Conversion material and schematic of mil receiver, R-45/ARR-7 
based on SX-28.  Compliments of Ray Colbert, W5XE and
Kenneth Colbert, KB5MLY.

Adding SSB to the ARR-7 

			George Marshall W6BHR
			554 Westborne Drive
			Los Angeles, Cal. 90048 

  I bought an ARR-7 from R. E. Goodheart after trying in vain to find anything 
with that complete coverage and overall quality at anywhere near the price. 
Although Goodheart had already removed and bypassed the reradiation suppressor, 
this article on adding SSB will be written for those who have an unmodified receiver. 
For those already possessing one of these versatile sets, or for those contemplating 
purchase, the ARR-7 is an extremely simple receiver in which to install a product 
detector. 
  Proceeding directly to the heart of the matter, the following steps make it 
possible to modify the receiver in a few hours' time. First, remove and discard 
the 6AB7 which precedes the first of the two rf amplifiers. This tube was used 
only as a reradiation supressor so don't worry about losing gain or sensitivity 
in discarding it. The socket is utilized inthe modification and the tube is replaced 
by a 6SN7 Product Detector.
  The front-panel screws are loosened sufficiently to get an end wrench between 
the front panel and the chassis in order to remove the spst bfo switch. When the 
nut on the switch has been considerably loosened, the switch may he rotated about, 
so that with a gun-type iron, or other iron with a small tip, the connections may 
be removed from the terminals. Replace the old switch with a DPDT and reconnect 
the wires removed from the old switch in such fashion that they are switched ON 
in the bfo "ON" position. Use the uppermost terminals, the ones closest to the 
top of the receiver, for these connections, the single wire going to the center 
terminal and the pair of wires going to the other terminal. 
  Returning to the vicinity of the 6AB7 socket, there is a terminal board 
immediately adjacent, on which are mounted ·79, C80, R54 and R55. Clip off, or 
unsolder these components so the terminal board can be re-used. Be careful when 
removing R-55, as this 47K resistor can be re-used as the plate load for the 6SN7. 
The B lead in the lower corner should also be carefully unsoldered, then the entire 
board can be removed for ease in installing the new components which consist of 
a .1 mf capacitor, a 10K ½ w resistor, and the reinstalled 47K resistor. The terminal 
board is modified as follows: Removethe ground connection which runs in the vertical 
plane and swing it around to the B lug.
  While the terminal board is out of the way the octal socket may be rewired for the 
6SN7 as follows: Remove the antenna lead from pin 4 and the lead connected to pin 8. 
These two leads may now be directly connected by placing them on the unused lug of 
the terminal board when it is replaced. The jumper going from pin 3 to pin 5 is 
removed, carefully, fron pin 5 and connected to pin 6. If carefully removed, the 
ground lead connected to pins 1 and 2 can also be reused. A "soldering aid' tool 
is an asset for this sort of operation. A piece of spaghetti is slipped over this 
ground lead and it is then connected to pin 8 which takes care of the heater circuit. 
The other components are now connected to the socket, the 1OOK resistor from pin 1 
to pin 8, the 1OOK resistor with a 100 pf capacitor across it, from pin 4 to pin 8 
and a 680 ohm 1 w resistor from pin 6 to pin 8. (This is the only 1 w resistor; all 
others, are ½ w.) The terminal board can now be reinserted. 
  When placing the .1 mf capacitor on the terminal board, leave enough lead on the 
B end and it can be used to connect directly to pin 5 on the octal socket. 
  Remove the 3 screws from the bfo compartment and remove the cover. Inside you will 
notice a "gimmick," two wires twisted together; remove these and replace them with 
a 100 pf capacitor. Remove the lead going from the lug to the 6H6 for bfo injection. 
Remove the #6- 32 machine screw and place a ground lug un- der this screw and replace 
the screw. Replace the cover on the bfo. 
  Prepare a 7" piece of small coax or shielded lead as follows. Strip one end so 
that about ½" of shield is exposed and about Ύ" of center conductor and its insulation. 
Strip off about Ό of this insulation exposing the center conductor. This end of the 
shield Will be connected to the ground lug installed on the bfo compartment and the 
Centex conductor connected to the lug which formerly went to 6H6. The othex end of 
the center conductor is connected to pin 1 of the tube socket. The 47K resistor 
from,the terminal board can now be connected to pin 2 of the socket. 
  An 8½" piece of small coax is stripped in the same manner as the previous piece. 
With a hot iron, a place can be puddled and tinned with solder on the vertical wall 
of the bfo compartment nearest to pin 8 of the last if tube. The shield of the coax 
is grounded at this point and the exposed center conductor is connected through a 
10 pf capacitor to pin 8 of the last if tube. The center conductor at the other 
end is connected to pin 4 of the 6SN7.
  Now, on the opposite side of the receiver there is a long terminal board. On it, 
near the rear of the receiver, is the audio coupling capacitor C77; the lead nearest 
you is removed and transferred to a blank lug which is toward the rear of the receiver.
  Now strip 2 26" pieces of small coax exposing the shield and center conductor at 
both ends. Strip another 26" piece so that the shield and center conductor is exposed 
only on one end. This end will be connected to the DPDT switch at the front panel. 
An three shielded leads can be snaked up through the harness along the right side 
of the receiver when looking at the bottom of the receiver, which will tend to 
keep things neat. 
  The center conductor of the coax which is stripped on only one end is connected 
to pin 2 of the 6SN7. The center conductor at the other end is connected to the 
lug of the unused section of the DPDT bfo switch is closest to the center of the 
receiver. The center conductor of the next coax is connected to the center lug of 
the switch and the other end of the center conductor is connected to C77. The third 
coax center conductor is connected to the remaining lug on the switch, and thence 
connected to the point that C77 was removed from. 
  The 3 shields at the point near the switch are wrapped with bare wire and soldered 
together. The other end of the two leads going to the audio can be tacked together 
in similar fashion. Where the lead which goes to the Product Detector, goes by the 
bfo compartment, about ½" of shield should be exposed and conneted to the same point 
as the lead which went to the last if (the solder puddle at the side wall of the bfo compartment). 
  With all leads now installed on the 6SN7 socket, room can be found to connect 
the 10 mf decoupling capacitor to the ground lug of the adjacent tube. This completes 
the modification; plug in a 6SN7, hook up the power and start product detecting 
whenever the bfo is on. This modification does not affect ordinaTy CW reception, 
but makes it easy to tune and receive SSB signals. Either side band can be selected 
by adjustment of the bfo knob. It works like a charm ...   W6BHR 

