[AMPS] Screen regulator circuit needed

[Steve Thompson]

In message <19981117194311.AAA10189@[209.239.238.87]>, Rich Measures
<measures@vc.net> writes
>>OK, I accept what Rich and Steve say about the possibility of using a
>>transistor shunt stablizer from a supply that's higher than its
>>breakdown voltage... but I still don't feel comfortable about it. To be
>>reliable, it certainly needs more careful design than most amateurs
>>would be prepared to put into a screen supply.

Without question - I'm not necessarily advocating it, although I will
get round to trying it one day...

>>
>So, operate a series string of name-brand 20v - 30v 5w zeners at no more 
>than 2w, biased from the anode supply through a suitable R, and one has a 
>foolproof screen regulator for smaller tetrodes.  For tetrodes with 
>handles, the positive floating 723 pass circuit works well.  

Or add a trip that detects the screen voltage wandering high (or zero
current in the regulated supply (opto isolator?)). It would, after all,
be a fault condition. I've lost a zener string and screen meter in a
flashover - my theory was that the VDRs actually limit at around
450-500V when carrying a current spike, and the zeners try to sink loads
of current.

Steve

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