Well, at the risk of being bombarded with criticism and vulgarities that are so common as of late, I just had to post this because it's amazing!

I've experimented with various methods of rejuvenating oxide coated cathodes with minimal success. Usually the result was temporary and undependable. However, upon reading that some fault was caused by gas and ion bombardment, and that the getter in really old tubes doesn't really do much unless it's heated, I decided to try something new. I just bought some nice G-45s for my Majestic, and they're great, but they are weak, which is why I could afford them. I'm not interested in experimenting with them at this point. However, I decided to experiment with an ST 45 I have that is less valuable, and tests in the REPLACE region on my tester. It still works fairly well, but definitely is weak. I put the tube in the oven (vertical with nothing touching the glass) and turned the control up to 500 degrees. Unfortunately the bakelite base started popping at about 450 degrees, so I had to turn the oven back off (I expected that this might happen). However, I let the tube cool with the oven, and then, after all was cool, I tested the tube. It tested in the GOOD range! It tested in the same exact place over and over again, even after putting it in the radio and running it for a bit. WOW! Too bad it isn't easier to remove bases from tubes, or else I'd bake more tubes. Baking the bakelite base not only ruins its appearance and makes a big smell, but it also spreads the pin spacing due to swelling, so the pins don't line up properly anymore. Also, as would be expected, the solder connections need to be remade. However, if a method can be devised of easily removing the base without destroying the tube, a lot of valuable/rare tubes might be able to be rejuvenated using this method.

T.

To remove the old hard glue inside of tube base I have put the tube in a sealed glass jar 1/2 full of lacquer thinner..It softens up old glue and pins can be un-soldered...Lacquer thinner will remove all labes printed on tube.

:Well, at the risk of being bombarded with criticism and vulgarities that are so common as of late, I just had to post this because it's amazing!
:
:I've experimented with various methods of rejuvenating oxide coated cathodes with minimal success. Usually the result was temporary and undependable. However, upon reading that some fault was caused by gas and ion bombardment, and that the getter in really old tubes doesn't really do much unless it's heated, I decided to try something new. I just bought some nice G-45s for my Majestic, and they're great, but they are weak, which is why I could afford them. I'm not interested in experimenting with them at this point. However, I decided to experiment with an ST 45 I have that is less valuable, and tests in the REPLACE region on my tester. It still works fairly well, but definitely is weak. I put the tube in the oven (vertical with nothing touching the glass) and turned the control up to 500 degrees. Unfortunately the bakelite base started popping at about 450 degrees, so I had to turn the oven back off (I expected that this might happen). However, I let the tube cool with the oven, and then, after all was cool, I tested the tube. It tested in the GOOD range! It tested in the same exact place over and over again, even after putting it in the radio and running it for a bit. WOW! Too bad it isn't easier to remove bases from tubes, or else I'd bake more tubes. Baking the bakelite base not only ruins its appearance and makes a big smell, but it also spreads the pin spacing due to swelling, so the pins don't line up properly anymore. Also, as would be expected, the solder connections need to be remade. However, if a method can be devised of easily removing the base without destroying the tube, a lot of valuable/rare tubes might be able to be rejuvenated using this method.
:
:T.

I have to give it a try!!!!!! Thankfully the tubes I am working with have engraved bases! I might try acetone since I don't have lacquer thinner at hand currently.

WOW! If I could make my Majestic G-45 tubes test like new again, that would be terriffic! I will stick to less valuable tubes for now.

T.

:I have to give it a try!!!!!! Thankfully the tubes I am working with have engraved bases! I might try acetone since I don't have lacquer thinner at hand currently.

Don't use acetone. That WILL melt the base. Lacquer thinner is what you need to get.

Thomas can't you just mount the tube in a holder of some sort and blast the upper glass area with a heat-gun for a few minuets?

Not sure, but acetone won't melt the base. It's bakelite.

I will consider the heat gun method. I like thoroughly baking the tube better, since it is thorough on all sides of the glass, but I may try the heat gun (if I can find my dad's). I do know that you can move the heat gun around, but I don't know how the glass will like that as opposed to an oven.

When the tube is in the oven, its glass must not touch anything, so if the base is removed, it would be best to hang it somehow by its wires (perhaps a vice grips).

