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Full text of "Surplus Radio Conversion Manual Volume 3"

SURPLUS RADIO 
COPERSIOfll MANUAL 




VOLU/ 


AE III 


Conversion of 




701 -A 


MBF (COL-43065) 


AN/APN-1 


MD-7/ARC-5 


AN/CRC-7 


R-9/APN-4 


AN/URC-4 


R23-R28/ARC-5 


ARA 


RAT, RAV 


BC-442, 453-455, 456-459, 603 


RM-52 (53) 


696, 950, 1066, 1253 


RT-19/ARC-4 


CBY-29125, 50083, 50141, 


SCR-274N 


52208-11, 52232, 52302-09 


SCR522 


FT-241A (for crystal filter) 


T-15/ARC-5 to T-23/ARC-5 



SEE TABLE OF CONTENTS ON PAGE 4 



For 



Amateur, Novice, Technician 

and 

Citizen's Radio Service 



L 



Just like OF Man River surplus equipment keeps rolling along. The 
supply waxes and wanes, but never completely dries up. Untold amounts 
of equipment are snapped up by "surplus hounds" only to be replaced by 
new, larger amounts of equipment arriving from unknown locations. Surely 
there must be some huge, hidden factory turning out tons of surplus 
equipment each day which will be sold to hams and others at bargain 
prices! 

Modifying surplus equipment to fit the needs of the Amateur or 
Citizen Radio fan is interesting and exciting work. The high quality of 
most surplus equipment cannot be matched by commercial equipment 
selling at many times the cost of the surplus item. The converted surplus 
item can be made a piece of high-grade "ham" equipment at a money 
saving price! 

However, every silver lining has a cloud. Some pieces of surplus 
equipment do not have schematic diagrams. Many items are modified from 
the original diagram, making the conversion process akin to a crossword 
puzzle. Other items are not worth the time to convert them! The enthusiast 
"surplus hound" must choose wisely and well when he buys, and must be 
adept at improvisation and "make-do." 

Because of the time required to enter into personal correspondence, 
and because of the rapid and chaotic changes in the surplus market (and 
surplus equipment) it is impossible for the editors of this Manual to answer 
questions relating to conversions of equipment, to requests for schematics, 
or for purchasing information. The reader is referred to CQ magazine, 
which runs a surplus column. This column often contains answers to the 
perplexing questions which may confront the "surplus hound." 

Good luck, and may your conversions always work! 

Special thanks are due the Arrow Sales Company, North Hollywood, 
California for the use of several difficult-to-locate schematics. 



$3.50 
Cat. No. EE-333 



SURPLUS RADIO 
CONVERSION MANUAL 



VOLUME III 



WILLIAM I. ORR 

Editor 



Copyright, 1960 by 

Editors and Engineers, Ltd. 

New Augusta, Indiana 

Copyright under Pan-American Convention 
All rights reserved 

Printed in U.S.A. 




Published and distributed to the electronics trade by 

New Augusta, Indiana 



EDITORS and ENGINEERS, Ltd. 



SURPLUS RADIO CONVERSION MANUAL 

VOLUME ill 



LIST OF EQUIPMENT 
on which data is given in this volume 



T-15 toT-22/ARC-5 ) 

?5; 4 ol/S 45 ? &696 t Transmitters/Receivers 5 and 41 

SCR-274N series \ 

CBY-52000 series } 

DY-8 or DY-2A/ARR-2 Dynamotors 11 

DM-34D Dynamotors 13 

BC-453 Receiver 14 

BC-455 Receiver for Citizens' Service 17 

BC-603 (SCR-508, 528, 538) Receiver for Citizens' Service 18 

AN/APN-1 Altimeter, as Transmitter 19 

AN/CRC-7 Transmitter/ Receiver 22 

AN/URC-4 (RT-159) Transmitter/Receiver as Handie-Talkie 28 

MD-7/ARC-5 Modulator 29 

BC-442 Relay for antenna changeover 30 

RM-52, 53 Telephone Unit as phone patch 30 

FT-241A Crystals to make crystal filter 31 

T-23/ARC-5 Transmitter, to 50 or 144 Mc 31 

BC-458 (SCR-274N) Transmitter, conversion to S.S.B 37 

WE-701-A W. E. Tetrode Tube 42 

BC-1253 Transmitter as radio control receiver 43 

BC-1066 Receiver 43 

R-9/APN-4 Receiver 46 

MBF/COL-43065 Transmitter/Receiver ...._ 46 

24-volt Dynamotors to 115 v.a.c. motors 49 

R-28/ARC-5 Receiver, Adding Variable Tuning Control 49 

RT-19/ARC-4 Receiver/Transmitter for 2 meters 52 

BC-624 (SCR-522) Transmitter, TVI-proofed 60 

BC-312 series Receivers 63 

BC-342 series Receivers 63 

BC-348 series Receivers 67 

BC-375/BC-191 As Modulator 69 

AN/ART-13 Autotune Transmitter 70 

LM Power Supply for LM Frequency Meter 76 

AN/APT-5 Radar Set schematic diagram 77 

CPR-46ACJ (ASB-5) Receiver schematic diagram 78 

BC-659 Receiver/Transmitter schematic diagram 80 

BC-1335A Receiver/Transmitter schematic diagram 82 

AN/ARR-2 Receiver schematic diagram 85 

AN/APA-10 Panoramic Adapter schematic diagram 86 

AN/APT-2 Radar Set schematic diagram 88 

Other Outstanding Books from the same Publisher 

The Radio Handbook 

The Radiotelephone License Manual 

Surplus Radio Conversion Manual, Volume I 

Surplus Radio Conversion Manual, Volume II 

The World's Radio Tubes (Brans' Radio Tube Vade Mecum) 

The World's Television Tubes (Brans' Television Tubes Vade Mecum) 

The World's Equivalent Tubes ( Brans' Equivalents Tube Vade Mecum ) 



Surplus Radio Conversion Manual, Volume III 



The "Command" Sets 

The "Command" Sets are probably the most popu- 
lar pieces of radio equipment on the surplus market. 
Designed in 1938, they were produced in prodigious 
quantities for over a decade for the Army, the Navy, 
and the Air Force, The various items of equipment 
that make up a complete set form a multi-channel ra- 
dio transmitting and receiving package for use on 
airplanes equipped with a 24 volt d.c. power source. 
The equipment is designed to transmit and receive 
voice, tone modulated, or continuous wave signals. 
Included in the equipment are various receivers, trans- 
mitters, modulators, and auxiliary items, tabulated in 
figure 1. 

The basic circuit for all Command transmitters is 
shown in figure 2. A master oscillator excites a pair 
of beam power amplifier tubes connected in parallel. 
The master oscillator and power amplifier tuning ca- 
pacitors are ganged for simplification of controls A 
quartz crystal resonator ( Y-50) is supplied with each 
transmitter for use with a "magic eve" tube to check 
frequency calibration at one spot on the dial. The 
crystal does not control transmitter frequency. Con- 
tinuously variable coupling between the power am- 
plifer tank circuit and the antenna circuit is achieved 
by a rotary loading coil i L-52 ) and a rotary link coil 
in the amplifier tank circuit. 

The basic circuit for the Command receivers is 
shown in figure 3. All receivers are one-band super- 
heterodynes, and except for L-C elements forming the 
ri. and i.f. tuned circuits, they are essentially alike 
electrically and physically. Each receiver employs six 
metal 12 volt tubes. 

All Command equipment is designed to mount in 
racks which make electrical interconnections via built- 
in plugs. In general, the racks for one series of equip- 
ment are not interchangeable with racks of other se- 
ries, as the plug sizes and pin connections differ for 
the different branches of the Armed Forces. The use 
of the racks is not necessary, however, for amateur 
service. 

The following information concerns the adaptation 
of the Command equipment for amateur use. Addi- 
tional conversion information for this popular equip- 
ment is given in Volumes I and II of this surplus con- 
version series. The material included herewith is new, 
and does not duplicate material given in the previous 
manuals. 

Converting the Command Receiver 
to Six Meters 

Technicians and v.h.f. operators are interested in 
a method of converting the Command receivers for 
v.h.f. operation. The conversion involves constructing 
a power supply, rewinding the receiver coils, and re- 
placing a tube. This conversion may be done with any 
receiver, but the use of the 3-6 Mc. receiver is recom- 
mended as the i.f. bandwidth is about optimum for 
general usage. 



Remove the top covers and the bottom plate, sav- 
ing the screws. Clean off the rear area of the receiver 
where the dynamotor was mounted and wire in the 
power supply shown in figure 4. Note that the two 
filament windings of the transformer must be correct- 
ly phased to produce 11.6 volts, a.c. The 12 volt tubes 
operate perfectly at this voltage. Make sure the re- 
ceiver works on a.c. before you start the rest of this 
conversion. 

Now, remove the coils by taking out the screws on 
each side of the receiver case that hold the assembly. 
Lift out the triple coil can and remove the 12 screws 
holding the coils in the cans. Remove the coils from 
the base and clean the terminals. Discard the original 
coils. Wind the self-supporting coils shown in figure 
5. Reassemble the coils in the shields and replace the 
unit in the receiver. 

Next, remove the 12SK7 ri. tube (immediately 
behind the tuning capacitor) and replace it with a 
W E-717A, available at any large surplus store. (This 
tube is an octal based 6AK5, and has the same pin 
connections as the 12SK7). Rewire the "hot" filament 
pin to the six volt \\ incline: of the filament transformer, 
as shown in figure 4. 

Inject a 50 Mc. signal into the receiver, holding the 
signal level clown to pivvent receiver overload. Adjust 
the oscillator padding capacitor C-4F. atop the tun- 
ing capacitor' until the 50 Mc. signal appears at 5.7 



FREQ, |- 



" COMMAND" T RANSMj TTERS 
NOMENCLATURE 



RANGE [JOINTARMY-NAVY; SIGNAL CORPsl NAVY " 1 DES|G 

(MC) (JAN) J (BC) — ■ 



-U 



(ATA) 



MODIFICATION 



T-18/ARC -5 i — 

— j BC-696 



j CBY-52232 
! CBY-52305 



T-19/ ARC -5 



T-20/ ARC-5 



CBY-52208 
| CBY-52306 



| CBY — 52209 
i CBY- 52307 



| T-21/ARC-5 



CBY -522)0 
CBY- 52308 



" ! T-22/ARC-5 

J_ 1 ~~~"_' 

i 0.5-0.8 I 

! j T-15/ARC-5 

| 0.8- 1.3 I 

i ! T-16 /ARC-5 



T-17/ARC-5 



CBY-52211 
CBY-52309 j 

CBY-52302 

CBY-52303 j 

CBY -52304 



T-23/ARC- 5 



MODUL. I 

UNIT j MD-7 /ARC-5 



BC-950 
8C-456 



ANTENNA] 
RELAY | 



CBY -50063 
CBY -5014 ! 



CBY - £ 9 ! 2 5 



NOTES: A -PLATE AND SCREEN MODULATED. 

^-MODULATOR INCLUDED IN TRANSMITTER. 

C-PLATE CIRCUIT OF P-A IS SHUNT-FED IN JAV MCDElS 



Figure 1 

CHART OF VARIOUS MODELS OF 

"COMMAND" TRANSMITTERS 



/2J5GT TaN£ OSC/ILAT0X 

PECEPTACLE _/N MODULATOP UNIT 
AND /N £EC£/)/£e £A C< / 

FOP CABLE -5308 



shunt 

F/ELO 



DYNAMOTOf 

/62S MOOOLATOZ 




COUP I I/VG PL UG J- 50 



COUPLING RECEPTACLE J- 51 




ve- /so 30 

/VOLTAGE ££GULAT0g 




AMP.C CZ JZ 



OSC. £a 



GZQUND s 



RECEPTACLES IN MOOULATQ£UHIT 
AND T£ANSMITTE£ £ACK 



CABLE 53Q4- 



V 



RECEPTACLES //V MODULATO/2 UNIT 

and neANSM/rrte control sox 



RECEPTACLE /N 
T£ANSMfTT££ CONTROL 80* 



MOTE ON 5tY/TCN£S SSO ANOS-52 
THE NUMBE£S ON THE VAP/OC/S 
CONTACTS REFE£ TO THE POS/T/ONS 
OF THE SWITCH LEVERS A T WHICH 
THESE PARTfCULAe CONTACTS APE 
CLOSED 3r THE ACT/ ON Of THE 
<SlN/TCH. "TONE " /S 1 } "CW/S 2, ANO 
"VOICE" fS 3. 



rrp£ csy-23243 

T#ANSMtTr£& CONTZOl BOX 



CAPACITANCES 


SrMBOL 


RELAYS 

T DESCRIPTION 


INDUCTANCES 


PES/5 

SYM&OL 

#-50 


TANCES 
OXMS__ A 
42 


RES/STANCES CONT 


SYMBOL 


MICROFARADS 


SYMBOL 


DESCRIPTION A 


SYMBOL.) OHMS 


c-so 


.006 

.65/05/05 


K-50 


DrNAMOToe JNPUT 


L-50 


£F CHOKE APPZOX 


^e- 70 


/OOO F0£ 2J-3MC T£ 


C-S/(A,Bp 








/S M/CJeOH£H£/£S 


£-5/ 


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#.-70 


7500 FOP 3-4 MC T£. 


C~$ 2 












£ '-52 


300,000 


£-70 


/OOO FOE 4-5 3 AtC T.?. 


C-33 


( 2 


K- 51 


S IDE TONE , VOICE 


1-5/ 


1. 7 HEN/5/ £S 


£-53 


91, OOO 


/e-70 


/OOO FO/PJ.3- 7 MO 7?. 


C -54(A,B) 


5/fO 




AND TONE 






J2-54 


200 


£•70 


/SOO F0£ 7 -9. IMC 7 P. 


C -55 


/ Z 






L-5Z 


ANT TUNING 


RSS 


/5000 


£-71 


726 


C-56(A,&) 
C-5 7 
C-58(A,BC) 


5/5 
.05 
05/05/05 


K-52 


JJrN/o^oTO:'. H/GH 
VOLTAGE OfETtNG) 




I HO L/C TOP 


£-57 
£-58 
PS 9 


390 

51,000 

30,000 


£-72 
£-73 
£-73 


5/ OOO 

/5.000 FO£ 2. / -3 MC r£. 

S, IOO FOP 3-4 Ate re. 


C-6G 


MO PADDING 


KS3 


TPANSPM rc& 






£-60 

je-6i 


75.000 
20 


£-73 
£-73 


/0, 000 FOP 4 5. 3MC '£ 
75000 FOP S3- 7 NC ,£■ 


C- 61 


006 




SELECTOP 






e-62 


10,000 


£■73 


SJOO F0£ 7-91 MC ?£ 


c-ez 


FIXED NEUTJS 










£-63 


20 000 


e-74 


'5,000 


C-63 


MO TUN /NO 


K-54 


T£ANSM/-T£/e 






£-64 


WO, 000 


£-7S 


51,000 


C-64 


.002 




[ OUTPUT 






/e-65 


/5,00c 


£-76 


20 


C-65 


PA TUN/NG 










e-6s 


5/0 


>P-77 


390 


C -66 


Of 


K-55 


ANTENNA SMTCtf- 






£67 


5/, 000 


£-78 


51 


C-67 


PA PADD/NG 




/NG, PEC. 70 T£ANS 






£-68 


SO 


£-79 


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C 68 


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£-69 


/,000 000 


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C-69 


.00005 














£1-5/ 


PA£A5JT/C 5OPPg£550£ 



Figure 2-A 

SCHEMATIC, "COMMAND" TRANSMITTER, MODULATOR AND 

CONTROL BOX (ATA-TYPE PLUGS). 



ttpc car-30033 MoouLArox ujv/r w/th 
rrp£ car-2/626 TXANSn/rrsx oynamoto^ unjt 



NOTES : 

/ ALL ££ LAYS SHOWN //V /SON- ENEPGf Z£D POS/TtON 
2. ALL COUPLING PLUGS AND /RECEPTACLES SHOWN AS 
VIEWED FPOM THE OUTSIDE. ALLPLUGSAS VIEWED 
FZOM THE COeOAGS £rtO MVE THE SAME OJPfEHTAT/ON 
OF COti DOCTORS AS TtfAT SHOWN HE PC POA? TN£/P 
PE5P£CT/V£ A?EC£PTA CLES 



• 4 S *• 



rrPf CBY- 52212 
rgANSMiTTCg £ACK western, rawtrra, 

, /" CONNECTS H£p£. 




PECEPTACLES WTZANSM/TTEJ? £ACK 
2 €4 ) AMD ANTENrt* #£LAY VHfT 



CABLE £8/0 




SJY/TCHES_ 



S-So 
SSt 

s-ss 

S-S3 



DESC^JPTION 



MAiH "OAf-OEF" 
BATTEgy UNE 

r#AffSM/rr€Je 

SELECTION 

SHUNTS MIC. 
SEIZES 
PES /S TOG 

ANrcUKRENT- 
M£T£# SW/7TMfHC 



SYMBQL^DESCP/PT/ON 



rs'O j tone osc. 

T-Sf MICROPHONE 

T-52 MODULATION 

fS3C4,8,C) MASTER OSC 

TS4(A,B) TPANS. OUTPUT 

T- 5 5 fa, 8) ANT Cape EN T 



MISCELLANEOUS 



SYMBOL X Pf-SCAjtPTfOfiL. 
TC -50 TAE/efifO COUPLE 

M-SO ANT CUP/PENT 

/HD/CATOeaoCAL) 

<S6 BUILT-/N JfEY 

r-SO CRYSTAL UNIT 



TYP£ CSV- 29/ 25 
ANT£MNA A£lAYUrtiT 



ESO 

rst 



eoA FUSE 
20 A FUSE 



SCHEMATIC, "COMMAND" TRANSMITTER, MODULATOR AND 
CONTROL BOX (ATA-TYPE PLUGS). 




1 ^- 



SLOT JN CM A 35/3 



BOTTOM V/£W 



Figure 2-B 
WIRING DIAGRAM AND PARTS PLACEMENT, "COMMAND" 

TRANSMITTER. 




RfAR V/£W 




CONN£CTtONS 0/V r-S3 



TO H/GHS/0£ 
0£ C-60 




fstrjeOTOJZS To£NGAG£ 
SrATOGS AS rOLL O WS; 
2 / -3 MC T&A/1S. 4/° 
3-4- MC T#AtfS. 72 '/4° 
4 -J". 3 MC Tie/MS. 78° 

s.3 -7 mc t&a/vs, a/'/ 2 * 

7-9.1 MC T&ANS. 9S'/ £ * 



2./-S MC r#ANS. 79S8 
3-4 MC TXANS. 6029 
4- -S3 MC r#AMS. 6030 
S.3'7 MCTRA/iS. 603 f 
7-9J MC T£AHS. 6032.) 



^ 



2/- 3 MCT£AMS. 799/ 
3-4 tfCT£A/*S. 7247 
4-S3A?Cr&AtfS. 724$ 
S.3-7MCTjeAAt3. 7249 

7-9./AfcreA/rj. 72S0 



\& 




Hi 

lib 







I 
I 

! 



r £S2 

2J-3 AfC WANS 
3-4 MC TfiANS 
4S3*fC r#4#S 
£3-7 MC r#AMS 







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6035 



\7-9J AfC TfiA/VS 603S 



Figure 2-B 
WIRING DIAGRAM AND PARTS PLACEMENT 

TRANSMITTER. 



'COMMAND" 



10 



Surplus Radio Conversion 



/2A6 
AUO/OAMP 




.-— t CAM 



2 3~ 

AS Vt£W£I> 

fgom oorsji>£ 



X5 V/£*£D L,fi£i 

I 



CM CSC 

s-Hur- orr 

l/M£ 



circuits in &f coil set, /f coupling units, cw oscillator, and output reANsroeME/e. 

THE T££M/NAL tfOMBEJZS ON THESE UNITS AGZEE W/TH THOSE SHOWN AT THE CoeZESPONDING 
lOCAT/ONS ON TNS W/je/NO D/A3/BAM. 



er co/l set 

SrMBOL z-s 




SYMBOL zsc 

gr osc/LLAToe 



SYMBOL Z-SB 

er amplified 



SYMBOL Z-S A 
jer ANTENNA 



/F COUPLING UNITS 




SrMBOL Z-I 

/st. /r 

(2830 ICC) 



SYMBOL Z-2 
2"° /F 
(2830 ATCj 



SYMBOL Z-3 
3** '/F 

(2830 AC) 





SYMBOL Z-4 
CH OSCILLATOR 
(2830 KC) 



SYMBOL T-l 

OUTPUT TRANSFORMER 



Figure 3-A 
SCHEMATIC, "COMMAND" RECEIVER (ATA-TYPE PLUGS). 



Manual, Volume III 



11 



CAPA C/TANCES 1 INDUCTANCES 


ZESISTANCES 


SYMBOL DESCPIPT/ON | SYMBOL 


D£SC£/PT/ON 


SYMBOL 


OHMS 


C-J 8.5 MMF 1 I-/ 


ANT INPUT 


£-/ 


620 


C 2 /5 MMF | L-2, L*3 


£F AMP 


e-z 


2,000,000 


C-3 f 00 MMF 


l'4,L-5 


£FOSC 


£-3 


51,000 


C-4.(AT9G)GA#n(62?iMr) 


1-6,1-7 


IN 1ST if 


£-4 


62 O 


C-5 


3 MFD 


L'8 t L-9 


IN Z** IF 


£-5 


/ 50,000 


C-6CA,B,C) 


.05/ OS/. 05 MFD 


L-IQ,L-II 


IN 3*0/F 


£-6 


150,000 


c-7(A.a,c) 


OS/OS/.OSMFD 


1-/Z.I-/3 


C¥f 06C 


e-i 


20O 


C~8 


zoo mmf 


1-/4 


R.F CHOICE, 


e-8 


ZOO 


C-9 


40MMP 




/1 2 MICGO- 


£-9 


620 


C-/0 


Z40MMF 




HEH£/ES 


£-io 


360,000 


C-li 


3 MMF 


l/S 


A F CHOKE 


X-fl 


100,000 


C-/2 


/SO MMF 




3 HEN/2IES 


e~tz 


SIO 


C-/3 


/7 MMF 






£-13 


200 


C-/4 


/SO MMF 






£-14 


WO, 000 


C-I5(A.8,C] 


.05/.0S/.05 MFD 






£-15 


5.160 


ottfrAc} 


.22/22/21 MFD 






£-16 


SI, 000 


C-/7 


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P*17 


SI, 000 


C-18 


(7 MMF 






£-/$ 


sio, ooo 


C-19 


/ 80 MMF | 




/e-19 


/oa, ooo 


c-2o<A,a,c) 


05/.0IJ.05 MFD 






£20 


2,000,000 


C-ZI 


17 MMF 






£-Zl 


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c-zz 


/SO MMF 






£-22 


7000 


CZ3 


/ 80 MMF 






£-23 


7000 


C-24 


200 MMF 










c-zs 


00/ MFD 










C-26 


/ 00 MMF 










c-sy 


/go MMF 










C-28 


34MMF 










C-29 


.006 MFD 










C-30 


/SMFD 










C-31 


.061 MFO 










C-3Z 


S MFD 










C-3 3 


WISING CAP- 
ACITANCE (USS 
THAN 2 MMF) 











rose socket teatm/mals 

*$ Y/EtYED FfiOM BOTTOM 




TO BE TERMINAL CODE. 



S~ SHELL 

M=HEATEA? 

X -CATHODE 

Su= SUPPRESSOR G£/D 

Dfc»rf/£ST DIODE PLATE 



Gs -. SCREEN G/2/D 

G sc»£X) = SCREEN G£/D, HEXODE SECT /OH 

G»(o$o*coMT/eoL cr/d, osc section 

P: PLATE 

P(HCK)* PLATE, HEX ODE SECTION 
0/02= SECOND D/OOE PLATE Pofasc)' PLATE, OSC. SECT/ON 
G-CONTROL GAl/D G (*£*)* CONTROL Ge/D,HEXODE SECT/ON 



Figure 3-A (continued) 



Mc. on the tuning dial, Retune the signal generator 
to 54 Mc. This should appear at 6 Mc. on the re- 
ceiver dial. Peak up the mixer trimmer (on the side 
of the tuning capacitor ) and the antenna trimmer on 
the front panel for maximum signal. Calibration may 
be varied by juggling the oscillator padding capacitor 
C-9 and the auxiliary oscillator capacitor C-4 on the 
side of the tuning capacitor. When the coverage is 
correct, the dial may be re-painted with white paint 



and the new calibration marks placed on the surface 
with India ink. 

A suitable "control panel" for the front of the re- 
ceiver is shown in figure 6. Remove the auxiliary plug 
at the bottom of the front panel, knock off the knob 
and use the panel as a mount for the components. 
Make a Novice Receiver for 
40 and 80 Meters from 
the 3 — 6 Mc. Command Receiver! 
The 3—6 Mc. Command receiver "just misses" the 
7 Mc. Novice amateur band. An excellent and easy-to- 
perform conversion of this receiver will permit it to 
cover both Novice bands! Simply remove the coil rack 
from the receiver, and remove the coils from the cans. 
Mark the coils so you can distinguish between them. 
With a pair of "needle-nose" pliers pull out the micarta 
clip that secures the powdered iron slugs within the 
coils. Remove the three slugs and discard them. Be 
careful not to damage the coil windings or the termi- 
nal connections. Reassemble the coils, solder all con- 
nections, and install the coil rack in the receiver. 

Using a signal generator, set the 6 Mc. dial mark- 
ing to a generator frequency of 7.4 Mc. by adjusting 
the high frequency oscillator padder (C-4G). Next, 
set the 3 Mc. dial marking to a generator frequency 
of 3.4 Mc. Go back to 7.4 Mc. and recheck this point. 
Re-set C4-G slightly, if necessary. Peak up the mixer 
trimmer, and the antenna trimmer. The receiver will 
now tune the range of 3.4 Mc. to 7.4 Mc, covering 
both the 80 meter and the 40 meter Novice bands. 
A Plug-in Power Supply for Your 
Command Receiver 
Many amateurs and experimenters have a whole 
"stable" of Command receivers. Not only is it ex- 
pensive to purchase power transformers for each re- 
ceiver but it is very difficult to adapt a receiver con- 
verted in such a manner for mobile operation. De- 
scribed herewith is a plug-in power unit that fits in 
the dynamotor space of the receiver. The supply can 
be easily removed and a converted dynamotor used 
for mobile operation. 

First, wire all filaments in parallel for 12 volt oper- 
ation. Locate a Command receiver dynamotor (DY-8, 
or DY-2A/ARR-2) and remove the base mounting 
plate. Discard the dynamotor. Remove everything 
from the base plate, including the sliding clips, but 
retain the three pin connector. Mount the new power 
transformer, rectifier tube, socket, and filter capacitor 
as shown in figure 7A. Note that the capacitor and 
rectifier tube socket are mounted on %" metal spacers. 
The transformer is mounted on }i" metal spacers so 
that the leads will not be pinched between the core 
and the plate. It is only necessary to drill holes in the 
base plate for the four metal spacers and the 6-32 
screws that secure the power transformer. The line 
cord is held in place with a cable clamp secured under 
one of the transformer mounting bolts. A switch may 
be placed in the line cord. 




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Surplus Radio Conversion Manual, Volume III 



13 



W/2MG ABOV£ TOSS 0iTCX 



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Figure 3-B (continued) 



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The schematic of the supply is shown in figure 7B, 
and a photo of a typical supply, installed in a receiver 
is shown in figure 8. 

A Twelve Volt Command Dynamotor 
for Mobile Service 

It is often desirable to employ a Command receiver 
for mobile or Field day operation. When using the 
a.c. power pack described in the previous section, the 
receiver may be easily powered with a 12-volt dyna- 
motor. Although 12-volt dynamotors for Command 
receivers have occasionally appeared on the surplus 
market, they are not generally available. The DM-34D 
(part of the BC-603 equipment) is quite common, 
however, and is the same physical size as a Command 
set dynamotor, delivering 220 volts at 80 ma., with 
a primary drain of 12-14 volts at 2.8 amperes. It may 
be used with the Command receiver with a simple 
conversion. 

Obtain a 28-volt Command receiver dynamotor. 
Remove the mounting base, complete with sliding 
latches, socket, and ground lug. Discard the dynamo- 
tor. Now, cut the DM-34 mounting brackets to 



2-9/16" so that the brackets will just fit inside the up- 
turned flanges of the Command dynamotor base. Drill 
a small hole in each DM-34 bracket and a correspond- 
ing hole in the base so that the dynamotor may be 



STANCOR PC-8401 6X4 




ORIGINAL CHOKE 
#5634 




25 Kf SAIN 



*• 11.6 V. TO ALL OTHER 
FILAMENTS 



*■ 6.3 V. TO WE-717A 
FILAMENT 



• TO GAIN CONTROL LINE 
(GREEN WIRE) 



Figure 4 
A.C. POWER SUPPLY FOR COMMAND RE- 
CEIVER. Power transformer delivers 235-0- 
235 volts at 40 ma., 5 volts at 2 amperes, and 
6.3 volts at 2 amperes. If 6.3 volt winding has 
two center-tap wires, cut them short and 
solder them together, then tape. 



