-Supply Hum Stabilizing with HiRh-Mu Tubes
An R. F. Volume Control Another Output Arrangement
Eliminating A. C. Hum
Strays from the Laboratory ,,,,,,*••**•
Music from the Ether Interesting Technical Literature
A. C. Tube Troubles Meters for Research Workers
"Gross Exaggeration" Short-Wave Notes
As the Broadcaster Sees It ,,,,,,,* dart L/reher
R. F. in Vaudeville Studio Slang
Rosa Ponsella before the Microphone When Orchestra Leaders Sing
Among the Broadcasters: WAAM-WOC- An Engineer's Embarrassment
3 LO, Melbourne — Sydney, Australia. Radio Inspectors— Fine Fellows
Studio Scandal Commercial Publications
No "Motor-Boating" H. O. Ward
An Experimental Screen-Grid Receiver - ' • Charles Thomas
PM~,-*-.-.AT.'«™ *-U/> "T4; fV P AT Rrnrt
electrifying tne m-v^ • * r. j\. uroc^
rvaaio rolK lou onouiu Know
(3). Lester Jones Drawing by Franklyn P. Stratford
Testing A and B Power Units Howard E. Rhodes
Radio Broadcast s Laboratory Information Sheets ' - ' - -
No. 177. Characteristics of Speech
No. 178. The Exponential Horn
No. 179. A Problem in Audio Amplification
No. 180. B Power Unit Characteristics
No. 181. R. F. vs. A. F. Amplification
No. i8». Filter Condensers
No. 183. The Type 280 and »8i Tube*
No. 184. Tuning
The contents of this magazine is indexed in The Readers' Guide
to Periodical Literature, which is on file at all public libraries.
$ AMONG OTHER THINGS. . .
THE issue before you contains a variety of articles appealing
to all tastes. For the short-wave enthusiast there is the
constructional article on the code and telephone transmitter
on page 410. For experimentes, we offer many articles, such as
those on a two-tube, screen-grid receiver, measurements on the
"Lab" circuit receiver, the circuit and description of a non-
motor-boating resistance amplifier, the technical editorials,
"Strays from the Laboratory," descriptions of tests on B-
power units for hum characteristics, how to operate the Ham-
marlund-Roberts "Hi-Q" set on a.c., and the story on how
to convert many standard receivers for a.c. operation. Of more
general interest, there are the reviews of new phonograph
records. "The Listeners' Point of View," the editorial section,
"The March- of Radio," the invaluable "As the Broadcaster
Sees It," the article by Sylvan Harris describing modern me-
thods of phonograph record making, and many others.
/'"AWING to causes which were beyond our control, we are
\^J unable at the last moment to present the article on a new
tube for B-supply units, promised in the announcement on our
cover. This article will appear as soon as it is finally released by
the manufacturer.
THE May RADIO BROADCAST will be full of features which
will make it one of the most important issues we have
had in many months. Lloyd T. Goldsmith of M. I. T. has writ-
ten a description of a short-wave receiver, and an intermediate-
frequency amplifier using the screen-grid tube. This receiver,
especially when used for code reception, provides efficiency
heretofore impossible before the advent of the screen-grid tube.
There will also appear in the May issue a most accurate list
of international short-wave stations. Many readers have asked
for a description of a power supply circuit for use in direct-
current districts and an article describing a practical circuit for
this purpose will appear in May.
THE problems of synchronizing broadcasting stations and,
in general, of accurate frequency control for radio sta-
tions, has assumed great importance in the past year. Edgar
H. Felix has prepared an accurate report of what has been ac-
complished to date and an analysis of the immediate possibilities
in an interesting article scheduled for the May number. For
radio constructors, Hugh S. Knowles is writing a description
of an a.c. operated "Lab" circuit receiver which has many
interesting features, besides its efficiency and flexibility of use,
to commend it. This story is also scheduled for May.
CEVERAL additional regular features are being planned
•^ for the coming numbers of RADIO BROADCAST and it is
hoped to start the first of them with the May issue. Each of
these features will appeal in a very practical way to a large
number of the radio fraternity. . . . Those interested in infor-
mation about the Cooley Rayfoto system of picture reception
who desire to be placed in touch with the manufacturers may
address their letters to the undersigned who will forward
them.
— WILLIS KINGSLEY WING.
DOUBLEDAT, OORAJi & COMPACT, IXC., Garden Qity, New Tor\
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RADIO BROADCAST ADVERTISER
401
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Radio is relied upon to maintain vital contact between district offices,
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An engineer was sent to investigate the permanency of radio apparatus
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His report, made to one of the largest operators, is typical: ". . .
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ulius Kirschner
Francis Gow Smith
THE INTREPID explorer whose recent expedition to the jungles of the Brazilian hinterland was facilitated by the use
of short-wave radio equipment carried by the party. Twice weekly time signals were sent out on one of WGY'S short-
wave channels to aid Mr. Gow Smith in his map making. The special microphone used for the purpose is still known up at
Schenectady as the Gow Smith "mike." The story beginning on the next page relates the amusing adventures of the explorer
in the smaller towns on his route leading to the heart of the dark continent. Listening-in was a pastime never before indulged
in by the inhabitants of many of these towns, and the explorer, who Otherwise might have been received coldly, was
acclaimed wherever he went, and was embarrassed by the great number of invitations to social functions which he received
402
MOUNTED BRAVADOS IN A MATTO GROSSO TOWN
The author frequently encountered mounted groups of nomadic ex-convicts whose thirst for
amusement seemed to be satisfied only by plundering. Sometimes they will lay waste a whole
settlement, murdering and robbing the inhabitants
Thanks to WGY-
By Francis Gow Smith
THIS is WCY calling Francis Gow Smith, on
the Upper Paraguay River, MattoGrosso:
The discovery made in the use of your set
without antenna or ground while you were on
the steamship Pan America this last March is
expected to have important results in the further
development of radio."
This message, broadcast for me by the General
Electric Company from Schenectady, and reach-
ing me one spring night in the tiny frontier town
of Sao Luiz de Caceres, forty-five hundred miles
south of New York, finally convinced my Brazil-
ian friends that I was not a magician or a faker
or a spy but a bona fide explorer.
And whatever value there may have been to
radio in the experimental short-wave broadcast-
ing that I received during my latest and most
adventurous trip into the wilderness of Brazil,
there is no doubt in my own mind that these
experiments helped greatly to build goodwill
for the United States in a backwoods region
where North Americans have hitherto been
looked upon with suspicion.
Incidentally, I owe my safe return from that
expedition very largely to the radio set I carried.
It was a neat, portable two-tube affair, spe-
cially built for me by RADIO BROADCAST. When I
sailed with it for Rio, aboard the Pan America, I
appreciated it rather as a possible source of
recreation during the long months I would be
isolated from civilization. I had no inkling of its
future utility in making my expedition a success.
Indeed, I was very much disappointed, the
first few nights out, when I strung the antenna
around my cabin expecting to get news reports
and actually getting nothing in the phones but
dead silence. Finally one night I turned it over
to the radio operators to experiment with.
"What's the matter with the darn thing?" I
isked.
"Give it a chance," said they. "Bring it up
on deck."
And then one of them, with the headphones
rumpling his hair and a delighted grin on his face,
remarked :
"What's the matter with the blamed thing?
Listen to this! I'm getting New York without
antenna or ground. We're close to seventeen
hundred miles out."
Every night thereafter we used the set on
deck and got code signals from Germany, Eng-
land, and Japan. The sensitivity of the set
SATURDAY NIGHT!
A community bathing "crevice" makes unneces-
sary the "hot and cold water" clause in the South
American Indians' lease
403
amazed the radio boys, and was the occasion for
that later message from Schenectady, which 1
received at Sao Luiz de Caceres.
In Brazil to-day, radio is barely emerging from
its infancy. There are two broadcasting stations
in Rio and one in Sao Paulo, while the General
Electric Company is erecting another. Enter-
tainment programs and lessons in English are on
the air constantly; but outside of the cities and
a few prosperous ranches, there is nobody in
Brazil equipped to hear the programs.
Here's a nation bigger than the continental
United States, with a population of more than
thirty million, and increasingly prosperous eco-
nomic conditions. Some day soon it is bound to
be a profitable market for American radio prod-
ucts. And when American radio programs are
being received by American radio sets through-
out Brazil, a greater influence will have come into
being for Pan American goodwill and commer-
cial development than all the spectacular good-
will flights and conferences that we can organize.
For radio will break down among the common
people that suspicion which at present is fed
by local propagandists to the detriment both of
political amity and friendly trade.
I'm positive of this, because I've seen how it
works out. When I reached Corumba, on the
upper Paraguay River, I was just another of
those Yankees, regarded with vague suspicion.
1 had a few acquaintances there, from previous
trips, but no friends to speak of and no entree in-
to the intimate social life of the town. I put up
at the hotel, and asked the proprietor's per-
mission to install my radio.
He looked at me blankly. Corumba has water
supply, electric lights, and telephones. But radio?
Huh! There was no use trying to persuade the
hotel man that the little wooden box I carried
could perform any of the radio miracles he had
indefinitely heard about. Still, he skeptically
authorized me to put up an antenna on his roof.
404
RADIO BROADCAST
APRIL, 1928
My opening act was unfortunate. One
of the poles slipped while I was erecting it,
fell through the red tile roof of the house
next door and just missed hitting on the
head one of the society leaders of the
town. She came storming outdoors and
gave me frankly a piece of her mind. Soon
it was all over town that this crazy Yankee
was destroying property with something
he called a radio.
But that night 1 invited the hotel pro-
prietor to bring a few friends into my
room. They stood around rather abashed.
What was the sense of all this fuss over
a box with some wires and two oddly
shaped electric light bulbs in it?
And then, singing sweetly in the phones,
came from Schenectady a musical pro-
gram given experimentally on short waves
for a man in Johannesburg!
My guests were thrilled as they had
never been in their lives. They were al-
most incoherent in their enthusiasm. The
news spread like wildfire through the
town. The leading citizens flocked into
my room, uninvited; the crowd jammed
the corridor outside. Men waited hours for
their few minutes' turn with the phones;
many went away disappointed and came
back night after night until they had heard
for themselves this miracle. The lady next
door was placated — she wouldn't even let
me pay for the damage to her roof. While
the hotel proprietor was in the Seventh
Heaven of bliss. His bar had never done
such a flourishing business.
SOME FRIENDLY INDIANS OF MATTO GROSSO
While these were only too willing to pose for their photographs,
there are others who could not be approached with safety
NDEPENDENT WlRELESS TELEGRAPH Co.« INC.
67 W,
fe,
„
Station..-..1/'.-....-^-.-./- X_._.
PART OF A LOG KEPT BY MR. GOW SMITH IN BRAZIL
The expedition came to an untimely end owing to the fact that the party was robbed of all its
belongings by a gang of bandits. This fragment was saved because Mr. Gow Smith covered it with
his foot while he was being searched
For eighteen days, while waiting for the
little stern wheeler that would take me
up to Sao Luiz de Caceres, I had the set
working. There was considerable fading at
times, but it worked, better after nine
at night. Soon 1 had become the personal
friend of the most important business men
and politicians in Corumba. They heard
dance music from the Waldorf and music
from Aeolian Hall; they heard Chauncey
Depew speak; they listened to plays and
to operas from the Eastman Theatre in
Rochester; they got the news of Amund-
sen's flight over the North Pole, and of
one of the attacks on Mussolini.
I translated the news every night for
the local newspaper. Corumba had never
before been so intimately in touch with
the outside world. The community be-
came pro-American. Nobody could do
enough for me; they wanted me to settle
down and stay with them; they all said
they were going to learn English; and I
could have sold the set a hundred times
over at any price I asked.
When 1 left, the leading citizen of the
town pressed on me a letter of introduc-
tion to an influential friend of his in
Cuyaba, the frontier capital of the state
of Matto Grosso. I wasn't going any-
where near Cuyaba, but he wanted me
to make a special trip there anyhow.
His letter read:
"This is to introduce to you my good
friend Mr. Francis Gow Smith, who is
coming to you with a most marvek —
machine called the radio telephonia, which
has proved in experiments here to be a very
amazing thing indeed and I want you to have
the privilege of listening to this truly magical
instrument."
\A/ARNED by my experience in Corumba, I
• ' rented a big twelve-room house when I
reached Sao Luiz de Caceres. I knew that no
hotel room would hold the crowds that would
come. And besides, Sao Luiz boasts no hotel
worthy of the name. It's the jumping-off place
on the Brazilian frontier — a town of five thou-
sand population, at the edge of the jungle. To
the northward beyond it are scattered ranches,
a few hamlets of rubber and ipecac gatherers, and
then unexplored wilderness, several hundred
thousand square miles in extent, peopled sparsely
with naked savages.
In Sao Luiz I was received with greater suspi-
cion than in Corumba. Many of the common
people thought I was some sort of gringo spy.
Why did I have a camera, if it wasn't to take
photographs of sites for future forts, when the
dreaded "Colossus of the North" should begin
the process of gobbling up Brazil? The people
misunderstand the United States completely.
They have been filled up with such fantastic
bugaboo stories about us that they extend
toward us a hazy mixture of dread and dislike
such as a child feels toward imaginary giants
and dragons.
The inhabitants are practically cut off from
the world. They have a weekly four-page news-
paper, but it publishes only items concerning
local society events — marriages and birthday
festivals, and perhaps a sprinkling of political
news. Besides, most of the people can't read.
The streets are unpaved; there is no electric
light, telephone, or water supply. Water from
the river is peddled in barrels about the streets.
On the edge of the barren plaza, fronting the
river, there stands an unfinished stone church,
APRIL, 1928
THANKS TO WGY— !
405
and the piles of building stones beside it are
alive with snakes, lizards, and rats.
Naturally, in this isolated community, I was
looked upon with disfavor by 'the uneducated.
My radio set in its mysterious box with the iron
handles was set down in their minds with my
camera as evidence that I had some mysteriously
unfriendly intentions. They couldn't believe I
was using the town merely as a jumping-off place
for exploration. Why should anybody in his
senses penetrate the jungles beyond and get
himself shot at with poisoned arrows? No; ob-
viously I had come for no good purpose, doubt-
less as a secret agent of the United States, either
to survey gun emplacements or to detect hidden
mineral wealth.
What a change in their attitude my radio
worked !
There wasn't a stick of furniture in the
house I had rented, except an old table. I set up
the radio on that table, and slung my hammock
in one of the bare rooms. I hired a boy to help
me, went into the jungle and cut down two fifty-
foot bamboos, which we erected as antenna masts
in the quintal, or back garden, of my house.
The villagers watched these proceedings with
growing suspicion. Many of them had never even
heard of radio. Then 1 invited the mayor and a
few prominent citizens to come and hear the set
work. To give a touch of festivity to the occasion,
I had hung Eveready electric flashlights around
the walls, and softened them with bits of colored
paper. The evening was a phenomenal success.
Three sets of phones were working all the time.
Sometimes a listener, after hearing ecstatically a
few bars of music, would drop the phones and
scurry out of the house, to round up his wife and
children and friends.
Soon 1 was mobbed, as I had been in Corumba.
Every citizen prosperous enough to wear shoes
felt himself privileged to come i.i; the barefoot
families humbly congregated about the doors and
windows and stared in, imagining some queer
sort of magic was going on.
So, within a few nights 1 was welcomed into
the center of the town's social life, invited to all
the most elite weddings, birthdays, and funerals,
and offered banquets in every home. The bare
rooms of my rented house began to fill up with
furniture — chairs, tables, wine glasses, and even
that rare and valued treasure, a bed! All contrib-
uted by the citizens to their distinguished guest
— who had done nothing to distinguish himself
but bring a radio set into their midst.
But suspicion still smouldered among the poor
and illiterate, and I was advised to allay it by
having a barefoot soiree, when the unshod por-
tion of the populace could hear the radio work
for themselves. Many of them heard it, but were
still unconvinced. They'd go out into the back
yard and stare up at the aerial; they poked about
in the rose bushes, and surreptitiously investi-
gated the empty rooms of the house. Somewhere,
they were sure, I had a confederate hidden, tc
play on a musical instrument.
Then came the three special programs, broad-
cast by the General Electric Company for my
benefit from Schenectady. The dentist in Sao
Luiz understood English, and when the rest of
the guests heard him translate the messages
addressed to me, the last bit of skepticism van-
ished. But my reputation was enormously en-
hanced. Everybody called me affectionately
"Mister," or "Mister Yank," and it was said
that I was a great and influential millionaire.
Certainly nobody but a millionaire could have
a wonderful radio set and receive special news
and musical programs sent through the air,
forty-five hundred miles over sea and jungle,
just so that his evenings on the frontier might
not be lonely1
AT CORUMBA
Listening-in with the short-wave receiver
built for the expedition by RADIO BROADCAST
The girls of the town could never quite get
over the notion, however, that I was some sort
of magician as well. Some of them asked me to
tell their fortunes with cards, and when I did so,
invariably predicting a forthcoming marriage,
the town's regular and previously prosperous
fortune teller was deserted. She couldn't compete
with the authentic forecasts that I had to offer —
for didn't I get them straight out of the air,
wearing my headset and listening wisely while
I read the cards?
The guests came to these radio soirees clad in
the strangest mixture of costumes. Some of the
men wore evening dress; others came in home-
spun. There were cowboys wearing sombreros,
gaudy neckerchiefs, and sidearms; there were
ranchers in khaki shirts and big boots. But many
of the women, with their bobbed hair, low cut
evening gowns and sparkling diamonds, might
have just stepped out of a Broadway night
club.
I understand that this experimental short-
wave broadcasting was of some interest to the
General Electric Company. However that may
be, it certainly put a backwoods community of
Brazil into a turmoil of excitement. The old
suspicions of the United States vanished, and the
town became a focal point of boosting for Uncle
Sam. Every inhabitant wanted a radio, and they
all insisted that nowhere else in the world could
it be so great a blessing as it will soon be in these
backwoods regions where there are only the most
meager entertainments and no contact at all
with outside events.
When finally my batteries gave out, it was con-
sidered a disaster. 1 left the set in Sao Luiz, and
carried out my expedition into the wilderness,
the entire services of the town being put at my
disposal while I was making ready. Months
later, having been waylaid by bandits, robbed of
all my equipment and left fever-stricken and
starving in the jungle, 1 was rescued by a boat
coming up the Sipotuba River from Sao Luiz.
They brought me down to the village too weak
to walk, put me up in a private home, nursed me
back to health, and lavished attentions upon me.
All this in the town that 1 had entered first
amid such an atmosphere of suspicion. And when
I was strong enough to leave 1 was escorted down
to the little river steamer by practically the en-
tire populace. Knowing that 1 had been robbed
and left penniless, they thrust handfuls of cur-
rency at me; and 1 even discovered that some
of them had secretly stuffed money into my
pockets.
Believe me, a radio receiving set will be an
essential part of my equipment on my next
exploration trip. I don't mind the isolation in
the jungles myself, and I dislike to increase the
weight of my equipment; but a radio works
wonders in building goodwill for the stranger
along the frontier. I might not have survived the
illness of my last trip but for the friendly atten-
tions which RADIO BROADCAST'S portable set
had won for me. And I think that, when it comes
to the touchy job of dealing with hostile Indians
in the wilderness, a radio would be even more
valuable in winning friendship and esteem.
THE CROSS MARKS THE HOTEL "GALILEO," CORUMBA
It was here that Mr. Cow Smith unfortunately permitted one of his
antenna masts to crash through the roof of a local society leader's house
Picture Broadcasting Becomes a Practical Reality
HARDLY a day passes without
some news of progress in radio pic-
ture transmission. On November
6, WOR broadcast its first complete radio
picture, using the Cooley system. On
January 13, Dr. E. F. W. Alexanderson
publicly demonstrated his television device
in Schenectady. On January 26, WEAF
broadcast its first picture, utilizing equip-
ment also developed by Doctor Alexander-
son. On January 31, WOR began the regular
broadcasting of Cooley radio pictures three
times a week. Each event is significant and
brings nearer the day when the radio recep-
tion of pictures becomes an integral part
of the broadcasting art.
The transmissions from WOR have been
continued since the initial experiment in
November, at first occasionally
and then on a regular basis. A
group of twenty or thirty enthu-
siasts have installed Cooley Ray-
foto receivers and the number
increases as rapidly as the equip-
ment is manufactured. These
experimenters are typical set
builders rather than specially
trained professional engineers.
Phonograph recordings of actual
pictures have also been made
successfully which make possi-
ble experiments with Cooley
apparatus at any time, regard-
less of the availability of broad-
casting. The sponsors of the
Cooley system advise that,
within two or three months,
their equipment will be available
in quantity and a rapid growth
of the picture reception audience
may be expected.
We witnessed a confidential
demonstration of Doctor Alex-
anderson's apparatus at Schenec-
tady some months ago. Several
radio channels are required to
transmit television images and
consequently the system is now
restricted to short-wave trans-
mission. The conventional broad-
cast receiver cannot be utilized,
therefore, in the reception of tele-
vision by this system. The Alex-
anderson television outfit, which
uses Daniel Moore's improved neon tube,
is infinitely simpler than the elephantine
apparatus demonstrated by the Bell
Laboratories a year ago. The picture, with
the Alexanderson system, is scanned eight-
een times a second. The received picture
is in the form of a pinkish glow, covering
an area of three by three inches. It is not
rich in detail. Presumably three to five
years of development are necessary before
this apparatus is capable of reproducing
sufficiently good moving pictures at a
reasonable cost to the average user.
The picture receiver, demonstrated at
WEAF, employs the neon tube and requires
about ninety seconds for the reception of a
picture. It utilizes high-grade synchronous
motors to keep transmitting and receiving
drums in step. The transmitted signal was
a high-pitched audio note, similar to that
used in sending Cooley pictures. No state-
ment has been made as to when the equip-
ment necessary to build these picture re-
ceivers will be on the market. Since the
synchronizing equipment is somewhat more
expensive than the "stop-start" system
used with the Cooley apparatus, its cost
may be fairly high. It is capable of excel-
lent detail and possesses considerable
reliability.
The adoption of a regular picture broad-
casting schedule by WOR, the fourth
significant event, is an indication that that
station has already established a picture
receiving audience and is preparing to
extend it. That this audience will grow
rapidly as soon as the apparatus
is available in quantity is fore-
shadowed by the fact that the
Cooley equipment is no more
expensive than the parts for a
good broadcast receiver.
At the same time that these
various news events occurred in
the field of radio vision, a repre-
sentative of the Baird system,
en route to the United States, an-
nounced that television between
London and New York had been
definitely established. One dem-
onstration for the press was held
some weeks ago and the first
transatlantic television trans-
mission is claimed by Baird's
representative in New York.
Possibilities of Still Picture
Broadcasting
T!
ANOTHER RADIO PICTURE RECEIVER
Readers of this magazine are familiar with the Cooley Rayfoto picture
system demonstrated at the New York radio show last September and
which was first heard over WOR on November 6, 1927. On January 26,
1928, Dr. E. F. W. Alexanderson of the General Electric Company dem-
onstrated one of his systems of radio picture transmission and reception
through WEAF. The illustration shows Doctor Alexanderson and the
receiver. The rectifier and amplifier unit is in the box near the wall and
the mechanical element with paper on the receiving drum is in the fore-
ground. Pictures are received in 90 seconds and are excellent in quality
406
TELEVISION, or radio
vision, naturally has a
much greater appeal to the
public imagination than the
transmission of still pictures.
Because of the tremendous num-
ber of images which must be
broadcast at an extremely high
rate of speed, the perfection of
radio vision is a problem a thou-
sandfold more complex than radio
photography. It is unlikely that
television will ever be possible in
APRIL, 1928
THE NUMBER OF SHORT WAVES IS LIMITED
407
the present broadcasting band, since it
requires a number of channels used simul-
taneously to transmit all the necessary
images. In its present development, the
subject of television transmission must
stand within a few inches of the scanning
device and, as a consequence, only the
bust of a single individual can be broadcast.
Any rapid motion is blurred. Under the
circumstances, present-day television has
few, if any, advantages over the transmis-
sion and reception of still photographs.
AH of the defects in television will, of
course, be remedied gradually and the
present state of the art is sufficiently ad-
vanced to make clear and entertaining
radio moving pictures a prospect of the
next few years. In the meanwhile, does
radio picture reception offer sufficient
fascination to promise rapid extension in
the homes of broadcast listeners?
The existing systems of radio picture
transmission and reception have many
practical advantages. The pictures may be
radiated from an ordinary broadcasting
station and received with the aid of any
good broadcast receiver. High-grade re-
production of pictures in the home is quite
possible with apparatus now available.
Broadcasting of pictures by remote control,
with the aid of wire lines, is feasible with
all existing systems. A news photographer
can take a picture at a broadcasting studio,
or at a remote point connected with the
studio by wire, and put it on the air within
two or three minutes. Radio picture broad-
casting serves the same useful purpose that
illustrations do in a book, magazine, or
newspaper and enhances a radio program
to an equal degree. The broadcasting
of sporting and news pictures, photo-
graphs of prominent artists, and technical
diagrams and data accompanying educa-
tional lectures is entirely possible and ade-
quately useful or entertaining. Whatever
the camera records, so long as the subject
is not entirely too fine in detail or lacking
in contrast, is suitable material for radio
picture transmission.
It is not unreasonable to expect, in radio
picture broadcasting, a new field destined
to rapid growth. Those who have the fore-
sight to participate in early experiments
will reap their reward in the manufacture,
marketing, and servicing of picture sets.
Foreseeing these possibilities, RADIO
BROADCAST has been diligent in presenting
all available information. So far, con-
structional information has been limited
to the Cooley system but, as rapidly as
information regarding other systems is
available, we will present it in these pages,
so that our readers may keep abreast of
progress in the art.
The Shrinking Sbort-Wave Spectrum
FORESEEING the international
complications which would result
from the indiscriminate assignment
of the higher frequencies to the numerous
applicants therefor, we have persistently
urged conservation of these frequencies.
Not until the hearings in Washington,
however, did we realize that the Federal
Radio Commission's problem in the short-
wave spectrum is already more complex
than that existing in the broadcasting field.
Competent engineering authorities, with a
long background of experience in short-
wave transmission, pointed out that a short-
wave radio telegraph station requires a
channel having a width of 0.2 of one per
cent, of the assigned frequency. Thus, im-
mediately below the broadcasting band, a
radio telegraph channel must be 3 kc.
wide, while, at 30,000 kc., or ten meters,
frequency variation is so great that the
channel must be 60 kc. wide.
Assuming this separation, or channel
width, to be necessary, there are only 1316
channels between 1500 and 30,000 kc. A
part of these has been assigned to mobile,
amateur, and broadcasting purposes, leav-
ing only 666 channels available to the
entire world for point to point short-wave
communication. Inasmuch as, even with
the most insignificant powers, a radio
telegraph transmitter, assigned to these
wavelengths, is likely to cause interference
in all parts of the world, duplication of
station assignments, for operating con-
tinuously is quite impossible.
Furthermore, to maintain continuous
service over long distances, the varying
transmission qualities of these frequencies
at different hours of the day and night
make it necessary to use two, three, and
four channels. Consequently, instead of a
host of channels, sufficient to meet the
needs of all communication interests, the
Army and the Navy, and the considerable
number of private concerns which desire
channels, there is only a very limited
number of channels to be divided among
the numerous applicants. Assuming that
the United States is entitled to twenty per
cent, of the channels available to all the
nations of the world, there are only ap-
proximately 126 channels to be considered
after discounting those assigned for broad-
casting, amateur, and experimental pur-
poses.
The Radio Corporation of America has
already established a number of short-
wave, transoceanic services. It desires to
extend these services greatly and, were all
its prospective requirements considered
exclusively, there would be no room on the
air for any but Radio Corporation stations
and the stations of the Army and the Navy.
The Mackay interests propose to enter the
radio telegraph field and have made de-
mands for channels in numbers sufficient
to absorb any reasonable allotment to the
needs of the United States.
How the demands of brokerage houses,
department stores, newspapers, oil compa-
nies, railroads, bus transportation services,
and the thousand-and-one other inter-
ests can be met with this meager allot-
ment of frequencies is not apparent until
considerable technical progress is made in
maintaining frequency stability. As soon
as we learn how to hold stations within a
few hundred cycles of their assigned fre-
quencies, the capacity of the short-wave
bands will be increased a hundredfold.
The Commission has announced that it
will require two months of study before it
can make any decisions. It is hoped that it
THE PRESENT AND PROPOSED MACKAY RADIO SYSTEM
Recently the Mackay Company entered the radio field and took over the Pacific Coast stations
of the Federal Telegraph Company. These stations are at Hillsboro, Oregon, and Palo Alto and
Clearwater, California. The points shown on the outline map are the basis of a short-wave system to
furnish communication which will supplement the present Postal Telegraph wire system. The pro-
posed channels will connect points most subject to storms and other interruptions to wire service.
In addition to this land radio system, the old Sayville station on Long Island has been purchased
and will shortly be opened for marine communication with ships on the Atlantic. The Mackay sys-
tem now holds 42 wavelengths in the short-wave spectrum, of which 34 are for a chain of stations for
transpacific communication
408
RADIO BROADCAST
APRIL, 1928
will establish a definite policy and stick to
it. In the broadcasting spectrum, expedi-
ency, rather than an established set of
principles, has ruled. In view of the com-
plexity of the short-wave problem, it is
most urgent that definite principles be
enunciated, lest the Commission be later
charged with favoritism or discrimination.
The first obvious principle is that there
is no short-wave channel available for any
service which can be conducted by wire.
The Mackay interests, as one of their plans
desire to establish an emergency network
so that, should wires break down, they
may use short-wave radio transmission.
There is every reason why a duplicate
emergency radio service should be available
in national emergencies but, should such a
system be established, permission to
utilize the radio network should be re-
stricted to grave emergencies.
The requirement that wire services be
used where available is complicated by
certain economic factors. A chain of depart-
ment stores, for example, can erect short-
wave transmitters and maintain communi-
cation at a much lower cost than entailed in
using public service wire telegraph chan-
nels. The application of this principle re-
quires, therefore, discrimination against
private interests in favor of the wire com-
panies. In view of the needs of transoceanic
services and the value of an independent
American communication service, this
discrimination against private interests
appears entirely necessary. Furthermore,
it is utterly impossible to serve all private
interests with the limited facilities avail-
able. Only a selected few could be ac-
commodated, were short-wave radio tele-
graph channels assigned to private in-
terests.
This suggests a second principle which
may be established as a policy of the Com-
mission. No short-wave channels shall be
assigned for any service unless such service
be opened to the general public upon an
equitable basis of charges without dis-
crimination.
It is unfortunate that the wire interests,
which are so well entrenched and estab-
lished in the United States, should seek to
enter the radio field and compete with
existing radio communication companies
and that radio communication interests,
on the other hand, should seek to compete
with the wire interests. For example, ap-
plication was made for the right to conduct
a New York to Montreal service by a radio
communications company. These cities
are already well linked by wire telegraphy
and telephony. Possibly there might be
some simplification of the situation if the
radio companies decide not to establish
radio communication networks where wire
services exist and the wire companies, in
turn, stay out of the radio field and stick
to their well established and profitable wire
business.
The stilling of competition is clearly un-
American in principle and carrying out this
suggestion would obviously tend to stifle
competition. But what alternative exists?
We do not grant street railway franchises
for routes along the same avenue to two or
three rival companies in order to establish
competition. If radio channels are limited,
they must be regarded as a franchise and
be distributed in such a manner as to assure
the greatest possible public service.
A further embarrassment in the situation
exists in the fact that long-distance radio
communication is dominated by a single
interest. Whatever the means used to gain
this acknowledged ascendancy, the fact
remains that it exists. In almost every
important line of industry there is a dom-
inant company which has established its
acknowledged leadership in the field. This
company is always the object of vilifica-
tion by politicians but, because of sheer
strength and competence, merrily goes on
occupying its position. Under the circum-
stances, the Federal Radio Commission is
bound to be criticized as the tool of monop-
oly and its activities will always offer sub-
ject matter for spellbinding politicians be-
cause the dominating company, if fairly
treated, will have a preponderance of as-
signed channels. For this situation, there
is no practical and fair remedy other than
the uneconomic proposal of government
ownership.
The demands of the press for short-wave
channels, although clothed in high-sound-
ing phrases regarding public service and
freedom of the press, are really an effort to
reduce its wire costs. Signals travel through
the ether no faster than they do over wire
circuits. The demands of the press for
special radio channels are in the same
category as all other requests of private in-
terests, excepting in those few instances
that wire services are not available. The
press already receives preferred considera-
tion from the wire services which carry
most of its communications at or below
cost.
The Commission Retreats
THE Federal Radio Commission has issued
new application blanks, requiring the sub-
mission of considerable information on
the part of broadcasting stations concerning
their technical equipment, their program hours,
the proportion of time devoted to commercial
broadcasting and facts regarding chain affilia-
tions. The Commission should have gathered
this information immediately on its accession,
to authority last March.
