02-11-2016, 04:12 PM
(02-11-2016, 02:19 PM)Mike Watterson Wrote: Does heater on and HT off really give cathode poisoning?
Yes or, at least, that is what I was taught.
Theory is that the space charge forms above the cathode in the normal way but it has nowhere to go. So, because of the shortage of electrons in the cathode, which would normally be satisfied by the current flowing through the valve, the cathode becomes increasingly positively charged, attracting the electrons back at high speed.
The constant - and continual - bombardment by the electrons eventually damages the emissive layer of the cathode, 'poisoning' it.
The term is incorrect in these circumstances as cathode poisoning is normally caused by impurities in the cathode material but the outcome is the same: the cathode 'dies'.