Today I'm going to try some all glass 12AU7s that are "Replace," and one that's definitely gassy. Then, if I have success with the bases, I have an 80 that is weak and gassy and a 47 that is Replace, but not gassy as far as I know. The 47, when it was used in a Century radio that I do not own, functioned very poorly (barely). The 45 I rejuvenated was not gassy to begin with and isn't gassy now, either. It'll be interesting to see the effects on the various tubes.

T.

:Not sure, but acetone won't melt the base. It's bakelite.
:
:I will consider the heat gun method. I like thoroughly baking the tube better, since it is thorough on all sides of the glass, but I may try the heat gun (if I can find my dad's). I do know that you can move the heat gun around, but I don't know how the glass will like that as opposed to an oven.
:
:When the tube is in the oven, its glass must not touch anything, so if the base is removed, it would be best to hang it somehow by its wires (perhaps a vice grips).
:
:Today I'm going to try some all glass 12AU7s that are "Replace," and one that's definitely gassy. Then, if I have success with the bases, I have an 80 that is weak and gassy and a 47 that is Replace, but not gassy as far as I know. The 47, when it was used in a Century radio that I do not own, functioned very poorly (barely). The 45 I rejuvenated was not gassy to begin with and isn't gassy now, either. It'll be interesting to see the effects on the various tubes.
:
:
:
:T.

you could probably rig up a fixture with an old turntable and use one of those silicone baking pads. a hole is made in the silicone pad so just the glass is exposed. the turntable at 16rpm speed rotates the tube like a rotissery and the heat gun is stationary sitting on its base. the silicone pad would prevent heat from hitting the base. i could sketch it but dont know how to post a sketch. or how about a few seconds with a torch like used to sweat plumbing copper pipes. you would only need a few seconds

Sounds like a good idea. As far as time goes, I'm not sure how much time is required. The tube sat in my oven for several hours, even as the oven cooled, so it was hot for a long time. I will have to see if the tube must be cooked for a while, or if it's only necessary to heat the getter for a moment. Baking the tube does drive gasses out of the metals.

I can't find my 12AU7s that are weak. Right now I'm trying to remove the base of the #47 tube.

T.

Heating unevenly with a torch/heat gun will probably fracture the glass. A turntable would help, but why bother with a new fixture, when an oven is near by. When the glass expands at different rates around the perimeter of the globe, its more apt to crack. The oven is best.

marv

:Sounds like a good idea. As far as time goes, I'm not sure how much time is required. The tube sat in my oven for several hours, even as the oven cooled, so it was hot for a long time. I will have to see if the tube must be cooked for a while, or if it's only necessary to heat the getter for a moment. Baking the tube does drive gasses out of the metals.
:
:I can't find my 12AU7s that are weak. Right now I'm trying to remove the base of the #47 tube.
:
:T.

That's what I was thinking.

As far as acetone is concerned, I did get the base off of the #47. It is now baking. I let it reach 500 degrees and now it is cooling, so I'll check on it later. I wish I could find my dud miniature tubes because it'd be easy to bake a batch of them. :D I took pictures of the 47 in the tester, and I'm also working on the 80, which I also took pictures of before soaking. ...So when all is through, I'll have pictures of what I found, if it looks good. Otherwise I'll just post that it was a fluke.

I wish that there was good music on the radio so that I could really put these tubes through a test. All I have right now is Pandora, so I pipe that in.

T.

I've always Used This method:
Unsolder pins first,
Let a pot of water come to a boil,shut the flame off,put the tubes in.
Wait about 10 mins.
Gently rock tubes in base,they'll come out.
It's fairly simple,I've rebased many 864's this way in WD11 bases and many other types.
:Sounds like a good idea. As far as time goes, I'm not sure how much time is required. The tube sat in my oven for several hours, even as the oven cooled, so it was hot for a long time. I will have to see if the tube must be cooked for a while, or if it's only necessary to heat the getter for a moment. Baking the tube does drive gasses out of the metals.
:
:I can't find my 12AU7s that are weak. Right now I'm trying to remove the base of the #47 tube.
:
:T.

Interesting method. I think that I may try it. Sounds less volatile. I managed to get the base off of the 47. There was enough of a leak at the top of the base that the acetone could get through the pins and rise up, since I removed the solder from the pins. However, I wasn't so lucky with the 80. It won't come undone. I may have to drill a very small hole at the top of the base. I don't like drilling holes, though, because that's how evacuation tubes, etc., get broken.

