Wed, 5 Dec 2001 14:04:41 -0500
> // Some Alphas apparently C-E-short their interrupt transistor.
If I am not mistaken, the original Alpha 77 (model PA-77) uses such a grid-protection circuit. However, I don't recall how well the
switching transistor is buffered and isolated from the grid. If I get a chance tonight, I'll look at the schematic.
On the other hand, my Alpha PA-70V (with a single 3CV1500A7) uses a factory-designed 1/4-amp/3AG grid protection fuse. The fuse
seems to work well and blows quite nicely when I accidentally apply full exciter power at 100-watts. What I don't know is the
long-term detrimental effect on the tube caused by these brief and occasional periods of excessive grid current. Of course, the
fuse blows well before the grid ammeter has an opportunity to display the excessive condition (due to the meter ballistics). But,
how fast is fast enough?
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