Does anyone have any hard data on the long term reliability of a 21AXP22? Assuming the metal rim isn't nicked and the tube doesn't fail catastrophically (implosion, being necked, uncontrolled internal arcing, etc) is a 21AXP22 a fairly reliable tube?

I have five in my collection now, two in sets (the Hoffman, and a CTC-4 Seville), and three spares. I would like to know if I should worry about any of them randomly leaking. Part of the reason I sold my CT-100 to John is because the 15GP22 is just too unreliable. In conversation with Ed Reitan shortly before he passed, he told me he randomly lost two 15GP22s to leaks over the years, one in a fully restored CT-100. Factor in the countless failed rebuild attempts, and any 15GP22 looks like a crap shoot. I'd like to avoid that fate with my 21 inchers...

If CRT rebuilding ever truly gets off of the ground at the ETF, can leaker 21AXP22s be re-welded along that rim, and are they going to be as difficult to rebuild as the ghastly 15Gs?

Does anyone have any hard data on the long term reliability of a 21AXP22? Assuming the metal rim isn't nicked and the tube doesn't fail catastrophically (implosion, being necked, uncontrolled internal arcing, etc) is a 21AXP22 a fairly reliable tube?

I have five in my collection now, two in sets (the Hoffman, and a CTC-4 Seville), and three spares. I would like to know if I should worry about any of them randomly leaking. Part of the reason I sold my CT-100 to John is because the 15GP22 is just too unreliable. In conversation with Ed Reitan shortly before he passed, he told me he randomly lost two 15GP22s to leaks over the years, one in a fully restored CT-100. Factor in the countless failed rebuild attempts, and any 15GP22 looks like a crap shoot. I'd like to avoid that fate with my 21 inchers...

If CRT rebuilding ever truly gets off of the ground at the ETF, can leaker 21AXP22s be re-welded along that rim, and are they going to be as difficult to rebuild as the ghastly 15Gs?
As long as they're stored where there isn't any real temperature extremes, I feel that it would insure their reliability.
Metal cones expand and contract with temperature changes.

I only have one 21AXP22 (out of a CTC-4) and it is gassy (no catastrophic failure)...Granted the set was in bad shape and I have no way of knowing the storage conditions it experienced, beyond that it was freezing in Nick's garage when I obtained it.

IIRC the guy that was trying to make an all glass 15GP22 did a test rebuild on a 21AXP22 and sealed the leaks, so it may be feasible.

The advantage of 21" sets over 15GP is that you can easily adapt them to more stable all glass CRT types (as I did with my CTC-4)......

Granted those 'all glass' tubes are not bulletproof either....I have two gassy 21FBP22 CRTs in my basement, and BOTH of them have copper metal evacuation nipples....Clearly metal-glass seals are the bane of holding vacuum reliably for more than 30 years.

It would appear that the 15GP22 is a total lottery: some will leak, some won't, with no good way of determining the losers from the winners. A 21AXP22 should be markedly more stable than a 15 incher, but still substantially less stable than the all glass types. I guess I'll just leave my spares on the shelf where they are and hope for the best. It's a fairly consistent 62 degrees (+/- 3) with extremely low humidity.

I have the only 21AX that has had a leak repaired. The leak was on the weld where the funnel is joined to the front section. John Yurkon did the repair to the leak and did a standard rebuild procedure with a new gun assembly. That tube is now in my recently restored CTC4 Cheltenham and it is producing a very strong, bright picture. It is our conjecture that it would be a rare occurrence for a 21AX to have a glass to metal interface leak. Most all of the leak failures are occurring in the weld between the funnel and the front section of the tube. If a 21AX has not leaked thus far, it is unlikely that it will leak in the future, barring careless handling causing physical damage to the weld.

As for the 15G; two types of leaks can occur. The first type is a failure of the weld or a failure of the fusion weld of the reinforcement ring in the ultor ring assembly. The second common 15G leak is a failure of the glass to metal bond. I have seen a number of 15G tubes that have small fissures in the glass to metal bond. These can propagate due to large temperature swings or from physical stress. If the glass to metal bonds are free of small fissures in the glass I would say there is a high probability that the tube will stay leak free provided it is not subjected to large temperature swings or any physical stress. One other issue is moisture. About half the leaker 15G's I have examined, have been subjected to moisture which has caused rust to form on the ultor ring to varying degrees. The rust between the laminations of the ultor ring expands between the laminations and causes physical stress. The stress results in micro cracks in the glass where the glass is bonded to the metal ultor ring, thus causing a leak. So if you have a good 15G, keep it in a temperature controlled dry environment and do not subject it to any undue physical stress.

