[Milsurplus] ARC-5 or SCR-274-N ID Question

[Mike Morrow]

>I have a somewhat cosmetically challenged black wrinkle Command Receiver
>that is lacking all data plates, top and bottom covers, and has the usual
>ham mods. The dial range is 1.5 M to 3.0 M.
>
>Am I correct in assuming this means that it is an R-20 from the ARC-5
>family, and is NOT part of the SCR-274-N?

There's only two possibilities for a 1.5 to 3.0 MC receiver, and the
R-20/ARC-5 is NOT one of them:

(1)  CBY- or CCT-46104, part of ARA (and RAV).
(2)  R-25/ARC-5

There was NO SCR-274-N receiver that covered this range.

The easiest way to distinguish between the two possibilities from
the outside of any given receiver in this frequency range is to check
for a yellow "S-in-circle" stamp on the front near the tuning spline,
and a small MC/DATES data plate to the right of the front panel adapter
space.  These two distinctions should appear on all AN/ARC-5 
"communications" receivers (R-25, -26, -27), indicating stability
modifications for lock-tuned service and providing a data plate to
indicate the lock-tuned frequency to which the unit should be set.
The earlier equivalent ARA CBY/CCT-46104 through -46106 units will
never have these.  Only very rarely will the R-25 to -27 be missing
them.

Even more obvious than THAT is the tube line-up.  The second IF stage
tube is a 12SK7 in the ARA.  It is a 12SR7 in the AN/ARC-5.

There are a fair number of other circuit differences between an ARA and
an AN/ARC-5 (such as AVC circuitry in the AN/ARC-5). 

Mike / KK5F