ORIGINAL MESSAGE:
On Wed, 28 Jul 2010 13:56:25 -0400, Bill Fuqua <wlfuqu00@uky.edu>
wrote:
>
> This third approach is not practical for several reasons.
>1. The VHF resonance(s) may not be on one frequency. When you tune the
>output or input circuits it may change as well as when you change bands.
>2. Adding such a circuit may only change the VHF resonant frequency by
>simply becoming part of the circuit. .
REPLY:
Regarding #1: A valid point and that's why I suggested de-Qing the
series trap circuit. In fact, one could use two or more series traps
if needed, stagger-tuned. They are simple, inexpensive and easily
added. On the amps where I have grid-dipped the VHF parasitic tank
circuit, the frequency did not change much by tuning the output
pi-network.
Regarding #2: Don't know about that except that you are adding a low
impedance series trap across a relatively higher parallel impedance.
Exactly what happens remains to be seen and that's why I said the
concept needs further testing.
In my own homebrew amps, my first and second approaches always took
care of the problem and I never had to go to number three.
73, Bill W6WRT
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