14 



Surplus Radio Conversion 




ANTENNA COIL 
IT. #16 ENAM. 



J%'T 



PRI.- 
SEC- 



Ml XER COl L 

10 T. # 22 PLASTIC- 
COVERED 
8 T. #16 ENAM. 



OSCILLATOR COIL 

PR/.- 31. #22 PLASTIC- 
COVERED 
SEC.-BT. #16 ENAM. 



NOTES: ALL COILS CLOSEWOUND, 1/4" DIAMETER 
VIEWS LOOKING DOWN ON COILS 
PRIMARIES WOUND OVER SECONDARIES 



-ELECTROLYTIC 

\ MOUNTING GROUND LUG 

\ PLATE TOPSIDE 




SHOWN TO SCALE 

■ ORIGINAL HOLE-DRILL OUT 
TO 1/6" 

■ NOT USED IN CONVERSION 
- AOD HOLE, 1/8* 



Figure 5 

COIL DATA FOR SIX METER CONVERSION 

OF "COMMAND" RECEIVER. 




Figure 6 
CONTROL PANEL CONNEC- 
TIONS FOR "COMMAND" 
RECEIVER. 



bolted to the base. Connect the white wire having a 
black tracer and also the white wire having a red tracer 
to the ground lug. Connect the white wire to the 
filament lug on the dynamotor base (see figure 7A 
for base connections ) . Finally, connect the white wire 
with the blue tracer to the B-plus lug of the base. 

The above connections are for automobiles having 
the positive terminal of the battery grounded. If your 
car has the negative terminal grounded, reverse the 
white wire with the white wire having a black tracer. 
A reworked dynamotor is shown in figure 8. 



\ r 




PHASE CORRECTLY 
FOR 11. 6 V., THEN 
SOLDER AND TAPE. 



POWER PLUG 

B-,FI L. 



ft 



Figure 7 
A — Layout, power supply mounting plate for 

Command receiver. 
B — Schematic, power supply. Power trans- 
former is the same as shown in figure 4. 

Converting a Q-5'er 
for Broadcast- Reception 

The Q-5'er (BC-453) covers 190-550 kc. and is 
generally used as a selective i.f. strip for communica- 
tion receivers. By modifying the coils it may be made 
to cover the broadcast band (550—1500 kc. ) for gen- 
eral broadcast reception. It also can be used with a 
converter for mobile work, or it can serve as a Q-5 er 
for receivers such as the BC-348 which have a 715 kc. 
intermediate frequency channel. 




Figure 8 
"COMMAND" RECEIV- 
ER POWER SUPPLIES. At 
left is converted DM-34 
dynamotor, and at right 
is the power supply of 

figure 7. 



Manual, Volume III 



15 



C29 



R20 



-jH2AL5( ^ R 21 




Nh 



\ NOISE LIMITER SWITCH 

GROUND FIL. PIN 3, 
CONNECT FIL. PIN 4 
TO FIL. LINE. 

Figure 9 

SCHEMATIC, NOISE LIMITER 

FOR COMMAND RECEIVER. 



The coil rack is removed and the following altera- 
tions are made to the coils: 

1-Remove 210 turns from the antenna coil (L-l). 
2— Remove 500 turns from the mixer coil primary 

(L-2). 
3— Remove 220 turns from the mixer coil secondary 

(grid). 
4— Remove 195 turns from the oscillator coil sec- 
ondary (L-5). 
Do not remove any turns from oscillator coil pri- 
mary (the grid winding). When completed, replace 
the coil rack. The receiver will now tune the fre- 
quency range of 550 kc-1600 kc. Adjust high fre- 



quency alignment with the oscillator shunt padders 
(C-4E, C-4G) on the variable tuning capacitor. Track 
the low frequency end of the band with the adjustable 
powdered iron slug cores in the three coils, plus the 
oscillator series padder (C-9) on the end of the tuning 
capacitor. 

A Noise Limiter for Your Command Set 

Tired of automobile QRM or static on your Com- 
mand set? A very simple but effective noise limiter 
can be connected as shown in figures 9 and 10. A 
12AL5 tube is used. The cathode of one-half of the 
diode is connected to the 12A6 control grid. The grid 
of the 12A6 is slightly negative, so the diode does not 
conduct; however, when a noise peak arrives (or a 
strong audio peak) the diode conducts and shorts the 
grid circuit out to ground. The limiting action is as 
good as the more complicated shunt-type limiter, but 
the audio distortion is a little higher. A switch may 
be incorporated to remove the limiter from the circuit 
when it is not required. 

Automatic Volume Control for 
Your Command Set 

Automatic volume control is extremely effective in 
preventing distortion or overloading on strong local 
signals. It is very simple to add a.v.c. to the Command 
receivers. (Note: A few "ARC" series receivers have 
a.v.c. incorporated). All the essential a.v.c. com- 
ponents are incorporated in all receivers, but there is 



Figure 10 
The 12AL5 noise 
limiter tube may be 
placed in the under- 
chassis area behind 
the panel of the re- 
ceiver. 




16 



Surplus Radio Conversion 



vr-iai 

12SK7 



VT-133 VT-131 
12SQ7 12SK7 



VT-133 
12SQ7 



3 r 




^ 



^© 



& 



3-E 



7T 



t 



ffto 



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70 K 



® 



TO JUNCT ION OF ■ 

Cl5A AND R1V REMOVE Rll 



MODIFI ED 



Figure 1 1 

SCHEMATIC, A.V.C. CIRCUIT FOR 

"COMMAND" RECEIVER. 



no connection between them. The purpose of this 
conversion is to provide a.v.c. action to the r.f, and ii. 
amplifier stages by completing the a.v.c. circuit. It 
requires two additional resistors and a capacitor. Refer 
to figures 11A and 11B. First, unground pin 5 of the 
12SQ7 (VT-133). Connect the 100 ^fd. capacitor 
across pins 4 and 5 of the tube socket. Connect the 
470K resistor from pin 5 to an adjacent ground lug. 
Connect the second 470K resistor between pin 5 and 
the junction of C-15A and R-ll. Remove R-ll from 
the circuit to increase the effect of the a.v.c. action. 
A Built-in Speaker for Your 
Command Receiver 

A small speaker may be mounted in the removable 
adapter plate in the front of the Command receiver. 
The "speaker" is the small receiver element in standard 
use in telephone handsets. It is only W in diameter, 
and 11/16" thick. It is available on the surplus mar- 
ket, and identifiable by the letters HA-1 stamped on 
the face. 

A blank aluminum plate replaces the original 
adapter plate. A hole is cut in the plate just large 
enough to clear the HA-1 unit. A second hole is made 
for the gain control, shown in figure 6. 

If the b.f.o. switch is not used, placement of parts 
on the new plate is not critical. However, if a b.f.o. 
switch is desired it will be a tight squeeze to get the 
three components together on the new adapter plate. 

A single layer of "Scotch" electrical tape is wrap- 
ped around the shell of the speaker to isolate it from 




HA-1 SPEAKER UNIT 



Figure 12 

SCHEMATIC, HA-1 SPEAKER 

FOR USE IN "COMMAND" 

RECEIVER. 



W 



■ OF BC-455 (6-9. 7 MC. ) 



MIXER 
STAGE 
V-5 V-6 



-M2SK7I ( 12K8 ) ^2 5K?)- 




300 KC. I-F 
SIGNAL 
FROM PIN 4, 
Z-3 



Figure 13 
BLOCK DIAGRAM OF DOUBLE - CONVER- 
SION AMATEUR BAND RECEIVER MADE 
FROM TWO "COMMAND" RECEIVERS. BC- 
455 serves as r.f. portion, and BC-453 serves 
as "i.f. strip." 



the chassis, and after placing the speaker in the hole 
in the plate a second piece of tape is wrapped around 
the body of the speaker to hold the unit from slipping 
out of the hole, 

Wire the positive side of the speaker directly to pin 
#4 of J-l (the front plug in the back of the adapter 
plate) . Mount the gain control. Wire the "hot" arm of 
the control to pin #2 of J-l, and the other side of the 
control to pin #1 of J-l. Finally, connect the other 
side of the speaker to ground. Screw the adapter plate 
to the front of the receiver, and you have a sensitive, 
clean-sounding speaker, audible many feet from the 
receiver. The complete wiring changes are shown in 
figure 12. 

A "Double Conversion" Command 
Receiver for Single Sideband Reception 
It is possible to combine two Command receivers 
to form a double conversion receiver, well suited for 
single sideband reception or selective c.w. reception. 
The BC-453 (190-550 kc.) and BC-455 (6-9.1 Mc.) 
receivers are used. A block diagram of the combina- 
tion is shown in figure 13. The BC-455 tunes the 7 Mc. 
amateur band ( or it may be modified for other bands 
as described later) and the intermediate frequency 
signal of this receiver (2830 kc.) is converted to 300 
kc, within the tuning range of the BC453. The com- 
bination provides excellent sensitivity, selectivity, and 
freedom from bothersome "image" signals. 

Only a portion of the BC-455 is used. The r.f. am- 
plifier, mixer, and first i.f. stage function in the usual 
manner, and are unmodified. The second i.f. stage 
( 12SK7 ) V-5 is changed into a mixer, and the b.f.o. 
section of the 12SR7 (V-7) is converted to a mixing 
oscillator. The 12A6 audio tube is removed. 



Manual, Volume III 



17 



The first step is to lower the frequency of the 
12SR7 beat oscillator until it operates 300 kilocycles 
below the intermediate frequency of 2830 kc. The new 
frequency of oscillation is therefore 2530 kc. To effect 
this change, solder a 100 /^fd. mica capacitor be- 
tween the plate (pin #5) and ground (pin #1) of the 
12SR7 socket. The desired frequency of 2830 kc. may 
now be tuned by adjusting the b.f.o. trimming capaci- 
tor C-28 on the side of the receiver. Check the fre- 
quency by listening to it on a nearby receiver or fre- 
quency meter. The old b.f.o. has now been trans- 
formed into a suitable mixing oscillator. 

The next step is to couple the new i.f. output fre- 
quency of 300 kc. (2830 kc. minus 2530 kc.) into the 
BC-453 which serves as the low frequency i.f. ampli- 
fier. Remove the third i.f. transformer from the 
BC-455 (transformer Z-3). Solder a 30K, 1-watt re- 
sistor between pin #1 and pin #2 of the i.f. socket. 
Solder a 100 wid. capacitor between pin #1 and 
pin #4, which is used as a tie-point terminal. Finally, 
cut a short length of shielded wire, long enough to 
reach from pin #4 to the antenna terminal of the 
BC-453. Solder the center conductor to pin #4 of i.f. 
transformer socket Z-3 and solder the shield to a near- 
by ground lug (pin #5 of 12SR7 socket). Connect 
the inner conductor to the antenna terminal of the 
BC-453, and ground the shield to the chassis of the 
second receiver. 

Tune the BC-453 to 300 kc, and tune the BC-455 
to 7 Mc. You can now tune in 40-meter signals by 
tuning either receiver. In general, tune the BC-455 to 
the edge of the amateur band, and then cover the 
band on the BC-453. The i.f. bandwidth of the high 
frequency receiver is broad enough to allow you to 
tune the BC-453 for 100 kilocycles or so without a 
drop in received signal strength. Use the b.f.o. in the 
BC-453 for s.s.b. or c.w. reception. 

As an example, suppose you want to tune in a sig- 
nal at 7150 kc. Set the BC-453 to 300 kc. and then tune 
the BC-455 to 7100 kc. Next, tune up 50 kc. on the 
BC-453, and you are "on the nose" at 7150 kc. In this 
way, you can read your frequency of reception to one 
or two kilocycles. Always remember to set the BC-453 
tuning dial to 300 kc. for general tuning with the BC- 
455. 

Converting the BC-455 for 

20, 15, ond 10 Meters 

Conversion for Citizens Rodio Service 

It is possible to buy extra r.f. coil racks on the sur- 
plus market for the Command sets. To change bands, 
it is only necessary to rewind these racks, and then 
to use them as plug-in coils in your BC-455, 

To rework a rack, the data of figure 14 may be 
used. You will need to borrow another receiver or fre- 
quency meter in order to listen to the mixer oscillator 
of the BC-455 during the tracking process. Remove 
the coils and rewind them to the specifications given 
in figure 14. You can check the approximate resonant 



frequencies by placing the coils in the receiver (with- 
out the shields ) and noting the resonant frequency on 
a grid-dip oscillator. Be sure to remove the iron core 
from the mixer and oscillator coils. When you have 
modified the coils, solder all connections, place them 
in the rack, and replace the rack in the receiver. Turn 
on the Command set, and then look for the signal of 
the high frequency oscillator in a nearby receiver. 
Adjust the trimming capacitors on the oscillator sec- 
tion of the tuning capacitor (C-4E, C-4G, and C-9) 
until the oscillator tuning covers the desired range. 
Finally, trimmers C-2, C-4D, and C-4F are adjusted 
for maximum strength of received signals. The last 
step is to cover the tuning dial with white enamel and 
recalibrate the high frequency bands with India ink 
directly on the dial face. Only one or two markings 
are required for each band, as the main tuning is done 
with the BC-453 dial. The 28 Mc. coil data, also ap- 
plies to the 27 Mc. Citizens Radio Service. 
"Hop-Up" Your Command Receiver for 
Improved High Frequency Reception 
It is possible to boost the gain of the Command set 
and to materially improve reception on the 10, 15, and 
20 meter ranges. To do this, the 12SK7 i.f. amplifier 
tubes are replaced with 12SG7 tubes, and the 12SK7 
r.f. amplifier tube is replaced with a 12SG7. It is also 
necessary to lower the cathode bias resistor R-l on the 
r.f. tube. Shunt R-l with a 620 ohm, Ja-watt resistor. 
In addition, bypass socket pin #5 to ground with a 
0.01 rfd. disc ceramic capacitor. To boost the gain 
of the i.f. amplifier, shunt* the screen resistor (R-22) 
with a 10K, 10 watt resistor. 



BAND 


ANTENNA COIL 
(Li) 


MIXER COIL 

CL5) 


OSCILLATOR COIL 
(L13) 




N° OF TURNS 


LENGTH 


N« OF TURNS 


LENGTH 


N° OF TURNS 


LENGTH 


14 MC. 


" 


3/8" 


1 1 


3/8* 


7 1/2 


1/4* 


21 MC, 


5 1/2 


1/4* 


5 


1/4* 


6 


1/4" 


27 MC. 

28 MC. 


3 


1/8" 


5 


1/8* 


2 1/2 


1/8" 



WIND ALL CO/LS WITH N° 7 8 EN AM. WIRE. 



NOTE: REMOVE WiNDING L2 FROM ALL MIXER CO/LS. (PLATE WINDING 
OF 1ZSK7 R-F STAGE) 

PLACE WOJUJUF CAPACITOR BETWEEN PIN*1 AND PIN #4 OF 
MIXER COIL SOCKET ZSB. 

PLACE SK, 1-WATT RESISTOR BETWEEN PINX1 AND PINXZ OF 
THE SAME SOCKET. 



ir© 



;;6K 
02 



e. 



12K8 
MIXER 



(SEE FIGURE 3B ) 



Figure 14 

COIL DATA FOR CONVERTING BC-455 TO 

14, 21, OR 28 Mc. 



18 



Surplus Radio Conversion 



If the gain of the receiver is too high, instability 
may result. It can be eliminated by experimenting 
with the value of these two shunting resistors. Try 
1000 ohms across R-l and 15K across R-22 if the re- 
ceiver shows signs of feedback or oscillation. See fig- 
ure 3 for receiver schematic and parts placement. 
Conversion of the BC-603 to o 
10-11-15 Meter AM/FM Receiver 
(Ideal for the Citizen's Band!) 
The BC-603 f.m. receiver is a component part of 
Radio Sets SCR-508, 528, and 538. It provides f.m. 
reception over the range of 20—27 Mc. ? has a sensi- 
tivity of one microvolt, and 80 kc. bandwidth. An in- 



termediate frequency of 2.65 Mc. is employed, and 
a self-contained audio amplifier provides 2 watts of 
power for a speaker, or 0.2 watts for headsets. On 12 
volts the battery drain is 4 amperes. Properly con- 
verted, this inexpensive surplus item makes a good 
high frequency a.m. /f.m. receiver. The original BC-603 
schematic is shown in figure 16. 

Adding An A.C. Operoted Power Supply 

The purchaser of the BC-603 should try to obtain 
both the 12- volt dynamotor (DM-34) and the 24- volt 
dynamotor (DM-36). The 28-volt unit is of little 
value, but the base makes an excellent foundation for 
the a.c. power supply. Remove all components from 




Figure 15 
BC-603 F.M. RECEIVER MAKES HANDY 10-11-15 METER A.M./F.M. RE- 
CEIVER. A.c. power supply is shown mounted in dynamotor well of receiver. 



Manual, Volume III 



19 



this base and discard them all, except the 18-pin 
"Jones" connector. Clean all lugs on this connector 
and open the eyelets. Jumper pins #3, 6, 9, 12, 15, and 
18, as shown in figure 17. Also jumper pins 16 and 17. 
Finally, jumper pins #1 and 2, and attach a three-inch 
length of hook-up wire to pin #1. This lead is ground- 
ed. Mount the new power transformer at the end of 
the chassis opposite the connector as shown in figure 
15. Mount the 6X4 tube socket near the power con- 
nector and place the filter choke above the connector. 
Wire as shown in figure 17. Be sure the filament wind- 
ings of the power transformer are phased properly to 
provide about 11.8 volts. Place the power supply atop 
the receiver, and vou are readv for a.c. operation of 
the BC-603. 

Converting the BC-603 to A.M. Reception 

The BC-603 was designed for f.m. reception only. 
However, some farsighted designer included an audio 
choke in the cathode circuit of the 6AC7 limiter (V-6). 
It was probably incorporated to facilitate sweep-align- 
ment of the ri. and i.f. circuits. In any event, this 
choke (L-l) permits the limiter also to act as an in- 
finite impedance detector for a.m. signals, and an 
audio signal appears across this choke when an a.m. 
signal is tuned in on the receiver. The problem, then, 
is to switch the audio circuit of the BC-603 between 
the f.m. detector and this choke. This conversion uses 
the "intercom" switch (D-2) as an a.m./f.m. switch. 

Remove the front panel of the receiver by taking 
out the four screws at each corner of the cast iron 
panel guard. The front panel controls will separate 
from the chassis, being interconnected by J-3 and 
PG-3. Locate the "intercom" switch (stamped D-2 on 
the back ) and remove the wire between D-2 and J-2. 
Also remove the wire running from D-2 to the resistors 
R-22, R-32, and R-33. (Some of these resistors are 
omitted from certain receivers, They are used as vol- 
ume correctors). Xow, locate the blue-green wire 
that runs from the audio output transformer T-l to re- 
sistors R-22, R-32, and R-33. Unsolder this wire from 
the resistors and connect it to the "hot" lug of phone 
jack J-l. Remove the three resistors. 

Next, remove switch D-2 and replace it with a 
s.p.d.t. toggle switch. Connect three pieces of short 
shielded wire to the three switch terminals. Mount the 
switch and ground the shield braids to the panel On 
the main chassis, locate C-ll, the audio coupling ca- 
pacitor connected to pin #1 of the audio amplifier 
tube V-10. One terminal of C-ll is connected to pin 
#1 of socket V-10, the audio amplifier tube. Leave 
this terminal of C-ll alone. Unsolder the other termi- 
nal of C-ll. Connect the shield wire from the switch 
arm to this terminal of C-ll, as shown in figure 18. 
Connect one of the other shielded wires from the 
switch arm to the terminal just vacated by capacitor 
C-ll. Connect the remaining shielded lead to pin #5 
of socket V-6 (6AC7 limiter). Replace the panel. 



10 — 15 Meter Coverage and Citizens 
Radio Service (27 Mc.) with the BC-603 

It is possible to retune the BC-603 to cover the 10 
meter band, as well as 11 meters (the Citizens Radio 
Service) and 15 meters. This is accomplished by ad- 
justing the capacitors on the left side of the chassis 
and the tuning slugs on the right side. Presetting the 
adjustments is an easy way of tuning the receiver to 
the proper ranges. 

Looking at the left side of the set ( with the front 
of the panel toward you ) set the red dot on capacitor 
C-1.7 toward the front panel (6 o'clock). Set the red 
dot on capacitor C-1.5 to 9 o'clock. Set the red dot on 
capacitor C-1.3 to 10 o'clock. Finally, set the antenna 
trimming capacitor C-l.l to 4 o'clock. 

Next open the covers exposing coils LCU-1, LCU-2, 
and LCU-3. Screw all slugs out counter-clockwise. 
Screw in the upper slug of LCU-2 three turns, and the 
lower slug eight turns. Screw in the slug of LCU-1 
eleven turns. It should now be possible to receive the 
full 10-meter band and 27 Mc. Citizens Radio Service 
at the high end of the tuning dial, and the full 15- 
meter band at the low end of the dial. Peak up the 
slugs (except LCU-3) for maximum gain at the low 
end of the dial. Peak up the capacitors (except C-1.7) 
for maximum gain at the high end of the dial. Repeat 
this process a few times until the receiver tracks across 
the entire range. Finally, adjust oscillator slug LCU-3 
and oscillator padding capacitor C-1.7 for full cov- 
erage of the amateur bands at each end of the dial. 
This completes the conversion. 

Using the AN/APN-1 Transmitter 
Section for 420 Mc. 

The APN-1 radio altimeter is widely available in 
surplus stores. Usually the frequency modulator 
(Y-101) is removed for use in television sweep genera- 
tors. The rest of the unit can often be bought for a 
very few dollars. The transmitter section is usable on 
the 420 Mc. amateur band for short-range work. The 
actual operating range depends upon the gain of the 
antenna system, rather than the power of the trans- 
mitter, however! 

Remove the transmitter from the APN-1 (figure 
19). The transmitter will be converted for six-volt 
filament operation, and a power supply and modulator 
will be constructed. Remove the modulator (Y-101) 
from the transmitter if it is still in place. 

The first step is to locate the filament wire running 
between L-105 and L-106. Clip this wire near the 
end of L-105. Cround the end of the wire emerging 
from L-105 to the chassis of the transmitter. Connect 
the free end of the wire emerging from the end of 
L-106 to the center terminal of the filament feed- 
through capacitor C-lll. The filaments are now wired 
in parallel for six-volt operation. Next, remove link 
coil L-107 and the associated coaxial line. 

The circuit of the power supply-modulator unit is 
shown in figure 20. It can be built upon one end of 



20 



Surplus Radio Conversion 



MODULATOR 
V2 



GO 



5»zo 

H CD V) 




APPARATUS LEGENO 



CAPACITORS 






COILS 












CI 1 


16 UUF MAX. 


C54 


50UUF "1 60 UUF 500 V 


LI 


LIMITER CATHODE CMOKE 


R22 


30,000-ft- 1/2 W 


V7 


VT-90 (6H6) 


C 1.3 


16 UUF MAX. 


C55 


10 UUF j SEE NOTE 2 


L32 


ANTENNA COUPLING 


R23 


5,000 -ft- 1/2 W 


V8 


VT-I07-AI6V6GT) 


C 1.5 


I6UUF MAX. 


C56 


006 UF 300V 


L33 


R F PLATE 


R24- 


50 -ft- I/2W 


V9 


VT-229 (6SL7GT) 


C 1.7 


16 UUF MAX 


C6I 


100 UUF 500V 


L34> 


MOO GRID 


R25 


2,500 -ft- 1/2 W 


VlO 


VT-229(6SL7GT) 


CIS 


62 UUT MAX 


C62 


001 UF 500V 


L4I 


R F OSCILLATOR 


R26 


1,200 -ft- 1/2 W 






C 1.4- 


62 UUF MAX. 


C63 


50 UUF > 60UUF500V 
10 UUF > SEE NOTE 2 


LSI 


1ST IF GRID 


R27 


2,500 -ft- I/2W 


DYNAMOTORS 


C 1.6 


62 UUF MAX 


C64 


L52 


MOOULATOR PLATE 


R28 


2,500 -ft- 1/2 W 


DM.34- 


-D 12 VOLJ 


C \£ 


62 UUF MAX. 


C65 


tOUUF^,60UUF 500V 
50UUFT SEE NOTE 2 


L6I 


2 NO IF GRID 


R29 


1 3,000 -ft- 2 W 


CAPACITORS 


C t 


0.006 UF 300V 


C66 


LS2 


I ST IF PLATE 


R30 


5-ft-4W 


C >0I 


003 UF 1000 V 


C 3 


0006 UF 300 V 


C67 


0006 UF 300V 


L7I 


LIMITER GRID 


R3I 


6,800 -ft- IW 


C702 


003 UF 1000 V 


C 4 


006 UF 300V 


C7I 


50 UUF 500V 


L72 


2 NO IF PLATE 


R32 


30,000 -ft- 1/2 W 


C703 


003 UF 500 V 


C 5 


006 UF 300 V 


C72 


.001 UF 5O0V 


LSI 


DETECTOR IN°UT 


R33 


30,000 -ft- uz w 


C704 


0.003 UF 500 V 


C6 


0006 UF 300 V 


C73 


50UUF^ 60UUF 500V 
IOUUFT SEE NOTE 2 


L82 


LIMITER PLATE 


R37 


2 50,000 -ft- 1/2 W 


C705 


0.003 UF 1000 V 


C7 


0006 UF 300V 


C74 


L9I 


IF OSCILLATOR 


R38 


l ( 000-ft- 1/2 W 


C706 


0.003 UF 1000 V 


C8 


500 UUF 500V 


C75 


lOUUFl 60UUF 500V 
&OUUFJ SEE NOTE 2 






R4I 


100,000 -«- 1/2 W 






C9 


0006 UF 300V 


C76 


LSI 


LOUO SPEAKER 


R42 


30,000 -ft- 1 W 


COILS 




CIO 


75 UUF 500V 


C77 


0006 UF 300V 






R43 


30,000-ft- IW 


L70I 


HV FILTER 


C II 


0006 UF 300 V 


cei 


250 UUF 500V 


POTENTIOMETERS 


R5I 


250,000 -ft- 1/2 W 


L702 


LV FILTER 


C 12 


001 UF 300V 


C82 


0.006 UF 300V 


PI 


l00,00O-ft 


R52 


30,000 -ft- 1/2 W 


L703 


HV FILTER 




500 UUF 500V 


C83 


006 UF300V 


P2 


200 -ft- 


R53 


loo.ooo -ft- i/ew 


L704 


MV FILTER 


04 


0006 UF 300V 


C84 


5UUF 500V 






R54 


)00,000-ft-l/2W 






CI5 


0.5 UF 600 V 


C85 


50 UUF OR 60 UUF 500V1 SEE 
50 UUF OR 60 UUF 500 Vj | 


PLUGS 




R6I 


lOO.OOO-ft-l'ZW 


J 701 


OYNAMOTOR JACK 


Clfc 


2UF 6O0V 


086 


PCI 


RECEIVER PLUG 


R62 


4.3,000-ft-l/2W 






CI7 


0.01 UF 300V 


C87 


25UUF^ R 3 5UU F500V 


P€2 


OYNAMOTOR PLUG 


R63 


10,000 -ft- 1/2 W 


MG7Q1 


tZV OYNAMOTOR 




001 UF 300V 


C8B 


10 UUF J SEE NOTE 2 


PG3 


FRONT PANEL PLUG 


R64 


1,000 -ft- 1/2 W 






Ct9 
C 20.1 


0002 UF 500V 
OIUF600V 


C9I 
C92 


50 UUF 500 V 
50 UUF 500 V 


RESISTORS 


R7I 
R72 


250,000-^- 1/2 W 
30,000 -ft- 1/2 W 


DM-36 


24 VOLT 


CAPACT0P5 


C 20 2 


1UF600V 


C93 


lOOUUF 500V 


Rt 


30,000 -ft- 1 W 


R73 


10,000 -ft- 1/2 W 


C80I 


0.003UF 1000 V 




1 UF 600 V 


C94 


50 UUF 500V 


R2 


25 0,000 -A- 1/2 W 


R74- 


1,000-ft- 1/2 W 


C802 


0.003UF 1000 V 


C2l 


01 UF 300V 






R3 


500 -ft- 1/2 W 


RBI 


70,000 -ft- 1/2 W 


C803 


003UF 500 V 


OOOS UF 300V 






R4 


50,000 -«- 1/8 * 


R82 


250,OOO-ft-l/2W 


C604 


0.003 \Jf 500 V 


C2^ 


40 UF 25V 


SWITCHES 


R5 


3O0 -ft- 1/2 W 


R63 


70,000 -ft- 1/2 W 


C805 


0.003 \tf 1000 V 


tUF 600V 


01 


REC ON OFF 


R6 


100,000 -ft- 1/2 W 


R84 


250,000-ft- 1/2 W 


C806 


0.003 UF 1000 V 


C?5 


2UF6O0V 


02 


RADIO- INT 


R7 


30,000 -ft- IW 


R85 


1,000 -ft- 1/2 W 






C26 


0.0005 UF 500 V 


03 


ON- OFF SPEAKER 


RB 


70,000 -ft- 1/2 W 


R9I 


100,000 -ft- 1/2 W 


COILS 




C35 


0.006 UF 300 V 


04 


ON -OFF SQUELCH 


R9 


1,000-ft- 1/2 W 


R92 


40,000 -ft- 1/2 W 


L80I 


HV FILTER 




10 UUF 500V 


05 


TUNE -OPERATE 


RIO 


Z50,000-^-t/2« 


R93 


40,000 -ft- 1/2 W 


L802 


LV FILTER 




10 UUF 500 V 






Rll 


1,000,000 -ft- 1/2 W 


R94 


2,000,000 n'/ 2 w 


L603 


HV FILTER 


C39 


0.006 UF 300V 
700 UUF 5O0V 


El 


CALL SIGNAL 


Ri2 
RI3 


2,000 -ft- 1/2 W 

10,000-ft- \/z™ 


R93 
R96 


IS.OOOA 1/2 w 
30,0OOA \/2 W 


L804- 


HV FILTER 


C42 


200 UUF 500 V 






Rl* 


2 50,000 -ft- 1/2 W 


Tt 


OUTPUT TRANSFORMER jao) 


OYNAMOTOR JACK 


G4-3 


100 UUF 500V 
30 UUF 500V 


Ft 


FUSE 15 AMP 


RI5 

RI6 


1,000,000 -ft- 1/2 W 
1,000,000 -ft- 1/2 W 


VACUUM TUBES 


MG80 




C4-4 


VI 


VT-112 (6AC7) 


1 24V OYNAMOTOR 


G45 


100 UUF 500V 






RI7 


250,000 -"- 1/2 W 


V2 


Vf-112 16AC7) 






C46 


20 UUF 500V 






RI8 


100,000 -ft- 1/2 V» 


V3 


VT-94. (6J5) 






C 51 


006 UF 303V 


JACKS 




RI9 


2,000,000-ft-l/2W 


V4 


VT 209 (I2SG7) 






C52 


I0UUF,}_60UUF 500V 


Jl 


PHONES 


R20 


500-ft-IW 


V5 


VT-Z09 (I2SG7) 






C53 


50 UUF j SEE NOTE 2 


J2 
J3 


PHONES 

FRONT PANEL JACK 






V6 


VT-1.2 (6AC7) 







Figure 16 
SCHEMATIC, BC-603 RECEIVER. 