Congressman Wallace H. White has expressed
again and in greater detail his disappointment
in the functioning of the Federal Radio Com-
mission. He has urged, as we have in these
columns for many months, that the future
appointees be possessed of sufficient technical
qualifications so that they may perform their
duties efficiently.
The members of the Commission have been
testifying before the House Merchant Marine
Committee and they have hardly had a pleasant
time of it. Judge Sykes admitted that a much
larger proportion of channels had been assigned
to New York and Chicago than those cities
deserved, an abuse which we have frequently
stressed in these columns for more than a year.
The favorable position of chain stations which,
the testimony brought out, occupy twenty-one
out of the twenty-five cleared channels, does
not please members of the Congressional com-
mittee.
The saddest news which we have heard from
the Commission so far is the announcement by
Acting Chairman Sykes that the 300 stations
which were to be scheduled for elimination on
March I will have their licenses extended. This
move, he says, is made because three of the four
members of the Commission are not confirmed
by the Senate. Naturally, each of these three
hundred stations is the pet of some congressman
or senator and the unconfirmed members of the
Commission could not hope for a confirmation if
they took the necessary and drastic action of
eliminating such stations. Politics now rule radio,
confirming our predictions made when a com-
mission control of radio was first proposed before
the Radio Act of 1927 was passed.
Representative White has presented a bill ex-
tending the powers of the Commission for an-
other year and including, in addition, some
provisions aimed at the Radio Corporation of
America and the National Broadcasting Com-
pany. An amendment to Section 10 of the Radio
Act, which he proposes, is to permit the Com-
mission to refuse a license to a station intended
for international commercial communication, if
the company operating that station has entered,
or intends to enter, into exclusive rights with a
foreign country. We understand that the Radio
Corporation has made several such agreements.
The Commission, however, may grant such a
license if the company will maintain just and
reasonable rates and will secure and maintain
equality of right and opportunity for other
American citizens to engage in competitive
services.
Other proposed changes in the Act are the
strengthening of the powers of the Commission
to revoke licenses for false statements in applica-
tions, or for failure to observe any of the terms,
restrictions, and conditions of the Act or regula-
tions issued by the licensing authority. To the
powers of the Commission, Representative
White proposes to add that it may fix the hours
during which chain broadcasting may be carried
on, designate the stations and limit the numbers
participating therein, and that it may prohibit
commercial broadcasting through chain stations
and, in fact, may make any rules and regulations
in the public interest, applying to chain broad-
casting.
The crowning touch of Representative White's
bill is a proposed provision to be included in the
Radio Act that it shall be unlawful for any firm
to import or ship in interstate commerce any
vacuum tube, whether patented or unpatented,
which shall have any restrictions of the use to
which such tube may be put or which shall have
the effect of fixing the price at which the tube
may be sold. It is doubtful whether this unusual
curtailment of patent rights of a single group is
constitutional. This proposal is really an amend-
ment to the patent law and is not properly a
part of the act regulating radio communication.
If the fundamental theory of our patent law
must be changed, why does not Congress under-
take its thorough study and pass a new patent
law instead of singling out vacuum-tube manu-
facture as a special case? High-grade vacuum
tubes, suited to all purposes, are available to
the public and sold without exorbitant profit. If
the R. C. A. is indulging in unfair practices, there
are adequate measures which can be taken with-
out depriving it of the benefits of normal patent
protection. If the patent monopoly, established
by patent law, confers too great powers on the
patent holder, then the patent law should be
modified. A possibility worth considering is the
compulsory issuance of licenses upon an equita-
APRIL, 1928
A WIDE FIELD FOR GOOD RADIO SETS
409
ble basis to all who apply, thereby assuring
patent holders of adequate reward, but prevent-
ing the use of patents to establish monopolies or
embarrass competition. The principle of singling
out a particular patent situation for special
legislation is contrary to the principle of equal
rights to all.
The Blue Laws of Radio
C AIRFIELD, IOWA, has passed an ordi-
» nance prohibiting the use of electrical
equipment which causes interference with radio
reception between noon and midnight. Inter-
preted literally, not only do vacuum cleaners,
washing machines, electric toasters and flatirons
fall within the ban, but also electrical incinera-
tors, elevators, refrigerators, cash registers, fire
alarm signals, and railroad block signals. Viola-
tions are punishable by a fine of one hundred
dollars or thirty days imprisonment or both.
There is nothing reasonable about this ordi-
nance. It is doubtful whether this practical con-
fiscation of property is legal. Electrical inter-
ference problems should be solved by aiming at
the cause rather than the effect. A modern cash
register, for example, should be designed so that
it cannot cause electrical interference, although
even the best of them do so. Any electrical device
can be equipped with suitable interference pre-
ventors which will eliminate the possibility of
interference with radio reception.
In Providence, Rhode Island, they have in-
voked an old blue law to embarrass a radio dealer.
The ordinance prohibits any person to ring a
bell or to use any other instrument or means
for the purpose of giving notice of any public
sale or auction of any article. This has been
interpreted by the police to embrace the use of
radio loud speakers in stores, although it is
doubtful whether the writers of the blue laws
had radio in mind. To be really fair in the mat-
ter, the police ought to be prohibited from using
whistles.
Here and There
A N APPEAL has been filed by the Westing-
*» house Electric and Manufacturing Com-
pany for a review of the decision of the Circuit
Court of Appeals which upheld DeForest against
Armstrong in the invention of the feedback
circuit, f I f THE HAZELTINE Corporation
has filed against the Charles Freshman Company
and the Stewart-Warner Speedometer Corpora-
tion in the Southern District, citing U. S.
Patent No. 1,648,808. Iff THE ORIGINAL
decision of the examiner, rejecting claims i to 6
inclusive, 8, 9, n, 12, 15, 19, 21, and 22 as un-
patentable over prior art, was affirmed in the
case of re-issue patent 16834, issued to Lloyd N.
Knoll on December 27, 1927. The references cited
were Bellini, Kolster, and a scientific paper issued
by the Bureau of Standards. I I f A SUC-
CESSFUL appeal from the decision of the primary
examiner, denying the patentability of several
claims of patent 1,654,285, issued to Charles
Fortescu, describing a modulation system for
quickly absorbing residual energy stored in the
antenna system after signal impress has been
completed, has been announced by the Board of
Appeals. £ t f CORNELIUS D. EHRET, coun-
sel for the applicant, Frederick A. Kolster, in
Patent 1,637,615, called our attention to the fact
that our item in the December issue, citing the
substance of the opinion of Second Assistant
Commissioner of Patents M. J. Moore, implies
that the claims referred to were rejected after
the patent was issued. While we fail to see how
this conclusion was reached from our item, we
are pleased to state, in deference to Mr. Ehret's
wishes, that no claims were declared invalid
after the patent was issued.
THE FIELD FOR GOOD RADIO SETS
ARTHUR SMITH, radio dealer of Tampa,
Florida, sends us a most lucid letter ex-
plaining the position of the radio dealer in loca-
tions where high-grade local broadcasting is not
available. He complains that radio manufactur-
ers concentrate their advertising almost ex-
clusively upon the cheaper models and fail to
point out the advantages to the user of the high-
grade, super-power, radio receivers, really neces-
sary in such areas. As a consequence, the dealer
is compelled to demonstrate the cheaper type
of receivers which do not give satisfactory re-
sults when remote from good broadcasting. He
states as his opinion that less than one per cent.
of the listeners in his area are utilizing receiving
sets with 210 power output tubes and that most
of them are still using the cheapest type of set
which has been so forcibly heralded in the ad-
vertising columns. He urges that set manufac-
turers devote more advertising space to high-
quality radio sets because the public, once ap-
preciating their capabilities, is quite willing to
spend the necessary money for better models.
E. T. CUNNINGHAM announces the in-
troduction of the cx-371-A tube which has the
characteristic of the 371 and 171 type except
that it has an oxide-coated filament. This re-
duces the filament current required to a quarter
of an ampere, effecting an economy of filament
current. The oxide coated filament also gives uni-
form emission throughout its life instead of
gradually falling emission which is characteristic
of the thoriated filament.
JUDGE HUGH BOYCE in the Federal Court
at Wilmington, Delaware, dismissed the suit
of the General Electric Company, charging the
DeForest Radio Company with infringement of
Langmuir's high-vacuum tube patent. If this
decision is sustained in higher courts, to which it
will undoubtedly be appealed, one of the most
important reliances of the R. C. A. in its hold
on the tube situation is destroyed.
THE Federal Trade Commission proposes
to broaden the scope of its investigation of the
radio combination, amending its formal com-
plaint against the radio group by adding the
following charge:
The defendants have: "8. Substantially les-
sened competition and tended to create a monop-
oly in the sale in commerce of unpatented parts
of chassis, and of unpatented consoles and cabi-
nets, and of other unpatented parts of radio
devices," etc. etc.
THE Mackay interests have acquired the
famous transatlantic station at Sayville, Long
Island, which they will use in ship-to-shore
service. Another station for the same purpose
is planned somewhere near Norfolk. The system
is already operating stations in San Francisco,
Los Angeles, and Portland on the Pacific Coast
and expects by next summer to have trans-
pacific service to Honolulu and the far east.
THE National Better Business Bureau col-
lected advertising literature at the Radio Show
in New York last September and analyzed the
inaccuracies and violations of their standard
code of radio ethics and advertising practice.
They found 232 inaccuracies, of which 39 per
cent, were violations of their Rule 4 which calls
for the accurate naming of cabinet woods.
Twenty-six per cent, violated Rule 2-B, which
provides that price quotations state clearly
whether the offer includes accessories or not.
Sixteen per cent, disregarded Rule 8 which holds
that superlative claims lack selling force. The
fact that only 58 complaints were investigated
during the year 1927, as against 123 in 1925,
is taken as an indication of the cooperation
which has been extended by the radio industry
in the work of the Bureau.
THE International Radio Telegraph Confer-
ence has adopted a new schedule of "Q" signals
and, in addition, has recognized a number of
one-, two- and three-letter combinations, some
of which have been widely used but did not here-
tofore have the stamp of official approval.
Prominent among these is the adoption of CQ as
the general calling signal, replacing the three-
letter combination QST. Some changes were made
in the assignments of alphabetical groupings to
the various nations from which each assigns call
letters to the radio stations under its jurisdiction.
The United States, hereafter, will have the en-
tire letter K combinations at its disposal, instead
of only a part, as well as the entire range of N
and W calls.
AN EARLY FESSENDEN RADIO RECEIVER
It was "wireless" in those days, however. The antenna and ground circuits enter on the left, through
the variable air condensers; the four drums, wound with wire, and each with its handle, illustrate
the ingenious method of continuously varying the inductance of the closed circuit; the crystal detector
and headset are on the extreme right
THE TRANSMITTER IN ITS FINAL FORM
By the mere throwing of a switch, it may be used for either c.w. or phone
signals. It has covered a thousand miles with phone signals during its
tests, although this figure is somewhat high to expect for regular work
A Short^ Wave Phone and C* W* Transmitter
By Kendall Clough
WITH appetites whetted by the remark-
able expanse of their eavesdropping,
consummated with the simplest of equip-
ment, the broadcast listener who became inter-
ested in short-wave reception, satisfied his curios-
ity, and listened half way round the globe, is now
ready for new fields to conquer. The logical outlet
for his enthusiasm lies in the construction of a
transmitter, for it is provoking to hear a fellow
a thousand miles away pounding out a crystal-
clear message, terminating such with a remark to
the effect that "I'm using a single 2OI-A, OM,"
and not to be able to answer him back, and report
a better "watts-per-mile" record.
To supply the demand created by this growing
enthusiasm, several well-known parts manufac-
turers have cooperated in the design of a short-
wave radio telephone transmitter which can be
built for about the same cost and with the same
ease as a good receiver constructed for the recep-
tion of broadcasting. While this design is of a
low-power type transmitter, it has been repeat-
edly demonstrated that the power is sufficient to
carry on conversations over surprising distances.
It will be noted from the photographs that the
manner of construction permits the isolation of
all the parts carrying radio-frequency currents on
the upper "deck," or shelf, while all the circuits
associated with the power or voice currents are
on the lower "deck." This form of construction
insures that the masses of metal contained in
power devices, such as transformers, condensers,
etc., will not be in the fields of any of the radio-
frequency coils, since this would introduce losses
therein. Corresponding to the arrangement of the
circuits in decks, the front controls are also
grouped. Thus, on the upper panel we have the
controls for the tuning condensers, the antenna-
current meter, and the plate-current meter for
the oscillator tube. On the lower panel we have
the plate-current meter for the modulator tubes,
the modulator C bias control, the switch for
changing from telegraphy to telephony, and the
necessary binding posts for the key, microphone,
and battery. The circuit diagram of the trans-
mitter is shown in Fig. i. That portion of the
circuit shown on the upper "deck" is the justly
famous tuned-grid, tuned-plate circuit, which
has been in use for several years. This circuit
employs a series feed for the plate voltage to the
oscillator rather than the shunt feed ordinarily
used. In this way an already efficient oscillator
circuit has been improved by eliminating those
losses in the choke coil that are bound to occur
when using shunt feed. Naturally enough any
losses eliminated in the choke coil result in ad-
ditional energy being available for actual trans-
mitting purposes.
Considerable voltage is developed between the
plate coil and the ground by this method, so that
it is necessary to use two condensers in series
(C3 in Fig. i) as an r.f. bypass. An r.f. choke, L4,
serves to keep the radio-frequency currents from
finding their way down to the lower "deck."
The power supply consists of a Silver-Marshall
328 transformer, TI, which supplies the plate
current as well as lights the filaments of the oscil-
lator and modulator tubes. In order to secure
direct current, which is necessary for phone oper-
ation, the high voltage of TI is rectified by means
of a gas tube, and filtered with a Silver-Marshall
331 Unichoke, Li, and Tobe condensers, Q, and
CT. It will be noted that two modulator tubes,
Vj and Va, are used in conjunction with one
oscillator, Vi, of the same type. This is in accord-
ance with the best practice and while the set is
perfectly operable with only one modulator,
it is recommended that two be used where the
410
best quality of transmission is desired. The mod-
ulator tubes and the oscillator tube are all of the
cx-310 (ux-2io) type.
In order to operate the modulator tubes at
maximum capacity, it is necessary to amplify
the output of the microphone transformer to
bring the speech to the proper volume level.
This amplification is accomplished by means of
a cx-312 (ux-i 12) tube, V«, and a Silver-
Marshall 240 transformer, T2. The proper C and
B voltages for the ex -3 12 are secured from the
power supply by means of the resistors Rj, Rs,
and Re, the latter supplying the C voltage for
this tube. During the preliminary experimental
work a cx-326 (ux-226) was used in place of the
cx-3i2 and was lighted from the power trans-
former. In view of the fact that a 6-vo\t battery
was necessary for the operation of the micro-
phone, however, the same battery was finally
used to light a ex -3 12 instead of the a. c. tube,
since a quieter signal from the transmitter
resulted.
DETAILS OF ASSEMBLY
p HE construction of the transmitter may well
' commence with the lower "deck" as this
unit must be assembled and wired before the
work is started on the upper structure, otherwise
the latter will hinder the wiring. The lower deck
is shown separately in an accompanying illustra-
tion. The board for this assembly is screwed to
the cleats below, and the screw holes for the
equipment are located with the aid of the full-
size template supplied with the foundation unit
specified in the list of parts.
After screwing down the parts for the lower
"deck" and wiring them in accordance with the
circuit diagram, the lower front panel and the
equipment on it should be screwed in place as
APRIL, 1928
A SHORT-WAVE PHONE AND C.W. TRANSMITTER
shown, after which the wiring of the lower "deck' '
may be completed. This unit may be tested sepa-
rately before proceeding with the work. In order
to do this the unit is connected, as it would be in
operation, with the microphone, storage battery,
etc., and the switch on the panel is thrown to the
"Phone" position. Most of the resistance, R,,
should be in circuit. The tubes should all light
properly and the needle of the modulation meter,
Ms, should jump up when the microphone is
spoken into. Now, to check the quality, a loud
speaker should be connected across the modula-
tion choke, U, by means of a long cord leading
into another room. It may be necessary to shut
the door between the rooms in order to keep the
loud speaker from transmitting acoustical
energy to the microphone and setting up a con-
tinuous howling noise. When the equipment on
the lower deck is operating properly, the micro-
phone speech input as heard by another observer
at the loud speaker, should be very clear and
distinct. The resistance, Rs, should be adjusted
during the test until speech is at its clearest point,
at which time the modulation meter will indicate
from 20 to 30 milliamperes.
The equipment on the upper "deck" should
now be assembled from the template and dia-
gram in the same manner as the lower "deck"
was, after which the whole frame (supplied with
the foundation kit) may be put together with
wood screws. The upper panel, with its equip-
ment, should be attached last. The wiring is next
completed in accordance with Fig. i.
LIST OF PARTS
Mi Weston Model 425 Thermoammeter, o-l Amp.
Mj Weston Model 301 Milliammeter, o-iooMils.
Ms Weston Model 301 Milliammeter, 0-50 Mils.
Li, Lj, Ls Aero Short-Wave Transmitting Coil Kit
(2O4OK, 4o8oK, or ooiSK)
U Aero 248 Radio-Frequency Choke (Included
with Above)
U. US-M 331 Unichokes
Ci Cardwell o.ooos-Mfd. Condensers
Cs Polymet o.oO2-Mfd. Moulded Condensers
Q Polymet o.ooO5-Mfd. Moulded Condensers
O Polymet o.coo25-Mfd. Moulded Condenser
Cs Tobe 2-Mfd. 30o-Volt Condensers
O Tobe 2-Mfd. iooo-Vo!t Condenser
C? Tobe 4-Mfd. looo-Volt Condenser
Cj Tobe i-Mfd. Condenser
Ri Yaxley 8io-Type lo-Ohm Resistors
Ri Polymet io,ooo-Ohm lo-Watt Resistor
Rj Yaxley 2Ooo-Ohm Potentiometer, No. 2000
Ri Polymet 25,ooo-Ohm lo-Watt Resistor
Ri Polymet I5,ooo-Ohm lo-Watt Resistor
THE LOWER DECK ARRANGEMENT
The circuits associated with the power or voice currents are located on this
deck. The two-deck arrangement prevents losses which would otherwise occur
113.50
8.00
8.00
16.00
1 5.00
.80
.70
.35
2.50
3.50
6.00
.80
.60
• 75
1.75
1.25
1 .00
Re Polymet 750-Ohm lo-Watt Resistor .75
R? Yaxley i.5-Ohm Resistor, No. 2L .15
Rs Yaxley loo-Ohm Resistance, No. 8100 .25
Ti S-M No. 328 Transformer 18.00
Tt S-M No. 240 Transformer 6.00
Ts S-M No. 242 Transformer 7.00
Si, Si, Si Yaxley 2-Pole Switch, No. 63 1 .60
Five S-M No. 51 1 Tube Sockets 2. 50
Aero Transmitter Foundation Unit 27.00
(Consists of drilled and engraved Westinghouse
Micarta upper front panel, 7 x 18 x i inches,
drilled and engraved lower front panel, 5 x 1 8 x
J inches, seasoned walnut lacquered frame kit
cut to size for making a stand 16 x 18 x \o\
inches, with all screw holes drilled that are
necessary to put framework together, wiring
diagram, and layout sheet.)
No. 159 Frost Desk Microphone 8.75
TOTAL $164.50
ACCESSORIES
cx-310 (ux-2io) Tubes % 27.00
cx-312 (ux-i 12) Tube 3. 50
Manhattan No. 2721 Gas Rectifier 7.00
Transmitting Key i . 50
Three Four-Inch Bakelite Dials 1.50
Six Binding Posts .90
TOTAL $41.40
V,, Vz, V:
V,
V,
Since the accompanying photographs were
taken, a "key click" filter, consisting of a i-mfd.
Tobe condenser, Cs, in series with a loo-ohm
Yaxley resistor, R8, has been connected across the
key terminals as shown in the circuit diagram.
Space is available for these items on the base-
board just behind the key binding posts. Its
use will be appreciated by near-by broadcast
listeners, who otherwise would hear the key
clicks in their receivers.
The set should be tested to insure that it oscil-
lates properly. The plug is inserted in the no-
volt6o-cycle light socket and the switch is thrown
to the c.w. side. This should leave only the oscil-
lator tube lighted and, on shorting the "key"
binding posts, current will be indicated in the
plate meter. Probably this current will cause
almost a full-scale deflection but by varying the
plate or grid condensers it will snap back to 20
FIG. I
The circuit arrangement of the c.w. and phone
transmitter. A dotted line drawn across this
diagram isolates the apparatus on the two decks
.'Shells of all transformers, chokes, and
'condensers.should be connected to this lead
412
RADIO BROADCAST
APRIL, 1928
or 30 milliamperes at a certain point, indicating
that the tube is oscillating. On connecting an
antenna and ground, and tuning the antenna
condenser, this reading will be increased when
resonance is obtained, and at the same time
some antenna current will be noted. If the cou-
pling is too close the tuning of the antenna will
tend to throw the tube out of oscillation and it
will be necessary to loosen somewhat thecoupling
between the hinged primary coil and the plate
coil (L] and LM).
Final tuning should always be done with a
wavemeter in order that transmission may be
within one of the bands licensed by the Govern-
ment. One of the features of the transmitter is,
however, that due to the interchangeable coil
feature, the set may be tuned to any wave be-
tween 18 and 180 meters so that it is not rendered
unserviceable by any slight changes in wave-
lengths granted by the Government. The trans-
mitter may not be used, of course, unless the
operator has a license which permits him to do so.
Space does not permit us to go into the an-
tenna construction, operating methods, etc., at
this time, and the reader is referred to The Radio
Amateurs' Handbook, published by the American
Radio Relay League, Hartford, Connecticut, for
. excellent information along this line. This trans-
mitter is now in operation at 2 GY, the RADIO
BROADCAST station at Garden City, New York,
and there is also a similar one now working at
the Aero Products station located at Chicago
and the results that have been obtained in a
limited time are very gratifying. With c.w., on
the 40-meter band, all U. S. districts have been
worked from Chicago as well as NC jzz in Van-
couver, British Columbia. Twenty-meter phone
work has been unusually successful. The follow-
ing stations have been worked on 2o-meter
phone with reports varying from R-j to R-y:
1 BBM, Harwich, Massachusetts; I ASF, Medford,
Massachusetts.; i sw, Andover, Massachusetts;
2 BSC, Glen Head, New York; 3 AKS, Phila-
A PHOTOGRAPH OF THE UPPER DECK
All the equipment carrying radio-frequency currents is mounted on this
deck. Fig. I will clearly show just what equipment is placed on this deck
delphia; 4 MI, Asheville, North Carolina; and
8cvj, Auburn, New York. In all cases where
the transmission has been on phone, the quality
of the speech has been reported to be very fine.
Even greater distances have been worked on
code with the transmitter located at Garden
City.
FOR CODE WORK ONLY
\\ ANY amateurs are interested in c.w.
*• *• transmission to the exclusion of phone. In
such cases the transmitter may be constructed
for that purpose only at a substantial saving in
parts. The conversion requires simply the omis-
sion of the parts that are necessary for phone
operation since the transmitter described here
is an ideal c.w. transmitter in itself.
The circuit diagram of the outfit wired for
c.w. only is shown in Fig. 2.
The values of the parts shown in Fig. 2 are
exactly the same as those of the parts in Fig. i.
The only addition is the inclusion of R« in the
second diagram. This is a 5O,ooo-ohm Polymet
resistor of 10 watts carrying capacity. It lists
at $1.50, and is used to prevent the voltage on
the final filter condenser from rising to an unsafe
value when the key is up.
As it will be noted in the above list of parts,
there are three distinct sets of Aero coils avail-
able for transmitting purposes. The most popu-
lar kit is the 4080 K, which covers a wavelength
range of 36 to 90 meters (8330 to 3330 kc.).
The 204oK kit covers the band between 18 and
52 meters (18750 and 5770 kc.). The No. goiSK
kit is suitable for the band between 90 and 180
meters (3330 and 1670 kc.).
FIG. 2
Here is the transmitter circuit diagram for the
experimenter who wishes only to transmit
c.w. signals. The upper and lower deck feature,
it will be seen, is still maintained
i — "\AAX\AA. — II ~
jfc*p C6
"ABOX" Condensers
LJ _ L
To A
Terminals
of Set,
RECTIFIER CIRCUIT
FILTER CIRCUIT
Pure D.C.
FIG. I : THE CIRCUIT OF THE "ABOx" UNIT
A SECTIONAL VIEW OF THE "ABOX
Its circuit arrangement is given in Fig. I
Electrification Without A. C. Tubes
JUST push the plug into the light socket,"
is the answer most radio set users would
like to give to the query: "How do you
turn on your radio receiver?" In this
classification, so many believe, are included
only those receivers using a.c. tubes, and so when
they go out to buy an "electric" receiver, they
examine it to be sure that it uses a.c. tubes.
Also, when they consider converting their
battery-operated sets for a.c. operation the
problem to most of them becomes one of adapt-
ing the set to use a c. tubes. It is possible, how-
ever, to electrify a receiver in another way
which is frequently much easier to accomplish
and generally just as satisfactory. We refer to
the use of accessories in conjunction with a
receiver originally intended for battery operation
so that the equivalent of light socket operation
is obtained without the substitution of new tubes.
Electrically there is practically no difference
in the operation of a receiver from a.c. tubes or
from storage battery type tubes in conjunction
with an external A power unit connected to an
a.c. source. With a.c. tubes we supply a.c.
power either directly or indirectly to the electron
emitting surface which then emits electrons.
With d.c. tubes we supply a.c. power first of all
to a rectifier which in turn supplies power to the
filaments, and these become hot and their sur-
faces then emit electrons. In neither case does the
current in the filament enter directly into the
operation of the tube; it is merely the agent
which causes the electron emitting surface to
become hot. Socket power operation is a means
of eliminating the problems associated with the
storing of electric power for the operation of the
receiver, such as by means of a storage battery,
and any method which enables us to do this
implies direct operation of the receiver from the
power mains. If you want to electrify your re-
ceiver, you can do it by using a good B' power unit
and a reliable A power unit, such as the " Abox."
Many of RADIO BROADCAST'S readers are at
present obtaining plate voltage for the operation
of their receivers from a B power unit and, there-
fore, a socket power A unit will complete the
electrification of the receiver. When the plus
and minus terminals on the "Abox" unit are
connected to the corresponding A terminals on
the receiver and the power lead is plugged into
the light socket, there will be available, from
the "Abox" unit, a source of filament current,
and from the B power unit, a source of plate
By Lewis B. Hagerman
voltage, both obtained directly from the light
socket.
Electrically, the problems associated with the
design of a satisfactory A power unit are similar
to those connected with the design of a B power
unit. In both cases the problem is to take alter-
nating current power from the light socket and
rectify and filter it so that it will be satisfactory
for the operation of the receiver. The problem
in the design of an A power unit is that it must
deliver large amounts of current, which necessi-
tates a great difference in the values of the con-
stants incorporated in a proper rectifier and filter
unit, as opposed to those of a B power device.
An A supply unit must deliver at least two
amperes to be universally adaptable to most
receivers and this value of current is approxi-
mately one hundred times the output in amperes
of a low power B device. As the current to be
handled increases, the capacity of the filter
condensers must also be increased in direct
proportion, which will be about 100 times, and
it is only recently that large capacity condensers
of reasonably small physical dimensions have
been commercially available at a low price.
Then we have the voltage factor. A given
condenser stores more power the greater the
voltage; at one hundred and fifty volts, therefore,
it will store much more energy than at six volts.
To compensate this, the capacity of the filter
condenser must be increased in proportion to
the difference in voltage, or another twenty-five
times. Since the A device delivers current to the
filament circuit, any hum will tend to effect the
grid bias and be amplified by the tube. The
capacity of the filter condensers must be in-
creased about seven times to offset this effect.
Thus it will readily be understood that the
filter condenser of an A power-supply device
must be one hundred times twenty-five times
seven times, or 17,500 times, as great as that
used in a B device. The capacity of a B filter
condenser is about 4 microfarads; the capacity
required for an A power unit is, therefore, in
the neighborhood of 70,000 microfarads.
To obtain this the "Abox" Company de-
veloped a condenser consisting of a number of
nickel and iron plates immersed in a caustic
potassium solution, which is not an acid. This
solution causes thin films of oxygen and hydrogen
413
to form on the surface of the plates, and these
films constitute the dielectric of the condenser.
The caustic solution is one side of the condenser
while the plates form the other.
Since the capacity of a condenser increases as
the thickness and amount of dielectric decreases,
this infinitesimally thin gas film is responsible
in part for the tremendous capacity obtained.
This film has several advantageous features.
Should an excess voltage be impressed on the
condenser, the film immediately breaks down and
bypasses the excess energy. When the output
returns to normal, the film forms again, and the
condenser is as good as new. The bugaboo of
burnt-out condensers is thereby done away with.
The capacity of the condenser is far in excess
of that required; it has been estimated that its
capacity is in excess of 200,000 microfarads.
When used with the "Abox" rectifier, it reduces
the alternating component of the input pulsating
d.c. to less than Wooth of its original value.
Both the rectifier and condenser work in the
same solution. The addition of distilled water
every six months or so is the only maintenance
needed. The condenser plates are never affected
by use or disuse, and the rectifier electrode has a
life of several years and can be replaced in a few
seconds at a very low cost. The tapped resistance,
RI, which compensates for the number of tubes
used is adjustable from the front of the unit.
Fig. I shows the circuit of the complete elimi-
nator. The alternating current from the house
lighting circuit is stepped-down from no volts
to the proper low voltage by the transformer, TV
The current then flows through the rectifying
valve which will pass current in one direction
only, thereby eliminating one phase of the al-
ternating current and creating a pulsating direct
current. It is next passed through the filter
circuit, where it is smoothed, and all variations
and pulsations in current are removed. The
drawings at the lower part of this diagram show
the effect of the rectifier and filter on the alter-
nating current. The rectifier changes the alternat-
ing current to pulsating direct current by elimi-
nating one phase of the a.c. wave, and the filter
then smooths out the pulsating current, produc-
ing practically pure direct current. When this A
power unit is used in connection with the average
receiver, it will not cause any hum.
A "HUDDLE" IN ONE OF THE VICTOR TALKING MACHINE COMPANYS STUDIOS FOR RECORDING, OLD STYLE
THE electromagnetic phonograph repro-
ducer, also often simply called the "unit"
or "pick-up," is acquiring great popularity
nowadays on account of the tie-up it creates be-
tween the radio receiver and the phonograph.
When static is bad, or when radio programs are
not to one's taste, it becomes a simple matter to
change over to the phonograph and enjoy the
best or the worst in musical art, according to the
choice of the person who purchases the records.
On the other hand, since most of us are able
to afford only a limited number of phonograph
records, and must play them many more times
than once in order to realize on our investment,
such repetition occasionally pafls, as it were, and
we turn to the "air" to supply us with programs
new to our ears.
Although there are a great many "pick-ups"
already on the market, and more are coming on
every day, their commercial exploitation is rela-
tively new. The development of a new device
requires the simultaneous development of a
technic particularly suitable to it. At this early
stage of the development, it is not to be expected
that all those who design reproducers know
everything about them, and it must also be re-
membered that many of those who are working
on the problem are radio engineers, and are not
versed in the phonographic art.
On the other hand, although the electric re-
producer is new to the radio public, it is not by
any means new to engineers. The writer remem-
bers a demonstration of a piezo-electric repro-
ducer which he witnessed in New York as far
back as 1921, and the engineer who developed
this reproducer had been working on it for a
period of several years before. Electromagnetic
pick-ups are likewise fairly old in the art, as also
is the capacity type of pick-up, but the advent
of these devices for practical and commercial
application had to await the development of
suitable amplifiers and loud speakers.
There are quite a few phases of the art to
consider. These may be listed as follows:
Recording
Method of sound pick-up (horn, microphones
of various types).
Method of actuating cutting head.
Amplification
Reproducing
Type of pick-up (capacity, piezo-electric, car-
bon, electromagnetic).
Amplification.
Conversion into sound (type of loudspeaker)
This list outlines the complete process from
beginning to end, which we will describe briefly
in the next few paragraphs.
At the recording studio we have a band, or-
chestra, singers, or other artists furnishing the
original music. The sound waves of this music
are collected by a horn, in the old "air-line"
method of recording, or by a microphone in the
newer system of "electrical" recording.
In the "air-line" method, the sound waves,
entering the collector horn, were concentrated
in it, so that sufficient energy could be obtained
for actuating a diaphragm, to which was rigidly
fastened a "cutting-head." Under this cutting-
head traveled the wax disk known as the "ma-
trix," on which the cutter engraved waves cor-
responding to the sounds entering the horn.
Naturally, the power available for driving or
actuating the diaphragm which carried the cutter
was limited to that which could be collected from
the original sounds in the studio.
