[Milsurplus] output - Redux!

[Mike Morrow]

I wrote:

>Transformer part number 6308 is the transformer used in the SCR-274-N
>receivers BC-453-A, BC-454-A, and BC-455-A.  It has a 4000:1800 turns
>ratio, and the secondary is untapped.
>
>Transformer part number ES-691027 is the transformer used in the 
>SCR-274-N receivers BC-453-B, BC-454-B, BC-455-B, and BC-946-B.
>It has a 4000:1800 turns ratio, and the secondary is tapped at 1325 turns.

(Actually, it's 475 turns, see below.)

>Transformer part number 5631 is the transformer used in *both* the ARA
>and the AN/ARC-5 receivers.  It has a 4000:500 turns ratio, and the
>secondary is untapped.

I should make this topic painfully even more complete by adding the following:

Transformer part number ESO-692327-1 is the transformer used in the AN/ARR-2 receivers.  It has a 4000:1800 turns ratio, and the secondary is tapped at 1325 turns.  (Actually, it's 475 turns, see below.)

Transformer part number ES-692327 is the transformer used in the VHF R-28/ARC-5 receiver.  It has a 4000:1800 turns ratio, and the secondary is tapped at 1325 turns.   (Actually, it's 475 turns, see below.)

This 692327-type transformer appears to be identical to the SCR-274-N 691027-type transformer except that it does not have a primary center tap.  Although the parts description of both of these transformer types says that the secondary is tapped at 1325 ohms, this is apparently from the top (hot) end and NOT the bottom (grounded) end of the secondary!  DC resistance readings confirm this.  Thus, the actual number of turns to ground on the secondary low-z tap is 1800-1325=475 turns.  This makes the lo-z turns primary-to-secondary turns ratio equal to 8.42 (impedance ratio 70.1).  

Since Western Electric was the most prolific source of SCR-274-N, R-28/ARC-5, and AN/ARR-2 receivers, it's logical that essentially identical transformers would show up in these three systems even though there's a very slight difference in turns ratio in the other AN/ARC-5 receivers (4000:500 vs. 4000:475).

With respect to nominal rated output impedance, there's further inconsistency.

The VHF AN/ARC-5 manuals say that the R-28 may be connected for 8000 or 600 ohm output.  The SCR-274-N manual says that the B-suffix receivers  may be connected for 8000 or 600 ohm output.  But...the AN/ARR-2 manuals say that the AN/ARR-2 (using the same transformer as the R-28 and SCR-274-N) may be connected for 4000 or 300 ohm output.

This has listed details of about every type of ARA, SCR-274-N, AN/ARC-5, and AN/ARR-2 receiver output transformer that I have come across.  I wonder if I've missed one?

Mike / KK5F