View Full Version : Requesting cateract removal info


jpdylon
10-15-2006, 12:10 PM
OK all your roundie nuts, The round tube noob has questions for ya'll:

How does one go about removing a cateract from the CRT? I've read about a few people who have done it, but they didn't provide a realy in-depth detailed explaination (or pictures for that matter) how its done properly.

The tube I have now is in fairly good shape and the cateract is only noticable on a bright scene, but I would like to remove it someday while I have the set apart.

More questions: What do you use to bond the safty glass to the tube after you have seperated the old bond and cleaned everything?
Does the glass have to sit a certain distance from the tube face?
What do you use to support the tube while performing the cateract surgery? A special lathe? Some other rig that keeps the tube in place? A big oil drum?
What do you use to remove the old bond? a solvent, heat?

I think all of your AK members other than myself would highly benefit from a thread detailing the procedure. If liabilty were to become an issue, perhaps we could stick a disclaimer on the thread, or members who would be willing to perform the surgery for a price could chime in.

Just my thought, what do you guys think?

drh4683
10-15-2006, 01:44 PM
Ive done a few catercat repairs, the most successful method involved using a heat gun. I suggested the use of the heat gun after experiementation and others have found it to be an effective way to remove the lens too.

The major factor is, who makes the CRT? Zenith or RCA? If its an RCA (type of cateracts that looks like mold inside the lens) the heatgun method is by far your best bet. If its a zenith (green halo symptom) the bonding material is different, much more gel like. If the heat gun method is used on a zenith green halo tube, you will probably crack the lens from overheating. The "electric hot wire" technique is your best bet there.

Assuming its an RCA, and by far the worst of all cateracts happens on RCA type tubes, I'll discuss the heatgun technique.

As for supporting the CRT, I have a Cardboard barrel thats 18" in diameter and supports the tube very well. I put blankets around the edge of the barrel as added cusion to the CRT.
RCA tubes will have a tape around the circumference of the lens, you will need to cut around that with a razor knife.
The next step I use, is to preheat the CRT with a 500 watt halogen work light, aimed directly at the face of the tube about 6" away. After about 30 minutes or so, the lens is hot to the touch, thats what you want. Using a heatgun on the high setting, I start at the edges of the CRT and move the gun very slowly in one area at a time. Once the screen lens gets hot enough, it will begin to seperate from the PVA material. You will see little "fingers" of air pockets begin to form. Continue to move the heat around untill these air pocket fingers merge together. You might want to insert a wood wedge (very thin) into this area on the edge as a slight upward pressure on the lens will assist in the airpocket breaking open, thus seperating the lens from the crt. You must be extremely careful when putting the wedge in, just a very very slight amount of pressure is needed. Do not attempt to use the wedge as a tool to lift off the entire lens, or you might break the lens. As you heat more and more of the lens use your fingers to gently pull up on the lens so you can get a feel as to how much more heat it will take to separate it.
You will notice that the air pocket fingers will begin to dissipate as you move away from a particular area you were just heating. Try to keep that pocket in there. Periodically, you will need to go back over the area you just heated to reform those air pockets.

Once you get the lens hot enough, you should be able to gently pull lens off of the CRT, with the the PVA material ONLY ON THE FACE OF THE CRT. If the PVA comes off in strands that look like the air pocket fingers, you didnt get the lens hot enough before you removed it. Its very difficult and time consuming to remove the peices of stuck PVA to the crt lens as its concave.

Now, assuming the PVA is only on the CRT face, quickly grab the edges of the PVA and pull up on it slightly. As its still hot, it should simply peel off the face very smoothly and easily.

Of course there will be small bits and pieces here and there that wont come off. Use a razor blade and scrape it off the lens and or CRT. Once you get it scraped off thin enough, use gasoline on a rag to help dissolve the remaining film thats left on the crt. You will get it near perfect. After that, use windex or some other glass cleaner with newspaper as the rag to clean the rest of the glass. This will insure a clean, streak free surface.

