[ARC5] BC-348M

[Dennis Pharr]

Bill:

OK, you and Ken are obviously correct.  I was thinking the caps were
single-section caps fully insulated from the can - but that must not be the
case.  They are multi-section with the can used as common.  

And, by the way, all but one of them show signs of leakage, so I am going to
remove them and do the re-build on each one - which is a huge PIA and messy
to boot. But, I can't bring myself to just gutting them out and replacing
them with the modern caps in plain view.  I might consider doing that, but
hate to since this particular radio is almost completely original - the only
visible mod is someone in the past re-wired the filaments for 6.3vac. Also,
all the paper caps need to be replaced - which will not look original either
- so it really doesn't make sense to re-build the canned caps if all the
other replaced caps will be visible.  I'm not sure which way to go here - I
may just flip a coin.  

Thanks for the help.

73
Dennis
WD5JWY

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Bill Cromwell
Sent: Friday, December 20, 2013 12:58 PM
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] BC-348M

On 12/20/2013 12:43 PM, Dennis Pharr wrote:
> I am also currently trying to restore a BC-348P model and I have the exact
> same problem - a short across the B+ line.  I suspect the issue is a
shorted
> cap as well.
>
> Also, while tracing the wiring I've noticed a very odd thing - one of the
> six "canned" .5uf 250V caps (39-1) has buss wire shorting the terminals.
> The buss wire shorting the cap appears to be "as-built" since the
pictorial
> wiring diagram also shows this cap as being shorted.  I can't understand
why
> the designers would include a large canned capacitor in the design and
then
> specify it as shorted in the documentation.
>
> If it was a last minute design change (possibly during production runs),
you
> would think they would modify the design and leave out that Cap on
> subsequent production runs.
>
> It just seems to be a very odd thing, but maybe I'm missing something.
>
> 73
> Dennis
> WD5JWY
> Oklahoma City
>
Hi Dennis,

I don't have a BC-348 of any flavor. I do have some mil surplus radios 
and I have dealt with "can caps". Does your cap have the terminals 
shorted to ground or to the can by that buss wire or does it have 
terminals shorted together so that two sections of the cap are in 
parallel? Many to most of the "can caps" I have dealt with contain more 
than one cap, each with a separate terminal. The electrical common is 
the can itself and THAT is what is usually grounded. I'm redoing a 
Heathkit DX-100 and the can in the low voltage plate supply filter has 
exactly what you describe for two of the three caps inside.

I don't recall seeing that on the smaller couping and bypass "can caps" 
but most of them have multiple sections. Paralleling then, of course, 
adds the capacitance of each to the total capacitance. I don't know if 
that's what you have but combining the caps in parallel is the only 
thing that makes any sense to me.

73,

Bill  KU8H
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