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  #106  
Old 04-27-2006, 08:38 PM
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Here's the url of the actual thread... http://forum.eserviceinfo.com/viewtopic.php?t=4002

Apparently, he didn't get any bites on his hook. It would still be interesting to find out what this guy has going on... if he even rebuilds tubes at all.
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  #107  
Old 05-14-2006, 07:37 PM
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Tube rebuilding

I make small vacuum tubes for a living. I am a production engineer in a glass tube line. We produce about 50,000 tubes per year. Our vacuum requirements far exceed anything ever required for television tube evacuation so I am quite intimately familiar with processes related to tube production and evacuation. I also worked indirectly with Universal Video, a Minneapolis color tube rebuilder, long since extinct.

My comment is, yes, the "frit" material is a glassy material that, in later tubes, long after the 15EGP22, was used to seal the faceplate to the funnel. This is STILL the preferred method for big tubes. Smaller tubes like the 5 inch monochrome tubes can be blow molded in one piece, with neck and tube entry chamfer molded in. But big tubes generally need to have the funnel molded, the neck added, and then the mask installed. Since the mid 1950's, the lighthouse method of patterning the phosphor dots via a light source at the gun position, through the shadow mask, to the photoresist on the face plate. This faceplate was then forever wedded to this funnel. Once the phosphors, and the metallization over the phosphor (aluminum) were depositied, the faceplate was fused to the funnel with the frit. After this process, the gun was installed into the other end in place of the light source.

Then the entire thing was evacuated to somewhere in the range of 1E-7 Torr, baked to temperatures of about 300C or so, induction fire of the gun and getter, and sealed. Then, of course, a run in process was carried out, including activation of the cathode.

Replacing the seal on a 15 EGP22 with frit migh not be a walk in the park, however. The nature of the mating joints where the adhesive or frit went was not very forgiving in terms of texture, area, degree of parallelism and many other "trade secrets".

While the phosphor on these old tubes does deteriorate, I would submit that a simple cathode replacement might make most tubes quite acceptable in performance. There once was a fellow in Pennsylvania who replaced the filament/cathode in 3KP4 tubes for Pilot Candid's. I had one once and it performed beautifully. Of course this was monochrome. He had worked out the details of removing the gun, replacing the filament assembly, adding a new tip-off tabulation to the wafer, resealing the entire assembly to the funnel and the easiest part, evacuation, baking and sealing.

Were this possible with the 15EGP22, I would think you could evacuate it at a temperature that is safe for the bonding adhesive used on the faceplate. Then you could leak test it with a helium mass spectrometer. Any leaks on the faceplate to funnel seal could be sealed indefinitely with Torr Seal, a sealing adhesive made especially for sealing UHV systems to vacuum levels of 2E-10 Torr! Then the tube could be baked on its dedicated vacuum system for a few WEEKS at a temperature well below the safe temperature for the adhesive. Remember, we don't have to make thousands of these - about 20 or so would do. Thus, for a fee, you could pump on one for weeks or more. Remember, the high temperature of bake out is simply a way to speed up the offgassing process. If the tube, once vented, is kept in a clean dry air atmosphere, no in-diffusion of water into the glass will occur. Thus you only need to bake away the water that forms a few monolayers or so on the surface of the glass and gun parts. This will easily take place in a week or so, even at room temperature. Again, the heat only serves to speed up the process. Once the vacuum gauge reads in the range of 1E-8 Torr or so, you can close off the pump valve and watch to see how fast the tube pressure rises to 1E-6 Torr. From this you can calculate how long it would take to reach excess pressure for tube life (rate of rise test). Please use a cryo pump or turbomolecular pump, not a diffusion pump, to evacuate the tube. Diffusion pumps invariably leave oils behind. An Ion Pump is even better but these typically have slow pumping speeds.

Thus I see no real issues for someone good with glasswork to do this task. It will just take some time.

Sorry for the long post but it's not a short process!

Vacuumguy
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  #108  
Old 05-15-2006, 12:16 PM
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Pete Deksnis Pete Deksnis is offline
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Vacuumguy, thanks for the fine information. Weeks evacuating each tube! Wow, but if it works...

Only thing that needs updating however is the number of 15GP22's out there waiting to be rebuilt. With well over one-hundred known CT-100's as well as dozens more other-brand survivors, the number of 15G's for rebuild is at least three times 20.
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  #109  
Old 07-23-2006, 08:29 AM
wiseguy wiseguy is offline
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what ever happened to that place that claimed they could rebuild 15gp22 and others? they still have that tube listed on their website as "rebuildable"
they never returned my calls after i questioned them on telling me the guns are on order..
false ads..?
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  #110  
Old 07-23-2006, 09:29 AM
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OK--so they can't bake the CRTs.

But my question would be, why can't they seal the glass-metal junction first. Then evacuate at room temperature, then flush with an inert gas to force out the remaining itsy-bitsy left-over air molecules, then seal the stem? Seems there should be some really inert material, that when used, and a few molecules remain inside the CRT, would not affect anything.

Or, how about putting in some chemical that super-absorbs oxygen. Evacuate until most oxygen is gone, then activate the chemical.

Maybe someone will take one up on the space shuttle, and open the neck on a space walk--look mom, no heat required--although those pesky micro-asteroids could do damage.

Damn, if they don't have anything handy, they could visit Roswell and get something to fit the bill. Those aliens must have had color TV in the 1930s!
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  #111  
Old 07-23-2006, 01:10 PM
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I think the closest that anyone has come is what Tom Ryan (not TD Ryan) is doing in San Diego. I think he talked about it earlier in this thread.