As for remonting the lens, the best way is to use double sided foam tape (by 3M) and put a few 1" long pieces around the circumference of the crt, being carefull not to place the tape too far in or you could see it when you remount the crt to the bezel. you must use the foam tape as a spacer/cushion. If you do not do this, the center of the lens will touch the center of the CRT, leaving about a 1/16" gap on the edges. If this is left unattended, remounting of the CRT will compress the lens creating undue stress to the glass.

Some have questioned wheter the PVA or lens spacing effect picture quality and or focus. the answer is NO, not at all. The PVA is clear and will not effect the appearance of the tube either.

After centering the lens on the CRT, seal the circumference of the tube using clear packaging tape. This will prevent dust and debris from entering the space between the lens and CRT. Remount the CRT exactly as it came out of the cabinet. You might need to adjust the CRT mounting hardware to compensate for the fact that the distance from the edge of the CRT lens contact point to the mounting bracket might have changed. This is because the orignal PVA material set the "gap". The foam is slightly thiner than the original thickness of the PVA at the edges of the CRT.

Once your reinstalled, the picture will be perfect as new and look great. You'll never have to worry about cateracts again.

Here are some pictures of a 1965 RCA roundie that I did cateract repair on.

drh4683
10-15-2006, 01:54 PM
Here are some actuall cateract removal pictures of a 1968 magnavox color TV. I did the work on this one back in '03. These pictures show the detail as to what the PVA looks like. Just to note, see the center of the CRT? Notice the airpockets impression that is still on the PVA. This is because I didnt get the lens hot enough in the center before I pulled it off. The second to last picture is the final finished CRT.
The last picture is the final insallation of the newly repaired CRT, looks as good as it did when new.

kx250rider
10-15-2006, 02:05 PM
That is a GREAT article!!!!!!!!!!!!!!!!!! This needs to be posted as sticky at the head of the early color TV column.

round tube noob I like that :lmao:


I might only add that when I did mine, I did NOT get it hot enough, and I did crack the lens. No loss for me though, because I wanted it to go in a CTC-9 with external glass anyway. The hardest part, in my experience (one experience only to date), is that those "fingers" of air go away fast! The whole project took me about an hour steady. I had not used the halogen lamp preheat, so I'll do that next time. I have a 1 Kw halogen dual-head lamp, so I bet that'll be even better.

AND A SAFETY NOTE :blah: ABSOLUTELY, POSITIVELY, USE SAFETY GLASSES AND FACE PROTECTION! I WORE A FULL-FACE MOTORCYCLE HELMET, MOTOCROSS CHEST PROTECTOR AND NECK WRAP. I KNOW IT SOUNDS NERDISH, BUT BELIEVE ME IF THAT TUBE FAILS WITH THE GLASS NOT ATTACHED, THERE WILL BE SHARDS OF GLASS THE SIZE OF SAMURAI SWORDS HITTING YOU IN THE FACE, FRONT OF BODY AND THROAT.

There must have been some kind of official tool for this purpose, and there were CRT rebuilders 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.

Charles

John Folsom
10-15-2006, 02:41 PM
The CRT rebuilders put the CRT in the oven and heated it to a high temperature (I don't know how high). When hot enough, the safety glass separates.

jpdylon
10-15-2006, 04:22 PM
Most excellent information. This is just what I was looking for. Many thanks drh4683.

I definitely agree that this should become a sticky.

bgadow
10-16-2006, 12:56 PM
I think those are excellent instructions. I stayed very close to this method. Instead of double sided tape I used a bead of automotive RTV clear sealant at the perimeter with small pieces of popsicle stick as spacers. I think the tape sounds better, and I'll try it should I do another. I would use black or clear tape; some is white and I think that would be more likely to show up once the crt is mounted. Just take your time, make sure both pieces of glass are extra clean prior to remounting.

