[MRCA] [Milsurplus] BC-223 Transmitter- Anyone?

[mac]

No experience here with getting at the cap in question.  The following  
originally posted on Yahoo Groups (BC-223) Aug. 1, 2009

"Restored one of these for the Ft. MacArthur Museum in San Pedro, CA.
Noted some odd choices in the design of this unit, the first being the
use of 20W wire-wound resistors where a 1W unit would have been
conservative. Also, the biasing of the VT-63 speech amp tube was all
wrong and allowed only about 50%modulation in the positive direction.
Replacing resistors 20 and 21 with a 15K pot and taking the bias off
the wiper allowed adjustment for symmetrical, 100% modulation.

The set FMs in typical MOPA fashion. Was able to virtually eliminate
this by slightly over neutralizing the PA, the same trick that works
with the BC-375. The sweet spot is very sharp, BTW, and easy to miss
the first time through.

Also found the oscillator does not provide enough drive to the PA for
phone use when operating xtal controlled.

Found 100pf series cap about right for matching a 50 ohm load (as
reported by others).

The SCR-245 was used to provide communications backup for the railroad
guns installed at San Pedro during WW2 and earlier."

Dennis D.  W7QHO
Glendale, CA


**********************


On Apr 9, 2014, at 6:40 AM, David Stinson wrote:

> Any experience restoring a BC-223 transmitter?
> I have one with issues in the big tuning capacitor.
> Does anyone know how to get at this variable?
> It looks like they started with the bottom plate,
> installed the big variable and other parts, then built the  
> transmitter up around it!
>
> 73 Dave S.
>
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