Regarding the 47, though, I baked it, and guess what??!! It tests in the good region!!!!! I tested it with heavy current, too, and it drew well. This is vague, I know, but at its proper #3 current setting (EICO 625), the needle would barely move, and at the #4 setting, which is higher current at 200 volts (I believe), the needle might go about 1/2 an inch. Now it goes into the good on 3 and pegs on 4. I am re-baking it to see if I can make any improvements from here (with my first baking I merely let the oven reach 500, and then I turned it off). I wanted to leave the oven at 500 for 45 minutes (while my clothes dry), but I couldn't stand the fumes of the extremely hot oven, so I turned it off after 25 minutes. Still it has residual heat, so it'll be cooking for a while. I wish that I had a radio to try the 47 in.

T.

In Rare Cases where I had a real stubborn tube, I used some lacquer Thinner or Denatured alcohol.
I applied through The unsoldered pins with no drilling.
i used an old Tin Oiler can somtimes to apply.
:Interesting method. I think that I may try it. Sounds less volatile. I managed to get the base off of the 47. There was enough of a leak at the top of the base that the acetone could get through the pins and rise up, since I removed the solder from the pins. However, I wasn't so lucky with the 80. It won't come undone. I may have to drill a very small hole at the top of the base. I don't like drilling holes, though, because that's how evacuation tubes, etc., get broken.
:
:Regarding the 47, though, I baked it, and guess what??!! It tests in the good region!!!!! I tested it with heavy current, too, and it drew well. This is vague, I know, but at its proper #3 current setting (EICO 625), the needle would barely move, and at the #4 setting, which is higher current at 200 volts (I believe), the needle might go about 1/2 an inch. Now it goes into the good on 3 and pegs on 4. I am re-baking it to see if I can make any improvements from here (with my first baking I merely let the oven reach 500, and then I turned it off). I wanted to leave the oven at 500 for 45 minutes (while my clothes dry), but I couldn't stand the fumes of the extremely hot oven, so I turned it off after 25 minutes. Still it has residual heat, so it'll be cooking for a while. I wish that I had a radio to try the 47 in.
:
:T.

Since you only need to heat the elements of the tube - and not the glass envelope or base - why not direct your energy (pun intended) there? You could experiment with infra-red, magnetic induction, rf or microwave - all of which could induce blistering hot temps to the elements whilst sparing the envelope and base..... There are plenty of MOV's to experiment with for cheap at thrift shops. Look here too - http://www.ameritherm.com/index.html

Also check out the video of Clade Paillard who makes his own tubes - I believe he uses both a home-built IR oven and a magnetic induction flash..... http://paillard.claude.free.fr/

The reason why I chose an oven is because the elements already get baked when the tube is on. I've tried running the filament too hot (which destroys oxide cathodes), and I've tried running the plate voltage high, and running the plate voltage high with the filament lower than normal (which sparks the cathode), and I even tried briefly microwaving a tube (bad idea). None produced good repeatable results. I did manage to get the gassy 80 to work by cooking it for a long time in my tester (higher filament voltage and plate voltage applied), and also by putting it in the freezer, but it measures very much in the "replace" region, and is still somewhat gassy (purple glow). It does work reliably. As far as the 45 I cooked yesterday, I've never been able to get it to stay in the good region before, using some of the above methods. However, now after baking it, even after playing it in my Majestic 181 for 2 hours, it still tests exactly the same in the good region, so I think that the baking method might have promise.

The reason why I selected baking is because it heats all items (especially glass) somewhat uniformly (heat transfer through a vacuum is minimal, but the internal elements do get warm eventually. It also heats the getter, which, as I recall, is only useful when hot (in early tubes with the bright silver). To prove the point, if you crack one of these tubes open, the getter will stay silver for years (doesn't react quickly). I read that when a tube is first made, it is baked while hooked to the evacuator. Baking drives out gasses, which both leaves through the evacuator, and also gets trapped in the getter as a chemical reaction. ...So I thought that I'd give baking a try, though I'm not evacuating the tubes.

Though they say that the oxide is poisoned from the filament being too hot, I also read something about excess gas in the early tubes that caused ion bombardment. I noticed that readings with these weak tubes were all over the place, climbing up, and then down, and then up, and down, at random times. While the filament oxide could be changing its bonding form, I feel that this is more from something very random like gas particles. Who knows, really. It's odd, but the first tube I tried became completely stable and much stronger after baking. I really need to do more trials though before I can surely prove anything.

T.

......heat transfer through a vacuum is minimal, but the internal elements do get warm eventually.......