drh4683
10-16-2006, 04:54 PM
This thread was perfect timing, as the combo I just got off ebay needed cateract removal work. I took many photos of the process. Like they say, a picture is worth one thousand words. The steps I described up above are in direct relation to what I have pictured, in that same order.
The cateract removal on this CRT went just fine and very fast. Once I applied the heat gun to the preheated lens, it took no more than 15 minutes to seperate! I finally took detailed pictures this time. Most of the time, I get too involved in the project and do not want to stop to take photos. I made sure I changed that this time as to help benifit others. Enjoy the photos.

jpdylon
10-16-2006, 05:06 PM
awesome! Love that beautiful color. Can't wait to see when the set is completely done.

fsjonsey
08-13-2007, 10:58 AM
Sorry to bump an old thread, but has anyone thought about removing the tape from the side of the tube and leave it to soak in some kind of solvent for a few days, untill the safety glass just falls off? A friend of mine used this method for a zenith CRT with the green halo with great results. I believe he just used kerosene.

bgadow
08-13-2007, 11:58 AM
Very timely, fsjonsey! I have wondered for quite awhile about a different method-not kerosene but water. I know that crts which have been exposed to the weather will have the PVA turn to jelly. The question is, how long does it take? I finally, just this past weekend, started an experiment to find out. I was going to wait before posting but I'll show what I have done so far. First problem was having a basin big enough for the tube to sit in. If I was single-or if I wanted to be single again!-I would do this in the bathtub. That is not happening! Then I got to thinking. I went to Dollar General and they had a clearance on their summer merchandise. I bought this little 4' blow up swimming pool for $3.75. For the experiment I chose this 25GP22 Zenith I had in the attic. It has the tough "yellow" pva that only responds to a hotwire. I removed the tape, placed the crt facedown in the pool, and added a few inches of water. I later covered the pins & ultor connection to keep any rain out. I will check progress daily with photos to be posted, assuming this all works out. After sitting overnight the pva at the very edges has started turning white instead of the yellow/green cast it had to begin with.

One note: the last picture shows detail of something that has been discussed before. There is a rubber cork of sorts in the tape. It seems obvious that they DID pour the pva in through that opening.

kx250rider
08-13-2007, 12:37 PM
I await the outcome of your experiment anxiously :)

I hate doing the heat gun method. I've done it twice, and I have 2 more sets that need to be done.

Has anyone tried a piece of piano wire with wood dowel handles (cold; not electrified?) It works with modeling clay.

Charles

andy
08-13-2007, 12:48 PM
---

fsjonsey
08-13-2007, 01:16 PM
I tried to use a wire on an RCA 21FJP22 with the green halo, but it didn't work. The wire just broke before it could do much cutting. I guess piano wire might be strong enough.

I ended up scooping out as much as I could around the edges, squirting various solvents in the gap, then gradually prying it off with some plastic tools. Even without heat, it eventually popped off. I'm not sure if the solvents helped, or not.

One idea I've had is to use a very long hypodermic needle to inject air, or water into the middle of the screen. I'm not sure where you'd get a 12" needle from though!

Any feed mill or store that sells livestock supplies will have large needles and syringes for injecting cattle and horses with antibiotics, vitamins, or medications. The longest ones actually have blunt tips, and are used to squirt the medication down the animals throat.

fsjonsey
08-13-2007, 01:20 PM
Someone should do a test of common household solvents and their effects on the different types pf PVA bonding material used on the RCA and Zenith tubes. I was thinking acetone, gasoline, kerosene, denatured alcohol, paint thinner, and water, the universal solvent. Take lumps of the PVA removed from a tube via the heat gun method, cut them into equal size pieces, and see how long they take to dissolve in a cup of each of the solvents.

El Predicta
08-13-2007, 02:08 PM
If you don't mind paying $80 each + shipping, there's a former employee of Video Display Co. (now relocated) that might help. He's in Dallas and did a couple that turned out good for me last winter.

Larry

Phil Nelson
08-13-2007, 02:16 PM
I would like to hear results of any solvent experiments, too. The heat method seems scary/dangerous, and I don't have a lot of Kevlar suits, space helmets, or other protective clothing lying around the place :-)

Dipping the whole thing in a kiddle pool filled with -- whatever -- for a few days sounds much more relaxing.

