[ARC5] [Milsurplus] BC-348 PSU questions

[Mike Everette]

Ian et al,
A really good source for info on the BC-348, including a proper AC power supply, is the following web site:
www.radioblvd.com
There is a very comprehensive article here on rebuilding/restoring the BC-348 (and many other types of receivers).
A lot -- probably the vast majority of -- AC supplies "hamstered" into BC-348s back in the day were not well designed and were poorly constructed. (I speak from direct experience; I've worked on a bunch of BC-348s-- many had some crazy hack-jobs done on them before I saw them -- for hams and Civil Air Patrol members over the years.)  It sounds as if your problem could indeed be a rectifier diode (if silicon diodes are used), or just a bad filter cap.  Maybe the filters -- one or both -- are grounded to the chassis instead of to the power transformer center tap. 
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...?).  Study the power supply schematic on the web site, read the info, and most if not all your questions will be answered.
The bias produced in the receiver is for the audio output stage, and for the mixer.
NOTE: The negative lead for the B plus does NOT come out to the connector on the back of the radio.  The connection is made to the terminal strip on the dynamotor unit, inside the receiver.  In the original dynamotor supply, the negative side of the dynamotor output was left floating and brought out to one of the terminals.
Good luck with it.  The BC-348 is a great receiver.  You'll love it!
73
Mike
WA4DLF
      From: Kenneth G. Gordon <kgordon2006 at frontier.com>
 To: Ian Wilson <ianmwilson73 at gmail.com> 
Cc: ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Monday, September 28, 2015 1:50 AM
 Subject: Re: [ARC5] [Milsurplus] BC-348 PSU questions
   
On 27 Sep 2015 at 20:07, Ian Wilson wrote:

> The center-tap of the transformer and the -ve side of the caps all go
> to one point. This point connects to the B- connection (not the chassis) of the
> receiver.
> 
> There is a hand-written note that says 'loud hum' so perhaps there is more
> to what's going on here than just the PSU wiring. Will look tomorrow in more
> detail.
> 
> 73, ian K3IMW

Didn't you say it uses solid-state rectifiers, i.e., diodes?

If so, undoubtedly one is bad.

Ken W7EKB
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