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Re: [Amps] W6PO 2m amplifier - input circuit adjustment

Subject: Re: [Amps] W6PO 2m amplifier - input circuit adjustment
From: Steve Thompson <>
Date: Fri, 09 Jun 2006 20:52:45 +0100
List-post: <>

David G4FTC wrote:
> Searching the amps archives, I know this question has been asked before 
> but........
> Apart from squeezing/expanding the coils of the input T network to obtain a 
> satsifactory match, has anyone tried using a PI-L or similar network to 
> simply the input tuning?
> The original W6PO design made one of the L in the T network variable to 
> simplifiy obtaining a match - but the chances of getting a suitable 
> ajustable core are probably nil, so adding a second variable C into the 
> network would seem to be a logical move.
> Before I take an electric drill to the chassis to mount another C, does any 
> one have any thoughts why this may not work?
> What worries me a little is that most tube VHF amplifiers use the same basic 
> T network for the input, and no-one seems to have considered that the T 
> needs to be improved.
Maybe, but make two coils like the airspaced one, spend just a few 
minutes getting them squashed/stretched right and you don't need to 
touch it again for 20 years. Beats drilling holes anytime :-)

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