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  #31  
Old 12-03-2005, 08:55 PM
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Chad Hauris Chad Hauris is offline
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Sylvania rebuilt tubes were classified as "new gun" or "new gun and screen" so I think a lot of rebuilt tubes , B&W and color, were just equipped with new electron guns.

I really have not seen the kind of phosphor burn you get on old computer terminals on many TV crt's, except in sets from college student union lobbies or motel lobbies, etc. where the Weather channel or cable TV info channel played constantly for many years and burned text into the screen.
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  #32  
Old 12-03-2005, 10:34 PM
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  #33  
Old 12-03-2005, 10:50 PM
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With regards to screen burn I've noticed a couple of things. Color CRTs don't seem to burn as "deeply" a mono CRTs. I've seen several mono CRTs that were used for either surveilance monitors or text displays where the burnt image is clearly readable when powered off. When powered on with a full white (or green, etc) raster the burnt areas weren't just dull, they were totally dark. This also happens with the old orange plasma displays used in some computers.

A while back here a load of ex-TAB 21" Orion TVs hit the market. The were used to display race information on teletext pages. When powered off several lines of text were clearly readable and several others visible as indistinct "shadows". When powered on it was only just noticable on a full white raster. Viewing a normal program you couldn't really see them unless you practically had your nose up against the screen looking for them. I sold several and never had any complaints or comebacks. As long as the customers got to see them running they were happy to take them, even after I explained the screen burn to them as showed them what they looked like when switched off. Of course it helped that I was selling them for half the price of a non-burnt set of the same size, and this was before the used TV market crashed. No-one would even ask about them when they were switched off, even when we dropped the price off the last couple of $20 to clear them out (this was back when a used 21" set would easily sell for $100, even without a remote).

I have a couple of Sony Trinitron studio monitors that were pulled from an edit suite. Both have time codes burnt into the bottom of the screen, but I don't really notice it. Otherwise they have beautiful bright sharp pictures with better color and geometry than many of the 1 year old sets that come through here. I like them enough to use them daily, one as a bedroom set and one in the workshop. Lately I've been watching more movies in the workshop than anywhere else (gotta test the DVD players before they go back out ).
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  #34  
Old 12-04-2005, 05:36 AM
frenchy frenchy is offline
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I remember going to videogame/pinball auctions, and it was kind of fun looking at the old videogames with used color monitors where you could sometimes decipher what game the monitor had been in previously just by looking at the burn-in pattern : )
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  #35  
Old 12-04-2005, 05:54 AM
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I haven't seen anywhere near as many burnt in arcade monitors as I would expect to see. Maybe around here the games were changed more often. The CRT rear projection monitors used in some big Sega and Namco cabinets are a different story though.
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  #36  
Old 12-04-2005, 07:05 AM
Tom_Ryan Tom_Ryan is offline
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Lightbulb IRE paper discusses 15GP22 desgin and manufacture.

Quote:
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

Last edited by Tom_Ryan; 12-04-2005 at 07:35 AM.
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  #37  
Old 12-04-2005, 11:08 AM
frenchy frenchy is offline
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<<<I always thought that the phosphors in black and white tubes degraded with use too. >>>

Since back then there were no news channel crawls, logos, videogames etc. it would have been evenly worn as long as the set was working right. I can see if something went wrong like you lost vertical for hours while nobody was tending to the set and it burned a horizontal line into the phosphors. Or the ion trap got messed up and it ended up causing a burn spot in the center.
Otherwise the big % of the cause of dimness in an old tube is probably the gun's fault or because of outgassing. Plus doing the guns is hard enough, I can imagine the pain it might be to remove/replace the phosphors. How was that done anyway? Or did they even do it?
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  #38  
Old 12-04-2005, 12:05 PM
RetroHacker RetroHacker is offline
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On the side-note of color tubes with burn, you don't _normally_ see modern color computer monitors with burn, until you start working with junked equipment from state offices, hospitals, etc. Server consoles are pretty bad too - I've seen monitors that very clearly show "Windows NT Server" or "Windows 2000 Server", burned sharply into the screen. Once I even saw one with Windows 2000 burn _and_ NT Server burn. They must have upgraded . Or offices that have their company logo as the desktop wallpaper, those typically get etched into the screen pretty good. You also see login screens burned into the tube quite a lot. Occasionally, you can see the whole desktop, complete with icons and readable text - even the icon headings of "Microsoft Word" are readable. And that little MS word 'toolbar' thing.

