> >It was not Rich's idea. Eimac recommends a shunt screen regulator
> >for smaller tetrodes. I used the circuit in two amplifiers and
> >dynamic screen V regulation was better than 1%. A caveat: Operate
> >zeners at no more than 33% of rated dissipation.
> If I remember correctly, the measurements made by GW4FRX (and/or
> G3SEK?) showed a significant improvement in IMD if screen regulation
> was improved from around 1% to around 0.1%. That's not the same as
> saying that 1% regulation produces unacceptable results in the real
> world, but shouldn't we aim for the better target? The effort of
> building a better screen supply is usually minor compared with the
> rest of PA building.
Regulation will be much better than 1% if you wrap around the
zeners with a gain stage. The overall cost will be the same, since
you can use cheap HV NPN or PNP transistors and smaller zeners.
In that case you can use a very high value resistor from the HV to
the zeners, and the ESR of the zeners is less important.
73, Tom W8JI
W8JI@contesting.com
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