[AMPS] Re: 8877

[Rich Measures]

>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....snip...

Yes indeed, and the total IMD level was probably -20db.  The all-time 
record that I measured was -11db.  

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

. ...snip... 
>
>>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. .....
>
Grid-driven is perfectly okay for a medium-Mu triode---provided that 
linear amplication is not the objective.  The only type of triodes that 
Eimac recommends for grid-driven linear amplifier service are low-Mu.  
The reason is that at zero grid-v, only low-Mu triodes are capable of 
drawing sufficient anode current.  
Rich---

R. L. Measures, 805-386-3734, AG6K   


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