[ARC5] Need source for ARC 9121 control plug on MD-7 - NOT 9121...ADDED NOTE

Sat Apr 8 13:08:54 EDT 2017

Here's one added note:  The only place you should find a drawing showing plug 9121 connecting to a transmitter control box or modulator is only in a SCR-274-N or ARA/ATA manual.  Those manuals should be completely ignored when seeking info about the AN/ARC-5 transmitting system and its connections.  Otherwise notbing but confusion will result.  There are no transmitting components except dynamotor and antenna relay that are electrically interchangeable with the earlier systems, so the connection cables are all different as well.

Mike / KK5F

-----Original Message-----
From: Mike Morrow 
Sent: Apr 8, 2017 11:35 AM
To: J Mcvey , "ARC5 at mailman.qth.net" 
Subject: Re: [ARC5] Need source for ARC 9121 control plug on MD-7

Refer to Figure 8-55 sheet 5 and 6.

The 9121 is a 18-pin plug equivalent to the common PL-153-A.  It connects the RECEIVER control box C-38 to connectors on the RECEIVER rack MT-65 and on the front of VHF homing RECEIVER R-4/ARR-2.  The 9121 has nothing to do with the transmitters in the AN/ARC-5.

In the TRANSMITTER system, the 18-pin connector on C-29, 30, 30A requires plug 9585, as does the MD-7.  It has no common equivalent...a price of $75 or more would be likely.  The same has been historically true of the 9589 12-pin connector (NOT equivalent to the common PL-154-A), until Steve found a supply of those a few years ago.  IIRC, I paid close to $100 for one about 20 years ago when collector demand was high.  I was assembling a 100 percent correct system as shown in Figure 8-55 sheet 5 and 6, with R-4A/ARR-2 VHF Homing, R-26/ARC-5 HF Comms, R-28/ARC-5 VHF Comms receivers and T-20/ARC-5 HF Comms, T-23/ARC-5 VHF Comms transmitters.

Because of much greater rarity and costs of racks, mounts, and connectors, an authentic and all-correct  3-receiver/2-transmitter AN/ARC-5 system is much much more expensive and time-consuming to assemble than is an all-correct SCR-274-N system.  There were many more SCR-274-N sets built.  I started with SCR-274-N (including AN/ARR-1 homing), then AN/ARC-5 (including AN/ARR-2 homing), then ARA/ATA (including ZB-3 homing).  I have all three systems complete, but for the ARA/ATA, but I still use some electrically-identical SCR-274-N mounts and racks in lieu of the rare ARA/ATA equivalents.  These types of projects (except for the common SCR-274-N) can take multiple **decades** to find ALL the correct components...and much longer were it not for eBay keeping some of this oddball stuff out of landfills and metal scrap.

There is almost infinitesimal chance that you or anyone except Mike Hanz will ever have a C-29/ARC-5, as I explained its great rarity in my last posting below.  The C-30A is the correct control to use in any common historical AN/ARC-5 system (even without VHF units) but it will take hard searching to find one.  The most commonly available control in surplus is its predecessor, the pushbutton C-30.  It is pretty common and usually not too expensive.  Though it looks funky, it will serve perfectly as a control for two MF/HF transmitters in a kosher-wired system as long as they are designated #2 and #3 at the transmitter rack.  Those two 9585 plugs become the hardest items to find.

Read about one of Mike's C-29 units here:  http://aafradio.org/garajmahal/C-29.htm

A photo of the C-30/ARC-5 will not be found in your ARC-5 manual because it was soon made obsolete by the C-30A.  A good photo is here:

 https://airandspace.si.edu/sites/default/files/images/collection-objects/record-images/A19840315000cp01.jpg

The 9585 plug goes in the right connector.  The left connector and the four VHF channel pushbuttons are ignored when using the C-30 in lieu of a C-29 or C-30A in a non-VHF installation.

To find these items, including the MT-71, eBay will be a mandatory tool.  These things are not found at hamfests and swap meets.  But as practical advice, you could scrap every piece of your AN/ARC-5 gear, start from scratch building a SCR-274-N system, and most likely complete it before you'll find those few items you need for a proper AN/ARC-5 system.

Some have discussed modifying the common PL-153-A to the 9585, and the common PL-154-A to the 9589, but I know of no one who has done that.  I believe it would be harder than you think.

Good luck...good hunting!

Mike / KK5F

-----Original Message-----
From: J Mcvey 
Sent: Apr 7, 2017 9:28 PM
To: Mike Morrow , "ARC5 at mailman.qth.net" 
Subject: Re: [ARC5] Need source for ARC 9121 control plug on MD-7

Thanks Mike,
Looks like the C-29 (C-30A?????) is more like the BC 451 which is all I need anyway.
My ARC5 manual has a section where it calls out the part numbers for the cable assemblies and I thought it had the the 18 pin control plug as 9121, but Obviously that's not correct or I am misinterpreting what the numbers were for.
I've located just about everything for the modulator BUT the 9585 , 
Looking at the two versions of the control plug, I noticed that it is different by one pin! they moved pin 1 more to the center of the of the 9585 plug, otherwise they are identical.
Has anyone ever tried drilling an extra hole in a PL-153 and installing a contact there?Otherwise, after making an impression of the pattern, a plexiglass plug could be made .Looks like it will be a while before I find a real 9585 or MT-71, so desperate times call for desperate measures.

Btw , the RF coil jacks harvested from a destroyed receiver were a good  foundation for a ARC-5 transmitter socket.That was a great tip!

On Friday, April 7, 2017 1:09 PM, Mike Morrow <kk5f at earthlink.net> wrote:

 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 ?