Adding SSB to the ARR-7 

			George Marshall W6BHR
			554 Westborne Drive
			Los Angeles, Cal. 90048 

  I bought an ARR-7 from R. E. Goodheart after trying in vain to find anything 
with that complete coverage and overall quality at anywhere near the price. 
Although Goodheart had already removed and bypassed the reradiation suppressor, 
this article on adding SSB will be written for those who have an unmodified receiver. 
For those already possessing one of these versatile sets, or for those contemplating 
purchase, the ARR-7 is an extremely simple receiver in which to install a product 
detector. 
  Proceeding directly to the heart of the matter, the following steps make it 
possible to modify the receiver in a few hours' time. First, remove and discard 
the 6AB7 which precedes the first of the two rf amplifiers. This tube was used 
only as a reradiation supressor so don't worry about losing gain or sensitivity 
in discarding it. The socket is utilized inthe modification and the tube is replaced 
by a 6SN7 Product Detector.
  The front-panel screws are loosened sufficiently to get an end wrench between 
the front panel and the chassis in order to remove the spst bfo switch. When the 
nut on the switch has been considerably loosened, the switch may he rotated about, 
so that with a gun-type iron, or other iron with a small tip, the connections may 
be removed from the terminals. Replace the old switch with a DPDT and reconnect 
the wires removed from the old switch in such fashion that they are switched ON 
in the bfo "ON" position. Use the uppermost terminals, the ones closest to the 
top of the receiver, for these connections, the single wire going to the center 
terminal and the pair of wires going to the other terminal. 
  Returning to the vicinity of the 6AB7 socket, there is a terminal board 
immediately adjacent, on which are mounted ·79, C80, R54 and R55. Clip off, or 
unsolder these components so the terminal board can be re-used. Be careful when 
removing R-55, as this 47K resistor can be re-used as the plate load for the 6SN7. 
The B lead in the lower corner should also be carefully unsoldered, then the entire 
board can be removed for ease in installing the new components which consist of 
a .1 mf capacitor, a 10K ½ w resistor, and the reinstalled 47K resistor. The terminal 
board is modified as follows: Removethe ground connection which runs in the vertical 
plane and swing it around to the B lug.
  While the terminal board is out of the way the octal socket may be rewired for the 
6SN7 as follows: Remove the antenna lead from pin 4 and the lead connected to pin 8. 
These two leads may now be directly connected by placing them on the unused lug of 
the terminal board when it is replaced. The jumper going from pin 3 to pin 5 is 
removed, carefully, fron pin 5 and connected to pin 6. If carefully removed, the 
ground lead connected to pins 1 and 2 can also be reused. A "soldering aid' tool 
is an asset for this sort of operation. A piece of spaghetti is slipped over this 
ground lead and it is then connected to pin 8 which takes care of the heater circuit. 
The other components are now connected to the socket, the 1OOK resistor from pin 1 
to pin 8, the 1OOK resistor with a 100 pf capacitor across it, from pin 4 to pin 8 
and a 680 ohm 1 w resistor from pin 6 to pin 8. (This is the only 1 w resistor; all 
others, are ½ w.) The terminal board can now be reinserted. 
  When placing the .1 mf capacitor on the terminal board, leave enough lead on the 
B end and it can be used to connect directly to pin 5 on the octal socket. 
  Remove the 3 screws from the bfo compartment and remove the cover. Inside you will 