I'll try to console myself with that factoid the next time I touch the rectifier tube in a set I'm working on...(LOL)

Well, from what I've read, and what I believe, since I do know that a vacuum cannot conduct heat, the heat is transferred to the glass by radiation and the very small traces of air still remaining in the bulb.

:Well, from what I've read, and what I believe, since I do know that a vacuum cannot conduct heat, the heat is transferred to the glass by radiation and the very small traces of air still remaining in the bulb.

I have learned on several occasions that the glass on a tube gets hot enough to remove skin from fingertips, however the heat gets there. Also, hot tubes can look exactly like cool tubes.
Lewis

Did you try soldering the pins before this exercise? If connections were poor before, expansion from the heating may have changed the resistance enough to make the tube happy.

:Well, at the risk of being bombarded with criticism and vulgarities that are so common as of late, I just had to post this because it's amazing!
:
:I've experimented with various methods of rejuvenating oxide coated cathodes with minimal success. Usually the result was temporary and undependable. However, upon reading that some fault was caused by gas and ion bombardment, and that the getter in really old tubes doesn't really do much unless it's heated, I decided to try something new. I just bought some nice G-45s for my Majestic, and they're great, but they are weak, which is why I could afford them. I'm not interested in experimenting with them at this point. However, I decided to experiment with an ST 45 I have that is less valuable, and tests in the REPLACE region on my tester. It still works fairly well, but definitely is weak. I put the tube in the oven (vertical with nothing touching the glass) and turned the control up to 500 degrees. Unfortunately the bakelite base started popping at about 450 degrees, so I had to turn the oven back off (I expected that this might happen). However, I let the tube cool with the oven, and then, after all was cool, I tested the tube. It tested in the GOOD range! It tested in the same exact place over and over again, even after putting it in the radio and running it for a bit. WOW! Too bad it isn't easier to remove bases from tubes, or else I'd bake more tubes. Baking the bakelite base not only ruins its appearance and makes a big smell, but it also spreads the pin spacing due to swelling, so the pins don't line up properly anymore. Also, as would be expected, the solder connections need to be remade. However, if a method can be devised of easily removing the base without destroying the tube, a lot of valuable/rare tubes might be able to be rejuvenated using this method.
:
:T.

:Well, at the risk of being bombarded with criticism and vulgarities that are so common as of late, I just had to post this because it's amazing!
:
:I've experimented with various methods of rejuvenating oxide coated cathodes with minimal success. Usually the result was temporary and undependable. However, upon reading that some fault was caused by gas and ion bombardment, and that the getter in really old tubes doesn't really do much unless it's heated, I decided to try something new. I just bought some nice G-45s for my Majestic, and they're great, but they are weak, which is why I could afford them. I'm not interested in experimenting with them at this point. However, I decided to experiment with an ST 45 I have that is less valuable, and tests in the REPLACE region on my tester. It still works fairly well, but definitely is weak. I put the tube in the oven (vertical with nothing touching the glass) and turned the control up to 500 degrees. Unfortunately the bakelite base started popping at about 450 degrees, so I had to turn the oven back off (I expected that this might happen). However, I let the tube cool with the oven, and then, after all was cool, I tested the tube. It tested in the GOOD range! It tested in the same exact place over and over again, even after putting it in the radio and running it for a bit. WOW! Too bad it isn't easier to remove bases from tubes, or else I'd bake more tubes. Baking the bakelite base not only ruins its appearance and makes a big smell, but it also spreads the pin spacing due to swelling, so the pins don't line up properly anymore. Also, as would be expected, the solder connections need to be remade. However, if a method can be devised of easily removing the base without destroying the tube, a lot of valuable/rare tubes might be able to be rejuvenated using this method.
:
:T.
Hi Thomas,
You have come up with a good one this time!

You may consider wrapping the base of the tube with cotton or styrofoam to insulate it from the high temperature.
Another option would be to place the base in water, that will keep it below the boiling point.

I expect this will not work on weak tuning eyes, since their problem is phosphor displacement, not emission. I am thinking of trying it, though.

Best Regards,

Bill Grimm

WOW! I should try it with eye tubes!!!!!!!! Probably won't work, though. They usually do test good even though they are dim.

