[Hallicrafters] SX 101A Challenge

[Rocco Lardiere]

To the Hallicrafters Experts:

OK - I am stumped.  My SX 101A local osciallator is warbling slightly,
and I can't stabilize it.  This is not the usual temperture drift.  This
is a slight delta frequency, continuous, perhaps only back and forth a
few cycles, but it is constant from turn on to whenever.  It just sounds
awful on CW.  It is more pronounced at higher frequency bands.  The
problem is in the 1st conversion oscillator - I can hear it clearly when
I couple my test receiver to the tube and listen to it directly.

I have rebuilt and resoldered the components around V3, the 12By7A, and
it is less prone to vibration now.  This problem is not related to
vibration or turn on temperature changes.  The B+ and bias to the
cathode look clean and stable.  The warble is not a steady beat note -
it is just back and forth at a few hertz, but not at a stable low
frequency.

I have tried tugging on every freq component, including the main
variable cap.  I resoldered everything in sight.  Everything looks
solid.

This is a really beautiful 101A - very, very clean, so I want to save
it.  I suspect the receiver is like new because this problem has been
there from very early in its life.

Any hints?

Rocco Lardiere N6KN