Re: EL34 Control Grid Voltage Maximum

seanbroderick20003@xxxxxxxxx <seanbroderick20003@xxxxxxxxx> wrote:
Thanks for the replies. The coupling caps are new, so that's not the
problem. The problem is, I think, I'm just ramming the EL34s with too
much signal, and they're arcing. But inside the tube, what is arcing
to what? What's the most common scenario?

Just about anything can arc to just about anything. Don't overdrive
the tube. If you run the grid anywhere near zero, bad things will happen.
If you run it too negative, bad things will happen in the other direction.

I mentioned the 450 volt figure with the idea that if a 12AX7 cuts off
suddenly, you could have a full rail valued pulse (with a source
impedance of the plate resistor) being applied to the next grid. I
was speaking in AC terms. In this case, the 12AX7s are fed from a 450
volt rail.

No, it doesn't work that way. Ignore that. Use a scope and stop guessing.

With tube output stages, where is a good place to look with a scope
for RF oscillations (without destroying the scope)?

You probably don't have an RF oscillation issue. If you were looking for
one, you would use a scope on the plate and all the grids of the final.
More likely you have a motorboating issue. What model amplifier is this
and how new are the supply bypass caps?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
.

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