[ARC5] Need source for ARC 9121 control plug on MD-7

[Mike Morrow]

There are ONLY TWO components in the entire AN/ARC-5;transmitter system that are electrically interchangeable with analogous components in the ATA or SCR-274-N:

1.  Dynamotor DY-8/ARC-5
2.  Antenna Relay RE-2/ARC-5

That's it...no ifs ands or buts.  The only two.

WRT transmitter control boxes, there are three in the AN/ARC-5, with the C-30A being the one most commonly used by the service:

1.  C-29/ARC-5 Provides controls for four MF/HF transmitters only.  It is similar to the CBY-/CCT-23243 and the BC-451-A transmitter control boxes except uses 18-pin ARC 9585 plug; has no key; has no mic or key jacks.  Not many were made because the typical AN/ARC-5 installation required controls for VHF components.

2.  C-30/ARC-5 Provides control with UK-style selector pushbuttons for two MF/HF transmitters and one four-channel VHF transmitter.  Provides VHF channel selection for both T-23 (or T-126) AND R-28.  Has no key.  Has no mic or key jacks.  Uses plug 9585 as for C-29, plus 12-pin plug 9122 to control VHF channel switching.

3. C-30A/ARC-5  Provides control with conventional rotary switches for four MF/HF transmitters and one four-channel VHF transmitter.  Other details similar to C-30, except emission switch is normally set to VOICE under a screw-held cover.

The C-30 is large, heavy, mechanically complex, limited versatility, and doubtless very expensive, compared to the C-29 and C-30A.  The C-30A is the same size as the C-29, and serves perfectly as direct replacement of a C-29.  That explains why there was no need for the C-29 even in non-VHF installations.  The C-29 is very rare as a consequence.

The C-30 is very common in unused condition as a result of stock left over when it was soon replaced by the far superior (more functional, more versatile, simpler, smaller, lighter, and less-expensive) C-30A.  All mention of the C-30 was removed from AN/ARC-5 documentation even while the rare C-29 remained.  It's hard to find even a schematic.  Good riddance, and a pox on its Rube Goldberg school designers!

The C-30A is the most desirable unit for any re-creation of an authentic WWII AN/ARC-5 system, but it can be somewhat hard to find.

Any AN/ARC-5 system that used only one MF/HF transmitter and no VHF (such as one on training aircraft) often eliminated the control box entirely.  The wiring harness makes the connections required for VOICE and to energize the one transmitter's select relays.  The PTT switch was the pilot's only transmitter control.

The AN/ARC-5 uses some plugs that can be difficult (or VERY difficult) to find, compared to plugs for the ATA and SCR-274-N.  These have NO "PL-###" equivalents:

ARC 9585  18-pin  MD-7 to C-30A
ARC 9589  12-pin  MD-7 to MT-71 (transmitter rack)
ARC 9821   8-pin  MD-7 to J-16 or J-22 (phone/mic box)
ARC 9488   3-pin  J-16 or J-22 to throttle switch

Plug numbers given are for the proper open-harness wiring.  The older less-used  conduit-style plug numbers are different.

For the best insight to how radically different the AN/ARC-5 system compares to the simple era of ARA/ATA and SCR-274-N, refer to the typical three-receiver/two-transmitter AN/ARC-5 system shown in Figure 8-55 sheets 5 and 6 of the Maintenance Instructions:

 http://tonnesoftware.com/Manuals/ARC5manual.pdf

Mike Hanz has excerpted the entire Figure 8-55 here:

 http://aafradio.org/docs/ARC-5-HF_manual_Figure_8-55_sheets.html

Compare that with the closest system in the earlier sets.  Here, SCR-274-N:

 http://bama.edebris.com/download/military/scr274/TO%2012R2-3SCR274-2.pdf

The AN/ARC-5 design sought to eliminate all unnecessary pilot controls like frequency tuning dials, emission select switches, keys, and mic and phone jacks on control boxes.

So yes...there is a lot of differences mechanically and electrically between any AN/ARC-5 control box and one for the earlier systems.

Mike / KK5F


-----Original Message-----
This one is a different configuration than the 18 pin PL-153 for the BC-456Although Steve on Ebay has them listed as the same part. 

I assume, then,  that a BC 451 tx control is not compatible with the ARC-5 C-30 since it probably uses the same style plug as on the modulator? Maybe electrical differences too ?