notice a "gimmick," two wires twisted together; remove these and replace them with 
a 100 pf capacitor. Remove the lead going from the lug to the 6H6 for bfo injection. 
Remove the #6- 32 machine screw and place a ground lug un- der this screw and replace 
the screw. Replace the cover on the bfo. 
  Prepare a 7" piece of small coax or shielded lead as follows. Strip one end so 
that about ½" of shield is exposed and about Ύ" of center conductor and its insulation. 
Strip off about Ό of this insulation exposing the center conductor. This end of the 
shield Will be connected to the ground lug installed on the bfo compartment and the 
Centex conductor connected to the lug which formerly went to 6H6. The othex end of 
the center conductor is connected to pin 1 of the tube socket. The 47K resistor 
from,the terminal board can now be connected to pin 2 of the socket. 
  An 8½" piece of small coax is stripped in the same manner as the previous piece. 
With a hot iron, a place can be puddled and tinned with solder on the vertical wall 
of the bfo compartment nearest to pin 8 of the last if tube. The shield of the coax 
is grounded at this point and the exposed center conductor is connected through a 
10 pf capacitor to pin 8 of the last if tube. The center conductor at the other 
end is connected to pin 4 of the 6SN7.
  Now, on the opposite side of the receiver there is a long terminal board. On it, 
near the rear of the receiver, is the audio coupling capacitor C77; the lead nearest 
you is removed and transferred to a blank lug which is toward the rear of the receiver.
  Now strip 2 26" pieces of small coax exposing the shield and center conductor at 
both ends. Strip another 26" piece so that the shield and center conductor is exposed 
only on one end. This end will be connected to the DPDT switch at the front panel. 
An three shielded leads can be snaked up through the harness along the right side 
of the receiver when looking at the bottom of the receiver, which will tend to 
keep things neat. 
  The center conductor of the coax which is stripped on only one end is connected 
to pin 2 of the 6SN7. The center conductor at the other end is connected to the 
lug of the unused section of the DPDT bfo switch is closest to the center of the 
receiver. The center conductor of the next coax is connected to the center lug of 
the switch and the other end of the center conductor is connected to C77. The third 
coax center conductor is connected to the remaining lug on the switch, and thence 
connected to the point that C77 was removed from. 
  The 3 shields at the point near the switch are wrapped with bare wire and soldered 
together. The other end of the two leads going to the audio can be tacked together 
in similar fashion. Where the lead which goes to the Product Detector, goes by the 
bfo compartment, about ½" of shield should be exposed and conneted to the same point 
as the lead which went to the last if (the solder puddle at the side wall of the bfo compartment). 
  With all leads now installed on the 6SN7 socket, room can be found to connect 
the 10 mf decoupling capacitor to the ground lug of the adjacent tube. This completes 
the modification; plug in a 6SN7, hook up the power and start product detecting 
whenever the bfo is on. This modification does not affect ordinaTy CW reception, 
but makes it easy to tune and receive SSB signals. Either side band can be selected 
by adjustment of the bfo knob. It works like a charm ...   W6BHR 

R-45/ ARR-7 Receiver Modifications 

						James M. Stueber W5UOZ-AF5UOZ
						8410 Flower Place N.E.
						Albuquerque, N. M. 