Phil Nelson

fsjonsey
08-13-2007, 08:01 PM
I was thinking, what about using your standard basement stationary tub filled with hot water? I imagine that warm water would loosen the PVA much faster.

kx250rider
08-14-2007, 12:10 PM
If you don't mind paying $80 each + shipping, there's a former employee of Video Display Co. (now relocated) that might help. He's in Dallas and did a couple that turned out good for me last winter.

Larry

Does he have an oven and facilities to rebuild tubes at home, or just the cataract repair? I'll be in Dallas in the next few weeks, and I might pay him a visit :banana:

Charles

polaraman
08-14-2007, 01:50 PM
Video Display moved their Dallas CRT operations to Pennsylvania and is no longer servicing CRTs there. Charlie started a thread about it here on Ak. They were rebuilding 21 inch roundies for $150. Not anymore!

Is this person rebuilding CRTs or just servicing the faceplate?

polaraman

El Predicta
08-14-2007, 07:04 PM
Just the faceplates.

Larry

bgadow
08-15-2007, 08:43 AM
After work yesterday I checked things out-it had been 48 hours. There really was no visible change over the last day. The pva that was exposed had turned a fatty white but there was no sign of delamination. I decided it was time for some gentle coaxing. I grabbed a handful of popsicle sticks and broke them in half. I started inserting them in the corners. I found that the top of the crt had slightly thicker pva than the bottom and thus I could insert them better there. The pva in those areas had softened, it seemed. Upon insert there were some bubbles in the area of insertion. I layed it back down in the water for another couple hours.

When I returned I spent a few minutes prodding the top corners with additional sticks. One corner in particular was responsive. In short order I had the situation shown in the first picture, an area roughly the size of my hand that had popped loose. I was being gentle. I know the crt faceplate is very thick and that did not concern me. The worry is that I have heard from several others about safety glasses that broke. Anyway, the other corners were not as responsive. I layed the glass back down for a few more hours.

At 10pm I went out with my flashlight and checked again. (I knew I couldn't stand waiting all night) After another few minutes of gentle prodding fully 1/4 of the face had popped and the other top corner was starting to loosen. I added additional sticks all around and went inside for about another hour.

When I returned the entire top half-more like the top three fifths-was delaminated. With the crt layed down I prodded and tugged and was able to feel the glass let go. It just took some gentle tugging to break the last bond-it was loose but rubbery.

I took these photos this morning. I left them in the pool for today because I didn't have time to work on it and the additional time under water will make it easier to clean the glass. I plan on trying double sided tape on this one. This is a spare crt that I just had in storage. It's not real strong on the tester but acceptable. It next goes back in the attic.

Is water the magic bullet? It's not perfect but, yes, it does work. I suspect eventually the pva would let loose entirely on its own without any prodding but what I did was gentle-not even as harsh as when I did one with a heat gun. If you have someplace where it can sit out of the weather you could leave it for quite a long time. The crt will float, sinking just enough to keep the faceplate underwater. The biggest advantage over a harsh solvent is that when you are done you can just drain it, and of course there are not the hazards involved with flammability. It may be that things could be added to the water to expedite the process-maybe lots of dish detergent? One issue with a solvent is that I doubt the vinyl of a pool like this would hold up to it. Finding a metal or poly container large enough might not be easy.

Between now and fall I am going to be working on a set with a crt that has the "gray" cataracts. I will try it in the pool-I suspect it will be quicker to respond if anything. I will report the results at that time.

fsjonsey
08-15-2007, 12:44 PM
After work yesterday I checked things out-it had been 48 hours. There really was no visible change over the last day. The pva that was exposed had turned a fatty white but there was no sign of delamination. I decided it was time for some gentle coaxing. I grabbed a handful of popsicle sticks and broke them in half. I started inserting them in the corners. I found that the top of the crt had slightly thicker pva than the bottom and thus I could insert them better there. The pva in those areas had softened, it seemed. Upon insert there were some bubbles in the area of insertion. I layed it back down in the water for another couple hours.

