Rebuilt 15GP22's?

[Eric H]

Picked this up from the A.R.F. Site.

Amongst other things they claim to be able to rebuild the 15GP22.

Anyone know about this place? I wouldn't mind having a 3KP4 rebuilt.

http://www.wmicronics.com/rebuilttubes.htm

[Steve K]

Eric:

That can not be correct. Pete Deksnis has been involved in a 15GP22 rebuilding project for the last several years and they are just finding a way that might work. The rebuilding progress can be followed on his site. I am sure that if some company was already doing that he would have known. I can't wait until someone does find a way!

Steve

[David Roper]

Ummm...why do you s'pose it would be listed along with the two early 21" round color tubes among "black & white picture tubes" they claim to rebuild? At first glance, less than credible to say the least.

[kx250rider]

No way, I'm afraid at this time. There have been many attempts to rebuild 15GP22s, and all have been unsuccessful. As was explained to me several years ago by Gino at MetroColor, the metal flange on the 15G will separate from the bell of the tube as soon as they try to heat it. They tried, with donor 15Gs from Ed Reitan, Gary Miller, and myself. And back in the late 80s, Gary Hough and I tried an experimental rebuild with Dunbar. We couldn't get the 15G gun, but we had two tubes that still had filament continuity re-evacuated. They lasted about a month. The best explanation of "why not?" came from the guys at MetroColor, who have been there since the 50s, and held government contracts and met all ISO guidelines. In other words, they know their tubes. To rebuild the tube, the oven will have to be modified to heat at a precise rate and at a precise temp. There are also many other problems.

Bottom line, be skeptical of anyone who claims they can do it. UNLESS it is one of the women who worked on the original assembly line for the 15GP22, LOL...

Charles

[kc8adu]

i call bs.
and the big problem with these tubes breaking in the oven is likely due to the complex mask parts and their different rated of expansion.
the mg seal is usually where they leak so no surprise they fail upon heating.

[Pete Deksnis]

Here's a snippet from an article in the Cleveland Plain Dealer on the 50th anniversary of the CT-100. It quotes Steve McVoy discussing the flange/baking-temperature issue associated with the ongoing 15GP22 rebuild effort.

When the picture tubes were manufactured, air was removed at room temperature by a vacuum machine. The picture tube then was heated in a 700-degree oven designed to excite the remaining air molecules so that as many as possible could be pulled out with the vacuum machine.

With time, the adhesive fails and air leaks through the seam. Restorers are experimenting with a new adhesive that has potential to keep air out for a long time, but the adhesive degrades at 500 degrees. Putting it in a 700-degree oven would not work.

"Right now, we don't know why 700 degrees is the magic number," McVoy said. "Was that the perfect temperature to remove all the air, or will something less than 500 degrees be enough?

"If it works, then we could have lots of tubes," he said. "I have four tubes and six sets that could use them." In addition to the RCA CT-100 and Model 5 prototype, several other brands of TVs of that era used the 15-inch color picture tube.

And another from the CT-100 news & noticespage of my site.

09-05-2005...on the 15GP22 rebuild front, a new, custom-made cam that controls the slew rate of the baking temperature has been ordered. After a few more hurdles (probably most of them as yet unknown), the rebuild team will attempt an engineering evaluation run using a damaged 15GP22 before a bona fide attempt is made to bring a rebuildable tube back to life.

Originally Posted by Kaye-Halbert TV

...but we had two tubes that still had filament continuity re-evacuated. They lasted about a month. Charles

Simply put, a month is plenty of time to slop on a bead of sealant and dry it. If the tube survives baking for that long without the custom slue rate, old 15GP22's may soon be looking a lot brighter!

[frenchy]

[QUOTEWith time, the adhesive fails and air leaks through the seam. Restorers are experimenting with a new adhesive that has potential to keep air out for a long time, but the adhesive degrades at 500 degrees. Putting it in a 700-degree oven would not work. tube back to life.[/I][/QUOTE]

So why can't they bake the tube with the old, less-than-ideal sealant that can take the 700 degrees with no problem, then seal THAT seal over with the stuff that will not eventually leak?

[Sandy G]

Wonder how they made th' damthings in the first place ? You mean back in prehistoric 19-fackin'-54 they did somethin' we can't do today, w/all our glorious tecknologically & such ?!? Of course, maybe they were a-feared of pissing off David Sarnoff...I hear he didn't exactly suffer fools gladly....-Sandy G.

[jpdylon]

If RCA originally designed these tubes, you would think there would be archives somewhere of the tube designs and how to manufacture them.

I would think it would be cheaper to manufacture brand new tubes than to break so many in existance trying to find a way to put a new phosphers and gun assembly in an old shell...

[polaraman]

When GE bought them the archives were trashed! At least this is I heard in the past. RCA was then bought by Thompson and now by a Chinese company.
I would say that only the name survives.


polaraman

[Tom_Ryan]

Originally Posted by jpdylon

If RCA originally designed these tubes, you would think there would be archives somewhere of the tube designs and how to manufacture them.

I would think it would be cheaper to manufacture brand new tubes than to break so many in existance trying to find a way to put a new phosphers and gun assembly in an old shell...

Good point. Actually there is an archive of information right under everyone's noses that was published in the proceedings of the IRE Vol. 42. Here it is:

Grimes, M.J, Grimm, A.C., Wilhelm, J.F. (1954). Improvement in the RCA Three-Beam Shadow-Mask Color Kinescope. Proceedings of the Institute of Radio Engineers. New York, N.Y., pp 315-326.

