[ARC5] BC453 repair

[Ian Wilson]

Most receivers of that vintage have B+ on one set of main tuning
capacitor plates. The RF amplifier is typically tuned grid, tuned
plate - and the plate tuned circuit is usually hot.

73, ian K3IMW



On Sat, Aug 23, 2014 at 1:06 PM, Tim <timsamm at gmail.com> wrote:

> Hi!  I've not seen them in my ARC-5 gear either - but both of my GRC-9's
> seem to produce them.  Drives me nuts... But you're right - unusual design
> to have B+ on plates and a whisker would have to be pretty stout to pass a
> bunch of milliamps for awhile...
> It's the journey!  LOL
> 73, Tim
>
>
> On Sat, Aug 23, 2014 at 6:30 AM, J Mcvey <ac2eu at yahoo.com> wrote:
>
> > I've never encountered "tin whiskers" in the arc-5 series before. It was
> a
> > pretty strong whisker at that, able to sustain the plate current without
> > burning out.
> > The cautionary tale here is to NEVER ASSUME that all variable gang caps
> in
> > receivers are connected to grids! I've fixed many antique receivers, and
> I
> > don't remember ever encountering a "hot" variable cap. Then again, maybe
> I
> > never had to deal with that circuit area for repair... I learn something
> > new every day...
> >
> >
> >   On Saturday, August 23, 2014 2:02 AM, Tim <timsamm at gmail.com> wrote:
> >
> >
> >  The dreaded Tin Whiskers?  Been there, done that...LOL
> >
> >
> > On Fri, Aug 22, 2014 at 7:07 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net>
> > wrote:
> >
> > I finally got around to fixing the "new to me, 28V virgin" BC453 today .
> > It started out pretty straightforward with a quick ESR cap check showed
> the
> > usual suspects  needing replacement ,such as the .22X3 ,etc. I replaced
> the
> > 10W diver resistor that someone has removed , lubed up the dynamotor and
> > applied 24 volts with anxious anticipation of hearing some beacon
> stations.
> > All I got was a brief cackling, then silence- NO JOY!
> >
> > I pulled the 12K8 grid cap and was encouraged when I was able to get
> noise
> > by touching the cap. When the cap wire was put back, it went silent
> again.
> > I thought it was the RF stage but everything checked out.
> >
> > It turned out that the oscillator was dead, in fact I was surprised to
> > find the osc plate at 2.6 ohms to ground! Why, might you ask? They plate
> > tune the oscillator stage, so there is B+ on the gang variable! There
> must
> > have been a tiny speck of metal shaving in there somewhere which I could
> > not see, before or after blowing it out with air which cleared the short.
> >
> > Once that was done the receiver was howling away with a 50 microvolt
> > signal lead laying on the bench about 3 ft away and no antenna.
> > I've got some more cleaning and tweaking to do, but I'm a happy camper
> > now, knowing that the radio is basically in very good shape.
> > ______________________________________________________________
> > ARC5 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/arc5
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:ARC5 at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> >
> >
> >
> >
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>