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

[W7QHO at aol.com]

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