Manual, Volume III 



21 



t ST A F AMP 

& I f osc 

VIO 




Figure 16 
SCHEMATIC, BC-603 RECEIVER 



22 



Surplus Radio Conversion 




d> 



TO BALANCED DETECTOR 



n 



Rt16 

12 ° 1 J102. 

R-F OUTPUT 



©' 



Figure 17 

SCHEMATIC, A.C. POWER SUPPLY FOR BC- 

603. Power transformer delivers 250-0-250 

volts at 70 ma., 5 volts at 2 amperes, and 6.3 

volts at 2.5 amperes. 




VW — *■ B+ 



NOTE: 
ALL RESISTOR VALUES ARE 
GIVEN IN OHMS AND CAPACITOR 
VALUES IN JJJUF. 



V112 

I HW^ 

4- rr 



V113 



~r^r 



6AC7 

LI MITER 



6SL7-GT 

A-F STAGE 

V-10 




Figure 18 

MODIFICATION OF BC-603 FOR 

A.M./F.M. RECEPTION. 

a 8"xl0"x2" aluminum chassis. The APN-1 oscillator 
unit is bolted to the opposite end of the chassis. 

Adjustment of the sliding bar on L-108 will tune 
the oscillator between 425 Mc. and 440 Mc. The spac- 
ing between L-lll and L-110 will determine the an- 
tenna loading. A 6.3 volt, 150 ma. pilot lamp (brown 
bead ) mounted in a coaxial plug will serve as a dum- 



Ct13 C115 C 

'56 56 f 56 -p 55 

© 4 

Figure 19 
SCHEMATIC, APN-1 OSCILLATOR. 

my antenna for tuning adjustments. A suitable an- 
tenna for the 420 Mc. band is shown in figure 21. 

Converting the AN/CRC-7 to 144 Mc. 

The AN/CRC-7 is a battery operated transmitter- 
receiver used for Air-Sea rescue work. It is capable of 
operation in the 144 Mc. amateur band, and purchase 

of components other than a set of batteries is unneces- 
sary. The complete unit is shown in figure 22, and 
an "exploded" view is shown in figure 23. The circuit 
is given in figure 24. 

The CRC-7 uses 1.4 volt d.c. tubes-three 3A5*s 
and one 3Q4. One half of a 3A5 is used as a super- 
regenerative detector having a tuning range of 135 — 
150 Mc. The second half of this tube is used as an 



C110 C11 




Figure 20 
SCHEMATIC 
POWER SUPPLY- 
MODULATOR 
CIRCUIT AND 
REVISED APN-1 
OSCILLATOR 
Power transformer de- 
livers 235-0-235 volts 
at 40 ma., 5 volts at 2 
amperes, and 6.3 volts 
at 2 amperes. 



Manual, Volume III 



23 



audio amplifier for reception and transmission. The 
3Q4 is employed as an audio power amplifier for re- 
ception and as a modulator for transmission. 

One 3A5 section is used as a crystal oscillator on 
17.573 Mc., with the second section acting as a fre- 
quency doubler to 35.146 Mc. A second 3A5 is used 
as a dual doubler, the first section doubling to 70.292 
Mc, and the second section doubling to 140.58 Mc. 
Transmitter output is on this frequency. 



f 



\WM 






Figure 22 

The AN CRC-7 is a 
battery-operated re- 
ceiver easilyconvert- 
ed for 2-meter ama- 
teur operation. 



Figure 23 

"EXPLODED" VIEW OF AN CRC-7 

The battery box is cut off, and the top section 

is cut open as shown. Cut top section ]/2-inch 

above push buttons, being careful not to cut 

too deeply into the case. 




MAKE ELEMENTS OF 
N° 12. E. WIRE. 




300 OHM TV-LI NE, RANDOM LENGTH. 
CONNECT 3 SHIELDS TOGETHER 
9-g-"0F RG-59/U 



TO OSCILLATOR 



Figure 21 

FOUR-ELEMENT BEAM ANTENNA 

FOR 420 MC. 

Opening A good, sharp hack-saw is an asset in 
the Cose opening the CRC-7 case. The unit is com- 
pletely heremetically sealed against mois- 
ture. Since the batteries are not available, the first 
step is to cut off the battery compartment. Measure 
along the side of the unit to the end of the brass butt 
plate. This will be Sis". Measure your unit to cut just 
below this brass plate. Do not cut too far into the in- 
terior of the battery compartment or you will saw off 
the battery pins. Remove and discard the shell. In- 
cidentally, the antenna should be fully extended to 
avoid sawing it off during the cutting operation. 

Next, remove the two screws that appear to hold 
the two halves of the unit together. Mark a line /2-inch 
















24 



Surplus Radio Conversion 



EXPRESSING THE TRAN 
KEY ALSO DEPRESSES 
THE REC KEY. 



MIKE-H£ADPHONE 



B^ 




lllfa^n 



'L 



bottom of plug 



ALL RESISTANCE* IN OHMS 
UNLESS OTHERWISE NOTEO 



VHF Sea Rescue Tratumitter-Receiver 
AN/CRC-7, Schematic Wiring Diagram 



Figure 24 
SCHEMATIC, AN/CRC-7 V.H.F. TRANSMITTER-RECEIVER 



above the push buttons, and scribe this line all the way 
around the cannister. Saw along this line, being care- 
ful not to cut into the interior of the case, particularly 
near the screw mounts. Just beneath this area are the 
audio transformer and r.f. choke, so take care! 

Now, you can slide off the cannister. It may take 
a little jiggling, but use only moderate pressure. Re- 
move the insulating tape to reveal the components of 
the set. To make sure that no damage has been done 
during the sawing process, connect a set of batteries 
as shown in figure 24. Press the "receive" button and 
you should immediately hear a hissing noise in the 
earphone unit. 

144 Mc. Operation The transmitter should be ad- 
of the Transmitter justed for 144 Mc. operation. 

All of the coil slugs are silver- 
plated and raise the resonant frequency of the tuned 
circuits as they are screwed clockwise into the coil. 
Since it is necessary to raise the frequency of the trans- 
mitter for 144 Mc. operation, it will be necessary to 
turn all slugs clockwise. This is fortunate, as the slugs 
are usually sealed with "glyptal" cement, and turning 



the slugs counter-clockwise will usually "freeze" them 
in the cement. 

The first step is to remove the transmitter crystal, 
which is held underneath the 17 Mc. coil form (the 
one having the most turns V Unscrew the coil bolts 
from the under-side of the chassis and remove the coil 
and the crystal. Handle the crystal with care. It is 
possible to mount a crystal holder on the outside of 
the case, grounding one lug of the holder to the case, 
and connecting a small piece of spring brass to pin 
#3 of the 3A5 oscillator tube socket. Then, when the 
case is slipped on, the spring brass will contact the un- 
grounded pin of the crystal socket. A second brass 
spring is soldered to the chassis deck to make ground 
connection to the ease for the return lead. Crystals in 
the 18 Mc. range are used for 2-meter work, 

A less expensive conversion is to make use of the 
crystal used in the original equipment. Take a piece 
of flat glass and put a few drops of water and a little 
tooth powder on it. Place the crystal blank on the 
glass and press it lightly but evenly, taking ten or 15 
circular "swipes" across the glass plate. Clean the 



Manual, Volume III 



25 



se^s^^W^^^^^^^^W"^*^^^ 8 ^^ 






tirm «jP^-' ©fS 




Figure 25 
The AN/URC-4 is a 

battery-powered 
transmitter- receiver 
suitable for conver- 
sion to the 144 *Mc. 
amateur band. Unit 
features built-in an- 
tenna and speaker- 
microphone. 



crystal with carbon tetrachloride (Caution! Do not 
breathe the fumes! ), replace it in the holder and check 
the frequency. It will probably be necessary to repeat 
this procedure several times (retiming the crystal 
oscillator coil each time) until the harmonic of the 
crystal falls at the desired spot in the 144 Mc. band. 

Next, cut holes at appropriate spots in the top of 
the cannister to gain access to the tuning slugs when 
the cover is replaced. It is necessary to tune the 
transmitter in this manner, since the cannister causes 
a considerable amount of detuning when it is re- 
moved, Peak the slugs of the four coils for maximum 
signal strength in a nearby receiver, with the antenna 
whip of the unit fully extended. This completes the 
transmitter modifications. 



144 Mc. Operation 
of the Receiver 



The receiver section of the 
CRC-7 only requires retim- 
ing for 2 meter operation. 
Screwing the slug into the detector coil about three 
turns will hit the band. Some receivers will not tune 
above 147 Mc. and it will be necessary to remove one 
turn from the detector coil to tune up to 148 Mc. If 
desired, the receiver slug can be removed and a M-inch 
extension shaft soldered to it. By slotting the side of 
the case, you can tune the receiver manually by 
means of a knob placed on the shaft. The sensitivity 
of the receiver is such that a signal of less than 3 
microvolts can easily be heard and copied. 

The CRC-7 requires two flashlight batteries paral- 
lel-connected for the filament supply (1.4 volts), and 
two 45 volt B-batteries series-connected for the B-plus 



26 



Surplus Radio Conversion 







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Manual, Volume III 



27 



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28 



Surplus Radio Conversion 



supply. The RCA battery pack VS-064 will work well 
with this unit. 

Using a converted CRC-7 with the self-contained 
antenna, contacts up to 30 miles distance have been 
made. 

Converting the AN/URC-4 to a 
2 Meter Handie-Talkie 

The AN/URC-4 is a battery powered transmitter- 
receiver intended for Air-Sea rescue service like its 
predecessor, the CRC-7. Unlike the CRC-7, the URC-4 
employs more "exotic" circuits, components and 
smaller construction. In addition, it is designed to 
operate on two frequencies: 121 .5 Mc. and 243 Mc. 
To convert the URC-4 to 144 Mc. it is necessary to re- 
wind a few coils, purchase a new crystal, and connect 




a set of batteries. The unconverted URC-4 is shown in 
figures 25 and 27. 

The URC-4 employs eight tubes, all of which are 
sub-miniature with the exception of the audio output 
tube. A dual frequency antenna folds completely into 
the case. Telescoping the antenna automatically shorts 
out the v.h.f. antenna loading coils and converts the 
antenna to u.h.f. use at 243 Mc. For a two meter con- 
version, the u.h.f. circuitry and tubes are not used. 

A complete circuit of the URC-4 is shown in fig- 
ures 26A and 26B. Two separate detectors are used, 
one for v. hi. and one for u.h.f. Each super-regenera- 
tive detector employs a type 6030 miniature high-/* 
triode. (Note; Some early models use 5676 tubes). 
Bandswitch S-l lights the filament of the tube in use. 
The detector audio output circuit is novel in that it 
incorporates a "bridge-T" filter tuned to the quench 
frequency of super-regeneration, A variable quench 
control is thus not required and improved audio re- 
sponse is realized. The v.h.f. detector (V-5) tunes 
only to 144 Mc. and must be modified for 2-meter 
work. 

The transmitter section employs a CR-24/U crystal 
at 10.12 Mc, ground for third-overtone operation with 
a 6050 oscillator (V-l) operating at 30,375 Mc. This 
tube drives a second 6050 doubling to 60.75 Mc. A 
beam-power pentode (type 5851) is used as a doubler 
to 121.5 Mc. For v.h.f. operation, signals are link- 
coupled out of the plate circuit of this stage. A second 
5851 acts as a doubler to 243 Mc. for u.h.f. service 
and is activated by the u.hi./v.hi. switch, S-l. This 
last tube may be removed and kept as a spare. 

The audio section consists of a 2E32 speech ampli- 
fier driving a 3Q4 power amplifier (reception). Dur- 
ing transmission, the 3Q4 serves as a modulator. A 
feedback circuit is incorporated in the audio system 
for modulated tone transmission, operated by switch 
S-2A. 

The Two Meter It is a good idea to establish first 
Conversion that the URC-4 is in working or- 

der on 121.5 Mc. when you re- 
ceive it. The original battery pack is unobtainable, 
but a good substitute is the RCA YS-064 pack (1.4 
volts, and 90 volts). Battery cables are usually avail- 



AN/URC-4, WITH COVER REMOVED 
At top of cabinet arevtubes V-1, V-2, and V-3. 
Oscillator coil L-l is behind V-l and is tuned 
to 30.375 Mc. Doubler coil L-2 is behind V-2 
and is tuned to 60.75 Mc. Doubler coil L-3 is 
behind V-3 and is tuned to 121.5 Mc. Coil 
L-4 is behind capacitor C-19 (20 /xfd.) and is 
tuned to 243 Mc. Tuning capacitor C-21 is 
next to L-4. Receiver coils L-5 and L-6 are at 

bottom of case. 

Coil L-l is retuned to 36 Mc, coil L-2 to 72 

Mc, coil L-3 to 144 Mc. Tubes V-4 and V-6 

(under the chassis) are removed. 



Manual, Volume III 



29 



able at the surplus store. Connect the battery as in- 
dicated in figure 26 to receptacle J-l. Press the 
receive button and a loud hiss should be heard from 
the combination microphone-earphone. Press the 
transmit button and check for r.f . with a field strength 
meter. Do not leave the transmitter operating for 
more than a few seconds when making this check as 
the 121.5 Mc. frequency is still used for military com- 
munication. 

The first step in the conversion is to modify the 
tuned circuits. Remove the chassis from the case by 
loosening the chassis mounting screws. Remove the 
u.h.f. detector (type 6050, V-6) located under the 
chassis. Save the tube for a spare. Remove the u.h.f. 
power amplifier tube (type 5851, V-4) and save for a 
spare. Coil L-3 of the second doubler stage ( V-3) will 
now rescnate to 144 Mc. without re-winding. 

Next, remove the neoprene waterproof cover over 
the microphone-earphone grill. This will improve the 
modulation. Now, locate the end of coil winding L-l 
that connects to pin #1 of socket V-l (6050, oscilla- 
tor ) . Unsolder this end of the winding, pull it through 
the eyelet of the coil form and unwind three turns. 
After unwinding, feed the wire back through the eye- 
let and solder to pin #1 of socket V-l, trimming off 
the excess wire. 

The next step is to locate coil winding L-2 that 
attaches to pin #1 of socket V-2 (6050, doubler). In 
the same manner as before, disconnect the wire, un- 
wind two turns, and resolder. Coil L-3 is left "as is." 
Coil L-4 may be removed, as it is no longer used. 

A transmitter crystal between 36 and 37 Mc. must 
be used for 2 meter service. A replacement type 
CR-24/U crystal is expensive, and a low-cost hermeti- 
cally sealed type FM-1 crystal is recommended as a 
substitute. This crystal may be obtained from Inter- 
national Crystal Mfg. Co., 18 North Lee St., Oklahoma 
City, Oklahoma. The new FM-1 crystal may be se- 
cured by lifting the old pressure spring and sliding 
the new crystal into position. Solder the two wires 
to the original crystal holder terminals. Make sure 
the crystal is not free to move about, or dropping 
the CRC-7 might fracture the crystal. This completes 
the transmitter modification. 

Receiver Modification Identify the wire running 
for 2 Meters between detector coil L-5 

and the transmit - receive 
switch S-2. Unsolder this wire at the switch, pull back 
to the coil, and unwind one turn from the coil, leaving 
1-1/6 turns on the link. Route the wire back to the 
switch, slip a piece of "spaghetti" tubing over the 
wire, and resolder to the original switch terminal. 
Next, identify the wire running between coil L-5 
and pin #1 of detector socket V-5. Disconnect this 
wire at the socket, and as before, unwind one turn 
from L-5, and reconnect the wire end to socket V-5. 
This completes the receiver modification, 



Antenna Modification For 121.5 Mc. operation the 
for 2 Meters dipole antenna system em- 

ploys two loading coils. For 
best results on 144 Mc., these coils must be retuned. 
Unfold the antenna completely to the v.h.f, position. 
Note that one of the vertical support rods of the an- 
tenna structure is grounded to the chassis and the 
other passes through an insulator into the case. Mark 
near the appropriate coil (on the cap) the letters "A" 
(for antenna) and "G" (for ground). Unscrew the 
vertical rods near the cap with a small wrench. Solder 
a one-inch loop of wire across the two contacts near 
the center of the antenna cap. Lift out the two load- 
ing coils and remove all but one turn from the coil 
marked "G". Remove all but two turns from the coil 
marked "A". Replace the coils. 

Now, insert the coil of a grid-dip oscillator into the 
loop of wire. Make sure the antenna is fully extended 
and clear of nearby metallic objects. Check the reso- 
nant frequency of the antenna, which should be close 
to 145 Mc. If not, adjust the coil "A" by spreading 
or compressing the turns which should put the an- 
tenna on frequency. Replace the antenna assembly. 
Testing the Insert the FM-1 crystal, and connect 
Unit the batteries. Press the "transmit" but- 

ton and listen for the carrier in a nearby 
receiver. If no signal is heard on the proper fre- 
quency, slowly unscrew the slug of coil L-l until the 
oscillator starts operation. Peak coils L-l, L-2, and 
L-3 for maximum received signal with the URC-4 
antenna fully extended. 

To tune-up the receiver, press the "receive" but- 
ton and adjust the slug of coil L-5 until local two- 
meter signals are heard. The slug should be almost 
completely inside the coil form. Placing the cover 
on the URC-4 will detune the circuits, so holes should 
be drilled at appropriate places in the cover, and 
final slug adjustments are made after the cover is in 
position. Under proper conditions, the unit is capable 
of transmitting and receiving over distances up to 
30 miles or more. The power of the transmitter and 
sensitivity of the receiver are well matched, and you 
should be able to work anyone you can hear. 

Converting the MD-7/ARC-5 Modulator 
for Amateur Use 

The MD-7 modulator unit is readily available on 
the surplus market and may be easily converted to a 
75-watt modulator for the ARC-5, or other transmitter, 
running up to 150 watts input. The MD-7 includes 
two 1625 modulators (12 volt 807's), a VR-150 voltage 
regulator, and a 12J5 tone modulator for m.c.w. 
service. 

The easiest way to adapt the modulator for gen- 
eral use is to strip the chassis of all components ex- 
cept the tube sockets, the input transformer T-l, and 
the output transformer, T-2. The modulator should 
now be rewired according to the diagram of figure 
28.^ The circuit is designed to be used with a surplus 



30 



Surplus Radio Conversion 



TO TRANSMITTER P-A SCREEN 

{COMMAND SETS ONLy) ■*— 



TO TRANSMITTER P-A PLATE CIRCU IT - 
B+- 300-600- VOLTS- 



CARBON 

MIKE 

(r- 77, ETC.) 




■SJUF 

ADJUST Rl FOP 4 VOLTS AT 
PIN 1 OF T\ WITH MICROPHONE 
OUT OF CIRCUIT. VARY R\ TO 
CONTROL GAIN OF MICROPHONE. 



Figure 28 

MODIFIED MD-7/ARC-5 UNIT MAKES 

MODULATOR FOR AMATEUR USE 

T-l and T-2 are original transformers. 

carbon microphone, such as the T-17. Adjust the slid- 
ing tap on the cathode resistor to produce six volts as 
measured across the microphone jack with the micro- 
phone removed. 

Rectifier V-l connected across pins #8 and 9 of 
modulation transformer T-2 is a ' Varistor" that serves 
as a protective device for the transformer. It is a 
round, red unit with black caps, and is mounted be- 
side the two large, black 15K wire wound resistors. 
Pins #1 and 3 are atop the modulation transformer, 
T-2. The empty 12J5 socket can be employed as a 
power socket. 

Converting the Command Transmitter 
Relay for Antenna Change-Over Use 

When converting Command transmitters such as 
the "ARC-5" or "BC" series, the antenna switching 
relay is usually discarded. This relay may be adapted 
for either 6- or 12-volt mobile operation. 

The relay (identified as K-54 in the ARC-5 units) 
employs two series-connected coils. The pole pieces 
pull the armature from both directions, so to speak. 
The armature in turn moves a spiral-wound silver- 
plated contact between the antenna and ground posts 
of the transmitter. 

Mount the relay on a small sheet of aluminum, as 
shown in figure 29. It may be placed on one side of 
a small chassis-box. Mount the spiral to one SO-239 
coaxial receptacle, and permit the contact arm to 
move between the old contacts which have been 
soldered to two SO-239 connectors mounted on each 
side of the movable arm. 

As wired, the relay coils are connected in series 
and work on 24 volts. To use the coils on 6 volts, wire 
the coils in parallel with the magnetic fields aiding 
each other. For 12-volt operation, merely connect to 
one of the coils. 



TRANSMITTER 




RECEIVER 



K-54- RELAY 



- (3 ) SO-239 
CONNECTORS 



ALUM INUW BOX 



Figure 29 
K-54 relay of BC-442 Antenna Control 
Unit is mounted on aluminum plate. 
Three coaxial receptacles are used for 
relay terminals. Coils may be connected 
for 6, 1 2, or 24 -volts, d.c. 

Converting the RM-52 (RM-53) 
Telephone Unit to a Phone Patch 

Two pieces of military telephone equipment 
readily available on the surplus market are the RM-52 
remote control unit, and the RM-53 control unit. Both 
of these units contain a high quality transformer suit- 
able for phone-patch service. The transformer carries 
the military part number C-280A, and the manufac- 
turer's part number 83718. The transformer has bal- 
anced 600, 150, 250, and 4000 ohm windings, and is 
well suited for many other devices, such as line match- 
ing, isolation, impedance step-up, etc. 

The phone-patch is built in a small aluminum case, 
and wired as shown in figure 30. A simple r.f. filter 
is placed in series with the telephone line to prevent 
r.f. feedback. A d.p.d.t. toggle switch is used to dis- 
connect the phone line and return the microphone to 
normal use. Always disconnect the patch when it is 
not being used. 

To use the patch, turn on the control switch and 
insert the phone plug in the receiver headphone jack. 
If your receiver has a 500 ohm output, it can be 
permanently connected to the 500 ohm terminals. At- 
tach your crystal microphone to the microphone jack, 
and run a shielded line to your speech amplifier. At- 
tach the phone patch to the telephone line at the base 
of the phone. Receiver output will now pass over 
the phone line, and the phone will modulate your 
transmitter. 



UTC-C-2.80 A 
TRANSFORMER FROM RM-52 



-VcJ 



-£Whj- |f 

ophone\ ulT'ea.'Tj,. 
i K4&L-J- 




x 2.5MH 0.5UF 

V RFC 100 V 




TO HEADPHONE JACK 
-OR- 
REC, OUTPUT 

TO MICROPHONE 



TO SPEECH AMP. 
INPUT 



2 POLE, 2 POS. TOGGLE SWITCH 



Figure 30 

SCHEMATIC, PHONE PATCH MADE 

FROM RM-52 TELEPHONE UNIT 



Manual, Volume III 



31 



MIXER TUBE 



RECEIVER l-F CAN 




CRYSTAL 
MARKING 



FREQUENCY 
CHANNEL 44 457.85 

CHANNEL 45 453. 70 

CHANNEL 326 452. 77 
CHANNEL 327 454.76 



Xl - LOWER CHANNEL (SUCH AS 44) 
X2 - HIGHER CHANNEL {SUCH AS 45) 
Li- L2- MILLER 72-C/ 455 KC. I-F 



Figure 31 

SCHEMATIC, CRYSTAL FILTER FOR 

455 KC I.F. AMPLIFIER 

Make a Single Sideband Crystal Filter 
for Your Receiver with Surplus Crystals! 

The type FT-241A crystals (used with the BC-604) 
are plentiful and cheap on the surplus market. These 
crystals cover the range of 370 kc. to 500 kc. in 1.85 
kc. segments. The crystals are used on their 54th har- 
monic, and are marked 20.0 Mc. to 27.9 Mc. in 100 
kc. jumps. Other crystals in the same range are avail- 
able that are separated by a frequency difference of 
1.39 kc. These crystals are marked 27.0 Mc. to 34.6 
Mc. (Channels 270-346). 

An efficient crystal filter may be made from four 
of these surplus crystals. The one stage full-lattice 
filter is shown in figure 31 and may be used in any 
receiver having a 455 kc. intermediate frequency 
amplifier. For everyday use it is not necessary to 
match crystals. The filter will greatly increase the 
selectivity of the receiver, reducing the interference 
level and permitting better reception. 

Any two adjacent channels may be used that fall 
in the i.f. range of the receiver. Channels 44 to 48, 
and 326 to 330 all fall within the tuning range of 
standard 455 kc. ii. transformers. 
Building the The layout of the filter is determined 
Filter by the available space within your re- 

ceiver. In general, the filter compo- 
nents should be mounted on a small aluminum plate 
having a small shield across the middle (on both the 
top and bottom sides ) to separate the input and out- 
put circuits of the filter. The filter should be located 

THE T-23/ARC-5 V.H.F. TRANSMITTER 
Coaxial connectors J-301 and J-302 are at 
upper left, with connectors J-307 and J-309 
at bottom of sloping front panel. R.f. tuning 
adjustments of amplifier stage may be ac- 
complished through "door" on panel. 



between the mixer tube and the first i.f. transformer 
can in the receiver. All interconnecting leads should 
be kept very short. The lead connecting the mixer 
tube to the transformer is broken, and the filter is in- 
serted in this circuit as shown in the diagram. 

Upon completion, tune a signal generator to the 
center frequency of the filter. (If channel 44 and 45 
crystals are used, tune the signal generator to 452.77 
kc. A surplus BC-221 frequency meter will come in 
handy). Peak filter transformers L-l and L-2 to this 
new frequency as well as all the i.f. transformers in 
the receiver. The insertion loss of the filter is only 
about 6 decibels, so the addition of an extra tube to 
boost the gain of the receiver is not required. The 
filter may be used for s.s.b., a.m. -phone, and c.w. re- 
ception. 

Converting the T-23/ARC-5 Transmitter 
to 144 Mc. or 50 Mc. 

The T-23/ARC-5 transmitter covers the v.h.f . range 
of 100—150 Mc. in four channels. It is a companion 
piece of equipment to the R-28/ARC-5 receiver. To- 
gether, these two pieces of equipment make up the 
v.h.f. portion of the ARC-5 radio set. The equipment 
is designed to operate from a 24—28 volt d.c. pow- 
er supply. The T-23 transmitter mounts in a MT- 
69/ARC-5 rack. Power output of the transmitter is 
10 watts into a 50 ohm antenna. 

The transmitter channels cover the following fre- 
quency ranges: 

Channel A: 100-124 Mc. 

Channel B: 122-146 Mc. 

Channel C: 122-146 Mc. 

Channel D: 132-156 Mc. 




