Will Matney wrote:
> > Really, the screen voltage is set by the tube manufacturer for an
> > allowable IMD, screen current, etc. by their voltage rating. The
> screen
> > voltage can vary some from their ratings. The different screen
> voltages
> > are done because of the design of each tube itself in order to
have
> it
> > work correctly and withing specs. I have seen 4CX250B's ran
anywhere
> > from +280 Vdc to +400 Vdc screen voltage. I think the factory spec
> is
> > around +350 if I recall without looking. It will also change by
what
> > mode of operation it is ran at A, AB1, AB2, etc.). Those ratings
are
> > found on the manufacturers spec sheets for each tube. If the
screen
> > voltage is raised, it amplification (gain) is raised thus
increasing
> the
> > IMD. Decreasing the voltage would do the opposite by dropping the
> gain.
> > Really, where you would personally set the G2 voltage at is up to
> the
> > builder and how clean he is trying to build it.
>
my 3x 4CX350FJ amp was starting to draw grid current quite early
and that ruined IMD of course and made me experimenting with
voltages.
Finally it run best with 400V screen voltage and 3000V anode
voltage, no grid current to 1400W output at all, very clean
73
Peter
>
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