In order to obtain sufficient power for cutting
the record, it was necessary to use a resonant
diaphragm, so that at the outset we have two
inherent difficulties in the air-line system of re-
cording; in the first place the horn which col-
lected or concentrated the sound waves was a
cause of distortion, due to its "resonance" at
various frequencies, and, secondly, the same was
true of the diaphragm, which was made resonant
in order to operate the cutter satisfactorily.
These difficulties are avoided in the electrical
system of recording, in which the sound waves
operate directly on the diaphragm of a micro-
414
phone. The energy pick-up of this microphone is,
of course, exceedingly small — much smaller than
that picked up by the collector horn in the old
system — but the advantage lies in the fact that
since the microphone converts the energy of the
sound waves into corresponding waves of electric
current, it is possible to amplify them to any
degree we might desire. On this acount distortion
need not be permitted at the outset, i. e., as in a
horn or resonant diaphragm. On the other hand,
we run into the difficulty of distortion in the
amplifier or in the microphone.
This is what we referred to previously when
we stated that the development of electrical
recording and reproducing had to await the de-
velopment of the amplifier. To-day we can build
amplifiers having negligible distortion, and the
microphone, collecting such a small amount of
power and having no extended surfaces, is in-
herently far superior to the collector horn of the
old system. The main advantage of the "air-
line" system of recording and the old method of
reproducing, is simplicity. The new electrical
systems show to greatest advantage in the record-
ing, for it must be understood that very good
quality is obtainable in reproducing by the old
system when slowly expanding exponential horns
are used in which the resonances have been re-
duced and the range of response has been ex-
tended to include the lower tones. But good
reproduction by the old method requires that the
recording be done properly, so it is here that the
electrical system is especially valuable.
VOLUME CONTROL
A NOTHER feature of the electrical system
** which is of great importance is the ability
to control the volume of reproduction. The phon-
ograph record is a form of mechanical power
amplifier, deriving its power to amplify from the
motion of the turntable which carries the record.
We can understand how this is by considering the
old "air-line" system. The acoustic power con-
HOW A VICTOR RECORD IS MADE NOWADAYS. FOOTBALL TACTICS HAVE BEEN FORGOTTEN, AND BETTER RECORDS RESULT
Recording and
Lucini
By Sylvan Harris
centrated in the collecting horn and which ac-
tuates the diaphragm to which the cutter is
attached is very small. After the record is made
and is being run on the turntable under the
needle of the pick-up, it is the motion of this
needle, caused by the rotation of the disk, which
furnishes the sounds which come out of the horn.
In other words, the power which drives the disk
causes the needle to vibrate in the grooves of the
record. The waves themselves, in the grooves of
the record, furnish no power. It is only the mo-
tion of the record which furnishes the power.
We have a very analogous situation in an
amplifier; a voltage is impressed on the grid of
the amplifier tube, but this voltage is not power.
It is only due to the influence of this voltage on
the power furnished by the B supply that an
amplified reproduction of it occurs in the plate
circuit. The alternating grid voltage is similar
to the waves on the record; the power of the B
supply is analogous to the power in the mechan-
ism which drives the record.
In spite of the inherent amplification in the
phonograph record, this amplification is not
always sufficient when there are wide ranges of
volume in the original music. It is also difficult
to obtain all the volume that one might desire
for ordinary purposes without introducing con-
siderable distortion, unless electrical amplifica-
tion supplements the mechanical amplification of
the record. First we must amplify the weak out-
put of the microphone, because the microphone
pick-up is so small. Yet we must not amplify too
much, for we run into other difficulties of record-
ing, as, for instance, where the cutter cuts
through from one groove to the next, or where
distortion arises in the cutting apparatus.
This brings us to the next phase of the subject
— the cutter. This is a specially ground amethyst
set into the end of a rigid rod or bar, which, in
the old system, was attached to the middle of the
diaphragm at the throat of the collector horn.
When the diaphragm was set into vibration by
the sound waves in the studio, this bar and the
jewel at its end were likewise set into vibration.
The jewel, cutting a groove into a heavy wax
disk (the matrix), at the same time cuts waves
in either the walls of this groove or at its bottom,
depending upon the particular construction of
the cutting-head, as it is called.
There are two methods of cutting — the "hill-
and-dale" cut and the "lateral" cut. In the hill-
and-dale method, the cutter vibrates up and
down in the groove, so that there are "hills"
and "dales" at the bottom of the groove. This
was the original method used in the phono-
graphic art, and is hardly ever used nowadays.
It has been superseded by "lateral" cutting, in
which the cutter is made to vibrate "laterally,"
or from side to side. The result is that the groove
cut in the wax, while circular around the center
of the disk, is at the same time wavy. We will
not discuss the advantages and disadvantages of
the two methods here; they are mentioned
merely to acquaint the reader with the general
ideas involved.
In either case the vibrating bar of the cutting-
head is connected (generally through a system of
levers) to an armature (in the electrical system)
which is actuated by an electromagnet. This
electromagnet obtains its power from the am-
plifier, the input of which is connected to the
microphone. The principle of the cutter is the
same as that of a loud speaker, excepting that
instead of having a cone for the load on the
armature, we have the jewel cutting into the wax.
So, in the electrical system of recording we
have first the microphone, which may be any
one of several types, next, the amplifier, which
may also be any one of several types, and finally,
the cutting-head, which includes an electro-
magnet for actuating the armature to which is
attached the cutter. There is no standard design
of cutting-head, the type used often being the
arbitrary choice of the man who does the record-
ing, and the design often being his own. The de-
sign of the cutting-head is, however, extremely
important, the success of the whole system de-
415
pending to a very great extent upon it, not so
much perhaps, upon the electrical part of it as
upon the mechanical arrangement of the levers,
the damping of the movable parts, the shape of
the cutting point, the depth of the cut, etc.
We will now skip over the actual making of
the records for this is a mechanical process; in
this article we are considering only the electrical
features. Suffice it to say that from the large,
thick wax disk (the matrix) upon which the
cutting is done, a "master" is made, and from
this master any number of impressions can be
made, resulting in the records as they reach the
music store.
In the old system of reproduction the vibration
of the needle in the grooves of the record actu-
ated a diaphragm of mica or other material,
which directly communicated the energy of
vibration to the air column of a horn of one type
or another. In the newer electrical method power
is communicated to the needle by the rotation
of the turntable in the usual manner, but now,
instead of driving a diaphragm, the needle drives
an armature located in the magnetic circuit of a
permanent magnet. A coil is also connected in
the circuit so that the variations of the magnetic
flux caused by the vibration of the armature
induce fluctuating voltages in this coil, and these
can be impressed on the input of an audio am-
plifier, the output of which is connected to a
high-grade loud speaker.
So we have a means of amplifying the "pick-
up" from the record, and of controlling the vol-
ume, neither of which could be done by the older
method of reproduction.
The main feature of the electrical system of
recording and reproducing is the fine quality
that can be obtained. Music obtained from old-
style records by old-style methods of reproducing
is greatly lacking in the bass notes, and sounds
thin and hollow. Very fine quality can, on the
other hand, be obtained by the new methods.
The tie-up between the radio and the phonograph
has turned out to be very successful indeed.
SIMPLE EQUIPMENT FOR UTILIZING A. C. TUBES WITH AN EXISTING RECEIVER
The photograph shows the various components — adaptors, C bias resistors, and cables — of the Carter a. c. harness
Electrifying Your Present Set
By Zeh Bouck
THE introduction of the alternating-
current tube has stimulated something in
the nature of a mild radio revolution. The
advantages of a.c. operation — reliability and
economy — in the majority of possible installa-
tions, are immediately obvious. This presents the
problem of what is to be done with several-
hundred thousand receivers of general efficiency,
the only deficiency of which is their inability to
be operated directly from an alternating-current
source of a hundred and ten volts.
From an engineering standpoint this, of course,
is merely a mechanical problem. Its solution was
a simultaneous by-product of the a.c. tube itself.
Any receiver in the world can be rewired for
the use of a.c. tubes. In the majority of cases the
changes are relatively few and simple. But the
actual alteration of a radio receiver, particularly
a commercial job, is repugnant to the average fan,
and it was up to the manufacturers to provide
FIG. I
suitable devices for the conversion of battery
receivers with little or no alteration of the re-
ceiver itself. Almost simultaneously with the
production of a.c. tubes — the Cunningham and
R.C.A. 226 and 227 types, the Arcturus line,
and a host of others — these desired devices ap-
peared upon the market in numerous quantities.
By referring to Figs, i and 2 it is obvious that
the mechanical and electrical requirements of
the new tubes, in reference to receivers originally
designed for battery use, can be satisfied by
means of a simple adaptor, which will insulate
the tube from the original filament terminals
on the socket and at the same time provide two
new filament or heater leads, and it was such
adaptors that appeared on the market concur-
rently with the production of a.c. tubes. Fig. I
indicates the familiar battery arrangement, while
Fig. 2 suggests the electrical change effected by
a simple adaptor. New filament leads have been
provided for, while the former negative A post,
to which the lower side of the grid coil or second-
ary is returned, remains open for biasing pur-
poses.
The manner in which a typical adaptor fits
between tube and socket is, shown in the photo-
graph, Fig. 3. The use of adaptors necessarily
FOR the convenience of our readers we have
collected together here the names of the manu-
facturers of apparatus for use in converting a re-
ceiver for a.c. operation. Many of these names are
also mentioned in the text of the article although
those of the manufacturers of filament-lighting
transformers are an exception for they are not given
specific mention in the article. Readers should
realise that, to light the filaments of a. c. tubes, a
step-down filament transformer is necessary, besides
the adapters and harnesses mentioned in the article.
A source of plate potential, and the necessary grid
voltage are of course, also, required.
Manufacturers oj A, C. Tubes:
Cunningham, R. C. A., Ceco, Arcturus, Sovereign,
Televocal.
Manufacturers of Harnesses:
Arcturus, Carter, Eby, Naald, Cornish Wire,
Harold Power, and Radio Receptor. The latter two
companies sell combined A, B, and C power units
and harnesses, as explained in the text.
Manufacturers of Filament Transformers:
Amertran, Dongan, General Radio, Karas,
National, Samson, Silver-Marshall, Thordarson,
and lies.
416
increases the effective height of the tubes which
in some cases makes it necessary to slightly gouge
out the covers of the receivers, before they can
be closed, or with suspended tubes as in the
Atwater-Kent Model 35, the receiver must be
raised on short legs. In consideration of this oc-
casional inconvenience, the Arcturus a.c. tube,
designed for cable or "harness" use, obviates
the necessity for the use of adaptors by means of
two small screws, one on each side of the base,
to which the heater leads are connected. The
manner in which the Arcturus a.c. tubes and
a.c. cable are mounted in the average receiver is
shown in Fig. 4.
"HARNESS" OUTFITS
THE use of adaptors alone solves only half
the rewiring problem. The adaptors them-
selves have to be wired, so the majority of manu-
facturers producing adaptors are also providing
FIG. 2
connecting cables, usually referred to as "har-
nesses," in the form of braid-covered leads
permanently connected to the adaptors. Other
manufacturers sell the "harness" complete with
an A, B, C power supply unit. Such devices are
made in special and general types, prominent
among which are those of the Radio Receptor
company and Harold J. Power, Inc.
Radio Receptor makes three types of "Power-
APRIL, 1928
ELECTRIFYING YOUR PRESENT SET
417
i?ers" (combining "harness," adaptors, and
complete A, B, and C power supply outfit)
designed especially for the Radiolas 20 and
28 and the Atwater-Kent models, which, how-
ever, are readily applied to an inclusive list of
receivers.
Harold J. Power, Incorporated, manufactures
an "A. C. Electrifier" which can supply A, B,
and C potentials to any ordinary a.c. receiver.
The filament potentials available are 1 1, 2j, and
5 volts. Harnesses are available for electrifying
the following receivers: Atwater Kent Model
35, Crosley "Bandbox" Model 601, Kolster 6,
and universal harnesses for standard 5-, 6-, and
7-tube tuned radio-frequency receivers.
So far as the plain "harness" is concerned, we
find that the Cornish Wire Company produces
four types of "harnesses," all general designs,
for five-and six-tube receivers with Arcturus
a.c. tubes and for five-and six-tube receivers with
the 226 and 227 type tubes.
The Arcturus Radio Company manufactures
one general "harness" and six special "harnesses"
or "a.c. cables," for use with the following re-
ceivers: The Freshman six-tube "Masterpiece,"
the Crosley "Bandbox," the Atwater-Kent
models 30, 33, and 35, the Stewart Warner model
525, and the Kolster 6-D.
Other manufacturers of "harnesses," generally
of a universal type and designed for R.C.A. and
Cunningham type tubes, are given in the list on
page 416.
FIG. 3
A close-up showing how the adapter plugs into the
existing socket and the a. c. tube into the adapter
equivalent substitute. The B and C potentials
must still be supplied by either batteries, a power
supply device, or a combination of the two. It
is only by the use of a B and C socket power
unit, in conjunction with a.c. tubes, that the
receiver becomes completely electrified. For oper-
ation from a house lighting socket, the following
apparatus may be used in combination with a
battery receiver:
A.C. TUBES, PLUS:
(i.) Filament-lighting transformer, an ef-
ficient B power device, and the necessary resistors
to supply two C potentials.
Or (2.) a combination power-supply outfit,
combining the necessary a.c. and d.c. potentials
in a single unit.
THE RECEPTRAD "POWERIZER"
THE Receptrad "Powerizer," mentioned be-
fore, is a fine example of a complete power
unit. The description given here of the installa-
tion of a "harness" and "Powerizer" in an
Atwater-Kent receiver is indicative of the general
procedure. Details regarding the conversion of
other receivers are contained in the direction
sheets with the different harnesses and cables.
Fig. 5 illustrates the circuit arrangement of
the "Powerizer." Rectification is effected by
a ux-28o (cx-38o). A 210 type power amplifying
tube is an integral part of the " Powerizer,"
the input of which is fed from the secondary of
the second audio transformer in the receiver
itself. There is no audio transformer in the
" Powerizer," as the diagram shows.
The resistors, RI and R2, are particularly in-
teresting, as the voltage drop across them sup-
plies the C bias potentials to the power tube and
FIG. 4
The Arcturus tube, and a.c. cable installed in a hypothetical
receiver. No adapters are required with Arcturus tubes
VOLUME CONTROL AND ACCESSORIES
\/ARIOUS accessories are furnished with the
• "harness" outfits in accordance with the
manufactuer's ideas of his obligations. In almost
every instance some form of volume control ap-
plicable to a.c. circuits is included in the cable
equipment, with the exception of such cases de-
signed for particular d.c. arrangements already
provided with an adequate control. The volume
control generally consists of a specially tapered
o-to-25,ooo-ohm potentiometer, the element of
which is connected across antenna and ground
and the variable arm to the grid of the first tube.
This type of volume control is easily attached.
Several manufacturers include C biasing re-
sistors, center tap resistors, and bypass conden-
sers, while others consider this auxiliary equip-
ment a part of the power supply unit rather than
a component of the adapting system.
COMPLETE ELECTRIFICATION
THE installation of a.c. tubes does not neces-
sarily mean that a receiver is capable of
being operated from the house lighting source
without additional assistance. The use of a.c.
itubes merely eliminates the A battery, or its
FIG. 6
An Atwater Kent model 35 receiver with a.c. tubes. The
"Powerizer,"shown on the next page, is used for power supply
110V.A.C.
OB-
Toset
FIG. 5
The circuit diagram of the "Powerizer"
418
the r.f. amplifying tubes respectively. A resistor
connected between the center filament tap of
any a.c. tube and B negative, will bias the grid
of the tube negatively, providing the grid of the
tube is returned (through a secondary or leak)
to B negative.
Fig. 6 shows the adaptors and tubes mounted
in the Atwater-Kent 35 receiver, and Fig. 7
shows the "Powerizer" itself. The rheostat panel
on the Atwater-Kent was removed and a special
volume control, supplied by Receptrad, was
mounted in its place. An external form of volume
control could have been employed.
The following are the steps taken in installing
the "Powerizer," along with the time consumed
for each operation:
Demounting the Receiver . . . 10 Minutes
Installing Volume Control . . 30 Minutes
Installation of Adaptors and Tubes 5 Minutes
Reassembly of Receiver ... 12 Minutes
Connection of "Powerizer" . . 2 Minutes
TOTAL TIME 59 Minutes
This time would be reduced to 34 minutes by
using the external form of volume control.
The result is a thoroughly up-to-date receiver,
capable of delivering remarkable volume with
fine quality, with a reliability of operation
achieved only by complete "electrification."
Fig. 8 shows a Radiola 28 superheterodyne in
which a somewhat similar installation has been
made with the Receptrad type 28 "Powerizer."
SPECIAL STABILIZATION
\A71TH some receivers, special devices (gen-
" * erally resistors in the grid circuits) must
be employed, aside from the volume control, to
achieve a satisfactory degree of stabilization.
The following list considers various receivers
that have been successfully adapted for a.c.
operation, employing the Receptrad type of
"Powerizer" and harness, with notes on special
requirements:
RADIO BROADCAST
FIG. 7
A neat unit — the "Powerizer"
ATWATER-KENT, Models 20, 30, 32, 33, 35:
For external control no change is needed.
BOSCH "CRUISER:" Regular harness. Requires
re-neutralization. Uses external volume control.
BOSCH, Model 46: Simply plug in adaptors.
No volume control necessary.
BOSCH, Models 66 or 76: Requires 400 ohms
in grid circuits of r.f. tubes. Also requires re-
neutralization. No volume control necessary.
BREMER-TULLY "COUNTERPHASE" 6-37: Re-
quires standard harness. May need re-neutrali-
zation or grid resistors. External type volume
control.
BREMER-TULLY "COUNIERPHASE" 8: Requires
standard type of harness with special distances
between adapters. May require re-neutralization
or the use of grid resistors. External volume
r
& o
1 I
FIG 8
A "Radiola" Model 28 super-heterodyne with a "Powerizer" mounted in the battery compartment.
This installation uses a 210 type power tube, doubly modernizing the receiver. It takes about forty-
five minutes to make the revision
APRIL, 1928
control. A high resistance of 50,000 or 100,000
ohms should be shunted across the secondary of
the 2nd audio transformer.
CROSLEY "BANDBOX:" Simply plug in stand-
ard harness. Control may be had by "accumina-
tors" or external. In some cases re-neutralization
is necessary.
DAY-FAN 6 JR: Plug in standard harness.
External volume control.
FADA SPECIAL 6, 265 A. R. P. 65: Standard
harness. External Volume control.
FADA 7 — 475 A-S.F. 45/75: Remove tube
housing. This is held in place by 6 or 8 screws.
Put in standard harness for seven-tube set with
distances between adapters slightly longer.
External control.
FADA 8 — 480 B-S.F. 50/80 B: Requires the
use of i6oo-ohm resistors in the grids of all of
the r.f. tubes. Standard harness for eight-tube
set with special distances between the adapters.
A high resistance of the order of 50,000 or 100,000
ohms should be shunted across the secondary of
the 2nd audio transformer. External type of
volume control.
FRESHMAN, Three Dial Type: 1600 ohms in r.f.
grid circuits. Special uv harness. External control.
GREBE Mu-i (5): 700 ohms in grids. Standard
harness. Requires re-neutralization. External
type control.
GREBE 7: Special distance harness. External
type control.
KOLSTER, Model 6D: 700 ohms in grids of r.f.
tubes. Standard type harness. No control needed.
Sensitivity control on set O.K. Must have very
good ground.
PFANSTIEHL 32: Standard harness. External
type control which may replace old switch vol-
ume control. Connections to switch joined to-
gether and leads to old volume control soldered
together separately from switch connections.
Accomplished by connecting 50,000 ohms be-
tween grid and old filament wiring.
RADIOLA 16: Plug in standard harness. Ex-
ternal control.
RADIOLA 20: For external control no change is
needed.
SiLVER-CocKADAY: Requires 3200 ohms in
grid of r.f. stage. Standard harness.
SPLITDORF 6: 4OO-ohm resistors in grids of r.f.
tubes. Special distances between adapters.
External control.
STEWART- WARNER 525: Standard Harness.
No changes. No volume control other than one in
set needed.
STEWART WARNER 705: Special distances.
No control needed.
STROMBERG-CARLSON 5OI-A: Special distances.
Re-neutralization required in some cases. Ex-
ternal control.
THERMIODYNE T.F. 5: Special uv adapters.
External type control.
ZENITH, Models 7, 8, 9: Special uv adapters,
400-ohm grid resistors. No volume control
needed. All C batteries must be removed and
gaps shorted.
ZENITH n or 14: Special length harness.
External control.
The Listeners' Point of View
ST BE MADE A NECESSITY
By JOHN WALLACE
M
R. H. A. BELLOWS, manager of wcco
and former member of the Federal
Radio Commission, can generally be
counted upon to say something sentient when
he speaks about radio. In a talk before the
National Electrical Manufacturers' Association
last winter he made several suggestions. One
of the most important was that if radio is to be
a stable institution it must become a necessary
institution. This idea seems to us basic. He says:
" Improvement in broacasting must follow two
distinct lines, one of them being better presenta-
tion of musical programs. The other is, I think,
still more important. Look for a moment at the
history of the automobile. For years the auto-
mobile was a luxury, and its market was limited
to those who felt they could afford luxuries of a
rather costly nature. The thing that has made
the automobile business what it is to-day is the
conversion of a luxury into a necessity. People
who would never own a single car as a luxury
now own two or three because they regard them
as absolute necessities, since our entire mode of
living has readjusted itself to this new type of
transportation.
"The real future of radio reception lies in a
similar conversion of broadcasting service from
a luxury into a necessity. This can never be
done by programs of musical entertainment
alone. You can never persuade the mass of the
people that they must be able to hear the New
York Symphony Orchestra once a week. You can
come nearer it with reports of baseball and foot-
ball games and of boxing matches. The stations
in the farm belt of the Middle West have done it
admirably, for a part of their audience, with their
market reports. For the people in the cities this
service feature of radio — this creation of a new
necessity — is still largely in the embryonic stage.
"Of course I like to get letters praising our
musical programs — we all do — but what I really
value is the letter which tells me that thanks to
our market service some farmer up in North
Dakota has saved two hundred dollars on a ship-
ment of wheat, or the letter saying that some
family in Minneapolis has come to find our morn-
ing comment on the day's news just as essential
a part of the day's routine as the morning news-
paper.
"Can we develop some form of centralized
teaching so that radio will establish itself in all
our schools? Can we cooperate with the great
news agencies so that, without competing with
the newspapers, radio can be made a dependable
and instantaneous means for sending out news
flahes? Can we make broadcasting a legitimate
agency for communicating between our govern-
ing bodies — national, state, and municipal — and
the people who pay the taxes? What, in a word,
can we do to make radio a necessity?
"Once again, let me cite an illustration. You all
know the horrible tedium of civic association ann-
ual banquets — the indigestible food, the entertain-
ment half drowned out by clattering waiters, and
the dreary reports. We are trying the experiment
of holding such an annual meeting by radio. The
members of the civic association in question are
being cordially invited to dine at home, to listen
to reports carefully boiled down, and to do the
necessary voting at the close of the meeting by
mail.
"'Radio must be a necessity, not a luxury.'
This 1 believe, is the solution of the future of
the radio industry, and it is for you to play a
large and active part in bringing it about. Con-
stantly improving network service will help, but
it will not be enough. The broadcasting stations
must vastly strengthen their local programs,
above all in the matter of the type of local
OSKAR SHUMSKY AT WBAL
Here is your chance to say you heard him "way
back when" — provided he turns out to have the
kind of future his press agent promises him.
At any rate, Oskar Shumsky, whose playing
and composition ability have already been
praised by none other than Fritz Kreisler, will
be heard from WBAL Sunday evening, March 18,
at 8, eastern time
service which carries radio out of the field of
mere entertainment and into that of household
necessity."
Mr. Bellows remarks were aimed primarily at
the radio manufacturer. He said earlier in his
speech: " I do not need to remind you gentlemen
that you are all engaged in manufacturing a com-
modity which of itself is entirely worthless. The
finest receiving set in the world is no better than
the broadcasting which comes within its range.
You do not have to be told what would happen to
the radio manufacturing industry if the public
should ever become really bored with broadcast
programs."
This must have sent the cold chills coursing
through the veins of his hearers, all of them with
their entire capital and future prosperity in-
extricably tied up in radio. Particularly since
the situation, if not probable, is at least con-
ceivable. The public is notoriously fickle, and if
it decided to become bored with broadcasting, all
the king's horses and all the king's men couldn't
change its whim. Where are the petticoat manu-
facturers and ostrich plume vendors of yester-
year? How can the man who invests in radio
stock to-day be certain that by 1938 the public
will not have capriciously shifted over to some
other mode of entertainment, that the broad-
casting stations will not be abandoned crumbling
ruins even as — alas — are the breweries to-day!
Certainly if the radio manufacturers are to
have any feeling of security they must see to it
that radio becomes a utilitarian device as well
as the entertainment device that it now is. If
it can be made an indispensable utility like the
telephone its longevity is practically assured.
But while it remains in the luxury class, like
the phonograph, its future is a gamble. The talk-
ing machine business, as is well known, almost
went on the rocks a little while years back; the
new fad which threatened its existence was radio
itself.
Mr. Bellows mentions four ways in which
radio can be practically utilized: Service to
farmers; dissemination of news; agency of com-
munication between governing bodies and the
public; and centralized teaching for the schools.
A REGULAR FEATURE AT WGR, BUFFALO
The Hotel Statler Concert Ensemble, which is heard daily from WGR in a program of luncheon music
419
420
RADIO BROADCAST
APRIL, 1928
The first mentioned, service to farmers, is al-
ready a tried and proved function of radio. A
survey recently conducted by WLS shows that
the value of radio as a means of entertainment
has been equalled and exceeded by its economic
utility as a daily aid in the production and
marketing operations of the far . It has taken
its certain place as an instrument of farm educa-
tion and has proved its dollars and cents value
many times over in the transmission of market
news, weather forecasts, and other items of
immediate importance to the farmer. "If you
had to give up either music or talks on the radio
which would you prefer to retain?" was a ques-
tion put up to a number of farmers by the United
States Department of Agriculture. "We will
keep the talks," answered 2358, while 1538 an-
swered "music." The most recent government
estimates place the number of radios on farms
at 1,250,000. The number is now doubtless more
than a million and a half. The radio farm and
market service has already done much in solving
the venerable problem of market gluts, with their
resulting demoralization of prices and wrecking
of values. Tens of thousands of farmers or their
wives hear and tabulate the market returns every
day on the particular product in which they are
interested, and plan their marketing accordingly.
Anent the second mentioned method, Mr.
Bellows asks: "Can we cooperate with the great
news agencies so that, without competing with
the newspapers, radio can be made a dependable
and instantaneous means for sending out news
flashes?" The answer is probably no, not without
competing with the newspapers. But why should
that consideration enter into it? If there is some
sort of lively instantaneous news which radio
can put over better than the newspapers and in
which dissemination it is fore-ordained to sup-
plant the newspaper, let the supplanting start
at once. Conservative maneuvers on the part of
the news agencies, and on the part of the news-
papers, can only succeed in postponing the in-
evitable, not in suppressing it.
Concerning the third suggested method of
giving radio a permanent utilitarian function
we can say very little. Our knowledge of the
workings of municipal, state, and national ad-
ministrative bodies is too sketchy to be revealed
here in its nakedness. But we see no reason to
believe that radio will not some day be an of-
ficial mouthpiece for governing bodies. And by
official we mean Official — that is, there will be
certain prescribed goveVnmental broadcasting
hours during which time certain prescribed in-
dividuals or bodies of individuals will be ex-
pected, by duty of their office, to listen-in and
make prescribed findings. (Which is about as
near as we can get to the jargon of law making.)
Anyway we venture to prophesy that before ten
years have passed radio will be in some way, if
only in a minor way, tied up with governmental
administration.
It is in the fourth suggested means of stabiliz-
ing radio that we are most interested. The
propounder of the idea asks: "Can we develop
some form of centralized teaching so that radio
will establish itself in all our schools?" The an-
swer is yes; the opportunity is now upon us.
We have made disparaging remarks about
radio education in the past and lest we should
seem to contradict ourself (not that we object to
contradictions; our opinion happens to be still
the same) let us reassert that as an "educating"
medium radio is the bunk. It is next to useless
as far as teaching such stuff as economics, horse-
shoeing, sociology, or play-writing goes. But we
have always believed that radio is peculiarly
well adapted to teaching music appreciation and
still think so.
Its possibilities in this field have long been
recognized and from time to time during the past
couple of years rumors have become current that
something was going to be done about it. Mr.
Walter Damrosch has been particularly active in
keeping the idea before the public. It is one of his
pet hobbies. And now, as the result of much
scheming and labor on his part, he has carried
the idea through to the point where it becomes a
live issue.
His plan, as you doubtless already know, is to
broadcast a series of his music appreciation lec-
tures next winter over a network of stations
during some daytime hour, the talks to be illus-
trated by his own piano playing and by an or-
chestra, probably the New York Symphony. So
much, in brief, for his end of the arrangement.
The other end is where the difficulties come in.
Each one of the many thousands of schools
throughout the country would have a first-rate
receiving set, in perfect operating condition,
available in its assembly hall or in one of the
larger class rooms. Into this room, at the sched-
uled hour, would be herded all those pupils who
had "Music Appreciation" on their program
of courses. They would be provided with advance
MR. WALTER DAMROSCH
Who for very many years was leader of the New
York Symphony Orchestra and now frequently
conducts that organization in the capacity of
of guest conductor. His experiments in broad-
casting musical appreciation courses to schools
has caused considerable favorable comment
notes on the lecture, sent to their teachers
through the mail by Mr. Damrosch, and each
lecture-concert would be followed by a written
"quizz," also furnished from the central head-
quarters of the "course."
There is no especial practical difficulty in the
way of carrying out this end of the scheme.
The rearranging of the schedules to embrace this
new hour of school work once every two weeks,
or perhaps once a week, could be done with little
trouble. Someone on the premises with sufficient
intelligence to supervise the upkeep and proper
operation of the receiving set could easily be
found. Furthermore, receivers and loud speakers
of adequate quality to reproduce the lectures
satisfactorily are available.
The obstacle to be met with is the difficulty
in arousing nation-wide interest in the idea to
the point where boards of education and school
trustees will undertake the red tape involved
in officially adopting the course and appropriat-
ing funds for the necessary equipment.
Of course the obvious way to "sell" the idea
to the school masters throughout the country
would be by a campaign of publicity and propa-
ganda. But this would involve an enormous
expenditure of money. And where is it to come
from? All Mr. Damrosch has to offer is the idea
and his own time and effort. Who is going to
sponsor it?
By way of giving the idea some publicity Mr.
Damrosch, with the cooperation of the Radio
Corporation of America and the National
Broadcasting Company, has already broadcast
experimental programs. We think they proved
conclusively that Mr. Damrosch will be able to
carry off satisfactorily his part of the arrange-
ment if the plan is ever put through. The first
program was as follows:
PART I
For Children of the Grammar Schools
(i.) Allegretto from Symphony
No. 8 Beethoven
(2.) Entrance of the Little Fauns. . . .Pierne
(3.) Scherzo from Symphony in B
flat Glazounow
PART II
For Students in the High Schools and Colleges
(i.) Overture to "A Midsummer
Night's Dream" Mendelssohn
(2.) Andante from Symphony No.
5 Beethoven
Before each of the numbers Mr. Damrosch
gave an introductory talk and called attention
to certain things to be watched for in the music,
much in his familiar manner, except that he
modified his material in accordance with the age
of the prospective youthful listeners.
You may not be thoroughly in accord with
Mr. Damrosch's method of explaining music
(we, for instance, think he lays a misleading
emphasis on the "story" content of non-
program music) but nevertheless he has had
some forty years' experience in giving such lec-
tures and ought to know what he's about. Be-
sides we can think off-hand of no one better
fitted for the job; no one who combines, as he
does, the qualities of authority on the subject,
wide and popular renown, distinctive and in-
triguing personality. We opine that it will be
radio's distinct loss if it finds itself unable to
take advantage of these rare qualifications while
they are available. Pedantry over the radio
simply will not work. The pedant needs the help
of bodily presence, and often too the help of school
regulations, such as the one forbidding sleeping
in class, to keep his audience attentive. A radio
course in music will succeed or fail according to
the personality of its spokesman. If Mr. Dam-
rosch's eminently suitable personality is not
made use of it may be a long time before another
such personality turns up.
We have said nothing here about the desir-
ability, in theory, of such a course, mostly be
cause we are confident that its desirability is>
already granted. Heaven knows, the young
hopeful is having enough stuff drummed into
him during his school years to "fit him for later
life." In this age of educational progress he is
given opportunity to take most anything in
"extra" courses from carpentry and cooking to
tire repairing and dentistry. These vocational
extras are useful. They make for remunerative
work hours after he leaves school. But lamen-
tably little attention is paid to equipping him to
enjoy his non-working hours in later life. Out
of every ten children exposed to eight years or so
of such musical training, at least one would dis-
cover that he actually liked the stuff. And that,
it seems to us, would justify the whole business.
