On Thu, 30 Jul 2026, Tony Duell wrote:
Perhaps you should learn the very old-fashioned way of valves/vacuum tubes :-)
There were some very early triodes that deliberately contains residual
gas. See here
https://www.museumoftechnology.org.uk/objects/_expand.php?key=954
There was a little side/top tube containing asbestos that you heated
to release some of said gas that was adsorbed onto the asbestos.
Interesting. The description there is a bit mis-leading. Asbestos does not
release any own gasses when heated. Instead, it can (obviously) bind gas
and release it. Never heard of that, to be honest. And apparently those
Marconi valves are the only valves with that asbestos tube on the top. So
practically, no valve contains asbestos, _except_ those Marconi.
Christian
