[Amps] tube replacement ?

[Dennis12Amplify at aol.com]

In a message dated 11/17/03 7:46:29 AM Central Standard Time, 
W.Posselt at maco.at writes:


> Hello!
> 
> I have an amplifier with 2x 4-400 which has a really big power supply and a
> very rugged design.
> The only thing I am missing is the appropriate output power.
> This lead to the idea to replace the tubes by something different.
> The two 4-400 are run as triodes in parallel.
> So what has to be considered when changing the tubes to let's say 2x GS31b ?
> 

Werner,

 If I were you I would either add a screen supply to those tetrodes to get 
the transconductance back again, or (since you said the 4-400s were running with 
grounded grids), try just plugging in a pair of 3-500Z's and see what 
happens.
 In either case you will probably have to modify the output matching network 
to match the 50 ohm load to the lower impedance plate circuit. (Try spreading 
the turns of the tank coil a bit further apart and hope you have enough range 
on the plate tuning cap.)
 By the way......, I have seen power supplies that appeared huge, but didn't 
perform very well under load. You may want to load test the power supply 
first, before you do anything else.

Regards,

Dennis O.

P.S.

Does the 'maco' in your email addr. stand for 'Majestic Communications' in 
Memphis, Tenn.?