The R-45/ARR-7 receiver is a continuous tuning type covering the range of .55 mc 
thru 42 mc. It is a single conversion superhetrodyne circuit, with two tuned rf 
stages and one untuned preselector rf stage. The design is a modification of the 
well known Hallicrafters SX-28 receiver. The particular modified receiver was 
built under a Signal Corps contract by the Belmont Radio Corp. Inclusion of the 
described changes will provide the user with a good communications receiver, 
overcoming the major disadvantage in the original design, which is the lack of 
bandspread tuning. A schematic of the receiver and a coil layout for alignment 
purposes is included for those who may require them. Appreciation is extended 
to Mr. Amos Peters, AF5LHX, for supplying the receiver through the MARS Central 
Technical Net, thereby making these modifications possible. The changes described 
consist of the following: 

1. Addition of bandspread tuning and dial
2. Addition of necessary wiring to provide ac power supply operation
3. Addition of Send-Rev. Switch
4. Improvement of "S" meter circuit
5. Audio amplifier modification for speaker connection
6. Low impedance antenna input stage 

Bandspread Tuning and Modification for ac Power 

1. Remove the screws holding the cover plate which houses the tuning dial motor 
reversing switch and stop mechanism. Discard. 
2. Cut the wires from the motor reversing switch SW3 and remove the switch. 
3. Remove the stop mechanism from the main tuning dial shaft and discard. 
4. Remove all the knobs from the receiver and the screws from the power connector 
so the front      panel may be taken off.
5. Remove the main tuning dial by loosening the allen-head screws.
6. Remove the cover from the cast aluminum housing containing the 28V dc motor 
and associated       parts. 
7. Remove the filter, motor and misc. parts from inside the box.
8. Remove the fiber gear from the vertical shaft. This may be sealed with paint 
and may be       difficult to loosen, but with the proper size allen wrench and 
solvent to loosen the paint, it    will come loose. 
9. Remove the potentiometer R41 and bracket, located on the top rear of the 
chassis. Cut the wire    leads free near the potentiometer terminals and 
leave them in position.
10. Remove the wires from the POWER switch, tie together, solder and insulate. 
11. Remove the white wire with blue and orange tracer from the MOTOR switch. 
12. Remove the ground connections from pins A and C of receptacle SO-1. 
13. Attach the white wire, with blue and orange tracer, which was removed from 
the MOTOR switch,     to one lug of the POWER switch. 
14. Attach the other end of the wire which was attached to the motor, to pin C 
of SO-1 connector.
15. Cut the white wire with green tracer from the MOTOR switch and attach to the 
other lug of the POWER switch. Pins C and D of SO-1 now become the ac switch-wires 
to turn ae power off and on. The bandspread tuning knob will project out of the 
top of the case, since there is no front panel space available. 
16. A three-eighths inch hole is drilled in the top of the cast aluminum motor 
housing located 11/16 inch from the front of the case, and Ό inch from the left. 
A shaft bushing is installed  in this hole to accommodate a length of Ό inch diameter 
shaft and solid shaft coupling. The bandspread tuning will be engaged by throwing 
the MOTOR switch to ON, which engages the electric clutch in the tuning mechanism. 
When fast tuning is desired, the MOTOR switch is  thrown to OFF and tuning is 
accomplished with the TUNING knob.  Parts are now installed to provide de voltage 
to energize the clutch. 
17. Mount a 6.3 volt 1.2 amp. filament transformer under the chassis on the side 
lip near the SO-1 connector. Refer to Fig. 1 for the schematic of this portion 
of the modification. 
18. Connect one of the 6.3 volt leads of the transformer to pin 7 of 6SA7 tube V4. 
19. The center tap connection of this winding is not used, so cut the lead off 
close to the transformer winding. 
20. Remove the wire with blue tracer from the MOTOR switch. 
21. Connect the other 6.3 volt lead to one con- tact on the MOTOR switch. 
22. Connect the other switch contact to a con- ven,ient ground. 
23. The 500 ohm 5 watt resistor, the 1N93 diode, and 10 mfd capacitor are 
conveniently located near the transformer on a three lug terminal strip and wired 
as shown in Fig. 1. 
24. Connect the wire with blue tracer, which was removed from the MOTOR switch, 
to the junction of the 1N93 diode and the 10 mfd capacitor shown in Fig. 1. 

