Gassy Tube.

[Atlasta]

Hey all...

I've a 6LQ6 tube that was humming right along and then quite suddenly went gassy, indicated by a lovely blue glow visible upon key-up (or is it key-down?)

Anyway, it's still showing almost 90% emission so I really don't want to toss the thing given the price of replacement.

Online searches on how to 'de-gas' the tube have left me confused. If anyone can explain the hows and whys of de-gassing it would be greatly appreciated.

Thanks!

 

[Shockwave]

If the tube does not arc internally when under load, I wouldn't worry about the blue glow or attempt to degas the tube. Many of these sweep tubes continue to work just fine under this condition.

 

[Atlasta]

If the tube does not arc internally when under load, I wouldn't worry about the blue glow or attempt to degas the tube. Many of these sweep tubes continue to work just fine under this condition.

I don't see any arcing but on-air reports indicate that the audio quality suffers. Also it makes the watt meter read far higher than it should.

 

[ElectronTubesRule]

Their are two different methods well 3 really but the third one is out their in left field....

Method 1: Start with 1/2 the heater voltage recommended put just enough power into the grid to get the tube's heaters to work, after a day or 2 at half power step it up to full power on the heater but again just enough power to the grid to allow the heater to function. after a day or two like that slowly bring the grid up to entire system up to half power output after a day of this take it up to full power and try using it it. Look for arcing and in this case the blue glow. This what is recommended basically by the Russians for old tubes that are new in every way other then long time as in 20+ years sitting on a shelf.


Method Two:The old American method is very much the opposite approach with it you basically are putting insane voltages through the tube at next to zero ma.I am talking NEon sign or furnace pilot lighter type voltages in excess of 30,000 volts for short periods of time with little current. If you google tube restoration or vacuum/electron tube rejuvenation you will find both methods in better detail.


Method 3: You put said tube in the mircowave and nuke it until you see arcing them stop the microwave. It either restores it or it kills it the rest of the way so it is high risk and truly makes little sense to me.

Generally tubes that have thoriated tungsten type design seem to respond the best to rejuvination methods. Magic Eye tubes never respond at all.


I think I would let the tube run a few days the heater works 24/7 as long as the tube is powered. I would leave the amp on for a few days with out any key up just let the girl run. After a few days of the heater running drop her into a dummy load or a light bulb and do some long winded key down's have a fan blowing on it if you need too. This will either fix the old girl it will kill her one of the two.

No one repairs sweep tubes and if she is already not working right you have nothing to lose. More then likely if she all of sudden went gassy your seals for the tube are bad. Not much you can do about that. I have no idea what they used back then but it has to have outlived it's original validation mandate for service life. The type of gassy condition that is normally fixable is when it has happened simply because of long time sitting on a shelf the seals are still good the glass and other materials just off gassed the entire time the tube was sitting. When one is in regular use and just lets go it is normal a sign of a bad seal and that is not something can be fixed. The only way to fix that is to tear the tube apart and re-manufacture it and no one does that for sweep tubes.

 

[Atlasta]

I kind of figured that a seal went bad... after all these tubes are over 40 years old now. Still it can't hurt to try to save it. Fortunately I've a decent supply of spares.

I can let it cook for a few days and see what happens.

Thanks!

 

[ElectronTubesRule]

Letting the heater run is basically trying to let the getter do it's thing.