I've seen plenty of threads where people "fix" a cataract, and I have also done many myself in the past. But I always had this feeling that the way we are sealing these jugs is all wrong.

Does anyone really believe that taping or caulking really makes the CRT front "safety glass"? If you think sealing only the edges of the now cataract free CRT gives you any real protection, you are fooling yourself. Why do you think that inner layer was put in there for in the first place? No, not just to keep dust out...

Real safety glass requires that the inner layer holds the front and back glass together, just like in automotive windshields. Removing that layer just gives you two pieces of glass with an air gap.

Has anyone tried doing it the correct way using a resin between the CRT and the "cover glass"? If so, please share details.

I think we all should reconsider how we remove cataracts, and come up with a way to put the "safety" factor back in.

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I'm all for it....if there's a way.

I fully understand the principle behind automotive safety plate glass. Why did we go for so long with a separate safety glass with a huge air gap between the glass and the CRT? Also consider CRTs with no safety glass, just a band around the tube under tension. All you want is that the safety glass stop the CRT glass from being projected outward toward the viewer, not hold it in place like a windshield.

You are correct. Little protection is given by taping the safety glass to the crt.

That said, as hobbyists, we do not have the materials or equipment to do this kind of rework.

Even at Hawkeye, a fairly large crt rebuilder, the safety glass was fastened in place with a bead of silicone sealant and carton sealing tape around the circumference. If Hawkeye didn't have the resources to bond the safety glass, then I think it unreasonable to think we can do it.

I fully understand the principle behind automotive safety plate glass. Why did we go for so long with a separate safety glass with a huge air gap between the glass and the CRT? Don't mistake plate glass for actual safety glass. I know that a lot of the 1950's TVs I junked in the past did have actual safety glass (with the internal bonding agent) in front of the CRT. And that safety glass was between the CRT and the viewer.

Also consider CRTs with no safety glass, just a band around the tube under tension. I'm assuming in the case of those CRTs there were improvements in the glass to bring up the safety margin.

All you want is that the safety glass stop the CRT glass from being projected outward toward the viewer, not hold it in place like a windshield.With the force of an implosion, a sheet of glass offers little actual protection to keep the front glass from shattering and sending its own shards everywhere.

I would imagine in every instance where a CRT was designed with the resin layer, it was there for a specific safety reason. Otherwise they would have come with just an edge bonding in the first place.

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There were both glass scatter tests and specifications and impact tests/specs over the years, I don't think we can definitively say that the resin bonding was intended specifically to limit scattering, or only to meet the impact tests. If there is someone around who has access to the historical development of UL tests, or very unlikely, some manufacturer's documents (boy, would they not want that to be public), I think we can't say. The resin bond MAY have been mainly for dust exclusion, while the glass continued to provide the same protection as when it was air-spaced.

Can someone who has witnessed breaking a resin tube tell us if it captured all fragments like a windshield, or did glass pieces spray?

If the latter, then the resin may have reduced the force/distance of the spray, or may not. Actual test results with/without resin would be needed to answer this.

I've done several cataracts and I don't really worry about implosion all that much. I once did a cataract removal on the bathroom floor in my pajamas. A few months ago, I needed to bust up an old dead Zenith 25GP22, and even with a good sized sledgehammer, it took a lot of force to get it to pop.

I've done several cataracts and I don't really worry about implosion all that much. I once did a cataract removal on the bathroom floor in my pajamas. A few months ago, I needed to bust up an old dead Zenith 25GP22, and even with a good sized sledgehammer, it took a lot of force to get it to pop.

Worry? No. Take sensible and reasonable precautions? Hell yes! I've never done a cataract removal but have popped a few CRT's in my youth (back in the early 7's we didn't know better!) and they can really throw some glass sometimes. A piece in the eye would really ruin your day. I'd be wearing a face shield, some gloves and a jacket. Maybe it goes back to my firefighter days, we did crazy stuff but with proper gear.

What about the air gap between a Predicta CRT and the plastic safety screen?

