25 Jul
2005
25 Jul
'05
2:19 a.m.
I have a large number of 5963 tubes (computer-rated
12AU7s) which I am
told "have gold-plated grids to guard against 'sleeping sickness' when
used as flip-flops".
My question: what is this "sleeping sickness"? Does this relate to the
long-periods-at-cutoff mentioned earlier on in this thread? How does
having gold-plated grids help this?
"sleeping sickmess" is basically a bunching up of electrons around the
cathode when the tube is cutoff. Think of it as a cloud. When the tube is
turned on, this cloud of electrons gets in the way, and must
"dissipate" before the grid can once again take control and let electrons
from the cathode (the "signal") do their
thing. Getting the cloud to go
away takes time, so the tubes can not react quickly -
exactly what an
engineer does not want a high speed digital circuit to do.
"Sleeping sickness" was cured mostly by purifying the elements in the
tubes - getting rid of imperfections and impurities in the cathodes and
grids. Gold plating is a way to do this. It is an expensive way, so most
5963s have normal grids.
William Donzelli
aw288 at osfn.org