= About removing cataracts =
 

I have been thinking about the methods talked about in removing the gooey material that causes the problem on the old tubes. I have seen Doug's you tube videos about removing it and then placing the tube, and safety glass back on with little spacers, so the two glass parts never touch...

Here's the question, and sorry if this was already covered, but, Safety glass as it applies to tv's in the days of 21AXP22, seemed to be partly for radiation protection, but in later sets, was it not for glass breakage...?

The way those tubes were constructed, the gooey stuff between both pieces of glass most resembles auto windshield safety glass, where there is a plastic between two pieces of glass, and it keeps the glass from flying all over when it gets hit and broken.....

So for safety sake, when removing cataracts, would it be best practice to put back some type of plastic, or rubber....?

Has anyone ever thought about using shoe-goo, or some rubber cement, or a liquid plastic, kinda like plastic resin, with hardener....?

I know I would not want to experiment on a picture tube, but easily an experiment could be done on two pieces of window glass.....

I know there would be all kinds of problems one could encounter trying to mate the two glass pieces with a liquid between them and not getting any bubbles.....

It was done at the factory somehow.....? Anyone think we should be putting something back in there....?

Or am I wrong, and in those later tubes was it still for radiation, where an addition of the second piece of glass, assuming it had some lead content, is all that we need think about when repairing the cataracts....?

I never thought that any CRT safety glass was meant for radiation protection, but I never looked it up one way or the other to find out.

Likely, the removal of the PVA on our bonded CRTs does reduce the overall safety of the sets, but I am not worried about it personally. When millions of TV sets were sold and treated casually in all types of environments, it probably mattered statistically. Non-bonded CRTs (21FBP22, for example) were always used with what I assume is a separate piece of true safety glass, but then if the faceplate from a 21FJP22 is just ordinary glass, the ultimate "added risk" of a no-longer-bonded tube is, I suppose, that it could implode in such a way that its pieces would also shatter the now-separate faceplate and send those pieces flying outward too. Again, it is not something that I am planning to worry about; I would like to hear the opinions of others.

I read the spec sheet this morning on the 21AXP22 and it specifically mentioned the safety glass as for radiation protection. But the PVA seems to be more suited to hazards of broken glass protection.... Thanks....

OK, thank you for that update.

I know the way many model builders get air bubbles out of silicone or other clear glues is to put the object in a vacuum chamber. But, I don't know where you'd find a vacuum chamber big enough for a CRT.

Plus, many of those glues like silicone and shoe goo are air curing and I don't think the stuff would ever really cure in the center of the CRT face. Besides, they may dry clear, but I'm not sure they'd be considered optically clear.

There are optically clear glues and UV cure glues that might work in this situation, but I'd bet it would costs a bundle for something as big as a CRT face.

Dont know for sure but the PVA may be there so no crud
could get between the glass. Remember cleaning many
safety screens in the olden days. Crap got in no matter how
tight & sealed they were. As far as implosion goes I would think
the glass is non shattering to begin with. PVA may add to
protection but I would guess there is a better chance of
choking to death on a hot dog than having the jug toss
daggers at you.

BTW some day I will put up the story about a tot that got sucked up by a CRT. Was going around back in the late 80's, urban myth ???

73 Zeno:smoke:

Is that the one where the mother goes into the kitchen and hears an explosion and comes out and finds everything in the room was sucked toward the tv and her child was missing?

Ha ! Ha ! !

5 picture tubes in a room couldn't do that if they all broke at once....

I'm curious to know which spec sheet said that the safety glass was providing protection from radiation. I have the RCA and Sylvania specs on the 21AX, and don't recall that being mentioned.
That being said, I did use a radiac meter on my CTC-4 with the 21AX, and found that with a white screen the measurement was .4 millirems per hour. According to our museums resident radiologist, that's a bit high. Not too many folks would be watching a color TV close enough to become sick with radiation poisoning. Wonder what a later glass tube would produce at 25 kilovolts. RCA reduced the second anode to 19.5 in the CTC-5, and 23.5 in subsequent chassis until rectangular and leaded glass envelopes became the norm, I believe. :scratch2:

Ahh, but could 6?

I have a service manual for an Admiral that used a 21AXP22 and it mentions there being measurable radiation at the center of the face. I would have to re-read it to see what it said about the safety glass. I don't see how the PVA could offer much more stopping power for radiation than the glass itself.

In an older thread it was stated that the factory poured in the uncured PVA, which must have been almost water thin (perhaps it was heated?) If you look at these tubes you can see a little stopper at the top.

As for the kid and the "exploding" TV, there are some interesting conspiracy theories and such out there. Search deep, deep into the internet and you will find a forum where it is generally believed that the key to unlimited free energy, something like cold fusion or whatever, lies in a GE color TV that malfunctioned in Chicago back in the 60s.

Yep, that's the story I was thinking of...the GE Color TV. Here's one version of the story that caused quite a stir on VK a few years ago: http://www.videokarma.org/showthread.php?t=145996

You know, GE's slogan used to be "We bring good things to life, and suck nails out of walls."

My beliefs about roundie safety glass (I could be wrong):

1) The reason for the safety glass was to survive a certain strength of impact; it had nothing to do with making the faceplate stronger, but only in preventing it being struck directly
2) I believe the impact resistance had little or nothing to do with the bonded or non-bonded construction, that is the bonded roundies were just depending on the impact resistance of the safety glass the same as with a separate glass
If the above is correct, replacing the bonding material with air will have no significant effect on safety; it will mainly provide a place that could collect dirt.

3) The safety glass may have had something to do with decreasing the radius of scatter in case the tube was imploded, but I don't think so.

Later banded tubes did depend on the banding to strengthen the tube by applying pre-stressing compression. Removing the band from a banded tube is dangerous because it can allow expansive forces to develop under an impact that is too small to reverse the pre-compression when the band is intact. Glass is much weaker under expansion than under compression.

4) Color set safety glass I believe did have some lead content, which could contribute to reducing X-rays in addition to lead in the faceplate

5) The introduction of all-glass color tubes brought the possibility of X radiation off the back as well as the faceplate. Thus the inclusion of lead in the glass and warnings to technicians in some cases to operate with all shields in place.

The attachment is of the last page of a rca 1956 tube manual print for the 21AXP22, and is of the x-ray radiation and the use of 1/4" safety glass, and they only mention x-ray protection.... While small, they do mention it. I'm sure once the words "x-ray radiation" made it into public knowledge some parts of the general public were nuts crazy and would not even go to a store that had a color tv in it.... My Mom would not have color tv for this reason, she even freaked out about the b&w sets, saying they had radiation too..... So for that reason, I'm sure rca at least partly used special safety glass to stop some of that deadly radiation.....

While this front glass would protect the more delicate tube from a direct hit, I think the bonded glass with the PVA was closer to safety auto glass with plastic between the two pieces of glass for strike protection, while the front glass could also have contained lead for radiation.....

I'm just wondering if there is any data to back up any of these ideas I had about the pva tubes...

Think about it - an auto windshield has ambient air pressure on both sides. The plastic is definitely strong, strongly bonded to the glass, and stretchy enough to capture the glass shards (and sometimes even the impacting object - but not if it's moving too fast).

Capturing the flying glass from an implosion seems hopeless, and I don't think the bonding material had the strength to prevent anything flying even if the CRT wasn't under vacuum. Simply an optical sealant, is my guess.