Apologies if this turns up twice, but the first send hasn't appeared and
something subsequent has.
Steve
>-----Original Message-----
>From: Michael Tope <W4EF@dellroy.com>
>To: AMPS <amps@contesting.com>
To: <amps@contesting.com>
>Date: 10 May 2001 23:41
>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.
>You need to be careful with manufacturer's capacitance figures, especially
>at higher frequencies. Usually Ca is measured using a shielded isolated
>fixture, where strays to the outside world are excluded or nulled out to
>give a 'pure' value for Ca. I've measured a number of different tubes when
>in the chassis, and Ca is usually around double the data sheet value. The
>only way I can get the data sheet value is to suspend the tube in mid air
on
>a long thread.
>
>Steve
>
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