I think what confuses people is that commonly used amateur
radio formulas for tank Q are really just rough shortcuts or
approximations for describing real world systems. The saving
grace is the system, unless Q is below a minimum value,
doesn't change nearly as much as many might think when
operating Q is not the magical numbers (like the popular "Q
must be 12") that we are so overly fond of zeroing in on.
The formulas are all approximations and should not be taken
as a description of what precisely happens in the network or
in the real world.
I wouldn't spend too much time worrying about making an
approximation fit a non-critical goal precisely!
The capacitor current, assuming a sine wave from a purely
resistive source driving the tank, would be simply the RMS
voltage at the tank input over the capacitor's impedance.
This is true regardless of inductor unloaded Q. Current in
the inductor is slightly different than that in the real
world because there are other shunt impedances at work in
the system, and the waveform is not a pure sinewave. But it
is close enough.
As for capacitor current, be sure to read the manufacturer's
detailed application guidelines carefully. There are many
people who apply a base number that is designed to be used
in a series of approximations directly as a limit, and who
wrongly assume any current beyond the number that was never
intended to be an absolute limit results in some component
life or operating catastrophy.
The two parallel capacitors in series with your tank
variable C clearly need to go. They are a sign of bad
engineering, just as the shorted taps on the toroid were.
73 Tom
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