[ARC5] Why is the ARC-5 Tx rack so hard to find?

[Mike Morrow]

I will respond, since the questions you ask appear prompted by my last post.

> Uh-oh I ASS-U-med that the MT 71 used the same connectors as the
> FT-226 but may be wired differently. no?

Definitely NOT!  Have you referred to the very freely available instruction books for SCR-274-N and AN/ARC-5?

Recall that I stated that  O N L Y  the dynamotor and antenna relay may serve in all three of the ATA, SCR-274-N, and AN/ARC-5 transmitter systems.  The AN/ARC-5 is sufficiently different electrically that different connectors were used in critical locations in order to prevent ATA components from being installed in AN/ARC-5 systems, and vise-versa.  The SCR-274-N components were just like the ATA units when wired for low-z AF.  Connector differences:

BC-456-* to FT-226-A:       Two 12-pin PL-154-A -> Common
MD-7/ARC-5 to MT-71/ARC-5:  Two 12-pin A.R.C. 9589 -> SCARCE (Steve has these)

BC-456-* to BC-451-A:       Two 18-pin PL-153-A -> Common
MD-7/ARC-5 to C-30A/ARC-5   Two 18-pin A.R.C. 9585 -> VERY SCARCE

The AN/ARC-5 control boxes have no AF connections.  Those are made using audio jack box J-16/ARC-5:

MD-7/ARC-5 to J-16/ARC-5:   Two 8-pin A.R.C. 9821 -> UNCOMMON

All the other connectors used in a typical AN/ARC-5 are common to the SCR-274-N and are easily-obtained PL-1## equivalents.

The most commonly used AN/ARC-5 transmitter control was the C-30A/ARC-5.  can serve in MF/HF-only, MF/HF/VHF, and VHF-only systems.  As such, the MF/HF-only C-29/ARC-5 transmitter control box is very very rare.  It is similar to a BC-451-A minus key, mic and key jacks, and different connector.  The C-30A/ARC-5 is somewhat difficult to find.  The earlier larger awkward pushbutton C-30/ARC-5 can be be used instead...it's much easier to find.  It was considered obsolete well before WWII ended, so there are a lot of NOS units around.

> I also thought that the BC-451 and cable/plug  config might work with
> both the BC-456 and the MD-7.

Definitely NOT!  Refer to the instruction books.

> Got lucky and Ebay steve even had those local operation shorting plugs
> for the receiver rack.

That's the MX-2/ARR-2 designed to be used with the R-4*/ARR-2 in a single-receiver MT-7/ARR-2 rack which has no AF bus A or B select switch.  When installed at the back of an AN/ARR-2 or AN/ARC-5 receiver rack, it connects 28 vdc to the rack's receiver connector AND connects the AF output of the receiver to AF bus B, regardless of what bus is selected at the front of the rack.  (MT-7A/ARR-2 and all AN/ARC-5 and SCR-274-N receiver racks have those switches.)  It you don't want that AF bus connection, open the MX-2 and lift the connection between pins 2 and 8.

> If I'm wrong please educate me!

I've tried.

> I have most of the ARC-5 items collected, but
> I haven't got down to the nitty-gritty yet.

Obviously.  You have a VERY LONG WAY to go with AN/ARC-5.  Consider the SCR-274-N instead.

> Do I need to start hunting for more obscure stuff?

Er...obviously.  Your SECOND priority.

The FIRST priority is to GET AND READ THE MANUALS!

The ARC-5 Wikipedia article has links to SCR-274-N and AN/ARC-5 instruction books.  If you are tempted to print them out, it'll be cheaper in terms of materials like printer ink cartridges to purchase the excellent "better than original" copies that Robert/WA5CAB sells.

Mike / KK5F
BTW:  It's customary and courteous to sign postings to this list.