Rich writes:
> > On the other hand, if most damage to the grid occurs very
> > quickly, then one would probably want fast-acting, electronic
> protection.
>
>
> ... provided that the transistor used to interrupt grid-current
> was up to the task.
There you do again ... there is no need to directly interrupt the
grid current with a transistor. As long as the anode has sufficient
current limiting (arc protection) which is normally provided by the
"glitch resistor," it is sufficient to bias the tube to cutoff.
That can be done by the normal T/R circuitry, particularly if fast
(electronic) bas switching is used. when coupled with an electronic
disconnect for the HV (e.g., shut off the primary to the HV) any
overcurrent pulse is not likely to last long enough to cause
significant damage. By the way, these are the techniques used
in the WD7S and G3SEK/GM3SEK control boards.
With exceptionally large "tubes with handles" and high stored energy
power supplies, additional protection in the form of arc gaps and
crowbars may be advisable but they should not be a requirement at
(legal) amateur power levels.
73,
... Joe, W4TV
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