Probably need to increase Q until Cout, plus strays, plus Ctune minimum
value will resonant. If Ctune has too much min C to produce a reasonable Q,
the trick is to insert an inductor between anode and Ctune. The reactance
of the anode "subtracts" from the reactance of Ctune and produce a better
tuning response at lower Q. The compensating inductor will have some
circulatiing current but not all so it doesn't needs about 1/2 to 1/3 the
wire diameter vs the tank coil.
jeff, wa1hco
----- Original Message -----
From: Michael Tope <W4EF@dellroy.com>
To: AMPS <amps@contesting.com>
Sent: Thursday, May 10, 2001 6:36 PM
Subject: [AMPS] 2 x 8877 on 6 meters?
>
> A friend of mine is working on a 2 x 8877 amplifier that
> he has setup to work on 20, 15, 10, and 6 meters. So far
> its working great on 20 thru 10, but he seems to be falling
> the victim of stray C at 50 MHz. His PI network design (Q=10)
> calls for 32 pf of tune-C, whereas he is measuring ~22pf of
> stray for each tube. Eimac specs for the 8877 suggest the plate
> C for each tube should be around 10pf plus whatever additional
> C is added by the layout, so his numbers, although perhaps
> a little on the high side, look like they are at least in the
> ball park.
>
> Can a design like this be made to work on 6 meters without
> gutting the 20 - 10 meter capability, or is this an unsolvable
> problem. What about running with a higher Q (this would allow
> for a larger tune C)? Any suggestions?
>
> Thanks,
>
> Mike W4EF...............................
>
>
>
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>
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