[Milsurplus] BC-348Q Modification identification

[Matthew Paulonis]

After following this group of distinguished and highly knowledgeable
individuals, I must draw upon your vast experience to help me identify
where to begin with identifying the modifications effected to a BC-348Q
that was given to me a few years ago.

I have been spending my spare time both acquiring new and replacing
electrolytics in my vintage gear to keep them all in one piece and
operational for anothet lifetime. While busy reforming capacitors to be
reinstalled in a long dormant HP bench power supply, I was listening to my
348 on the top shelf of my bench. I don't think I was out of the garage for
15 minutes, but when I returned, the garage was nearly full of smoke. From
the smell of burned varnish, I could tell immediately that it was the 348.

This radio was very carefully refurbished and modified by KE0GN (SK) with
great care probably back in the 50's or 60's, and used fairly regularly for
the past 25 years before being passed along to me. The power supply has 2
transformers, a 12BW4 rectifier tube, assorted caps, chokes, and a 12 volt
vibratory all mounted on the original dynamo to plate. The power input to
this is a 9-pin "octal type" plug on the back of the radio so it was
capable of being powered by either 115vac or 12vdc. Before I go about the
forensics to try and locate the fault causing the "meltdown" of the large
power transformer, I would like to see if this was a standard modification
for which I could get a schematic so that I can try and rebuilt to its
original specs. Then from this I could study and try and determine what
could possibly have failed to cause the meltdown: there are no other signs
of excessive heat or bulged/popped capacitors within the entire chassis
with the exception of one 5 watt ceramic resistor in which one end lead had
lifted off of a terminal on the underside of the power supply plate. Any
ideas? My initial thoughts of possible failure points are:
a) failure/internal short of the rectifier tube;
b) overheating of the power transformer that was probably designed for 110
- 115vac, not the modern day 120;
c) a possible short within the 12v vibrator???;
d) a downright mystery.
 I have a selection of pictures of the damage if any of you care to see
(and perhaps help to identify the design). I guess then I could also use
suggestions for removing all of the melted varnish covering parts of the
chassis.

Thank you in advance.

Matt P.
W2NS
Houston, TX
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