>
>
>On Mon, 16 Apr 2001 04:36:23 -0700 measures <2@vc.net> writes:
>
>>When the screen arcs to the anode, and the SCR has not yet fired, we
>have
>>several kV on one end of the 2-ohm R. My thought is that c. 1500A
>>might damage the gate.
>>
>>cheers, Marv
>>\
>>thanks
>>>
>>>
>
>Good Morning Rich,
> True, 1500A would not make for a happy gate... but, that is not the
>case here.
>
> I'm guessing to arrive at that figure you have de-installed the glitch
>R, assumed some perfect power supply filter caps with no ESR, ignored the
>inductance in the plate circuit (including the plate RFC) and ignored the
>screen supply bypass capacitor... etc.
>
> In the real world, the glitch risetime will be sufficient to allow the
>SCR to trigger (in 2uS or so) thus protecting its own gate as well as the
>zener string and the screen socket cap.
>
> In the other world, you could still lilkely protect the screen
>circuitry by upgrading to a 100A fast SCR. Of course, this arrangement
>guarantees to disintegrate the screen itself....
>
> The idea here is to protect a zener string screen regulator (and the
>tube socket bypass cap as a bonus)... not to replace any other protection
>circuitry.
>
5w zeners are cheap enough. I have never had a string short in a screen
regulator.
cheers
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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