32 



Surplus Radio Conversion Manual, Volume III 



The crystal frequency is 1/18 of the carrier fre- 
quency in all cases. Front, top, and bottom views of 
the unconverted transmitter are shown in figures 32, 
33, and 35, and the schematic is given in figure 34. 

Three of the transmitter channels (B, C, and D) 
will function on 2 meters without alteration. Channel 
A is converted to 50 Mc. (six meters). The tube line- 
up of the transmitter is: 

1-1625 (V-301) crystal oscillator 
1—1625 (V-302) first harmonic generator 
1— 832A (V-303) second harmonic generator 
1-832A (V-304) ri. amplifier 
The power amplifier is plate and screen modulated 
by the separate MD-7/ARC-5 modulator. This unit 
is shown fully converted in another section of this 
Manual 

In order to use the original tubes, a 12-volt filament 
transformer is included in the power supply unit. The 
ARC-5 transmitter employs six d.c. relays. These are; 
K-301— Antenna changeover relay 
K-302— Plate and screen voltage control 
K-303— Modulator screen and key control 
K-304— Motor tuning control 
K-305— Auxiliary plate and screen voltage con- 
trol 
K-306— Modulator plate and voltage regulator 
interlock 
All relays except the antenna changeover unit 
(K-301) are removed in the conversion. The complete 
conversion is outlined in steps to ensure that changes 
are made properly and in the correct sequence. Check 
off each step as you do it. 



1— Cut the wires going to the coil of relay K-305. 
Tape the leads. 

2— The red/white wire coming from one of the 
terminals of K-305 is cut, stripped, and soldered 
to the top terminal of resistor R-315 (300 
ohms). This resistor is in the cathode circuit 
of the 832A amplifier (V-304). The top termi- 
inal has two green and white wires attached 
to it. Leave these wires in position. 

3— Remove the ground connection from- R-315. 
The resistor now serves only as a tie-point. 

4— Slip the large, black 15.000'ohm resistor, R-329 
(front of chassis near 1625 oscillator socket) 
out of its bracket. Save the resistor. 

5— Remove the two wires from the back end (to- 
ward the crystal socket) of the bracket. Twist 
the wires together. They will be attached to a 
terminal strip in a later operation. 

6— Remove R-327 (3,600 ohms— oraimc. blue, red) 
from the contact terminal of relay K-303 and at- 
tach it to the back end of the 15,000 ohm re- 
sistor bracket. 

7— Remove the two leads from the front end of the 
15,000 ohm resistor bracket and tie them to- 
gether. They will be attached to a terminal 
strip in a later operation. 

8— Remove the green/white wire from the contact 
terminal of relay K-303 and attach it to the 
front end of the 15,000 ohm resistor bracket. 

9— Replace the 15,000 ohm resistor in the bracket. 
10-Remove the three relays K-303. K-302, and 
K-305 from the side of the chassis. Do not re- 
move the wires from the relavs. 



1 




Figure 33 

TOP VIEW OF T-23/ARC-5 WITH DUST COVER REMOVED 

Amplifier coils are near front panel, next to tuning motor, with 832-A 

tripler at rear. Oscillator and multiplier tubes are next to 832-A's. Drive 

shaft for rotary turrets runs along the side of amplifier chassis. Each 832-A 

stage mounts in removable sub-chassis. 



j h .m.i 




aL 



5 

Z 
< 



CD LO 

u_ i 

CO 



y 

i- 
< 

LU 

X 

u 



34 



Surplus Radio Conversion 



12V0LT FILAMENT CIRCUIT 



V-301 V-302 V-303 V-304 




© 



J 3^8 CONNECTIONS 




*- B+250 V. 



MOTOR MODIFICATION 



1-EXCITER PLATE CIRCUIT 


TO J 306 


2-EXCITER SCREEN CIRCUIT THRU R319 


PIN 8-*-h 


3 -BLA NK 


24 V O. 


4- GROUND 




5- FIL. CIRCUIT 




6-SCREEN CIRCUIT 832.A 




7- B+ AMPLlFt ER, {MODULATED) 




8- MOTOR CI RCUIT 





r 

T I I 



-O— 



© 



1625 

OSCILLATOR 
V301 



1625 
MULTIPLIER 
V302 



832A 

MULTIPLIER 

N/303 



832A 
AMPLIFIER 

V304 L.3M 




J 308 
PIN 6 



J 308 

PIN 7 



Figure 36 
A — 12-volt filament circuit for T-23/ARC-5 
B — New octal plug to replace J-308 
C — Bandswitching motor circuit modifications 
D — Schematic of modified r.f. circuit 



UNDER-CHASSIS VIEW OF T-23/ARC-5 TRANSMITTER 

Relays K-303, K-302, and K-305 are mounted to side of chassis. Crystal 

receptacles are placed between 1625 tube sockets. 




Manual, Volume III 



35 



11— Install a terminal strip having five ungrounded 
terminals in the space left by the removal of 
the relays, 

12— Attach the two wires removed in step 5 to one 
of the terminals of the strip, 

13— Attach the two wires removed in step 7 to a 
second terminal of the strip. 

14— Attach the two solid white wires going to relay 
K-303 to a third terminal of the strip. 

15— Locate the yellow and white wire going to re- 
lay K-302. Locate the blue and white wire go- 
ing to relay K-305. Remove and solder these 
wires together and attach to a fourth terminal 
of the strip. 

16— Locate and remove the blue and white wire 
going to relay K-302. Locate and remove the 
red, black, and white wire going to relay K-305. 
Solder these wires together and attach to the 
fifth terminal of the strip. 

17— Remove completely the red and white wire 
attached to the coil of relay K-306. 

18— Disconnect the 20 ohm resistor-fuse (R-326), 
and the red, green, and white wire from the 
ceramic end plate of relay K-306. Solder the 
resistor and wire together. Tape the joint. 

19— Cut the other two leads going to relay K-306. 
Tape each end so they will not short out 
against the chassis, or to each other. 

20— Remove relay K-306 from the chassis. Install 
a cable clamp to hold the cable next to the 
side of the chassis. Install a terminal strip with 
one ungrounded tie-point under the relay bolt. 

21— Attach the 20-ohm resistor to the tie-point. 

22— J-308, the 7-pin plug on the rear of the chassis, 
should be replaced with an 8-prong male plug 
for convenience. Remove the wires one at a 
time from J-308. Remove the wire from termi- 
nal #1 and place it on pin #1 of the tube 
socket. Do the same with terminal 2. Continue 
this procedure until all of the wires are trans- 
ferred. Remove J-308 and mount the male plug 
in its place. 

23— Cut all the wires connected to relay K-304. Re- 
move from the chassis the 10-ohm resistor 
(R-330, brown, black, black) and the 15 fiid. 
capacitor associated with K-304. Remove 
K-304 from the chassis, and in its place sub- 
stitute a terminal strip having one ungrounded 
tie-point. Take the green and white wire from 
the K-304 wiring cable and attach it to the 
terminal. Tape the other wires separately for 
insulation, 

24— Install a lead connecting the wires on the 
terminal strip to terminal 8 of receptacle J-308 
on the front of the unit. 

25— Locate the two 0.002 /*fd. bypass capacitors 
(C-329A, B) at the base of the tuning motor. 
Disconnect the white lead, leaving the green 



and white wire connected. Tape the white 
wire. Short together the two leads coming 
from the motor. The motor windings are now 
connected in parallel instead of in series. The 
motor will now function on 24 volts, a. a, rotat- 
ing the coil assembly when 24 volts a.c. is 
applied to pin #8 of J-308. 

26— Remove the black and white wire from the 
coil terminal of relay K-301, the antenna re- 
lay. Ground this terminal. Tape the wire. 

27-The sockets of V-301 (oscillator) and V-304 
(832- A amplifier) need not be modified for 
12-volt filament operation. On socket V-303, 
the two solid white wires should be discon- 
nected and then attached to the terminal that 
is occupied by the single black and white wire. 
The terminal formerly occupied by the two 
whites wires is now jumpered to the ground 
terminal located next to it. 

28-Now go to socket V-302 (1625 multiplier). 
Remove the green and white wire from pin 
#7 and solder it to pin #1. Ground pin #7. 
Check all connections. Modification of the 
transmitter for 144 Mc. is now complete. See 
figure 36. 

Transmitter Modification 1— Remove tube V-303 
for 50 Mc. (832-A tripler) from 

the transmitter. Save 
the tube for a spare. 
2— Set the transmitter turret on channel D. 
3-Remove the 20,000-ohm resistors (R-312, 
R-313) and the 3 /-t/Jd. coupling capacitors 
(C-315, C-316) from the grid circuit of tube 
V-304 (832A amplifier). 
4— Run a jumper wire from pin #6 (grid termi- 
nal) of socket V-303 (tripler) to grid pin #6 
of socket V-304 (amplifier). 
5— Run a second jumper from pin #2 (grid termi- 
nal) of socket V-303 to grid pin #2 of socket 
V-304. 
6- Remove coil turret Z-301 (front turret for 832A 
amplifier stage). Mark the channel D coil, 
L-311-D. 
7— Remove the plate circuit winding, and replace 
it with 19 turns of #18 enameled wire, close- 
spaced. Replace the coil in the turret. The 50 
Mc. conversion is complete. 
A crystal having a frequency between 8.334 Mc. 
and 9.0 Mc. is required for six-meter operation. Tube 
V-301 is an oscillator doubler, producing output in the 
17 Mc. region. Tube V-302 is a tripler to the 50 Mc. 
region and tube V-304 is a straight amplifier at six 
meters. 

It is possible to return to 144 Mc. operation by 
replacing the buffer tube and reworking the grid cir- 
cuit to the original configuration. If two-band opera- 
tion is desired, there is no reason why a plug-in board 
could not be adapted to replace the 832A buffer, in- 



36 



Surplus Radio Conversion 



UTC S-40 250 MA. 



1-25H 20 H 






RYi 
I* 





Figure 37 

A.C. POWER SUPPLY FOR T-23/ARC-5 

TRANSMITTER 

corporating the necessary 50 Mc, circuit changes. In 
this fashion, one transmitter would serve for both six- 
and two-meter operation. 9 



Transmitter The transmitter may be aligned with 
Tuning the aid of a small neon bulb. A tuning 

wand may be made from a pencil. Re- 
move the eraser from the end of a wooden pencil and 
crimp the metal band with a pliers to fit the end of the 
tuning slugs. Tuning may be facilitated if a drop of 
penetrating oil is placed on the threads and allowed 
to stand overnight. The slugs are at a high d.c. poten- 
tial so it is necessary to wrap the pencil completely 
with two layers of electrical tape for protection. 

First, adjust the oscillator coil ( turret Z-302, center, 
right side) for output at the third harmonic. Use a 
nearby receiver as a monitor, or check frequency with 
the aid of a grid-dip oscillator. Next, tune each buffer 
stage for maximum brilliance of the neon bulb when 
held near the plate lead of the tube in question. Check 
for correct frequency tuning with the grid-dip oscilla- 
tor. Channel D is best suited for operation at the high 
frequency end of the 144 Mc. band. 



Transmitter Power 
Supply 



The transmitter requires a 
power supply delivering 400 
volts at 200 ma. for the plate 
supply, 270 volts at 75 ma., 12 volts a.c. at 2.5 amperes 
for the filaments, and 24 volts at 1 ampere for the 
tuning motor. A suitable supply is shown in figure 
37. Plate input to the amplifier stage is about 30 
watts (400 volts at 80 milliamperes ) . Note: Turn off 
the high voltage before you run the tuning motor, or 



Figure 38 

TOP VIEW OF COMMAND TRANSMITTER CONVERTED FOR 

SINGLE SIDEBAND SERVICE 

Placement of major components is shown in figure 40. Pi-network circuit 

for linear amplifier is at right of chassis. Unit shown is for 80-meter 

operation. 





Manual, Volume III 



37 



it is possible to blow out the 47-ohm resistor (R-316) 

in the 832-A plate circuit. 

Convert Your BC-458 Into o 
Single Sideband Transmitter! 

The BC-458 is part of the SCR-274N radio equip- 
ment. It is a compact v.f.o. transmitter, covering 



the range of 5.3—7.0 Mc. (Navy version is the 
T-21/ARC-5). Four tubes are used in the transmitter: 
1626 oscillator, 1629 "magic-eye" tuning indicator, and 
two 1625 power amplifiers. 

This Command transmitter may be easily con- 
verted to a phasing-type s.s.b. transmitter for either 



Ai/QtQ 



AUDIO DRIVER 
V3 
4-12AU7 



V28 
12AU7 




Bl 250 MA. 
PILOT LAMP 



©Pi 

B-t- 300-1000 V- 



Figure 39 
SCHEMATIC, SINGLE SIDEBAND TRANSMITTER 



C-l — 3 M/ifd. This capacitor may not be 
necessary. Leave it out unless car- 
rier balance can not be set with 
slugs of L-l and L-2. 

C-2 — Original oscillator tuning capaci- 
tor, panel-driven 

C-3 — Original oscillator padding capaci- 
tor 

C-4 — See coil table 

C-5, C-6— 140 wifd. 

C-7 — 1250 volt mica padding capacitor, 
300— 1500 ^fd. 

C-8A-B-C-D— 10-10-10-10 /*fd. electro- 
lytic in metal can. 



FL-1 — Barker & Williamson type 350 

phase-shift network. 
T-l — 20K to 600-800 ohms. Thordarson 

TR-17, or Arrow Sales Co. type TR- 

29. 
T-2, T-3 — 15K to 200 ohms. Thordarson 

TR-25, or Arrow Sales Co. type TR- 

29 (use Yz of secondary winding). 
RFC-1 — 2.5 mh. choke 
RFC-2 — 5 turns #18 e. wire around 47 

ohm, 2-watt composition resistor. 
RFC-3 — 2.5 mh. "transmitting type" 

choke 
See figure 43 for coil data 



38 



Surplus Radio Conversion 



80- or 40-meter operation. Either sideband may be 
transmitted, and the completed transmitter includes a 
high stability vi.o. Peak power output is about 100 
watts when a 1000-volt plate supply is used. 

The Sideband The complete circuit of the convert- 
Circuit' ed command transmitter is shown 
in figure 39. The original oscillator 
tube and circuitry (V-10) is retained, as well as the 
1625 amplifier tubes and sockets (V-8, V-9). The 
sideband signal is generated at a crystal controlled fre- 
quency of 9 Mc. Tubes V-l and V-2A are the audio 
stages that develop sufficient voltage from a crystal 
microphone to drive phasing network FL-1 prop- 
erly. The two audio output signals from the net- 
work are further amplified by tube V-3 and applied 
in series with the r.f. output of the 9 Mc. crystal 
oscillator through circuits T2-L1 and T3-L2. Two 
r.f. signals are available at points "A" and "B". Each 
signal is amplitude modulated, but of a different r.f. 
phase. These two signals are applied to the diode 
balanced modulator (V-4, V-5) through two balanc- 
ing potentiometers, R-2, and R-3. The signal de- 
veloped in the output circuit of the balanced modula- 
tor (L-4) is a single sideband signal at 9 Mc. The ac- 
tion of the modulator has balanced out the carrier 
and one sideband, leaving the desired single side- 
band. Reversing switch S-l will change the sideband 
appearing at the output of the balanced modulator. 
This signal is amplified by V-6. 

The 9 Mc. signal must now be changed in fre- 
quency by a mixing process to the desired output fre- 
quency in either the 80-meter or the 20-meter band. 
This is done by combining the 9 Mc. sideband signal 
with the 5 Mc. output signal of the variable fre- 
quency oscillator, V-10. Mixing is done in tube V-7. 
Twenty-meter output is a summation of the two sig- 
nals (9 Mc. plus 5 Mc. = 14 Mc.) and eighty-meter 
output is the difference of the two signals (9 Mc. 
minus 5 Mc. = 4 Mc. ). Both signals appear in the 
plate circuit of V-7, and the desired signal is obtained 
by tuning the circuit C-4— L-7 to either 20 or 80 meters. 
Data for this circuit for either band is given in figure 
43. 

The final step is to amplify the s.s.b. signal to a 
usable level. This is done in the linear amplifier, 
V-8, V-9. When operated at 1000 volts plate potential, 
s.s.b. peak output is over 100 watts, dropping to 20 
watts at 300 volts. The transmitter is placed on the 
air by energizing V-7 when switch S-2 is closed. 

Vi.o. operation is obtained by tuning capacitor 
C-2. The range of 5.0-5.4 Mc. covers the 20-meter 
band (14.0-14.4 Mc), and the range of 5.2-5.0 Mc. 
covers the 80-meter band (3.8—4.0 Mc). It is a sim- 
ple matter to increase the setting of the oscillator 
padding capacitor C-3 to lower the oscillator fre- 
quency to 5.0 Mc at the low frequency end of the 
dial. 



Converting the The first job is to strip the 

Command Transmitter Command transmitter of 

all the parts you do not re- 
quire. Refer to figure 2 for wiring diagram of orig- 
inal transmitter. Remove all of the original wiring 
below the chassis except the 1626 oscillator circuit. 
Remove R-71, C-64, C-66, K-53, C-62 and R-76. Also 
remove C-65. Leave capacitor C-61. The amplifier 
capacitor (C-67) of the tuning gang is removed, and 
a new tuning shaft for oscillator tuning capacitor C-63 
is made from the knob and shaft from the variable 
link coupling coil above the chassis (part of T-54). 
Above the chassis, the loading coil, antenna relay, and 
plate coil T-54 are removed. 

The new parts, tube sockets, and other com- 
ponents are now laid out atop the chassis, as shown 
in figure 38, and the chassis is drilled. A new alumi- 
num panel is placed over the old front panel of the 
transmitter. At the rear of the chassis a miniature 
coaxial receptacle (J-2) is mounted, and the original 
power plug is removed and an 8-pin socket substi- 
tuted. Also mounted on the back apron is a high 
voltage terminal (Mitten). Placement of the com- 
ponents is indicated in figures 40 and 41. 



Wiring the S.S.B. 
Transmitter 



The filament circuits are wired 
first. Next, the oscillator coil 
(L-3, figures 39 and 40, old 
T-53, figure 2) is wired. Terminal #5 of L-3 is at- 
tached to capacitor C-61, and the opposite terminal 



S2 



J2 



-fli 



JS 



-^ 



V6 
12BA6 



OSC.COIL 

AND 

TUNING 

CAPACITOR 



n ft*" 



T) 



T2 ! T3 ! 
I ! 



s& 



~P^ 



~ C S T ~ 



" V4, 6AL5 
^V5, 6AL5 



- V1 12AT7 
AUDIO 



AUDIO BALANCE V3,12AU7 V2.12AU7 

R5 AUDIO AUDIO DRIVER ' AUDJO, XTAL OSC. 

BALANCE 
FU 

PLACEMENT OF PARTS ON CHASSIS, TOP VIEW 

Figure 40 
Placement of parts on chassis, top view 



CONNECTIONS. L3 




PLACEMENT OF PARTS 
ON PAN EL 
B1 




Figure 41 
Panel layout and coil connections, L-3 



Manual, Volume III 



39 



of C-61 is grounded. The "hot" terminal of C-61 is 
wired to the 12-volt filament circuit. Pins #1, 6 
and 7 of L-3 are left empty. 

The next step is to wire the audio stages and the 
audio filter. Mount the /2-watt resistors and ceramic 
capacitors directly on the socket pins to conserve 
space wherever possible. Capacitor C8A-B-C-D is a 
four-section can mounted to the chassis, and balance 
control R-5 is on the chassis deck, above R-4. Because 
of restricted space, R-5 is a subminiature control, only 
%" diameter (CTC type "Mini-pot"). 

Now, wire the crystal oscillator, balanced modula- 
tor, and 9 Mc, amplifier stages. Wind coils L-l, L-2, 
L-4, and L-5 according to the data of figure 42. 
Mount 9 Mc. crystal X-l to the inner wall of the 
chassis by means of a small aluminum clamp. Capa- 
citor C-l is merely the capacitive coupling between 
coils L-l and L-2, which are separated about one 
inch, center to center. The leads from the link coils 
to potentiometers R-2 and R-3 are twisted together. 
Silver mica capacitors are employed across L-l, L-2, 
L-4, and L-5, and also across L-7. 

Finally, wire the mixer, V-7, and the 1625 amplifier 
stage. Plate coil L-8 is supported at one end by the 
stator of loading capacitor C-6, and at the opposite 
end by the 500 ^fd. TV-type coupling capacitor, 
which is mounted on a small metal bushing between 
the 1625 sockets. Choke RFC-3 is placed between the 
capacitor and the oscillator shield, as seen in the top 



L-l, 



. L-2, L-5, L-6 — 25 turns #22 e. wire, slug- 
tuned form, 5/16" diam. Link 4 turns over 
"cold end" 
L-3 — Original oscillator coil, see figure 41 
L-4 — 8 turns #16 e., slug-tuned form, 5/16" diam. 

Link, 1 turn at center 
L-7 — 3.5 Mc. 39 turns #26 e., slug-tuned form, 
5/ 1 6" diam., tuned by 1 50 mitd. capacitor 
(C-4), 14 Mc, 25 turns #22 e., slug-tuned 
form, 5/16" diam., tuned by 56 nixfd. capaci- 
tor (C-4). 
—3.5 Mc. 46 turns #20, 16 turns per inch, 1" 
dram. (3. & W. 3015) 14 Mc. 12 turns #14, 
1 " diam., 1 - 5/8" long. 



L-8- 



Figure 43 
COIL TABLE FOR S.S.B. EXCITER 

view photograph. Capacitors C-5 and C-6 are mount- 
ed to the front panel, with their rotors grounded 
to the panel. A short length of coaxial line is run 
from capacitor C-6 to coaxial receptacle J-2 mounted 
on the rear of the chassis. Ground the outer shield 
of the line at both ends. 

As a last step, check all your wiring against figure 
39. 



Adjusting the S.S.B. 
Transmitter 



Adjustment of this transmit- 
ter is done in steps. First, 
plug in all tubes and deter- 
mine that the filaments operate when 12.6 volts is 
applied between the filament pin and ground of the 
power plug. Remove all tubes except the oscillator 



Figure 42 

Under-chassis view of S.S.B. transmitter. Audio system components occupy 

space of old amplifier tank capacitors. Coils L-l and L-2 ore mounted 

behind one 1625 tube socket, near center of chassis. Coaxial lead runs 

from C-6 to coaxial output jack J-2 on rear of chassis. 










40 



Surplus Radio Conversion 



tube V-10 and the regulator tube, V-ll. Apply 300 
volts to the transmitter and check v.f.o. operation by 
listening to the 5 Mc. region in a nearby receiver. 
Adjust capacitor C-60 (atop the chassis, see figure 2) 
to bring the 5.3 Mc. dial point down to 5 Mc. Now, 
plug in tube V-2 and listen at 9 Mc. Adjust the slug 
of coil L-2 until the crystal stage oscillates. 

You now need an audio oscillator for the next ad- 
justment step. A high quality, low distortion oscilla- 
tor (such as the Heathkit AG-10 or AG-9A should be 
employed). A low level, 1200 cycle audio signal is 
injected in microphone jack J-l. Coils L-4, L-5, and 
L-6 are peaked for maximum 9 Mc. signal as measured 
with a vacuum tube voltmeter connected from pin 
#5 of socket V-7 to ground, or with a antenna lead 
of a nearby receiver held close to pin #5. 

As long as the audio signal is applied, a signal 
at the sideband frequency will appear in circuit C-4— 
L-7. Let us assume, as an example, that this circuit 
is tuned to 80 meters. Tune your receiver to 80 meters 
and listen for the signal. You will hear a signal, 
modulated with the 1200 cycle tone at a frequency 
that is the difference between 9 Mc. (the crystal fre- 
quency) and the frequency of the v.f.o. Adjust L-7 
for maximum signal. Next, turn off the audio signal, 
and adjust carrier balance potentiometers R-2 and 
R-3 for minimum signal. 

The audio balance controls and coils L-l and 
L-2 are best adjusted with the aid of an oscilloscope 
using "ripple" patterns. These adjustments are cov- 
ered in detail in the Radio Handbook (published by 
Editors and Engineers, Summerland, Calif.), or in the 
Handbook Single Sideband for Radio Amateurs, pub- 
lished by the American Radio Relay League. In brief, 
the vertical plates of the 'scope tube are link-coupled 
to coil L-6, and oscillator tube V-10 is removed, leav- 
ing only the 9 Mc. signal input to V-7. The 'scope 



pattern will have a modulation "ripple" upon it. 
Listening to the 9 Mc. signal in a nearby receiver will 
allow you to hear the 1200 cycle audio tone impressed 
upon the speech system. During adjustments, the 
audio level should be held as low 7 as possible to pre- 
vent overloading the phasing system of the transmit- 
ter. Couple the receiver to coil L-6 and reduce the 
gain to prevent overloading. Now, adjust balance 
controls R-5 and R-4 for minimum "ripple" on the 
'scope pattern. Also adjust the slugs of coils L-l and 
L-2 for minimum ripple. Keep the audio level as 
low as possible, and go over the adjustments several 
times. Also rebalance the carrier balance controls R-2 
and R-3 for minimum pattern. Reverse sideband 
switch S-l and recheck your adjustments. You should 
strive to obtain minimum "ripple" regardless of the 
setting of switch S-L Once this point has been 
reached, disconnect the audio generator and 'scope 
and connect a microphone to J-L You should hear a 
clean s.s.b. signal at 9 Mc. 

Linear Amplifier Plug in the 1625 tubes and apply 
Adjustment about — 18 volts bias (use flash- 

light batteries or small "C" bat- 
teries) and jumper high voltage terminal P-l to the 
250 volt supply, placing 250 volts on the plate circuit 
of the tubes. Resting plate current will be about 90 
milliamperes or so. Unbalance carrier control R-2 or 
R-3 and you will obtain an 80-meter carrier in the 
plate circuit of the linear stage. You can now resonate 
and tune this stage like any other amplifier. For 80- 
meter operation, capacitor C-7 must be placed across 
the output jack J-2. The value of this capacitance 
depends upon the impedance of the antenna system, 
and will vary between 300 /x//fd. and 1500 ^fd. As a 
starter, parallel two sections of a broadcast-type vari- 
able capacitor and use it for C-7. Set it at maximum 
capacity. 



Figure 44 

"COMMAND" 

TRANSMITTER MAY 

EASILY BE 

CONVERTED INTO 

HIGH POWER S.S.B. 

LINEAR AMPLIFIER 

250 watts peak power is 

run by inexpensive 1625 

tubes (center). Voltage 

regulator tubes are at 

rear of chassis. 




Wtl#^ 



Manual, Volume III 



41 



After you have become familiar with operation at 
250 volts, you can boost the plate voltage to 1000 volts 
or so. The bias voltage for the 1625 tubes should be 
raised until the no-signal plate current is about 35 
ma. at 1000 volts. For other plate voltage values, the 
bias should be adjusted so that the product of the 
voltage and the no-signal plate current results in a 
power input of 35 watts to the two tubes. Under full 
voice input signal, the plate current will kick up to 
120 milliamperes or so. 

Convert Your Command Transmitter to a 
S.S.B. Linear Amplifier 

The Command transmitter makes an excellent 
linear amplifier for 40- or 80-meter operation, capable 
of running a peak power input of 250 watts. It makes 
a good linear amplifier for the 10A or 20A sideband 
exciter, or for any s.s.b. exciter ctvpable of delivering a 
few watts of power in the 40- or 80-meter amateur 
band. 

For 80-meter operation, the 3-4 Mc. (BC-696, or 
T-19 ARC-5) or the 4-5.5 Mc. (BC-457, or T-20/ 
ARC-5) transmitter mav be used. For 40 meters, the 
5.3-7 Mc. BC-45S, or T-21 ARC-5) or the 7-9.1 




COIL T-53 



Figure 45 
SCHEMATIC, S.S.B. LINEAR AMPLIFIER 
MADE FROM A "COMMAND" 
TRANSMITTER 
C-l— 300 M/xfd. Bud MC-1860 
L-l — Adjust to tune to output frequency with 
C-l nearly fully meshed. Air-Dux 1610, 
or B&W 3907-1 coil stock (2" diam., 10 
turns per inch). Adjust antenna tap for 
optimum loading 
RFC- 1 — — 2.5 mh. choke "transmitting type." 



6 







Figure 46 
UNDER-CHASSIS ViEW OF S.S.B. LINEAR AMPLIFIER 
Screen resistor R-l is mounted to rear of chassis above the voltage regulator 
tube sockets. Plate tuning capacitor C-l is adjustable through side of 
chassis. Shielded wire is employed for filament, screen, and bias leads. 
Tuning capacitor near dial is not used, serving only as a bearing for 

extension drive shaft. 



42 



Surplus Radio Conversion 



Mc. (BC-459, or T-22/ARC-5) transmitter may be 
used. Power requirements are 12.6 volts at 0.9 am- 
peres, 350 volts at 35 ma., and 500 to 1000 volts at 
150 ma. plate potential. 