As a follow-up for the #47, after further baking it now tests even better than before. Again, this is vague, as it is an emissions tester, but originally the meter read 600 and now it reads 800. The tube started out reading about 20-50. The original test was made with the base on. I did heat the pins before testing to be sure that the solder connections were good. The 'good' tests were made after the base was removed (after baking once and twice). I merely inserted the wires into the 7 pin socket on my tester. The most difficult connection to make was the filament, due to its current. All other connections were made well, and I ascertained this by throwing the various levers down from their up positions. Since they handle higher voltage at very low current, it will be easier to make a good connection.

I wonder what would happen if I baked the tube for an hour! I do notice a darkening of the glass as I bake the tube. Something is coating the inside of the glass. Perhaps it is getter or perhaps it is some other foreign material. It's an even smoky coating--very light. I'll have to search through my big box of tubes to find the weak 12AU7s. I think that they were Mullards. There are quite a few of them. It would be nice to batch test them. I thought that they'd be in my miniature tube box, but, as usual, they weren't (mess).

T.

My understanding is that the getter was flashed in the factory, by heating it inductively with an external source. True?

If so, is it possible to re-flash the getter on a weak tube?
Doug

I baked a weak 6K6G tube, and it measures similar to before, and now is definitely gassy--purple glow, so I guess this method isn't a sure fix.

T.

Tom, I tend to think the base soldering may have corroded some. The getter is used to remove any remaining oxygen from the vacuum envelope. The getter was coated with a flammable substance and when heat applied by a high voltage flash, the material would ignite only if there were oxygen present in the envelope. The idea being that with no oxygen in the envelope no elements could oxidize or burn (fire=oxygen/fuel/ignition temp) Theoretically, no oxygen, no oxidation. Like every thing, its never 100% and thats why heater elements burn out. Enen the getter cant get it all. Taking all things in to consideration, I can not think of a reason that heating the tube in an oven would be regenerate it any more than when it is running in a set and heating itself from its core. I'm not doubting that the tube's performance may not have improved by I think its due to your re-soldering the pins on the base. That, by the way, may be a good idea on older tubes eg re-solder pins. If you try your experiment on the miniature tubes (no base) and they do not improve that may tell you something.Again, I'm not poo pooing your endeavers, just pointing out another possible cause of the improvement. Interesting aside, Edison added a "getter" of sorts in an attempt to draw the ions to a small point on the lamp bulb as it was coating the entire surface and clouding the lamps. He did note that when he applied a potential to the getter he did note a small voltage passing to getter but didn't catch its significance (he had a diode!)PLchange

:I baked a weak 6K6G tube, and it measures similar to before, and now is definitely gassy--purple glow, so I guess this method isn't a sure fix.
:
:T.

We will have to see. I will have to test more tubes. It may have to do with what materials they used, which changed over the years.

I have further read on the web that the getter actually doesn't vaporize again or become useful again (old silver getter, not the more modern barium, which is always active) unless it is raised to several thousand degrees, which might melt the glass, so I don't think that I was reactivating the getter. I don't know what I did, but with two tubes it worked very well. They have good solid tests over and over again, even after one of them has been used. A third tube, more modern, became gassy, and readings did not improve. However, with that tube I let it bake for over a 1/2 hour at 500 degrees, where-as the other tubes I only allowed to get up to 500, and then I turned off the oven. Whatever I am doing is definitely putting a brown deposit on the glass.

I have further read on the web that there are others out there who bake tubes, and have success for various reasons.

I only have one 1L6 tube, and it tests good, but if I can find other weak battery tubes, I will try to rejuvenate them.

T.

:We will have to see. I will have to test more tubes. It may have to do with what materials they used, which changed over the years.
:
:I have further read on the web that the getter actually doesn't vaporize again or become useful again (old silver getter, not the more modern barium, which is always active) unless it is raised to several thousand degrees, which might melt the glass, so I don't think that I was reactivating the getter. I don't know what I did, but with two tubes it worked very well. They have good solid tests over and over again, even after one of them has been used. A third tube, more modern, became gassy, and readings did not improve. However, with that tube I let it bake for over a 1/2 hour at 500 degrees, where-as the other tubes I only allowed to get up to 500, and then I turned off the oven. Whatever I am doing is definitely putting a brown deposit on the glass.
:
:I have further read on the web that there are others out there who bake tubes, and have success for various reasons.
:
:I only have one 1L6 tube, and it tests good, but if I can find other weak battery tubes, I will try to rejuvenate them.
:
:T.

I remember reading in a old radio electronics magazine about putting a weak tube in the oven at 200 degrees for several hours.
I have never tried it but the article claimed it worked.