When I returned I spent a few minutes prodding the top corners with additional sticks. One corner in particular was responsive. In short order I had the situation shown in the first picture, an area roughly the size of my hand that had popped loose. I was being gentle. I know the crt faceplate is very thick and that did not concern me. The worry is that I have heard from several others about safety glasses that broke. Anyway, the other corners were not as responsive. I layed the glass back down for a few more hours.

At 10pm I went out with my flashlight and checked again. (I knew I couldn't stand waiting all night) After another few minutes of gentle prodding fully 1/4 of the face had popped and the other top corner was starting to loosen. I added additional sticks all around and went inside for about another hour.

When I returned the entire top half-more like the top three fifths-was delaminated. With the crt layed down I prodded and tugged and was able to feel the glass let go. It just took some gentle tugging to break the last bond-it was loose but rubbery.

I took these photos this morning. I left them in the pool for today because I didn't have time to work on it and the additional time under water will make it easier to clean the glass. I plan on trying double sided tape on this one. This is a spare crt that I just had in storage. It's not real strong on the tester but acceptable. It next goes back in the attic.

Is water the magic bullet? It's not perfect but, yes, it does work. I suspect eventually the pva would let loose entirely on its own without any prodding but what I did was gentle-not even as harsh as when I did one with a heat gun. If you have someplace where it can sit out of the weather you could leave it for quite a long time. The crt will float, sinking just enough to keep the faceplate underwater. The biggest advantage over a harsh solvent is that when you are done you can just drain it, and of course there are not the hazards involved with flammability. It may be that things could be added to the water to expedite the process-maybe lots of dish detergent? One issue with a solvent is that I doubt the vinyl of a pool like this would hold up to it. Finding a metal or poly container large enough might not be easy.

Between now and fall I am going to be working on a set with a crt that has the "gray" cataracts. I will try it in the pool-I suspect it will be quicker to respond if anything. I will report the results at that time.


Thats great news! I have the exact same tube that I've been wanting to do since I got the TV. It has the yellow cataracts pretty bad around the top edges. This Zenith is my first tube color set, and its in one of the most hideous colonial cabinets I've ever seen, plastic woodwork and all. Beggers cant be choosers i guess? I've been thinking about having someone build a custom cabinet for it, seeing that the tube tests strong on all guns, and the chassis is in good original condition. Time to go to walmart for a baby pool, and maybe an aquarium heater to keep the water warm.

captainmoody
08-19-2007, 10:34 AM
Great idea Bryan! Wow! That worked so well, I am now going to try it on one of my tubes. I always stayed away from the green pva problem ones due to the difficulty. Thanks to you, it looks like we have another way to keep them going!

bgadow
08-20-2007, 08:21 AM
Yes, Captain, I figured I was just stuck with green halos because I really didn't want to try the hotwire trick. I'll add a couple observations: the real progress came when water started getting under the glass. Once one corner opened up I think the water was able to seep down. The pva is tenacious. It took some time to remove it all from the glass-with some of it I ended up taking a brillo pad to get it clean. One of the things that happens here is that the pva absorbs water. Even after a couple days underwater the crt face looked just like it did when I started. But by the time the safety glass came off the adhesive was white in color. I piled up the stuff and once it dried it was again yellowish/clear. It has a foul smell. I would warn anyone who tries this to take your time, don't force things. And keep your hand away from that ultor connection while you're moving that crt around!

I've posted a pic of the finished product.

fsjonsey
08-20-2007, 11:55 AM
Yes, Captain, I figured I was just stuck with green halos because I really didn't want to try the hotwire trick. I'll add a couple observations: the real progress came when water started getting under the glass. Once one corner opened up I think the water was able to seep down. The pva is tenacious. It took some time to remove it all from the glass-with some of it I ended up taking a brillo pad to get it clean. One of the things that happens here is that the pva absorbs water. Even after a couple days underwater the crt face looked just like it did when I started. But by the time the safety glass came off the adhesive was white in color. I piled up the stuff and once it dried it was again yellowish/clear. It has a foul smell. I would warn anyone who tries this to take your time, don't force things. And keep your hand away from that ultor connection while you're moving that crt around!

