Yikes! Another CT-100 !

[jeyurkon]

Originally Posted by jr_tech

I think that there might be a couple of reasons to proceed with caution.

1. Liability... I really would not want to be the person operating the CRT checker, if that test blows the heaters, unless the owner of the tube fully understands the the possibility that the test might "finish off" the tube.

2. If the heaters blow it is indeed "game over" for the tube (except for rebuild). If they are intact, there still might be a very slim possibility to save it... Perhaps Scotty can re-flash the getters?

just my 2cents (or less) worth,
jr

The issue of dealing with an irate seller who thinks you just blew his 15GP22 is certainly a worry. A noisy hand held Tesla coil might have him wondering too.

As far as "game over" or not... I'm skipping definition of terms because I know you're very knowledgeable technically.

The getter flash probably has a capacity of a few hundred liter-microns before it is used up. If the getter flash is gone you've probably had that much air enter. It's less effective for nitrogen, the few hundred liter-micron figure is for oxygen. You probably have at least a few hundred liter-microns of air to deal with once you find a gassy 15GP22.

I'm not sure how the getter in the 15GP22 is made, but it's probably a large ring at the end of the gun. The ring could be a channel or a tube. If it's a tube then it has a thin wall that bursts when it's heated and the barium evaporates out. If it's a channel, then it's probably a stable barium alloy like BaAl4, that reacts exothermically with a nickel support once above 800C and quickly reaches higher temperatures evaporating the barium. Nickel powder is also added to BaAl4 powder, but I don't think this technology existed then.

Any barium left to flash will be minimal and you have a lot of gas to deal with.

The cathodes will be deactivated. During the activation barium oxide is reduced to barium forming a thin layer of barium metal on the barium oxide. Any metallic barium will have turned to an oxide if the tube was gassy. It is reduced either by silicon that was added to it or by the nickel cathode base metal. The nickel will have formed some nickel oxide and might prevent another reduction of the barium oxide.

I have a bunch of 6J6's that have air in them. I've thought about adding a pump-out and see if I can reactivate the cathodes. I suspect it won't work, but it would be fun to try. Finding the time is hard though.

John

[jr_tech]

John said:

"I'm not sure how the getter in the 15GP22 is made, but it's probably a large ring at the end of the gun. The ring could be a channel or a tube. If it's a tube then it has a thin wall that bursts when it's heated and the barium evaporates out. If it's a channel, then it's probably a stable barium alloy like BaAl4, that reacts exothermically with a nickel support once above 800C and quickly reaches higher temperatures evaporating the barium."

In the case of the 15GP22... The getters appear to be the "stirrup" style mounted in the neck... looks like there are 6. IIRC, not all getters were exothermic.

"Any barium left to flash will be minimal and you have a lot of gas to deal with."

I 100% agree with this. But if the tube were mine and I had an RF generator, and a getter "wand" I would try it.

"I have a bunch of 6J6's that have air in them. I've thought about adding a pump-out and see if I can reactivate the cathodes. I suspect it won't work, but it would be fun to try."

Back in my old "poor starving young engineer" days, I kept an old CTC-4 going by re-flashing and re-activating the 6CB5 HO tubes several times (darn things were expensive and I had access to an "engineering tube lab")... your experiment sounds like fun

jr

[jeyurkon]

Originally Posted by jr_tech

John said:

"
"Any barium left to flash will be minimal and you have a lot of gas to deal with."

I 100% agree with this. But if the tube were mine and I had an RF generator, and a getter "wand" I would try it.

jr

I would too. I just wouldn't have my hopes up. On the other hand, I have seen a number of vacuum tubes where it looked like they barely flashed the getter and there might be much left.

Your comments about the 6CB5 are encouraging. I'll have to try it. I can evacuate the 6J6 without needing to bother with the getter and I can RF heat the elements to outgas them.

Originally Posted by TubeType

No John, it's to protect my rear from the CT-100 owner who's trying to get me to bid on his priceless vintage set.
I don't want to watch the expression on his face when I destroy his crt's filament.
I can't run that fast, anymore.

I guess it would depend on whether the seller would understand well enough what you were doing. The value of the set would be greatly enhanced with a good 15GP22 and I would hope they would let me test it and understand if the result was a briefly glowling filament. Otherwise I'd be reluctant to pay top dollar not knowing if it was good or not.

The Tesla coil vacuum tester that I have would probably scare them if they had never seen one before.

Of course since I'm not actively searching for one, it's easy for me to say. Maybe I'd be of a different opinion if I were about to make an offer for one.

John

[WA3WLJ]

Isn't there a small copper tube nipple under or around the Black pin base?
If the filaments are good and then the base carefully removed; couldn't one vacuum pump the tube back down to around 1 X 10-5 or 1 X 10-6 ,and after applying VAC-U-Seal over the leak paths while still pumping (of course) . But then again you would only tap into this tube nipple if you knew the tube had already gone to air.

[TubeType]

Originally Posted by WA3WLJ

Isn't there a small copper tube nipple under or around the Black pin base?
If the filaments are good and then the base carefully removed; couldn't one vacuum pump the tube back down to around 1 X 10-5 or 1 X 10-6 ,and after applying VAC-U-Seal over the leak paths while still pumping (of course) . But then again you would only tap into this tube nipple if you knew the tube had already gone to air.

Unfortunately, not all of the air can be removed with a vacuum system alone.
You can read more about the process by searching this forum for "15GP22".

[jeyurkon]

Originally Posted by WA3WLJ

Isn't there a small copper tube nipple under or around the Black pin base?
If the filaments are good and then the base carefully removed; couldn't one vacuum pump the tube back down to around 1 X 10-5 or 1 X 10-6 ,and after applying VAC-U-Seal over the leak paths while still pumping (of course) . But then again you would only tap into this tube nipple if you knew the tube had already gone to air.

If I understood John and Bob correctly, most of them haven't gone completely up to air, but are gassy. I think you could tap into the line without breaking the residual vacumm and reach the pressure range you mention.

You need much better vacuum than this for long life. If rebuilding options were available I'd rather go that route if I had one that didn't work, rather than expending resources on a repair that wouldn't last long.

John

[jr_tech]

Originally Posted by jeyurkon

If I understood John and Bob correctly, most of them haven't gone completely up to air, but are gassy. I think you could tap into the line without breaking the residual vacumm and reach the pressure range you mention.

You need much better vacuum than this for long life. If rebuilding options were available I'd rather go that route if I had one that didn't work, rather than expending resources on a repair that wouldn't last long.

John

I wonder if a small turbomolecular pump would fit in the base of a CT-100, I think they are good for 10-8 or so.

jr

[jeyurkon]

Originally Posted by jr_tech

I wonder if a small turbomolecular pump would fit in the base of a CT-100, I think they are good for 10-8 or so.

jr

Or an ion pump so you wouldn't have to deal with the sound of the backing pump.

I think some of the high power klystrons basically have an ion-pump built into them.

John