[Milsurplus] "Correct" fuses for BC-342??

[Barry Hauser]

It's funny -- as I'm catching up on the posts, there's a program on the
History Channel about "Digging for the Truth" -- archeological digs to check
out the Old Testament.  Meanwhile, on the Hallicrafters list, what do I
find?  A discussion about cubits.

On this list (Milsurplus) there's this thread on the various configurations
and possible intentions of the designers of the filament circuit
and fusing of the BC-312's, 342's, etc.  The Tech Manuals in this case are
much more recent, about 60 years old, but still a bit of a mystery.

Then, the "BC" prefix helps round out the coincidence.

Barry

----- Original Message ----- 
From: <W7QHO at aol.com>
To: <beaconeer at elite.net>
Cc: <milsurplus at mailman.qth.net>
Sent: Tuesday, May 25, 2004 2:40 AM
Subject: Re: [Milsurplus] "Correct" fuses for BC-342??


> In a message dated 5/25/2004 12:52:28 AM Eastern Daylight Time,
beaconeer at elite.net writes(in part):
>
> > In the BC-342 there is another
> > odd thing about the filament fusing.
> >
> > The center tap of the transformer is grounded.  In one side of the
> > transformer there is a 10 Amp Fuse, in the other side, nada!  If there
were
> > to be a short in the unfused side the power transformer
> > would probably do a
> > meltdown, UNLESS the primary fuse blew first.
>
> Probably a holdover from the BC-312 which came first.  In the 312 design
the tubes were wired series/parallel to accommodate the 12vdc primary supply
and this was carried over into the 342. The side of this circuit that is
unfused in the 342 is grounded in the 312.  Somewhere in the development of
the 342 it was decided to balance the AC feeding the tube series/parallel
string probably as a hum reduction measure and the transformer in the RA-20
power supply included a center-tapped 12 volt winding. A second 12 volt
winding was also included to feed the pilot light string, one side of which
was grounded, and also the oscillator heaters in the earlier 342s.  This
made the 342s and 312s identical electrically and the AC and DC power
supplies interchangeable.
>
> Actually, there are a couple of minor differences in the BC-342 and 312
receivers besides the nameplate.  The lead bringing 12 vdc from the pilot
light circuit over to the SPEAKER 2ND AUDIO jack in the 312 is omitted in
the 342.  Also, capacitor CA276, a triple 0.1 mfd bathtub unit is in a
different location in the 342 to avoid overheating by the RA20 (from TM
11-310).
>
> Dennis D.  W7QHO
> Glendale, CA
>
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