Steve wrote:

One of the last issues is with the HT-44. The output stage
wants to break into oscillation at (about) twice the freq
its tuned to. I have been unable to neutralize the finals.
The tubes are good (and matched), band switching has been
checked (switches and coils), bypass caps, etc. Everything
looks OK. All of the obvious stuff has been checked (biasing,
power supplies, etc).

snip

You should check the brand of the final tubes.
GE 6DQ5's will neutralize quite differently than RCA's.
You can see the difference in the construction -
some 6DQ5's have a U-shaped clip at the top mica,
surrounding the plate lead, and some don't.
(I think the U-clip is connected internally
to the screen). If you mix the two types, you will
never get the final stage to neutralize.
Some rig manufacturers caught on to this problem,
and specified which brand of 6DQ5 to use in their rigs.

73,
Ed Knobloch