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#31
08-22-2007, 12:00 PM
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Quote:
I've had a few run-ins with it in my car hobby. And RCA used it to hold the glass to the CRT bezel on a lot of early/mid 50s consoles (including the CT-100.) It defies the laws of physics: one cubic mm of that stuff can spread its self out enough to have blobs and smears all over your face, in your hair, all over your dog, floor, and somehow it will work its way into a hermetically-sealed environment  . It takes a gallon of lacquer thinner to clean it off the windshield after you accidentally smear a blob of it while trying to clean the windshield months after being installed.I'll stick with the tape and silicone  Charles
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Collecting & restoring TVs in Los Angeles since age 10 
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#33
10-22-2007, 01:56 PM
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An update, or, Bryan's further adventures with swimming picture tubes...
So, before the weather turned colder I decided to drag out the kiddie pool one more time and take a stab at a couple more with cataracts. As you'll remember, I last was able to succesfully remove the faceplate from a "green halo" tube by soaking it in a pool for several days, then using gentle prodding to pop the lens. My next "patient" looked to be easier: a "gray halo" tube. This is the more common type which can be removed with a heat gun. How would it respond to the water? I expected it to take less time. I have had past experience with this type in which tubes exposed to the weather for years on end had a completely disintegrated cataract. The CRT in question is a Sylvania; these usually have the green stuff. This one is kinda early (first part of 67) and has a not-so-common non-frosted faceplate. So, into the water it went. I checked daily. Much to my surprise, there was no change in the PVA. Something I noted: the edges of the green PVA tend to be rubbery and sticky, while the gray PVA is fairly hard, sort of like cured Duco cement. The green stuff absorbs water fairly fast, turning white and losing its grip, but not the gray stuff. I let the tube sit for about a week. I could just start to see some deteroration around the edges. Unfortunately it had rained and a little bit of the aquadag had washed loose. With more storms forecast I decided not to chance it, and removed the CRT. I then proceeded to remove the faceplate the "old fashioned" way, with a heat gun. No problems there. While working on it I noticed some deep scratches on the faceplate. I decided finally to replace it with a frosted glass off a dud tube I have. (I had already removed that glass previously) All went reasonably well. Next tube: 22GWP22 in a Motorola, green halos. Maybe the deepest green halo I've seen, enough that it was distracting to watch. Mean set to work on-CRT has to be removed from the front, which might be easy except the front trim has to come off; the chassis still has to be pulled. This set had a rough life, with a dented top and several broken mounts on the trim. When I was unwrapping the tape from the edge of the CRT I found that the faceplate was cracked on one corner. It's a good thing it didn't go further-that almost certainly would have condemned the set. Then, I did something really stupid. I was prodding under the edges of the glass with a popsicle stick, since the PVA was quite soft. That's when I heard a terrible "C-R-A-C-K!" and that was the end of that faceplate. I could blame it on the previous crack, but that would be sour grapes. It's my own dumb fault. Luckily I had some spare tubes in the attic. One proved to be a tension band tube. A quick check revealed it might be a little tricky to mount. The original mounting band on top of the tension band would make for a tight fit. The other spare was a Channel Master with gray cataracts. (actually, frosty white) It tested strong on blue & green guns but the red showed no movement; could just be due to pin corrosion. So I decided to just pull this faceplate and put it on the Motorola tube. I used the heatgun and it proved to be the easiest I've done yet. Less than 10 minutes to pop the glass; only slight residue stuck to the faceplate. The PVA actually came off in one piece. Meanwhile, I stuck the Motorola tube in the pool so I can remove the broken glass. It is already progressing nicely-the exposed green pva had turned white within an hour or so. The replacement glass off the C-M tube isn't quite as nice, as it has a lighter tint and some scratches, but then this Moto is a real junkyard dog anyhow. So, there you go. Swimming pool for green, heatgun for white/gray. Your mileage may vary!
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Bryan
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#34
10-22-2007, 03:34 PM
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Thanks for the update bryan. I look forward to trying this method on a green halo zenith. Ive never seen a zenith survive with out green halo in some form. However, sometimes you get lucky and find an RCA with no cateracts at all!
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I tolerate the present by living in the past... To see drh4683's photo page, click here To see drh4683's youtube page, click here
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#35
10-25-2007, 08:44 PM
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OK, Here's how we did it on a production scale in a tube rebuilding facility. You could put it in an oven but a lot of trouble and perhaps dangerous.