"Our Readers Suggest-
9 9
lm
OUR Readers Suggest. . ." is a regular feature
of RADIO BROADCAST, made up of contri-
butions from our readers dealing with their experi-
ences in the use of manufactured radio apparatus.
Little "kinks," the result of experience, which give
improved operation, will be described here. Regular
space rates will be paid for contributions accepted,
and these should be addressed to "The Complete
Set Editor," RADIO BROADCAST, Garden City, New
York. A special award of $ro will be paid each
month for the best contribution published. The
prifc this month goes to William C. Duer, Den-
ver, Colorado, for his suggestion entitled "Elim-
inating A.C. Hum."
— THE EDITOR.
Testing an Audio Amplifier
I HAVE used the following method for localiz-
ing trouble in audio-frequency amplifiers
with considerable success.
The average manufactured receiver, as well
as most home-built sets, make no provision for
outputting the detector circuit to telephone re-
ceivers. Thus it is difficult to locate definitely a
fault in either the radio- or audio-frequency
channels. The system 1 am recommending will
indicate immediately in just which section of the
receiver the trouble exists.
Secure a hand microphone. If one is not availa-
ble, a transmitter button may be used with
equally good results if it is backed to a diaphram
so that vibration will actuate the button moder-
ately well. Connect this microphone, through a
push-button, in series with the primary of a 25
to I induction coil, such as is available from any
junked telephone set, and a six-volt battery.
The regular filament battery of the set may be
used. The secondary of the induction coil has
two leads, with clips, soldered to it for con-
venience in setting up. The following is the
method of operation:
Disconnect the detecjor plate-voltage lead
from the B battery or power-supply device,
and attach one of the clips mentioned to the
detector plus post on the set. Connect the other
clip to the point on the battery or power-supply
device on which the lead to the set was formerly
connected (22.5 or 45 volts), as shown in Fig. I.
Now push the button in the microphone circuit
and speak into the microphone. Speaking into the
microphone causes a varying current to pass
6V
To * 45 V on B Bat
or oower device
FIG. I
An interesting circuit arrangement which
may be used for testing an audio amplifier
through the primary of the induction coil. This
induces current variations in the induction coil
secondary, which, being in series with the de-
tector plate lead through the primary of the first
audio transformer, in turn affects the battery
current in this winding, producing a variation
in the balance of the audio-frequency circuit.
Speech will be reproduced in the loud speaker
as the microphone is spoken into. If the audio
circuit is not functioning properly, no speech, or
at most, a distorted voice, will issue from the
loud speaker, thus indicating the trouble to be in
this part of the set.
W. J. MORROW,
Macon, Georgia.
STAFF COMMENT
THE method suggested by Mr. Morrow pro-
vides a convenient means of testing the audio-
frequency channel of a receiver. For experimental
and entertainment purposes a greater response
can generally be secured to voice variations by
inputting the secondary of the modulation
transformer or induction coil to the grid circuit of
the detector tube. This is easily accomplished
by connecting the secondary terminals across the
grid leak, which is generally an accessible por-
tion of the receiver.
Sources of Power-supply Hum
THE output of many receivers taking some of
their power from the mains is marred by an
excessive 6o-cycle hum.
Investigation in many instances reveals the
trouble to be due to sources often unsuspected.
In the case the writer has in mind, a non-techni-
cally trained friend bought a socket-power kit
about a year ago, and assembled and wired the
device himself. It was less satisfactory than
battery power because of the intensity of the
hum, which defied all efforts made to eliminate
it. He asked the writer to look the outfit over.
Upon opening the output circuit it was found
that only part of the hum came from the loud
speaker. The laminations in the power trans-
former were so loose that the resulting vibrations
could be heard ten or twelve feet away in a quiet
room.
Further examination disclosed that the voltage-
divider section consisted of a number of adjust-
able resistors of the carbon-pile type. Operating
the equipment with the power transformer re-
moved from the socket-power baseboard con-
firmed the belief that a portion of the hum was
due to the microphonic action of the carbon-pile
resistors brought about by the vibration trans-
mitted from the transformer through the base-
board.
The transformer case was opened and, after
the transformer had been warmed up cautiously
to about 100° C, was filled with molten battery
compound. The primary was energized while the
compound was still liquid so that the latter could
penetrate between the vibrating laminations.
421
The hum soon fell to a slight murmur, inaudible
six inches from the transformer.
As an additional precaution, the carbon-pile
resistors were replaced by the wire-wound type
which are now generally available.
HERBERT J. HARRIES.
Pittsburgh, Pennsylvania
STAFF COMMENT
THE microphonic effect caused by loose
carbon-pile resistors is unusually interesting.
The department editor has run across several
such cases in his own experience. Microphonic
hum will generally be eliminated when the ad-
justment of the carbon-pile resistors is tightened.
An R. F. Volume Control
OWNERS of three-dial five-tube radio
receivers who live near »one or more
powerful local stations often find that they have
such strong reception that the last audio tube, or
even the detector, is overloaded. Even where
there is no overloading there is often too much
volume for ordinary use, or control, by the usual
methods.
This difficulty may be remedied and at the
same time more economical operation secured
by the addition of a switch so connected in the
circuit that the first radio-frequency stage of
the set may be laid aside, so to speak, at the
desire of the operator. When the first stage is
not being used, one tube will be automatically
turned out and it will become unnecessary to
adjust the first tuning dial. The switch can be
installed in any commercial or home-made re-
ceiver, and its use will result in no loss of stability
or efficiency.
The author recommends a Yaxley radio
jack switch No. 60 for this purpose, but any
compact double-pole double-throw switch may
be used with complete success. The switch may
be mounted securely at any convenient place on
Tubes in operation
5 4
FIG. 2
A simple method of cutting out one radio-
frequency stage for local reception. In addition
to its economy this method of volume control
is conducive to high-quality reproduction from
near-by stations
422
RADIO BROADCAST
APRIL, 1928
the panel, preferably near the first tuning dial.
If a separate rheostat or ballast resistance is
not used in connection with the first tube of the
receiver, it will be well to obtain a resistance of
the proper value for the type of tube in the first
stage.
Connect the switch as shown in the diagram,
Fig. 2. In one position, all five tubes should light
and the first tuning dial should be in operation.
In the other position, the first tube should not
be lighted, and the first tuning dial should be out
of operation. For local work, and when extreme
selectivity is not desired, the latter position will
be found ideal, since it simplifies operation and
prevents the unnecessary use of one tube with
resultant extra load on the batteries. This switch
will be found to be a very effective, though rough,
volume control. Instead of tending to cause
distortion, as some volume controls do, it helps
to prevent distortion, by preventing tube
overloading.
ALBERT R. HODGES,
Clinton, N. Y.
STAFF COMMENT
IN SOME cases a similar degree of volume
* control can be obtained merely by turning off
the filament of the first tube, a switch being
provided for this purpose. In some receivers,
merely removing this tube from the socket will
effect the desired control, sufficient energy being
fed through various inductive and capacitative
channels to supply an adequate signal on local
stations.
Eliminating A.C. Hum
IN SPITE of the many improvements incor-
* porated in the modern socket power device,
a.c. hum has not been eliminated in many
receiver-power combinations in use to-day.
After trying various methods of getting rid of
this nuisance and achieving no real results, I hit
upon the hook-up shown in Fig. 3, which really
eliminated that a.c. hum.
The filter used was an output device designed
to keep the high d.c. current out of the loud
speaker windings. It was rated at 30 henries.
By hooking up the 2-mfd. condenser as a
shunt across one side and using three of the four
posts of the filter, the desired result was obtained.
Many of these "tone filters" already contain
condensers integral with the choke, which further
simplifies the hook-up. Fig. 3 shows the conden-
ser as part of the filter, and is self-explanatory.
WILLIAM C. DUER,
Denver, Colorado.
STAFF COMMENT
THERE seems to be no end of the possible
uses of the output device. Here we have an
interesting and logical use distinct from the
original purpose of the unit. Mr. Duer's sugges-
•Bon power ~
Unit
1
I
1
1
-OMMLH
To-Bon
Set
•
•
(Output device) •
mW.
O< Output ><
Unused
Det. Bt
—i n
|
To Det B +
tion recommends the use of a filter circuit in
addition to that already provided as a part of the
power-supply device, which, as our correspondent
suggests, is occasionally inadequate.
Phonograph Pick-up Switch
I AM using an electrical pick-up in conjunction
* with my phonograph and radio receiver. The
pick-up is of usual design calling for the removal
of the detector tube from its socket and the
substitution of a four-prong plug. This arrange-
ment is rather clumsy mechanically so I devised
the simple switching arrangement shown in Fig.
4, using a Yaxley No. 60 switch, which is
mounted on the panel of the receiver. An extra
socket is placed in the receiver into which the
pick-up plug is inserted. The switch throws the
input to the amplifier from the detector circuit
to the pick-up circuit.
FRANKLYN F. STRATFORD.
Jersey City, New Jersey
STAFF COMMENT
ASIDE from the convenience of Mr. Strat-
ford's arrangement, the switch short-
circuits the output of the detector when the
phonograph is being used, and vice versa, of
course, so that there is no danger of "cross talk"
On power unit
FIG. 3
An arrangement of apparatus which has been
successfully applied in the elimination of a. c.
hum
Switch
FIG. 4
A convenient switching arrangement for
controlling phonograph and radio pick-ups
between two audio circuits. This is particularly
desirable when the receiver is powered from
the lighting socket, since leaving the detector
output open, or suddenly throwing the amplifier
to it, may cause oscillations.
Stabilising With High-Mu Tubes
I HAVE been building and experimenting with a
^ Browning-Drake receiver, and after trying a
"Phasatrdl" and different neutralizing conden-
sers, I find that a cx-340 (ux-24o) tube in the
r.f. stage, with ninety volts on the plate, will
neutralize easily. A small balancing condenser
should be used. Considerable volume, with no
sacrifice in efficiency of the set, will result.
MIUTON HICKS,
Rockville Centre, Long Island.
STAFF COMMENT
IT IS possible to stabilize many radio-frequency
' circuits in this manner. The fact that the
high-mu tubes have a higher plate impedance
than those generally employed in radio-frequency
circuits in many cases more than counteracts the
increased regenerative effect due to higher am-
plification constant of the tube, with the result
that the circuit into which they are plugged is
relatively stable. Also, in the cases of two or more
tuned radio-frequency stages, the use of a single
high-mu tube, preferably in the radio-frequency
stage preceding the detector tube, will have a
slight detuning effect upon the tandem circuits
due to the introduction of a capacity discrepancy.
In other words, one circuit will be slightly off
tune, with the usual stabilizing effect.
It is always a good idea to switch the tubes
around in an oscillating circuit in an endeavor
to arrive at a combination giving the best results.
Another Output Arrangement
CEEING an article on output devices in a
^ recent issue of RADIO BROADCAST, I have
decided to send you a diagram of one which I
have used for three years. I tumbled on it in
fooling around with a choke output and find it is
particularly satisfactory as it provides for a head-
set without changing the loud speaker circuit.
It requires an amplifying transformer, two
condensers (of 2-mfd. and o.5~mfd.), and two
open-circuit jacks.
It will be noted, from the wiring diagram, Fig.
5, that the output of the set is fed through the
secondary of the transformer and that the 2-mfd.
condenser and loud speaker (in series) are
shunted in the usual manner. The variation from
the conventional circuit lies in the primary side
where you will note that a "jumper" is attached
to only one side of the B circuit. This gives
plenty of power for the headset without depriving
the loud-speaker circuit of enough energy to de-
crease volume.
Another advantage peculiar to this output
device is the fact that the total load on a power-
supply device remains constant when the loud-
speaker is removed from the circuit, thereby leav-
ing all voltages on tubes the same, regardless of
whether phones or loud speaker is employed.
I have made four of these in the past three
years using different audio transformers and
find that results are equally good; a relatively
cheap transformer I found to be as satisfactory
as an expensive one.
F. W. WOOLWAY,
Newton Centre, Massachusetts.
STAFF COMMENT
THE average audio transformer secondary
has a rather high d.c. resistance so that the
voltage actually on the last tube plate will be
quite a little below the terminal voltage of the
B voltage supply. Experimenters can try revers-
ing the transformer windings, i.e., keeping the
primary in the plate circuit and the phones
across the secondary.
FIG. 5
A flexible output circuit
A SET-UP OF APPARATUS IN ONE OF THE "RADIO BROADCAST" LABORATORIES
The measurements which are outlined in the article were made with this equipment. Note the radio frequency oscillator at
the extreme left. It is housed in a large tin wash boiler. The large loud speaker is the new Western Electric j6oAW cone
The Four-Tube "Lab" Receiver
By Keith Henney
Director of the Laboratory
A THOUGH many receivers have come and
gone since June, 1926, when the R. B.
"Lab" circuit was first described in
RADIO BROADCAST, the latter still represents the
criterion by which all other receivers are
compared in the Radio Broadcast Laboratory,
and the measure by which all four-tube receivers
are judged. There are several reasons for the
continued popularity of the "Lab" receiver;
the most important lies in the fact that, with good
component parts and a good layout of apparatus,
four tubes in this circuit seem to require a
minimum amount of energy from the ether to
deliver any required loud speaker power.
The "Lab" circuit receiver is a member of
that famous family which includes the Roberts
and the Browning-Drake, to mention but two,
and it employs, therefore, a single stage of neu-
tralized radio-frequency amplification followed
by a regenerative detector and the usual audio
amplifier. Since June, 1926, few startling inven-
tions or discoveries to do with circuits have ap-
peared in the field of radio, so the circuit itself
has changed but little. Experience has taught,
however, just where the inductances and their
related parts, condensers and tubes, should be
placed behind the panel for most efficient opera-
tion, and this alone might be considered quite a
big step forward so far as efficient design is con-
cerned. A bad layout of apparatus
can mean all the difference between
poor and good reception.
The following article, which is pre-
liminary to the publication of a
constructional article on the "Lab"
receiver, gives some useful informa-
tion on how receivers are designed,
how the component parts are meas-
ured, or what the voltage ampli-
fication of the detector or the
amplifier may be. The information
is available as a result of exhaustive
tests conducted in the RADIO BROAD-
CAST Laboratory, and although the
measurements were made with the
prototype of the "Lab" receiver scheduled for
description next month, they should appeal to
anybody interested in radio receiver design and
measurements generally.
A certain amount of engineering data can be
collected at home; to gather other data a labora-
tory equipped with instruments is necessary.
A typical "armchair" investigation was de-
scribed in the March RADIO BROADCAST. It told
how one could calculate the voltages appearing
at various points in an audio amplifier if one
knew the electrical dimensions of his apparatus
and the amount of power he desired from his
output tube. The data presented below result
from a definite series of laboratory experiments
designed to learn what is going on between the
detector output circuit and the antenna of a
receiver; in other words, their purpose is to take
up where the armchair engineer left off. As the
investigation tells a great deal about the "Lab"
circuit it should be interesting to those who al-
ready own such receivers, or those who are being
introduced to it for the first time.
In the "Armchair Engineer," which was the
title of the March article, we showed what
voltages were necessary in an audio amplifier
when a maximum of 700 milliwatts of undis-
torted audio power was to be delivered to a
loud speaker of 4000 ohms impedance, which
Detector
= 3
1-1
FIG. I
423
conditions obtain when a 171 type tube is in use,
delivering its maximum quota of undistorted
power. We have chosen 4000 ohms for the im-
pedance of the loud speaker as representing the
best value (twice that of the tube) for maximum
undistorted power output. Seven hundred
milliwatts of power is small compared to that
taken by a 4O-watt incandescent lamp with
which we are all familiar, smaller compared to
the 500 watts required by that common home
apparatus, the electric iron, but is greatly in ex-
cess of the power that can be collected from one's
antenna from a distant broadcasting station.
In other words, between the antenna and the
loud speaker, there must be considerable power
amplification. How great is this amplification,
how can it be measured? These are questions
that a laboratory investigation can answer, and
these figures enable a laboratory to form some
kind of an opinion on the overall efficiency of a
receiver.
In Fig. I is a two-stage audio amplifier which
includes two transformers whose turn ratios,
secondary to primary, are about 3 to I at 1000
cycles, a tube the amplification factor of which is
8 (about 7 of which can be realized), and a power
tube with an amplification factor of 3. The volt-
ages at several points in this system are given on
the diagram, showing that about 0.42 volts must
appear across the primary winding
of the first audio transformer if a
value of 700 milliwatts is to be
delivered to 4000 ohms.
It will be noted that the voltage
across any point is found by multi-
plying together the voltages appear-
ing on the grids of tubes in the cir-
cuit, the amplification constants of
these tubes, and the turn ratios of
the audio transformers. Thus the
voltage across the output of the
second audio tube (note that its
effective mu is 7 and not 8) will be
approximately:
0.42 x 3 x i .26 x 7 = 8.8
424
RADIO BROADCAST
APRIL, 1928
In Fig. I it will be seen that the voltage appear-
ing across the output of the final tube is not
26.5 x 3 (the grid voltage multiplied by the mu),
since only two thirds of the a.c. voltage in this
circuit is usefully employed across the output
load. The output, then, is about 53 volts.
We resort to Ohm's law to prove that this
value of 53 volts is adequate to give the requisite
0.7 watts of power, and in doing so we find that
the current in amperes (output voltage divided
by loud speaker impedance) is:
- Amperes
4000
And that the power in watts (voltage multiplied
by current in amperes) is:
. 0.7 Watts
A.F. Osc.
A.F Amp
R.F.Osc.
_Shie[dj_ _
+90
Ljand L2=90 T No.24 S.C.C.,2.5" Diam.
L3=10 T Wound about Center of Lj
4000
Thus we have proved that a voltage of 0.42
across the primary winding of the first audio
transformer is adequate for our purposes. Given
the constants of the transformers, tubes, and
loud speaker in an audio circuit, it is a simple
matter, therefore, to calculate the requisite volt-
age for any given power output, across any point
of the circuit.
ABC
0.7 0.14 0.014
0.6 0.12 0.012
0.5 0.10 0.010
1.5V.
FIG. 2
change when a signal is tuned-in. For example,
WEAF, 8 miles from the Laboratory and with
50 kw. of power in the antenna, reduces the
average plate current of this type of detector
to the low value of 300 microamperes, in other
words, produces a change of 1000 microamperes.
Signals from wjz, 30 miles distant with somewhat
0.4 0.08 0.008
e
0.3 0.06 0.006
0.2 0.04 0.004
0.1 0.02 0.002
100 150
DETECTOR DEFLECTIONS,// AMPERES
FIG. 3
200
THE DETECTOR CIRCUIT
less power, cause a change of 100 microamperes.
These changes in detector plate current are then,
a measure of the strength of incoming signals.
We must know the voltage across the first
audio transformer primary, produced by various
r. f. voltage inputs to the receiver and what
effect modulation at the transmitter has. We
learn from Carl Dreher, Staff Engineer of the
N. B. C., that the two stations mentioned above
are modulated, on the peaks of the audio signals,
to about 60 per cent., so that if we modulate a
local oscillator, or generator of radio-frequency
waves, to about 60 per cent, and impress known
radio-frequency voltages upon our receiver, we
can note the change in plate current and the
voltage across the primary of the first audio
transformer.
Instead of measuring the voltages across the
primary, in the Laboratory, we measured those
appearing across the secondary by using the
first audio tube as a vacuum-tube voltmeter
and then calculated that across the primary.
This was done by biasing the grid of this tube to
about 10.5 volts with 90 volts on the plate, when
the plate current was about 30 microamperes,
with no signal, and increased up to about 100
microamperes when there was a reading of 1.5
volts across the transformer secondary. Known
audio-frequency voltages impressed across the
input of this tube were plotted against plate
current to calibrate it as a voltmeter.
The steady detector plate current of 1.3 milli-
amperes was balanced out by placing a battery
and resistance across the microammeter, the
battery being poled so that it opposed the flow
of steady plate current. A key was placed in the
microammeter circuit so that the latter did not
read until the key was closed.
We then noted the vacuum-tube voltmeter
HAVING decided that we require 0.42 volts
across the primary of the first transformer,
we must now set about producing this voltage.
Up to the present time our calculations have
been purely mathematical but from now on we
shall require the help of laboratory instruments
before we can conclude our calculations.
Because we desire maximum sensitivity in
the new "Lab" circuit we shall use a grid leak
and condenser detector the average plate current
of which is about 1.3 milliamperes if a II2-A
type of tube is used with conventional values
of grid leak and plate voltage. We use this type
of tube because it is much less microphonic than
a 20 1 -A tube, because of its lower plate imped-
ance which gives us better low audio-frequency
response, and because it is capable of somewhat
greater amplification than its smaller brother
tube.
This 1.3 milliamperes plate current will
0.09
0.08
0.07
0.06
0.05
0.04
0.03
E = Voltage on R.F. tube grid to produce"
Detector Deflection of 100 (i Amps.
TurnRatw S.SStol'
_^~ "^ ^T T^^i f\ t n 1
Turn Ratio
600
1200
FIG. 4
APRIL, 1928
THE FOUR-TUBE "LAB" RECEIVER
425
0.009
0.008
0.007
0.006
i
0.005
0.004
0.003
0.002
\\
JE on Antenna to produce constant
Detector Deflection of lOOfiAmps.
600
1200
FIG. 5
deflections against input r. f. voltages and
percentage modulation, and the change in de-
tector plate current — which we shall call de-
tector deflections — against r. f. voltages.
The set-up used is shown in the photograph
at the head of this article, and in Fig. 2. It
comprised an audio-frequency oscillator, a
General Radio push-pull amplifier, and a radio-
frequency oscillator, the latter housed in a tin
wash boiler with a tight fitting lid. Across the
output of the audio amplifier is a 4O-milliampere
thermocouple in series with 1000 ohms to act
as a voltmeter for the looo-cycle modulating
energy. Across the output of the radio-frequency
generator is a variable resistance in series with
a thermocouple which measures the current
through this resistance. The voltage drop, at
radio frequencies, across this resistance, is
utilized to drive our receiver under test. This
voltage can be varied by changing the value of
resistance used, or by changing the current
through it. Large changes in voltage are pro-
duced by the former method, small changes by
the latter.
These are crude methods of measuring voltage
gain compared to the ultra refinements employed
in the Crosley Laboratory for example, where an
accuracy of better than 2 per cent, is possible,
or in the General Electric Laboratory, but they
are effective, as the following data will show.
Measuring the plate voltage of the oscillator
we find that it is 69 volts, and noting that the
current in its tuned circuit varies directly with
the plate voltage we assume that the ratio be-
tween the fixed plate voltage and the low-
frequency voltages from the amplifier fed into the
plate circuit of the r. f. generator is a measure of
the percentage modulation. The looo-cycle
voltages obtainable are from about 18 to about
35 r. m. s., which give us modulation percentages
of from 36 to 71 approximately.
If the modulation is changed while a constant
r. f. voltage is applied to the receiver in series
with its artificial, or "dummy," antenna, and,
secondly, if the modulation is held constant
while the r. f. voltage is changed, the following
facts are noted: the detector deflections are in-
dependent of percentage modulation, the a. f.
voltages appearing across the secondary of the
first audio transformer vary almost directly as
the modulation and as the r. f. voltage applied,
and the detector deflections vary approximately
as the square of the input r. f. voltages.
We learn that a 66o-kc. wave modulated 54
per cent, and producing a change in detector
plate current of 100 microamperes produces an
audio voltage of i .67 across the secondary of the
transformer. If this is a 3 x i turn ratio unit, the
voltage across its primary will be 0.56, which will
furnish ample power to the loud speaker from
a two-stage transformer-coupled amplifier of
the type shown in the photograph of the receiver
upon which these measurements were taken.
So far we have established several important
points. We have determined the relation between
detector deflections and detector output audio
voltages; we have found out the relation between
audio voltages and radio input voltages; and
we have decided that to get about 0.5 volts
across the input to the audio amplifier we need
a radio signal, 54 per cent, modulated, which
will cause a detector deflection of about 100
microamperes. We may now neglect the audio
amplifier, and deal only with the part of the cir-
cuit between the antenna and the detector plate
circuit. What we now desire is to get this 100-
microampere deflection with the least input
r. f. voltage to the antenna, the greatest amount
of selectivity, and the best characteristic, that
is, the most even amplification over the broad-
casting band.
There are several variables that need in-
vestigating; for example, the number of turns
included in the r. f. tube plate circuit must be
determined. Let us start by placing various
voltages at 660 kc. on the detector input di-
rectly, i. e., without going through the tuned
circuits or the first tube. Then we shall apply
voltages to the grid of the r. f. amplifier, and
finally to the artificial antenna. The result is
shown in Fig. 3, and was obtained by applying
the voltage drop across 20 ohms to the detector,
that across 3.3. ohms to the grid of the r. f. tube,
and that across 0.191 ohms to the antenna.
To get our loo-microampere detector de-
flection required about 0.5 volts when applied
to the detector input, about 0.085 volts when
applied to the r. f. grid, and only o.oo5-volts
when impressed across the artificial antenna.
It is difficult to translate these differences in
voltages into "gain," but it is interesting to
note that a ratio of about 6 to I in voltage ap-
peared by removing the driving r. f. voltage from
the detector grid and placing it across the r. f.
grid, and that an input voltage of five millivolts
produced 100 microamperes detector deflection,
and, therefore, if modulated about 54 per cent,
produced our required 700 milliwatts of audio
power.
Now let us vary the frequency of the impres-
sed voltages and see what happens. The de-
tector input has essentially a flat characteristic
over the broadcasting band. Applying voltages
to the r. f. grid gives the result shown in Fig. 4,
in which various turn ratios between detector
input and r. f. tube output are given. At a turn
ratio of 2.25 to I, where nearly one half of the
detector coil is in the plate circuit of the previ-
ous tube, the curve is flat, and as- the turns ratio
is increased more input voltage is necessary at
high frequencies to deliver the same detector
deflection.
When voltages are impressed upon the
"dummy" antenna, the characteristic changes,
and becomes peaked, with maximum amplifica-
tion near the middle of the broadcasting band,
the ratio between the lowest and highest point
in the curve being about two to one. This curve,
Fig 5, gives the input voltage required to give a
A FOUR-TUBE "LAfl" RECEIVER
An experimental breadboard layout of the "Lab" receiver which will be described constructionally
next month. The measurements outlined in this article were made with the layout shown here
426
RADIO BROADCAST
APRIL, 1928
12
constant deflection of 100 micro-
amperes, and when turned upside-
down, gives an idea of the overall
amplification characteristic.
Investigation of the artificial an-
tenna and coupling coil, consisting
of ten turns wound about the cen-
ter of the r. f. input coil, shows that
it resonates at about 900 kc. which
accounts for part of the humped
characteristic. Part of it is accounted
for by the rising characteristic toward
the higher frequencies noted in Fig.
5 and part by the looser coupling
between antenna and r. f input coil
at the lower frequencies.
Placing a coil and variable con-
denser in series with the antenna, so
that the entire system may be reso-
nated to the frequency desired, will
bring up the overall amplification of
the receiver as well as improve the
characteristic. It necessitates an ad-
ditional tuning control, and has the
unfortunate habit of making neces-
sary readjustment of the r. f. tuning
condenser whenever any change is
made in the setting of the antenna
series condenser. For these reasons, and because
a 2 to I characteristic such as shown in Fig. 5
is not bad enough to worry about, the antenna
series resonant system has not been added to
the "Lab" circuit. A further study of antenna
coupling systems is under way and it is hoped
that the result can be given to interested experi-
menters soon. The turn ratio of any good coil
should be 3 to i since greatest amplification re-
sults thereby. J
SELECTIVITY
ONE thing remains to be investigated — the
selectivity of the two tuned circuits and
that of the receiver as a whole. A small con-
denser of o.ooooj-mfd. capacity bridged across
the main tuning condensers and varied through
the point which resonates the circuit will
give an idea of the selectivity. Fig. 6 shows
both the selectivity curve on the r. f. circuit
and the overall curve.
A word about the
practical result of all
this investigation may
be interesting. In Gar-
den City, 8 miles from
WEAF, it is possible to
receive wjz 50 kc.
away without inter-
ference. It has been
easily possible to re-
ceive WJR when wjz
was on the air, a dif-
ference of 20 kc., and
on the higher frequen-
cies many stations
outside of Manhat-
tan, 15 miles distant
with perhaps 30 local
stations in operation,
have been received
regularly. In an Ohio
town, 100 miles from
panel. Coil resistance is especially
to be avoided in the antenna stage
for here the losses in amplification
and selectivity are directly propor-
tional to the resistance in the tuned
circuit.
Coils of small diameter may be
placed as close together as shown
in the photograph on page 425, al-
though it will not be possible to
neutralize the amplifier at one ex-
treme of the broadcasting band and
have it remain neutralized at the
other. If neutralization is carried
out in the middle of the band, it
will be fairly complete at other fre-
quencies and will not oscillate at
any frequency. The parts used in
the four-tube "Lab" receiver on
which the above tests were made,
are as follows:
LIST OF PARTS
4048
MMFD. OFF RESONANCE
FIG. 6
a broadcasting station, a similar receiver has a
choice of over 40 stations without appreciable
interference.
In none of these experiments has regeneration
been added to the detector, which, in fact, has
been operating at poor efficiency, since it has. a
high-impedance plate circuit at high frequencies.
As soon as the regeneration condenser is con-
nected, partially bypassing some of the r. f.
load, the detecting efficiency goes up, and adding
regeneration increases the overall gain and selec-
tivity at all frequencies, and improves the
characteristic. Figs. 2 and 7 give all electrical
constants for the two-tube "Lab" circuit. Owing
to the superior gain produced by the 1 12 type
of tube, we recommend it in both the r.f. am-
plifier and detector sockets.
As in all similar tuning systems, the efficiency
of the circuit as a "whole depends solely upon the
quality of the apparatus (especially the coil)
put into it, and their relative location behind the
12
UX-112
Shield (Optional) (CX-312)
UX-112
(CX-312) R.F. Choke
2 — o.ooo5-Mfd. Rernler Conden-
sers
I — 0.00005 j-Mfd. Precise Conden-
ser
I — Type N X-L Condenser
i — o.oooi Mfd. Averovox Condenser
i — o.ooi-Mfd. Aerovox Condenser
2 — Aero Inductances
2 — Samson 85-Mh.Chokes
4 — Benjamin Sockets
2 — Sangamo Type A Transformers
i — Ferranti Output Transformer
2 — Amperites, o.j-Ampere
i — Lynch Resister Mount
i — i.5-Meg. Aerovox Resistor
i — Yaxley y-Wire Cable
2 — cx-3i2-A (ux-ii2-A) Tubes
i — cx-371-A (ux-37i-A) Tube
i — cx-3oi-A (ux-2oi-A) Tube
If the receiver is to be operated in a location
where there are many stations, it will be well to
shield at least the r. f. stage. In the layout
shown in the photograph care has been taken to
keep all amplifier apparatus to one side of a
middle line, and all detector equipment on the
other side of that line. This facilitates the in-
troduction of a shield between the two circuits.
If the approximate
layout shown in the
photograph is followed,
constructors should
have no difficulty in
making the receiver
operate. Any good ap-
paratus may be used;
coil dimensions are in-
cluded in Fig. 2 and
commercial induc-
tances from General
Radio, Aero Products,
Silver-Marshall, and
Hammarlund have
been used with com-
plete success. An article
scheduled for the next
issue of RADIO BROAD-
CAST will describe the
construction of a four-
tube "Lab" receiver
in detail.
To Audio Amp.
o-*-
FIG. 7
This is the circuit diagram of the two-tube "Lab" receiver. As will we noted, the 112 type tube
is used in both r.f. and detector stages and the gain will be greater than that possible were 2OI-A
type tubes employed
gtfustc
from the
Ether
IT is with consider-
able difficulty and
some reluctance that
we report the first
public demonstration in America of
Professor Leon Theremin's "Music from
the Ether" on January 3151, 1927. We
sat in the passing glory of the Metro-
politan Opera House surrounded by a
typical opera audience, all in evening
dress, and watched and heard Professor
Theremin and his associate, Dr. J. Gold-
berg, extract violin-like notes from two
beating radio-frequency oscillators, and
our emotions, we must admit, were mixed.
Musically the demonstration was not
good, but one cannot criticize an amateur
who makes no effort to set himself up as a
musician; as a scientific demonstration
before a S. R. O. audience in no less a
place than the Metropolitan, .it was grand.
The audience was enthusiastic, it ap-
plauded, and roared "bravo" and "hero-
ique" and begged for more all because they
had watched two men without any visible
connection with the instrument they were
playing, wave their hands before a slender
rod standing vertically in the air, and
heard the tremolo notes of "Ave Maria,"
"Song of India," and other old favorites.
