[ARC5] BC221 etc

[Mike Hanz]

Kevin Heyward wrote:

> I am a recent subscriber to the list and was interested to see Dave Merrill's post with 
> the pictures of the B-29 radio equipment. On top of the ART-13, on shock mounts there 
> appears to be a BC-221 frequency meter. The case of this one appears to be a shortened 
> version. Is it an original case and if so what is the model number of this BC-221. The dial 
> lock is the same as on my BC-221-J but different from my BC-221-M which has the lock in 
> the 9 o'clock position of the dial. 
> 
> If this is a special aviation model, what are the power supply arrangements? Where is the 
> power inlet connector and is it the same as on the LM-10? 

This is a TS-164/AR encased -221, though it is occupying a space 
normally reserved for the SA-22/ART-13 LF antenna switch or CU-25 LF 
antenna tuner.  This was the AAF's answer to the useful airborne shock 
mounted LM case that the Navy used for years before the TS-164's 
appearance, and accommodated any of the BC-221 variants, so I can't tell 
you which BC-221 suffix this particular one represents.  The manual 
(such as it is) indicates it deriving power from the BC-348 dynamotor. 
No power switch in this - it senses B+ being available from the BC-348 
and then turns its own filaments on, there being no switched 28v 
available from the BC-348.  There's a slightly better view of one at 
http://members.cox.net/aafradio/flight%20deck/b29.htm, along with a 
brief description.  Power is delivered via a small 4 pin Jones plug, 
which is somewhat surprising as there is no positive retention mechanism 
for this kind of plug and it can vibrate out under certain conditions. 
A complete TS-164 was delivered with a pigtail for connection to the 
connector on the BC-348.  Incidentally, the case also accommodates the 
VHF -221s (the TS-323 et al) quite nicely.

> I also have an  LM-10 which is in excellent original condition both inside and out but lacks 
> the calibration chart. 

Doesn't make it useless, but does require cobbling up an equivalent at 
the frequencies you're interested in.  One from any other LM won't have 
the same calibration, though it is possible to tweak it into compliance 
for a narrow band of frequencies.

> I am also looking for a copy of the handbook or at least the circuit for the LM-10. 
> Does anybody have anything on file that could be uploaded to the reflector?

I think I have that manual down in the basement - will try to scan it in 
the next couple of days.

> Apologies for all the questions but I am keen to find out about this particular BC-221.
> Maybe it is just a one-off modification.

Fairly common after the war, though it's pretty difficult to find one 
that still has the power sensing and VR tube circuitry in the rear of 
the case.

Best 73,
Mike