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Magic eye "Off" mode

I want to make an "Off" switch on the target pin of the tube so that the green light is not visible at all.
I can disconnect all HT from the tube, but please do not discuss this.
Will turning off the target pin degrade the tube parameters?
 

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There are 3 ways:
1) Switch the heater (not good for filament)
2) Turn B+ off with 4V heater (may be better or worse for cathode depending on tube type)
3) Turn target pin off and cathode will work through triode part of tube.
 
I have not found any information in literature about operation without heater, but with HT. I will be grateful if you give me any info in old literature about it.

But I found a topic that after half a year in such mode the tubes lost emission.
In any case, some slow process of ion bombardment, or something in the cathode can degrade its emission. Room temperature is not "zero", but 300K, and the cathode works with "room" heating. The anode can also emit electrons (during normal operation), the vacuum in the tube has impurities, so I do not want to risk.
I think that turning off HT and heater is the best way.
 
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