We must admit that we were more
interested in the audience than in the
music or the musicians; we wondered
how they would take it — those trembling
notes, often off key; we wondered who
they were, whether music critics, scien-
tists, or merely curious people, amazed in
any sleight-of-hand performances, or demonstra-
tions of forces unseen. We were interested, too,
in the electrical mechanism, which is so well
known to all workers in radio frequencies, in the
loud speakers, great triangular green boxes
standing high above the stage and showing off
very well against a black velvet drop.
Electrically, Professor Theremin's apparatus is
simple. It consists, according to La T. S. F. Pour
TOMS, for December, 1927, of a crystal-controlled
generator oscillating at a frequency, let's say,
of 100,000 cycles per second, and another oscil-
lator whose frequency may be varied continu-
ously so that the beat note between these two
generators, when fed into a detector and ampli-
fier, will cover the entire audio range of tones.
Because there is always an attempt on the part of
two such generators to "pull together" when
their frequency difference is small, some diffi-
culty is noted in securing low or bass notes. An
ingenious trick, also well known to radio experi-
menters, is used here in an attempt to avoid
such trouble; the second harmonic of one oscil-
lator is made to beat with the third of the other.
In this way Professor Theremin got down pretty
low in the frequency scale, but because his loud
speakers began to rattle at these frequencies or
because he was still bothered by his oscillators
"pulling together," these notes were not
good.
The loss in audio-frequency output occasioned
by using harmonics instead of the fundamentals
is not serious; the volume can always be brought
up by proper amplification. In fact the audience
seemed astonished at the volume produced by
these beating generators of radio-frequency
waves, for at times it was "sufficient to fill the
Metropolitan." Of course the audience did not
know, as our readers do, that volume much in
excess of this could have been produced if
needed; all that was necessary was additional
amplification.
In Professor Theremin's cabinets, then, were
two generators, one fixed in frequency, the other
variable. Tunes are played by bringing the hand
near a metal rod which is attached to the tuned
circuit of the variable oscillator, the hand, which
is connected to ground through the performer's
body, serving to change the capacity of the
tuning condenser — "body capacity," nothing
less, the bane of all radio experimenters of a few
years ago.
Volume is controlled by another conductor at
right angles to the tone
control and placed so
that it can be approached
by the other hand of
the performer. It is a
single loop of wire and
constitutes part of the
tuned circuit of the
crystal-controlled oscill-
ator. As is well known,
when the tuned circuit
of such an oscillator is
properly adjusted, maxi-
mum power is produced,
and at any adjustment
different from this condi-
tion, less power is gen-
erated. Thus, bringing
the hand near this loop
detunes the closed cir-
cuit and reduces the
power generated in the
fixed oscillator, but be-
cause of the crystal, its
frequ ency does not
change appreciably.
The device is extreme-
ly simple to " play,"
there is no complicated
fingering or bowing, as
of a violin, and there is
no labor on the part of
the musician to get
fortissimo passages, but
in this very simplicity
there are disadvantages. The violin gets its
timbre because of the complex manner in
which its strings vibrate; its notes are not
pure, »'. <;., good sine waves, but they are
more or less complex at the will or skill
of the musician. The violin, the tone of
which the "Thereminvox" most nearly
approaches, can be bowed on more than
one string at a time, thereby producing a
still more complex wave form, while the
electrical instrument can hit but one note
at a time, and that note ordinarily is
quite pure, like that of a child's voice. By
throwing a switch or two, the operator,
or player, can bias grids differently and
put into the output of one or both oscilla-
tors various harmonics, which results in a
change of timbre.
The "Thereminvox" glides smoothly
from one frequency to another; it cannot,
in its present form, jump from one note
to another an octave, more or less, dis-
tant. It cannot produce staccato effects,
or those of plucked strings, nor can it
produce any of the effects of percussion
instruments.
Let us not be too harsh on Professor
Theremin of the Institute Physico-
Technique of Leningrad. He is not a
musician. He is a physicist and has
several inventions to his credit, in-
ventions on such things as methods of
measuring weak field strengths, and as
early as 1926 made contributions to
what has come to be called television.
According to a Paris interview published
in La T. S. F. Pour Tous he stated of his
latest development:
This is not at all a plaything for me. It is much
more a concrete proof, an incontestable demon-
stration, of my conception of the arts and the
sciences. The two are but one to me. I have al-
ways been disturbed by the disdain with which
followers of art treat questions of science and of
engineering. And conversely, how many times
have these savants claimed that art was a word
PROFESSOR LEON THEREMIN "PLAYS" HIS "THEREMINVOX"
427
428
devoid of all meaning. To prove to the one that
science can render the greatest services in the
development of the arts, to demonstrate to the
other the fertility of an intimate collaboration
of the arts and sciences, is my aim.
Perhaps the orchestra of the future will con-
sist of many of these oscillators and many men
before them waving their hands. Certainly there
will be plenty of engineers who can put all the
harmonics into the tones the musicians desire,
and perhaps then the timbre will be more
pleasant to musicians.
It is reported that Rachmaninoff turned to a
member of the private audience which first wit-
nessed the demonstration of the apparatus, and
said, when she shouted "Bravo:" "Madame,
you exaggerate!"
of. C
Tube
Troubles
FROM various sources comes
the rumor that set engineers
are more pleased with the
heater type of tube, the 227
type, from the standpoint of lack of hum and
of general operating characteristics, than they
are with the straight a. c. filament tube. It is
said that set manufacturers would like to use
this type only and to forget the low-voltage,
high-current tube. How we run in circles, we
radio engineers. Three years ago a heater type of
tube, the McCullough, appeared on the market
after many demands from those (notably Pro-
fessor Morecroft in RADIO BROADCAST ) who
knew the possibilities of a unipotential cathode
tube. In Canada this tube became very popular;
in this country the manufacturers sold a com-
fortable lot of tubes. But in general the tube
people, independent and "corporate," have taken
a "high hat" attitude about it. And now, per-
haps, it will become the preferred tube after all.
Several readers have noted a strange periodic
increase and decrease in filament current in a. c.
tubes. These fluctuations are reflected, naturally,
in signal strength. On one occasion a reader
remarked about the fading he noted on his new
a. c. set while his neighbors were not so afflicted.
What is the reason? Perhaps it is the following:
If an a. c. tube has an open filament or heater,
it frequently happens that the broken ends actu-
ally make contact so that when the tube is
turned on current passes through the filament
or heater, causing it to expand in such fashion
that the ends are pulled apart. Thereupon the
signals disappear and a cooling of the filament
or heater takes place. After the cooling process is
completed the ends may again come together
and signals will be received until expansion
causes the ends to part once more. It may hap-
pen, too, in some localities, that a severe over-
voltage is applied to the heater or filament ter-
minals, due to line fluctuations. The heater tube
may get so hot that it refuses to operate. When
the voltage goes down the tube cools off and it
returns to normal functioning.
The a. c. tube presents a more severe problem
than does that of combined B and C voltage sup-
ply units. Line fluctuations may cause such
changes in the filament, or heater, terminal
voltages that the life of the tube is decreased,
while in a plate power outfit the increase in
plate voltage is balanced by a corresponding
increase in C bias and thus the tubes will not
be impaired.
Incidentally, the Samson Electric Company
take great pride in the production of a power
transformer which has a regulation of 5 per cent.
That is, the voltage across the secondary at no
load is only five per cent, higher than at full
load. We understand some transformers have
regulations as poor as 50 per cent., which may
RADIO BROADCAST
explain why filter condensers in power supply
units are prone to end their useful purpose at
odd intervals.
Another peculiar case of "fading," which has
nothing to do with a. c. tubes but is mentioned
here as an interesting case of possible incorrect
diagnosis, has been reported by A. H. Grebe and
Company. An owner of a Grebe "Synchrophase"
in Atlanta, Georgia, reported severe fading from
WSB about two miles distant. A. Gilette Clark,
the Grebe engineer who investigated the phe-
nomenon, found that the fading took place in
regular intervals, that the maximum signal did
not increase beyond a certain value which was
normal for a station of WSB'S power and dis-
tance, but abnormal for a case of ordinary fading
in which the peak values of signal strength might
be somewhat high, and finally, after a little time,
it was discovered that the fading coincided with
the passing of a trolley car, starting as the car
approached and continuing for some time after
the car had passed. This gave a clue upon which
to work.
"The most logical explanation that occurred
to us," says Mr. Clark, "was that the trolley
line, coming so close to the transmitter and re-
ceiver, acted as a conductor for 'carrier,' or
wired-wireless, propagation of the WSB signals.
Instead of coming in a direct line, the signals
received by this set probably followed the wires.
Now, in technical parlance, we find that if
'standing' waves were present on the trolley
wire and track, in the fashion of Lecher wires,
the trolley cars might act as sliders along the two
parallel wires, reducing the volume delivered to
the set as they passed through points of high
potential and not affecting it when at the nodes.
"Further investigation with regard to the
trolley car clue revealed that the lines of this
car service ran directly parallel with the WSB
antenna system in Atlanta and almost parallel
to the set owner's antenna system, although the
course altered slightly at about half way between
the station and the point of reception. Since the
nodes are one half a wavelength apart and the
station's wavelength is 476 meters, the action
should take place every time the car moves 238
meters, or about 785 feet."
ANOTHER wonderful new
"Gross invention has come to the at-
Exaggerations'- tention of the Laboratory.
It costs but $4 and anyone
wanting a good job can make from $i 50 to §300
a week selling the gadget to gullible radio
listeners! It will:
(1) Eliminate 50 to 90 per cent, of static
(2) Increase volume
(3) Save 30 to 40 per cent, on batteries
(4) Separate short-wavelength stations
(5) Bring in distant stations
(6) Tune-out powerful local stations
(7) Add a stage of amplification to your set
We suspect it is a wave trap, consisting of less
than a dime's worth of wire, a cheap variable
condenser, a box, and two binding posts.
Interesting
Technical
Literature
THREE booklets have ar-
rived in the Laboratory re-
cently. One is a handsomely
bound treatise on Cunning-
ham tubes. It contains, in eighty -four large-size
pages, data on all tubes made by this well-known
tube manufacturer; characteristic curves, as
well as a considerable amount of information
that will appeal to all who have read the tube
articles appearing from time to time in RADIO
BROADCAST, are also given. The book sells for
$2.50.
APRIL, 1928
"The Absorption of Sound by Materials" is
the title of Bulletin No. 172 of the Engineering
Experiment Station of the University of Illinois.
In the Bulletin, Professor Watson describes
methods of determining the absorption coeffi-
cients of many substances. The bulletin costs
twenty cents and should be useful and interesting
to studio designers and builders. The " Bureau
of Standards Circular No. 300" describes similar
data. This latter circular was issued in February,
1926, and can be obtained from the Government
Printing Office for five cents.
&feters for
Research
Workers
EVERY laboratory worker
takes keen delight in handling
beautiful instruments, be
they meters for measuring
millionths of amperes or Curie balances for
weighing radium. A catalogue from the Sensitive
Research Instrument Corporation has come to
the Laboratory. We regret that we have not
known this maker of precision meters before,
and are glad to be able to recommend the
Sensitive Corporation to readers who are en-
gaged in research requiring microammeters,
vacuum thermo-couples, radio frequency-
voltmeters, resistances, etc. All direct-current
meters from this corporation, even down to the
very sensitive meter reading four microamperes
at full-scale deflection, are protected by a
specially developed fuse wire so that it is im-
possible to burn out the moving coil system. We
feel sure that the makers of Sensitive Research
meters will be glad to furnish readers with in-
formation regarding their products.
DURING the last few
Short-Wave months we have listened to
"Hotes short-wave broadcasting from
PCJJ, Eindhoven, Holland,
and from the experimental station 5 sw at
Chelmsford, England, as well as to occasional
programs from American short-wave broad-
casters. We must admit we are not enthusiastic.
The quality is invariably poor, the fading severe,
and the whole affair strongly reminiscent of the
early days of broadcasting, when any signal was
worth getting, so long as it was from a long
distance. The quality from Europe may be due
to the poor transmission, but more probably is
due to what happens between transmitter and
receiver, and under the best conditions is not
worth listening to except as a stunt.
Ben B. Skeete, radio operator of the S. S.
Samuel Q. Brown, in a letter dated at Balboa,
Canal Zone, December 30, remarks upon the
short-wave broadcasting from American stations
and brings up one interesting point. This is the
fact that fading does not seem to ruin reception
of music, while it makes reception of sport events
highly unsatisfactory. Perhaps it is because the
ear supplies the missing measures of music, while
no stretch of imagination will tell one what is
happening in the final round of a closely fought
boxing contest.
Mr. Skeete states that best reception is had
from WGY'S experimental transmission on 32.77
and 21.96 meters, that KDKA on 26 meters seems
to tune so sharply that it is difficult to get the
modulation, that the latter's 62-meter wave is
strong but the modulation badly garbled, and
that WLW can be heard better on the Pacific
coast than in the eastern waters and that it is
difficult to get the modulation although the car-
rier is strong. Perhaps WLW is not modulating
the carrier to a very great degree? Station
KDKA on 62 meters is heard with great strength
and clarity in Garden City. The distance is about
300 miles.
AS THE BROADCASTER SEES IT
L. F. In Vaudeville
SOME twenty years ago, when most of
the great figures in the radio world of
to-day were still in the pants business,
or sending comments to each other in Morse
across the barren acres of West Farms in New
York regarding the excellence or otherwise of
their "sparks," a popular type of vaudeville act
was evolved from the work of Nikola Tesla on
high-frequency currents. The Tesla coil con-
sisted of two windings, with non-ferric coupling;
the primary was part of a closed oscillating cir-
cuit, with a condenser and spark gap. The con-
denser was charged by a spark coil or high-ten-
sion transformer. The secondary of the Tesla coil
usually led to a spark gap. The arrangement was
no more or less than a wireless transmitter with
the open, radiating circuit replaced by another
spark gap. In the larger sizes the Tesla coil
proper had to be immersed in oil, to control the
corona. Very high voltages could be secured at
radio frequency. Since the currents passed over
the surface of conductors, including the human
body, a man could allow potentials of a few mil-
lion volts to leap to a metal ball held in his hand,
without hurting himself, but scaring the wits
out of anyone who did not know what he was up
to. Hence the vaudeville application. I did it
myself on a small scale, with a Tesla coil fed
from a quarter-inch spark coil. I proudly pub-
lished an article on this marvel which, I asserted
without fear of contradiction, was the smallest
Tesla coil in the world. The secondary was
wound on a test tube, and protected by several
layers of empire cloth from the primary, which
consisted of a few turns of heavy rubber-covered
wire. In its full glory the apparatus threw a half-
inch spark which stung slightly when taken on
the bare skin, but produced no sensation at all
if allowed to jump to metal in contact with the
body. I astounded my family and the neighbor-
hood with it, at the age of twelve, while various
"professors" were profiting by the same stunt
at the sublimated nickelodeons, using much
larger coils, of course. Incidentally, DoctorTesla,
at that time an electrical investigator of the
highest renown, and in his productive period,
was something of an amateur vaudeville actor
himself, and once sent Sarah Bernhardt into
hysterics by sticking his head into a ball of
high-frequency fire generated in his laboratory.
Bernhardt was harmed more than he was.
But to return to the vaudeville aspect. It sank
into partial oblivion for a decade or two, ap-
parently. It is now being revived. In Variety, the
theatrical magazine, a review appeared a while
ago under the following caption: " Bernays
Johnson (4), Electrical Novelty, 18 Mins. ;
One and Full Stage, Hippodrome (V-P)." The
review was by the talented "Abel." He put the
seal of his approval on the act, devoting a full
column to the task, and ending with this sen-
tence: " nson is a natural for thrill exploita-
tion." The grounds for this verdic are worth
recounting.
After speaking of the stunt as a "dignified
ballyhoo act," Abel pays tribute to Johnson as a
"corking showman without being 'professional'
or show-wise in his manner of speech or presenta-
tion," which begins with a "scientific" exposi-
tion before the curtain. Then follow some high-
frequency demonstrations, such as the lighting
of a lamp without wires, the frying of an egg
ditto, and the transmission of the mysterious
energy through a bowl of goldfish and the human
body, "employing a comely woman for this
demonstration." A beautiful girl will help sell
anything, as the hosiery manufacturers know.
There is also a "defiance-of-gravity" experi-
ment, the idea of which, as explained by Mr.
Johnson, is to improve transportation by allow-
ing the traveler to get up into the air quite a
way, whereupon the earth obligingly revolves
beneath him, until he lets himself down where he
wants to go. Jules Verne stuff.
But this is only the introduction. "The big
punch in Johnson's act," Abel tells us, "is his
billing as ' the man who defies the electric chair.' "
The chair is stated to cost $6000. "Johnson an-
nounces that he will receive 350 amperes of cur-
rent through his body, thrice the quantity neces-
sary to electrocute a human being. Johnson
states that it is fear which paralyzes an electro-
cuted person and not the actual juice that kills
him, inferring that possibly the ensuing autopsy
has something to do with the physical destruc-
tion of a condemned murderer. Johnson con-
tends that by keeping cool and dry (perhaps a
trying condition for the average death-house
victim), one can withstand the shock. On that
theory, Johnson presents its demonstration. To
further prove that the juice is actually passing
through his body, a bar of metal is burnt to white
heat from a wire on his person, the dismembered
piece is caught in a pan by a 'nurse.' Two male
attendants in regulation prisoner's uniform com-
plete the cast."
Of course if even an ampere of honest-to-
goodness d.c. or low frequency a.c. passed through
Bernays' bones his soul would fly to heaven with
the speed of light (300,000 kilometers a second),
and his body would fall, a veracious carcass, on
the Hippodrome stage. But as he is working well
429
up in the kilo- or megacycles he gets away with
his fustian, and no doubt provides good enter-
tainment for the customers. He doesn't let it
get under his skin, to use the phrase literally.
I am told, however, that he is unable to follow
his own advice to the death-house inmates to
keep cool and dry. At least, one close-up witness
to Brother Johnson's demonstration told me that
he (Johnson) was sweating copiously and looked
uncomfortably scared while working his magic
at the last radio show in New York. He may have
been thinking of what would happen to him if
his Tesla transformer broke down. Such mis-
givings would not be irrational. I wish Bernays
luck, but, in my capacity as a consulting engineer,
bestow on him gratis the advice that he had
better filter and dry the oil in the said trans-
former frequently.
Rosa Ponselle Before the
Microphone
I CAN see where singing before the microphone
must be simpler in some ways for, say, an
opera singer, than performing before an audi-
ence. Not as much voice need be used, and acting
becomes unimportant. But if any one thinks that,
on the whole, singing for the radio is less com-
plicated than doing it on the stage, he should
watch Miss Rosa Ponselle modulate her way
through a Victor hour, as 1 did recently. Lately
1 have become interested in how great artists
get their effects, as far as one can judge out-
wardly, and wherein they differ from the amiable
but depressing amateurs who helped us out in
1923.
Miss Ponselle is a handsome and robustly
built young woman, who looks the prima donna
and would get a seat in the subway, even in this
unchivalrous age, if she ever rode in it. She does
not appear at all nervous as she faces the micro-
phone, although there is some tension in her
attitude — mainly energy and determination.
She stands about three feet from the microphone
and not much farther from the conductor, who is
one of the regular maestri from the Metropolitan.
The orchestra of about thirty-five is behind
her, and a mixed chorus of about the same num-
ber in back and to one side, fully thirty feet from
the transmitters; but they come through very
well. Miss Ponselle, when she is in action, does
five things; she sings, acts the role in a modified
way, varies her distance from the microphone,
follows the conductor, and watches her own
monitor or coach who signals to her from the
control booth. Talk about coordination! The last
430
RADIO BROADCAST
APRIL, 1928
stunt is accomplished as follows: The singer
faces a side of the studio in which there is a large
window through which she can see the group in
the monitoring booth, consisting of a few engi-
neers and program people, maybe a vice-president
or two, and Miss Ponselle's assistant. The
window is double glass, with an air space inter-
vening, and those on the booth side hear only
through a loud speaker. Miss Ponselle weaves
back and forth as she sings, varying her distance
from the microphone according to the loudness
of the passages. During piano portions she ad-
vances to a point where her mouth is about
eighteen inches from the transmitters, while
when she wants to hit a note hard she may get
as far away as four feet. By this device she sings
the aria so that it sounds natural to her, and at
the same time she compresses her volume range,
as far as input to the microphones is concerned,
for the best results on the air. The control opera-
tors have little to worry about, but Miss Ponselle
has enough, because, after all, she does not hear
the results of her divagations in a loud speaker.
Her assistant supplies the loud speaker ear for
her. When he considers that she is getting too
close he moves his hands apart with the familiar
"So big!" gesture of the fisherman: when she is
an ordinary artist is one of character as much as
physical equipment, which is no doubt true,
especially as no one can say where the one begins
and the other ends, nor precisely how they inter-
act.
Miss Ponselle does five things when she broad-
casts. But those are only the main heads. Each
one of them includes a multitude of minor
coordinations. The singing itself, for example —
breathing and voice production and diction and
all the rest of it. The acting, as I remarked, is
somewhat mechanical in a broadcast rendition,
but the fact that the artist retains it even when
her audience cannot see her shows how intricately
such habit-formations are organized. She evi-
dently feels that, if she dropped it altogether,
her vocal expression might suffer. As one watches
the headliners one realizes, if it was not plain
before, that this business of singing and playing
is a hard game, if one wants to excel in it. So
many things must be done at once, and all timed
to a split second. For myself, I return thanks
that my feet were never set on that path. I should
as soon think of walking a tight-rope stretched
over Niagara Falls and at the same time de-
monstrating Green's theorem in mathematical
physics to the newly-weds on the shore.
leading to the station, either through a trans-
former or by means of a loud speaker placed
before a microphone. I should imagine that the
transformer coupling would be preferable. A
number of outdoor antennas are available. The
procedure of listening and re-broadcasting is
quite intricately systematized, there being a
scouting operator who catches stations for Mr.
Godley, the latter exercising his fine hand only
on valuable prospects, such as West Coast broad-
casting stations. Mr. Godley listens to the signals
as they sound on the air after re-broadcasting,
by means of a monitoring receiver tuned to
WAAM. Special attention was paid to eliminating
electrical noise in the neighborhood of the listen-
ing post, so that man-made static has been re-
duced to a minimum. The DX re-broadcast is
said to be a popular feature on WAAM 's programs.
woe
THE well and favorably known Davenport,
Iowa station stays on its assigned frequency by
means of a beat frequency indicator developed
by the Washington Radio Laboratories, of
Washington, D. C. This device mixes the out-
put of a crystal oscillator, calibrated by the
TWO OF THE 3 LO STUDIOS AT THE MELBOURNE STATION
The illustration on the right shows the main studio of the station. The studio is only partially acoustically treated and the presence of spectators
in the wicker benches helps to deaden the room. In both these studios the use of an illuminated device for communicating with the performers while
they are before the microphone is shown. This signal system has gradually been abandoned in the United States with the increase in the number of
professional microphone performers
too far from the pick-up he advances the parallel
palms of his hands to within a few inches of each
other, and when she is hitting it right the coach
signals with a short vertical gesture, palms
down, quite like an umpire saying "Safe!" to a
runner who has just slid into a base. He also
nods his head, to reassure the diva still more.
Almost all the time she is right, but no doubt
she gets considerable comfort from the signalled
affirmations to that effect. It is very comical,
as she goes more or less mechanically through
the actions natural to the aria — clasping her
hands on her chest and so on — to see her glancing
constantly, with the hundred-thousand candle
power eyes which are part of her operatic equip-
ment, now filled with mute appeal quite apart
from the beauty of the notes, to see whether she
is treating the microphone properly. It is also
impressive. Genius, it has been said, is an infinite
capacity for taking pains. It is that, partially,
and in a broadcast studio as much as anywhere.
Maybe one of the obscure girls in the chorus
started with a voice as good as Ponselle's, but
was too easy-going to get very far with it. All
that amounts to saying, of course, is that the
difference between a successful opera singer and
Among the Broadcasters
WAAM
WAAM of Newark, around this time of the
year, is just getting through with its winter
DX re-transmissions. The transmitter, situated
in Newark, New Jersey, is fed for this purpose
from a battery of receiving sets in a more rural
location at Cedar Grove, presided over by no
less a distance shark than Paul F. Godley. It
was Paul Godley, as no good radio man has for-
gotten, who first received American amateur sig-
nals in Europe, something like six years ago. He
sat in a tent on a beach in Scotland, and picked
up the signals of U. S. hams on a Beverage wave
antenna. The phones kept his ears from freezing.
Now he listens in a sort of dug-out underneath
a house — what might be called a radio cellar —
and probably keeps more comfortable. The DX
re-broadcasting starts at about i A. M. Several
receivers are used, the main one being an eight-
tube loop outfit using a.c. tubes, affording four
stages of radio amplification, a detector, and
three stages of double-impedance audio ampli-
fication. The receiver is coupled to the land line
Bureau of Standards, with radio-frequency from
the broadcast transmitter. The latter voltage is
picked up by means of a small antenna. The two
radio-frequency voltages are mixed in a com-
partment which is shielded from the standard
oscillation generator. A beat frequency is pro-
duced in the output of a rectifier tube. This beat
frequency indicates its presence in two ways.
When it is sufficiently high it produces an audi-
ble note through a loud speaker. Below about
forty cycles per second the indication is visual.
A relay capable of following fluctuations up to
forty per second lights a green light when the
broadcast transmitter is radiating the same fre-
quency as that generated by the standard oscil-
lator. When the transmitter frequency deviates
a red light glows, or the red and green lights
flicker in alternation. If this frequency is above
fifteen per second both lights appear to be lit
continuously, owing to the well-known phe-
nomenon of persistence of vision. The operator
of course endeavors to keep the transmitter
frequency so close to his standard that the green
light glows alone, or the two lights alternate
very slowly, corresponding to a beat note of
only a few cycles per second.
APRIL, 1928
AUSTRALIAN BROADCASTERS
431
AT PENNANT HILLS, SYDNEY, AUSTRALIA
The transmitting room whence broadcasting programs received in England, Canada, and the United
States have issued. In addition to the broadcasting transmitters, there is a marine transmitter at the
extreme left, while the other panels fcrm the short-wave set
The device operates on batteries, the voltage
of which must naturally be kept constant.
Meters are provided for checking. The highest
voltage required is 100. Storage batteries are
recommended as a source. Like other piezo-
electric controls, this indicator must be kept
in a constant temperature box if its indications
are to be relied upon.
3 LO, Melbourne
WE PRESENT photographs of the studios and
control equipment at the Australian station,
3LO. The main studio, it will be noted, contains
plenty of wicker settees, for visitors. There is
room for two hundred in the studio, which is
therefore as much an auditorium as a broadcast-
ing studio, and spectators are not merely wel-
come, but necessary. Every one adds a definite
amount to the total absorption of the room, and
when the place is filled the period of reverbera-
tion is markedly reduced. The platform for the
performers is partly covered with carpet, as the
picture shows, and the wall nearest the camera is
draped. The absorption of this end of the studio
is fixed, therefore, and with an audience in the
body of the room the period is about right for
broadcasting, there being enough reverberation
to produce a lively effect, and not enough to set
up standing waves and disturbing rattles.
The announcer, it would appear from the
picture of the main broadcasting hall, sits at the
table on the right and talks into his own micro-
phone. The concert microphone is stage center.
Each microphone box is surmounted with a
signal lamp. There is also an illuminated device
for communicating with the performers during a
number; it may be seen hanging from one of the
rafters, over the center aisle. This scheme was
formerly used at some United States stations — •
WGY, for example — but with the advent of pro-
fessional performers it is no longer very service-
able. At most of the large stations many of the
artists are on the air several times a week, and
they know precisely where to stand and what to
do for given effects.
The photograph of the control room shows a
good-sized PBX, and an amplifier panel not
unlike the American layouts. The boxes on the
table may be portable amplifiers.
Sydney, Australia
ANOTHER accompanying photograph gives
one a good idea of the transmitting room at the
Pennant Hills station whence broadcast pro-
grams received in England, Canada, and the
United States, have issued. The control table
with a monitoring receiver and apparently a
small telephone switchboard is in the foreground,
with a telegraph table to the right. The trans-
mitter panels stand along the rear wall. The
marine transmitter is at the extreme left; the
other panels comprise the short-wave set. The
design is a combination of panel -and pipe-rack
construction probably all right if the place
doesn't catch fire.
Studio Scandal
XAOST tenors start rehearsals with nicely
*** starched collars and cute neckties, only
to tear off both before they get halfway through.
Few male singers appear in evening dress. The
headliners. with occasional exceptions, dress very
informally. Soft collars, in blue or some other
fairly bright color, are the rule. When wjz had
its studio on Forty-Second Street in New York
City one Italian tenor got down to his under-
shirt on a warm night. He wouldn't sing in his
shirt, so what could the studio staff do? But
ultra-modern studios are artificially ventilated,
so that the air remains at sixty-eight degrees
Fahrenheit, winter and summer, while the humid-
ity is kept at the optimum figure of fifty. Thus
the artists remain comfortable, although dressed.
They are right, however, in taking off whatever
incommodes them. The late Victor Herbert, in
the year when he conducted the Stadium con-
certs during the summer in New York, used to
rehearse the men clad in his white flannels from
the waist down and only B.V.D's from the waist
up, on hot mornings. He was a fine old Berserker,
and looked better with his chest bared to the
zephers than when he appeared, starched per-
force, before the haute monde in the evening.
Studio Slang
HP HE operators used to yell, "You're on the
1 air!" when handing the program over to
studio or to the field forces. This phrase has
changed. "Take it away!" is now de rigueur.
"It" refers to the program, of course. This
phrase seems very picturesque to me and I get
a certain kick out of hearing it. The NBC slang
for "field" or "outside" annoys me, on the con-
trary. It is "Nemo" and was originally adopted
for purposes of camouflage in some obscure and
forgotten contractual tangle. But now that it
has become a habit it cannot be eradicated and
I expect to hear it for the next forty years, unless
broadcasting kills me earlier.
When Orchestra Leaders Sing
THE best conductors seem to have the
worst voices, and when they sing a bar to
show the musicians what they want even the
page boys around the studio snicker behind their
handkerchiefs (when they have any). Mr. Setti,
the brilliant maestro of the Metropolitan Opera
Company who frequently broadcasts incognito,
should be excepted. He has a good voice and
sometimes sings right through a selection, ac-
companying the orchestra. He may have been
CONTROL ROOM OF 3 LO, MELBOURNE
432
RADIO BROADCAST
APRIL, 1928
8175Q
an opera singer himself once, before he started
conducting for them. Now and then he goes
flat, but it does not bother him, for after all his
singing is supererogatory. He. annoys the control
operators, who- maintain that his singing inter-
feres with their getting a balance during the
rehearsal. But none of them has ever had the
nerve to go out and tell him so. They are right; but
if a man wants to sing it is generally dangerous
to interfere with him. He will let you criticize his
wife, his children, and the shape of his head be-
fore he will let you stop him from singing when
the spirit moves him.
An Engineer's Embarrassment
IT IS true that the more a man is educated,
soundly, the less he is surprised at any-
thing. And conversely, if he knows little, he is
frequently astonished at perfectly rational be-
havior which happens to be beyond his compre-
hension. In the last few months I have had
occasion, quite often, to venture into unfinished
studios where painters were at work, there to
warble various notes or to clap my hands to get
some idea of the reverberation. The results have
been almost as dreadful as when Mr. Hanson
and I invaded a church for a similar purpose, as
recounted in these columns a
while ago. Some of the painters
have nearly fallen off their
scaffolds, causing me no small
amount of anxiety lest 1 should
give rise to a damage suit z=200Q
against my company. Others
have apprehended that I was
mocking them, and the looks
they directed toward me said 81.75 Q
as much as that they were
ready to paste me in the eye or
to go on strike. In most cases I
have slunk out after banging
my hands together much fewer
times than I had intended. Then the painters
would glance at each other, and 1 knew as soon
as the sound-proof door closed they would say,
"The poor nut!" Well, they may be right, but
not on the grounds they thought. What I was
doing was just as rational as painting.
Radio Inspectors — Fine Fellows
WITHOUT doubt there is something magical
about radio. Have you ever considered the
remarkable infrequency of bureaucrats among
the government employees in the business? The
fact that where I have my office now no trans-
mitting apparatus exists, so that the radio in-
spectors do not visit the place, has made me
think of them. The men in the U. S. Super-
visors' offices are a fine lot of fellows. It is rarely
that an operator is high-hatted by one of them.
On the contrary, the inspectors and their as-
sistants frequently go out of their way in order to
help some boy in difficulty about his ticket. They
form a marked contrast to the poisonous snobs
in the naturalization offices, for instance. Maybe
part of the difference is due to radio; 1 like to
think so, anyway.