Addition of SEND-RCV Switch 

1. Drill two holes in the front panel which will accommodate a SEND-RCV switch and 
a pin jack (RCA Phono jack) for a keying relay connection. Due to the close 
spacings and limited panel space available, care must be exercised in location 
of the two holes. A ½ inch hole for the SEND-RCV switch is located 5½ inches 
from the left and 1 13/16 up from the bottom. A three-eighths inch hole for 
the pin, jack is drilled 6 inches from the left and 2 7/16 inches up from the 
bottom of the front panel. Refer to Fig. 2 for the schematic of the circuit.
2. Estimate the length of wire needed to go from pin A and B of SO-1 to the new 
SEND-RCV switch, a SPST toggle switch on the front panel, and install these leads. 
Do not solder these leads at the toggle switch at this time but solder at pin A 
and B of SO-1. 
3. Estimate two lengths of wire to run from the toggle switch to the pin jack. 
The toggle switch wire from pin A of SO-1 goes to the insulated lug of the pin 
jack and the other wire from the    toggle switch to the ground lug of the pin 
jack. Solder all these leads at this time.
4. The main tuning dial, front panel, and knobs may now be reassembled. 

Improvement of "S" Meter Circuit

It was found that the maximum deflection that could be had from the local 
broadcast signals was S-6 with the original circuitry. The following changes 
will improve the circuit. Refer to Fig. 3 for the revised circuit. 
1. Replace the 6SK7 tube V5 with a 6SD7 tube.
2. Change the 100 ohm resistor R22 tb 1000 ohms. 
3. Add a 1000 ohm resistor in parallel with the 330 ohm resistor at he 
cathode of V5.

Audio Amplifier Modification

  Refer to Fig. 4 for the revised circuit.
1. Remove the 68k resistor R39 located on the terminal board on the back 
chassis lip.
2. Tie a jumper wire across the two terminals where R39 resistor was removed 
and solder.
3. Remove the 7500 ohm 10 watt resistor R40 located in a cluster of four 
upright resistors under the chassis near the rear. 
4. Connect the two white wires with red tracers together after removing them from 
R40, insulate and solder them. 
5. Install a 5000 ohm to 8 ohm output transformer in the location on top of the 
chassis near the rear where the R41 potentiometer and bracket were removed. 
6. Remove the white wire with blue tracer attached to pin 3 of 6V6 tube V9. This 
wire leads to a .5 mfd capacitor C52 which is a metal can type and is the bottom 
unit of two stacked ones near the cluster of upright mounted 10 watt resistors. 
This capacitor may be removed or left in, as desired, and white wire with blue tracer 
may be removed from the harness or clipped short and left in. 
7. Install a wire from the other terminal of C52 to a lead of the 8 ohm secondary 
of the output transformer. (There is already a shielded wire attached to this 
terminal of C52, leave it there.)
8. Tie the other lead of the 8 ohm transformer secondary to any convenient ground. 
The white wire with black tracer which attached to the potentiometer R41 may he used 
for this ground. 
9. Connect one wire of the output transformer primary to pin 3 of 6VO tube V9. Do not 
solder.
10. Connect the other primary wire to pin 4 of OVO tube V9. Do not solder. 
11. Remove the 100k resistor R47 connected from pin 3 of 6V6 tube V9 to a terminal 
board on the rear chassis apron. Removal of this negative feedback resistor 
will result in greater output and better communications quality. 
12. Install a .02 mfd 600 volt capacitor from pin 3 to pin 4 of 6V6 tube V9 to 
reduce high frequency response. Solder the connections. Either headphones 
or a speaker may be connected to the PHONES jack. 

