[AMPS] Re: 8877

[Rich Measures]

...snip... 
>>2.  Low Mu triodes are not appropriate to use in Class AB2 
>>cathode-driven 
>>linear amplifiers because they exhibit low gain.  
>
>So what do you consider low gain Rich? 

3 in 7 out.  (3cx3000F1/A1 in g-g)  

>What is your example of a good AB2
>grid driven triode? 

810, 1000T, 450TL, et cetera---but not for linear service.  The only 
tubes I know of that are usuable in grid-driven Class AB2 linear service 
are the 4CX600J and the 4CX1500B.  However, the permitted grid currents 
are less than 1 mA. 

>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.  The 4CX3000A 
and the 5CX3000A, yes.  

>...... The final system
>complexity is not much different from a 3CX3000A7 that requires 400-500W
>of drive in GG  or a A3 version in grid driven service that wants 1000V+
>of grid swing. 

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---


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


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