Consider the arc as a zero ohm resistor. The current peak is limited by
the glitch resistor and the impedance of the HV caps
jeff, wa1hco
On Thu, Mar 3, 2022 at 8:35 AM Steve Thompson <g8gsq72@gmail.com> wrote:
> 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, <4cx250b@miamioh.edu> 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!
> >
> >
> >
> >
> http://www.w8zr.net/160amplifier/images/Amplifier%20Schematic%20Package.pdf
> >
> > 73,
> >
> > Jim W8ZR
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