Low Impedance Antenna Input Stage

  Refer to Fig. 5 for the revised schematic.
1. Remove the wire lead from pin 5 to pin 3 of 6AB7 tube V12.
2. Connect a wire from pin 3 to pin I of this tube socket and solder.
3. Remove the .0082 mfd capacitor C79 from the terminal board on the underside 
of the chassis near the tube socket of V12.
4. Disconnect the center wire of the shielded antenna wire lead where it terminates 
at the terminal board on top of the chassis near the 6AB7 tube V12.
5. Ground the terminal from which this wire was removed.
6. Connect one end of a .0082 mfd capacitor to the free end of the wire removed 
in step 4 and add on a piece of wire to the other end of the capacitor, long 
enough to go through the chassis grommet. Connect it to pin 5 of the 6AB7 tube V12. 

  A typical power supply is shown in the schematic of Fig. 6. No attempt is made 
to design an exact supply for the receiver in this article, since most users have 
power supplies capable of supplying adequate power to the receiver. 
  A white wire with blue and black tracer will be left over from the modifications. 
It may be cut close and left in the harness under the chassis. 
  A slot is cut in the cover to allow it to be slipped over the bandspread tuning 
knob. This shaft may be cut short enough to allow a knob to fit flush with the 
case cover.
  A dummy knob is installed on the shaft on the front panel from which the stop 
mechanism was removed.
  A bandspread dial is attached with cement to a Ύ inch diameter knob and installed 
on the tuning shaft. This dial is reproduced in Fig. 7 as a guide only because each 
receiver will vary slightly in calibration and the,dial will have to be tailored to 
each case. A suitable pointer for the dial is made from a short length of solid #20 
wire which is attached under the screwhead of the nameplate.   . . . W5UOZ

Parts List

1-Shaft bushing for Ό inch shaft
1-Ό inch dia. shaft approx. 4 inches long 
1-shaft coupling for 1/4 inch shaft 
1-2 inch dia. bandspread tuning knob 
1-SPST toggle switch (SEND-RCV switch) 
1-Pin jack (RCA phono jack) 
1-Ύ inch dia. tuning knob (mount bandsproad tuning dial to this knob) 
1-6.3 volt 1.2 amp filament transformer 
1-1N93 diode 
1-10 mfd 150 volt elect. capacitor 
1-500 ohm 5 watt resistor 
1-8 Ing terminal strip 
1-6SD7 tube 
2-1000 ohm ½ watt resistor 
1-5000 ohm to 8 ohm output transformer, 5 watt 
1-.02 mfd 600 volt capacitor 
1-1 Mh rf choke  

R-45/ ARR-7 Receiver Modifications 

						James M. Stueber W5UOZ-AF5UOZ
						8410 Flower Place N.E.
						Albuquerque, N. M. 


The R-45/ARR-7 receiver is a continuous tuning type covering the range of .55 mc 
thru 42 mc. It is a single conversion superhetrodyne circuit, with two tuned rf 
stages and one untuned preselector rf stage. The design is a modification of the 
well known Hallicrafters SX-28 receiver. The particular modified receiver was 
built under a Signal Corps contract by the Belmont Radio Corp. Inclusion of the 
described changes will provide the user with a good communications receiver, 
overcoming the major disadvantage in the original design, which is the lack of 
bandspread tuning. A schematic of the receiver and a coil layout for alignment 
purposes is included for those who may require them. Appreciation is extended 
to Mr. Amos Peters, AF5LHX, for supplying the receiver through the MARS Central 
Technical Net, thereby making these modifications possible. The changes described 
consist of the following: 

1. Addition of bandspread tuning and dial
2. Addition of necessary wiring to provide ac power supply operation
3. Addition of Send-Rev. Switch
4. Improvement of "S" meter circuit
5. Audio amplifier modification for speaker connection
6. Low impedance antenna input stage 