Commercial Publications
THE Daven Radio Corporation, of 158 Sum-
mit Street, Newark, New Jersey announces
"Super-Daven" resistance units, wire wound,
available in values from 10,000 to 3,000,000
ohms, and accurate to within one per cent. The
inductance is given as "practically negligible,"
with the distributed capacity likewise minimized.
The temperature coefficient is o.oooi. At a
slight additional cost, resistors are furnished with
a closer tolerance than one per cent, and with
zero temperature coefficient. These units mount
in clip holders. The line is offered for use as lab-
oratory standard resistors, voltmeter multipliers,
plate and grid resistors, high-voltage regulators,
and in telephone and telephoto work. No doubt
broadcasters will find uses for them.
I. E. JENKINS & S. E. Adair, of 1500 North
J Dearborn Parkway, Chicago, describe in their
Bulletin No. 5 a wire-wound gain control,
Type GL 35. This instrument contains n sepa-
rate resistance units, each wound non-inductively
with enameled Nichrome wire. The total resist-
ance is 350,000 ohms, arranged in logarithmic
steps, resulting in a straight-line TU variation.
The resistance values are good to less than one
per cent. The housing is an aluminum shield, the
end pieces being three inches square; a depth of
4! inches is required behind the panel.
IN MARCH we started a review of the pam-
phlet entitled Samson Broadcast Amplifier
Units, issued for limited distribution by the
Samson Electric Company of Canton, Massachu-
81.750
163.5Q
163 5 Q
40.4 Q
Z=?OOQ
Z=200Q
40.4 Q Z=200Q
81.75Q
(A)
(B)
FIG. I
setts. This detailed review will now be continued.
On Page 18 we find a discussion of the design
of a volume control arranged in 2-TU steps, with
a maximum resistance of 100,000 ohms. The
2-TU drops may be secured by tapping off 79
per cent, of the voltage each time, or 79 per cent,
of the resistance, as long as the voltage is pro-
portional to the resistance. The first tap would
therefore be at 79,000 ohms.- The description is
not entirely clear in the pamphlet, and there is
an error in that the first tap is given as 59,000
ohms. On Page 19 there is further discussion of
gain controls, and the design of one covering a
range of loTU in i-TU steps is given. This starts
with a minimum, or first tap value, of 161,000
ohms, and continues in progressively increasing
steps until the whole 10 TU have been covered.
Another potentiometer affords a range of 50 TU
in 10 steps of 5 TU each. The total resistance of
each device is 500,000 ohms. One of these may
be used across the grid and filament of one tube
of an amplifier and the other across the input of
a succeeding tube, thus providing fine and coarse
regulation of gain as required.
The material presented under "Pad Design"
will prove extremely useful to many broadcasters
although there is no attempt to derive the formu-
las given nor to adhere to a conspicuously logical
sequence in the discussion. The relationship be-
tween the impedance on either side of a con-
ventional resistive T- or H-network, the im-
pedances of the legs, and the TU loss introduced,
are given at length and worked out to a practical
conclusion in the form of a table (Table III).
From this tabulation, knowing the TU drop
desired, one may read the value of Zi and Zz for Z
equals 200 ohms and Z equals 600 ohms. Z is the
impedance on either side of the pad (only bi-
laterally symmetrical pads are discussed); Zi is
the total value of the series or X-legs; Z2 is the
value of the shunt or Y-member. For example,
if one requires a 20 TU pad presenting 200 ohms
each way, one finds from the table that Zi must
be 327 ohms, while Z2 is 40.4 ohms. The result,
for an H-network, would be the pad of Fig. i-A,
while if a T-network with the same electrical
characteristics is chosen the arrangement will be
that of Fig. i-B. Numerically the difference is
simply one of splitting Zi into four parts or into
two parts, for the corresponding number of legs,
depending on whether a balanced network is
required or not.
On Page 21 there is apparently an error, L]
and Lj having been printed for Zi and Z2, re-
spectively. The article as a whole seems to have
been written by an engineer who knew what he
was about but had no unusual skill in presenting
the subject for the education of others. This de-
fect is not extremely important, inasmuch as
most of the people who consult the pamphlet
will be more interested in the results than in
the procedure required to reach them. In some
ways the treatment is more extensive than that
given in the article devoted to
the same subject in this depart-
ment for September, 1927, par-
ticularly in the working out of
the table, but in other respects
it is less thorough than the
latter, and readers who are
much interested in pad design
might go back to the Septem-
ber, 1927, RADIO BROADCAST
article after reading the Samson
pamphlet, and also to the dis-
cussion of the General Radio
write-up on pads in the Janu-
ary, 1928, RADIO BROADCAST.
The limits within which all these pad designs
hold good are well stated in the Samson booklet,
which broadcasters may secure by writing for it
on their letter-heads; this portion is well worth
quoting:
"It is assumed that the transformer is ideal, that
is, that it has. a negligible resistance in its wind-
ings, and an infinite input impedance with the
output windings open-circuited, and vice-versa.
It is also assumed that the line or other circuit
element into which the transformer is working
has pure resistance of the impedance value given
as the impedance which the transformer is de-
signed to match. It is also assumed that the
transformer has no leakage reactance, that is,
that all magnetic flux which links one winding
links the other. In order that all these different
things may hold, it is necessary that the con-
sideration be based on a certain range over which
the transformer practically meets all these con-
ditions, and where those not depending on the
transformer hold. Of course, as the frequency is
reduced more and more, or as it is increased
more and more, below and above this range
respectively, these assumptions must fali down.
Therefore, it must not be thought that a 'pad
is a pad ' over all ranges of frequencies. However,
over the range that the circuit element is de-
signed to work, these ideas hold very closely,
and the simple addition of the attenuation of
individual pads to obtain the total attenuation
gives the desired working result, and that is the
justification for its wide use in communication
circles."
No "Motor-Boating"
A Quality Audio Amplifier Which Will Not "Motor-Boat"
By H. O. Ward
RADIO BROADCAST Photograph
A HIGH-QUALITY RESISTANCE-COUPLED AMPLIFIER
The two condensers and the resistance in the lower left-hand corner
prevent the amplifier from "motor-boating." The loud speaker con-
nects to the two Fahnestock clips alongside of the output condenser:
the two similar clips in the lower right-hand corner are used to read
the plate current of the last tube
(EVERAL years ago the resistance-coupled
amplifier was much in vogue, and justly so,
for it is an excellent type of audio amplifier
and is capable of giving practically equal re-
sponse over the entire audio-frequency range.
Its popularity at that time was comparatively
short-lived — just why, it is hard to say. Since the
introduction of the 240 type tube some time ago,
however, there have been indications that the
resistance amplifier will stage a comeback.
The amplifier described in this article has a
fiat frequency response curve from 60 cycles up
to about 6000 cycles, it will not "motor-boat"
when operated from any ordinary B power unit,
and it has a voltage amplification of about 400
from the input of the amplifier to the grid of the
power tube. A curve showing the frequency re-
sponse curve of the amplifier is given in Fig. i.
In Fig. 2 is given the circuit diagram of the ampli-
fier. There is nothing unusual about this amplifier
with the exception of the anti "motor-boating"
circuit which we have indicated by enclosing it
in dotted lines. This anti "motor boating"
circuit originated in the engineering department
of the F. T. Cunningham Company a short while
ago, and the circuit, tested in RADIO BROADCAST
Laboratory, has proved very satisfactory. It
should be noted that the circuit is arranged so
that the plate current of the detector and first
audio tubes must pass through resistance RI.
To test the circuit the amplifier was con-
nected to a B power unit and with the resistance
RI short-circuited the amplifier immediately
began to "motor-boat." As soon as the short-
circuit was removed the "motor-boating"
stopped. It was found that the value of RI,
necessary to produce stable operation of the
amplifier, varies with different B power units.
With some power units a resistance of 20,000
ohms is sufficient, while with other power units
a resistance of 100,000 ohms is necessary. Since
the latter size resistance seems to be effective
in all cases, it is suggested that those who con-
struct the amplifier use this value of resistance.
As the plate current of the first tubes in the
4M
I"
i -
^-NS.
RADIO BROADCAST
LABORATORY
To Plate Circuit 0 006 mfd
of Del. Tube
FIG. I
amplifier and the detector tube must flow
through this resistance, it might be thought
that there would be an excessive loss in voltage
across it. Such is not the case, however, as the
following data
will show.
For this test
the amplifier was
set up with a
detector circuit
connected ahead
of it. The detec-
tor tube used was
also a 240 type
tube and the
same voltage was
applied to the
detector tube as
was applied to
the first and sec-
ond audio tubes
in the amplifier.
433
\OLTAGE
OHMS
DETECTOR
'35
O
45
135
[ OO.OOO
40
190
O
55
190
1OO.OOO
43
This table indicates the voltage actually
at the plates of the detector and first audio
tubes for two different values of applied volt-
age. A difference of 10 or 20 volts at the plate
of a tube will not change the characteristics of
the amplifier and since the loss in voltage due
to- the resistance RI is of this order, it is evident
that the amplifier will not be affected.
The following data were obtained:
FIRST AUDIO
83
95
115
93
The reason that the detector plate voltage is
lower than 'that of the first audio stage for the
same values of resistance is because the current
drawn by the latter is less than that drawn by
the detector.
The recommended values of plate and grid
resistances and coupling condensers are as in-
dicated in Fig. 2 and the frequency response
curve shows that the values specified give the
desired flat characteristic. If larger values of
resistances are used the gain of the amplifier
will fall off at the high-frequency end. Larger
values of coupling condensers tend to better the
response at low frequencies but since the re-
sponse is satisfactory with the values given, it is
a waste of money to use any larger condensers
unless you have them on hand.
The correct voltages to use on the grids and
plates of the three tubes of the amplifier are
given below. The letters Bi, Ci and B2, C2 in the
table below refer to similar notation in Fig. 2.
TST AND 2ND AUDIO Tubes
Grid Plate
Voltage Voltage
Ci B,
i ,o to 1.5
1.3
3.0
135
'5?
POWER TUBE
1 12 TYPE
Grid
foliage
Ci
6
9
10.5
Plate
Voltaic
82
go
135
157
Grid
Voltage
Q
16.5
27
33
40.5
171 TYPE
Plate
Voltage
62
90
137
157
180
The following parts were used in the amplifier:
i — Durham o. i-Megohm Resistor
3 — Durham o.25-Megohm Resistors
3 — Durham 2. o-Megohm Resistors
3 — Sangamo o.oo6-Mfd. Fixed Condensets
6— X-L Binding Posts
3 — Benjamin Sockets
i — 4-mfd. Tobe Condenser
i — Amertran Choke Coil, Type 854
5 — Fahnestock Clips
i — 6-Ohm Pacent Rheostat
4 — i Mfd. Dubilier Bypass Condensers
3 — Lynch Double Resistor Mounts
i — Lynch Single Resistor Mount
0.006 mfd. UX-112(CX-3ir)Of 2-4 mfd.
Output dipt
FIG. 2
A TWO-TUBE SCREEN-GRID RECEIVER
Maximum efficiency is obtained by using metal front and sub-panels while there is also a metal plate
between the r.f. and detector tube circuits. The active parts used in this receiver are listed on
page 435, and the circuit diagram is also given there. A copper cylinder is used to shield the tube
An Experimental Screen-Grid Receiver
THE introduction of the screen-grid tube is
most opportune for that section of the radio
world which is constantly in search of a
new plaything. The ux-222 (cx-322), or
screen-grid tube, offers the advantage of an
extremely high gain per stage when used with
the inside grid as control grid and with a steady
polarizing voltage impressed on the screen. As
is to be expected, the high amplification factor
is accompanied by a very high plate impedance,
necessitating a high impedance in the coupling
unit if the advantage of the high amplification
factor is to be realized to its fullest extent.
While the screened-grid tube requires no
neutralization, careful shielding is necessary,
particularly if several stages are used.
Elaborate shielding is not required if only a
single stage is used. For this reason, a single-
stage amplifier adapts itself to preliminary
experiments with the new tube. The set described
here is purely experimental and no claims are
made as to the results obtainable. Tests have
shown that it is stable, and results in operation
approach those obtained with three tuned cir-
cuits and fixed input in a three-stage amplifier
using standard tubes. The selectivity without
regeneration is comparable to that obtained in a
normal two-circuit system but the figure of merit
of both circuits is somewhat reduced because the
Charles Thomas
first circuit is coupled to the antenna and the
second feeds the detector. Two-circuit selectivity
is insufficient for broadcasting reception in this
country, hence the detector is made regenerative.
Regeneration more than compensates the losses
TlflTHOUT a doubt tie screen-grid tube is
rr attracting the attention of every serious experi-
menter and engineer in the radio field. Readers
of RADIO BROADCAST are by this time familiar
with the theory of this tube, and something of its
operation and application has already been in-
cluded in the contents of this magazine. The follow-
ing brief description of a two-tube tuning unit, to
which may be added any audio amplifier, is the
forerunner of a construction article telling exactly
how to build the receiver. This article, and the com-
pleted receiver, which is being thoroughly engineered,
are products of a well-known engineer, whose real
name, unfortunately must be hidden with a pseudo-
nym. Articles on the new screen-grid tube appeared
in RADIO BROADCAST as follows: "Applications
of the Four-Electrode Tube" December, 1927;
"The Screened-grid Tube" January, 11)28; The
Screened-grid Tube" February, 1928; "A Four-
Tube Screened-grid Recever" March, 1928
— THE EDITOR.
434
in the tuning unit feeding the detector and im-
proves both selectivity and sensitivity.
The shielding required, as shown in the
photograph, is not very elaborate. Brass panel
and baseboard are used, and a brass partition
between the two stages is also advisable. The
screen-grid tube is enclosed in a copper cyl-
inder which fits closely around the tube and
extends about half an inch above it. It is also
necessary to shield the short lead between the
plate of the screen-grid tube and the detector.
In general, shielding is required between all
parts of the plate circuit and all parts of the
control grid circuit.
The circuit of the experimental set, which
includes only detector and radio-frequency
amplifier, follows conventional lines. The an-
tenna is coupled through a tapped coil to the
control grid of the screen-grid tube. The position
of the tap controls to a certain extent the gain
and selectivity of the set. Its position must be
determined experimentally. The plate of the
radio-frequency amplifier is coupled to a tuned
impedance. Parallel coupling is used, the d. c.
plate circuit going through a radio-frequency
choke to the plate supply.
The method of regeneration control is some-
what unusual. The regeneration coil Lt is not
appreciably coupled to the grid circuit. Re-
APRIL, 1928
AN EXPERIMENTAL SCREEN-GRID RECEIVER
435
THE FRONT PANEL OF THE TWO-TUBE SET
The two variable condenser dials are made by Genera Radio and they come with the condensers.
The smaller knobs provide for vernier tuning. The panel is of aluminum and is 7 x 14 inches in size.
generation is controlled by varying the effective
inductance of the plate circuit. The effective
value of Lt, shunted by the resistance, is varied
by changing Ri. In this type of plate circuit the
effective inductance increases with increasing
wavelength, which tends to minimize the range
L4,93-95 Turns No.30 D.C.C.
FIG. I
of adjustment of the regeneration control as the
tuning is varied. So far as sensitivity and selec-
tivity are concerned a plain variometer might be
used in the detector plate circuit, or a fixed
inductance with a small variable condenser
coupling back to the detector grid.
As shown, the circuit is wired for use with a
6-volt battery and 2OI-A. type detector tube.
Satisfactory operation using the method of ob-
taining regeneration described was not obtained
with a 199 type tube as detector. The uv-227
(0-327) a. c. type tube may be used as a de-
tector if a transformer of proper voltage is used
to feed the heater. This tuning and detector
unit should be satisfactory for use with alter-
nating-current screened-grid tubes when, as,
available. The parts used in the receiver shown
in the accompanying photographs
are as follows:
LIST OF PARTS
LI Lj — 45 Turns No. 26 D. S. C.
2f" Diameter
Li — General Radio No. 37 Choke
of 60 Millihenries
Li — Regeneration Coil (Construc-
tional Data Below)
Ci, Cj — General Radio Type 334
or 247 5Oo-Mmfd. Variable Con-
densers
Cs, Ci — i-Mfd. Bypass Condensers
C6 — o.ooj-Mfd. Fixed Condenser
C» — o.ooo25-Mfd Fixed Condenser
Cj — o.ooi-Mfd. Fixed Condenser
Ri — Carter 5000 Ohms, Variable
Rs — 3-Carter Megohm Resistor
Ri — 4-Ohm Fixed Resistor
Ri — General Radio Type 214 50-
Ohm Variable Resistor
R6 — General Radio Type 301 30-
Ohm Variable Resistor
Two Sockets
Eight Binding Posts
One Copper Shield for Tube, 2"
Inside Diameter and 5j" High
One ux-222 (cx-322)
One ux-2oi-A (cx-3Oi-A)
One Aluminum Front Panel, 7" x 14"
One Aluminum Sub-Panel, 13" x 9"
Hardware, Etc.
The construction of the regeneration coil, Lt,
is shown in Fig. I. The coil form is a wooden
spool with an inside winding diameter of J" and a
groove J" wide. An outside diameter of I J" pro-
vides sufficient winding space. A coil wound with
93-95 turns of No. 30 d. c. c. will be found suffi-
cient for the general run of 2OI-A tubes. Coils Li
and Lz may be General Radio coils type 2?7C
with 10 turns removed.
If loud speaker operation is desired, any stan-
dard d. c. audio amplifier or a. c. power audio am-
plifier may be used with this unit.
UX-222
(CX-322)
0.005 mfd. 0.00025 mfd.
UX-201-A
(CX-301-A)
135
A SCHEMATIC DIAGRAM OF THE TWO-TUBE SCREEN-GRID RECEIVER
THE Roberts receiver, of which the Ham-
marlund "Hi-Q" is a semi-commercial
model, was first introduced to the radio
public by RADIO BROADCAST so many years ago
that the author has neither the ambition nor
time to go through his files to determine just
when Dr. Roberts presented his first article.
This momentary reminiscence perhaps has
little in common with the point to be discussed
in the present writing, but there is significance
somewhere in the thought that this is the only
circuit, of the many hundreds introduced in
broadcasting's nebulous days, that has remained
standard and popular to the present time.
Simple efficiency is responsible for this consistent
popularity.
The 1927-1928 Hammarlund Roberts "Hi-Q,"
described in RADIO BROADCAST for October,
1927, departed somewhat from previous models
in mechanical and electrical design, though the
ultimate effects are consistently in line with
previous designs. The last two models of the
"Hi-Q" receiver have incorporated variable
coupling between the radio-frequency primary
and secondary circuits. The possibilities of such
an arrangement were pointed out by Zeh Bouck
in an article appearing in the September, 1926,
issue of this magazine, entitled "Higher Effi-
ciencies in R. F. Amplifiers." The argument,
in brief, is as follows:
At every frequency or wavelength there exists
an optimum value of coupling between primary
and secondary circuits — a value of coupling
which provides the maximum signal intensity
compatible with quality and stability. This
optimum degree of coupling varies, however,
with the frequency. To maintain optimum con-
ditions over the entire tuning range, therefore,
it is desirable that the coupling be varied with
the wavelength. This is accomplished automati-
cally in the Hammarlund-Roberts receiver.
The general characteristics of the Hammar-
lund "Hi-Q" receiver remain unaltered in the
adaptation of this receiver for the use of a. c.
tubes, as comparison of the circuits shown in
Figs. I and 2 with the direct-current arrange-
ment illustrated in the October, 1927, RADIO
BROADCAST, will indicate.
The changes effected have merely been in
the nature of the substitution of heater type
a. c. tubes for the d. c. ones, accompanied by
slight alterations in the constants of the circuit
to compensate changes in tube characteristics.
The receiver has been redesigned for the use
of two different makes of a. c. tubes, the R. C. A.
227 (Cunningham 327) type and the Arcturus
a c. amplifier, detector, and power tubes. The
selection of two types of tubes has been sug-
gested by motives of general convenience.
Electrifying the "Hi-Q'
By F. N. Brock
THE "HI-Q" WIRED FOR CUNNINGHAM OR R.C.A. A.C. TUBES
The use of the R. C. A. tube in the "Hi-Q"
receiver will be first considered.
The following is a list of the essential parts
employed in the construction of the receivers:
i Samson "Symphonic" Transformer
I Samson Type HW-A3 Transformer (3-1 Ratio)
4 Hammarlund o.ooo5-mfd. Midline Condensers
4 Hammarlund "Hi-Q" Six Auto-Coupled Coils
4 Hammarlund type RFC-S; R. F. Chokes
Hammarlund Illuminated Drum Dial
Sangamo o.ooo25-Mfd. Mica Fixed Condenser
Sangamo o.oooi-Mfd. Mica Fixed Condenser
Pair Sangamo Grid Leak Clips
Durham Metalized Resistor, 2 Megohms
3 Parvolt o.5-Mfd. Series A Condensers
6 Benjamin No. 9040 Sockets
3 Eby Engraved Binding Posts
i Yaxley No. 660 Cable Connector and Cable
i Hammarlund Roberts "Hi-Q" Six Foundation
Unit
(Containing drilled and engraved Westinghouse Bakelite
Micarta panel, completely finished yan Doom steel chassis,
four complete heavy aluminum shields, extension shafts,
screws, cams, rocker arms, wire, nuts, and all special hard-
ware required to* complete receiver.)
For the construction of or adaptation of an
existing "Hi-Q" receiver to one employing the
227 type tube the following additional parts were
used in the adaptation:
5 Benjamin Green Top A. C. 5-Prong Sockets
i Thordarson Type 2504 Filament Transformer
(or Karas AC Former)
FIG. I
i T2oo Electrad Variable Resistance to Permit
Temperature Regulation
I o.5-Mfd. "Parvolt" Series A Condenser
I 2oo-Ohm "Truvolt" Grid Resistance (Elec-
trad)
I Samson 3o-Henry Choke or a Samson Type O
Output Impedance
i 2- or 4-Mfd. Series A "Parvolt" Condenser
i Electrad Type J Resistance for Volume Control
5 R. C. A. uv-227 or Cunningham c-327 Tubes
i ux-i7i-A or cx-37i-A power tube.
CONSTRUCTIONAL DETAILS
THE construction of the receiver remains
practically identical with that of the direct-
current models. The general layout of the parts
and the mechanical mountings have been
described in detail in articles on the d. c. set
and in the Hammarlund Roberts "Hi-Q" Six
Manual.
The five-prong sockets are mounted in the
same places and with the same screws as the old
sockets. An extra hole for the cathode lead must,
however, be drilled just under the K or cathode
terminal In the a. c. models of the Hammar-
lund " Hi-Q" the right-hand control (the rheostat
in the battery-type receiver) may be used to
control a I lo-volt line switch, such as the Carter
"Imp" type 1 15.
The similarity of the a. c. and the d. c. me-
chanical layouts is evidenced by comparing the
accompanying photographs with those of the
d. c. models which have frequently appeared.
The circuit of the Hammarlund Roberts
"Hi-Q" Six receiver employing type 227 tubes
is shown in Fig i, in reference to which the fol-
lowing points are worthy of mention:
All filament or heater wiring should be made
with a twisted conductor. It is desirable that
consistency be observed in the socket connec-
tions with these power leads. In other words,
it is preferable that the same heater terminal
on each socket be connected to the same heater
lead. This is most readily accomplished by em-
ploying a twisted pair of two colors. Corwico
flexible red and black Braidite is a convenient
recommendation.
The red and green leads on the Yaxley cable
are not used.
Heater tubes are employed throughout the
circuit (with the exception of the output ampli-
fying stage) due to the simplicity and consist-
436
APRIL, 1928
ency of the circuit arrangement and the low
hum characteristics of these tubes.
The Electrad T2oo variable resistor is wired
in series with the primary of the filament lighting
transformer to provide a desirable amount of
regulation of the secondary potential. The
heaters of the 227 tubes should be operated at as
low a temperature as will insure satisfactory re-
ception. With the proper adjustment of the
primary resistor it will take about 55 seconds
for the tubes to reach an efficient operating
temperature after the current is turned on.
The life of the tubes will be considerably
abbreviated if more than the rated operating
filament potential is applied.
The bias to the radio-frequency and first
audio transformer tubes is supplied through the
drop across the Electrad 2oo-ohm grid bias re-
sistor.
The pilot light is connected in parallel with
the I7I-A tube filament.
One side of the o.5-mfd. bypass condenser
across the grid biasing 2oo-ohm resistor is
grounded to the chassis.
Sensitivity and selectivity may be controlled,
in the usual manner, by varying the mechanical
adjustment controlling the height of the primar-
ies, particularly in the case of the last r. f. stage
and the detector stage. Selectivity will also be
considerably affected by the tightness of the
antenna coupling. In order to attain satisfactory
sensitivity and selectivity on the higher fre-
quencies it will occasionally be desirable to use
lower values of grid suppressor resistors than
those recommended in the d. c. circuit, due to
the alteration in the radio-frequency characteris-
tics occasioned by the lower input impedance of
the heater cathode type tube. The sensitivity
of the receiver may also be increased by employ-
ing a higher resistance grid leak. The value of
this resistor should, however, be increased
cautiously with the possibility of overload on
local stations in mind. In the case of a rewired
d. c. receiver, originally operating with a radio-
frequency plate potential of 67.5 volts from a
B supply device, it is desirable to raise the volt-,
age to about 80 to compensate the increased
drain. The type J 2OO,ooo-ohm resistor is used
for a volume control. This is mounted in the left-
hand panel hole in the place of the filament
switch employed in the battery set. The last
three or four turns on the volume control (on the
clockwise end, that is) should be clipped in
order to give an "open" or maximum volume
position.
The potentials, other than the a. c. voltage
for the heaters of the tubes, indicated in Fig. I,
may be supplied either from B batteries or from
an adequate B supply device, such as the Ham-
marlund Roberts "Hi-Q" Six power supply
described in the Hammarlund Manual. The
fhordarson 2504 filament transformer and this
power unit will take care of all A, B, and C
potentials.
USING ARCTURUS TUBES
FROM an electrical point of view the "lli-O"
receiver rewired for the use of Arcturus
a. c. tubes is practically identical with the 227
type tube design. Mechanically, the Arcturus
system offers certain advantages which partic-
ularly recommend it for the adaptation of exist-
ing battery receivers. Arcturus a. c. tubes are of
the four-prong heater type and they plug into the
standard ux sockets without the use of adaptors
and which, therefore, necessitate neither the
use of special sockets nor a comparatively elab-
orate mechanical rearrangement.
In addition to the essential "Hi-Q" apparatus
listed earlier in this article, the following extra
ELECTRIFYING THE "HI-Q"
components will be required in the adaption or
construction of the Arcturus model:
i Electrad Royalty Type J Variable Resistor
4 Arcturus Type A. C. 28 Amplifier Tubes
I Arcturus Type A. C. 26 Detector Tube
i Arcturus Type A. C. 30 Power Tube
I Step-Down Transformer, Having a 15-V'olt
Secondary, Such as the Ives Type 204, or the
Thordarson TY-m.
A receiver employing Arcturus tubes is
illustrated diagramatically in Fig. 2 and in the
accompanying photograph. Referring to Fig. 2,
it will be noted that the following alterations
have been made on the original d. c. circuit:
The three fixed and one variable filament
resistors are eliminated. Similarly all connections
between grid returns and filament circuits are
broken. The connection between ground and A
minus is likewise removed. These changes are
best made by completely rewiring the filament
or heater circuits with flexible Braidite — red and
black wires — twisted into a single pair. Con-
nect the red wire consistently to the positive
filament terminals on the sockets. These two
leads are wired to the filament lugs on the
Yaxley cable post, the red wire being soldered
to the plus terminal '(polarity, however, being
meaningless at this point). Another pair can be
led to the switch on the "Hi-Q" which later is
connected in series with the primary (or I to-volt
lead) of the filament lighting transformer for
turning on and off the tubes. The switch must
not be wired in the conventional manner, i. e.,
in series with the tubes themselves.
A fifteen-volt pilot light bulb can be secured
from any store dealing in electric trains, and
should be screwed into the socket provided for
this purpose, and wired parallel to the tube cir-
cuit.
The grid returns from the radio-frequency
amplifier, detector, and first audio-frequency
secondaries are brought down to a common
lead connected to ground, and this post should
also be designated as "C Minus 1.5 volts."
Theo.j-mfd. bypass condensers connected from
the lower side of the radio-frequency primaries
to the filament circuit in the original arrange-
ment should be returned to the plus filament or
cathode posts of the respective sockets.
The detector grid leak is disconnected from
the A plus terminal of the socket and is brought
down to a separate lead or post to be designated
200,000-Ohm.Vol.
Control
437
as " D Plus 4.5 Volts." The detector r. f. grid
return, i. e., the low-potential end of the second-
ary coil, is wired, as already indicated, to the
common radio-frequency grid return
The grid return from the first audio-frequency
amplifier is rewired as described, to the post
marked "C Minus 1.5 Volts," which is grounded
on the receiver. No change is made in the power
tube socket.
A separate wire is led to the plus filament
or cathode terminal of the detector tube,
designated as "B Minus, C Plus, and D Minus."
The zero to 200,000 ohms Electrad Royalty
or any other satisfactory variable resistor is
connected across the secondary inputting to
radio-frequency tube number two, and mounted
in place of the rheostat.
Arcturus type a. c. 28 tubes are used in the
first, second, and third r. f. stages and in the
first a. f. stage. A detector tube, type a. c. 26,
is plugged in the detector socket, and a power
tube, type a. c. 30, into the power stage, which
feeds the loud speaker.
OPERATION
nr H E operation of the a. c. " Hi-Q" receiver is
1 practically identical with that of the d. c.
model. The indicated connections to batteries
and transformer should be made.
A. C. heater type tubes do not function effi-
ciently as soon as the heater current is turned on.
With the correct voltage (15 volts) applied to
the heater terminals of the Arcturus tubes, it
requires just 30 seconds for the tubes to heat to
the proper operating point. The filament
potential should be adjusted by means of the
taps on the transformer until satisfactory opera-
tion is obtained. It is needless to say that the
heaters must be given three to four minutes to
cool before making additional adjustments of
this nature. It is desirable, wherever possible, to
utilize an a. c. voltmeter for the adjustment of
the heater potential.
Any efficient B and C socket power device
may be substituted for the indicated battery
potentials. Briggs and Stratton are marketing
an efficient A, B, and C power unit supplying all
the necessary potentials for the operation of
Arcturus tubes.
The various points mentioned in the recom-
mended adjustments effecting selectivity and
sensitivity in the 227 type tube receiver apply
equally as well to the Arcturus arrangement.
C-22%
O
B+180V
110 VAC.
FIG. 2
A COMMERCIALLY AVAILABLE LOFTIN-WHITE RECEIVER
The Arborphone 37-AC set employs 3r.f. stages, detector, and
two audio stages. The output audio stage is a push-pull one
An A* CX Loftin- White Receiver
By John F, Rider
|ROMPTED by the great interest which
hinged on the announcement of the
Loftin-White circuit several months ago,
the writer has endeavored in this article to
describe in brief the outstanding features of a
commercial receiver which makes use of this in-
teresting circuit. The receiver in question has
much to commend it, not the least important of
its features being the fact that it is designed to
use the new a.c. tubes.
The Arborphone 37-AC set, for that is its
name, comprises three stages of tuned radio-
frequency amplification, a non-regenerative de-
tector, and two audio-frequency stages. The last
audio stage, as will be seen by reference to the
accompanying circuit diagram, is a push-pull one,
making use of two parallel 171 type power tubes.
The radio-frequency stages use tuned trans-
formers and a stabilizing system developed
as a result of the combined efforts of
Messrs. Edward H. Loftin, former Lieutenant-
Commander, United States Navy, and S. Young
White, a well-known radio engineer. The ar-
rangement used in this receiver is really a
modified version of the original, but in its func-
tion, is very similar.
This radio-frequency amplifying system ac-
complishes two things. In the first case it stabi-
lizes the circuit, or the individual stages, which-
ever way we wish to view it, and secondly, it
affords a certain uniformity of response over the
tuning frequency spectrum.
A glance at the wiring diagram of the receiver
shows the plate supply of the r.f. tubes being
fed to the tube through a choke, and the plate
coupling coil coupled to the plate through a
variable condenser, C. This condenser, because of
Wavelength
Low >• High
MUTUAL INDUCTANCE
its function, is greatly responsible for the stabi-
lization of the stage. Its purpose is to change the
phase of the alternating potential in the plate
circuit due to the a.c. signal impressed upon the
grid of that tube, so that it will not combine
with the a.c. signal in the grid circuit. The maxi-
mum capacity of the phase-shifting condenser
employed in such systems is approximately
0.0005 mfd., and it is usually adjusted to a point
where the phase shift is such that the stage
operates with a definite amount of feedback, or
regeneration, which amount, however, is less
than that required to cause a continued state of
oscillation. The inductance value of the plate
feed choke is of such proportion that, when
resonated by its distributed capacity, its fun-
damental is above the longest wavelength which
can be tuned-in with the receiver.
