[AMPS] Re: 8877

Thu, 24 Jul 1997 09:52:56 +0000

From:          Rich Measures <measures@vc.net>
Date:          Thu, 24 Jul 97 02:15:00 +0000

>>Why do you continue to make such a big deal over driving voltages? 

>The grid has C.  Developing 1000V or so across the typical grid's C 
>at 28MHz is not a piece of cake.  Another complication is that when 
>you are trying to drive a triode's grid in the positive-going 
>direction, the anode is headed in the opposite direction.  Since the 
>anode/grid C in a 3cx3000 is about 20pF, it is a big deal at 28MHz.  
>Have you ever seen a 3CX3000A1 in grid-driven linear service at HF?  
>I have not.

I've seen plenty of 811A's and 812A's. I've seen 100TL's and 
100TH's also, right up to 450 TH's and TL's. My very first SSB PA was 
a pair of 812's grid driven by a homebrew 6L6 phasing exciter. I 
later converted the 812's to 811's. 

I really don't understand all the fuss and argument.

Grid driven AB1 and AB2, as well as B or C triodes were quite common 
before the hi-mu zero bias triode displaced them from service. B+W 
made a mint selling link coupled coils that were used for push-pull 
or for single ended neutralized grid driven systems.

Concentrating on one or two certain tube types and trying to use 
them for proof something CAN' T  be done in any circumstance won't 
change the facts. It won't make ALL those hundreds and thousands of 
old grid driven PA's disappear.    

>IMO, the A3 would not be suitable for grid-driven linear service.  
>Eimac does not recommend it.  The A1 would be suitable for 
>grid-driven linear service up to a few hundred KHz.

Rich, just so we don't have to take your word for it, please quote 
for us the page number and text where Eimac states tubes with the 
suffix A3  are not recommended for grid driven service. What book or 
data sheet gives that all inclusive warning?

73, Tom W8JI 

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