HW-101 erratic on 80 and 40 metets

[CyberGeezer]

[As you'll see, this is really a question about variable capacitors.]

I've been using this HW-101 for about a year now, during which time I knew
that it was flaky on 80 and 40, but that didn't used to matter because I
didn't have antennas for 80 and 40.  Now I've put up more antennas and I
want to get it working on 80 and 40.

I've identified the problem component to be C421A.  C421 is the more forward
of the two variables that are operated by the DRIVER PRESELECTOR knob.  It
tunes the driver grid on transmit and the rf amp input on receive.  It has
two sections--  C421A (200 pf.) and C421B (20 pf).  C421B is always in the
circuit.  Bandswitch section 3R puts C421A in the circuit only for 80 and
40.

The problem with C421A is that its rotor plates intermittently short to its
stator plates (verified with ohmmeter).  The shaft does not appear to be
bent or misaligned, the bearings do not appear to be loose, and no plates
appear to be bent.  (And the O-ring drive belt is not too tight.)

My question --  I'm not really sure what my question is --  the plate
spacing is so small that there's just barely room for the rotor plates to
get in between the stator plates, so what should I look for that's supposed
to guard against their making contact?

This is probably a dumb question, but do they employ some kind of dielectric
coating on the plates in case there's contact?

All ideas and suggestions will be considered.  It probably is impossible to
obtain a replacement capacitor, and even if I had one I would not relish the
prospect of replacing it--  I'd have to take out (unsolder) all the
bandswitch sections . . .



73 de W2GERry

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