I've posted a pic of the finished product.

Wow! That looks like a brand new tube! What method did you use to remount the glass? A bead of silicone or double sided tape?

bgadow
08-21-2007, 10:01 AM
This time I tried double-sided tape. (first time) Overall I liked it, though with one layer of tape it didn't fully touch the tape. It was enough, though, so I left it. A second layer or some thicker tape would be better but I wouldn't want to go too thick with these etched safety glasses because you could lose too much picture clarity by being too far away.

kx250rider
08-21-2007, 12:24 PM
Nice work!!!!

I'm impressed with how original it looks. What kind of double-sided tape was that? I thought about using the foam house window insulation tape, which comes in various widths and thicknesses.

Charles

bgadow
08-21-2007, 02:33 PM
I used some automotive tape as used to hold moldings on cars. Some brands are gray, others white. The stuff I have is black so it doesn't show up under the glass. There are various widths. This was 1/2". Kind of expensive, though, at $25/roll. Good stuff-if the conditions are right it has a death-grip. This stuff is fairly thin, compared to some household weatherstripping tape that can be on the thick side. Just using the sealant works fine, too, just takes a few more minutes. If you make continuous corners with the tape it can kinda bunch up. I'm not sure if that would be easier or harder with a round tube. Another idea would be to use the old-style butyl rubber like what was once used to hold auto windshields in. It stays gummy and is black. I have seen it in tiny ribbons that would work well, probably 1/8" thick would do. Windshields use nothing less than 1/4" which I think would be too heavy.

andy
08-21-2007, 03:29 PM
---

kx250rider
08-22-2007, 12:00 PM
the old-style butyl rubber like what was once used to hold auto windshields in. It stays gummy and is black.

That stuff is HORRIBLE!

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 :scratch2: . 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 :thmbsp:

Charles

bgadow
08-23-2007, 11:23 AM
Yes, you're right! I hesitated to mention it! Perhaps worse is the more modern urethane rubber used for windshields. It will jump on you, somehow.

bgadow
10-22-2007, 01:56 PM
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!

drh4683
10-22-2007, 03:34 PM
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!

julianburke
10-25-2007, 08:44 PM
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

jeyurkon
10-29-2008, 01:04 PM
would have been a liquid poured in between the glass and CRT, covering the entire viewing surface, forming to a crystal-clear, rubber-like sheet about 1/8" thick.
I had removed the glass by lightly heating the center area with a hair dryer. The outer areas were seperated because the material was rotted by some white mold-like substance. Thanks for thinking about it.

I would have recommended RTV-615, but the price has gone through the roof. Sylgard 184 would work, but will still cost about $100 assuming no mistakes. I've not used Sylgard 527. but it sounds like it would work and be less expensive. It would be a very soft layer.

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/productdetail.html?productid=263&Tab=Vendors

http://www.ellsworth.com/display/productdetail.html?productid=216&Tab=Vendors

And after reading the thread in this forum I'll see what I can find out about PVA. John

radotvguy
10-29-2008, 02:29 PM
Be very careful on removing a safety glass . I had a crt implode on my bench and it was only inches away from me . Wear safety glasses, long sleave shirt and be careful!!!!!!!!!!!

radio63
10-29-2008, 06:14 PM
Be very careful on removing a safety glass . I had a crt implode on my bench and it was only inches away from me . Wear safety glasses, long sleave shirt and be careful!!!!!!!!!!!

This thread:

http://www.audiokarma.org/forums/showthread.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

Tomcomm
10-29-2008, 06:50 PM
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

radotvguy
10-30-2008, 08:21 AM
This thread:

http://www.audiokarma.org/forums/showthread.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

I do remember this posting .

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

jeyurkon
10-31-2008, 01:28 PM
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.