[AMPS] 4-1000A Configuration

[Jon Ogden]

>>Is the tube better in grounded grid configuration as I see 
>>most 4-1000A schematics, or is it better in grid driven configuration?
>>
>How better?  The answer is not yes or no.   Efficiency is a bit higher in 
>AB2 cathode-driven, however, the drive requirement is higher than for AB1 
>grid-driven.  For wide freq. coverage, the tuned input circuit for 
>grid-driven is less complex than for a cathode-driven amplifier. 

Well, since the efficiency of a tube PA ain't real good anyhow, big deal 
from what I can tell.  The fact that drive power is less and that the 
tuned input is less complex seems to outweigh the efficiency side.  How 
much higher is a "bit higher." 
>
>>I know that grid driven will give me more gain, but how much more?  
>
>Roughly double for a one-tube amplifier.  Roughly quadruple for two-tubes 
>in parallel.  

So going from 12 dB gain to 24 dB gain is a BIG deal.  To me having more 
available gain would mean that in order to drive the tube to legal limit, 
it does not have to be driven so hard.  That means: less strain on your 
rig, less strain on the amp since it's not being run full out and quite 
possibly better linearity.
>
>
>>What about stability?  
>
>The output-input feedback C in AB2 grounded-grid is similar to that in 
>AB1 grid-driven  because, in both instances, the screen is grounded. 

OK.  So that doesn't seem to be a problem. 
>
>>I've already seen stability problems in GG, so with 
>>more gain and the lack of the neutralization inherent in a GG amp, am I 
>>asking for trouble?
>
>Neutralization in AB1 is only for the fundamental frequency, not for the 
>VHF anode resonance.  It is my opinion that VHF oscillation is similarly 
>problematic in either config.   

Well, I'd agree.  However, with more gain at all frequencies, your gain 
and phase margins have shifted a bit and that is what concerns me.  But 
perhaps it's not that bad.

Interesting stuff to think about.

Thanks Rich.

73,

Jon
KE9NA


--------------------------------------------------------------------------
Jon Ogden

jono@webspun.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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