Question about 15GP22 production

[ohohyodafarted]

Tom,
Even if no leaks were found, When you finally put the tube under vacuum and heat, this is the point where the leaks are created. The heat and physical vacuum stress, causes weak areas (usually in the glass) where micro cracks form at the juncture of the glass and the ultor ring.

It is an easy matter to find out if the envelope is leak free before evacuating. The leaks are created during the evacuation process. Even if you could test for a leak during evacuation during pump down, prior to pinch off, What good would it do? You could shut down, but you still have a new gun installed in a envelope that has a leak. I guess you might be able to salvage the gun and stem assembly by cutting it of and possibly re-using it on another tube. But we are better off finding a method of reliably sealing the envelope. Without a method of reliably sealing the envelope so that it doesn't leak during evacuation, attempting rebuilds of 15G's is pointless and we are just crossing our fingers that maybe 1 in 10 attempts might yield a good tube.

The one tube that RACS was successful with was a tube that did not have any leaks to begin with. It was pure luck that It did not develop any new leaks during the evacuation. It was just pure dumb luck. But it does demonstrate that it can be done under the right circumstances. RCA was rebuilding duds that were not leakers.

That's why we are hoping that a long, slow, low temperature pump down, combined with a special high temp epoxy that we have worked with, may help to lessen the possibility of causing new leaks in an envelope that is leak free prior to evacuation. It may even be able to seal micro fractures that exist in tubes that have a slow leak.

The epoxy would be applied in a manner similar to what RACS did with frit glass in France. However their attempts to seal with the frit were utter failures. IMHO frit was not the correct approach. Frit is designed to be placed between 2 precission ground glass surfaces. RACS thought it might work by slathering it on the outside of the tube. Frit was never meant to be used that way.

And there is no assurance that we would have any better luck with a low temp pump down and the special high temp epoxy. We will never know unless we are able to do some more experiments. Perhaps some day when Nick gets his crt rebuilding facility up and running.

As for me, until I am free of the responsibility of caring for my 102 year old mother, I rarely have any time for pursuing my hobby. I have care giving responsibilities 7 days/week, 365 days/year.

[Tom9589]

Bob, I remember a while back that someone was attempting to do an all-glass version of the 15GP22, thus eliminating the troublesome, leaky ultor ring. Do you (or anyone else) know the status of this project?

[ohohyodafarted]

Progress is slow, it is still a work in progress. It still has to have the gun installed and be evacuated. It currently holds a good vacuum under test conditions.

[Electronic M]

Originally Posted by Tom9589

Bob, I remember a while back that someone was attempting to do an all-glass version of the 15GP22, thus eliminating the troublesome, leaky ultor ring. Do you (or anyone else) know the status of this project?

This is what you're remembering.
http://www.earlytelevision.org/yurkon_15g_project.html

[benman94]

Originally Posted by Electronic M

This is what you're remembering.
http://www.earlytelevision.org/yurkon_15g_project.html

I think John's approach is likely to yield a good tube for him, but I doubt very much it could be repeated with any degree of success say three or four dozen times.

I hope the Epotec solution works, but I'm not holding my breath. There have been how many attempts to rebuild 15GP22s? And one successful tube (the 15GP22 in the ETF's Sparton) that appears to be little more than dumb luck.

Is it technically possible to rebuilt a 15GP22? Undoubtedly. Can a suitable solution be found to the problem, that is fairly trivial to repeat on dozens of tubes, and at a cost that a collector with a dud 15GP22 would be willing or able to pay? Maybe, maybe not. My gut says no.

My advice for anyone with a working 15G is twofold: treat it with kid gloves, and use the damn thing! I would rather get a solid year or two of enjoyment from the 15GP22 in my Westy, than turn the set on one day to find a bright pink neck and wish I had watched it more. That's why I'm having Nick do the restoration. It'll be done faster than I'd ever be able to complete it, and I'll be able to enjoy the set some.

[dtvmcdonald]

I DID watch my 15GP22 (above) until it died by arcing. I watched NFL
and the World Champion Chicago Cubs games on it.

OF course they can be made to work again, as long as we can get
guns. At worst, due to the way the front end is made, the metal parts
could be installed in a completely new glass envelope. The problem
is getting alignment good enough for ok convergence.

The price I'll pay .... I'll give no number, but note that I own a TT5 and a Marconi 702.

I'm still considering replacing it, at least temporarily, by a rectangular Trinitron tube
that does not need convergence, and a fake external mask. I will try talking to people
about that at the ETF. If I ever succeed, it would make a great ETF talk. The problem of course
is horizontal drive ... maybe use the transistorized board of the donor set?

[benman94]

Originally Posted by dtvmcdonald

I DID watch my 15GP22 (above) until it died by arcing. I watched NFL
and the World Champion Chicago Cubs games on it.

OF course they can be made to work again, as long as we can get
guns. At worst, due to the way the front end is made, the metal parts
could be installed in a completely new glass envelope. The problem
is getting alignment good enough for ok convergence.

The price I'll pay .... I'll give no number, but note that I own a TT5 and a Marconi 702.

I'm still considering replacing it, at least temporarily, by a rectangular Trinitron tube
that does not need convergence, and a fake external mask. I will try talking to people
about that at the ETF. If I ever succeed, it would make a great ETF talk. The problem of course
is horizontal drive ... maybe use the transistorized board of the donor set?

My comment about watching the set while the tube is good didn't apply to you Doug. You seemed to be playing your CT-100 very often, at least from what you posted on VK. That's the way it ought to be. Use it before you loose it...

I was referring to a collector that I know, who shall go nameless, who watches his restored CT-100 once, or at most twice a year, in order to "save the cathode material". You can have the best cathodes in the world, but if the tube is gassy, it doesn't matter.

[wkand]

All I know is that I am utterly fascinated by the CRT restoration efforts whether directed to 15G's or other tubes. The revisiting of the original RCA docs to understand the material science involved is epic.

The re-creation of the original or improved materials in this day of everything being labelled a carcinogen, and blocked from access to the general public or even technical workers, goes way beyond anything I've ever seen.

Special jigs and fixtures built from scratch with great attention to detail is an art form, as is the entire process. No doubt about it.

I live in the Seattle area where a certain Mr. Chihuly lives are creates fantastic glass sculptures. Many buildings in the area are endowed with his work. This effort is no less significant than that.

To all of you, RESPECT!!!

[vts1134]

Originally Posted by wkand

All I know is that I am utterly fascinated by the CRT restoration efforts whether directed to 15G's or other tubes. The revisiting of the original RCA docs to understand the material science involved is epic.

The re-creation of the original or improved materials in this day of everything being labelled a carcinogen, and blocked from access to the general public or even technical workers, goes way beyond anything I've ever seen.

Special jigs and fixtures built from scratch with great attention to detail is an art form, as is the entire process. No doubt about it.

I live in the Seattle area where a certain Mr. Chihuly lives are creates fantastic glass sculptures. Many buildings in the area are endowed with his work. This effort is no less significant than that.

To all of you, RESPECT!!!

Couldn't agree more!