A piece of glass in an eye? Meh. I've got two of 'em.

I've said this before, just buy a shitload of UV-activated LOCA glue. (https://www.ebay.com/sch/i.html?_odkw=uv+loca+glue&_udlo=20&_udhi=100&_mPrRngCbx=1&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xuv+loca+g lue+50.TRS1&_nkw=uv+loca+glue+50&_sacat=0) It's the stuff they use to glue cell phone's glass to the screen. Kind of expensive for that much, but hey, that's the price of 'safety.'

Game is hard.

Also, while I agree that the mushy stuff between the CRT and the safety glass does definitely add some protection... I'm pretty sure that if the tube wanted to implode, anybody in the vicinity would have a really bad day, whether or not it had the mushy stuff.

Also, while I agree that the mushy stuff between the CRT and the safety glass does definitely add some protection... I'm pretty sure that if the tube wanted to implode, anybody in the vicinity would have a really bad day, whether or not it had the mushy stuff.And I'm sure it would have given more protection when the tubes were fresh, and not with 50+ year-old crusty mushy stuff like we see nowadays.

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Life was simpler then.

[QUOTE=Tom9589;3195034]I fully understand the principle behind automotive safety plate glass. Why did we go for so long with a separate safety glass with a huge air gap between the glass and the CRT?


We had a 21FB set with come in with a BB hole in it that went through both the safety glass and the CRT face glass. Just left a hole the size of the BB. We couldn't believe it. A one in a million shot, kid.

BTW, there was no "huge air gap".

We had a 21FB set with come in with a BB hole in it that went through both the safety glass and the CRT face glass. Just left a hole the size of the BB. We couldn't believe it. A one in a million shot, kid.

Must've been one hell of a bb gun. You sure the kid wasn't playing with his dad's .22?

BTW, there was no "huge air gap".I assumed Tom was talking about those sets that have the CRT about 1-1/2 to 2 inches behind the flush mounted glass on many of the old TVs.

http://www.videokarma.org/attachment.php?attachmentid=196384&stc=1&d=1516456338

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Exactly.

I hold the opinion that based on design evolution there is no significant danger to caulking the glass on at the edges...Allow me to explain my basis for that statement.

I will use roundy color sets as an example. In the beginning, the 21AXP22/21CYP22 sets had a completely separate (from the CRT with a big air gap) planar safety glass that consisted of two planar sheets of glass laminated together. (This was consistent to precautions in monochrome sets before and up thru that time period.) Next came the 21FBP22 (the original CRTs that never developed cataracts are these)...It also had a safety glass that was not glued to the CRT, but this glass was curved. It had a rubber gasket around the edge (to minimise dust ingress) that spaced it a fraction of an inch away from the CRT face...This curved glass was not laminated. There was just a single curved layer of glass. No one ever worries about implosion with an FB in their TV. Next came the 21FJP22 which was the same as the FB except they replaced the air gap and rubber gasket with glue...
They would not have switched from the laminated planar glass to the curved single sheet glass if there was a significant reduction in safety (and bodies like UL would have given them grief). When the FJ came out the FB did not disappear, but rather for several years makers used both types simultaneously/interchangeably in their sets as sam's parts lists, and tube layouts support. If there was a marked improvement in safety with the FJ then the FB should have rapidly vanished...It did not.

Based on the above I believe that removing the original glue of an FJ and caulking the safety glass back on is no different than converting an FJ over to being an FB type, and thus the safety factor should be the same as the FB CRTs (which everyone considers safe). Maybe the original glue makes it somewhat better, but lack of that glue only sets it back to another design that passed safety standards of the time well enough for the two to be made alongside each other for years... I also feel it is reasonable to carry that logic over to other types of cataracted CRTs.

Every night I sleep with a caulked CRT ~3' from the foot of my bed, and I don't lose a wink of sleep over it. I plan to keep using the caulk method indefinitely.