Referring to the method of obtaining what is
called "constant coupling" between the plate
and grid circuits of subsequent tubes, we find the
system used differing somewhat from the original
Loftin-White arrangement. An idea of the operat-
ing principle of the system can be gleaned from
a study of the wiring diagram.
The plate and grid coils of the r.f. stages being
inductively coupled, a certain amount of mutual
inductance exists between the two coils. This
mutual inductance is the path of energy transfer
between the two coils, but the magnitude of
energy transfer varies with the frequency of the
signal. The higher the frequency (the shorter the
wavelength) the greater the amount of energy
transferred. The lower the frequency (the longer
the wavelength) the less the energy transferred.
Rut the coupling between the plate and grid cir-
cuits is not obtained solely through the mutual
Wavelength
Low
High
MUTUAL CAPACITY
FIG. I
438
inductance between the two coils. The fixed con-
densers in series with the grid circuits also func-
tion as coupling capacities, but their coupling
value is governed by the ratio between their own
capacity and the capacity of the variable tun-
ing condensers in the grid circuits. Now mutual
capacity behaves in a manner opposite to that of
inductance, being more effective on the longer
wavelengths and less effective on the shorter
wavelengths. As the capacity of the tuning con-
denser is increased when tuning for the longer
wavelengths, the effect of the fixed condenser
is increased. The converse is true when the re-
ceiver is tuned to the shorter wavelengths and
the value of the variable condenser is decreased.
• A graphical representation of the energy trans-
fer by means of mutual inductance and mutual
capacity for a single stage is shown in Fig. i. An
idea of the overall energy transfer as a result of
the combined coupling mediums is also shown
in Fig i. The response curve of one stage with the
combined coupling mediums is not a perfectly
straight line, but has a depression around 300
meters and slightly higher response on the
lower end of the broadcast spectrum than on the
higher end. These data were obtained after
several measurements of different installations
which employed the Loftin-White system. The
greater amplification on the shorter wavelengths
is probably due to inherent regeneration. The
complete response curve, however, is of very good
formation. The usual capacity of the variable
condensers is 0.0005 mfd. and that of the fixed
coupling condensers is 0.004 mfd.
The use of a push-pull audio output stage
affords certain advantages not obtained when
only one tube is employed in the output. First,
Wavelength
Low >- High
COMBINED COUPLING
APRIL, 1928
AN A. C. LOFTIN-WHITE RECEIVER
439
THE SHIELDED STAGES OF THE RECEIVER
it affords a greater signal output with much
less distortion. Secondly, the increase in signal
output is greater than the proportion of i to 2
tubes because somewhat greater input voltage
can be tolerated without overloading or distor-
tion. Thirdly, a push-pull output stage minimizes
"hum" due to the use of a.c. on the filaments.
The receiver utilizes 226 type tubes for three
radio-frequency amplifiers and the first stage of
audio. The detector tube is a 227 and the push-
pull output tubes are 171*5.
Physically, the receiver is an interesting unit.
In the first place the radio-frequency and de-
tector systems are completely isolated from the
audio and B power supply units. Each tuning
stage is individually shielded, the whole forming
one large can. The audio and power supply sys-
tems combine to form another shielded unit, thus
precluding reaction between the two amplifying
systems and minimizing radio-frequency reaction
between the power unit and the radio-frequency
amplifier. The shielding material is -3'a-" aluminum
of high conductivity and low mass resistance;
there is a double thickness between stages. The
chassis of the radio-frequency system forms one
part of the can and is grounded.
Each can contains the chokes, plate and grid
coils, the necessary phase shifting and coupling
condenser, and the tube socket. Single-layer
solenoids are used for the radio-frequency trans-
formers and are placed parallel to each other.
Reaction between these inductances is eliminated
by means of the shielding. The phase shifting
condenser and its associated radio-frequency
choke are located adjacent to the socket con-
nected thereto. The adjustment of the capacity
•of the phase shifting condenser is accomplished
by means of a protruding screw head.
The inductances are wound on bakelite tubes
and the turns are spaced 0.002" by means of a
machine, as the coil is wound. A layer of collodion
sprayed upon the turns keeps them in place. The
inductance value of these coils is such that,
with the condensers used, the wavelength range
is from 200 to 550 meters (1500 to 545 kc.)
The plug located between the two inner sockets
and in the groove reserved for the drum dial,
carries the connections for the plate and filaments
of the tubes in the radio-frequency and detector
portion of this receiver. The female portion of
this plug is located in the container housing the
audio amplifier and the power supply, and the
power is fed to the r.f. system by means of this
plug-
Rigid sockets are utilized for all tubes, thus
showing that very little concern is placed upon
the necessity of cushion sockets in the modern
receiver. It seems as if we have very little to
worry about microphonic tubes. A rigid socket
appears satisfactory for the detector tube.
Four tuning condensers are used, one for each
stage of radio-frequency amplification. All four
are simultaneously controlled from one point and
are actuated by means of a small knob attached
to a drum dial. The four condensers are divided
into two groups of two each, the rotors of each
group being on one shaft. The two groups are
then coupled together by means of a steel cou-
pling unit. The condenser which tunes the input
stage is so arranged that its rotor operates in
conjunction with the other rotors, but its stator
is located on a rocker arm, which can be actuated
by means of a small knob located on the receiver
panel. In this way it is possible to make easy
adjustment to compensate antenna variations.
The condensers are of the straight wavelength-
line type and are very accurately and rigidly
made. The bearings are of fabricated bakelite on
steel. The condenser plates are wedged into
grooves in the side spacers. All grooves are
simultaneously milled with a gang cutter,
hence the spaces are uniform. Supplementing this
design, in the effort to obtain accurancy, short,
stubby plates are used in place of long, thin ones.
Bakelite end plates are used on the condensers
and this material is used for insulating the rotor
from the stator.
The method of testing the variable condensers
and the inductances is novel and precise. Two
radio-frequency oscillators are adjusted for beat
note resonance. One unit is maintained as the
standard. The condenser to be tested is applied
to the other. Perfect uniformity would mean a
zero beat. The tolerance value is a 2oo-cycle beat
note.
The B supply comprises a full-wave rectifier
employing a 280 tube. One transformer carries
the windings necessary to supply the filament
voltages for all the tubes used in the receiver.
One winding supplies the 1.5 volts required for
the 226's; another winding supplies the 2.5 volts
for the 227; a third supplies the 5 volts necessary
for the I7i's; a fourth supplies the filament
voltage for the 280 tube; a fifth supplies the plate
voltage for the rectifier tube.
The primary winding of the power transformer
is tapped for no-, 120-, and i3O-volt supply. A
short-circuiting plug shorts a portion of the wind-
ing when the line supply is 1 10 volts. The entire
winding is used for i3O-volt systems. All filament
windings, with the exception of the 226 winding,
are mid-tapped right in the transformer, thus
eliminating necessity for mid-tap resistances and
adjustments. The 226 winding is equipped with
a potentiometer shunt, whereby the correct
electrical center can be obtained.
The B supply utilizes a two-section filter, in-
corporating two chokes and three reservoir con-
densers. The plate current for the 171*5 is caused
to flow through only one choke, the filtering ac-
tion of this one section being sufficient for the
push-pull tube plates. The voltage reducing re-
sistance is, therefore, a single mid-tapped unit
arranged as a potentiometer across the power-
unit output. The high end of this resistance sup-
plies the 90 volts required for the plates of the
first audio stage and the three radio-frequency
amplifiers. This tap is fixed in the process of
manufacture. The mid-tap of this resistance sup-
plies the 45 volts for the detector tube plate.
All C bias voltages are obtained directly from
the B unit. Because of the heavy plate current
drain of the two I7i's (approximately 38 to 40
mils.), it is necessary to isolate the loud-speaker
winding. This is accomplished by means of an
output transformer.
Loud Speaker
THE CIRCUIT DIAGRAM OF THE LOFTIN-WHITE RECEIVER DESCRIBED IN THIS ARTICLE
5- Lester L. Jones
AS PRESIDENT of the Technidyne Corpor-
^* ation in New York, Lester L. Jones plays
an important role in radio research and labor-
atory investigation. His academic training as an
engineer was received at the College of the City
of New York, which, during the years when
Alfred N. Goldsmith was a professor there, prob-
ably ranked as the foremost scholastic source of
radio engineering personnel in the country. Mr.
Jones graduated in 1913 with the degree of Bach-
elor of Science, cum laude. During the summer
following his graduation he pursued special
work at the College laboratories in various
problems of radio engineering, including deter-
mination of the action of underground antenna
systems, studies of the heterodyne system, using
a Poulsen arc, and investigation of the charac-
teristics of the then modern German quenched
spark transmitters. The heterodyne tests were
conducted in part with the Bush Terminal sta-
tion of the National Electric Signaling Com-
pany, and presumably Mr. John V. L. Hogan
was present at the Brooklyn end of the circuit.
In the winter of 1913 Mr. Jones was engaged
as a civilian inspector of electrical and radio
materials at the Brooklyn Navy Yard. He was
responsible for the testing of all the radio trans-
mitting and receiving equipment purchased by
the Navy Department and delivered to the
New York yard. In about a year this work led
to Mr. Jones's promotion to the position of Ex-
pert Radio Aide, which included not only the
former inspection responsibilities, but also the
planning and testing of complete radio installa-
tions on battleships, destroyers, and submarines.
While he was engaged in these specialized tasks
Mr. Jones did not neglect the other branches of
radio engineering, and the early issues of the
"Proceedings of the Institute of Radio Engi-
neers" frequently contain his name as a partici-
pant in the discussions, which were recorded at
that time by the devestatingly charming Miss
Nan Malkind, the only skilled and accurate
radio stenographer who has ever appeared in the
art. In the 1914 "Proceedings," for example,
there appeared a learned discussion by Mr.
Jones on the subject of why the audion bulb
causes a click in the receiving telephones when
the filament current is shut off. Dr. Lee De
Forest, the author of the paper that evening,
observed laconically, "This is probably the cor-
rect explanation," a remark which must have
been pleasing to the younger engineer, and
which has been preserved for posterity in the
"Proceedings," together with many words of
contrasting asperity.
As an Expert Radio Aide Mr. Jones was not
confined to the New York Navy Yard. At various
times his duties carried him to outlying land
stations of the Navy Department, such as the
post at Guantanamo, Cuba, to suggest improve-
ments and to supervise installations of new ap-
paratus. The position also included design of
transmitting equipment for the special condi-
tions of naval radio communication, supervision
of manufacture, installation, and testing of
models, and the preparation of specifications
under which contracts were let for the furnishing
of sets in quantity by commercial manufac-
turers.
The New York yard was primarily a trans-
mitter-developing base. In 1917 Mr. Jones was
transferred to the Washington yard, which
specialized in naval receiver design and investi-
gation. During the year and a quarter Mr. Jones
spent at Washington, he was the civilian in
charge of development of naval receiving equip-
ment for use on battleships, submarines, and
airplanes, including the well-known two-stage
audio amplifier with non-ferric transformer
coupling, which became the despair of many a
graduate of the Harvard Radio School, although
it was probably the best thing in its line at that
period. The Washington Yard, incidentally, has
some claim to rank with Brant Rock, the Aldene
factory of the Marconi Company, and the G. E.
test shop at Schenectady, as a nursery of famous
radio men. Besides Mr. Jones, at various times
during the war period Professor Hazeltine,
William H. Priess, Joseph D. R. Freed, and
440
others worked there on the SE line of naval
receivers and auxiliary apparatus.
In addition to these more or less orthodox
radio duties, Mr. Jones was charged with in-
vestigation of war-time devices offered to the
government by inventors confident that the
offspring of their brains was required to beat the
Germans. Machines for detecting submarines
and killing the magnetos of aeroplanes were
among them. Some of the ideas were insane and
others offered practical possibilities. Only scien-
tific analysis could separate the chaff from the
wheat. But Mr. Jones did not spend all his time
on radio development and related investigations
at the Washington yard. At intervals he made
observation trips in naval craft, in connection
with submarine signaling, search-light communi-
cation, and -other special problems.
Mr. Jones left the service of the Navy Depart-
ment in the spring of 1918 and spent a short
time in the employ of commercial radio compan-
ies which were supplying apparatus to the Army
and Navy. In 1919 he established himself as a
consulting engineer specializing in radio. Among
his clients (in 1920-21) were the Mackay inter-
ests, then contemplating establishing their own
transatlantic radio circuits on behalf of the
Postal Telegraph-Commercial Cable system.
The developments considered at that time have
only recently been projected anew in the an-
nouncement of the Postal Company that long-
and short-wave radio channels are to be oper-
ated as adjuncts to the cable circuits of the
company.
Mr. Jones has patented numerous radio inven-
tions at home and abroad. In December, 1925,
he was elected a Fellow of the Institute of Radio
Engineers. His career is an illustration of the
value of broad technical training and experience
in the radio engineering field. For every promin-
ent radio man in the technical end who entered
the business when broadcasting began to agi-
tate the ether in 1920, there are ten who spent
years in developing radio telegraph communi-
cation, while wireless telephony was still a
poet's dream.
WE ARE beginning to comprehend
vaguely the extent of the phonograph
industry. That we had not done so
before is due to the fact that we never could
visualize figures. Units, tens, and hundreds we
can manage very well but when the thousand
mark has been passed our brain reels, and the
very numbers jump before our eyes. And so, al-
though we knew that some sixteen hundred re-
cordings were made annually by the Victor,
Brunswick, and Columbia companies, we were
not impressed because the figure was meaning-
less. Now we have a dim idea. An average of
thirty-four records a month have been reviewed
in this department for the last four months.
Our statistical department reports that this
totals one hundred and thirty-six records. These
records occupy a considerable portion of our
apartment, to be exact, a couch, a large mahog-
any office desk, one stool, and three chairs, not
to mention the overflow on the floor. Walking
has become dangerous and sitting is well nigh
impossible. In another four months the records
will have reached the kitchen and we will be
forced to take our meals out. If we ever review
all the records each month we will move into
Carnegie Hall. Nice little industry!
Many of these we could lose without a tear.
Then again there are those we will cherish for-
ever. Already we have formed a permanent at-
tachment for some of this month's supply: two
selections from // Pagliacci sung by Giovanni
Martinelli, a Percy Grainger record, two delight-
ful numbers by the Elman String Quartet, two
old and one new waltz from the Whiteman or-
ganization, and several better-than-usual dance
numbers by the usual dance orchestras. These
have gone into our library. Into the ash can we
would like to put a Ted Lewis record and an Al
Jolson song. The rest are chiefly dance records
which will provide good entertainment for the
moment.
We welcome the appearance of eight waltz
numbers. We hope that means that the waltz
is coming back but there have been so many
false alarms already that we refuse to send out
searching parties for our old waltz partners, yet.
In the meantime we waltz alone in the privacy
of our home.
More or Less Classic
Andante Cantabile (from String Quartet, Op.
1 1 , by Tschaikowsky) and Theme and Variations
(from The Emperor Quartet by Haydn). By the
Elman String Quartet (Victor). Delicate cham-
ber music exquisitely played by Mischa Elman,
Edward Bachmann, William Schubert and
Horace Britt. Both performances are richly
colored by the beautiful tone of the Elman
violin.
Pagliacci — Vetti la Giubba (Leoncavallo) and
441
The
s New
Phonograph
Pagliacci — No Pagliacci Non Son! (Leon-
cavallo). By Giovanni Martinelli (Victor).
Martinelli's powerful tenor voice combined
with his dramatic ability fit him eminently to
sing the emotional Leoncavallo music. He
handles these two glorious selections magnifi-
cently.
Andrea Chenier Improwiso — Come un bel di,
Parts i and 2 (Giordano). By Arnoldo Lindi
(Columbia). An imported recording of a fine Ital-
ian tenor who just misses being better than that.
Mazurka in B Minor (Chopin) and La
Campanella (Liszt-Busoni). By Ignaz Friedman
(Columbia). We would like to enthuse over this
record because the Columbia Company has
done an excellent job of recording Mr. Fried-
man's fine display of piano technique in La
Campanella, but how can one enthuse over pas-
sionless music?
Dubinuschka and (a) Old Forgotten Wall^ and
(b) Bouran by the A. & P. Gypsies (Brunswick).
If there is aught of the spirit of Terpsichore in
you these gypsyish rhythms will make you yearn
to express yourself in dance. Meaning: our
grading of this offering — 50 per cent.
Traumerei (Schuman) and Mazurka in A
Minor '(Chopin-Kreisler). By Max Rosen
(Brunswick). Adequate violin solos unemotion-
ally delivered.
Don't Miss These New Records
Andante Cantabile (Tschaikowsky) and
Theme and Variations (Haydn) played by
the Elman String Quartet (Victor).
Pagliacci — Vesti la Giubba and Pagliacci —
No Pagliacci Non Son! (Leoncavallo) sung
by Giovanni Martinelli (Victor).
Cradle Song (Brahms-Grainger) and Molly
on the Shore (Grainger) played by Percy
Grainger (Columbia).
Voices of Spring and Enjoy Your Life
(Strauss) played by Johann Strauss and
Symphony Orchestra (Columbia).
Dubinuschka and (a) Old Forgotten Walt:
and (b) Bouran by the A. & P. Gypsies
(Brunswick).
'S Wonderful and My One and Only
(Gershwin) by the Ipana Troubadours
and Clicquot Club Eskimos respectively.
(Columbia).
My Heart Stood Still and / Feel at Home
Witlo You by George Olsen (Victor).
/ Live, I Die For You and Eyes That Love
by the Troubadours (Victor).
Beautiful Ohio and Missouri Walti by Paul
Whiteman and His Orchestra (Victor).
A Shady Tree and Dancing Tambourine by
Paul Whiteman and His Orchestra (Victor).
442
RADIO BROADCAST
APRIL, 1928
Cradle Song (Brahms-Grainger) and Molly
on the Shore (Grainger). By Percy Grainger
(Columbia). To realize how thrillingly alive
piano music can be one should hear the vibrant
beauty of Grainger's rendition of The Cradle
Song. Molly on the Shore is the familiar Irish
reel, jovially played by its composer.
La Boheme: Musetla's Walii Song (Puccini)
and Mignon: Connais-tu le Pays? (Thomas). By
Maria Kurenko (Columbia). One moment we
like this soprano voice exceedingly and the next
it develops a harsh pinched nasal quality which
is most unpleasant. In spite of this shortcoming
we liked Mignon.
Voices of Spring and Enjoy Your Life
(Strauss). By Johann Strauss and Symphony
Orchestra (Columbia). Strauss waltzes beauti-
fully played. Need we say more?
Do You Call That Religion and Honey by the
Utica Institute Jubilee Singers (Victor). Two
of the best songs in the repertory of this Negro
quartet, sung with the subtle harmony which
only Negro voices can achieve.
"Popular" and Such
'S Wonderful by the Ipana Troubadours and
My One and Only by the Clicquot Club Eskimos
(Columbia). 'S Wonderful now holds first place
in our own personal Best Number of the Year
Contest. It is a swell Gershwin song and the
Troubadours have done it full justice. The
Eskimos were not quite as successful with the
other Gershwin number but it is worth honorable
mention.
My Heart Stood Still and / Feel at Home With
You by George Olsen (Victor). The A side is
runner-up in our contest but the B is a come-
down.
(Note: If you want to be a social success you
can't afford to be without both the above-
mentioned records.)
Together, We Two and die Me a Night in June
by Johnny Johnson and His Statler Pennsylvan-
ians (Victor). Despite their age these two
numbers remain vigorous, due to the excellent
Johnson rejuvenation.
A Shady Tree and Dancing Tambourine by
Paul Whiteman and His Orchestra (Victor).
Your neighbors will cry for, not at, this record.
The waltz with its haunting melody is our
favorite.
Beautiful Ohio and Missouri Walt^ by Paul
Whiteman and His Orchestra (Victor). Beautiful
revivals of the fittest.
/ Live, I Die For You and Eyes That Love by
the Troubadours (Victor). Both these numbers
from "The Love Call" have good tunes as
backgrounds. Vocal refrains by Lewis James help
put them across.
There's One Little Girl Who Loves Me by the
Ipana Troubadours and that'll You Do? by
Leo Reisman and His Orchestra (Columbia).
Two melodious dance numbers with a good
chorus by Scrappy Lambert in the first.
'5 Wonderful and Funny Face by Bernie
Cummins and His Orchestra (Brunswick).
This orchestra unfortunately misses most of the
Gershwin subtlety and messes up the Gershwin
time, but they can't completely ruin either of the
songs.
I'm in Heaven When I See You Smile — Dijne
and Worryin' by the Regent Club Orchestra.
(Brunswick). Two good languorous waltzes
with old fashioned whistling effects.
The Hours I Spent With You and An Old Guitar
and An Old Refrain by Roger Wolfe .Kahn and
His Orchestra with vocal refrains by Franklyn
Baur (Victor). The first is a fair waltz. The
second is called a fox trot but it cries out to be
tangoed to!
Up in the Clouds and Thinking of You by
Nat Shilkret and the Victor Orchestra (Victor).
Hot and snappy in the usual Shilkret manner.
There's a Cradle in Caroline by Nat Shilkret
(Victor). Why didn't Mrs. Victor let Shilkret
show the rest of them how to do it at the begin-
ning? The Song is Ended by George Olsen and
His Music. A good interpretation of a good
waltz with a vocal chorus that's terrible!
Down the Old Church Aisle and Is Everybody
Happy Now? by Ted Lewis and His Band
(Columbia). The first number stirs unpleasant
memories. Has Ted Lewis been robbing the song
cemetery? If so, he'd better replace the corpse.
And, oh, Mister Lewis! lay the second number
beside the first, while you're at it.
From Saturday Night Till Monday Morning
and She'll Never Find a Fellow Like Me by Ted
Weems and His Orchestra (Victor). At last, a
new idea in lyrics! And a catchy tune well
played. We refer, of course, to the first number;
the second is just a really good song on the old,
old idea.
Dear, On a Night Like This by Cass Hagan and
His Park Central Hotel Orchestra and I'll Think
of You by Al Lentz and His Orchestra (Colum-
bia). Two smooth, gliding fox trots, if you know
what we mean.
Thinking of You and Up in the Clouds by
Harry Archer and His Orchestra (Brunswick).
Direction without enthusiasm.
Where Is My Meyer? by Nat Shilkret and the
Victor Orchestra and Blue Baby by George Olsen
and His Music (Victor). Fast-moving numbers
handled by experts.
Make My Cot Where The Cot-Cot-Cotton Grows
and Sugar by Red Nichols' Stompers (Victor).
Why, this orchestra must have been up all
night! Or, how do you explain the monotony?
Wherever You Are and Hcadin' For Harlem
by Nat Shilkret and the Victor Orchestra
(Victor). Franklyn Baur helps the orchestra
make the best of two fair numbers.
Worryin by Don Voorhees and His Orchestra
and Where in the World by The Cavaliers
(Columbia). If they got rid of their worries they
might play better, or perhaps it's the song. The
other number is not much better.
The Song Is Ended by the Columbians
(Columbia). "But the melody lingers on." And
why not? It's a good one and well treated by the
Columbians. There Must Be Somebody Else by
the Radiolites. Nice orchestration and a good
vocal chorus by Scrappy Lambert, formerly one
half of the Trade and Mark combination.
Mother of Mine, I Still Have You and Blue
River by Al Jolson and William F. Wirges and
His Orchestra (Brunswick). Just your mother's
boy, aren't you, Al?
Two Black Crows, Parts 5 and 6, by Moran and
Mack (Columbia). More an* more Moran and
Mack.
Good Records of Operas You Have Heard
POURING the current radio season, parts of many great
'-•^ and popular operas have been heard in the Balkite Hour,
relayed from Chicago with the Chicago Civic Opera Company.
And on the N. B. C. Networks, many well-liked operas have
been done in tabloid form by the National Grand Opera
Company. New electrical recordings of some of the most
popular operas are offered by the leading phonograph com-
panies. Some of these listed below are new, some not so new,
but all are excellent and worth adding to one's collection.
Celeste Aida
Celeste Aida
Ritorna vincitor
O patria mia
La fatal pietra
Morir! si pura e bella!
Grand March
Nel fiero anelito )
O terra addio \
,1
Air des Bijoux
Le Roi de Thule
Parlate d'amore
Ballet music (four parts on two
records)
Soldiers' Chorus
Serenade Mephistopheles
Duet from Garden Scene
Aida (Verdi)
Giovanni Martinelli
Ulysses Lappas
Elisabeth Rethberg
Ponselle-Martinelli
Columbia Symphony Orchestra
G. Arangi-Lombardi and
Francesco Merli
Faust (Gounod)
Edith Mason
Florence Easton
Margarete Matzenauer
Sir H. J. Wood and the New
Queen's Hall Orchestra
Victor Male Chorus
Marcel Journet
Vessella's Italian Band
*!
Prologo, Si puo
Prologo, Un nido di memorie
Selections
Ballatella — "Che volo d'augelli"
No Pagliacci non son! )
Vesti la Giubba >
Di Provema il mar
Prelude
II Pagliacci (Leoncavallo)
Lawrence Tibbett
Creatore's Band
Florence Easton
Giovanni Martinelli
La Traviata (Verdi)
Giuseppe Danise
Capitol Grand Orchestra
(Mendoza conducting)
Viclor
Columbia
Brunswick
Victor
Columbia
Columbia
Brunswick
Brunswick
Victor
Columbia
Victor
Victor
Brunswick
Viclor
Viclor
Brunswick
Victor
Brunswick
Brunswick
Photograph
A SET-UP OF APPARATUS FOR MEASURING CHARACTERISTICS OF A AND B UNITS
It is not a difficult matter to measure the voltage output of A and B devices at different loads — This article
explains. More complicated equipment is necessary, however, to determine the amount of hum in the output
Testing A and B Power Units
THE testing of radio power-supply devices
sent to RADIO BROADCAST by manufactur-
ers has, for some time, been an important
part of the Laboratory's work. What these tests
are, how they are conducted, and what apparatus
is used to make them, should be of general interest
to our readers, and it is the purpose of this article
to explain the procedure adopted for these tests.
The information given here will also be helpful
to manufacturers who, perhaps, contemplate
sending power units to our Laboratory and are
therefore interested to know to what tests their
devices will be subjected. The tests described are
applicable to either A power or B power units
and the apparatus used in the tests is illustrated
in the photograph at the head of this article.
It was the desire of the Laboratory staff to
make the tests such that the data obtained would
be most useful from the standpoint of the user
of the device. With this point in mind the follow-
ing tests were decided upon:
(a.) Determination of the maximum output of
the device at various current drains.
(b.) Determination of the amount of hum in
the output at various current drains.
(c.) Determination of the cost of operating the
unit.
With this information available we can de-
termine whether a device is capable of supplying
sufficient current at the correct voltage for the
operation of any particular receiver, whether or
not the device has a good filter system in it (de-
termined by the amount of hum in the output),
and how much it will cost to operate any receiver
from a particular power unit. In the following
paragraphs we will explain how these tests are
made. Although they will be explained separately,
all the tests are made at the same time in the
Laboratory.
DETERMINING THE OUTPUT
THE circuit used in determining the output
of a unit at various current drains is given
m Fig. i. If the unit under test is an A unit,
then the resistance R consists of a heavy-duty
Carter rheostat with a maximum resistance of 6
By Howard E. Rhodes
Laboratory Staff
ohms so that with the resistance all in the load
of the unit will be about i.o ampere, which will
be indicated in the ammeter A. The voltmeter,
V, used to measure the output voltage, may be
a Weston Model 301 meter with a maximum
reading of 10 volts. By moving the arm on the
rheostat the load may be varied so that the A
unit is placed under actual working conditions,
the load (read on the ammeter) corresponding
FIG. I
to what would be drawn by the tube filaments
were the A unit to be actually connected to the
A posts of a set. At each setting of the resistance
R, the voltage control knob on the A unit under
test should be so adjusted that the voltage on V
reads six, which is the value that the unit will be
called upon to deliver under actual conditions of
operation. At a certain reading of the ammeter it
will be found that the voltage shown by the volt-
meter is not as high as six, indicating that the A
device is being overloaded. The maximum cur-
ent output of an A de-
vice at rated voltage,
which is six, can there-
fore be determined by
setting the voltage con-
trol knob on the device
at maximum (which will
boost up the voltage
to a figure above six at
low values of current)
and adjusting the resis-
tance R until the volt-
meter reads just six. The
ammeter reading then
represents the maximum
permissible drain of the
unit. When the A device
is being used in con-
443
junction with a receiver consuming less than this
maximum current output, the voltage control
on the device is of course turned to a lower tap,
otherwise the voltage output will be excessively
high. Data of this kind obtained on three A
power units recently tested in the Laboratory
are given in the second and third columns of
Table I.
From these data we are able to determine
whether an A power unit is capable of supplying
filament current to any particular receiver, pro-
vided we know the filament current drain of the
receiver. Since this merely depends upon the
number and type of tubes used in the set, it is
easily determined.
If the unit being tested is a B power device, the
same circuit is used but instead of the rheostat
there is used a variable high resistance — a power
Clarostat.The meter M becomesao-ioomilliam-
meter and the voltmeter is generally a Westing-
house high-resistance meter with a maximum
reading of 2 50 volts and a resistance of i ooo ohms
per volt. Some sample data on four B power units
are given in the columns of Table 2.
If we know the total plate-current drain of a
receiver we can easily determine from the figures
given in Table 2 the maximum voltage the vari-
ous units will supply at this load. For example if a
receiver uses a 171 type tube in the output, on
the plate of which we desire to place 180 volts
tMI
LOAD IN
VOLTS
WATTS
HUM
PER CENT.
No.
AMPERES
OUTPUT
INPUT
VOLTAGE
HUM
o
7-3
20
i
o. 5
1 .0
6.0
6.0
2)
26
Too small to Measure
2.0
4-3
40
3.0
4.2
54
o
8
18
o.oi 5
0.187
I
6
28
o.oi 5
0.2;
2
6
44
o.oi 5
0.25
3
6
62
0.015
0.25
l
6
60
0.007
O. 12
2
6
7t
0.007
0. 12
3
2-7
6
101
0.017
0. 17
3
5-2
loo
0.065
I . 1
3-5
2.8
109
0.4*
7-5
TABLE I
444
RADIO BROADCAST
APRIL, 1928
and the total plate current drawn by the receiver
is 50 milliamperes, then unit No. 3, supplying
only 120 volts at this current drain, would not be
satisfactory. Units Nos. i and 2 would be more
satisfactory as they deliver considerably higher
voltage at the current drain specified. Although
they do not supply quite as much as 180 volts, a
matter of 20 or 30 volts less than 180 on the plate
of the power tube does not make a difference
sufficient to be noticeable in the output of the
loud speaker.
These data also give us the "regulation " of the
unit, which is generally specified as the voltage
drop per milliampere of load. For example, taking
the following data from unit No. i, Table 2:
LOAD
MA.
10
40
VOLTAGE
216
182
Difference 30 34
and dividing the difference in the voltages by the
difference in the loads, we obtain a value of 1.13,
•which is the voltage drop per milliampere load.
This is quite a good value for the regulation.
Compare it with the value obtained from unit
No. 3, which figures out to be 4.3. Power units
•with good regulation have the advantage that
the voltage they deliver will be more nearly
constant at all loads.
HUM
IT IS the function of the filter system in an A
' or B power unit to filter the output of the
rectifier so that the output at the end of the filter
system will be as free as possible of any hum or
"ripple." Even from a comparatively poorly
designed power unit the hum is too small to
measure directly. Consequently, it was necessary
to construct an amplifier for this test so that the
hum voltage could be amplified sufficiently so as
to be readily measured. A three-stage resistance-
coupled amplifier is being used in the Laboratory
for this purpose. Two 240 type tubes are used in
the first and second stages and a 201 -A type tube
is used in the last stage. The circuit diagram
is given in Fig. 2.
When an A or B power unit is to be tested for
hum the input of the amplifier is connected to the
power unit under test, and switch Si is thrown
to point A. This causes the hum voltage from the
power unit to be impressed across the input of
the amplifier (note that the d.c. voltage is
blocked by the o.oi-mfd. condenser). The
amplified hum causes the plate current of the
last tube in the amplifier to increase and this
increase is indicated by the meter M in the plate
circuit. The gain control (a o.j-megohm po-
tentiometer across the
input of the amplifier) is
then adjusted so that
the meter M gives a de-
flection that is easy to
read. The switch is then
thrown to the B position
which connects the in-
put of the amplifier to a
source of known 6o-cycle
a.c. voltage the value of
which is variable, as will
be explained below. The
6o-cycle voltage is so
adjusted that the read-
ing of the meter in the
plate circuit of the out-
put tube is the same as it
was when the amplifier
was connected to the
power unit, and in which
case this value of 60-
cycle voltage is then
equal to the hum voltage impressed upon the in-
put of the amplifier.
