Chuck Harris wrote:
Hi Mike,

Neutralization is more than just interelectrode capacitance. It is
also affected by plate to everything outside the tube capacitance, and,
of course, the layout of the transmitter finals cage.

The plate of the 6146B is bigger than the 6146, or 6146A. It has about
33% more plate dissipation as a result. There is more coupling between
this bigger plate, and the outside world.

I don't have an example of both tubes in front of me, but I don't
remember the plate structure of a 6146B being larger than a 6146(A).
Can anybody confirm that the 6146B plate structure is bigger? I
thought the higher plate dissipation was due to some combination of
different plate material and/or thicker plate material.

Is it possible that the Collins neutralizing capacitor range was
marginal to begin with, and that the higher power that the B tubes were
capable of just brought the problem to the surface? Just wondering...

73,
Mike, KK6GM