One thing I've seen/have is a vintage rebuilt roundy color CRT (labels are gone) that had the glass foam taped on...So it was a standard practice of the day too.


If someone wants to bond their glass back on and can find a cost-effective product or wants to spend the money on something expensive then more power to them....However, I'd like them to consider one thing: At some point, your new glue is probably going to fail....Have you selected a glue that is practical/economical for a user to remove like the original, or have you doomed the tube to looking terrible for some unknown period of time (possibly forever) at some point in the future?
This type of change should be reversible for the sake of the set and the future generations of owners of the set!

Tom,
I have to agree 100% with your thesis about the safety of the FB vs the FJ tube. Upon thinking about the reasoning for the manufacturers to transition from the air gap to the bonded resin face plate, I think this may have been more a mater of not having to clean the dirty inner glass surfaces of the FB type, and less a mater of safety.

Even though the FB type had a gasket at the circumference of the face-plate, it does not create a perfect hermetic seal. The action of heating and cooling the air between the safety glass and the surface of the crt, causes the air to "breath". In a similar fashion, changes in atmospheric pressure will cause the air in the gap to breath. As a result, especially in homes of the 60's when cigarette smoking was still commonplace, that polluted air was drawn into that air gap and could create a film of smoke on the glass surfaces in the air gap.

Manufacturers may have decided that it was time to eliminate the possibility of degrading the image via dirty glass surfaces of the crt by "bonding" the safety glass to the crt face, and thus moved to a bonded configuration. In the end I think this bonding was more about keeping the dirt off of the face of the crt and retaining a factory fresh crt image. This way anyone could take some Windex and clean the face of the safety glass and have a fresh clean image again. There may or may not have been some additional safety attained by the bonding, but it is my opinion that it was more of a selling feature to be able to tell the potential customer the set had a "bonded safety glass" and the picture tube would never need a service call to have the glass cleaned. (though I doubt many people had a special service call for cleaning alone)

But I do remember at least one service tech who asked if mom and dad wanted him to clean the glass (on a B&W set). And when he showed them how much smoke film was on the face of the crt and the inside of the safety glass, mom and dad were astonished. And the picture was visibly much sharper and brighter after the cleaning.

But I do remember at least one service tech who asked if mom and dad wanted him to clean the glass (on a B&W set). And when he showed them how much smoke film was on the face of the crt and the inside of the safety glass, mom and dad were astonished. And the picture was visibly much sharper and brighter after the cleaning.[/QUOTE]

That's why I always carried some Windex and paper towels on service calls.

Well, maybe my safety fears were without merit. But I still think I'd feel safer if the glass was bonded.

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A lot of people debate about glass. In everywhere except the US, front windshields are tempered, not safety plate glass. All of the remaining glass has been tempered on US cars since about 1959.

I'm on the side that thinks bonded faceplates were developed to keep dirt out. Any place you have high voltage to attract dust, it will find a way in unless it is sealed very well.

Must've been one hell of a bb gun. You sure the kid wasn't playing with his dad's .22?

It was a BB gun.

Well, maybe my safety fears were without merit. But I still think I'd feel safer if the glass was bonded.

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The local rebuilders used the Scotchmount and the caulk method. I never thought it was the proper safe way. I knew the resin was used as an impact cushion. The outer glass was nothing like tempered glass, just regular glass like window or bottle glass. I only used a few of those tubes, as I was never happy with the picture quality.
I started using Sylvania, Channel Master, RCA Colorama or the Zenith rebuilts.
In a way, it was the best move to avoid getting sued over damage or injury. If that happened with a higher quality, name brand tube, you had some kind of a legal recourse. They were only a few bucks more. :thmbsp:

They were only a few bucks more. :thmbsp:Don't you need to get to bed? You have somewhere to be in the morning. See you there...

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as do I.

I have to agree with the safety assessment made by Tom and Bob. In addition, the is one topic that needs to be discuss, which is esthetic. Would you have your pride and joy color tv in your living room with a green black eye to say the least? when we show our tv to other and to yourself, we must have it to state of the art condition. if not the first question you will encounter is why the picture tube looks like that. the set will look "junky" with out cataract removal.

