HELP: Knob inserts

[Ian Webb]

I've just finished the electrical restoration of the first of two
NC-125s that I'm working on (plus a parts receiver.)

The National main and band spread tuning knobs for the NC-125 have
chrome inserts over about the outer 1/2 of the knob, stopping just
inside an outer plastic ring area on the periphery of the knob.

I have 3 different NC-125s and all have quite poor and in some instances
extremely rusted inserts.  The inserts are ALL buckled and thus even if
they could be cleaned of the grime and rust would look strange as they
are not flat anymore.

In looking closely at the backs of the knobs it appears as though with
age they have become out of round.  They are not solid and have three
small solid areas with only a shell between them on the outer edge.  The
portions of the knob between the ribs are definitely flattened.  Since
the front of the knob IS solid it isn't noticeable form the front, but
I'm wondering if this is causing the knob to flex a bit and buckle the
inserts?

*  Has anybody a good way to remove the inserts without destroying
them?  Heat? Cold?  Solvent?  I've pried out one of the badly rusted
ones and it eventually will lift but I'm afraid I'll damage the best
inserts which might be usable though not as nice as I'd like.  The do
have to be glued back in flat though.

*  Has anybody experimented with replacements for the chromed ring of
the insert?  Metalized mylar?  OR???  Something at a hobby shop?  If so,
how do you cut it cleanly and what type of glue to fasten it in without
buckling it?

*  Does anybody sell replacement inserts???  ...or is anybody able to
fabricate them at a reasonable cost?

I'd sure like the benefit of the experience of others who have dealt
with this problem.  I know that many of the National receivers use
similar knobs.

Ian, K6SDE

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