The URL worked today, must have been a network problem.
Look at this text........
Triodes are Good, Tetrodes are Better....
Unlike triode amplifiers, the PLA800 uses tetrode tubes, which have a
control screen grid. The screen grid not only adds to the
amplification factor of the tube, but also controls the electron flow
to the plate. When voltage regulation is used for the screen grid and
with the plate overload circuit, as with the PLA800, plate and screen
currents are limited to their maximum value. As a result you will not
overdrive the PLA800 creating sideband distortion or splatter.
Increasing the drive power beyond 50 watts, does not increase the
power output. Because of this self-limiting feature, an ALC circuit
is not needed. The amplified audio, as in SSB service, is clear and
clean, void of sibilance and distortion.
xxxx
What an unusual technical explanation about screen current limiting
and distortion!!!
The schematic shows a cathode driven PA with no tuned input and no
swamping resistance, just straight from the driver into the cathode.
A totally non-regulated control gid bias system without a control
grid current indicator.
He uses the center tap of the HV transformer to supply screen
voltage, and that is a good system.
73, Tom W8JI
W8JI@contesting.com
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