Adding the bead of silicon around the perimeter of a decateracted CRT at least adds some level of impact and scratch protection. What you achieve is a nearly sealed cushion of air that resists any moving object from directly striking the CRT face. Effectively it spreads any impact over the entire face of the CRT. I wonder if the FB glass was not of different temper than a bonded FJ type?

I've wondered about this many times myself - although, as it applies to smaller tubes like used in computer equipment. I collect old computers as well as televisions, and have done the cataract repair on CRTs used in old computer video terminals. It's the same process as on a roundie - just a much smaller tube. I've never had one implode, but I have often wondered about the ramifications of that safety glass being stuck on with tape or caulk. At least on a television, you're generally watching it from several feet away - but a computer terminal, you're right directly in front of it.

Also, I've wondered what the problems with heating and cooling cycles would be, on a tube that's had the safety glass sealed on with caulk. The air is sealed in that gap between the safety glass an the CRT face, what happens when it goes through a severe temperature change - say, for instance, in a car overnight in the winter, then brought inside? Has anyone ever had the safety glass crack in this situation?

-Ian

Silicone caulk stretches...Expansion should not be an issue.

It seems it should be possible to re-attach the safety glass with the same material used originally, or it's modern equivalent.

The problem is it's probably not available to the general public, and if it is it's probably only sold in 55 gallon drums or larger.

Even if you could get the proper resin to do the rebonding, it likely needs to be done under vacuum to prevent entrapping air bubbles between the faceplate and the tube.

i believe it was put on the front of the crt to prevent small pieces glass from flying outside the tv set only , i have a zenith roundie with oil between the crt face and the safety glass ,no pva material .

I've said this before, just buy a shitload of UV-activated LOCA glue. (https://www.ebay.com/sch/i.html?_odkw=uv+loca+glue&_udlo=20&_udhi=100&_mPrRngCbx=1&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xuv+loca+g lue+50.TRS1&_nkw=uv+loca+glue+50&_sacat=0) It's the stuff they use to glue cell phone's glass to the screen. Kind of expensive for that much, but hey, that's the price of 'safety.'

Game is hard.
'Nuff said.

I recall your mentioning that before but didn't remember the name of the stuff, must make a note of it.

I think its important to distinguish between roundie color and rectangle. Since this is being discussed on the early I will assume roundie. I would highly recommend care when dealing with rectangle sets that had bonded faces. I have had one go off in the process of removal of a cat and it was something you will not forget, BIG chucks of broken glass flying everywhere covering 20ft or more. I would think that for those you should leave them be (if its just a slight green halo zenith) or maybe try banding, but not sure about how that would work. I suspect the rectangles were never designed to have NO protection at all.

i believe it was put on the front of the crt to prevent small pieces glass from flying outside the tv set only , i have a zenith roundie with oil between the crt face and the safety glass ,no pva material .
Are you sure the whole thing is filled with oil? Have you ever tried to drain all of it, and is there a cataract forming? I've seen some normal tubes that were developing a cataract where the outer edge of the PVA was breaking down into an oily substance. I think you're mistaking this oily broken down PVA for an oil filling.

'Nuff said.

I recall your mentioning that before but didn't remember the name of the stuff, must make a note of it.

But is that glue feasible to remove for a future re-cataract removal? If that glue ever discolors or becomes hazy there needs to be a practical way to separate it without harming either piece of glass that it bonds.

One other argument for the caulk edge method: if the tube you did ever becomes weak or defective you may want to re-remove the safety glass and transfer it to a better tube with bad or missing glass....I have had this happen to me twice.

I've done 2 tubes that were dead before cataract fix and died a while after respectively...Their subsequent replacements had the safety glass ruined or missing, removing the glass from the de-cataracted duds by cutting the caulk was a convenient source of quality safety glass.

