[Amps] 3cx3000a7

[Mark Hill]

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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>e-mail  joefran at camline.net.mt
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