[AMPS] Screen Supplys

[w8jitom@postoffice.worldnet.att.net (w8jitom@postoffice.worldnet.att.net)]

> From:          "Ian White, G3SEK" <G3SEK@ifwtech.demon.co.uk>
> Subject:       Re: [AMPS] Screen Supplys

 Hi Ian,

> If you look at the datasheets, you will see that a string of high-
> voltage zeners cannot have a output impedance less than a few hundred
> ohms - a load pull will confirm this. A few hundred ohms is big enough
> to have a very noticeable effect on the IMD. 

I certainly agree with you Ian.

Zeners make poor regulators for screen supplies unless you use some 
type of gain loop to reduce the effective ESR of the supply, and 
hold the current in the zeners constant.

As you say, even a few hundred ohms of impedance the shunt 
device (in the clamping system of a shunt regulator) will screw up 
the IMD performance. Zeners fit that class of poor regulators.

73, Tom W8JI

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