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