[ARC5] [Milsurplus] BC-348 PSU questions

[Ian Wilson]

Mike - thank you for the link: hadn't seen that one before. Tons of good
stuff there!

I rebuilt the power supply, replacing diodes, capacitors, etc. Kept the
transformer and
choke. Then I dismantled it and measured the power transformer HT windings.
Clearly
something is wrong. Am going to test using a PSU I have used before (with
floating
B-) and then look in stash of iron for a suitable transformer.

73, ian K3IMW


On Tue, Sep 29, 2015 at 4:26 PM, Mike Everette <radiocompass at yahoo.com>
wrote:

> 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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