Joe,
I think Henry may have used some sort of transformer arrangement in it's 8k
Ultra amplifier? The discussion about flywheel-effect going on now is
relevant to this as one possible approach. Personally I would not use a
transformer.
I use a number of relay switched, fixed component values, Pi-networks, each
having a Q of around 2. I think I once worked out that the average drive
impedance of the valve was in the region of 45 Ohm - close to 50 Ohm
anyway. As I recall, Eimac recommends a Q of 4 for the input network, but
this is difficult to achieve with the requirement for low input VSWR across
each of the low bands without having adjustable components.
I have seen designs where 'L' and 'C2' (valve-side) in the input matching
are made adjustable. Extra controls to adjust when tuning-up, but probably
optimum in performance terms.
Regards.
Mark.
------------------------------------------
At 22:25 29/03/2005, you wrote:
>Hello
>
> I am biulding an HF amplifier using the 3CX3000A7 tube and i
> like to ask if some one have any diagram of a simple input circuit for it
> as i do not like to coplicate things as i was trying to find some kind of
> input transformer but no luck...can any one help....
>
>
>many thanks
>joe
>9H1GT Joe Francalanza
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Mark Hill - G4FPH
E-mail: g4fph@mjha.co.uk
Current web pages at: www.qsl.net/g4fph
Old web pages at: www.g4fph.freeserve.co.uk
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Dipoles resonant on 1942/3695/7065 kHz
2 ele delta loop beam resonant on 14180 kHz
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S witch off
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