In the era when FBP & FJP were both being sold, the bonded tubes used frosted faceplates rather than clear (at least, every one I've seen did). I believe the PVA could help the optics in that case as just having the faceplate a hair too far away from the crt can result in a big loss of focus.

I've read an article in one of the TV repair trade magazines c.1959 talking about Sylvania introducing the first bonded tubes (b/w). I don't recall it mentioning safety, just how it freed up TV designers vs. separate glass. Personally, I do the edges either with double-sided tape or silicone & will continue to do so.

I suspect the original material had a very low viscosity when it was poured/pumped in. Maybe it was heated? Were it as thin as water or mineral oil perhaps air bubbles wouldn't be an issue. I'm not sure how they do it with modern auto glass.

Meanwhile, the vent windows on my '51 Ford have "cataracts" of their own. Rather than replace them I'm tempted to try taking them apart and then re-laminating them with silicone.

electronic m , no its definite oil what kind not sure , but doug has a rca metal table top with oil in the face plate to, he posted it on youtube a few years back, they have a o-ring around it that dries out and they begin to leak everywhere trust me , mine was leaking from day one , on carpet , basement floor , and so on. it's the 21fbp22 doug did his garage i think in that video , he points out how nice and easy they are to redo . rca 1964 ctc-16 drh4683 ,part 2 ,of his video you see the oil before he reinstalls the face plate .

I think on the 21fbp22 equipped sets, that the rubber face plate gasket breaks down and excretes an oily substance. Some folks have mistaken residue for a cataract forming. My Zenith 21fbp22 equipped set has just the slightest oily film forming around the outer edges. I can't imagine one of those rubber gaskets could contain all the oil if the entire face gap was filled. :scratch2:

The "oil" is likely a plasticizer leaching out of the resin.

This has been quite a discussion on this subject, so I'd figure I would chime in. It's always been my understanding the PVA bonded safety glass on the 21fj and others was used to protect the tube from external objects striking the face plate that could result in an implosion. Not the other way around. The 21fj without the safety glass is just as structurally sound as the 21fb, so it shouldn't matter how anyone chooses to re attach the safety glass. Think about it, there's no way these tubes had the safety glass bonded to them during the evacuation process ( I assume pumped down to the 7th scale) and exhaust process. The PVA bonding could not have handled that kind of heat for the time required. I also find it interesting that some of these guys claim the bonding or coupling agent is some form of optical oil on some of these tubes. That could very well be as that was the case on CRT based projection TVs between the tube face and magnifier lense.

There is definitely oil in front of some projection CRTs to keep the tubes cool. My son and I took a projection TV apart for the heck of it. I have even seen kits offered for sale which contain cleaning supplies and fresh oil as the oil gets cloudy after a few years of use.

Tom,
I have to agree 100% with your thesis about the safety of the FB vs the FJ tube. Upon thinking about the reasoning for the manufacturers to transition from the air gap to the bonded resin face plate, I think this may have been more a mater of not having to clean the dirty inner glass surfaces of the FB type, and less a mater of safety.

As a result, especially in homes of the 60's when cigarette smoking was still commonplace, that polluted air was drawn into that air gap and could create a film of smoke on the glass surfaces in the air gap. <snip>

But I do remember at least one service tech who asked if mom and dad wanted him to clean the glass (on a B&W set). And when he showed them how much smoke film was on the face of the crt and the inside of the safety glass, mom and dad were astonished. And the picture was visibly much sharper and brighter after the cleaning.

Oh, the memories! The first TV I trashpicked and repaired (a circa 1959 blond Zenith 16C21 I found in the summer of 1980, I was sixteen) had a weak 1B3 (I was beaming with pride to have recognized the blooming failure and knowing how to fix it immediately!), only to find the picture had a deep brown cast. I removed the safety glass, and used an hour, a whole roll of paper towels, and a lot of window cleaner to get it all done.

Had a lot of fun with that set. It was extraordinarily sensitive on lowband VHF, and made great use of it to chase TV DX by Sporadic-E skip over the next three summers (longest catch: KREM Spokane, 1702 miles from Detroit's East Side).

