Yikes! Another CT-100 !

[ohohyodafarted]

Originally Posted by TubeType

"I Am Not Not Affiliated With This Auction"

Current bid is at $1700. The reserve has been met and the $5000 BIN has been lifted.

The seller reports, the chassis S/N appears to be B8000316 and the cabinet S/N is 538; the getters are shiny and there is filament continuity.

I would not place bets that the tube is good. In two of the photos you can see a milky white residue around the getters. That is a very bad sign. The tube that John and I rebuilt went gassy and the getters are still nice and silver with NOT any sign of milky white residue. This tube is most likely under partial vacuum, but probably gassy. And in any event the seller disclosed that somebody had wired a makeshift brightner in the filiment circuit and that is sure sign that the crt is toast.

[TubeType]

Originally Posted by ohohyodafarted

I would not place bets that the tube is good. In two of the photos you can see a milky white residue around the getters. That is a very bad sign. The tube that John and I rebuilt went gassy and the getters are still nice and silver with NOT any sign of milky white residue. This tube is most likely under partial vacuum, but probably gassy. And in any event the seller disclosed that somebody had wired a makeshift brightner in the filiment circuit and that is sure sign that the crt is toast.

Bob,
I couldn't agree with you more.
Also, it would be best for any potential bidder/buyer to arrange for an exhaustive crt check by a qualified person and to make the sale contingent upon the crt test results.

[jr_tech]

Originally Posted by ohohyodafarted

I would not place bets that the tube is good. In two of the photos you can see a milky white residue around the getters. That is a very bad sign. The tube that John and I rebuilt went gassy and the getters are still nice and silver with NOT any sign of milky white residue. This tube is most likely under partial vacuum, but probably gassy. And in any event the seller disclosed that somebody had wired a makeshift brightner in the filiment circuit and that is sure sign that the crt is toast.

I 100% agree with your observation... even though some "silver" is seen in the center of the getter flashes, the other side of the getter is likely to be white and "used up". I suspect that if the tube is powered up with a tube checker the heaters will quickly burn out from excess current, if they are not blown already.

jr

[TubeType]

Originally Posted by jr_tech

I 100% agree with your observation... even though some "silver" is seen in the center of the getter flashes, the other side of the getter is likely to be white and "used up". I suspect that if the tube is powered up with a tube checker the heaters will quickly burn out from excess current, if they are not blown already.

jr

Jr,
I'd recommend testing the crt for gas (air), with an HV source, before connecting a tester.

[jeyurkon]

Originally Posted by TubeType

Jr,
I'd recommend testing the crt for gas (air), with an HV source, before connecting a tester.

Why? To protect the tester? Once the CRT is up to air I don't think there's anything left to protect.

John

[jr_tech]

Originally Posted by jeyurkon

Why? To protect the tester? Once the CRT is up to air I don't think there's anything left to protect.

John

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

[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

[TubeType]

Originally Posted by jeyurkon

Why? To protect the tester? Once the CRT is up to air I don't think there's anything left to protect.

John

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.