If the tube is gassy, then it will usually fail various interelectrode leakage tests. Testers that have neon lamp leakage indicators will show leakage if the lamps blink or stay illuminated under test. A blue glow near the glass and not in the electrode assembly will not be a problem at all. Best way to check is to try the tube in its intended application if it passes a tube checker test first.
A number of hours ( 4-8 ) at 100-140deg C ) will activate the getter material.
To much heat will ruin octal sockets.
To much heat will ruin octal sockets.
Good info, thank you. Does this happen during normal operation, or does it have to be 'forced" (i.e., by putting them in an oven). Thanks.
If you do it in an oven you get rid of the gasses before you put it in service avoiding the potential fireworks the gasses could cause. If there is a very small amount of gas that is what the getter is designed to eliminate in use more than that try using the oven before hand. As was said there are some tubes that have a blue glow naturally that is not from gas but can fool you. Make sure your tubes are not one of those by doing a search for it.
The getter is active when hot. To use an oven is to make the getter do some work before
high voltage is applied.
Why is the vacuum depleted ? Long time storage may cause gas trapped inside the tube coming loose.
Normal usage will find that the getter is perfectly balanced to keep vacuum good.
Eventually the getter might be consumed ( rainbow at edges, gray/white color) and the vacuum
starts to be bad. Then it's time to replace the tube.
I had some problems with NOS GU50 date codes 90-xx what may have been the last production runs of GU 50.
They are a tiny bit gassy and start to exhibit gas discharge with voltages over 250v when brand new. Looks like a flash over but does no harm if current limited.
All that is required is to run the heaters only for an hour or so to activate the getter to remove those traces of gas.
After that they are good for 800V.
Only the late date codes seem to be affected, maybe a final production step was left out with the last batches ...
They are a tiny bit gassy and start to exhibit gas discharge with voltages over 250v when brand new. Looks like a flash over but does no harm if current limited.
All that is required is to run the heaters only for an hour or so to activate the getter to remove those traces of gas.
After that they are good for 800V.
Only the late date codes seem to be affected, maybe a final production step was left out with the last batches ...
I have made my self a valve tester. It has fairly low z grid impedance. I have put a couple of my gassy tubes, a Russian 6l6, and a Teonex EL34 on it to cook. after a while the grid current substantially went a way, but not completely. Haven't tried the tubes in a amplifier. The 6l6 used to run away and red plate on cathode bias. This is a relatively new toy so I can't give any long term test results.
Factory degassing involves putting tube inside a powerful transmitter induction coil and heating internal parts red or even orange hot, so they release trapped gas.
No oven can approach that, not even close.
No oven can approach that, not even close.
No. But this degassing occurs while the tube is still connected to a vacuum pump. When the
tube is sealed the getter is the only "pump" available.
I'd suggest there are a few influences to appreciate. 'Gas' level can increase through a few processes, like leakage through pin seals, and outgassing from material structures (especially materials that get over-heated such as from red-plating anode and glass envelope that has become hotter than designed). A valve is manufactured with enough active getter to maintain a suitably low level of 'gas' for many thousand hours of operation - meaning that getter material slowly becomes inert. Whatever active getter is still available becomes more capable with increased temp (ie. the rate of passivating gas gets higher). It is all a mix of 'rates' as to whether the concentration of gas increases or decreases, and how much active getter remains available. That is why one hears of such a range of trial outcomes.
As such, heating a tube up increases two competing 'rates' - outgassing on one side, and getter capability on the other side - and a nominal operating temperature typically keeps gas concentration at a low level. Go too high in temp and outgassing would normally win the battle. Time is also a factor when it comes to 'rate' and gas concentration, but if there is little active getter left then it is a downward spiral.
One could contemplate 'helping' the getter material by adding thermal insulation to the glass where the getter has been splattered, and operating the tube normally (ie. heater on, and some anode dissipation) - that way the valve materials don't get too hot, but also the getter material does get hotter than normal.
As such, heating a tube up increases two competing 'rates' - outgassing on one side, and getter capability on the other side - and a nominal operating temperature typically keeps gas concentration at a low level. Go too high in temp and outgassing would normally win the battle. Time is also a factor when it comes to 'rate' and gas concentration, but if there is little active getter left then it is a downward spiral.
One could contemplate 'helping' the getter material by adding thermal insulation to the glass where the getter has been splattered, and operating the tube normally (ie. heater on, and some anode dissipation) - that way the valve materials don't get too hot, but also the getter material does get hotter than normal.
Did the baking thing with a few gassy WE 429a. Can't recall the temp but it was probably 150c or so for three hours. Absolutely no change. They draw very little current until the grids get near -1v or so. Blue glow is visible between the internals.
I got an amp from the late 1930s, with a gassy 6L6. Cathode bias. I just let it run for a week, watching the cathode voltage (thus current) until the tube stabilized and the grid was less than 1V.
I used to test for gas on my DIY tube tester with 500K in series with G1. A good tube would give only one or two percent of anode current rise, whereas a bad tube had more than 30% anode current rise.
12Ax7 ~10s
KT88 ~20s
Corn on the cob 2min 30s.
On a serious note why not build an induction heater. C1 is made up of many smaller ceramics. L2 L3 is the induction coil.
https://www.diyaudio.com/community/threads/re-activate-getter-save-gassy-tube.298744/
KT88 ~20s
Corn on the cob 2min 30s.
On a serious note why not build an induction heater. C1 is made up of many smaller ceramics. L2 L3 is the induction coil.
https://www.diyaudio.com/community/threads/re-activate-getter-save-gassy-tube.298744/
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This relatively simple device will heat any metallic part inside a tube: the getter holding ring, the anode, etc. without heating the glass, pin holder, etc.
A caveat, as mentioned by one of the members is that liberating more getter material will also liberate the elements it is associated to, unless it is purely metallic:
https://www.diyaudio.com/community/threads/a-universal-regettering-station.317055/post-5300124
A caveat, as mentioned by one of the members is that liberating more getter material will also liberate the elements it is associated to, unless it is purely metallic:
https://www.diyaudio.com/community/threads/a-universal-regettering-station.317055/post-5300124
No I was joking when suggesting microwaves. The power is very high and the frequency 2.4GHz is so high that it more likely the internal valve components will act as antennas and cause high internal voltages plasma and destruction of the device. 1.5MHz seems the right choice of frequency. Have you had luck with induction heating i.e. a non working device works again. My understanding is that all the getter material should be on the tube top so if its gone that's the end.
I don't see much danger in building one seems more benign than the valve amps. Your more like to destroy the semi's or caps than yourself. Mind don't stick your finger with a ring on in it. If you want something more dangerous maybe a valve induction heater out of an RF tube transmitter. Anyway will do wonders for your AM reception.
Stick to food for the microwave and no eggs. However if somebody has an old microwave and a 12ax7 please post a video of what happens.
I don't see much danger in building one seems more benign than the valve amps. Your more like to destroy the semi's or caps than yourself. Mind don't stick your finger with a ring on in it. If you want something more dangerous maybe a valve induction heater out of an RF tube transmitter. Anyway will do wonders for your AM reception.
Stick to food for the microwave and no eggs. However if somebody has an old microwave and a 12ax7 please post a video of what happens.
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