----- Original Message -----
From: "measures" <2@vc.net>
To: "Ian White, G3SEK" <g3sek@ifwtech.com>; "AMPS" <amps@contesting.com>
Sent: Saturday, April 14, 2001 4:17 PM
Subject: Re: [AMPS] Zener screen supplies
>
> >
> >Tom Rauch wrote:
> >>
> >>You need enough capacitance near the screen to absorb the initial spike.
> >>Neither a MOV or gas tube will work well by itself. Even a modest
> >>overvoltage is too much for regulators. Slow the transient down.
> >>
> >>Actually, the MOV is a last resort just to protect the socket
> >>capacitor...as would be a gas tube.
> >
> >The MOV or gas tube at the screen terminal is actually the *first* line
> >of defense because that is where the arc hits. Tom correctly identifies
> >that the screen bypass capacitor in the socket is at least as valuable
> >and important as the tube. The tube may survive,
>
> A tube that arced is already a proven leaker.
>
> >but if you blow that
> >capacitor, you need a whole new socket.
>
> The last two tetrode amplifiers I built were grid-driven and they had
> directly grounded screens. ....... Direct screen grounding is how large
> tetrode amps are normally built.
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
I have to say that I have used grounded screen on two occasions and the
results have been very satisfactory.I think that I will go for this with the
2 x GU74b amp that I am working on.It does seem to take a lot of worry out
of the equation.
Regards
Conrad G0RUZ
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