I guess that answers the question about the feasibility of sealing and rebuilding leaker 21AXP22s. It's not only possible; it's been done. The whole collecting community really owes you and both Johns quite a bit for working out the finer details of bringing these monsters back to life. Thanks guys! :)

A kinda dumb question, but what about the large temperature swings in the TV set itself from cold to full operating temperature?

I would vacseal the funnel weld and the face plate weld. Although I'm not sure what the thermal expansion ratio of the vacseal would be and wether it would stay solid while the glass and metal contracts and expands possibly causing micro fractures in the glass sections. I do think Phil vacsealed his 15gp and as far as I know it's holding up well.

Vacseal is useless. The cracking and gaps allowing leaking are way too small for Vacseal to effectively "plug up".

Back when I worked for RCA Sarnoff Labs in the 1980's, they had epoxy like stuff called "Torr-Seal" which I think was meant to seal vacuum systems. It dried hard. Don't know if it could take expansion of metal or glass parts though. And even if you put this stuff on the joints, there may still be enough air in air pockets under this stuff that would make the tube gassy if the original seals failed.

Bob nailed it. AXP's are vastly easier to repair than a 15G, though I've had success at welding both types of ultor flange material at home. The AXP appears to be made of ordinary spun mild steel, so all the rules for welding steels apply there. The 15G may be a little different metallurgically, I can say for sure that the metal 'flows' a lot better than mild steel does. It has a great affinity for itself, all you have to do is get the parts close to each other and apply the TIG torch and they zip together like they always wanted to be that way. Unlike aluminum where you have to keep dabbing filler into the puddle, or it forms a giant keyhole as the hot material expands away from itself.

A kinda dumb question, but what about the large temperature swings in the TV set itself from cold to full operating temperature?

That is a very good point! I never thought about the large heat build up that develops inside the set from the 40 or so tubes and other heat generating components. I guess if I was to be on the safe side, I would install an equipment fan in the set to force cool it.

There is also another consideration in the rebuilding of a 15G which could potentially be a very large problem.

Some years ago John Folsom and I had Scotty at Hawkeye rebuild a 15G which, up to that time, had been leak free. Scotty successfully installed a rebuilg 15G gun assembly and evacuated the tube using a slow ramp 6 hour evacuation cycle in his oven.

The rebuild was a success and the tube was shipped to Florida where John Folsom and I installed it in a 15" Westinghouse set. It produced a beautiful picture for a short period. 30 days later the tube had become gassy. We surmise that somehow during the evacuation cycle the stresses of temperature and physical forces involved in relieving the original vacuum, and then pulling a new vacuum on the envelope, caused some sort of defect in the envelope. We have not pulled the tube to examine it and determine exactly what kind of leak it has, but that is something that we will need to do before proceeding on any further attempts to rebuild a 15G.

There is the possibility that the envelope had a micro crack that propagated due to heat and physical stresses. And it should be noted that we had sealed the envelope with VacSeal which points to the complete ineffectiveness of using VacSeal to eliminate vacuum leaks on a 15G.

John Yurkon and I have discussed the possibility of doing a very long low temperature evacuation. By not subjecting the envelope to such high temperatures, the amount of stress from thermal expansion and contraction would be reduced, and hopefully this would help to minimize the tendency to cause a physical defect in the envelope. It would also help protect the phosphor dot plate from cracking like occurred in several tubes that RACS worked on.

John Yurkon did the repair to the leak and did a standard rebuild procedure with a new gun assembly.

Was that back when Hawkeye was still in business?

No after

My 21CT55 (CTC2B) has a 21AXP22 and has never lost it's vacuum. I understand that the set originally came from the Las Vegas area to Omaha and has been moved around locally, and still has really good emission. Although It was replaced with a "new" 21AX in 1957, so the original must have crapped out a few years after the set was built.

No after

So who did it? I thought you haven't done a color tube yet?

So who did it? I thought you haven't done a color tube yet?

It's a side note near the bottom of this page.
http://www.earlytelevision.org/yurkon_15g_project.html

Twas' a cattle call for dud 21AXPs here for that attempt some time ago...

John Yurkon here in Michigan did it. He apparently has a rebuilding setup.

Oops wrong thread! My bad!

I was moving it at the same time you were editing it! :yes:

My 21ax is a colorama rebuild from '62. The emissions are very strong and it performs great. It's a tough one having survived the 1200 mile trip from mass through multiple potholes and frigid weather. I attribute it's long life to the conditions I have in my room. I run a dehumidifier and keep my room at a constant 72 degrees. The only thing that scares me is that the damn evacuation nipple is one of those copper ones that have been known to leak rarely.