#16
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We rebuilt 21AXP22's in the same process by heating it up the same way in the ovens and had a 80% sucess rate
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julian |
#17
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What about monochrome?
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#18
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21AXP22's have to be put into the oven even when new which we did, and had a 80% success rate with no problems. They went through the same process as a 21FBP22. We never did any 15GP's (too old then) and they were not a good item in the '60's.
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julian |
#19
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Monochrome = black & white. Those mentioned are tri-color tubes
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#20
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B & W Tubes
B & W tubes are rebuilt the same way as color. All you are doing in the process is installing a new gun mount and evacuating the glass bulb.
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julian |
Audiokarma |
#21
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Any experience in rebuilding metal B&W tubes? I was referring to the high failure rates with these while in the oven.
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#22
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Quote:
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#23
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Quote:
I should mention, though, that at least one type of 23" B&W CRT can have its band removed safely-in fact, you have to do so because new CRTs (National brand) in the early 1990's came without the band. We may have one or two still in the box here that I have not used yet. The band has a hex-head bolt and nut assembly that is loosened to remove the tube. I have always been a bit nervous when changing them, though, because I wondered if the band "held together" a CRT, and you just confirmed that. |
#24
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Last edited by andy; 12-07-2021 at 02:07 PM. |
#25
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Not to highjack the thread, but what would happen if the button was broken, or it lost vaccum while a CRT was in operation? The heaters would burn up as soon as air enterd the tube, right?
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Audiokarma |
#26
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Not much you can do except make sure the oven stays at a constant temperature (400 degrees) with no sudden temperature change. In the late 60's we never did many metal tubes because they were old then and Paul, the owner never wanted to mess with them because when a tube blows in the oven, you lose labor and materials. Plus you have to clean the oven out. All of our ovens had "scars" in them from when tubes went off.
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julian |
#27
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There is a difference between a pressure band and a mounting band. The banded tubes use steel like a packing band and is crimped with a similiar seal. You can remove it AFTER the tube is let down to air which you HAVE to do when rebuilding it. You would normally use a hacksaw and can reuse the band on a smaller tube. The idea is that if a tube is struck from the front, the sides of the tube will have to expand in order to implode. With the band wrapped around it, the perimeter cannot expand thus making the tube safer.
A mounting band has a clamp that you can screw down and doesn't count here. Some tubes have the mounting ears made in with the pressure band for a specific application. If you use a hacksaw to remove the band on a live tube, the band flies apart, dangerously and the tube suddenly "expands" enough that the bulb will rupture and implode. It doesn't bother a tube already let down to air because there is no tension on the glass bulb. The glass bulb or envelope cannot be scratched anywhere because the scratch makes a weak point and you CANNOT put a scratched bulb in the oven as it has an 90% chance of imploding because of that scratch. (On the faceplate esp) Somehow a few tubes get scratched on the face in the process (both new and rebuilt) that it was a good tube and putting a bonded face on it would hide the scratch with the resin between the two glass surfaces. Many others were called "seconds" if it wasn't a bad scratch as well as tubes that developed "pimples" in the phosphor. RCA made test jigs using a 19" tube (19EYP22) that had "TEST TUBE ONLY" sandblasted on the front upper corner of the tube so that you couldn't sell it as a replacement tube. They were that valuable back then.
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julian |
#28
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A CRT without vacuum doesn't suck.
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#29
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No. If a tube starts to lose its' vacuum during operation, it will immediately begin to arc all over the gun mount with blue sparks. This is how you can tell quickly in a solid state set if you have a broken tube or not and you can certainly hear it with a distinctive sound that sounds like a loud hissing in the tube itself. Strangely, the filament will not open up as it is very tough and goes to almost zero ohms as like a dead short. There is not enough current in the filament voltage to make it burn out. (later sets mostly)
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julian |
#30
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I respect all these opinions, but I have personally had CRTs with a broken tip re-evacuated (and cooked in the oven) and they worked fine. I was advised that it might be a waste of money, but it did work. One was an 8" Arvin metal tube which had a metal tip that leaked, the other was a 21" B&W bakelite base tube. No phosphor problems, but the 21" did get a new gun. When they cook the tube, it forces the air, gases, and moisture out while they evacuate. The Arvin gun was still OK, although maybe a little less emission. In another case, I had a Sony 30" Trinitron CRT rebuilt after it had the neck cracked and lost vacuum. That one too got a new gun, since they were cheap and available. But again, no stains or phosphor problems.
I also had a 21AXP22 rebuilt after being with lost vacuum for a long time. It worked fine, but lost vacuum again. As far as the pressure band, I have heard both ways on that. In theory, it shouldn't implode. The band is applied AFTER the tube is evacuated, and often my local rebuilder (Dunbar Sales in Los Angeles) would store the tubes without the band, so that they could slap it on with whatever mounts were needed for a particular request. The newer tubes all have the pressure band holding the mounts on, not like the older ones which had the pressure band plus another screw-tight band for the mounts. I'll stay on the fence on this issue of what happens when the band is cut off after the tube is evacuated, as I haven't done it (and DON'T PLAN TO). Charles
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Collecting & restoring TVs in Los Angeles since age 10 |
Audiokarma |
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