Thread: Zero emission?
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Old 1st Aug 2021, 6:02 pm   #9
Heatercathodeshort's Avatar
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 8,223
Default Re: Zero emission?

The EDICRON EL34 on the right appears to have suffered overload possibly due to a biasing problem.
It is possible that either the screen grid or anode may have been raised to a red hot condition releasing gas molecules that the getter finds it impossible to mop up.

I had a similar problem with an amplifier I built a few years ago using 807s in the output stage. I accidently removed the anode voltage from one valve [top cap]to see the screen grid glow red hot followed by a blue fog in the valve envelope as the gas was liberated.

All seemed well after replacing the T/C and the blue fog reduced to zero after about 5 mins. Two weeks later the valve failed completely giving almost zero emission possibly caused by contamination of the cathode.

Just a possible answer. John.
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