>
>
>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.
>
Ol' P.T. Barnum was apparently right, Gary.
cheerz
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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