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Re: [Amps] Modern Op-Amp shunt stabilizator power supply (for tetrodescr

Subject: Re: [Amps] Modern Op-Amp shunt stabilizator power supply (for tetrodescr
From: Steve Thompson <>
Date: Thu, 3 Mar 2022 13:35:38 +0000
List-post: <>
A while ago I breadboarded a screen regulator supply with some
similarities to Jim's design. One of these was that the 'pull down'
transistor could act as a clamp if there was a flashover to the screen.

I was fortunate enough not to test that function but I had a couple of
questions which I never found answers for:

How much current flows during a flashover to the screen (assuming the
amp has a sensible glitch resistor in the HV supply) and

How long does a flashover last?

Worst case guesses are simple enough but I don't know how the physics
of the arc affects things in practice.

Steve G8GSQ

On Mon, 28 Feb 2022, 21:37 Jim Garland, <> wrote:

> Attached is the screen voltage regulator I designed for my 160m/80m
> duo-band amplifier using three GU74B tetrodes. From your msg, I suspect
> it’s similar in some ways to the circuit you’ve described. The circuitry is
> deceptively subtle, however, in that it provides protection against damage
> from grid-plate flashovers in the tubes, which can be a problem, especially
> with new (NOS) Russian tetrodes. I’ve used this circuit for more than five
> years and found it to be always stable, with tight regulation. The
> circuitry mounts on a small file card-sized PCB. The screen voltage is
> adjustable and I set it at a nominal 340V.
> If the attachment doesn’t come through (I’m away from my home QTH and have
> limited internet coverage, here’s a link to the complete schematic package
> for the amplifier. Pse email me if you can’t get any of the diagrams to
> load!
> 73,
> Jim W8ZR
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