Conversion to S.S.B. This conversion entails the 
Service removal of the oscillator and 

auxiliary equipment, and the 
conversion of the oscillator coil to form an amplifier 
grid coil. Voltage regulator tubes are added to the 
screen circuit of the final amplifier. A new amplifier 
plate circuit is also required. 

The first step is to remove the unwanted com- 
ponents. Beneath the chassis, remove R-71, C-58, 
C-64, and all small components on the three rear tube 
sockets. Remove R-75, R-76, and auxiliary padding 
capacitor C-67. Remove relay K-53, and resistor R-78. 
Above the chassis, remove the antenna relay K-54 and 
the loading coil. Remove the plate coil T-54 and the 
rotary link control. Remove all loose leads and 
wires. 

Wiring the A schematic of the converted 

Linear Amplifier Command set is shown in figure 
45, and top and bottom photo- 
graphs are given in figures 44 and 46. A five-prong 
socket replaces the rear power receptacle, J-64. The 
VR-150 and VR-105 regulator tubes are placed in 
two empty octal sockets at the back of the chassis. 

Tap #1 on the old oscillator coil (T-53) is used 
as the r.f. input circuit for the amplifier. Excitation 
may be controlled by tuning the main dial of the 
transmitter for greatest grid drive. The plate circuit 
of the linear amplifier uses a new tuning capacitor, 
C-l. The old, ganged capacitor is not used, but is 
retained to act as a bearing for the oscillator tuning 
shaft. 

Plate coil L-l is mounted above the chassis as 
seen in figure 44. It should be pruned so that reson- 
ance on 80 meters occurs with C-l almost fully 
meshed, and 40-meter resonance occurs with C-l 
about 75% meshed. The antenna tap on L-l is connect- 
ed to a coaxial receptacle mounted on the front panel 



* FU-PLATE 



7-3-13- *■ 4i-MAXr-* 





r ^MAX. 



BOTTOM VIEW 



Figure 47 

OUTLINE DRAWING OF W.E. 701 -A 

VACUUM TUBE, SHOWING TERMINAL 

CONNECTIONS 



of the amplifier. An external 0-250 ma. d.c. milliam- 
meter may be placed in the B-plus lead for tune-up 
purposes. Pins #6 and #7 of each 1625 socket are 
grounded to the metal shell, and the "hot" filament 
line is bypassed with a 0.01 ^fd. ceramic disc capaci- 
tor. Pin #3 of each socket is also bypassed to the 
metal shell with a similar capacitor. 

Linear Amplifier Bias voltage is applied to the 
Operation amplifier, and the B-plus lead 

is temporarily connected to the 
350 volt supply for tune-up purposes. Bias voltage 
is varied (about —18 volts) until the no-signal plate 
current of the amplifier is about 90 milliamperes. A 
small s.s.b. signal is applied to the input and the tun- 
ing dial varied until a rise in the plate current of the 
amplifier is noted. It may be necessary to adjust pad- 
ding capacitor C-60 or the slug of coil T-53 to obtain 
resonance. Plate tuning capacitor C-l is tuned for 
plate circuit resonance, and the tap on coil L-l is ad- 
justed for optimum antenna loading. Resistor R-l 
should be adjusted for about 30 ma. of regulator tube 
current. When the amplifier is operating properly, 
the 1625 plate voltage may be raised to a maximum 
of 1000 volts. Bias should be adjusted to provide a 
no-signal plate current of about 35 ma. Under full 
excitation, maximum average plate current will be 
about 125 ma., providing a s.s.b. input signal of about 
300 peak watts. The antenna tap on coil L-l may be 
readjusted at the higher value of plate voltage for 
optimum antenna loading. 

Using the Western Electric 
701 -A Tetrode 

The large Western. Electric 701-A tetrode is avail- 
able on the surplus market for a low price. The phy- 
sical size of the tube (7W high, 4Ji" diameter) sug- 
gests that it would make a good high power r.f. am- 
plifier. The tube is a tetrode intended for pulse modu- 
lator operation. It has an indirectly heated cathode, 
with the plate terminal of the tube at the top of the 
glass bulb. Connections to the terminals and the 
outline of the tube are shown in figure 47. A modified 
Western Electric 153A socket may be used, or the 
experimenter can easily build his own socket. The 
tube should be mounted in a vertical position, and 
there should be a free circulation of air around the 
glass envelope. 

The pulse modulator ratings of the tube are: 

Heater Voltage, 8.0 volts, a. c. or d.c. 

Heater Current, 7.5 amperes. 

Maximum plate voltage (pulse), 12,500 volts. 

Maximum screen voltage i' pulse), 1,200 volts. 

Average plate current (pulse), 80 ma. 

Peak pulse plate current, 10 amperes. 

Plate dissipation (pulse). 100 watts. 

Screen dissipation (pulse), 15 watts. 

The suggested class-C operating conditions for 
amateur service are; 



Manual, Volume III 



43 



ANTENNA 19" 




RFC 
2144 



— r • f-nnftp^_ 

3 ,5-L ^4 7 3? 

!l T r 4 M 7 i 



67.5 V. 

H|l|l|l|lP 



>>. 



G-BAND SECTION 



I- BAND SECTION 



SIGMA 
4F6K 

RELAY 



Figure 48 

SCHEMATIC, MODIFIED BC-1253 

METEOROLOGICAL TRANSMITTER 

Filament voltage, 7.5 volts. 
Filament current, 7.0 amperes. 
Plate Voltage 2000 2500 3000 3500 (volts) 
Plate current 350 300 250 250 ( ma. ) 
Power Input 750 750 750 875 (watts) 
Plate dissipation 220 200 160 175 (watts) 
Screen voltage 400 400 400 400 (volts) 
Screen current 40 40 40 40 ( ma. ) 
Screen dissipation 20 20 20 20 ( watts ) 
Grid voltage -150 -150 -150 -150 (volts) 
Grid current 15 15 15 15 ( ma. ) 

Note: It is suggested that a 6Y6 

screen clamper tube to protect the 

cessive screen dissipation. 

Inter-electrode capacitances: 

Input 15.6 /i/tfd. 

Output 8.5 /L^tfd. 

Grid-plate 0.16 w fd. 



G be used as a 
701 -A from ex- 



Converting the BC-1253 to a 
Sensitive Radio Control Receiver 

The BC-1253 meteorological transmitter, available 
in quantity in the surplus stores can easily be con- 
verted to an excellent radio control receiver, featuring 
high sensitivity, good stability, and light weight. The 
receiver is suitable for use in model airplanes, boats, 
etc. The BC-1253 was originally used in weather bal- 
loons to send upper-atmosphere weather information 
back to earth. The transmitter is contained in a small, 
strong cardboard box that is attached to the sounding 
balloon. A lightweight battery pack accompanies the 
transmitter on its flight into the heavens. 

The BC-1253 employs a single 955 acorn triode 
tube as a milliwatt oscillator, with the socket of the 
oscillator built into the end of a silver-plated tank 
circuit. The converted circuit of the oscillator is 
shown in figure 48. Note that the only steps necessary 
for the conversion are to remove the unnecessary com- 
ponents, change the value of the 955 grid resistor, and 
make the wiring changes shown. 



Conversion to a Radio 
Control Receiver 



The original transmitter 
circuit uses several con- 
nections on a socket strip 
that it is mounted on. All connections to this strip are 
removed. To do a neat job, the contact pins should be 




* - PLACE 10 MEGOHM, 1/2. 
WATT tN SERIES WITH 
GRID CHOKE FOR RECEIVER 
MODIFICATION. 



Figure 49 

SCHEMATIC, MODIFIED BC-1066 I.F.F. 

TEST SET 

drilled off and the space provided used to mount the 
additional parts. It is necessary to add a 3—30 wifd. 
variable compression trimmer capacitor across the 
tuned circuit line. It will be necessary to slide the 
trimmer up and down the lines while adjusting the 
capacitor to hit the 2 meter ( 144 Mc. ) amateur band. 
Varying the antenna tap and the tuning capacitor will 
permit the detector to remain in oscillation across the 
complete band. 

A super-regenerative detector circuit is employed 
for maximum sensitivity. For optimum results, the 
plate circuit relay (Sigma type 4F) should be set to 
pull in at 1 milliampere of plate current. This can be 
checked by connecting the relay coil in series with a 
50K potentiometer, a 45 volt batteiy, and a milliam- 
meter. Adjust the point spacing of the contacts and 
the spring tension so that the relay pulls in at about 
1 milliampere, and drops out at about 0.8 ma. Now, 
insert the relay back into the receiver circuit and ad- 
just the variable plate voltage control until the relay 
pulls in. Next, back off slightly on the control until 
the relay drops out. A nearby 2-meter r.f. signal 
picked up by the receiver should now cause the relay 
to pull in. Adjust the antenna tap for maximum re- 
ceiver sensitivity. 

Converting the BC-1066 to a 
144 Mc— 220 Mc. Receiver 

The BC-1066 Test Equipment is a dual v.h.f. oscil- 
lator intended to check the operation of the SCR-695 
"I.F.F." radio equipment. The BC-1066 consists of two 



44 



Surplus Radio Conversion 



cm 

IOMM 



METER / SI04 / 
SWITCH 




RF POWER AMPLIFIER 



ANTENNA 
COUPLING 
ANTENNA 

JI03, 



ANTENNA TUNING 

kJ SI03 SPEAKER ON-OFF 



RI04 RI05 
3300 2.4 







3RD IF AMPLIFIER 




D 

a 



C 1 9 6 ~Y.0O05 s QUEL CH SENSI T IV I TV PRE SS'^OCUT SQUELCH 



Figure 50 

SCHEMATIC, NAVY TYPE COL-43065 (MBF) 

TRANSMITTER-RECEIVER 



Manual, Volume III 



45 



VOLUME 
I 



AF AMPLIFIER AF DRIVER 



AF POWER AMPLIFIER 



HANDSET SCHEMATIC 
I r>»-CABLE 




note: unless otherwise specified: 
all resistance values are in ohms, 
capacitance values are in micromicro- 
faraos and inductance values are in 

HENRIES. 



Figure 50 

SCHEMATIC, NAVY TYPE COL-43065 (MBF) 

TRANSMITTER-RECEIVER 



46 



Surplus Radio Conversion 



super-regenerative detectors, tunable over the two 
I.F.F. bands. The weak pulses of the detectors were 
picked up by the I.F.F. set, which responded by re- 
turning a series of coded pulses which could be heard 
by the receiver portion of the BC-1066. This inexpen- 
sive surplus item consists of two type 957 acorn triode 
tubes used as v.h.f. detector-oscillators, and a 1D8-GT 
audio amplifier. The two tuned circuits are tunable 
over ranges close to the 144 Mc. and 220 Mc. amateur 
bands. A panel switch (I-band: G-band) selects the 
audio output of either detector. The audio is ampli- 
fied by the 1D8-GT tube. 



Conversion to a 
V.H.F. Receiver 



The BC-1066 can be converted to 
a sensitive receiver for the ama- 
teur 144 Mc. and 220 Mc. bands. 
The original circuit of the unit is shown in figure 49. 
It is only necessary to unground the end of each r.f. 
choke in the 957 circuits. In series with this choke, 
connect a 10 megohm, ?2-watt resistor to ground. 

The G-band receiver can be tuned up to the 220 
Mc. band by adjusting the padding capacitor, and the 
I-band receiver will tune to 144 Mc. with a simple 
adjustment of the padder capacitor. The BC-1066 
draws only a small amount of current, and a size D 
cell, plus two small 67/2-volt batteries will last for many 
months. It is an excellent receiver for "Field Day" 
or any portable v.h.f. use. Two M-wave whip antennas 
mounted atop the case and link coupled to the respec- 
tive tuned circuits will be satisfactory for portable 
work. 

Conversion of R-9/APN-4 for 
115 Voir A.C. 60 Cycle Operation 

R-9/APN-4 makes a good 160 meter receiver when 
converted for 50—60 cycle operation. The receiver op- 
erates on four preset channels, any one of which can 
be selected by the main channel switch. In this conver- 
sion, the power supply is adapted for operation from 
your light line, and the receiver is modified for opera- 
tion without auxiliary equipment. The 1400- volt supply 
in the receiver for the Loran 'scope tube is not used. 



Receiver Section 
Conversion 



Check off each step as you do the 
conversion. 
1— Remove J-104 (red) from the 
panel and install a phone jack in its hole. Solder 
the center wire of the coaxial cable to the tip con- 
nection of the jack. 

2— Remove the wires from the "Filter In— Out" switch. 
Splice the wires together near the 6SL7 socket. 
Tape the wire joint. 

3— Cut away the wire between pin #8 of 6SN7 socket 
and pin #1 of 6SL7 socket. 

4— Remove J-103 (blue) but leave its wire. Install in 
its hole a 3K potentiometer. Connect the wire to 
the center terminal of the potentiometer, and 
ground one other terminal. This is now the audio 
volume control. 



Power Supply Section 1— Remove J-102 (yellow) 

Conversion and switch S-103 (line 

voltage ) . 
2— Remove the wires between pins #3 and #4 of 

J-106 and the power switch. 
3— Unsolder the black wire (which goes to terminal 
#1 of T-105) from standoff insulator and resolder 
to terminal #3 of J-106. 
4— Remove the white wire from terminal #3 of T-105 
and connect terminal #3 of T-105 to pin #4 of 
J-106. Tape the end of the white wire. 
5— On T-105: Move blue (blue-red on R9-B receiver) 
wire from terminal #2 to terminal #3. Solder 
other end of this wire to end-lug of spare fuse 
holder. 
6— Connect side-lug of spare fuse holder to one side 
of old "Filter Out— In" switch. Solder white wire 
which went to S-103 to other terminal of old 
"Filter Out— In" switch. 
7— Remove blue wire from end-lug of F-101 and con- 
nect in its place the white-black lead which used 
to go to the line voltage switch. Tape the blue 
wire end. 
8— Remove the voltage control potentiometer R-121 
together with its series resistor and re-install in old 
line voltage switch mounting hole. Ground the 
loose end of resistor R-128. 
9— Move red-black wire from terminal #2 of T-104 
to the point on the terminal board where blue 
( blue-red on R9-B receiver ) wire from R-121 
originally terminated (see step 5). Solder the 
other end of this red-black wire (find correct one 
of two) to potentiometer R-121 in its new location. 

10— Connect center terminal of R-121 to point on ter- 
minal board where green wire was connected, 

11— Install switch S-103 in J-102 hole. Run wire from 
the center terminals to terminal -12 of T-104. 
Connect lower pair of terminals to "hot" lug of 
pilot lamp receptacle. 

12— Protection from heavy current surge must be used 
in series with primary winding of power trans- 
ormer. Place three 200-watt. 115 volt light bulbs in 
series with the line, using primary terminals #1 
and #3, Safe operating voltage for the transform- 
ers is indicated by a voltage of 5M across terminals 
#12 and #13. Ninety-eight to 100 volts should 
be indicated across terminals "1 and #3 for good 
operation. 

Converting the MBF Transmitter- 
Receiver for 6 Meters 

The Navy MBF transmitter-receiver (Navy type 
COL-43065)'is designed to operate in the 60-80 Mc. 
range. It will operate from 115 volts, a.c. or d.c. The 
MBF has crystal controlled receiving and transmitting 
channels, but may be converted for manual receiver 
tuning. The schematic of the MBF is shown in figure 
50. The following tubes are used, with their filaments 
connected in series-parallel across the 115 volt line: 



Manual, Volume III 



47 




■<§) TERMINAL 




6AK5 
Vtio 



GREEN LEAD ■+ AAA- 

TO METER 
SWITCH 



7^23? r 



® 



© 



Figure 51 
A — Modified oscillator circuit for MBF receiver section 
B — Modified r.f. circuit for MBF receiver section 
C — S-meter circuit modification 



Transmitter tubes 

V-101— Transmitter oscillator, 6C4 

V- 102— Frequency multiplier, 6C4 

V-103-Second multiplier, 6C4 

V-104-R.f . power amplifier, 28D7 
Receiver tubes 

V-108-Ri. amplifier, 6AK5 

V-109-Mixer, 6AK5 

V-110-5.3 Mc. ii. amplifier, 6AK5 

V-lll-5.3 Mc. Li. amplifier, 6AK5 

V-l 12-5.3 Mc. ii. amplifier, 6AK5 

V- 113— Injection frequency multiplier, 6C4 

V-114— Injection crystal oscillator, 6C4 

V-115-A.v.c. amplifier, 6AQ6 

V-116-Second detector, 6C4 

V-117-SqueIch amplifier, 6AQ6 

V-123-Noise limiter, 6C4 
Modulator and Power supply 

V-105-Ai. amplifier, 6AQ6 

V-106-A.f. driver, 6C4 

V-107-ModuIator, 28D7 

V-118-Rectifier, 25Z6 

V-119-Rectifier, 25Z6 

V-120-Modulator, 28D7 

V-121-Notuscd 

V-122-Relav rectifier, 6C4 

V-124-Relay rectifier, 6C4 

Receiver Modification First, remove the MBF from 
for 50 Mc. Operation the case, and set it on end 

with the receiver section up. 
Remove the screws and cover which is over the first 
two receiver stages. The long bar on the back should 
also be removed. This bar connects the receiver 
chassis to the transmitter chassis. There are also sever- 
al bolts holding the receiver chassis to the main chassis 
which should be removed. Place all of the nuts, bolts, 
and washers in a safe place as you will need them 
later. Now the receiver chassis is loose with the excep- 
tion of the wiring passing through a grommet to the 
main chassis. Do not turn the equipment on when dis- 
assembled, for if the chassis touches the front panel 
you will either blow a fuse or receive a shock. 



Remove the receiver crystal holder Y-102, the first 
variable capacitor C-192, and the capacitors and re- 
sistors from the first oscillator tube socket V-114. Save 
all parts. Leave the 6C4 tube filaments in series with 
the rest of the circuit. Leave the tube in the socket. 
Now, remove oscillator coil L-114, being careful not 
to break the form. Remove the solvent from the coil 
form bolts, and it will be easier to remove the coil. 

The second 6C4 (V-113) will now become the tun- 
able oscillator for the receiver. The new oscillator 
circuit is shown in figure 51A. Compare it with the 
existing circuit of figure 50. First, take the 100K re- 
sistor (R-149) that you removed from the old oscil- 
lator stage and connect it in parallel with R-150, the 
grid resistor of tube V-113. The old coupling capacitor 
(C-147) is returned to the rotor of tuning capacitor 
C-166. 

Remove capacitor C-140 from pin #7 of socket 
V-113. Remove the wire from pin #7 and clip it off. 
Remove capacitor C-146 attached to the coil and to 
tuning capacitor C-166. Now, take out the plate coil, 
L-113. This coil has 5 turns. Remove the wire, and 
rewind it with similar size wire, 8 turns tapped approx- 
imately one turn from the bottom. Leave the coil wire 
ends long and run them through the eyelets on the coil 
form, the bottom wire about 1" long, and the top wire 
about 3" long. Put the new coil back in place and re- 
wire as shown in figure 51. 

Lead "A" is the original length of coaxial cable 
coupling the stage to the mixer tube, V-109. It con- 
nects to its original place, at the top of the coil, or to 
the variable capacitor. The plate terminal of V-113 
is attached to the top of the tall stand-off insulator, 
which is bypassed to ground with capacitor C-146 
which was removed previously. Make sure that one 
terminal of the variable capacitor is grounded, and 
that pin #7 of the socket is not grounded, but re- 
turns to the coil tap. This completes the oscillator 
conversion. 

The r.f. input circuit is converted next. The an- 
tenna coil L-lll is tapped. It is near the r.f. amplifier 
tube, V-108. Note where the coil leads go, then re- 



48 



Surplus Radio Conversion 



ORIGINAL CIRCUIT 



MODIFIED O SCILLA TOR CIRCUIT 




ORIGINAL SOCKET J 1 1 



s$ 



MODIFIED WITH PL-Q8 JACK 
T101 



- RED WIRE 
(RELAY CONTROL) 




1,5 VOLT - 

batteryT 



Ri42> §Rioa 

f i © 

Figure 52 

A — Original MBF transmitter oscillator circuit 
B — Modified oscillator circuit for use with 

surplus crystals 
C — Replacement of socket J- 101 with micro- 
phone jack 

move the coil. Unsolder the connections carefully, as 
they must be replaced later. Unwind the 5 turns on 
the coil, and replace with 7 turns of similar size wire, 
bend the ends around the eyelets and solder. Leave 
the hole open in the eyelets. Replace the coil The 
bottom terminal goes to pin #1 of socket V-108, and 
to tuning capacitor C-123 and padding capacitor 
C-1S9. The top goes to the other side of the tuning 
capacitor, and to C-124A, and R-117. 

The antenna lead is terminated near the coil at a 
stand-off insulator. The capacitor (C-168) attached 
to the insulator now goes to the top of a new two turn 
coil wrapped over the top turns of coil L-lll. Use 
insulated wire for the new coil, and ground the free 
end to the chassis next to the coil form. Use a hot iron, 
and don't damage coil L-lll. See figure 51B. 

The final modification in the receiver r.f. section is 
to modify mixer coil L-118-119. Both coils are wound 
on the same form. Remove the form, remembering 
where the connections are attached. The coils have 4 
turns each. Remove the windings, and rewind with 
similar size wire, 6 turns each. Replace the coil, and 
solder all leads. 

Other Receiver 1— The "Press to cut Squelch" 
Modifications switch (S-105) should be changed 
to a d.p.d.t. toggle switch. The 
wires to the top two terminals should be interchanged 
with the wires to the bottom two terminals on the 
new switch to make the panel markings read right. Be 
sure not to cross-connect the wires. 

2— Remove the two brackets on the panel holding 
the cover over the receiver tuning capacitors. 



3— It is easy to make meter position # 1 a "S-meter" 
for the receiver. Remove the green lead attached to 
pin #7 and R-144 of socket V-114. Connect this lead 
to the cathode (pin #2) of the first i.f. tube socket, 
V-110 through a series resistor of IK. Shunt cathode 
resistor R-123 with a 470 ohm, M-watt resistor (figure 
51C). 

The receiver chassis is now remounted to the front 
panel. Remember to replace the phenolic insulator 
the right way with the bolt holes in the right place. 
Make sure the front panel mounting screws do not 
touch the chassis since there is a potential difference 
between the two. 

Testing the Place a short antenna on the receiver 
Receiver (use J-103), and tune the oscillator 

tuning capacitor until you hear a sta- 
tion. You can probably hear TV channel 2 or 3 (a 
strong, a.c. buzz). Peak the other stages by ear. If you 
hear nothing, check your squelch switch. 

Transmitter Modification The original MBF cir- 
for 50 Mc. Operation cuit uses expensive high 

frequency crystals. In 
order to employ the plentiful 6 Mc. type FT-243 cry- 
stals, the oscillator circuit must be modified as shown 
in figure 52. A 6BH6 regenerative oscillator replaces 
old oscillator tube V-101 (6C4). The new tube has 
the same filament current as the old for proper series 
string operation. Terminals #3, 4, and 7 are un- 
touched, and terminal #2 of socket Y-101 must be 
grounded. Terminals #1, 5, and 6 are rewired as 
shown in figure 52B. Plate coil L-101 tunes to the sec- 
ond harmonic (12 Mc. ) of the crystal and is rewound 
with 26 turns of #26 e. wire. The multiplier stage 
(Y-102) now should tune to the 24—25 Mc. region. 
Coil L-102 should be altered to 17 turns of -22 e. wire. 
Space the turns to grid-dip to 25 Mc. The second 
multiplier tube (V-103) doubles to 50 Mc. Rewind 
L-103 to 18 turns, center-tapped. -14 e, wire, ?2-inch 
diameter, turns spaced one wire diameter. Adjust 
spacing to grid-dip the circuit to 51 Mc. 

The plate coil of the push-pull 2SD7 is modified to 
8 turns, center-tapped. -14 e. wire, one-inch diame- 
ter, turns spaced two wire-dLimcters. Adjust spacing 
to grid-dip to 51 Mc. The new antenna coil, L-109 is 
3 turns, #12 e. wire, one-i 
one wire diameter. Thi< 
the r.f. circuitry. 



diameter, turns spaced 
ipletes modification of 



Miscellaneous Transmitter 
Modifications 



1— Change socket J-101 
to a PL-68 micro- 
phone jack mounted 
on an insulating plate. Remove the two back 
wires from terminals -1 and #2 of transformer 
T-101. Tape each wire. Run a wire from the 
PL-68 sleeve contact to terminal #1 of T-101, and 
another wire from terminal #2 of T-101 through 
1/2-volt flashlight battery to ground. Tape the tube 



Manual, Volume III 



49 



shield next to the microphone jack to keep it from 

shortening out (figure 52C). 
2— Place a 10 /*fd. 25-volt electrolytic capacitor across 

cathode resistor R-lll (4.7K) of tube socket V-105 

(6AQ6), Positive terminal of the capacitor goes 

to pin #2 of the socket. 
3— Parallel audio coupling capacitor C-119 with a 

0.01 ftfd. ceramic disc capacitor. 

Convert Your Surplus 24-Volt 
Dynamotors to 115 Volt A.C. Motors 

You can convert almost any 28-volt dynamotor to 
a 115- volt motor by the following changes: Remove 
the brushes from the motor end of the dynamotor. 
Next, move the two field wires from the motor end to 
the generator end, and connect them in parallel with 
the generator field winding. (You have a fifty-fifty 
chance of guessing the correct polarity of the connec- 
tions. If the motor does not run, reverse the motor 
field connections.) Finally, connect a 115-volt line 
cord across the field coils and generator brushes. You 
might have to drill and tap the shaft for an extension 
if it is not long enough to fasten a coupling to it. 
Your converted motor does not have as much torque 
as a standard motor, but it may be used for turning 
fans, grinding wheels, etc. 

Adding a Tuning Control to the 
R-28 ARC-5 V.H.F. Receiver 

The R-28 ARC-5 receiver is a ten tube superhetero- 
dyne covering the frequency range of 100—156 Me, in 



four crystal controlled channels. The receiver requires 
24 volts a.c. for the filaments, and 250 volts at 75 ma. 
plate potential. The complete schematic of the re- 
ceiver is given in figure 54. It is a very simple matter 
to change the crystal controlled oscillator to a tunable 
oscillator for 144 Mc. reception. The receiver can 
thereby be used for general 2-meter reception. 

First, remove the sides and top cover, and the 
oscillator compartment covers. Locate the crystal os- 
cillator stage, V-108. Connect a 100 wid. mica capa- 
citor from the junction of coil L-lll and R-152 to pin 
#4 (grid) of socket V-108 (12SH7). Install a variable 
10 ttpfd. tuning capacitor in series with a 3—30 wid. 
zero temperature coefficient ceramic variable capa- 
citor. Ground the rotor of the variable capacitor to 
the chassis. Connect the free terminal of the ceramic 
capacitor to pin #8 of socket V-108 (plate). The 3-30 
/x/ifd. capacitor acts as a bandspread capacitor so that 
the 144 Mc. band can be spread across the full dial of 
the 10 fjififd. tuning capacitor. When the ceramic ca- 
pacitor is fully meshed, the tuning range of the receiv- 
er is 140—150 Mc. Converted in this manner, the oscil- 
lator acts as a tunable oscillator in the region of the 
original crystal frequency. The succeeding multiplier 
stages increase this frequency up to the region re- 
quired for local oscillator injection. Set the receiver to 
channel B or C for optimum 2-meter reception. The 
automatic tuning unit may be reworked as described 
in tjie section of this book dealing with the T-23/ 
ARC-5 transmitter. 



Figure 53 
R-28/ARC-5 V.H.F. receiver may be 
used for 2-meter reception. Recep- 
tacle J-103 is at bottom of front 
panel. Dynamotor space is at rear 
of receiver deck. Approximate tun- 
ing of receiver is indicated by edge- 
dial at top of panel. 




'■Mv> 




r .* ,ioo i> 



I T3NMVK), . 20 1 A 

s* H — 



* t3nw»wo |_i ia 



fch^- 





*»900 ,,6610 



JW 900)10^3 



■H 




_^J 



nn I j, I 

0* zoo T*o1 | 
" iww{4W l '**3* -- i — --' " " 



Surplus Radio Conversion Manual, Volume III 



51 




ORIGINAL 



Vl06 R143 C154 V107 

■*—m 1 



-e © 




Figure 55 
A — Modified filament circuit for 6 volt op- 
eration, R-28/ARC-5 
B — Modified audio circuit 



Rewiring the Filament 
Circuit for Six 
Volt Operation 



It is necessary to replace 
all the 12-volt tubes with 
their 6-volt equivalents for 
6-volt operation. The 717- 

A tubes have 6-volt filaments and are not changed. 

The following wiring changes in the filament circuit 

are made: 
1— (Refer to figure 55A). Remove the wire from pin 



#2 of socket V-102 and connect this lead to pin 
#7 of socket V-102. Ground pin #2 of V-102. 

2— Remove the wire from pin #2 of socket V-103 and 
connect this lead to pin #7 of socket V-103. Also 
remove the two IK resistors connected between 
pin #2 and pin #7 of V-103. Ground pin #2 of 
V-103. 