During the third summer, the abused tuner was getting glitchy. I cleaned the tuner contacts, but when I fired it back up, the performance was only ordinary (sigh).

My guess is that the dirty tuner had been allowing some regeneration to occur, reducing bandwidth and increasing gain.

removing the glass from the de-cataracted duds by cutting the caulk was a convenient source of quality safety glass.
After several people said they cracked/broke the glass on 21FJP22s while trying cataract removals, I would not have thought the piece of glass (the anti-glare "lens") was "safety glass" at all, in the sense that it might resist breaking or would break into small bits as car windshields do. Am I misunderstanding what "safety glass" is/does?

Also, on the TV sets that had 21FBP22s as opposed to 21FJP22s, I always think of the separate, flat piece of glass that was common on many sets over the years, but it seems that some 'FBP' sets had a separate piece of glass that was basically conical and shaped to fit right in front of the CRT itself; were those pieces a more-"safe" type of glass than the anti-glare pieces that come off 21FJP22s?

I believe the real reason behind the PVA bonded safety glass might be to minimize reflections between interfaces.

Consider light emanating from a source outside of the set and falling on the screen:
In a set with a 15GP22, you have the interface between the air and the safety glass, an interface between the safety glass and the air behind the safety glass, and interface between the air behind the safety glass and the front of the tube, an interface between the front of the tube and the vacuum of the tube, and finally between the vacuum of the tube and the phosphor dot plate. There are going to be reflections at any interface where the light passes from a low index to a high index material. This is basic optics. In the case of light that makes it to the dot plate, there are now a bunch of low-to-high interfaces on the path back out of the set.

All this reflecting has the effect of washing out the picture and reducing the apparent contrast.

The later 15HP22, 19VP22, 21AXP22, 21CYP22, 21FBP22, etc, eliminated the interface between the vacuum of the tube and the dot plate by depositing the phosphor directly on the glass that makes up the front of the tube.

Now consider that the refractive index of PVA (1.48) is much closer to that of the various glasses (1.40 to 1.60 for most varieties) than it is to air. You would be replacing a air-to-glass interfaces with PVA-to-glass, and since the indices of refraction are much, much closer, you would minimize the reflections to some degree. Granted, there would still be reflections at the interface between the PVA-to-glass interfaces. Even glass-to-glass interfaces (with two seperate pieces in direct contact) must exhibit some reflecting as the structure of the glass itself is not continuous and there are gaps and voids between them, etc. Still, the severity of the resulting reflections is substantially lower.

The PVA bonded tubes should give less "glare" from ambient light than a 21FBP22 set. I can say that there is much less glare on my CTC-7 than the Westinghouse H840CK15, and I suspect that a CTC-16 with its bonded tube would exhibit less "glare" than say a CTC-7.

Here's the video showing the oil https://www.youtube.com/watch?v=VlWXNVJ5fN0

I believe the real reason behind the PVA bonded safety glass might be to minimize reflections between interfaces...

Maybe not THE reason, but definitely a benefit. In medicine, the saying would be "There are no side effects, there are only effects."

Here's the video showing the oil https://www.youtube.com/watch?v=VlWXNVJ5fN0

This video shows an unbonded tube. The 'oil' is exuded from the rubber edge gasket. While the rubber is still flexible on an old tube, the surface is not clean, but covered in this sticky substance, and may carry some black material from the rubber. I'm guessing that they were made with an excess of "plasticizer." In the case of my tube, there was some residue on the inside of the cover glass that never came completely off. So, there must be some volatile substances given off also. Not visible under normal operation, but still visible when the cover was off and reflecting a ceiling light. The gasket at first was covered in black goo, which I suppose was a combination of deteriorating "rubber" and plasticizer. It came off on my hands when I picked up the lens. After the first cleaning, I made the mistake of setting the lens gasket side down on the cabinet, where it immediately left a dark circle in the wood finish.