[Amps] 4-1000 amp

[R L Measures]

On May 28, 2006, at 6:24 PM, Gudguyham at aol.com wrote:

>
> In a message dated 5/28/2006 7:16:12 P.M. Eastern Standard Time,
> aa4lr at 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 at somis.org