[ARC5] Smart People - OT Why pentods fail (was Triodes & Pentodes)

[Leslie Smith]

 "The screen failure will not be due to voltage over max but excess
 dissipation."
> 
> I agree.
> 
> Ken W7EKB

Aw- Ken! 
The above is nonsense, and I'm onto you.   :-;    It's not dissipation
(I-squared R heat) that causes the damage.

The screen sags from the weight of accumulating electrons; the flow of
electrons is impeded by the thin wire.  :-(
We get the word, impedance from the latin, "impedire", meaning "to
shackle the feet" - and this is exactly what the thin grid wire does -
it impedes those little electronic feet.

Note:  Screen-grids built from thicker wire allow the electrons to
escape; there is no sagging.  :-)
As for the the plate - it doesn't sag even a little.  Being thicker and
more robust, it can take the weight.

As more electrons accumulate the screen grids sags, more and more, until
it touches the cathode.
The resulting short circuit  results in a decent "bang!".
This is the true failure mode.  Trust me.  
I know nearly list-reader here will agree, particularly the better
informed readers.  :-) :-)  :-)  

Les

(PS  I hope I don't get banned from  the list for stating the truth)

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