Arcade machines, especially the old ones, get burn in attract mode, or just from use. You can always tell a monitor from a Pac-Man or Ms. Pac-Man machine, the maze is clear as day. One time I even saw a TV set in a thrift store with Atari 2600 Pac-Man burn in it.

I guess that under _normal_ use, the phosphors in a TV shouldn't degrade too much, so rebuilding the tube would be only a replacement gun. It seemed like I read somewhere that the really old B&W tubes suffered worse phosphor degredation - until they switched to an aluminized screen or something like that. But the tube rebuilders probably would look very closely at the duds as they came in, and only rebuild the ones that were going to work well when rebuilt. But I am really curious, if they did replace phosphors in the tube at some point - how did they do it? I can just see someone trying to scrub the old phosphor off the tube with a long brush or something, like cleaning out a bottle.

-Ian
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  #39  
Old 12-04-2005, 12:47 PM
frenchy frenchy is offline
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<<<It seemed like I read somewhere that the really old B&W tubes suffered worse phosphor degredation - until they switched to an aluminized screen or something like that.>>

Very early tubes didn't trap the ions so would get an ion burn spot eventually, later they added angled guns + ion trap magnets to suck up the ions, then came phosphors coated with very thin film of aluminum which stopped the ions and eliminated need for traps.
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  #40  
Old 12-04-2005, 12:48 PM
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Steve McVoy Steve McVoy is offline
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Tom, the 15GP22 is different from other guns in two ways: First, it uses high voltage (around 5 kv) focus, and second, it has electrostatic convergence, with an additional element in each gun. There have been a couple of attempts to use 21AXP22 guns in 15G rebuilds, the assumption being that the screen size is so small that convergence would be adequate without dynamic convergence. I've never seen the results, though.

Black and white tube rebuilds were done with new phosphor (more expensive), or re-using the existing phosphor. This is still true today - Clinton Electronics is attempting a rebuild of the prewar 12AP4, a tube that didn't use an ion trap and therefore had ion burns. They remove the old phosphor and re-coat the tube:

http://www.earlytelevision.org/prewar_crt_rebuild.html

Last edited by Steve McVoy; 12-04-2005 at 12:51 PM.
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  #41  
Old 12-04-2005, 03:12 PM
Tom_Ryan Tom_Ryan is offline
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True, the 15GP22 uses electrostatic convergence; however, regardless of the method of convergence in any color tube, the outcome is the same - focusing the electron gun on the phosphor plate. Of course, the physical principles and subsequence circuitry is different (15G uses electrostatic fields and the 21AX gun uses magnetic). Say, glad use did mention the use of 21AXP22 guns - it would be cool to find out who tried it and what finally came of it.

On the subject of phosphors, I've had the unpleasant experience of discovering the non-aluminized black & white tube phosphor the easiest to damage if you suddenly break the seal off nipple at the base of the gun. You can blow away a circular patch of phosphor several inches in diameter off the face plate. I recall calculating the velocity of air once as it enters the tube. At the instance the nipple is broken air rushes into the tube at something like up to 300 miles per hour - depending the length of the tube. Air traveling at this speed does a nice job of blowing away the phosphor. Sort of like sand blasting the phosphor off the glass! Of course, aluminized phosphor is strong enough that this doesn't seem to happen. Guess if you're going to go to all that trouble to rebuild a 12AP4 pre-war tube to recoat the phosphor you're basically building a whole new tube. At least it looks authentic on the outside - not sure how safe the integrity of the old glass bottle would be though. Why not take the last step and replace the old glass too!
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  #42  
Old 12-04-2005, 03:23 PM
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If there was a way to replace the glass at a reasonable cost, making a whole new tube would be an attractive alternative. However, the cost of building the molds and having the shells produced would be prohibitive, especially with the limited number that are needed.
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  #43  
Old 12-04-2005, 04:52 PM
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Last edited by andy; 12-07-2021 at 02:27 PM.
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  #44  
Old 12-04-2005, 08:29 PM
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Chad Hauris Chad Hauris is offline
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How about the Sylvania "new gun and screen" tubes...did they maybe cut off the front part of the tube?
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  #45  
Old 12-04-2005, 10:34 PM
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Quote:
Originally Posted by Chad Hauris
How about the Sylvania "new gun and screen" tubes...did they maybe cut off the front part of the tube?
Aren't almost all color tubes made with two piece shells?

I believe if you look closely you'll see a bonding agent holding the front of the tube to the bell, how else could they build them?
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