Barry Mann wrote:

In another reply, Mark has the right answer. If you look closely at the
tuning capacitor (the thing attached to the dial cord that looks like
an egg slicer) you'll see some very fine metal "whiskers" are shorting
the plates together. This is a standard mid-life crisis for analog
tuners.

Pretty much what I expected. I wasn't sure about whiskers (I'd heard
about them long ago, but couldn't remember in what context), but I
was (and am) expecting something shorting the plates.

I'll also use a tiny drop of contact cleaner at each of the bearings.
(This is not an attempt to lubricate or clean the bearings. The
japanese use a little clip beside each bearing to make good contact
with the moving vane. I'm just making sure that the contact is clean
and solid.)

Good point--thanks!

Sometimes the trimmer capacitors (the screws on the main tuning
capacitor) will degrade and become intermittent. I've never been able
to develop a log term solution for that one. Sometimes, I can
temporarily improve the situation by injecting cleaner and rotating
them, but the problem usually returns. (You should not do this, unless
you are prepared to tweak the alignment) The whiskers will return in a
few years, but you can blow them out again.

So what DOES cause the whiskers to grow? And is there any hope of
aligning a tuner with typical bench equipment (DVM, scope, signal
generator)?

Thanks,
Colin