Tom said:
>Output capacitance of the tubes is not an issue at all.
Adding tubes increases capacitance in the same proportion as
it reduces optimum load impedance, and tank operating Q
isn't a critical parameter at all as long as it exceeds a
certain amount.<
Not only that, but the stray capacity around the tuning cap, bandswitch etc
generally doesn't go up in proportion, so you can end up with less of a stray
capacity problem. As Tom says, feedback capacitance is a problem, and there's
also the possibility of some interesting parasitics - you can get several tubes
going off in a ring oscillator, a bit like the original XAM US Navy radar power
oscillator. I think that was 250TH, 6 off, from memory of the article, but they
may have been 100TH.
73
Peter G3RZP
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