[R-390] Variable caps in coils

[Jim Temple]

I found three variable caps in the coil line-up that had cracked wafers.  I
replaced the wafers with spares I had from other value variable caps.  This
cured the snapping and popping that was a problem with this rig.  Thanks for
the insights.

Jim

----- Original Message -----
From: "Norman Ryan" <nryan@intrex.net>
To: "Jim Temple" <jetemp@insightbb.com>
Cc: <r-390@mailman.qth.net>
Sent: Tuesday, April 30, 2002 1:54 PM
Subject: Re: [R-390] Variable caps in coils


> Hi, Jim,
>
> If I recall right, the variable cap ceramic bits aren't matched, but one
> piece or the other will have more or less metal visible when you take
> them apart.  That determines their capacity.  I think that's the piece
> which has the capacity printed on top.
>
> It's the base that's the "one size fits all," isn't it, and it's usually
> the piece that cracks.  I've replaced them with no problem.
>
> If you're feeling REALLY lucky, you can slip all of the variable caps
> apart and clean them carefully, being sure not to leave any residue in
> the ceramic.  However, you have to be very careful around fine Litz
> wire, because if you break one, it's a beast to repair.
>
> I did break a Litz wire once and tried the aspirin-tablet-as-flux trick
> and it worked like a charm.  For Litz wire to repair correctly, I think
> you have to connect as many strands as possible.  To use aspirin, take
> the hot iron to the tablet and melt a lot of it and transfer it quickly
> to the joint to be soldered.  The aspirin dissolves the insulation so
> you don't have to worry about trying to strip wire as fine as the hair
> on a gnat's eyebrow.
>
> This amazing cure supplied by someone on the r-390 list.
>
> After you're done, put a teensy dab of De-oXit on the bit that turns
> inside the three prong clip underneath so as cut out noise due to
> oxidized contacts.  THEN do your alignment!  :-)
>
> Good luck and 73...
> Norman
> KG4SWM
>
>
> Jim Temple wrote:
> >
> > I have one more "gotcha" that I hope the collective knowledge of this
group
> > can answer.
> >
> > I have found that a source of considerable noise, popping, and static
are
> > broken wafers (the wafer that sits between the rubber grommet and the
actual
> > cap).
> >
> > The question is:  Do both the cap and the brittle wafer work as a
matched
> > pair?  Is it possible, permissible, to retain the cap and replace the
broken
> > wafer from another cap of a different value?  Are all wafers created
equal
> > (from within the set in these radios)?
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