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kalee20 · 5th Jun 2020, 10:42 pm

1 is OK. (Dodgy condition is HT on, lukewarm heater).

2 is not brilliant, but lots of equipment did it. Can lead to cathode interface resistance. If it's going to happen, it'll take tens to hundreds of hours.

3 Avoid this (unless you can keep a strong negative grid bias to cut off the valve).

4 OK. (If HT is there, make it very, very low). A cool heater will vastly increase the time the problem in (2) takes to appear. You really don't want to try to pull any significant prolonged current with a cool heater - cathode bombardment damage can arise.

5th Jun 2020, 10:42 pm	#2
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Valve question 1 is OK. (Dodgy condition is HT on, lukewarm heater). 2 is not brilliant, but lots of equipment did it. Can lead to cathode interface resistance. If it's going to happen, it'll take tens to hundreds of hours. 3 Avoid this (unless you can keep a strong negative grid bias to cut off the valve). 4 OK. (If HT is there, make it very, very low). A cool heater will vastly increase the time the problem in (2) takes to appear. You really don't want to try to pull any significant prolonged current with a cool heater - cathode bombardment damage can arise.