3— Remove the wire from pin #7 of V-109 and con- 
nect it to pin #2 of V-109. Ground pin #7 of 
V-109. 

4— Remove the two IK resistors between pin #2 and 
pin #7 of V-108. Remove the wire on pin #7 of 
V-108 and connect it to pin #2 of V-108. Ground 
pin #7 of V-108. 

5— Remove the wire on pin #7 of V-107 and connect 
it to pin #2 of V-107. Ground pin #7 of V-107. 

6-Remove the wire on pin #7 of V-106 and connect 
it to pin #8 of V-106. Ground pin #7 of V-106. 
This completes the conversion of the filament circuit 
for 6-volt operation. 



Modifications of 
Audio Circuits 



1-Remove R-143 (1 meg.), C-154 
(0.006 jifd.), and R-144 (0.47 
meg.) in the grid circuit of 
the 12A6 (V-107). Replace R-143 and C-154 with 
a 0.01 /*fd. capacitor. Replace R-144 with a 500K 
potentiometer. Connect the arm of the potentio- 
meter to pin #5 of V-107. This volume control is 
mounted on the front panel and leads to it are 
run in shielded wire. Ground the shields at both 
ends of the leads. 
2-Remove R-145 (1.5K) from pin #8 of V-107. Re- 



TOP VIEW OF R-28/ARC-5 RECEIVER WITH DUST COVER REMOVED 

Tuning system gear drive is at left, with crystal relays and crystal receptacles 

at right. Dynamotor mount is at rear of receiver. 




52 



Surplus Radio Conversion 



place it with a 470 ohm, 1-watt resistor from pin 
#8 to ground. 
3-Remove output transformer T-101, capacitor 
C-157, and limiter R-16B (all in plate circuit of 
V-107). Replace T-101 with small 5K plate to 
voice coil output transformer. Connect 0.01 /*fd. 
ceramic disc capacitor between pin #3 and pin 
#4 of V-107 socket. The secondary leads of the 
new transformer connect to your low impedance 
speaker. 
4-Connect the rear power plug ( J-102) as follows: 
Pins #1, 3, and 4: B minus, one side of 6-volt fil, 
Pin #7: B-plus 250 volts. 
Pin #6: 6 volt filament. 
Pin #2: Auxiliary audio output. 
Pin #3: A.v.c. lead. Open connection between 
pin #3 and pin #1 to disable receiver 
during transmissions. 

Converting the RT-19/ARC-4 Receiver- 
Transmitter for 2 Meter Operation 

The RT- 19/ ARC-4 is a complete v.hi. station cap- 
able of operation on any one of four crystal controlled 
frequencies in the 140-148 Mc. range. The transmitter 
develops approximately 10 watts output over a 1 
megacycle bandwidth without retuning. Crystals in 



the 5.83—6.0 Mc. frequency range are employed. The 
complete schematic of the ARC-4 is shown in figure 
58. 

Description of the The transmitter of the ARC-4 
Transmitter Section consists of a crystal-controlled 

oscillator stage (6 Mc), fol- 
lowed by three harmonic generators. The oscillator 
(6V6-GT, Vl-T) plate circuit is tuned to approxi- 
mately 18 Mc. The second 6V6-GT (V2-T) doubles to 
36 Mc, and V3-T ( 1614 or 6L6 ) doubles to 72 Mc The 
final multiplier V4-T (1614 or 6L6) doubles to 144 
Mc The r.f. amplifier (V5-T) is an 832-A, which is 
plate modulated by two class AB 6L6's (V6-T and 
V7-T). A carbon microphone is used, and a push-to- 
talk system is incorporated in the transmitter. The 
transmitter is designed to be used with a 50— 70-ohm 
coaxial transmission line system. 

The Receiver The receiver portion of the ARC-4 
Section employs ten tubes and has two com- 

plete ri. input circuits connected to 
a common ii. amplifier. One input circuit ("plane-to- 
plane") will be removed, and the other one ("plane- 
to-ground") will be reworked for 2-meter reception, 
and provided with a tunable oscillator. The "plane-to- 



UNDER-CHASSIS VIEW OF R-28/ARC-5 RECEIVER WITH DUST COVER 

REMOVED 
717-A tube is at left, with i.f. stage at center. Power receptacle is at rear 

of chassis. 







Manual, Volume III 



53 



ground" section employs a 6AC7 (V3-R) mixer, cou- 
pled to three stages of 10 Mc. ii. amplification (V4- 
5-6-R) having a passband of about 80 kc. A 12SQ7 
( V7-R) is used as an audio squelch tube, and a second 
12SQ7 (V8-R) serves as the second detector and audio 
stage. Two audio output stages employing 12A6 tubes 
(V9-R and V10-R) are provided. The output of V9-R 
may be taken from pins 22 and 23 of the plug terminals 
on the rear of the unit (500 ohm circuit), and the out- 
put of V10-R appears at panel jack Jl-R and pins #24 
and 25 of the same plug. 

A 6N7 double triode (Vl-R) serves as a conver- 
sion crystal oscillator and frequency quadrupler. A 
second 6N7 (V2-R) acts as a tandem doubler to the 
v.h.f. conversion frequency. 



Power Supply and The ARC-4 is powered from 
Control System either 12- or 24-volts d.c, and 

employs either a DY-9/ARC-1 
dynamotor (24 volts ), or a DY-10/ARC-4 ( 12/24 volt ) 
dynamotor. Neither dynamotor is required for the fol- 
lowing conversion. The ARC-4 is designed to be re- 
motely controlled from the C-51/ARC-4 control box 
which has a channel selector and audio input and out- 
put circuits. The control box is not required for the 
conversion. 



Transmitter Crystals of the surplus FT-243 type are 
Conversion used in this conversion. The two-meter 
band requires crystals in the range of 
6.0 Mc. to 6.16 Mc. For the Novice band, crystals 
ranging from 6.045 Mc. to 6.125 Mc. should be em- 
ployed. To make these crystals operate properly, two 
capacitors in the oscillator circuit must be changed. 
Remove C2-T (50 ^fd.) (between pin #5 and pin 
#8) on socket Vl-T and replace with a 15 /^fd. mica 
capacitor. Next, remove capacitor C3-T (400 wld.) 
across oscillator coil Ll-T and replace with a 100 wid. 
mica capacitor. 



Microphone Voltage At the rear of the chassis on 
for Transmitter the transmitter side are two 

resistors: R3-C (30 ohms, 
marked Z30 W-L), and R32-T (200 ohms, marked 
Z200). Remove R3-C from the chassis and disconnect 
the white wire with red-yellow tracer connected to the 
junction of the two resistors. Ground the end of R32-T 
that was connected to this wire. Terminals #19 and 
7 on the rear chassis plug are connected together to 
complete the circuit of R26-T and R32-T. This places 
R32-T in series with R26-T, which is the modulator 
cathode bias resistor. Next, the lead of R29-T is dis- 
connected from the filament circuit and attached to 
the terminal of R32-T (figure 60A). Both terminals of 
R29-T are bypassed to ground with 50 ^fd., 50 volt 
electrolytic filter capacitors. 



Receiver Audio A portion of the audio signal volt- 
Modifications age from the microphone is fed to 
the receiver audio section for the 
intercom circuit. Disconnect the bare wire lead from 
the grid (pin #5) of 6L6 tube socket V7-T that runs 
to the terminal board adjacent to the tube, and con- 
nects to resistor R28-T (250K). Now disconnect the 
white wire with green tracer on the grid (pin #5) of 
12A6 tube socket V10-R. Disconnect the white wire 
with red-brown tracer that connects to the junction of 
R47-1R and R47-2R (10,000 ohms), which is mounted 
on the receiver side of the chassis. Now, connect a 
wire from this center tap junction to the end of R42-R 
(1500 ohms) located en the side at the rear of the 
chassis. The correct terminal is the one nearest the 
rear. This removes the B-plus from the receiver audio 
stages when transmitting. 

Relay Circuit A Sarkes-Tarzian M-500 silicon recti- 
Modifications fier is used in the circuit of figure 
60B to rectify the filament voltage 
for operation of relay S5-C. The rectifier and filter 
capacitor are mounted near the crystal sockets. The 
two leads (white with blue-green tracer) that were 
formerly connected to R3-C (30 ohms) are attached 
to the positive terminal of the rectifier. The negative 
terminal of the rectifier is attached to the 12.6- volt fila- 
ment line through a 100 ohm resistor. A 500 j^fd., 25 
volt electrolytic capacitor is placed between the posi- 
tive terminal of the rectifier and ground as shown in 
the schematic drawing. Finally, remove the crystal 
switching relays. 



Filament Circuit 
Modifications 



To operate the filaments from the 
power supply, strap the following 
terminals on the rear power re- 
ceptacle plug in groups, as follows: Group 1: 1 and 2. 
Group 2: 5, 6, 15 and 16. Group 3: 3, 4 and 19. Group 
4: 28 and 18. Group 5: 8 and Al. Connect a 30K, 1- 
watt resistor from pin #18 to A2. Filament voltage is 
applied to pins Al and A2 (ground), as shown in the 
power supply schematic (figure 65). 

Receiver Remove the "plane-to-plane" chan- 

Modifications nel tuning unit located in the center 
of the chassis by unscrewing the four 
10-32 machine screws beneath the chassis. Remove 
the top cover plate of the first i.f, transformer FL1-R 
and loosen the screw inside that holds the coaxial line 
entering the top of the transformer. Pull up on the 
tuning unit and it will come free. Take the sides off 
the timing unit and remove the 6N7 oscillator plate 
coil L5-R. This coil may be identified by the great 
number of turns on it. Also remove one of the 50 /*/tfd. 
ceramic capacitors in the unit. It will be needed later, 
along with the coil. Finally, remove the plate holding 
the auxiliary capacitors of the tuning unit from the 
back of the ARC-4 panel. 



54 



Surplus Radio Conversion 




Figure 58 
SCHEMATIC, RT-19/ARC-4 



Manual, Volume III 



55 




Figure 58 
SCHEMATIC, RT-19/ARC-4 




Figure 59 
PANEL LAYOUT 
OF CONVERTED 
ARC-4, SHOWING 
PLACEMENT OF 
MAJOR CONTROLS 
0-1 d.c. milliamme- 
ter and selector 
switch are at left of 
tuning dial. Type 
F T- 24 3 crystal 
mounts in holder be- 
neath dial. Pilot 
lamp, a,c. switch 
and i.f. gain control 
ore above dial. 



Coil L5-R is now mounted on the ARC -4 chassis, 
about 6rz" belli nd the front panel, and positioned as 
shown in figure 61. The bottom end of the winding is 
grounded, and a 20 ^fd. ceramic capacitor is connect- 
ed across the winding. Connect the coil to a 50 ju//fd. 
ceramic capacitor which goes to the bottom end termi- 
nal on the nearby phenolic strip as shown in figure 
62. This coil converts the oscillator from crystal control 
to a tuned-plate tuned-grid circuit (figure 60 C). 



A clearance hole is now drilled through the chassis 
near the second bottom terminal of the phenolic strip, 
and a small ceramic feed-thru insulator is placed in the 
chassis hole. The terminal of the mMiLttor is connected 
to pin "6 (plate) of the 6\" M.eket Yl-R, behind 
the phenolic strip. 

About this stage of tlie gaiut . a new panel plate 
should be cut and mounted in position on the front of 
the ARC-4. Position of the main controls can be seen 



p.,:. 



CONTROL CKT 




> 50_JUfT"- T" 5GJUF 

_LS0V_L 1 50V 



-• W M-500 ' '" ■ ' ■■ 

■ 2 6 V.> /vV — ►Fr y W ^ 



500 JUF 
2b V." 



T 
I 



ORIGINAL CiRCUn 
Vi-R 



.■■ ■--/£ D C IRCUIT 



CsRCU- OF 









B- 

C- 



Figure 60 
-Microphone circuit of ARC-4. The microphone power iead to R32-T 

may be removed and attached to cathode pin -8 of socket V6-T to 

raise modulation level if a low output carbon microphone (T-17 type) 

is employed. 
-Rectifier system for relay control. 
-Revised receiver oscillator circuit. The 10 ^fd. capacitor is tuned from 

the front panel, as shown in figures 63 and 59. 



Surplus Radio Conversion Manual, Volume III 




■VWW— B+- f FR0 ^T, CENTER 
^W b+ PIN OF 2ND I.F. 
\ TRANS. FL.2- 




ORIGINAL CIRCUIT 



HtS- 



-TO 12A6 
AUDIO 
STAGES 



— Q ► TO 12A6 

-H AUDIO 



NEW CRYSTAL 
SOCKET MOUNTED 
ON PANEL . 



57 




I 



fp> 



"--" MODIFIED CIRCUIT 

Figure 62 
A — l.f. gain control (labeled "noise") for ARC-4 
B — Small neon tube makes inexpensive modulation indicator. Neon lamp 

is mounted in rubber grommet in panel. Capacitance to ground of 

shell permits bulb to light (see dotted line). 
C — Modified volume control circuit for ARC-4 
D — Coaxial lead for transmitter crystal socket (see figure 61). 



® 



UNDER-CHASSIS VIEW OF ARC-4 SHOWING CASCODE RF 

AMPLIFIER (RIGHT) AND MODIFIED RECEIVER OSCILLATOR 

Coaxial lead to panel crystal holder passes along center of chassis. Silicon 

power supply for change-over relay is at left. 




/ 



iSF 



J K*2*m* 



/ 



58 



Surplus Radio Conversion 



l_3 L9.1-R C46-R 




REMOVE CAPACITORS 

C11-R AND C12-R IN 
COUPLING NETWORK 



L)-L3 = 



TURNS # 20 E, ON 
SLUG TUNED FORM, 
-J-" DIA., 4-" LONG 



HHi' 

.001 
TO 6.3 V. (FIG. €5) 



» "5" 

l_2-l_4 = 12 TURNS #22 E. 

■g-'oiA., -^-"long 



Figure 64 
CIRCUIT OF CASCODE R.F. AMPLIFIER 
FOR ARC-4 
Grid-dip coils L-l and L-2 to center of 144 
Mc. band. Shield is placed across center of 
6BQ7-A socket to reduce coupling between 
the coils (see figure 61). Link coils are two 
turns of hookup wire. 

in figure 59. A soft aluminum plate is placed over the 
opening left by the removal of the auxiliary tuning 
unit, and a National type MCN dial is mounted on the 
panel. The shaft of the dial is about 4" from the top 
edge of the panel, and about 4%" from the left edge 
of the panel. The dial drives a small 10 /i/ifd. "APC- 
type" variable air capacitor that is mounted on an 
aluminum bracket placed about 4/2" behind the front 
panel (figure 63). The capacitor, therefore, is im- 
mediately adjacent to the ceramic feed-thru insulator 





■*. PIN#A1 (12V.) 



PIN #AZ (GND) 



4? 

1 1 5 V. Of 

Figure 65 
POWER SUPPLY FOR ARC-4 
Transformer is rated at 325-0-325 volts at 
255 ma., C.C.S., 5 volts at 3 amperes, and 
12.6 volts, center-tap at 5.3 amperes. Pilot 
lamp balances current drain of 6BQ-7A cas- 
code tube. 



mounted on the chassis deck. The capacitor is driven 
by the dial through a phenolic rod and a shaft coupler. 
The rotor of the capacitor is grounded, and the stator 
is attached to the terminal of the feed-thru insulator. 
The modified oscillator circuit is shown in figure 60C. 

Panel Controls Various other controls are placed 
on the front panel, as seen in figure 
59. Across the top are (left to right) a 0—1 d.c. millia- 
meter used as a tuning meter, an i.f. gain control 
(250K, see figure 62A), the a.c. power switch, and the 
antenna loading capacitor, C10-T. Below this, at the 




Figure 63 
TOP VIEW OF ARC-4 
SHOWING TUNING 
CAPACITOR 
The opening left by re- 
moval of auxiliary tuning 
unit is covered with alum- 
inum plate. "APC-type" 
tuning capacitor is 
mounted to bracket atop 
the plate, and connected 
to oscillator circuit via 
ceramic feed-thru bush- 
ing. Oscillator coil is at 
rear of capacitor, with 
slug projecting through 
chassis. 



Manual, Volume III 



59 



left is the meter selector switch, receiver tuning con- 
trol, and modulation indicator (figure 62B). The 
transmitter amplifier tuning control is at the far right. 
Receiver adjustment controls, transmitter crystal 
socket, transmit switch, and phones and microphone 
jack are placed at the bottom panel edge. 

The 500K volume control has one terminal ground- 
ed. Remove the wire connecting the grid of 12A6 
socket V59-R to resistor R40-R (100K) which is the 
second resistor from the end of the terminal board 
located near the four relays beneath the chassis. Con- 
nect a wire from the grid of tube VS9-R to the center 
arm of the volume control (use shielded wire). Con- 
nect a wire from the remaining terminal of the volume 
control to resistor R40-R at the terminal where the 
wire was previously removed (use shielded wire). 
Remove resistor R40-R by clipping the leads. 

A short length of RG-59/U coaxial cable is used 
to connect the crystal socket to the oscillator tube 1 , as 
shown in figure 62D. The shield is grounded to the 
chassis at both ends of the conductor. 



shield. Coils L-l and L-2 are mounted on either side 
of the shield plate. The cascode schematic is shown 
in figure 64. 

The Power Supply The power supply is placed in 
the rear chassis area, as shown 
in figure 66. The wiring of the supply is shown in 
figure 65. To balance the filament drain, the 6BQ7-A 
and the pilot lamp are wired as shown in the sche- 
matic. All other filaments are wired correctly when 
the rear power connector terminals are strapped as 
previously described. It is necessary to insert a 750- 
ohm, 20-watt resistor in series with the receiver B- 
plus terminals of relay S5-C to hold the receiver 
voltage to 300. 



Alignment- of the 
ARC-4 



A Cascode Amplifier 
for the Receiver 



The sensitivity of the ARC-4 
receiver leaves much to be 
desired if stations beyond 
the line of sight are to be worked. A simple 6BQ7-A 
cascode amplifier may be built into the receiver sec- 
tion that will greatly enhance the performance. The 
placement of the amplifier can be seen in figure 61. A 
small copper shield plate is mounted across the 
6BQ7-A socket, and is grounded to pins #4 and 9 
and the center stud of the socket. The neutralizing 
coil L-3 passes through a K-inch hole drilled in the 



The first step is to align the re- 
ceiver oscillator. The slug of the 
oscillator grid coil (L5-R) is ad- 
justed to resonate the circuit to 8550 kc. (use a grid- 
dip oscillator). The plate coil slug (Ll-R) should be 
adjusted so the receiver tuning capacitor tunes the 
range 8.5 Mc. to 8.8 Mc. Set the oscillator to approxi- 
mately 8.65 Mc. and tune the harmonic generator cir- 
cuits for maximum meter reading as shown in figure 
67. The slugs in these circuits are set very close to 
the correct adjustment when you receive the ARC-4, 
so do not alter the setting too much! With an antenna 
on the receiver, you should now start to hear two- 
meter signals. Adjust the three ri. trimmers (lower 
left corner of the panel) from left to right for maxi- 
mum signal strength. One adjustment will hold over a 
tuning range of about one megacycle. Finally adjust 




Figure 66 
POWER SUPPLY IS 

INSTALLED IN 
DYNAMOTOR AREA 
OF ARC-4 
Transformer is at left, 
with filter capacitor to 
right of tube. Extra 20 
/*fd., 450 volt capacitor is 
added to output of supply 
to reduce hum. Small 
aluminum box is placed 
over rear of rectifier tube 
socket to prevent danger 
of shock from terminals. 



60 



Surplus Radio Conversion 



RECEIVER TUNING CHART 


METER POSITION 


TUNING ADJUSTMENT 
{TUNE FOR MAX. READING ) 


METER READING (0-1 MA.) 


OSC. GRID 


Ll-R 


0.2 - 0.6 


2.ND MULT. GRID 


La-R 


0.1 - 0.14 


3RO MUL T, GRID 


l_3-R 


0.08-0. t 


A.V.C. 


L4-R 


MEASURE WITH VTVM 
ON A. V.C. BUSS 


TRANSMITTER TUNING CHART 


METER POSITION 


TUNING ADJUSTMENT 
{TUNE FOR MAX. READING) 


METER READING (0-1MA.) 


OSC. GRID 





0.2 


1 ST MULT. GRID 


Ll-T - L2-T 


0.3 -0.5 


ZNQ MUL T. GRID 


L3-T — L4-T 


0.3 - 0.5 ] 


3RD MULT. GRID 


L6-T 


0.3-0.5 


R.F. AMP. GRID 


C6-T 


0.25 


R.F. AMP. GRID 


L8-T 


0.25 


R. F. AM P. PL A TE 


L9-T 
(M/N. READING ) 


0. 5 


Figure 67 
METER CHART FOR TUNING RT-19/ARC-4 



the slugs of cascode coils L-l and L-2 for best signal 
reception. 

The crystal is now plugged in the transmitter and 
the multiplier circuits are tuned for maximum meter 
current, as indicated in figure 67. Load the antenna 
by increasing the loading capacitor (C10-T) and then 
tune the r.f. amplifier stage for minimum dip. Repeat 
until maximum loading is obtained while still observ- 
ing a plate current dip. 



Modern, TVI-Proof Conversion of the 
SCR-522 Transmitter 

Many conversions have been shown for the BC-624 
transmitter portion of the SCR-522 v.hi. receiver- 
transmitter. The conversion described in this section 
is recommended for two and six meters, as it elimi- 
nates the t.v.i. difficulties normally encountered with 
this equipment. The unconverted transmitter is shown 
in figure 68. 

First of all, remove the transmitter from the cabinet 
and strip off unnecessary components, such as the 
tuning slides, etc. Move the power connector to the 
rear of the chassis as shown in figure 69A. Make up a 
power cable as shown in figure 69B, using #14 wire 
for the filament leads, as shown. Next, mount a 
SO-239 coaxial connector near the tripler stage, as 
shown in figure 69C, and run a coaxial lead from the 
connector to the antenna link of the transmitter. 

If a carbon microphone is used, it is necessary to 
install four "pen-lite" batteries in series with the pri- 
mary winding of the microphone transformer. Better 
still, a crystal microphone can be employed with the 
transmitter if the simple transistorized speech ampli- 
fier shown in figure 70 is installed in the transmitter. 
It is recommended over vacuum tube amplifiers since 
there is less danger of audio feedback. A 1N34 diode 
rectifies the filament voltage to deliver a small nega- 
tive potential suitable for the transistor. Remove the 
microphone transformer and connect the output of the 
transistor amplifier to the "hot" terminal of volume 
control #125. 



Figure 68 

THE 

UNMODIFIED 

BC-624 
TRANSMITTER 
SECTION OF 
THE SCR-522 
V.H.F. 
TRANSMITTER- 
RECEIVER 




Manual, Volume III 



61 



FILS- 
GND- 



fea 



BIAS MOUNT IN— *\\ j 

LI NE WITH 
7ZA6'S 



POWER SWITCH 



CONNECTOR DETAIL - TOP VIEW 



I I 
2J*— USE STANDOFF 
PILLAR 




O 



rf 



Tfc^JJ 




PLUG[ a^ 6 7 

1 6 



o 



-MOUNT SO-239 ON / 3/B* PILLARS. 
WIPE WITH COAX, UP TO ANTENNA 

LINK. 




CABLE DETAIL-XMTR TO SUPPLY 



ANTENNA CONNECTOR DETAIL 



® 



© 



Figure 69 
A — Power plug modification x for 522 transmitter, for use with a.c. supply 

shown in figure 75. 
B — Connecting cable between transmitter and power supply. 
C — New coaxial antenna receptacle is mounted in corner of transmitter 

chassis near 832-A tripler stage. 



T.V.I.-Proofing the 
Transmitter 



Install a 0.001 ftfd. disc ceramic 
capacitor across the filament 
pins of each tube socket. By- 
pass all leads on the power connector with 0.001 jufd. 
disc ceramic capacitors. In addition, bypass each 
meter lead with 1.5 KV, 0,001 ^fd. disc ceramic capa- 
citors. Use a meter with a metal case, or else cut a 
section of a tin can to cover the rear of the meter if 
a phenolic-cased meter is used. Ground the can to 
the transmitter panel, permitting the meter terminals 
to pass through holes cut in the rear disc of the can. 

To shield the transmitter completely, it may be 
mounted in the metal case from a BC-375 tuning unit. 
Small, M-inch holes should be drilled in the case to aid 
ventilation. The completed transmitter, mounted on 
a relay rack panel is shown in figure 71. 



high r.f, resistance. Transmitter output increases when 
the braid leads are replaced. Modulation is also im- 
proved when the 12A6 audio tubes are replaced with 
12V6-GT's. No wiring changes are necessary. 

A crystal— v.f.o. selector switch that may be in- 
corporated in the transmitter oscillator circuit is shown 
in figure 72. 

To operate the 522 transmitter on six meters, the 
following coil changes are necessary: Replace the 
tripler (first 832-A) plate coil with a new inductance 
consisting of 14 turns of #14 enamel wire, %" diameter, 
and about IK" long. The B-plus lead is attached to 
the center of the coil. The antenna coil consists of 5 
turns of #14 insulated wire wound over the center of 
the plate coil. The tripler stage now acts as a six- 



Circuit Modifications The braid straps that con- 
nect the plate terminals of 
the 832-A tubes to the tank circuits should be removed 
and replaced with copper strap. The braid gets warm 
during operation of the transmitter because of the 



CRYSTAL 
MIKE ft 

CONNECTORS 



PC A 

2N105 



& 



r 



f K> .001 >K + ^ 

_L Jp 15< iL J_ 



T 



T 
T 



) k lr*— ° — - G 



X.VOL, CONTROL 
-ORIG. #725 



!N34 
-:H, V W •■ TO 12.6 V, 



DISC 
ALL RESISTORS 0.5 WATT 



, 'M^t' ;j ^^;y*i| , "' ,, V"" V '-'''- * 









M^&M 












Figure 70 
SIMPLE TRANSISTOR SPEECH AMPLIFIER 
PERMITS USE OF CRYSTAL MICROPHONE 

WITH SCR-522 TRANSMITTER 

Small amplifier may be mounted between 

volume control and the microphone jack on 

the inside of the chassis. 



Figure 71 
MODIFIED 522 TRANSMITTER IS 
MOUNTED ON RELAY RACK PANEL 
Case from BC-375 tuning unit is slipped over 
chassis to complete anti-T.V.I. shielding. Ad- 
ditional conversion information is given in Vol. 
I of the "Surplus Radio Conversion Manual/' 



62 



Surplus Radio Conversion 



INPUT ($). 



CRYSTAL 
SELECTOR 
I SWITCH 




MOUNT THIS CIRCUITRY 
IN POSITION FORME RL Y 
OCCUPIED BY CRYSTALS. 



NOTE: A HEATH VF-1 CAN BE 

CAN BE MODIFIED TO BMC. FOR 

— USE AS A V.F.O. 



MODIFIED TRANSMITTER OSCILLATOR 

CIRCUIT PERMITS USE OF HEATH 

VF-1 V.F.O. (RETUNED TO 8 MC.) 

WITH 522 TRANSMITTER 

meter amplifier, and the 832-A two-meter amplifier 
tube is removed. Six Mc. crystals are used, and all 
multiplier stages can be retimed for six-meter opera- 
tion. See Volume I of the Surplus Conversion Manual 
series for additional circuit modification information. 




■ STANCOR P-8339 
- STANCOR PA-842 7 
-STANCOR C-J703 



v " SCHEMATIC, POWER SUPPLY FOR 

SCR-522 TRANSMITTER 
Transformer T-l delivers 325-0-325 volts at 
255 ma., C.C.S., 5 volts at 3 amperes, and 
12.6 volts at 5.3 amperes. Transformer T-2 
delivers 125 volts at 50 milliamperes. Choke 
CH-1 is 4 henries at 250 ma. 



~r 



-4-T 




( 



n-i-5_» 



-H*- 



I 
I 



frsr 



uuua. inir inir l— _ 



4>- 



H 



XTAL XTAL 

B D VFO 



^J-^MOD. 
f ^ T LEWEL 

,±_ 



1" 



A = 8/32. SCREW 
C = 3/8" HOLE 



8/32 NUT AND WASHERS BETWEEN 
RACK AND 522 CHASSIS 



B = 1/4" HOLE 
D = 1 / 2 ' HOLE 



Figure 76 

LAYOUT OF PANEL FOR SCR-522 

TRANSMITTER 





O-ZOi iZOl 

HHi' HHl' 

>-tii \i-eci ztcn z-tti 




ui§H^+ 



4vwvj 






r 



1 — s^ww 



. X2 



HHi' 






& 




VWrf-M/V-pWHi. 




-AVV |l' 



■77^' 1" 






— ^ ii- 



^tVM\ — L. 



