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

[Roy Morgan]

On Nov 14, 2013, at 1:16 AM, Leslie Smith <vk2bcu at operamail.com> wrote:

> "The screen failure will not be due to voltage over max but excess
> dissipation."
> 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; ...
> As for the the plate - it doesn't sag even a little.  Being thicker and
> more robust, it can take the weight.

But, but !  

I have an 811 (the non-A version, apologies to the R-390 mailing list) that has a hole in the plate.  
The plate does seem to have sagged quite a bit around the hole.  
No doubt this is due to some phenomenon I’m not too familiar with, possibly "11-meter overdrive".

> We get the word, impedance from the latin, "impedire", meaning "to
> shackle the feet" 

Maybe the earlier 811 (non-A) has thinner plate construction, not being made with the much acclaimed RCA multi-layer plate material.  (Or was it Tung-Sol and their also much acclaimed 6550’s that had that plate material?)

Boatanchor historical reference:  The Collins 30L-1 may have been equipped early on with the 811 (non-A), and there was the early Central Electronics 200V SSB no-tune transmitter that used 6550’s as the finals.

Roy


Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958