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[Amps] 4-400A Plate

To: <amps@contesting.com>
Subject: [Amps] 4-400A Plate
From: 2@vc.net (Rich)
Date: Fri, 8 Nov 2002 07:24:28 -0800
>The first glowing plate amplifier I made was using a pair of
>250th's.  I drove them with a pair of 6146B and had about
>2Kv on the plate.  Naturally I had to provide bias to the tube
>even though it was cathode driven.  When I tuned up the plates
>not only glowed red you could see the dark shadow of the
>grid on them.
>         I was only a young ham then and did not know that
>you "can't  run 250th in grounded grid".  

Any triode will run in g-g.  The higher the Mu, the less cathode driving 
V needed.  A 250TH is easier to drive in g-g than a 250TL.  The "you 
can't" is running a high or medium Mu triode in grid-driven Class AB1.  
For example, a grid-driven, Class AB1 8877 - Mu=200 -  looks like it 
might produce 20w in that configuration.   Actually, the "you can't" 
should be a "... but you won't get much output".   For a grid-driven 
triode in Class AB1, a Mu of under 5 is desirable.

>But it worked just
>fine and I did get about 1KW plate input power to the
>amp. ...

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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