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Re: [Amps] No parasitic choke question

To: <amps@contesting.com>
Subject: Re: [Amps] No parasitic choke question
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Reply-to: dezrat1242@yahoo.com
Date: Wed, 28 Jul 2010 12:04:24 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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