[Milsurplus] [ARC5] BC-348 PSU questions

[WA5CAB at cs.com]

Two comments - the metal box that most hams always call the "output 
transformer" is properly called the "audio pack".  In the BC-348-JNQ, it contains 
the audio output transformer and the B- filter choke.  I don't know what the 
DC resistance of the choke in this pack is as I don't have any left and 
didn't think to measure it when I did.  However, it may not be the same as the 
one in all of the other models.  The choke in the JNQ pack does not go to 
chassis.  It goes to two 50 ohm resistors in parallel, both of which go to 
chassis.  The bias for the 6K6 audio output tube is taken across the choke and 
resistors.  Connected across the two resistors alone is one of the grids in 
the 6SA7 1st DET/HF OSC.

In all other models of the BC-348 and in all models of the BC-224 the Audio 
Pack also contains a .05 ufd 400 V capacitor.  The other end of the choke 
goes to chassis, and the grid bias for the VT-152 Audio Output tube is taken 
across the choke alone.  The mixer does not have fixed bias.  The resistance 
of the choke is 300 ohms.  And the capacitor is switched across the AGC 
line when the BFO is turned on.

Unfortunately, the choke in all other models except JNQ goes to chassis 
internally (inside the audio pack).  So you can't use  these audio packs in a 
JNQ.  I have never found time to open up one to see whether or not the choke 
could be easily un-grounded so that you could use the pack in a JNQ.  I have 
many of the audio packs for the HKLR and the EMOPS but none left for the 
JNQ.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 09/29/2015 20:24:38 PM Central Daylight Time, 
k1lky68 at gmail.com writes: 
> >>
> >>NOTE WELL: For an AC supply in this receiver, the negative side of the
> >>supply must be left floating.  It goes to ground through a bias filter
> >>network which is part of the audio output transformer (I hope yours 
> still
> >>has the original transformer...?). 
>