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#1
11-06-2002, 11:58 AM
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15gp22
Having some engineering experience, I've consulted with some other engineers to study the feasibility of saving 15GP22's which are currently considered to be non-rebuildable due to loss of vacuum via failed glass-to-metal seals. My research has only started this week, so I don't have any real answers yet. I hope to find a solution which is aimed squarely at historic preservation of the surviving Merrills and H840CK15's far beyond our lifetime. The way I'm approaching the problem is by applying the fact that our technology has advancd significantly since 1954, therefore, it must be possible to detach and replace the original seals using materials which will be less prone to leakage. Has anyone considered the possibility of perhaps manufacturing 200 or so NEW 15GP22's? It may be possible to develop a replacement tube in which the phosphor dot plate and shadow mask are supported by structures inside the tube while the anode connection flange becomes an external band around the rim of the tube much like the bands which protect modern tubes against implosion. The requirement for an electrical connection between the phosphor dot plate and anode flange may then be satisfied by a small connection through the envelope which would require a much smaller glass-to-metal seal than that of the original tube. The new tube could be made such that it is virtually indistinguishable from the original by anyone other than an engineer and designated a new type number. If 15JP22 is unused, perhaps that would be the most logical choice. I will follow up on this thread as the research is conducted. The minimum I hope to accomplish is a feasibility study which will weigh the technical obstacles against the costs of overcoming them. From there, a decision can eventually be made of whether the cost is justified.
Last edited by jshorva65; 11-06-2002 at 01:54 PM. 
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#2
11-07-2002, 01:33 AM
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I would think engineering a new tube would be impossibly expensive.
There doesn't even seem to be any progress on building a new gun. Disassembling and resealing the original CRTs would seem a more feasable option but then the question is are the phosphors ruined by years of exposure to air. Could the phosphors be redone perhaps?
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#3
11-07-2002, 06:10 AM
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Well, if somebody can figure something out (or get close), please let me know.....I have a dud ready for a rebuild
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia."
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#4
11-18-2002, 02:59 PM
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15gp22
there is another dud 15GP22 on e-bay..
i had a talk with a professor who teaches at the college i work at about the phosphors in these color sets..he teaches both in chemistry and physics and seems to think that the aluminum layer should somehow preserve the phosphor dot layer,i didnt get to get into details about it yet from him..but the amount of time is an issue and amount of vacuum left. anyone know who is trying to rebuild these tubes yet? there is also rebuilding equipment for sale on e-bay,i am sort of tempted to call the person ,but dont know how much room it all takes up and if it would pay for it self.. tempting side jobs though, still makes me think.. what is everyones thought on all this?.. terry
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#5
11-18-2002, 03:58 PM
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There is a project underway to try to rebuild the tube, but it is a very complicated process. Guns are no longer made for the tube, so the original ones must be rebuilt. Then, they must be attached to a stem, which is also no longer made. Finally, the problem of leakage has to be solved. The bond between the metal face and the glass shell has admitted air on most dud 15GP22s. The only sealant that has been found cannot be used at the high temperatures that are required in the rebuild process. And, there is the question of whether the phosphors will survive the process.
The first tube to be tried will be one that still has its vacuum but has no emission. If it is successful, a tube full of air may be tried.
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#7
11-18-2002, 07:24 PM
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Sealer
Steve,
I probably have no clue here but modern color CRTs seem to have their faceplates glued on to the bell with some type of Epoxy and those tubes get rebuilt, is this not suitable for the 15gp22? Never having seen a 15GP22 in person I don't know what your up against. In any case this is a facinating quest, I hope someone is going videotape it for a documentary  Eric
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#8
11-19-2002, 07:58 AM
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Based on the engineers' preliminary comments, the 15GP22's gun structure appears to be the most significant hurdle. It seems that there are no surplus guns as there are for the later 21" tube designs. Making new guns for the tubes appears to be the only way to proceed. Re-gunning a 15GP22 would be more expensive than installing a new surplus gun in a 21FBP22, but the high value ($3,000+) of the CT100 and other 15" sets in working condition would justify the anticipated $500-$600 cost per tube. For the 15GP22 rebuild cost to be about the same as that of having two 21" tubes rebuilt seems reasonable considering that some of the parts will likely need to be custom made for the application. If the rebuilding equipment can be bought at a reasonable cost, is relatively compact and supports the 50mm neck diameter of early color tubes (both 15" and 21"), then it may be a good idea for one of us to purchase it. What is its item number? I'd like to see its listing and evaluate whether or not setup at my location is feasible. I assume it requires electric power for the vacuum pump and sealing device among other functions. If the power requirements and physical size are comparable to a large household appliance (refrigerator or washer) then I might buy it. If it's the size of a car and/or requires 3-phase or 480-volt power, then I would not be able to set it up here.
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#9
11-19-2002, 08:38 AM
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I've been following the rebuild project with interest for some time now and it's good to see others interested in it. I recently tested the CRT in my CT100 that I'm working on and it has very low emission and a H-K short as well. I have a good spare with nice output so this weak tube is certainly available for a rebuild attempt. I hope the tube in my H840CK15 is good. I'll test it later this week.
Last edited by fredh; 11-19-2002 at 08:57 AM.
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#10
11-19-2002, 11:19 AM
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15gp22 ect. on e-bay
Looks like Chuck Pharis is listing a "dud" 15gp22 and the mumetal shield as separate items. Chuck recently aquired a new-in-box 15gp22. A rare and lucky find. The story is on his web site.
The e-bay #'s are:802535976 and:802536877
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#11
11-19-2002, 01:01 PM
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The 15GP22 was never a practical tube, and its high cost of manufacture was a major factor in the stiff price tag on the CT100 and other sets using it. That's why the CBS 19VP22 was such an advancement in 1954. RCA immediately dropped the flat plate phosphor screen & planar mask design, and launched a crash program that resulted in the 21AXP22, with phosphors deposited directly on the inside of the bulb face and using a spherical mask like the CBS tube. (RCA traded patents with CBS for use of this design; RCA had patented a photosensitive adhesive for the phosphors that CBS needed to attach them to the bulb face. The 15GP22 has the phosphor dots silk screened on a flat glass plate).
My impression is that for a practical replacement for the 15GP22, a new design using modern guns and methods needs to be built using a compatible glass envelope. This would also require a precision yoke, designed for compatibility with CT100 circuitry, be aligned and attached at the factory. This might cost several thousand dollars per copy, but with prewar black & white sets now crossing the $10K price line, that may not be an unreasonable price in the future when all the existing 15GP22's have died. Last edited by wvsaz; 11-20-2002 at 11:01 PM.
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#12
11-23-2002, 05:12 PM
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eBay
There's another one on eBay.
http://cgi.ebay.com/ws/eBayISAPI.dll...item=802535976 This is the more common "White Getter" version. Most Videophiles prefer the "Shiny Silver Getter" verison because those tubes produce the warm full bodied color that is so desireable 
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#13
11-23-2002, 10:30 PM
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White getters are a sure sign of AIR in the tube. Silver getters indicate the tube is still under vacuum. Gases reacting with the getter material cause its color to change. The more silver the getter "flash spots" appear, the harder the vacuum. A good tube has bright silver getter spots, "soft" (gassy) tube will have dull grayish spots, while a tube that has virtually no vacuum at all will have white getter spots. This applies to 15GP22's just like it does to 6L6's, 5U4's, 6AS7's, etc. If the getter is white, the vacuum is gone.
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