-V/A — * — /A\~ 



aojoroooH 



I" 




; S 



QhT 



»pn: 



Mi. 






s*r&4 ou isjw ^ 



,vo^«*a? rj&Mp 



&CU2VUM03 



_**»- -*<777tf . 



y/**«v**" d/ STJWtt 



Manual, Volume III 



63 




Figure 74 

POWER SUPPLY 

FOR SCR-522 

TRANSMITTER 

IS ASSEMBLED 

ON AUXILIARY 

CHASSES 

See figure 75 for 
schematic 



The BC-312 and BC-342 Series Receivers 

The BC-312 and BC-342 series receivers are, with- 
out modification, acceptable communications receiv- 
ers. However, their performance can be greatly im- 
proved for amateur communication work by making 
certain modifications in various portions of the re- 
ceiver. Any one of the changes or all the changes 
may be made, each change adding a certain amount 
to the performance and flexibility of the receivers. 
The various changes will be treated separately so that 
any one or all the changes may be made at the discre- 
tion of the owner of the receiver. 



Power Supply 
for the BC-312 



If the receiver is a BC-312, a 
power supply must first be con- 
structed. The BC-342 is equipped 
with an integral 115- volt power supply but the BC-312 
has a 12- volt dynamotor in place of the a.c. power 
supply of the BC-342. Otherwise the receivers are 
substantially identical. It will be assumed throughout 
this and subsequent discussions that the owner of the 
receiver has a copy of TM 11-850 or one of the other 
instruction books on this series of receiver since these 
instruction books were furnished with the receivers 
or were generally available at the time the receivers 
were sold. 

The Dynamotor must first be swung out on its 
hinges, and then the leads from the dynamotor to the 
9-terminal connection strip removed. A power supply 
such as shown in Figure 77 and diagrammed in Figure 



79 must then be constructed. The one illustrated em- 
ploys a Signal Corps C-228 power transformer, which 
is the same one as was used in the RA-20 power sup- 
ply for the BC-342. A large number of these power 
transformers have been available, but if one cannot be 
obtained, any power transformer having a 650-volt to 
750-volt center-tapped high-voltage winding, a 5-volt 
filament winding for the 5Y3-GT, and one or two 6.3- 
volt filament windings at 1.75 amperes or greater will 
be satisfactory. If the transformer has two 6.3-volt 
filament windings (such as the UTC type R-12) they 
are connected in series to obtain the 12.6 volts neces- 
sary for heater operation of the receiver. If the trans- 
former has only one 6.3-volt winding an additional 
very small 6.3-volt 2-ampere filament transformer must 
be placed in the power supply and connected in series 
with the 6.3-volt winding on the main power trans- 
former to obtain the 12.6 volts. The junction between 
the two 6.3-volt filament windings should be grounded 
in the power supply. 

One complication is introduced by the fact that 
the dial-lamp circuit uses two 6.3-volt lamps in series 
to ground, so that if the lead to the dial lamps is con- 
nected to either of the hot 6.3-volt filament leads the 
lamps will only receive half voltage. This may be sat- 
isfactory, since the lamps give adequate light at this 
voltage, or the two lamps may be connected in parallel 
by removing the bezel that covers the two lamps and 
rewiring them. 



64 



Surplus Radio Conversion 





Figure 77. 
FRONT VIEW OF THE CON- 
VERTED BC-312 RECEIVER 
WITH THE POWER SUPPLY 

ALONGSIDE. 
The coaxial i.f. energy output fit- 
ting can be seen on the panel in 
the position formerly occupied by 
the power connector. The switch 
mounted at the bottom of the 
vertical row of jacks is the noise- 
timiter on-off switch. The power 
supply is normally mounted re- 
motely from the receiver and con- 
trolled by the OFF-MVC-AVC switch. 



The balance of the power supply is quite conven- 
tional. The VR tube shown in Figure 79 need not be 
used unless desired, but its use does afford improved 
oscillator stability. 



Voltage Regulation for 
H.F. Oscillator 



The high-frequency oscil- 
lator used in the receiver 
is quite stable, but when 
operating on the 14-Mc. band there is some variation 
in the tone of a c.w. signal when the ri. gain is varied, 
or when the line voltage varies as a result of a house- 
hold refrigerator turning on or off or from some sim- 
ilar cause. This condition is cured by using voltage 
regulation on the plate supply voltage to the high- 
frequency oscillator. The incorporation of voltage reg- 
ulation on the oscillator requires that a lead be 
brought out of the oscillator compartment for separate 
plate-voltage feed to the tube. This operation requires 
removal of the cover from the oscillator compartment, 
and the removal of 30,000-ohm resistor R 4 i. This re- 
sistor is replaced by a 1000-ohm M-watt carbon resistor. 
The r.f. stage chassis is then lifted back, after re- 
moving the leads to the tube caps, and the plate- 
voltage terminal coming out of the oscillator com- 
partment is by-passed with a 0.002-yufd. postage-stamp 
mica capacitor which can be placed flat against the 
chassis below the terminal strip. The lead for plate 
voltage to the oscillator is then brought under the r.f. 
chassis and down through the hole where the other 
leads feeding the r.f. chassis pass. This plate-voltage 
lead then goes, of course, to the plate of the VR-105. 

R.F. Changes The r.f. system in the standard re- 
ceiver is slightly lacking in gain and 
signal-to-noise ratio on the highest frequency range. 
This condition can be checked by removing the an- 
tenna lead from the receiver, turning the receiver wide 
open on MVC, and then rotating the trimmer APC on 



the first r.f. stage through resonance. Only a very 
slight increase in noise level will be noticed when this 
trimmer passes through resonance. 

The most satisfactory way of correcting this condi- 
tion (and this method was proven best after trying 
a number of other expedients) is to replace the 6K7 
first r.f. stage with a 6SH7. It so happens that the re- 
ceiver is laid out in such a manner that a single-ended 
tube in the first r.f. stage gives much more direct 
leads than the double-ended tube originally used. The 
procedure is as follows: 

Remove the tubes from the r.f. chassis and invert 
the chassis as far as possible. Remove the leads from 
pins 3, 4, 5, 6, and 8 of the tube socket for the first r.f. 
stage. Remove the old cathode-bias resistor RS-164. 
Run a 100-ohm 1-watt resistor from the small micarta 
terminal block for the MVC lead to pin 5, and also run 
to pin 5 a lead from the cathode by-pass section of the 
capacitor block for the stage. Install an additional 
0.002-/iifd. postage-stamp mica capacitor as a cathode- 
by-pass from terminal 3 to terminal 1. Separate the 
screen-voltage lead that went to terminal 4, shorten it 
imtil it fits more neatly and solder to pin 6. Now run 
the plate lead for the tube, which did go to terminal 3 
and run it tinder all the wires near the heater end of 
the socket and connect this lead to terminal 8. Remove 
the lead which went to the grid cap of the 6K7, solder 
a wire about VA inches long to this terminal on the 
main chassis, push the sub-chassis down as far as it 
can go and still reach terminal 4 on the tube socket 
with a soldering iron, and solder this new lead to 
terminal 4. Then push the chassis back into place 
gently, at the same time making sure that the grid 
lead to the tube (terminal 4) keeps free of the chassis 
and bends out toward the ganged tuning capacitor. 

It will now be necessary to re-align the r.f. stages 
of the receiver slightly (not the hi. oscillator how- 



Manual, Volume III 



65 



Figure 78. 

UNDERCHASSIS VIEW OF THE 

RECEIVER AND POWER 

SUPPLY. 

The bent-aluminum chassis holding 
the 7 AS noise limiter tube can be 
seen behind the power-cable recep- 
tacle. The added chassis is mounted 
to the front panel. 




ever). Peak up the 6L7 mixer stage first, then the 
second ri. stage, and then the first ri. stage. The gain 
will be found to be much greater than before, and the 
increase in noise when the first ri. stage is trimmed 
through resonance will be found to be very pro- 
nounced. If a tendency toward instability is encoun- 
tered near maximum gain on MVC, re-trim the mixer 
stage padders slightly until the instability disappears. 
All these receivers have a certain amount of back- 
lash in the vernier tuning control. In several receivers 
the amount of backlash has been reduced to a very 
small amount by carefully lubricating all the gears 
with a small amount of vaseline, using a toothpick or 
a matchstick to apply the lubricant. Then the back- 
lash, which in the receivers mentioned was caused by 
axial motion of the tuning-capacitor gang, can be sub- 
stantially eliminated by careful adjustment of the ball 
thrust bearing at the oscillator end of the tuning gang. 
This bearing is inside the oscillator compartment. 

I.F. Amplifier The i.f. amplifier operates quite sat- 
Changes isfactorily, but the action of the crys- 

tal filter leaves much to be desired. 
The reduction in set gain when the crystal filter is 
switched into operation can be greatly reduced by the 
following procedure: Remove the cover from the crys- 
tal-filter transformer. Scrape the stud which serves as 
a stop for the rotation of the crystal-phasing capacitor 
and solder a very small wire to this stud and to the 
small switch contact on the other side of the phasing 
capacitor. Then turn the phasing control until the 
moving contact rests firmly against the stud. Re-install 
the cover of the transformer and align the slug which 
comes out of the top of the crystal-filter transformer 
for maximum noise with the antenna removed from 
the receiver. This position of the control (180° from 



the old position) now serves as the crystal-out posi- 
tion, and the reduction in gain when the crystal filter 
is switched into the circuit will be very small. 

A further change in the i.f. amplifier was made in 
the receiver shown in Figure 77 to bring out i.f. energy 
for the operation of external devices such as a panor- 
amic adapter, a narrow-band F.M. adapter, or another 
external unit such as a single-sideband channel. The 
change consisted in merely wrapping^ turns of hook- 
up wire around the form between the two i.f. coils in- 
side the last transformer, connecting one side of this 
coil to ground and the other side to the center con- 
ductor of a piece of RG-58/U cable. The cable is 
brought into the transformer by first removing the 
black wire going into the transformer and grounding 
the capacitor to a soldering lug under the screw adja- 
cent to the terminal from which the black wire was 
removed. It may be necessary to ream the hole from 
which the black wire was removed slightly in order 
to be able to insert the insulation and the inner con- 
ductor of the coaxial cable. The outer conductor of 
the coaxial cable is grounded outside the transformer. 
The coupling connector for the coaxial cable was 
mounted on the front panel of the receiver in the 
position formerly occupied by the power-cable con» 
nector, which had previously been removed. 

With the i.f. energy obtained from the panel co- 
axial connector coupled to an external coil resonated 
to the intermediate frequency by means of a small 7- 
turn coupling coil, approximately 10 volts peak was 
measured with a normal signal input and the receiver 
operating on a.v.c. With the receiver on MVC, more 
than 50 volts peak could be obtained. This voltage is 
of course quite adequate to operate any of the acces- 
sories mentioned in the previous paragraph. 



66 



Surplus Radio Conversion 



CONNECT TO THESE NUMBERS ON RECEIVER CONNECTOR 
3 4 9 5 1 2 6 10 11 8 7 12 

I I I Ijumpe r I I I I I I I I 

0©®®(0)Cp(p(5)®©@e) ( 3> AU0 , 0TOsreAKtB 

PI 1 TO KEYING RELAY 



"O. 



"©■. 



W W uu 



) KEYING RELAY 
IN TRANSMITTER 



TO 12 V. SOURCE 



J_ CH _ 



-L R, 





5Y3-GT 



JIMMj 



npnrj_ 



■V. 



o cr\jo 1 



#' 



RED = 110 VOLTS COMMON, BLACK = 120 VOLTS 
GREEN = 105 VOLTS 
BROWN = 12 VOLTS, NO C.T. 

BLUE = 12 VOLTS, SLATE WITH TRACER = CT. ■' 
BLACK = H.V., YELLOW = C.T. 



Figure 79. 
SCHEMATIC DIAGRAM OF THE POWER SUPPLY UNIT. 

The color code shown at the bottom of the drawing is for the 
C-228 power transformer which may be available. If this trans- 
former is not available a conventional power transformer having 
two 6. 3 -volt windings may be used as described in the text. 
Ci, Ci — 16-^fd. 450-volt elect. CH — 15 henrys 100 ma. 

T — 700 v. c.t. 100 ma.; 5 v. 3 Ri — 12,500 ohms 10 watts 

a.; 6.3 v. 3 a., 6.3 v. 3 a. R 2 — 100,000 ohms 2 watts 

in series with center S — S.p.s.t. a.c. line switch 

grounded. Or 12.6 v. c.t. F — 3-ampere fuse 

Audio System The audio system of the 312 and 342 
Changes receivers leaves much to be desired. 

There is inadequate gain for recep- 
tion of weak signals on crystal filter, the frequency re- 
sponse is quite poor ( though intentionally so for mili- 
tary use), and the harmonic distortion is severe. All 
these undesirable conditions were overcome by the 
relatively simple change in the audio system shown 
in Figure 80. A 6B8 diode-pentode was used to re- 
place the 6R7 diode-triode previously used, and the 
6F6 was replaced with a 6\ 7 6. Shunt feedback from the 
plate of the 6V6 to the plate of the pentode section of 
the 6B8 was used to improve the frequency response 
and reduce harmonic distortion. Also, the feedback 
almost completely eliminates the hum in the audio 
system of these receivers. The cathode resistors for the 
two stages were left the same, but an additional 25- 
^fd. 25-volt electrolytic was placed across the cathode 
resistor of the 6B8 so that the gain control would 
completely cut off the audio output when turned clear 
down in the a.v.c. position. 

The audio transformer that was used in the plate 
circuit of the 6R7 is removed from the circuit but was 
left in place since the space was not required and it 
appeared to be difficult to remove. When a noise 
silencer, to be described later, is to be used in receiv- 
ers of the BC-342 series, it would probably be best to 
remove this transformer and install the noise limiter 



tube in the place formerly occupied by the transform- 
er, since the presence of the power supply inside the 
receiver will preclude installing the noise silencer in 
the place shown in the photograph of the BC-312. 

If desired, the volume control and gain control 
system can be left unmodified, in which case the green 
wire coming from S i2 is removed from the bottom end 
of R 49 on the Group 1 terminal board on the right out- 
side wall of the chassis and run to the noise silencer. 
The grid leak on the power audio tube R 33 is removed 
and changed to a 470K )k watt. Capacitor C 6 has been 
added to couple to a conventional 5000 to 8000 ohm 
output transformer on the external loudspeaker. The 
impedance ratio of T 2 inside the set is 7:1 so that an 
impedance of about 1000 ohms is required on the 
speaker transformer if the audio output is to be taken 
through transformer T 2 . Due to the voltage step down 
in T 2 the secondary of this transformer was used to 
feed the phones. The 60-ohm filament current equal- 
izing resistor R 47 should be removed, and if a 7A6 
is used as noise limiter its heater should be placed 
across the heater of the 6V6-GT. In any event it is 
wise to ground terminal 7 of the socket for the 6B8 to 
insure that all the tubes will be operating at proper 
heater voltage. 



TO SPEAKER 




12. « V. TO HEATERS 
C.T. GROUNDED IN 
POWER SUPPLY 



SEND-RECEIVE SWITCH ON 
PANEL IN SERIES WITH CT 
OF POWER TRANSFORMER 




AUDIO OUT 



-B+-105 V. REGU- 
LATED TO OSCIL- 
LATOR 

._ -12 V. TO O/ALLIGHT 



4 6 6 6 



Figure 80. 
CHANGES IN THE BC-312 RECEIVER 

Unmarked components are already in the receiver and need not 

be removed or replaced. 

Ci — 0.1 -jufd. 400-volt tubular R,, R„ — 470,000 ohms V 2 watt 

R.; — 1.0 megohm 1/2 watt 



Cn — 25-/ifd. 25-volt elect. 

C; — 0.1 -/jfd. 400-volt tubular D 1 ft „„„„!.«. „»*„„«.: *«., 

C— O.OS^fd. 400-volt tubular p ~ ion nnn u potentiometer 

C .-.— 0.01 -/ifd. 400-volt tubular R 22n /000 ohms i/ 2 watt 

C — 8-ufd. 450-volt elect. R ■■# R "> — 470,000 ohms i/ 2 watt 

Ri — 100,000 ohms V2 watt Rn, Ri^ — 22 ohms 2 watts 

R^ R — 1.0 megohm i/ 2 watt RLi — Relay inside receiver 



Manual, Volume III 



67 



Figure 81. 

BC-348P RECEIVER, SPEAKER 

AND POWER SUPPLY 

The power supply is mounted in the 
speaker housing. 




Noise The noise silencer shown in Figure 80 has 

Silencer been found to be very effective on the 14- 
Mc. band, and on the 28-Mc. and 50-Mc. 
bands when a converter is used ahead of the receiver. 
One half of a 7A6 tube has been used, and since this 
tube draws only 150 ma. of heater current the heater 
may be fed with a balance to ground by means of two 
22-ohm 2-watt carbon resistors from the 12.6-volt 
heater line. Or, if desired, the heater may be placed 
in parallel with the 6V6-GT heater as discussed in the 
previous paragraph. One half of a 6H6 or 6AL5 tube 
could also be used for the noise limiter, but these lat- 
ter tubes require 300 ma. of heater current. It is 
possible that a 12H6 could also have been used, but 
one has not been tried. Make sure that the return for 
the noise limiter (the bottom end of Ci, R 5 and R 4 ) 
is made to the cathode of the 6B8 and not to ground— 
if the return is made to ground proper noise-limiting 
action will not be obtained. A switch Si has been pro- 
vided to take the noise silencer out of the circuit, since 
the circuit does introduce a detectable amount of dis- 
tortion on a short-wave broadcast program. 

Gain Control It is a convenience in a communi- 
Changes cations receiver to have a separate 

control for audio and ri. gain. To 
accomplish this in the series of receivers under dis- 
cussion it is suggested that the dual control at the top 
of the panel be replaced by a single M-megohm audio- 
taper potentionmeter. C S i and R 32 are removed, and 
the low-potential end of the audio gain control is 
returned to ground. The r.f. gain control leads can be 
pulled down to the underside of the chassis and con- 
nected to a separate 15,000-ohm r.f. gain taper rheostat 
which can be placed either in the position formerly 
occupied by the MIKE jack or just to the right of the 



SEND-RECEIVE switch. The a.v.c. position of the 
switch will still short out the r.f. gain control in the 
conventional manner. 

Control In the case of the BC-312 receiver as shown 
Circuits the 9-terminal power-connection strip was 
removed and the somewhat unsightly multi- 
connection receptacle on the front panel was removed 
and replaced by the "i.f. output" coaxial receptacle. 
Power and control connections were brought out to a 
12-contact Jones P-312-RP connector which was 
mounted by means of a bracket to the rear of the 
chassis. The receptacle was aligned with the hole 
which already exists on the rear of the cabinet hous- 
ing. The connector on the end of the power cable is a 
Jones S-312-FHT. The key, shorting relay, and switch 
inside the receiver were then rewired to connections 
on the connector on the rear of the cabinet as shown 
on Figure 80. The switch is connected so that it is in 
series with the center tap of the power transformer. 
Since a 12-volt keying relay is used on the transmitter, 
the antenna-shorting relay inside the receiver was 
wired so that it closed every time the transmitter key- 
ing relay closed. 

In modifying the BC-342 series of receivers the 
external control circuit connections for the transmitter 
can be brought out of the front panel by replacing 
the connector which is installed on the front panel by 
an Amphenol MIP-8 octal socket, which fits the same 
mounting holes. 

Hints on the BC-348 Series Receivers 

The BC-348 series of receivers are quite satisfac- 
tory for communications use in the amateur station, 
but as in the case rf the BC-312/BC-342 series, there 



68 



Surplus Radio Conversion 



'■}*■ 'iMBr$a:ffR:0^MS 





Figure 82. 

REAR VIEW OF THE BC-348P 

ASSEMBLY. 

Showing the power supply mounted 
in the speaker housing and the 
octal power piug on the receiver. 



are several minor modifications which may be made 
to improve the performance and flexibility of the 
equipments. 



BC-348Q General 
Information 



The BC-348 series of receivers 
may be operated with the heater 
circuits unchanged from a 26- 
volt a.c. supplv. But a power transformer with such a 
filament winding is not readily available ( although the 
C-228 transformer mentioned in connection with the 
BC-312 may be used with the filament windings in 
series) so it is in most cases best to rewire the heat- 
ers for operation from 6.3 volts. This means that one 
side of the heater of each tube should be grounded 
and the other side should be brought out as a com- 
mon for feeding from the 6.3-volt line. In many cases 
the original "seriesing" wires between tube sockets 
may be used either for the grounded side or the hot 
side of the heater circuit, requiring addition of fewer 
wires and a solution to the problem of working in 
cramped spaces. 

The a.c. power supply for the receiver may be 
mounted in the space formerly occupied by the dyna- 
motor if space considerations and portability are very 
important. However, this procedure is not desirable 
from the standpoint of ventilation since an a.c. power 
supply dissipates a great deal more heat than the dy- 
namotor originally installed. The space is more useful 
for additions to the receiver such as a noise limiter, 
an extra audio stage, or a broad-band converter. 

The external a.c. operated power supply may be 
made somewhat oversize for operation of a frequency 
meter or a converter or an additional station accessory. 
In this event it is desirable to be able to ground the 
negative lead of the plate supply, which is not done 
on the BC-348Q. It is necessary to change the bias 



circuits of the 6K6-GT audio stage and the 6SA7 con- 
verter to accomplish this. The first step is to ground 
the B minus and remove connections to choke 155-B 
and resistor 108-2. This leaves both the above stages 
unbiased. A 470-ohm 2-watt resistor should be placed 
in series with the cathode terminal of the 6K6-GT 
audio stage. A 25-volt 25-^fd. electrolytic capacitor 
should be placed across this cathode resistor. 

About 1.8 volts of bias is used on the grid of the 
6SA7 converter stage. To obtain this, resistor 108-1 
in the oscillator can should be clipped out of the re- 
ceiver. The contact at the junction of this resistor and 
resistor 87-2 is available as a projecting lug. Upon this 
lug may be mounted a standard miniature bias cell 
with the positive side grounded and the negative side 
to the lug. 



Audio 

Considerations 
in the BC-348Q 



Addition of a noise-limiter (see 
Radio Handbook) will improve 
operation in the presence of igni- 
tion interference on the 14-Mc. 
band and is almost a necessity- for use of the receiver 
with a converter on the 28-Mc. or 50-Mc. bands. The 
addition of an extra stage of audio is also desirable, 
especially for use with the crystal filter on 14-Mc. c.w. 
The added tube may be a 6SF5 triode with conven- 
tional circuit values (see any standard reference), or 
a 6SJ7 stage with feedback may be added. 

Difficulty may be encountered with the audio sys- 
tem of the receiver after the addition of the audio 
stage and the noise limiter due to the common cathode 
resistor on the second detector and the third i.f. stage. 
This trouble may be avoided by isolating these two 
cathode circuits. The lead between the two cathodes 
is removed and resistor 105 is either removed or short- 



Manual, Volume III 



69 



ed. This leaves the third i.i. stage with resistor 102 
and capacitor 61-4 in its cathode circuit to ground. 
The cathode of the second-detector tube is now 
grounded to the chassis. The large capacitor can 70- A 
and 70-B may now be removed to make additional 
room inside the equipment. The 6-jufd. section is ideal 
as a portion of the filter capacitance in the external 
power supply. The lead^at the low-potential side of 
the third i.f. transformer should be opened and the 
noise limiter inserted at this point. Capacitor 27-3 
should be left to by-pass the secondary of the trans- 
former. The on-off switch for the noise silencer may be 
placed in a panel position in place of one of the head- 
phone jacks. 

Mechanical If a plug to fit the rear connector 

Considerations block cannot be secured, an octal 
socket may be fitted into the set by 
liberal use of a round file and then by drilling and 
tapping mounting holes for the socket. If the cast 
aluminum guide box is removed from the case it will 
not be necessary to enlarge the rectangular hole in 
the case to pass an octal power plug. 

A socket punch may be used to make two holes in 
the back of the case. One hole is used to pass the plug 
for the speaker connection, and the other hole to reach 
a two-post terminal strip which is wired to the receiv- 
er silencing circuit (terminals 2 and 6 in the circuit 
diagram). These two terminals may then be shorted 
or wired into the transmitter control circuit in such a 
manner that the receiver is disabled whenever the 
transmitter is on the air. 

The seriesed dial lamps should be parallel and 
connected to the 6.3-volt neater circuit with the dial 
light control resistors 111 and 81 out of the circuit. 

BC-348E, M # Changes in this series of receivers 

and P Receivers are generallv the same as in the 
(jMN),aiid (Q) series of 348's, 
except that only the power audio stage must be modi- 
fied when grounding the negative lead of the power 
supply. Also, the second detector and third ii. stage 
cannot be isolated since they are in the same tube 
envelope. 

Figures 81 and 82 show a convenient method 
whereby the power supply for a BC-348 series re- 
ceiver may be mounted in the housing for the loud- 
speaker. 

A 120 to 140 Watt Modulator from the 
BC-375 or BC-191 

One way in which to solve the problem of making 
good use of the BC-375E or the BC-191 is to dis- 
assemble the tuning drawers for components, use the 
housings for the tuning drawers as cabinets for ac- 
cessory pieces of test equipment, and use the main 
housing of the transmitter along with the audio trans- 
formers and miscellaneous other components to as- 
semble a modulator. Figures 83 and 84 show one such 
assembly which operates quite satisfactorily. 




Figure 83. 
MODULATOR AS MADE FROM A BC-375E. 

The front cover has been removed to show the placement of 
components on the new chassis. 

All components on the upper deck were removed, 
including the chassis, and a new chassis was bent from 
sheet aluminum to hold the components shown in 
Figure 85. The end of the main housing which held 
the antenna tuner was sawed off as unnecessary, but 
it might be retained to house the power supply for the 
modulator if components of the proper dimensions 
should be obtainable. The components mounted on the 
upper deck of the chassis include the power supply 
for the speech amplifier, a simple regulated bias cir- 
cuit for the negative 100 volts on the 211 grids, and 
the audio transformers. 

The clipper-filter audio amplifier and driver is 
mounted in the housing for one of the tuning drawers 
after all the ri. components had been removed. The 
circuit for the speech amplifier is shown in Figure 86. 
An additional panel was placed in front of the original 
panel to cover the multitude of holes that had been 
left by removal of the ri. components. The clipper- 
filter speech amplifier is quite conventional, ending 
in a single-ended 6B4-G which acts as driver for the 
211's. Provision has been made in the input circuit of 



70 



Surplus Radio Conversion 




Figure 84. 
REAR VIEW OF THE BC-375E MODULATOR. 

the speech amplifier for both a single-button micro- 
phone and a crystal-microphone input, with a switch 
S to select either input circuit. The clipping level con- 
trol R 14 , must be substantially full open for maximum 
undistorted output from the 211 tubes in the output 
stage. 

Measurements of the complete modulator, with a 
1250-volt power supply feeding plate voltage to the 
211 tubes, showed that it was possible to obtain 120 
watts of audio output from the tubes with no distor- 
tion discernible to the ear or noticeable on the oscillo- 
scope. An output of 145 watts was obtained with an 
amount of distortion which would be quite tolerable 
for amateur communications work. No heating of the 
output transformer was noticed with 120 watts output 
from the stage into a 7000-ohm load resistor over a 
test period of about one hour. 

The 7000-ohm load impedance could be represent- 
ed by a Class C modulated r.f. amplifier operating 
from the same plate supply as the 21Ts (1250 volts) 
at a plate current of 180 ma. This represents an input 
of 225 watts to the Class C stage, an amount which 
may be modulated without difficulty by the modula- 
tor unit. 



AN/ART-13 Autotune Aircraft Radio 
Transmitter 

The AN/ART-13 Autotune aircraft radio trans- 
mitter makes a very satisfactory amateur transmitter 
for phone and c.w. operation on the 80, 40, 20 and 10 
meter bands. Under normal conditions the transmitter 
operates very stably and puts out a cleanly modulated 
or smoothly keyed signal when it is running about 
200 watts input. The Autotune feature is a great oper- 
ating convenience whether the transmitter is to be 
remotely controlled or controlled from the operating 
position. With the circuit modifications described 
herein the Autotune system allows operation on 10 pre- 
set frequencies throughout the 80, 40 and 20 meter 
bands and one additional frequency in the 10 or 11 
meter band. Operation with phone or c.w. on any one 
of these frequencies is obtained simply by moving the 
panel selector switch to the desired position and 
waiting approximately 25 seconds for the Autotune 
system to operate. If desired, several frequencies sep- 
arated by not more than about 50 kc. may be set up 
in the 28-Mc. band with an increasing reduction in 
the frequencies available for lower frequency opera- 
tion. 




6 6 

ITE +! 
LG 
TO SPEECH AMPLIFIER 

Figure 85. 

MAIN ASSEMBLY SCHEMATIC OF THE BC-375E 

MODULATOR. 



Ci — 8-/xfd. 450-volt elect. 
C 2 — 40-jufd. 350-volt elect. 
C ;# Ci — 8-^fd. 450-volt elect. 
Ri — 100,000 ohms i/ 2 watt 
Rl — 7500 ohms 10 watts 
R, — 5000 ohms 10 watts 
Rt — 50,000 ohms 20 watts 
Ti — Driver trans, from 375E 
"T> — Mod. trans, from 375E 
Tu — 10-volt 6.5-amp. fil. trans. 



