[Amps] Tank circuit Q

[Tom W8JI]

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