> >The series resonance actually makes the input impedance of the
> >tank look like only a few ohms!
> >
> This is true only when the series resonance is not offset from the
> parasitic freq. L-networks are never resonant. When the resonance is
> Near but not dead-on the parasitic freq., the L-network effect comes into
> play and the potential is substantially increased.
You must be using a new definition of resonance. Can you tell me
what you mean?
This is a series-resonance, not L-network, and it is shunting the
path the tube must drive on VHF.
If the tank could freely pass harmonics, or step up the voltage at
VHF to high levels, the amplifier would be a TVI nightmare.
> >It actually makes it impossible for the tube to drive significant
> >voltage at the tank at VHF!
> >
> ? You seem to have missed the word "Near", Tom.
The impedance of the capacitor is highest at dc, and is reduced as
frequency is increased. That's why the tank is a low-pass network.
If the parasitic is NEAR the fundamental frequency, or lower than
the fundamental frequency, it could indeed arc the tank
components over...maybe.
Most people know the tank is a poor pass system for VHF energy,
you might have a hard time confusing them.
> ? Which TV station is on 120MHz?
Nice try. Now we have single frequency parasitics exactly on 120
MHz, where the tuning capacitor has about ten ohms of reactance,
driving the tank capacitor with thousands of volts.
What happen to your claim about grid resonance at 80 MHz, did it
move in this application to fit your needs?
73, Tom W8JI
w8ji@contesting.com
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