BFoelsch wrote:
Watch the DC voltage on the grid. You will see it follow the relaxation
oscillator waveform when the thing is squegging.

What you write, which relates the Q (probably very low hundreds) of the
tuned circuit and it's frequency to the period the squegging, is in
good agreement with the squegging I observe. Will check the DC grid
voltage with the scope tonight.

Start by lowering the grid circuit resistance and lowering the capacitance
of the grid coupling capacitor. This will work to cure both evils. Taking a
quick look at the 6AH6 curves I would guess that, at 6 MHz, your coupling
cap should be about 22pF and the grid return about 10K.

The grid tuned circuit is at 1.8Mc, and the squegging seemed
insensitive to the coupling cap. 100pF is the handbook value, but I did
play around with it. Too small (39pF) and no oscillation. At 56pF there
was squegging.

Did not try playing with the grid return value (still at 47K from the
handbook), that may indeed be the key.

Tim.