[R-390] Variable caps in coils

[Norman Ryan]

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)?