Magic eye "Off" mode

[Bigwolf]

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?

 

[Tom Bavis]

Better to switch the heater. Cathodes degrade when heater is on without B+.

 

[Bigwolf]

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.

 

[Kay Pirinha]

Turning off the plate and target supply indeed has been the most usual way in tube radios when switched to TT reproduction. So, why not?

Best regards!

 

[Merlinb]

Will turning off the target pin degrade the tube parameters?

Interesting question. I don't think turning off the target would harm the tube, but I'm open to education.

Turning off the heater is fine, it will not damage the 'filament'.

 

[gerrittube]

Without heater voltage no electrons will flow. This way the tube will not even know it’s connected.

Regards, Gerrit

 

[Bigwolf]

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.