[AMPS] 4-1000A Configuration

[Rich Measures]

>OK all,
>
>I've been unable to get a satisfactory answer on this question, so I'll 
>ask the whole reflector:
>
>The other day, someone posted a question about wanting a schematic for a 
>grid driven 4-1000A.  This got me to thinking.  I am in the process of 
>completely rebuilding my 4-1000A amp so I was wondering what is the best 
>way to go.  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.  

>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.  


>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.  

>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.    
>
>Now is a perfect time to make this decision as I am still working on 
>modifying the mechanics in the PA cabinet and have not started circuit 
>construction.
>
>Thanks,
>
>Jon



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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