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

[Tim]

Hi Les - Thanks for explaining that....Very interesting!  I had previously
thought that the main failure mode was caused by the vacuum leaking out.
Who knew?
Tim
N6CC


On Wed, Nov 13, 2013 at 10:16 PM, Leslie Smith <vk2bcu at operamail.com> wrote:

>  "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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