At 09:29 29/05/2006, R.L. Measures wrote:
> The 3-1000Z has a grid that does a marginal job of shielding the
>input from the output -- which means it has more feedback-C than need
>be. The 3cx1200A7 is the external anode version of the 3-1000Z and
>it apparently uses the same grid and filament. Both tubes have a
>reputation for squirreliness -- especially with higher anode PS
>voltages. Eventually, Eimac discontinued making the 3-1000Z and the
>3cx1200A7 evolved into the 3cx1200Z7, which has less feedback-C --
>and better stability. Unfortunately, the ...A7 and the ...Z7 are not
>interchangable.
I cannot help but wonder why you keep pedalling this one. I have
been, yet again, to the Eimac/CPI data sheets which read as follows:
grounded grid capacitance in pf
in out feedback
3CX1200A7 20 10.3 0.6
3CX1200Z7 17.6 9.7 0.8
This does not accord with your comments. Are the Eimac figures incorrect?
Chris
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