Carl,
My feeling is that 572Bs are a bit close to the edge anyway once you get to
28MHz.. They have very long grid leads, especially when compared with a 3-500Z.
Even a copper strap to ground from the grid pin won't reduce the inductance
that much, because it's such a small fraction of the total inductance, although
it's worth trying.
I've never understood the raison d'etre for the introduction of the 572B. I
gather it was meant as a cheap SSB tube: just how much would it have cost to
put it on the same base as a 5894? that would have given it much better
performance, and it wouldn't be such a bear to tame parasitic wise.
73
Peter G3RZP
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