We had a special rack to hold it at about a 45 degree angle. We had a gas fired radiant heater, (the kind you hang from a ceiling in a commercial metal warehouse) place it facing about 18" or so at the front of the tube and heat the faceplate for about five minutes or so. This would heat the faceplate up quickly and when it was ready, would then take the tube (using thick gloves of course) and set it on a small wood table with a 12" or so hole in it with the neck down in the hole. The faceplate is exposed and then we would take two wooden dowels about 1" in diameter and 6" long or so with about 34" of heavy piano wire (about 16-20 gauge or so) securely tied/wrapped/secured around the center of the dowels. You would start at the top of the tube away from you and using your knee would pull the wire through the bonding and this would quickly separate the glass faceplate from the tube depending on how hot you got the faceplate. The residue of the Dow bonding material would peel off from both the tube and faceplate. We also used a razor blade scraper to get it off faster. The heater would be a little larger than the faceplate for even heating as you cannot heat parts of the face. Heating must be uniform to avoid breakage of the faceplate. Julian
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julian
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#36
10-29-2008, 01:04 PM
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I thought this might belong here from a thread in B&W
Quote:
The problem is that 1/8" over 10" diameter is 644 ml of material. The Sylgard 184 0.5kg kit would provide about 485 ml since it has a density of 1.03 You'd want at least 20% more than 644 ml to work with. So, you'd need to buy two kits. The 527 is much less expensive, but less rigid. Over such an area I don't know that it would be an issue. After mixing either of them you would need to vacuum degas them to get the bubbles out. Silicones are pretty permeable to oxygen and if you don't degas it some of the oxygen may form bubbles when it cures even though you didn't see any to start with. On the other hand, often small bubbles will dissappear during the cure if you degassed it to begin with. They just get disolved into the silicone. You would have the safety glass face down on a soft surface that keeps it from rocking. If it wouldn't be distracting, the easiest thing would be to superglue three 1/8" thick disks around the outer edge to act as spacers. Pour the silicone into the center without entrapping bubbles. Then slowly lower the CRT touching the center first in only one spot. Being care to not wiggle about continue lowering it letting the contact spread slowly outward displacing the air. Done carefully, there will be no bubbles. It's important to have only one contact spot to start with. The cure of these materials is inhibited by contaminates. Vinyl tape, anything with plasticizers, oils etc. will cause them to not cure. Acrylic resins would be less expensive but are quite hard and shrink a lot during the cure, which might damage the CRT. They probably used some heat curing or melting polymer that would be difficult to work with, without the proper equipment. It's important to try a small sample of the encapsulant to see how it cures and applies. It cures slowly so you have time to take things apart if it doesn't look good and you only lose the cost of the silicone. It's a bit difficult to clean up in such a case. The safest solvent would be 200 proof ethanol or denatured ethanol. No guarantees. There are special primers to increase the adhesion to glass. I wouldn't recommend it because you might need to take it apart later. Oh, and when you pump on it to degas it, it's like soap. It really foams up before collapsing into a clear pool. You need a large container to start with or else be extremely patient. The latter is probably required. It might work without degassing, but for my applications I can't risk that. http://www.ellsworth.com/display/pro...63&Tab=Vendors http://www.ellsworth.com/display/pro...16&Tab=Vendors And after reading the thread in this forum I'll see what I can find out about PVA. John
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#38
10-29-2008, 06:14 PM
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Quote:
http://www.audiokarma.org/forums/sho...d.php?t=184752 goes hand in hand with this one and shows the dangers one can face while trying remove cateracts from a CRT. Gilbert
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I don't know anything about ignorance and I could care less about apathy. www.galaxymoonbeamnightsite.com
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#39
10-29-2008, 06:50 PM
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Hot wire in West LA
Charles wrote: "There must have been some kind of official tool for this purpose, and there were CRT re builders all over the place. I can think of a half dozen in the West Los Angeles area. Some of them were just one oven and lathe in the back of a regular TV repair shop (such as West Coast TV repair on Sepulveda Bl in Culver City). So we should all keep an eye for articles, and for any stuff like that on eBay."
Ah yes, West Coast Rebuilders, located near the Culver City Drivein. I knew them well. I got all my rebuilds from them including the 21FBP22 in my 21CT55. It was really dark in there. I recall they even had a dirt floor, although I might be mistaken, senior memory and all. But I'm positive they used a red hot piano wire connected to a car battery to remove all face-plates before rebuiding. At $45 a rebuild they couldn't waste time on some of the dainty procedures described above.......Tom
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#40
10-30-2008, 08:21 AM
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crt
Quote:
I myself do not attempt to remove safety glass unless its in the soaking in water(kiddie pool ) way . That seem to be the best and safe approach for me . After having a crt implode once , i have not wanted to attempt with a heat gun again . But as i have read others like Doug have had success
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#41
10-31-2008, 01:28 PM
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Update on Sylgard 184
I tried the method I suggested using two 8" watch glasses. It worked well, except that it's difficult to control the lowering of the watch glass. I would suggest instead that if the CRT can be supported face down, to raise the lens up to it using a lab jack.
I also made a mistake in my message to JB5pro. When I estimated the volume needed I did pi*d**2 instead of pi*r**2 for the area. I was a factor of 4 too high.
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