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Argus25 · 5th Sep 2019, 11:33 pm

Probably the only likely way the grid electrode could acquire a positive charge is if it was being bombarded positive ions. Normally there should be very few of those in the valve, provided that is, that the metallurgy of all the electrodes is high purity and specifically that metalwork is not raised to a temperature above that which was present when the valve was evacuated at the factory. This of course is the factor that sets the published specification on a valve's maximum dissipation. If the temperature is raised above that manufacturing value, contaminants exit the metalwork and "poison" the valve.

Probably a lot of new manufacture clone valves have issues with the metal purity and might not have been out-gassed at the correct electrode temperatures, so in use the problem crops up, but it might not in a lower power dissipation application.

5th Sep 2019, 11:33 pm	#8
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: ECL86 issues Probably the only likely way the grid electrode could acquire a positive charge is if it was being bombarded positive ions. Normally there should be very few of those in the valve, provided that is, that the metallurgy of all the electrodes is high purity and specifically that metalwork is not raised to a temperature above that which was present when the valve was evacuated at the factory. This of course is the factor that sets the published specification on a valve's maximum dissipation. If the temperature is raised above that manufacturing value, contaminants exit the metalwork and "poison" the valve. Probably a lot of new manufacture clone valves have issues with the metal purity and might not have been out-gassed at the correct electrode temperatures, so in use the problem crops up, but it might not in a lower power dissipation application.