I agree with Steve, the range of adjustment by squeezing the coils is
entirely adequate, this is one of the best behaved input circuits I have
ever experienced. I will be duplicating it on my YC-156 2m amplifier which
will be finished some time this summer.
73
Conrad G0RUZ
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Steve Thompson
Sent: 09 June 2006 20:53
To: amps@contesting.com
Subject: Re: [Amps] W6PO 2m amplifier - input circuit adjustment
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 :-)
Steve
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