In this article Grimes, Grimm, and Wihelm describe the advances RCA has made in the design of the all glass color kinescope type 15GP22. Over what you ask? The original prototype was not the all glass tube everyone knows and fears can't be rebuilt today. The 15GP22 design originally started life as a modified 16AP4 metal shell. The 16AP4 was a glass-metal tube that found use in b&w sets that first appeared in the late 1940's. RCA simply added a color viewing screen assembly consisting of a shadow mask + phosphor dot plate and then added a tricolor electron gun. However, RCA quickly discovered a bunch of problems inherent to glass metal tubes adopted for color use. The authors interviewed many RCA engineers and assembly line workers to write their research paper. Maybe even the 80+ year old tech that Charles knows was interviewed.

The authors disclose a ton of information that led to changes in materials, assembly techniques and tips for factory production. For example, tube evacuation techniques, e.g. placing the mu metal shield outside the tube to reduce outgassing, improving the tension on the shadow mask by increasing heat dissipation 2.5 times to allow for increase beam intensities to produce brighter pictures, and changes to the blue phosphor to help reduce the classic "trailing edge" effect. The authors even reveal the composition of the shadow mask and the dichromating process used to improve thermal radiation and reduce buckling. Lots of other stuff is discussed too.


But the real kicker for RCA in moving to an all glass tube design was that it couldn't build the glass metal color tubes fast enough. The authors reveal that RCA management wanted a new color tube to role off the assemble line every 2.5 minutes. The 15PG22 did improve upon the modified 16AP4 in three ways: improved tube performance, parts interchangeability, and decrease in tube cost. RCA eventually lost millions on this tube because the demands of mass production were never realized. The tube also had a high mortality rate in the field. Tubes were failing after assembly or losing their vacuum after delivery in new sets or just simply sitting in inventory. So, anyone who has a working 15GP22 tube needs to understand that it is essential to VacSeal seal all vacuum joints on this tube immediately to guard against the possibility of vacuum failure in the future.

Corning Glass Works originally manufactured the molds that made the face plate section and the cone (funnel) section of the 15GP22. Prior to assembly a metal flange is sealed onto each part separately. This was done by RCA in a refractory oven using similar techniques for b&w tubes. Glass frit is used to bond the metal flange surface to the glass at extremely high temperatures. NOTE: at this point you are only sealing metal to separate glass parts. They are not yet joined together to form a CRT. The second major assembly step was the use of a very complex jig called an assembly lighthouse. The lighthouse was used to set the mechanical position of the phosphor dot plate to the shadow mask. A special jig is also needed to secure the shadow mask to the cone section flange collet assembly at the correct tension. The phosphor dot plate was then attached to a collet assembly on the face plate section. Once the alignment was completed in the lighthouse jig the flanges of the two halves were then heli-arc welded together.

From my experience, a tri-color electron gun assembly may be substituted into a 15GP22 as long as it meets one very critical requirement: the electron beams from the gun must focus at the plane of the phosphor dot plate exactly as simulated using the small light source in the alignment lighthouse during manufacture of the original tube. This would first require precise mechanical alignment during a rebuild so that the replacement gun is attached at the correct position, and establishing the correct electron field density to focus the electron beam during operation.

Finally, I would like to share with everyone what the authors had to say about baking the assembled 15GP22 after final assembly. This was especially critical during outgassing and evacuation. The authors pointed out that the manufacturing of b&w tubes used higher temperatures which were found not suitable for manufacturing color tubes. Why? Slow thermal cycling is required to prevent the shadow mask from bucking. The face plate must be also shielded to prevent it from cracking due to non-uniform thermal shock. Most importantly baking temperatures were tipped off at 300 degC.

See, when you stop and think about it the 15GP22 resulted because RCA engineers failed in making the "old design" 16AP4 glass-metal color tube work cost effectively. Grimes, Grimm, and Wihelm provide a wealth of information in their article about 15GP22 construction and assembly. The article also reveals what later become known as common sense techniques for color tube production: success depends on using moderate temperatures, slow thermal cycling and long tube evaluation time.

Tom Ryan

[bgadow]

Makes me wonder if a new all-glass crt based on the later 21" tubes would be at all pracitical. It would be terribly expensive & I think that would kill it. Probably one of those things that would cost $10,000 per unit to cover the setup costs. And then it wouldn't be original.

The discussion of the adhesive is interesting. There are some amazing epoxies being made but I don't know how they work as far as heat. This may be a silly question, but I wonder if modern plastics have advanced to the point that a PLASTIC crt could be made? Thats kinda hard to imagine, I know. If it could somehow be done that would do quite a lot to reducing setup costs. That would have to be some tough plastic, though, wouldn't it?

[Charlie]

Has anyone (with a little bit of CRT knowledge) thought to call Western Micronics and inquire about the 15gp22 rebuild process? Hell... it couldn't hurt to ask... and it would shed some light on whether or not these yahoos got all of their marbles!

There is always the possiblity (although unlikely) that they might actually have an "all-wise all-knowing big giant head" with the secret to this tube.

[Steve McVoy]

Some time ago I tried to contact them. Their phone had been disconnecteed.

[Charlie]

Originally Posted by Steve McVoy

Some time ago I tried to contact them. Their phone had been disconnecteed.

Apparently, this would not be a good sign!