On Jul 21, 2006, at 3:20 AM, Peter Chadwick wrote:
>>> If the tube is not gassy, and the grid is floating, the
>>> electron
>>> stream from the cathode probably raises the grid-cathode
>>> (fil-CT)
>>> potential to a few volts negative
>
> So if it doesn't matter, why do tube manufacturers specify a
> maximum grid - cathode resistance for a lot of tubes?
To keep the grid potential from wandering and degrading performance,
not to prevent a catastrophe.
- note - If there's someone here who is presently working on a 3-500Z
amplifier, please float the grid and report back what happens.
> Even low power audio tubes used in Class A?
> My experience is that exceeding the the maximum grid-cathode
> resistance can (but not always does) lead to a plate current
> runaway, even in tubes with no measurable gas (as measured by grid
> current)
Why doesn't the effect of arriving electrons take the grid in the
negative direction?
> 73
> Peter G3RZP
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>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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