[Amps] No parasitic choke question

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Wed, 28 Jul 2010 13:56:25 -0400, Bill Fuqua <wlfuqu00 at 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