Maybe I take too simplistic a view. I figure as follows:-
When the tube is drawing the peak plate current (i.e. at the peak of the rf
cycle), the plate voltage should be at its minimum value. So the load
resistance that the plate needs to see is the (HV supply minus the minimum
plate voltage) divided by the peak plate current.
The Q is then the ratio of the load impedance as transformed to the plate
circuit divided by the reactance of the tank circuit input capacitance.
Once you've fixed the value of the input capacitance ( which must include
all strays) the rest of the values can be determined from the various
formulas or froma Smith Chart or you can even derive your own equations.
Note that if you have a low enough reactance in the plate feed choke, you'll
need to take this into account: you'll need more tuning capacity. For
instance, a 120 microhenry choke on 3.5 MHz will need an extra 17pF. When
you have these dreaded choke resonances, they can modify the choke impedance
and require more or less C to cancel it, depending on where they are. Or
sometimes, they just commit suicide in spectacular self-immolation!
73
Peter G3RZP
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