Bandspread Tuning and Modification for ac Power 

1. Remove the screws holding the cover plate which houses the tuning dial motor 
reversing switch and stop mechanism. Discard. 
2. Cut the wires from the motor reversing switch SW3 and remove the switch. 
3. Remove the stop mechanism from the main tuning dial shaft and discard. 
4. Remove all the knobs from the receiver and the screws from the power connector 
so the front      panel may be taken off.
5. Remove the main tuning dial by loosening the allen-head screws.
6. Remove the cover from the cast aluminum housing containing the 28V dc motor 
and associated       parts. 
7. Remove the filter, motor and misc. parts from inside the box.
8. Remove the fiber gear from the vertical shaft. This may be sealed with paint 
and may be       difficult to loosen, but with the proper size allen wrench and 
solvent to loosen the paint, it    will come loose. 
9. Remove the potentiometer R41 and bracket, located on the top rear of the 
chassis. Cut the wire    leads free near the potentiometer terminals and 
leave them in position.
10. Remove the wires from the POWER switch, tie together, solder and insulate. 
11. Remove the white wire with blue and orange tracer from the MOTOR switch. 
12. Remove the ground connections from pins A and C of receptacle SO-1. 
13. Attach the white wire, with blue and orange tracer, which was removed from 
the MOTOR switch,     to one lug of the POWER switch. 
14. Attach the other end of the wire which was attached to the motor, to pin C 
of SO-1 connector.
15. Cut the white wire with green tracer from the MOTOR switch and attach to the 
other lug of the POWER switch. Pins C and D of SO-1 now become the ac switch-wires 
to turn ae power off and on. The bandspread tuning knob will project out of the 
top of the case, since there is no front panel space available. 
16. A three-eighths inch hole is drilled in the top of the cast aluminum motor 
housing located 11/16 inch from the front of the case, and Ό inch from the left. 
A shaft bushing is installed  in this hole to accommodate a length of Ό inch diameter 
shaft and solid shaft coupling. The bandspread tuning will be engaged by throwing 
the MOTOR switch to ON, which engages the electric clutch in the tuning mechanism. 
When fast tuning is desired, the MOTOR switch is  thrown to OFF and tuning is 
accomplished with the TUNING knob.  Parts are now installed to provide de voltage 
to energize the clutch. 
17. Mount a 6.3 volt 1.2 amp. filament transformer under the chassis on the side 
lip near the SO-1 connector. Refer to Fig. 1 for the schematic of this portion 
of the modification. 
18. Connect one of the 6.3 volt leads of the transformer to pin 7 of 6SA7 tube V4. 
19. The center tap connection of this winding is not used, so cut the lead off 
close to the transformer winding. 
20. Remove the wire with blue tracer from the MOTOR switch. 
21. Connect the other 6.3 volt lead to one con- tact on the MOTOR switch. 
22. Connect the other switch contact to a con- ven,ient ground. 
23. The 500 ohm 5 watt resistor, the 1N93 diode, and 10 mfd capacitor are 
conveniently located near the transformer on a three lug terminal strip and wired 
as shown in Fig. 1. 
24. Connect the wire with blue tracer, which was removed from the MOTOR switch, 
to the junction of the 1N93 diode and the 10 mfd capacitor shown in Fig. 1. 

Addition of SEND-RCV Switch 

1. Drill two holes in the front panel which will accommodate a SEND-RCV switch and 
a pin jack (RCA Phono jack) for a keying relay connection. Due to the close 
spacings and limited panel space available, care must be exercised in location 
of the two holes. A ½ inch hole for the SEND-RCV switch is located 5½ inches 
from the left and 1 13/16 up from the bottom. A three-eighths inch hole for 
the pin, jack is drilled 6 inches from the left and 2 7/16 inches up from the 
bottom of the front panel. Refer to Fig. 2 for the schematic of the circuit.
2. Estimate the length of wire needed to go from pin A and B of SO-1 to the new 
SEND-RCV switch, a SPST toggle switch on the front panel, and install these leads. 
Do not solder these leads at the toggle switch at this time but solder at pin A 
and B of SO-1. 
3. Estimate two lengths of wire to run from the toggle switch to the pin jack. 
The toggle switch wire from pin A of SO-1 goes to the insulated lug of the pin 
jack and the other wire from the    toggle switch to the ground lug of the pin 
jack. Solder all these leads at this time.
4. The main tuning dial, front panel, and knobs may now be reassembled. 

Improvement of "S" Meter Circuit

It was found that the maximum deflection that could be had from the local 
broadcast signals was S-6 with the original circuitry. The following changes 
will improve the circuit. Refer to Fig. 3 for the revised circuit. 
1. Replace the 6SK7 tube V5 with a 6SD7 tube.
2. Change the 100 ohm resistor R22 tb 1000 ohms. 
3. Add a 1000 ohm resistor in parallel with the 330 ohm resistor at he 
cathode of V5.