Using this method (of connecting to the input
of the amplifier a krtown voltage equal in value
to the unknown voltage) makes unnecessary
the calibration of the amplifier. It is necessary,
however, to have available a source of 6o-cycle
voltage from which voltages can be obtained
comparable in value to the hum voltages ordi-
narily obtained from radio power units. These
voltages, which are around o.oi volt in the case
of a poor unit, can be obtained using the circuit
indicated in Fig. 2 as: "Source of known voltage."
The transformer T in this circuit is an ordinary
one designed to supply voltages to a.c. tubes.
The i.j-volt winding is used and across its
terminals is connected a 6-ohm rheostat with an
additional connection soldered to the free end of
the resistance wire so that the rheostat might be
used as a potentiometer. The voltage across the
voltmeter can be adjusted to any value, between
oand 1.5 volts, by means of the sliding contact on
the rheostat. Across the voltmeter are connected,
in series, a 4-ohm and two 2-ohm resistances,
these resistances constituting a voltage divider
the effect of which is to extend the voltmeter
range downwards. Connections from these re
sistances are brought out to four pin jacks
marked \,%,\, and o, indicating the portion of the
voltage associated with the particular pin jack.
Thus, if P is connected to the jack marked i, the
actual voltage impressed across X-Y is only one
half of that indicated by the meter, etc. To the
pin P is connected one end of a 4OO-ohm cali-
brated potentiometer, the purpose of which is
to subdivide the voltmeter readings to even
smaller fractions than is possible with the other
resistances. By means of
these adjustable units it
is possible to impress
across the input of the
amplifier any voltage
from 1.5 volts down to
about 0.005 volts with
an accuracy of not less
than about go per cent.,
which is sufficiently ac-
curate for measurements
of this type.
Some examples of
measurements of this
sort are given in col-
umns 5 and 6 of Tables
i and 2. Column 5 gives
the value of 6o-cycle
voltage that is equal to
the hum voltage. Col-
umn 6 gives the per-
UNIT
LOAD IN
VOLTS
WATTS
HUM
PER CENT.
No.
MILLIAMPERES
OUTPUT
INPUT
VOLTAGE
HUM
o
24?
9
O.OI
0.004
|
10
216
1 1
0.03
0.014
1
20
205
'4
O.O2
O.OI
I
30
193
Ifi
0.02
O.OI
40
182
'9
O.O5
0.027
50
170
22
0.05
0.03
o
215
34
0.075
0.035
10
204
35
0.067
0.033
2
20
195
37
0.067
0.034
40
170
40
0.067
0.039
50
164
44
0.067
0.041
o
270
88
0.27
0. I
10
250
9'
0.26
o. 105
3
20
2IO
92
0.25
O. 12
40
150
' 96
0.315
0.2]
1
50
I2O
98
o. 165
0.14
;
o
24O
17
o. 14
O.O58
10
22O
18
0.15
0.068
4
20
IQ5
20
o. 17
0.087
40
150
24
0.23
o. 153
!
50
135
26
0.28
O.21O
TABLE 2
centage hum in terms of the d.c. voltage output
of the device. Power unit No. i (Table i) shows
the smallest amount of hum in the output but it
could not deliver more than one ampere at 6
volts. Unit No. 3 has more hum voltage than
unit No. i, but is capable of supplying up to
2.7 amperes at 6 volts.
The hum voltage measurements given in
Table 2 give some idea of the magnitude of hum
voltage obtained from some present-day B power
units. It is possible to make some interesting
mathematical calculations regarding the hum in
B power units to indicate the effect in the loud
speaker of various values of hum voltage, and
this subject will be discussed in an early issue of
RADIO BROADCAST. There is room here only to
point out briefly the salient points regarding the
matter. It can be shown that with a given audio
amplifier, capable of amplifying down to 60
cycles, the permissible amount of hum in the
output of a B power unit decreases:
(a.) as the amount of audio amplification in
the receiver is increased and (b.) as the voltages
on the various tubes, especially the detector tube,
is increased.
Just how much hum is permissible is, of course,
a function of the amount of amplification the
audio amplifier gives at the hum frequency and
how well the loud speaker will respond to these
frequencies and their harmonics.
COST OF OPERATION
THE cost of operation per hour of an A or B
power unit is found by first determining the
amount of power the device consumes in watts
when supplying the receiver, multiplying this
power by the cost of power per kilowatt hour, and
dividing by 1000. The cost of operation per
month can, of course, be found by multiplying
the cost per hour by the number of hours the set
is in use per month. An example will make the
whole calculation clearer. Suppose that a receiver
drawing 40 milliamperes of plate current is
operated from B power unit No. 4, Table 2, and
that the set is in operation on an average of three
hours a day. What will be the cost of operation
per month, if the cost of power is $0.10 per
kilowatt hour? From Table 2 we know that this
particular B power unit draws 24 watts of power
when supplying 40 milliamperes. Following the
information given at the beginning of this para-
graph, we multiply 24 by o.io and then divide
by looo. This gives $0.0024 as the cost of oper-
ation per hour. Since the set is in use 90 hours
per month, then the cost per month is $o.2ij.
Other examples can be worked out in the same
manner.
RADIO BROADCAST ADVERTISER
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FOR SALE AT ALL GOOD PARTS DEALERS
Write for this free booklet
THORDARSON ELECTRIC MFG. CO.
500 W. Huron St., Chicago
GENTLEMEN: Please send me, free of charge, your booklet describing your
210 power amplifier on the metal baseboard.
Name
Street and No.
Tallin State -
446
RADIO BROADCAST ADVERTISER
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described in
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THESE inst'ruments are designed
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Prompt instrument deliveries can be made
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2"
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WESTON
RADIO
INSTRUMENTS
The Radio Broadcast
SHEETS
THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this
magazine and have appeared since our June, 1926, issue. They cover a wide range
of information of value to the experimenter and to the technical radio man. It is not our
purpose always to include new information but to present concise and accurate facts in
the most convenient form. The sheets are arranged so that they may be cut from the
magazine and preserved for constant reference, and we suggest that each sheet be cut out
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should
be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to
that time was printed.
All of the 1926 issues of RADIO BROADCAST are out of print. A complete
set of Sheets, Nos. i to 88, can be secured from the Circulation Department,
Doubleday, Doran & Company, Inc., Garden City, New York, for $1.00. Some readers
have asked what provision is made to rectify possible errors in these Sheets. In the unfor-
tunate event that any serious errors do occur, a new Laboratory Sheet with the old
number will appear.
— THE EDITOR.
No. 177
RADIO BROADCAST Laboratory Information Sheet
Characteristics of Speech
April, 1928
ARTICULATION
/"*LEAR speech is only possible when the person
^ speaking uses careful articulation. Articula-
tion is especially important in radio for if we do not
understand something, we cannot have it repeated.
In analyzing speech sounds a clear understanding
of how the various sounds are produced is essential.
The human voice consists of sustained and tran-
sient notes and noises. The sounds which are ordi-
narily difficult to recognize (and which therefore re-
quire careful articulation), are the transients such
as are associated with the sounds "t" and "d" or
"p" and "b." These sounds are hard to reproduce
accurately for they contain many of the highest
frequencies found in sounds of speech.
If we examine the manner in which the sounds
"p" and "b," for example, are produced, they will
be found to have much in common. They are both
produced by first compressing the lips together and
then rapidly opening them. To pronounce the word
"pa," we first produce the "p" sound by suddenly
opening the lips and permitting the air to rush
through them and then the vocal chords are set in
motion to produce the vowel sound "a." The sylla-
ble "ba," is produced with a very similar motion
of the lips but the vocal chords are set into motion
and the lips open at the same instant and also there
is only a slight rush of air from between the lips.
The "pa" sound is characterized by an initial
sound of high intensity; the "ba" sound does not
have this feature. If the radio loud speaker cannot
reproduce accurately the strong portion of the
former sound, "pa," it will sound very much like
"ba."
Some of the sounds most difficult to reproduce
accurately are noises such as the dropping of a book
on a table, for these sounds contain frequency com-
ponents extending throughout the entire range of
audible sounds.
The study of how words are formed is very in-
teresting and can best be done with the aid of an
oscillograph, which is an instrument with which
we can obtain photographic records of the wave
form associated with any sound. An analysis of
these records, which are sometimes termed "audio-
grams," is helpful in determining the*range of fre-
quencies which must be handled by a radio broad-
casting system if the reproduction is to sound nat-
ural.
No. 178
RADIO BROADCAST Laboratory Information Sheet
The Exponential Horn
April, 1928
THE CUT-CFF FREQUENCY
THiE LOWEST frequency transmitted by a horn
•*• of the exponential type is determined by the
rate of expansion of the cross sectional area of the
horn, and to eliminate reflection the diameter of the
mouth of the horn (if it is round) must be made
equal to one-quarter of the wavelength correspond-
ing to the lowest frequency to be transmitted.
The velocity of sound in air is 1 120 feet per second
and, therefore, the wavelength (in feet) correspond-
ing to any particular frequency may be found by
dividing 1120 by the frequency. The diameter of
the mouth of the horn in feet must then be equal to
this wavelength divided by 4.
The accompanying curve shows graphically the
relation between the diameter of the mouth of a
round horn and the cut-off frequency. It should be
realized that the diameter of the mouth is not the
only factor determining the lowest frequency that
the horn will satisfactorily transmit and that the
size of the mouth is an indicator of this frequency
only if the remainder of the horn has been correctly
designed. As shown by the curve, to transmit fre-
quencies down to 64 cycles, for example, it is neces-
sary that the horn's mouth have a diameter of
about 4.5 feet.
If the horn is square rather than round, it will
be satisfactory to make the area of the mouth equal
to that of the equivalent round horn.
64 96 128
CUT-OFF FREQUENCY
192
RADIO BROADCAST ADVERTISER
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ELECTRIFY YOUR SET
WITH THE
MARATHON JKUT
SIMPLE AS A-B-C
-\ 4-ARATHON AC Tubes
IVL have the standard 4 prong
UX bases. No adaptors or
center top resistors.
Replace qour old Tubes
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' I "HE Marathon harness is universal, and can
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\*J nects with the Marathon
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on one voltage — 6 volts — so
there are no taps. Simply plug
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Plug in the light socket YOU CAN'T MAKE IT
-that's all there is to do CO M P L I CATED
No need to wonder if the Marathon AC Kit
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The Marathon AC Kit is Complete
Nothing else to buy — everything is complete.
For example the six tube kit includes 6 Mara-
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JOBBER DEALER PROFESSIONAL BUILDFR USER
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Addre
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RADIO BROADCAST ADVERTISER
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No. 179 RADIO BROADCAST Laboratory Information Sheet
A Problem in Audio Amplification
April, 1928
THE EFFECT OF TRANSFORMER RATIO
TDROBLEM: — The audio amplifier in a receiver
•*• comprises a 3:1 transformer in the detector
circuit, followed by a 201 -A type tube in the first
audio stage, a 4:1 audio transformer for the second
stage, and a power output tube. What will be the
effect on the amount of signal voltage supplied to
the grid of the power tube of substituting a 6:1
transformer for the 4:1 transformer?
ANSWER:— Let us first calculate the gain of the
original amplifier. The total amplification to the
grid of the power tube will be equal to the turns
ratio of the first transformer multiplied by the effec-
tive amplification of the tube times the turns ratio
of the second transformer. The effective amplifica-
tion of a tube in a properly designed transformer-
coupled audio amplifier can be taken as about 80
per cent, of the amplification constant of the tube;
for a 201 -A type tube, therefore, we take 80 per cent,
of 8, which is 6.4. The total gain of the amplifier is,
therefore:
3 x 6.4 x 4 = 76.8
Similarly the amplification with the 6:1 transformer
substituted for the 4:1 will be:
3x6.4 x6 = 115.2
The substitution of the 6:1 transformer, therefore,
has increased the voltage gain by 50 per cent.; this
represents a gain of 3.6 TU.
Now, the power into the loud speaker is propor-
tional to the square of the signal voltage on the
grid of the power tube feeding the loud speaker.
When the voltage gain is increased 50 per cent.,
therefore, the power into the loud speaker is in-
creased 125 per cent. This corresponds to a power
gain of 3.5 TU which, while not very great, is ap-
preciable. (The minimum gain audible to the ear is
ITU.)
If the power tube is a 171 type with 40 volts on
the grid, then using the original amplifier, approxi-
mately 0.5 volts (40 divided by 76.8) are required
out of the detector tube in order to place 40 volts
signal voltage on the grid of the 171. When the
6:1 transformer is used, only 0.3 volts (40 divided
by 115.2) are required from the detector in order to
"load up" the power tube.
No. 180
RADIO BROADCAST Laboratory Information Sheet
B Power Unit Characteristics
April, 1928
EFFECT OF TRANSFORMER VOLTAGE
THE CURVES published herewith were made
by the Raytheon Manufacturing Company
using one of their BH type tubes with an ordinary
filter, as indicated in the accompanying circuit
diagram. The curves show the relation between
the voltage, Et, across the secondary of the trans-
former and the input voltage, Eo. The output load
in milliamperes as measured by the meter I is
plotted along the horizontal axis and along the
vertical axis has been plotted the difference be-
tween the effective value of the transformer voltage
Et and the average value of the voltage Eo into
the filter system. The line marked +20, for ex-
ample, indicates the voltage Et to be 20 volts
greater than Eo; the line marked -|-£0 indicates the
converse.
These curves show that (to take an example)
with a transformer voltage of 300 volts per anode,
the average value of the voltage into the filter is 27
volts higher than the transformer voltage when the
load is 10 milliamperes. At a load of 28 milliamperes
the voltages are equal and at a load of 60 milliam-
peres the input voltage to the filter has dropped to
a value 25 volts below the transformer voltage.
During these tests the transformer voltage, Et, was
held constant.
Other data showing the effect of various trans-
former voltages, obtained with the same circuit
used here, were given on Laboratory Sheet No. 146,
published in the December, 1927, RADIO BROADCAST.
"^ 0 20 30 40 50 60 70 80 90
MILL1AMPERE LOAD
No. 181
RADIO BROADCAST Laboratory Information Sheet
R. F. vs. A. F. Amplification
April, 1928
A COMPARISON
TPHE SIGNAL output from a radio receiver may
1 be increased by augmenting either the audio-
frequency or radio-frequency amplification or by
boosting the detecting efficiency. On this Labora-
tory Sheet we give briefly the comparative merits
of audio-frequency and radio-frequency amplifica-
tion. In the accompanying table is shown the
effect on the power into the loud speaker of increas-
ing the a.f. or r.f. amplification. The first column
gives the increase in amplification and the second
column the increase in power into the loud speaker
if this extra amplification is introduced in the audio
amplifier. The third column shows the increase in
power into the loud speaker if the extra amplifica-
tion is placed in the r.f. amplifier.
This table is based on the fact, first, that the
power into the loud speaker is proportional to the
square of the voltage on the grid of the power tube
and, secondly, that the output of the detector is
proportional to the square of the voltage on its
grid. When the audio-frequency amplification is
multiplied by 10, for example, the power into the
loud speaker is 100 times greater. When the radio-
frequency amplification is multiplied by 10, how-
ever, the output of the detector is 100 times greater
and the power into the loud speaker is 10,000 times
greater. It is evident from these figures, therefore,
that increases in r.f. gain are much more effective in
producing greater signal than increases in audio-
frequency gain.
Increase in Power into Loud Speaker
Added
Amplification
2
5
10
20
50
A. F.
4
25
100
400
2500
R. F.
16
625
10,000
160,000
<i,2fiO,<XK)
RADIO BROADCAST ADVERTISER
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RADIO INSTITUTE OF AMERICA
Dept. E-4 326 Broadway, New York City
RADIO INSTITUTE OF AMERICA, Dept. E-4
326 Broadway, New York City
Dear Mr. Duncan:
Please send me your new catalog. I want to
know more about your new radio course.
Name. . .
Address.
No. 182 RADIO BROADCAST Laboratory Information Sheet April, 1928
Filter Condensers
HOW TO CONNECT THEM IN SERIES
TF WE desire to place a filter condenser across,
-1 for example, a 1000-yolt source of direct cur-
rent and we have available two large-capacity
500-volt condensers, it is ordinarily not possible to
connect them in series across the 1000-volt leads
with safety. Why this is so will be explained on this
Laboratory Sheet.
At A in the diagram is shown the connection of
two condensers, Ci and Ca, in series across the 1000-
volt source. Now, a condenser has a definite d.c.
resistance, which is generally very high but never-
theless finite, and this resistance is represented as
Ri and Ra in B as external resistances across each
condenser. A small amount of current will flow
through these resistances and the voltage drop
across the two resistances will be in direct propor-
tion to the resistances. The resistances of condensers
vary widely and therefore it is extremely unlikely
that we would have two condensers with the same
d.c. resistance. For example, condenser Ci might
have a d.c. resistance of 100 megohms while the
d.c. resistance of condenser Ca might be 900 meg-
ohms. The d.c. voltage drops across the two conden-
sers being proportional to the resistances there would
then be 100 volts across Ci and 900 volts across d.
If the two condensers were both rated at 500 volts,
the obvious result would be that condenser Ca would
have a very short life because of the overload being
placed on it. The solution for this difficulty is to
connect external resistances Ri and R» across each
condenser as indicated at C with a sufficiently low
value in comparison with the internal resistance of
the condenser (which is always very high) so that
the voltage drops will be determined by the external
resistances rather than by the internal resistances
1000-VoIt
Source
ABC
of the condensers. If we have two 500-volt con-
densers connected to a 1000-volt source, we might
equalize the voltage across them by connecting two
100,000-ohm resistances in series across the source,
as indicated at C. There would be 500 volts drop
across each resistance and, therefore, 500 volts
across each condenser, and the latter would then
be satisfactory in operation and have normal life.
No. 183
RADIO BROADCAST Laboratory Information Sheet
The Type 280 and 281 Tubes
April, 1928
THEIR CHARACTERISTICS
'T'HE characteristics of the type 280 and 281
•*• rectifier tubes are given below. These tubes
are for use as rectifiers in B power units, the 280
in circuits designed for full-wave rectification and
the 281 in half-wave circuits. Two 281 tubes may
be used, if desired, to give full-wave rectification:
TYPE 280 FULL-WAVE RECTIFIER
Filament Voltage 5 Volts
Filament Current 2 Amperes
A.C. Plate Voltage (Max. Per
Plate) 300 Volts
Max D C. Output Current 125 Milliamperes
Max. D.C. Output Voltage 260 Volts
Height of Tube 51 Inches
Diameter of Tube 2 A Inches
TYPE 281 HALF-WAVE RECTIFIER
»
Filament Voltage 7.5 Volts
Filament Current 1.25 Amperes
A.C. Plate Voltage (Max.) 750 Volts
A.C. Plate Voltage (Recommended) 650 Volts
D.C. Output current (Recom-
mended} :.. .\ ...... 65 Milliamperes
D.C. Output Current (Max.).-. . 110 Milliamperes
D.C. Output Voyage (Max.) 620 Volts
D.C. Output Voltage (Recom-
mended) 620 Volts
The type 280 tube may be used in circuits de-
signed especially for it or may be used in circuits
designed for the type 213 tube. The characteristics
of these two tubes are similar with the exception
that the former tube is capable of somewhat greater
output than the 213. If a 280 tube is used in place
of a 213, the 280 will be operating at less than full
load and will consequently have a very long life.
These facts are also true with regard to the 281,
which may be used satisfactorily.in place of a 216-B
type tube.
If more than about 65 milliamperes at 600 volts
is necessary to operate a radio installation, it will
be a good idea to use two type 281 tubes in a full-
v/ave circuit with about 650 or 700 volts a.c. on the
plate of each tube. With this arrangement an output
in excess of 100 milliamperes at 600 volts will be
available.
No. 184
RADIO BROADCAST Laboratory Information Sheet
Tuning
April, 1928
THE EFFECT OF DISTRIBUTED CAPACITY
A RADIO receiver to cover the broadcasting
band must be able to tune-in signals from
550 kc. to 1500 kc., a ratio of 2.73 to 1 in frequency.
It can be shown mathematically that, in order to
obtain this range, the ratio of fhe maximum to
minimum of the capacity across a tuning coil must
be 8.6 to 1 approximately. If we use a tuning con-
denser with a maximum capacity of 0.0005 mfd.
then the minimum capacity across the coil must
theoretically be (if the desired tuning range is to
be obtained) 0.0005 divided by 8.6, or 0.000058
mfd An ordinary condenser might have a minimum
capacity of about 0.000025 mfd. and, therefore, it
appears that we should be able to cover the broad-
casting band very easily. In the circuit, however,
there is another capacity across the coil which has
an important effect. This additional capacity is the
effective input (grid-to-filament) capacity of the
tube, indicated as Ci in the diagram, and this capac-
ity varies with the amount of amplification the tube
is producing in the circuit. This capacity, Ci, is in
parallel with C, the tuning condenser, and its effect
must therefore be added to that of C. The result is
that the actual minimum capacity of the circuit is
greater than that of the minimum capacity of C,
and this will tend to restrict the tuning range of
the receiver unless the precaution is taken that a
variable condenser with a low minimum capacity
is used to tune the circuit, that the coil itself does
not have much distributed capacity, and that long
leads in the circuit do not introduce objectional
capacity.
If a station transmitting on the lowest frequency
(longest wavelength) used in the broadcasting
band tunes-in on the set with the condenser plates
all in (as they should be) but it is found impossible
to tune-in a station operating on the highest fre-
quency (shortest wavelength), it is possible that the
cause may he due to a tuning condenser with a large
minimum capacity or excessively long leads con-
necting the coil with the condenser.
RADIO BROADCAST ADVERTISER
451
Custom
Set Builders
Building, as you do, a receiving set for the
buyer who insists upon the best in radio,
you naturally seek the very latest in de-
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DONGAN ELECTRIC MFG. CO.
2991-3001 Franklin St., Detroit, Michigan
^TRANSFORMERS of MERIT For FIFTEEN YEARS/,-.
Set Builders!
Free I9Z8 Radio Guide
The hie liarawlk Radio Guide book is used by
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Chicago, I . S. A.
Mail Thin Coupon Now! For Free Copy
Name
HAMMARLUND
"Midline"
CONDENSER
Soldered brass plates with tie-bars;
warpless aluminum alloy frame;
ball bearings; bronze clock-spring
pigtail; full-floating, removable
rotor shaft permits direct tandem
coupling to other condensers.
Made in all standard capacities
and accurately matched.
Write for Folder
HAMMARLUND MFG. CO.
424-438 W. 33rd St. New-York
The Remarkable
HAMMARLUND-ROBERTS
HiQ Six RECEIVER
(Both A. C. and Battery Models)
Is Equipped with
This Famous Condenser
Take a tip from the experts and place your
reliance in the Condenser they all respect — the
condenser that most of them specify for their
newest circuits.
The Hammarlund "Midline" embodies the best
Condenser thought and engineering skill in the
history of radio.
// Your Dealer Can't Supply You
Write Direct to Us
HooUxy
ammarlund
f F<£C ISIOM
PRODUCTS
NEW
N A TIC N A
DRUM DIAL
Type F
Velvet Vernier Quality
and Tuning. Beautiful
Hammered Silver Fin-
ish. Quick and Easy to
Install.
List Price $4.00
Type 28 Illuminator
50c
NATIONAL COMPANY, Inc., Maiden
Radio
Convenience
Outlets
Wire your home for radio. These out-
lets fit any standard switch box. Full
instructions with each outlet.
No. 135— For Loud Speaker Jl.OO
No. 137 — For Battery Connections 2.50
No. 136— For Aerial and Ground 1.00
With Bakelite Plate*
Now furnished with a rich satin brown Bakelite
>late. with beautiful markings to harmonize, at
15 cents extra. See Illustration.
At Your Dealers
Yaxley Mfg. Company
Dept. B, 9 So. Clinton St.
Chicago, 111.
You Can't Control
Lightning
WHEN lightning goes on a rampage no one can
tell just what is going to happen. When it
strikes it generally takes the shortest electrical path
to ground. When an outdoor antenna is used that
path may be through the radio set if the set is not
protected by a reliable lightning arrester.
The Jewell Lightning Arrester is the best pro- Jewell Lightning Arrester
tection available for radio sets against Lightning. As
an indication of its reliability, it is listed as Standard by Underwriters' Laboratories, who
give it regular periodic tests for performance. It consists essentially of an accurately cali-
brated air gap enclosed and sealed within a glazed brown porcelain case suitable equally for
indoor or outdoor installation.
Radio dealers everywhere carry Jewell Lightning Arresters in stock. Ask your dealer
to show you one or write us directly for descriptive information.
Jewell Electrical Instrument Company
1650 Walnut Street, Chicago
"28 Years Making Good Instruments"
452
RADIO BROADCAST ADVERTISER
AT LAST/
A Real Radiophone Transmitter
a reasonable price!
Employs
Low Power
Surprisingly
Long Range
Easy to Build
Easy to Operate
For All Low
Wave Work
The Aero Radiophone Transmitter —
Ready to Plug into Electric Light Socket
Here is a low power radiophone transmitter that every true radio fan will
want to own. An extremely efficient circuit, designed by some of the best
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government licensed low wave bands.
Simple to operate, easy to build, its cost is no more than" that of a good
broadcast receiver!
500 to 1000 Miles on Phone — Several
Thousand Miles on Code
The New Aero Radiophone is a thoroughly tried and proved transmitter. As
installed at station 9DBM, Chicago, the results on 20 meters have been re-
markably good. Reports varying from R-5 to R-7 have been regularly re-
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Medford, Mass.; 1SW, Andover, Mass., 2BSC, Glen Head, N. Y.; 3AKS,
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Adapted to code work, the Aero Radiophone Transmitter has produced out-
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worked with CW on the 40 meter band, as well as NC5ZZ, Vancouver, B. C.
Outstanding Performance Assured By
Carefully Selected Parts
Only the best quality parts have been incorporated into the Aero Radio-
phone Transmitter. Products of the following manufacturers — all with a
national reputation — are specified exclusively!
Aero Products, Inc.
Chicago, 111.
Allen D. Cardwell Co.
Brooklyn, N. Y.
Herbert H. Frost, Inc.
Klkhart, Ind.
Polymet Mfg. Co.
New York, N. Y.
Silver-Marshall, Inc.
Chicago, 111.
Tobe Deutschmann Co.
Cambridge, Mass.
Yaxley Mfg. Co.
Chicago, 111.
Westinghouse.Micatta
Chicago, 111.
INVESTIGATE NOW Write for FREE BOOKLET
The Aero Radiophone Transmitter is worthy of your careful investigation. Send your
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how easily you can get into the fascinating field of radiophone transmission. Address
AERO PRODUCTS, Inc.
Dept. 109-R, 1772 Wilson Ave. Chicago, 111.
MOTP • The parts for the aAero 'Radiophone Transmitter are standard parts and are available at all
[*v/ •*• •*• ,;,.,./,.,-, when completed is ready toplug into your electric light socket. All have been care fully
chosen to give the maximum in transmitter performance. Complete drilled and engraved foundation units
are also available.
BANDBOX
1 Single Unit AC Bandbox 7O4, $95.
•*•• Genuine neutrodyne fully shielded- selective.
O Dry cell operated Bandbox Junior, #35.
~* Loud speaker volume — most economical.
2 Bandbox 601, #55. Operates from bat-
-^ • teries or power supply units.
4 Double Unit AC Bandbox, #90 for console
• installation. Adaptable to any installation.
5 New Type — D Musicone, #15. Loud speaker
• leadership in popular price field since 1925.
Write Dept. 20 for descriptive information.
THE CROSLEY RADIO CORPORATION
Powel Crosley, Jr., Pres. Cincinnati, O.
Cronlfy in licensed only for Radio Amateur. Ksperimental and
Broadcast Receptwn. Prices aliglilly higher in far Western *tatt*.
RADIO
CONDENSERS
B-BLOCKS
VER1TAS RESISTORS
Universally accepted as standard for
the construction of Radio Receiving
iSets, Resistance and Power Oupply
Amplifiers and Power Supply Units.
Send 25$ for new Power Supply Handbook
Tooe Deutschmann Co.
Cambridge, .Mass.
ACME
WIRE CO.
CJELATSIT
for RADIO
WIRING
Flexible stranded Celatsite
composed of fine, tinned cop- ;
per wires with non-inflammable
Celatsite covering in 9 bright
colors. Strips clean, solders
readily. Sold only in 25' coils, in cartons colored
to match contents. Solid Celatsite has same col-
ored covering, but over bus har wir«.
ACME SOLID CELATSITE is a tinned copper
bus bar hook-up wire with non-inflammable Celat-
site insulation, in nine colors. Sizes, 14, 16, 18,
19, 30" lengths. Write for folder. The Acme
Wire Co., Dept. B, New Haven, Conn.
Thirteen years of concen-
trated effort on a single
product has brought such
uniform perfection that con-
fidence in these tubes and
the name they bear is al-
most universal among radio
enthusiasts.
E.T.CUNNINGHAM, Inc.
New York Chicago San Francisco
SINCE 1915
STANDARD
For .ill sets
CRYSTAL
a
CARBORUNDUM STABILIZING
REG. U. S. PAT. OFF.
DETECTOR UNIT
A LL the volume you need and selectivity
**• too, when you attach this unit — but,
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tones — natural, true, and crystal clear.
Can be used on nearly all sets.
The Complete Unit No. 32 for $3.50
The Detector alone No. 30 is $1.5O
Buy from your dealer, or we
wilt send direct.
Use coupon to get our Hook-Up
Book, sent free.
THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y.
CANADIAN CARBORUNDUM CO., LTD., NIAGARA FALLS, ONT.
/ The
/ Carborundum
/ Company
/ Niagara Falls, N.Y.
Please send free
IIook-VpBookD-2
COMPLETE PARTS FOR
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AC SUPERHET.
GET prompt, efficient service
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Dealers — Write for Catalog
WESTERN RADIO MFG. CO.
134 W. Lake St. Dept 44, Chicago
ELKAY
Controls the Squeals
The Hammarlund "Hi-Q" Receiving Set
which uses box shields oj Alcoa Aluminum
Sheet and special corner post moulding.
NOW-
Fiiier Reception
for Amateurs
A.UMINUM BOX SHIELDS will
help you to get greater dis-
tance,better selectivity — closer tun-
ing. Their use eliminates or
greatly reduces interference.
They are ideal for shielding cir-
cuits using the new shielded grid
tubes.
The superiority of Aluminum
is recognized by Hammarlund in
the design of the "Hi-Q" receiver
(above). Two special Hammar-
lund Box Shields made of Alcoa
Aluminum Sheet are used.
Aluminum Company of Amer-
ica's standard box shields, de-
signed especially for amateur
sets, are made of heavy Alcoa
Aluminum with satin-dip finish,
size 5 in. x 9 in. x 6 in. high.
They are easily adapted to
smaller sizes. They require no
soldering. They embody the ideal
combination of high electrical
efficiency, mechanical strength,
lightness, fine appearance and
long life.
Be sure to use Aluminum Box
Shields, for finer results. If your
dealer cannot supply you, send
us your order and we will have an
authorized dealer ship promptly
at $3.50 each (standard size).
You simply pay the postman.
ALUMINUM COMPANY
OF AMERICA
2454 Oliver Bldg., Pittsburgh, Pa.
F. A. D. Andrea, Inc., uses Alcoa Aluminum j or Shielding
and other parts of "Fada" receiving sets.
Expect Better Results When
You See This Metal in Radio
w
HEN you look at ra- ers employ parts of Alcoa
dio receivers using Aluminum so that the pur-
aluminum shielding or con-
denser blades; aluminum
castings, front panels,
chasses or sub-panels you
will know that
the manufactur-
er has chosen the
one metal that
most efficiently
meets all the
widely differing
conditions en-
countered in ra-
dio design.
Such famous
makers as Atwater Kent,
Crosley, Fada, Freed-
Eisemann, Grebe, Howard,
R-C-A, Stewart -Warner,
MR. L. M. CLEMENT
Chief Engineer of
F. A. D.Andrea, Inc.,
commenting on shielding
says,"In a radio receiver
aluminum, because of its
electrical conductivity,
makes a more efficient
shield than any other of
equal weight. The ma-
terial can be easily drawn
into the desired shape
and its finish is perma-
nent and pleasing to the
eye."
chasers of their receivers
may enjoy the best of radio
reception.
These makers recognize
the superiority
of Alcoa Alumi-
num. They ap-
preciate its ideal
combination of
high electrical
conduct ivi ty,
lightness,
strength, and
beauty. Lookfor
Aluminum in the
set you buy —
when youfind it youmay ex-
pect the best results that the
^j/radioengineershaveyet
achieved. Sendforacopyof
S tromberg - Ca rlson, our new booklet, "Alumi-
Zenith and a host of oth- num for Radio." It is free.
ALUMINUM COMPANY OF AMERICA
2464 Oliver Building
Pittsburgh, Pa.
All MINI N
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