[ARC5] [Milsurplus] 1930s Air Corps Equipment

[Mike Morrow]

It has been asked yet again:

> Can anyone provide information (and preferably photos) of the aircraft
> radio system consisting of:
> BC-AA-179 Receiver
> BC-AA-180 Transmitter
> BC-AA-182 Control Box
> MC-125 Tuning Unit
>
> I don’t know what system these were a part of, but they were standard GFE
> in the Curtiss A-12 Shrike attack plane (developed 1933; in service 1934-41)
> and may have equipped the Boeing P-35, which was of about the same vintage.

I provided you with the answer to your present question four days ago, with this posting:

 http://mailman.qth.net/pipermail/milsurplus/2016-August/051500.html

My reply contains this excerpt of a posting with identical question posted a few days before that on the ARC5 list:

>> Also the Army had  a plane called the "Shrike" which had radio
>> capability. I wonder what those radios were?
>
> You refer to the Curtis A-12, a 1933-entry aircraft.  In 1933,
> the likely command set would be the 1932 SCR-AA-183 (first of
> 21 different SCR-A*-183/283 sets):
>
> SCR-AA-183:  Receiver BC-AA-179, transmitter BC-AA-180.

The SCR-AA-183 is the very first of the 21 different models of the SCR-A*-183/-283 USAAC command set radios that appeared between 1932 and 1942.  This earliest model looks nonetheless similar to the latest models like the 1942 SCR-AR-183, for which pictures are easily found.

The following is an excerpt of my work-in-progress documenting all 59 military radio sets that used a receiver similar to the original A.R.C. Model D:

SCR-AA-183   14 VDC [Items with * are also part of SCR-AA-192, SCR-202]

Made by Aircraft Radio Corporation, Contract SC-132311, 06-25-1932

BC-AA-179*  Receiver
BC-AA-180   Transmitter
TM-AA-153*  Junction Box
BD-AA-69*   Dynamotor Unit, 14 vdc IN, 235 vdc OUT
BC-AA-181*  Receiver Control Box
BC-AA-182   Transmitter Control Box
Receiver Coil Sets:
C-97   224- 448    C-115  6200-7700
C-101 2500-4700    C-119  3050-3800
C-102 4150-7850
Transmitter Coil Sets:
C-115  6200-7700
C-119  3050-3800

RECEIVER:            Tuned Radio Frequency
Modes:               KEY (A2)/MIC (A3) (no mode switch)
Receiver Stages:     RF AMP1, RF AMP2, RF AMP3, RF AMP4    4x(VT-36 –> 36)
                     DETECTOR/AGC (diode connected)          (VT-37 –> 37)
                     AF AMPLIFIER                            (VT-38 –> 38)
Loop Connection:     None
AUTO/MANUAL Gain:    AGC is applied to first two RF amplifier stages.
                     MGC is applied to first three RF amplifier stages.
                     In AUTO, INCREASE OUTPUT changes receiver audio output
                     and transmitter side-tone level in headphones.
Screen Volt Divider: In dynamotor unit
AF Output Impedance: HIGH or LOW selected by internal wiring
AF Low Pass Filter:  In AF transformer primary

TRANSMITTER:         Master Oscillator-Power Amplifier
Modes:               REC(eive), (transmit) KEY (A2), (transmit) MIC (A3).
Power Output:        1.5 watts
Transmitter Stages:  MASTER OSCILLATOR                       (VT-25 –> 10)
                     POWER AMPLIFIER                         (VT-25 –> 10)
                     PA PLATE MODULATOR                      (VT-52 –> 45Spl)
                     TONE OSCILLATOR                         (VT-25 –> 10)

- The transmitter coil set consists of two physically separate coil assemblies:
    Master Oscillator – Plug-in, but requires removal of transmitter case
                        to change.
    Antenna           - Plug-in.  May be removed from the left side of the
                        assembled transmitter to adjust antenna load coil.
- Coils C-101 and C-119 are not normally supplied.
- The SCR-AA-183 is the earliest production military Model D set.
- This is the only receiver in the series that uses tube VT-36 in the RF
  amplifier stages.
- This is the only transmitter in the series that does not provide CW (A1)
  transmission.
- This is the only transmitter in the series that does not provide push-to-talk
  transfer from receive to transmit.  The REC-KEY-MIC switch on transmitter
  control box BC-AA-182 is used to switch between REC(eive) to (transmit) KEY to
  (transmit) MIC functions.  The key is part of control box BC-AA-182.
- There are no receive-transmit circuit or antenna switch relays in this system.
- Separate receive and transmit antennas are required.
- This set was intended to use keyed A2 MCW (KEY) rather than A3 voice (MIC) as
  the principal operating mode.  Thus the transmitter mode/transmit-receive
  switch first selects KEY from the REC(eive) position, and then MIC.
- Dynamotor BD-AB-69 may be used in place of BD-AA-69.

As the design particulars above indicate, this was a very limited-capability set.  By the end of 1934 there were three other sets in the series that offered a more performance:

SCR-AC-183:  Receiver BC-AB-199, transmitter BC-AB-200
SCR-AD-183:  Receiver BC-AD-199, transmitter BC-AD-200
SCR-AB-183:  Receiver BC-AD-219, transmitter BC-AD-219

I suspect that the SCR-AA-183 would have been replaced in short order when more versatile sets were available.

WRT to your request that this information be provided "off-list", that defeats entirely the purpose and value of lists like this.

Mike / KK5F

PS:  I'm pretty sure that this posting will again fail to gain notice, but at least I have made the effort (again).  :-)