Audio Amplifier Modification

  Refer to Fig. 4 for the revised circuit.
1. Remove the 68k resistor R39 located on the terminal board on the back 
chassis lip.
2. Tie a jumper wire across the two terminals where R39 resistor was removed 
and solder.
3. Remove the 7500 ohm 10 watt resistor R40 located in a cluster of four 
upright resistors under the chassis near the rear. 
4. Connect the two white wires with red tracers together after removing them from 
R40, insulate and solder them. 
5. Install a 5000 ohm to 8 ohm output transformer in the location on top of the 
chassis near the rear where the R41 potentiometer and bracket were removed. 
6. Remove the white wire with blue tracer attached to pin 3 of 6V6 tube V9. This 
wire leads to a .5 mfd capacitor C52 which is a metal can type and is the bottom 
unit of two stacked ones near the cluster of upright mounted 10 watt resistors. 
This capacitor may be removed or left in, as desired, and white wire with blue tracer 
may be removed from the harness or clipped short and left in. 
7. Install a wire from the other terminal of C52 to a lead of the 8 ohm secondary 
of the output transformer. (There is already a shielded wire attached to this 
terminal of C52, leave it there.)
8. Tie the other lead of the 8 ohm transformer secondary to any convenient ground. 
The white wire with black tracer which attached to the potentiometer R41 may he used 
for this ground. 
9. Connect one wire of the output transformer primary to pin 3 of 6VO tube V9. Do not 
solder.
10. Connect the other primary wire to pin 4 of OVO tube V9. Do not solder. 
11. Remove the 100k resistor R47 connected from pin 3 of 6V6 tube V9 to a terminal 
board on the rear chassis apron. Removal of this negative feedback resistor 
will result in greater output and better communications quality. 
12. Install a .02 mfd 600 volt capacitor from pin 3 to pin 4 of 6V6 tube V9 to 
reduce high frequency response. Solder the connections. Either headphones 
or a speaker may be connected to the PHONES jack. 

Low Impedance Antenna Input Stage

  Refer to Fig. 5 for the revised schematic.
1. Remove the wire lead from pin 5 to pin 3 of 6AB7 tube V12.
2. Connect a wire from pin 3 to pin I of this tube socket and solder.
3. Remove the .0082 mfd capacitor C79 from the terminal board on the underside 
of the chassis near the tube socket of V12.
4. Disconnect the center wire of the shielded antenna wire lead where it terminates 
at the terminal board on top of the chassis near the 6AB7 tube V12.
5. Ground the terminal from which this wire was removed.
6. Connect one end of a .0082 mfd capacitor to the free end of the wire removed 
in step 4 and add on a piece of wire to the other end of the capacitor, long 
enough to go through the chassis grommet. Connect it to pin 5 of the 6AB7 tube V12. 

  A typical power supply is shown in the schematic of Fig. 6. No attempt is made 
to design an exact supply for the receiver in this article, since most users have 
power supplies capable of supplying adequate power to the receiver. 
  A white wire with blue and black tracer will be left over from the modifications. 
It may be cut close and left in the harness under the chassis. 
  A slot is cut in the cover to allow it to be slipped over the bandspread tuning 
knob. This shaft may be cut short enough to allow a knob to fit flush with the 
case cover.
  A dummy knob is installed on the shaft on the front panel from which the stop 
mechanism was removed.
  A bandspread dial is attached with cement to a Ύ inch diameter knob and installed 
on the tuning shaft. This dial is reproduced in Fig. 7 as a guide only because each 
receiver will vary slightly in calibration and the,dial will have to be tailored to 
each case. A suitable pointer for the dial is made from a short length of solid #20 
wire which is attached under the screwhead of the nameplate.   . . . W5UOZ

Parts List

1-Shaft bushing for Ό inch shaft
1-Ό inch dia. shaft approx. 4 inches long 
1-shaft coupling for 1/4 inch shaft 
1-2 inch dia. bandspread tuning knob 
1-SPST toggle switch (SEND-RCV switch) 
1-Pin jack (RCA phono jack) 
1-Ύ inch dia. tuning knob (mount bandsproad tuning dial to this knob) 
1-6.3 volt 1.2 amp filament transformer 
1-1N93 diode 
1-10 mfd 150 volt elect. capacitor 
1-500 ohm 5 watt resistor 
1-8 Ing terminal strip 
1-6SD7 tube 
2-1000 ohm ½ watt resistor 
1-5000 ohm to 8 ohm output transformer, 5 watt 
1-.02 mfd 600 volt capacitor 
1-1 Mh rf choke