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-   -   Cataract repairs - are we missing the safety glass aspect? (http://www.videokarma.org/showthread.php?t=270024)

Electronic M 01-20-2018 10:42 AM

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!

ohohyodafarted 01-20-2018 01:09 PM

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.

Tom9589 01-20-2018 01:22 PM

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.

WISCOJIM 01-20-2018 03:08 PM

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

.

Tom9589 01-20-2018 04:05 PM

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.

reeferman 01-20-2018 08:04 PM

Quote:

Originally Posted by MadMan (Post 3195062)
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.

dieseljeep 01-20-2018 09:39 PM

Quote:

Originally Posted by WISCOJIM (Post 3195113)
Well, maybe my safety fears were without merit. But I still think I'd feel safer if the glass was bonded.

.

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:

WISCOJIM 01-20-2018 09:42 PM

Quote:

Originally Posted by dieseljeep (Post 3195164)
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...

.

Electronic M 01-20-2018 10:08 PM

as do I.

bluenorm 01-21-2018 09:08 AM

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.

Kevin Kuehn 01-21-2018 09:41 AM

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?

RetroHacker 01-21-2018 03:00 PM

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

Electronic M 01-21-2018 03:11 PM

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

Eric H 01-21-2018 05:17 PM

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.

N2IXK 01-21-2018 06:51 PM

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.


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