If there's enough of a market, I wonder if the Russians would take an order and give a try at building new 15GP22s with the old RCA specs? Maybe modified to eliminate the metal ring? They do a great job making fake 2A3s and EL-34s. This is a serious thought; not a joke...

Charles
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  #112  
Old 07-23-2006, 04:06 PM
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How did they build the *&#! things back in '53-'54 in the 1st place? Hard to believe they did something back then we can't do today...
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  #113  
Old 07-23-2006, 06:15 PM
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The problem we face is that RCA ran as fast as it could from the 15G once the "BIG Color" models went into production. The 15G was the end result of research goals going back to the 1940's, and was simply out-of-date. Once they had made the leap to the 21-inchers, the marketing folks had no reason to dote on the smaller tube, they wanted, no, they HAD to sell the new models. We forget, deep in our intoxicating nostalgic fog, that this was a business risk, and RCA had to work desperately to keep it's dream alive financially. It would be years before color TV sold worth a darn. Our longing for spare 15G's just wasn't anticipated back then, future nostalgia is not factored in to the end-of-life decisions all manufactured goods face. Manufacturing resources were simply shifted to producing the big tubes. At some point, It had no bearing on the bottom line, the materials specific to it were used-up or even discarded, the production line retooled, the documentation archived, only to be tossed at some recent date. I cannot accurately guess when the last 15G was produced new, but I was surprised to find the one I submitted to Pete's site with the 1959 date-code was the only one he'd seen. It is probably a rebuild.

Having said that, one last hurdle is the Grim Reaper. If you were an engineer in your prime, oh, say, age 40-50 in those days, you are now just plain old dead. Much of the knowledge we collector/restorers thirst for went to the grave with those brilliant minds long ago. I personally tried getting archived RCA data from a kid on the phone at GE back in the '90's, and it proved fruitless. With the sale to Thomson, then to the new owners, I don't hold out any hope. But keep looking!
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  #114  
Old 07-23-2006, 06:25 PM
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Quote:
Originally Posted by wiseguy
what ever happened to that place that claimed they could rebuild 15gp22 and others? they still have that tube listed on their website as "rebuildable"
they never returned my calls after i questioned them on telling me the guns are on order..
false ads..?
They'll start rebuilding 15Gs as soon as they buy some rebuidling equipemnt, find a building, raise a little capital, and find the expertise to do it. I'm sure they'd be glad to collect a deposit from you to help them out.
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  #115  
Old 07-24-2006, 12:17 AM
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I could imagine an all-glass 15" round color tube being built in Russia (or somewhere). It would not satisfy the purists but it would wake up some dormant tv sets. But even then the start-up costs-configuring the equipment to make the envelope, designing the shadow mask, all the engineering needed to put it all together-even in a third world country to cost would be very high.
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  #116  
Old 07-24-2006, 01:03 AM
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Pete Deksnis Pete Deksnis is offline
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new-design 15GP22...?

Sounds like a nightmare to me. They almost certainly would use 'new' phosphors. The new tube would be driven by a CT-100 designed for the 'old' phosphors. So you'd have to modify the matrix to match the 'new' phosphors. Doubt that you'd ever match the '53 NTSC colors. 'course, it'd be better than a universe of dark 1954 15-in. roundies, I guess...
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  #117  
Old 07-24-2006, 02:24 AM
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No promises, but I'll launch an effort to find a woman who I met in the early 90s; a 15GP22 assemblyline worker. She was about 70 or so when I talked with her, and she was still 100% sharp on her memories. She lives a block from Colortel (Westwood apartment, not Omaha). I know I have her name & number someplace, but it will take some searching. I recall in our conversation that she was still friends with others who worked with her at the time. But again, this was 15 years ago so she is now more like 85, and same for the friends she spoke of... Let's be hopeful, because I have another lady customer who is now 101 and is still working as manager of a trailer park, and travels all over the world each summer! And she has a rare TV too...

Charles
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  #118  
Old 07-24-2006, 02:52 AM
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  #119  
Old 07-24-2006, 04:49 PM
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Quote:
Originally Posted by Pete Deksnis
Sounds like a nightmare to me. They almost certainly would use 'new' phosphors. The new tube would be driven by a CT-100 designed for the 'old' phosphors. So you'd have to modify the matrix to match the 'new' phosphors. Doubt that you'd ever match the '53 NTSC colors. 'course, it'd be better than a universe of dark 1954 15-in. roundies, I guess...
You're right about the color. Some early rear-projection TVs went to P1 green because the modern sulfide green saturates at high beam current, giving magenta highlights. However, the modern matrix with P1 green makes flesh tone too sensitive to hue variations. The fix could have been to go back to the NTSC matrix, but usually it was to introduce a rare-earth/P1 or other mixture that matched the sulfide green. If you put a modern green in a CT-100, you will have the opposite effect - greens, yellows, oranges and flesh tones will move closer together and toward red, and the hue variation over this range will be less than nominal. The major tweak to the matrix for sulfide green would be to increase the R-Y drive, but there are related minor tweaks, so all the matrix resistors would require a change.

By the way, modern blue phosphors are also considerably off the mark from the NTSC phosphors (more towards violet, which moves yellows more towards green, since yellow has to be complementary to the blue to make the proper white). This means that modern sets have improved saturation in the magenta region compared to the NTSC gamut.

Such matrix corrections are always approximate due to being in the wrong place in the system for the gamma characteristic of the picture tube. In modern NTSC sets, this results in reds being overly bright (and cyans being dark) when the hue variation is corrected.

All this explains why HDTV colors are more accurate than current NTSC, even though the green area is more restricted than true NTSC - the HD cameras and receivers actually have color characteristics that are matched to each other, producing colors that are the correct saturation, brightness and hue. PAL has had this since they started, because they standardized on the newer phosphors for their primaries.
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