T 4 — 700 v. c.t. 90 ma., 5 v. 3 

a., 6.3 volts 2 amperes 
CH— 12-hy. 90-ma. choke 
MA— 0-500 d,c. ma. from 375E 
V— Voltmeter from 375E 
Si — Phone c.w. switch from 375E 
S- — Main a.c. line switch 
S — S.p.s.t. test switch 
SOi, SO:: — Twistlock receptacles 



Manual, Volume III 



71 



-£6SN7GT Cb 




TO DRIVER 1 
TRANS. 

Ta _ i 



POWER 
115 AND 

V.A.C. MOD. 

UNIT 



O«N0. 



Figure 86. 
SCHEMATIC OF CLIPPER-FILTER SPEECH AMPLIFIER FOR THE BC-375E MODULATOR 



Ci — 25-^ifd. 25-volt elect. 

C 2 — 0.1-jufd. 400-volt tubular 

C t — 8-/ifd. 450-volt elect. 

C — 0.01 - ; ;fd. 400-volt tubular 

C — 0.1 -,.ifd. 400-volt tubular 

Co — 175-jijifd. mica 

Ct/ Cs — 200-/ ; /;fd. mica 

Ci) — 0.01 -,fd. 400-volt tubular 



Cio — 25-/ifd. 25-volt elect. 
C u — 10-/ifd. 100-volt elect. 
Ri — 1.0 megohm Vz watt 
R2 — 1300 ohms V% watt 
R:j — 1.5 megohms 1/2 watt 
r 4 — 220,000 ohm V 2 watt 
Rs — 47,000 ohms V2 watt 



R; — 500,000-ohm potentiometer 
r 7 — 100,000 ohms 1 watt 
Rs — 100,000 ohms V2 watt 
R ;i — 100,000 ohms 1 watt 
Rio — 330 ohms ]/ 2 watt 
Ru, R12 — 620 ohms V2 watt 
R13 — 47,000 ohms 1 watt 



Ru — 250,000-ohm potentiometer 

R15 — 750 ohms 10 watts 

Ti — Mike-to-grid transformer 

Ta — 6.3 volts at 3 amperes 

CH — 3.5 to 3.75 henry choke 

Ji — Crystal-mike jack 

j 2 — Carbon-mike jack 



Power The major change required to adapt the 
Supply ART-13 for amateur use is that of providing 
for operation of the equipment from the 
115 volt a.c. line. All other changes described are in 
the nature of operating conveniences or are for the 
purpose of obtaining operation in the 28 Mc. region. 

The simplest way of converting the equipment is 
to provide a source of 26 volts d.c. at about 9 amperes 
for operation of the tube filaments and heaters and for 
the relays and Autotune motor. Conventional a.c. oper- 
ated power supplies are then used for plate and grid 
bias voltages. However, due to the difficulty in ob- 
taining components for a high current 26-volt d.c. 
supply, it was deemed desirable in the conversion 
portion to use a 4-ampere 26-volt d.c. supply for the 
neater tubes relays and Autotune motor, and to supply 
the filaments of the 813 and the 811 from filament 
transformers. 

The power supply unit shown in Figure 88 has 
been designed and constructed especially for opera- 
tion with the AN/ART-13 transmitter. In addition 
to a complete set of control circuits the unit supplies 
the following potentials to the ART-13 through the 
power cable: 1250 volts at a maximum of 300 ma., 
400 volts at 225 ma., 26 volts at 4 amperes, 350 volts 
of negative bias for keying the 813, and 115 volts a.c. 
for the blower and for the filament transformers for 
the 811's and the 813. The power supply is housed in 
a standard cabinet which takes a 12K by 19 inch front 
panel. Careful component placement is necessary to 
house the power supply unit in a cabinet of this size. 

Several of the components used in the 26-volt d-c 
supply are surplus items since standard manufactured 
items are not available. In certain cases it will be 
necessary to have either the transformer or the filter 
choke for the 26-volt d.c. supply made up especially 



for the job. If a 10-ampere 26-volt output selenium 
rectifier is obtainable it will probably be best to have 
a 10-ampere power transformer and choke wound also 
so that no changes will be required in the filament 
circuits of the transmitter. The high voltage power 
supply and control circuits can be the same whether 
the filaments are all lighted from d.c. or some of them 
are lighted from d.c. and some from a.c. 

Initial operation of the equipment at full input 
for a period of time showed that considerable heating 
takes place in the region behind the plate tank circuit 
for the 813. It was therefore deemed desirable to in- 
stall a cooling exhaust blower on the back of the 
equipment. The particular blower used is a surplus 
item but similar a.c. operated blowers running at ap- 
proximately 1500 r.p.m. are available from the larger 
hardware stores. With this blower in operation the 
unit runs quite cool and overheating of components 
is completely eliminated even with long periods of 
operation. In the particular unit shown in Figure 87 
the blower has been mounted in a box on the rear of 
the housing for the transmitter with the filament trans- 
formers for the 811's and the 813 also included within 
this box. 

Control A time-delay relay which operates from 
Circuit the 26-volt d.c. supply has been included 
in the equipment to insure that all tubes 
have reached normal operating temperature before 
plate voltage is applied. If a 26-volt time delay is not 
available, a 115-volt a.c. relay of the same type may 
be used. Protective interlocks have been provided in 
the power supply unit and in the actual cabinet for 
the ART-13 transmitter. These two interlocks are con- 
nected in series and in turn the two of them are con- 
nected in series with the lead to the plate power relay 



72 



Surplus Radio Conversion 




Figure 87. 

TOP OF THE CONVERTED 
AN/ART-13. 

The box containing the blower and 
the filament transformers for the 
813 and the 81 Vs can be seen on 
the rear alongside the small box 
which holds the 6L6 multiplier for 
the 28-Mc. band. The 26-Mc. tank 
for the 813 can be seen inside the 
Cabinet. 



RYi so that plate voltage cannot be applied to the 
transmitter if the cover has been removed from the 
ART-13 or if the top door to the power supply box 
has been opened. 

Provision has been made in the control circuit for 
the transmitter so that when Su on the front of the 
ART-13 or its counterpart at the remote control posi- 
tion is moved from the off to either the voice or the 
c.w. position, the transmitter will be turned on. Since 
this switch closes a circuit to ground, it was necessary 
to find an isolated source of potential to operate the 
main control relay. This source of potential was ob- 
tained by leaving the small transformer T 4 connected 
across the line at all times that the unit is plugged into 
the socket. However, when the transmitter is switched 
off there is no power drain from any of the secondaries 
of this transformer. 

The push-to-transmit circuit which has been in- 
cluded in the power supply unit is very pleasing to 
operate and relatively simple in design. It consists of 
a single 6C5 tube operating from the bias supply along 
with its associated components. The complete circuit 
is shown in Figure 88. When the key is up relay RY r , 
is open and the voltage drop across R r> to the slider 
is impressed on the grid of the 6C5 tube, cutting off 
its plate current. When the key is pressed RY 5 closes 



and the right-hand side removes the blocking grid bias 
from the 813 by shorting the grid return to ground 
through R 9 and CH . These latter two components 
in conjunction with C 8 make up a very* effective key- 
click filter. The effectiveness of the circuit is illustrat- 
ed by the fact that clicks cannot be heard from the 
transmitter on a communication receiver tuned to the 
same band for break-in c.w. operation. 

At the same time that RY :> is closing, the other set 
of contacts on this relay shorts the grid of the 6C5 
to its cathode, causing full plate current to flow 
through RY and R 7 , thus closing RY G . When RY C 
closes the antenna changeover relay in the ART-13 
operates and plate voltage is applied to the transmit- 
ter by RYi. Then when the key is lifted RY 5 opens 
so that plate current to the 813 is stopped, but due 
to the time constant of the R ); -Co combination, plate 
current still flows through RY . Hence the plate volt- 
age remains on the transmitter and the antenna relay 
is still in the transmit position. The transmitter re- 
mains in this condition until the voltage across C 6 has 
built up to such a value that RY drops out, changing 
everything back to the receive condition. The amount 
of this delay is variable, by adjustment of potentio- 
meter R 5 from a fraction of a second up to about 15 
seconds. The normal setting is for about 3 seconds so 



Manual, Volume III 



73 



-^m^-r^ 1 ^^ 



C 3 CH 3 



CH 2 



C 4 CH 4 



^MSLr-^MSi/ 



866A/866's 




'mMmJ 



Tt 



w 



w 



T 2 



?_ 



r-x. 



RY 4 




uj_± 



E 



RY 3 

rv 



T 3 



X^: 



t_r 



c> 



fti 



UJ 



a.3v. 



LmqmJ 



T 4 



C K 



I RY 5 T 



Rj 




C» 



(5) +28 V. 

-® »v. 

-(?) STANDBY 
@H.V. ON 



— — <@-»-t250 V. 



""VS'CHANGE 
-(7)ON-OrF 

-® 115.V. 

©-^ 

+26 V. 

<T) PLATE 



^5> BIAS 
— (?) + 400 V. 



< 



Figure 88. 
SCHEMATIC DIAGRAM OF THE POWER SUPPLY FOR THE AN/ART-13. 



C 1# C2 — 4-jufd. 1500-volt 

capacitors 
C 3 , d — 4-/xfd. 600-volt 

capacitors 
C 5 — 10-/tfd. 600-volt capacitor 
Cc — 0.5-Afd. 600-volt tubular 
C 7 — 0.1 -/ifd. 400-volt tubular 
C 8 — 0.05-/ifd. 400-volt tubular 
Co — 4000-/*fd. 50-volt elect. 
C 10 — 8-/ifd. 450-volt elect. 
r x — 50,000-ohm 100-watt 

bleeder 
R2, R3 — 22 ohms 2 watts 



R4- 
R 5 - 
Rc- 
Rt- 
Rs- 

Rr 

Ti- 



-10,000 ohms 10 watts 
-100,000-ohm potentiometer 
-2.7 megohms V2 watt 
-15,000 ohms 10 watts 
-50,000 ohms 20 watts 
-15,000 ohms 2 watts 
-1500 v. each side at 300 

ma., 400 v. each side at 

175 ma., common c.t. 

(UTC PA-303) 
-5 v. 3 a., 2.5 volts 10 a. 
-700 v. c.t. 70 ma., 5 v. 2 a., 

6.3 v. 2 a. (UTC R-2) 
-35 volts at 5 a. (special) 



CHi — 250-ma. swinging choke 
CH 2 — 250-ma. filter choke 
CHs, CH, — 200-ma. filter chokes 
CH 5 — 0.05 henrys at 4 amp. 

(special) 
CH«r— 13-henry 65-ma. filter 

choke 
RYi — 28-volt d.c. 4-pole d.t. 

relay 
RY2 — 115-volt a.c. 2-pole relay 
RYs — 6.3-volt or 5 volt 2-pole 

relay (RY2 and RYi may be 

combined if contacts cf 



RY3 can carry about 8 
amperes and if 3 contacts 
are available.) 

RYj — 28-volt d.c. time-delay re- 
lay (115-volt a.c. time-de- 
lay relay may be used 
across primary of T3 if 28- 
volt relay not avail.) 

RY 5 — 28-volt d.p.d.t keying 
relay 

RYe — 2500-ohm sensitive relay 

Elimstat — A.c. line filter 



that the plate voltage will remain on for the normal 
short pauses in a c.w. transmission but will drop back 
to the receive condition 3 seconds after a transmission 
has been completed. 



Changes in 
ART- 13 Control 
Circuits 



It is necessary to make a certain 
number of modifications in the 
various circuits of the ART- 13 in 
order to allow the equipment to 
operate from the power supply unit described before 
and illustrated in Figure 88. It is necessary first that 
the meter switch circuit be changed in the following 
manner: Remove ground from bottom end of Rm 
(235-ohm resistor) and connect this end of the resis- 
tor to terminal A 2 of S105. Remove the wire that now 
goes to terminal B 3 of Si or, and connect this wire to 
terminal A 2 of Si 05 along with the bottom end of 



Rm above. This series of changes brings the grid 
return of the 813 tube out to terminal 2 on the main 
power connector Jios- 

The following changes are required in the power 
control circuits: Ground the lead inside the cabinet 
which now goes to terminal 8 on Jios- Remove the 
lead now going to terminal 14 of Jn 6 which is mounted 
on the side of the antenna changeover relay Ki 02 . In- 
sulate this lead. Now run a lead from terminal 8 of Jios 
to terminal 14 of Jn 6 . A lead is now run from terminal 
2 on the loading coil relay connector J107 to terminal 
C in the power supply unit. This is the only lead 
brought out of the transmitter which does not go 
through the main power connector Jios- 

The filaments of the 813 and of the 811's should 
be re-wired to operate from separate transformers 
mounted on the rear of the equipment. One side of 



74 



Surplus Radio Conversion 



the filament may be left grounded on the 813 but the 
center tap of the filament supply to the 811's must be 
grounded in order to eliminate hum modulation on 
audio peaks. The primary of the filament transform- 
er and the cooling blower for the equipment should 
now be connected to terminals 6 and 9 on J 108 . These 
terminals are supplied with 115 a.c. from the power 
supply unit when the equipment is in operation. The 
driver transformer returns which formerly went to one 
side of the filament of each 811 are now grounded to 
the chassis of the transmitter. 

Several changes may be made in the vicinity of 
the high-frequency/low-frequency relay Ki 05 whether 
or not the 10-meter band is to be included in the 
transmitter. In the first place the low-frequency choke 
L 10 d may as well be removed from its present position 
and C128 mounted in the space formerly occupied by 
Lio9- One additional hole must be drilled in the fire 
wall of the equipment. It is suggested that a protective 
interlock now be mounted in the position formerly oc- 
cupied by Ci2 8 on the fire wall of the transmitter. The 
leads to this interlock should be connected in series 
with the lead now going to terminal 3 of J 108 . The 
interlock should of course be mounted in such a 
manner that it is closed only when the cover is firm- 
ly in place on top of the transmitter. 

A slight increase in operating convenience can be 
obtained through replacing the 0-5 r.f. ammeter with 
a 0-300 or a 0-500 d.c. milliammeter. The r.f. trans- 
former T102 may be removed after the leads have been 
clipped by unscrewing it from the chassis. With the 
installation of this additional milliammeter it is possi- 
ble to read grid current and plant current on the 813 
simultaneously. 

Converting for The conversion of the ART-13 

28-Mc. Operation for 28-Mc. operation may be ac- 
complished in several different 
ways of varying difficulty. However, in converting the 



47 it. 2W., RESISTOR, 
1ST. N* 24 AROUND IT. 

Of 7T. N»14 3/4" 
DIA. 1" LONG 




6.3 V. TO 6L6 HEATER 



Figure 89. 
SCHEMATIC OF THE 28-MC. MULTIPLIER STAGE. 



unit shown in the photographs it was felt that a con- 
version method which did not involve any disassem- 
bly of the Autotune mechanism and which required 
no changes in the exciter of the transmitter would be 
best. So it was felt best simply to add a 6L6 outboard 
tripler stage on the rear of the transmitter in the vicin- 
ity of the grid of the 813. The 6L6 tripler is fed energy 
from the 1625 second multiplier in the ART-13 in the 
9.0 to 10.8 Mc. frequency range. The plate circuit of 
the 6L6 then may be tuned to any frequency between 
27 and 32.4 Mc. for feeding excitation to the grid of 
the 813 amplifier. In fact, if desired, the 6L6 may be 
used as a doubler from the same frequency range to 
deliver excitation to the grid of the 813 in the 21-Mc. 
range. 

The 6L6 multiplier is housed in 2" by 4" by 4" 
standard metal "cabinet" which has been mounted 
to the side of the cabinet which houses the blower and 
the filament transformers for the 811's and 813. Si in 
the circuit diagram of the multiplier, Figure 89, may 
be either a double-pole double-throw ceramic switch 
or a 28-volt d.p.d.t. relay which may be operated 
from the 28-volt supply for the transmitter. In the 
particular unit shown in the photographs a switch is 
used but it is planned to replace the switch with a 
relay for completely remote operation of the trans- 
mitter. The relay will be operated by another set of 
contacts on the channel-selector switch which will be 
closed whenever the 28-Mc. band is chosen. Heater 
voltage for the 6L6 may be obtained from a small 
transformer or from the supply for the 811's if they 
are operated from a.c. 

The circuit of the 6L6 multiplier is otherwise quite 
conventional except for the manner in which plate 
voltage is obtained for the 6L6 multiplier. Careful in- 
spection of the circuit diagram of the ART-13 will 
show that the 400 volts applied to the plate of the 
1625 multiplier appears across only one section of the 
padder capacitor Cn 3 at a time and only when that 
particular section of the padder capacitor is in use. 
Hence, by connecting an r.f. choke to padder capacitor 
which is used to excite the grid of the 6L6 in the 9.0 
to 10.8 Mc. range, 400 volts from the exciter power 
supply may be obtained by filtering the ri. out of the 
d.c. line with an r.f. choke and a by-pass capacitor. A 
50-^fd. mica capacitor is then used to excite the grid 
of the 6L6 multiplier from the hot side of the r.f. 
choke. In this way the 6L6 multiplier is completely out 
of the circuit except when control A is in position 9. 

The lead from coupling capacitor Cue to the grid 
of the 813 is broken and a lead brought out from each 
side of the point where the connection is broken. 
These two leads are then connected as shown in Fig- 
ure 89 to the 6L6 multiplier unit. One set of contacts 
on Sx is used in addition to close Ki -„ which switches 
the plate of the 813 from the network used on the 
low-frequency bands to the separate 28-Mc. tank 



Manual, Volume III 



75 




Figure 90. 

SCHEMATIC OF THE SIMPLE 

LM POWER SUPPLY. 



The S-volt and 6.3-vo/t windings on 
the transformer are connected in 
series to obtain filament voltage 
for the LM. Due to the light load 
on the filament windings the fila- 



ment Yoltage measures about 7 7.9 
volts on the filament lead. This 
value of voltage is well within the 
filament voltage tolerance of the 
heater tubes used in the frequency 
Meter. 



ngure 91 
PHOTOGRAPH OF 
THE SIMPLE LM 
POWER SUPPLY. 

An LM frequency meter is 

shown alongside the power 

supply for comparison. 



which has been placed in the position inside the 
cabinet of the ART-13 which was designed to hold 
the low-frequency oscillator unit. In the particular 
transmitter shown the 28»Mc. tank for the 813 con- 
sisted of a 6-turn coil of number 10 enamelled wire IK 
inches in diameter and 1% inches long. A two-turn 
link feeding a piece of 300-ohm line is then run over 
to the left wall of the transmitter where it terminates 
in a pair of terminals. With this tank the 813 dips to 
about 30 ma. on 28 Mc. 

The two terminals which close K i0 5 may be picked 
up as terminals 7 and 4 on the connector J 115 which 
feeds plate and filament supply to the multiplier unit 
of the ART-13. Two leads from these two termin- 
als are run to the 6L6 multiplier unit so that they are 
closed whenever the 6L6 is in operation. With the 6L6 
frequency tripler as shown it is possible to obtain half 
scale on the grid current meter throughout the 28-Mc. 
band; this represents about 8 to 9 ma. of grid current 
on the 813. 



Note in Regard 

fro the Output 

Network of the ART-13 



The output network of 
the AN/ART-13 is de- 
signed to operate as an 
"L" network on frequen- 
cies up through about 5 Mc. This is required since the 
transmitter was designed to feed an antenna installed 
on an aircraft which would have a very low radiation 
resistance at these low frequencies but would have a 
relatively large value of capacitance to ground. This 
network will not feed satisfactorily the type of an- 
tennas commonly used by amateurs for fixed-station 
use in the 3.5 to 4 Mc. band. Hence it is desirable to 
convert the L network into a pi network when operat- 
ing on the 80-meter band. The simplest way to do 
this is merely to place a capacitor of 100 to 400 fifitd. 
from the "COND" terminal on the left end of the 
transmitter to the ground terminal on the case. A 
variable capacitor may be used to determine the best 
value for this capacitor, and then a fixed air capacitor 
or a ceramic transmitting capacitor of the type used 
in the transmitter may be hooked in place. Experiment 



76 



Surplus Radio Conversion 



showed that a value of about 200 /-t/xfcL was best for 
feeding a folded dipole with 300-ohm twin line on 
the 3.5-Mc. band. 

Tests of the completed transmitter have shown that 
there is no appreciable increase in output after the 
plate current on the 813 is increased above 160 ma. 
This represents a power input of 200 watts at 1250 
volts and the plate circuit efficiency runs from 70 to 
75 per cent on all bands. The out-of-resonance plate 
current will be from 180 to 200 ma. with normal exci- 
tation, and antenna coupling should be adjusted until 
160 ma. of plate current is drawn by the 813 tube. 

Simple A.C. Power Supply for the LM 
Frequency Meter 

Figures 90 and 91 illustrate a very simple power 
supply for operation of one of the LM series frequen- 
cy meters from the 115-volt a.c. line. Plate voltage for 
the frequency meter is obtained from a small power 
transformer with a 6X5-GT rectifier. Due to the very 
low plate current requirements of the frequency meter 
a resistance-capacitance filter has been used on the 



plate voltage supply. With the transformer shown and 
the values of resistance and capacitance listed the 
plate voltage supplied to the frequency meter is 255 
volts. This voltage is sufficient to cause the neon regu- 
lator tubes to strike with certainty when the voltage- 
change strap in the LM is adjusted to the 200-260-volt 
position. 

By connecting the two filament windings on the 
power transformer in series it is possible to obtain 
adequate heater voltage for the frequency meter. Due 
to the light load on these two filament windings the 
voltage applied to the LM under normal operating 
conditions is 11.9 volts; this value of voltage is well 
within the plus or minus 10 per cent heater voltage 
limit on the tubes used in the equipment. Through the 
use of a 6X5-GT rectifier, which has the heater well 
insulated from the cathode, the rectifier may be light- 
ed from the same filament windings, which light the 
tubes in the frequency meter. No changes whatever 
are required inside the LM frequency meter when it 
is used with the power supply shown in these illus- 
trations. 



LIST OF EQUIPMENT 

on which data is given in Volume I of the 

"Surplus Radio Conversion Manual" 



LIST OF EQUIPMENT 

on which data is given in Volume II of the 

"Surplus Radio Conversion Manual" 



BC-221 Frequency Meter 

BC-342 Receiver 

BC-312 Receiver 

BC-348 Receiver 

BC-412 Radar Oscilloscope (Conversions for 
TV Receiver and Test Oscilloscope) 

BC-645 Transmitter-Receiver (420 Mc.) 

BC-946B Receiver (Conversion to Auto Receiver) 

SCR-274N (BC-453A Series) Receivers 
(Conversion to 10-meters) 

SCR-274N (BC-457A Series) Transmitters 
(Conversion to V.F.O.) 

SCR-522 (BC-625) Transmitter (Conversion to 
2 meters) 

SCR-522 (BC-624) Receiver (Conversion to 
2 meters) 

TBY Transceiver (Conversion to 10 and 6 meters) 

BE-103A Dynamotor 

BC-1068A 1161A Receiver (2 meters) 



ARC-5 (B-454) Receivers (Conversion to 28 Mc.) 

AN/APS-1 3 Transmitter-Receiver 
(Conversion to 420 Mc.) 

ARC-5 (BC-457) Transmitters (Conversions to 
28 Mc.) 

Selenium-Rectifier Power Units 

ARC-5 V.H.F. Transmitter-Receiver Operation 

GO-9/TBW Transmitter (Conversion to 28 Mc.) 

BC-357 Marker Receiver (Conversion to 
Capacity Relay) 

BC-946B Receiver (Conversion to 
High-Fidelity Tuner) 

BC-375 Transmitter (use with external V.F.O.) 

TA-12B/C Transmitter Conversion 

AN/ART-13 Transmitter (Conversion to A.C. 
and 28 Mc.) 

Coil-Winding Charts 

AVT-112A Transmitter for Light Aircraft 

AM-26/AIC Interphone Amplifier (Conversion 
to 9-watt Amplifier) 

LM Frequency Meter 
Beam Rotating Mechanisms 
ARB Receiver (Schematic only) 



Manual, Volume III 



77 




$ 

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Surplus Radio Conversion 



R. F. AMPLIFIER 
Z 101 



PLATE CAP 
PLATE A/ 

connection 

connection! 



. Tf 4MO R/ 

^.L jrVyvV [ ^CATHODE RF 



INTERNAL CONNECTIONS FOR 
VIOI-l l VIOI-2,VI0l-3 
TUBE TT« 44«A 



HCATER 

SMELL 

BASE VIEW SHOWING 

PIN LOCATION 




Figure 93 
RECEIVER UNIT, CPR-46ACJ, SCHEMATIC DIAGRAM 



Manual, Volume III 



79 



16 MC CONVERTER 



FIRST 16 MC I F AMPLIFIER 



SECOND I6MC IF AMPLIFIER 



THIRD I6MC IF AMPLIFIER 




Figure 93 
RECEIVER UNIT, CPR-46ACJ, SCHEMATIC DIAGRAM 



80 



Surplus Radio Conversion 




Figure 94 
SCHEMATIC, BC-659 RECEIVER AND TRANSMITTER 



Manual, Volume III 



81 



O 
00 



V3 

VT-185 

TRANS. OSC. 







V SW. Q ! U, it 



"" "~ ^"^ c 21 



C20 




VT-185 

TRANS. REACT. .rfOD. 



HI- 



MICROPHONE WITH _ 
N PUSH-TO-TALK' rPTT 
SWITCH ' 



JC23 




^24 




R44 



WHT-WSQ TW.3 



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c 28 



0*Q-y 



WHT-REO TW.-i 



HT-BRW TR.-y 



SO 2 
METERING 
. SOCKET 
UJG VIEW) 



V10 

VT-179 

REC'VR. 
I-F AMP 




CDS 
CM 




110 



WH'.dcO TR 7 



-*W»- 







WHT-BRH TR. 



SM2 

c 29 



DJod — , 



POWER a CONT. 
CABLE PLUG 



KEY TO SYMBOLS 



VARIABLE 
AIR 

CAPACITOR 



FIXED MICA 
OR CERAMC 
CAPACITOR 



— J. 

T T 5 



^ 








FIXEO 

PAPER 

CAPACITOR 



NOTE!- ALL COILS VIEWED FROM 
BOTTOM Or CHASSIS WITH FRONT 
PANEL ON LEFT 



v 13 

VT-177 

REC'VR. OIOOE RECT. 
a DC AMP. 



Figure 94 
SCHEMATIC, BC-659 RECEIVER AND TRANSMITTER 



82 



Surplus Radio Conversion 



S-2D 




L-29 




POWER AMPL I POWER 

V-l AMPL 

JAN-3A5 I V-2 

JAN-3A5 
TRANSMITTER FILAMENT 



' XMTR OSC 
y V-4 

JAN-3A5 
REACT TUBE 
V-l 6 JAN-IR5) V-5 



STRING 



Ls6X 



DiSCR 

V-12 

JAN-IA3 



I 



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L-39 



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V-13 
JAN-3A5 



JDISCR 
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AUDIO 

/ 

D-C AMPL 

V-17 
JAN-IL4 






NOTE . CHANNEL SWITCH S"2A, S"2B, S-2C, S"2D, 
S-2E, S-2F, S-2G, S"2H, S~2J SHOWN IN 
B POSITION 



Figure 95 
SCHEMATIC, BC-1335-A, TRANSMITTER - RECEIVER 



Manual, Volume III 




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up 



\ L-36 f 

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< -^JOtf^ ^W^ r^JC^ 



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L n L-38 • 
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XTAL OSC LIMITER 2D-HF 1ST l-F 1ST R-F 

V-15 J_ V-l! V-IO V-9 V-6 

JAN-3Q4 -JAN-IL4 JAN-IL4 JAN-IL4 JAN-IL4 



DEB ; 



2D R-F 

V-7 
JAN-IL4 



MIXER 
V-8 

JAN-IR5 



XTAL AMPL 

V-14 
JAN-IL4 



RECEIVER 



FILAMENT 



STRING 



ALL RESISTOR VALUES IN OHMS UNLESS OTHERWISE SPECIFIED 
ALL CAPACITOR VALUES IN UUF UNLESS OTHERWISE SPECIFIED. 

Figure 95 

SCHEMATIC, BC-1335-A, TRANSMITTER - RECEIVER 



84 



Surplus Radio Conversion 




Figure 95 (continued) 
SCHEMATIC, BC-1335-A, TRANSMITTER - RECEIVER 



Manual, Volume III 



85 




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Surplus Radio Conversion 




Figure 97 
SCHEMATIC, AN/APA-10 PANORAMIC ADAPTER 



Manual, Volume III 



87 



CONVERTER *2 CHASSIS 
T - 2_0J 

f£\ 3 9 MC 1 



~T^VS-\m] ^300 It T *3 CHASSIS I 

r-JU -M45 ' H H 




Figure 97 
SCHEMATIC, AN/APA-10 PANORAMIC ADAPTER 




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Cat. No. EE-333