Provided that the grid parasitic tuned circuit is resonant at a higher
frequency than the anode parasitic tuned circuit, the amplifier will be stable.
Unless Terman got it wrong........
This suggests that well grounded grid through say a collet ring fixture may
well not need an anode parasitic suppressor if the rest of the design is right
- and that may need all sorts of niceties taking into account, such as the
amount of shielding adding capacity to the anode circuit.. It also suggests why
572Bs are such wotsits to keep free of parasitics, they having a lengthy grid
structure.
Very often, parasitic suppressors are fitted on a 'belt and braces' ('belt and
suspenders' in American English!) basis, and are determined experimentally -
even on big transmitters. I suppose one of the EM modelling programs could
predict the result if you had good enough models of everything in the box, but
the usual approach may well provide suppressors where they aren't needed.
73
Peter G3RZP
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