Tom Rauch wrote:
> 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
>
Tom,
I guess you haven't been keeping up. There has been a change in the laws
of physics.
A floating control grid will now automatically bias the tube back to a
safe level with overdrive without creating distortion.
73
Gary K4FMX
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