On May 28, 2006, at 6:24 PM, Gudguyham@aol.com wrote:
>
> In a message dated 5/28/2006 7:16:12 P.M. Eastern Standard Time,
> aa4lr@arrl.net writes:
>
> Curious question -- I recently wondered why it is that the 3-1000Z
> was never that popular a tube in amateur circles, but the 3-500Z was.
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.
> Why did many amateur designs use two 3-500Zs instead of one 3-1000Z.
> Seems like it would simplify things. One bottle and you could to the
> legal limit with a simple grounded-grid circuit.
If the 3-1000Z had had less feedback-C, it might have caught on.
>
> The market made some determination, as 3-500Zs are still being made,
> and 3-1000Zs are unobtainium....
>
The 3cx1200Z7 is a better choice, unless of course one is building a
VHF oscillator.
>
>
> Not positive to the answer to this but I think it has to do with the
> physical size of the tube.
A possibilty
> Could you imagine the size of an Sb-220 if it used a
> 3-1000? Hunter used one in their amp and it was not a very
> popular amp. There
> may be other reasons, but -physical size comes to my mind right away.
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R L MEASURES, AG6K. 805-386-3734
r@somis.org
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