did my 1st cateract removal

[DaveWM]

this was a 25AXP22 out of an old RCA ctc 17. It had a very weak red gun, I had replaced it with another cat free some time ago for a buddy. Anyway the CRT has been aging outside for several month. It had a very bad moldy cat (big nodules growing around the edges). I checked it out and the time outside had def increased the cat so maybe in time it would come off.

I mounted it on a stand and had it outside in the hot FL sun, my guess was about 130-140 degrees after about 1 hr (its very sunny today and warm).

First I tried a variac and hot wire on a bow to try and slice it, no dice. it sorta worked but not very well and I ended up cranking up the voltage too high trying to make progress, the wire went slack and broke from the heat.

Next up I just tried putting pressure on the edges and in the sunlight I could see stress "fingers" forming in the plastic as the sun created shadows on the tube face. this was encourging but I could not see myself standing out in the hot sun trying to maintain the pressure.

I got some chop sticks out and wedged them in the edges just enough to maintain the pressure, I could see the fingers slowing growing across the tube face, so I tapped them in a bit more and then left it be. came back about 20min later and the fingers had progressed passed the 1/2 point. I removed them and inserted on the opposite side, this time the progression was much larger and faster. In about 1-2 min the lens just popped loose.

it was really pretty anti climatic and a real confidence booster to see it happen.

I did have on a face shield the whole time, and the CRT mount was very secure. I will be trying this on a roundie soon, wish me luck!!

[marty59]

That is good news and encouraging. This summer I hope to do a Roundie myself and it would be my first attempt. I've really been following these cateract issues!

[VintagePC]

Indeed, good news.
Out of curiosity, what actually constitutes a cataract? Is it just delamination of the safety glass, or does the sealant actually "go bad"?

[marty59]

Originally Posted by VintagePC

Indeed, good news.
Out of curiosity, what actually constitutes a cataract? Is it just delamination of the safety glass, or does the sealant actually "go bad"?

The "bonding material" between the tube and the safety glass is breaking down mostly due to age. Here's my patient:

[DaveWM]

I think the key to a low stress removal it like in the shaw shank redemption movie, time and pressure...

a concern is the effect of the intense direct sunlight on the phospors on the screen, I know its only going to be an hour or 2 but still...

I was thinking of placing a sheet of black tin foil on top of the screen during the warm up phase. The idea is to put it out in the sun early in the day and let it warm up over hours until high noon, then take off the covering so the fingers can be observed to be starting then recover. I know its prob not a big deal but I figure it cant hurt.

The warm up phase (start early) would allow the entire CRT to come up to temp to avoid distortion (the theorized reason for implosion on other attempts that used heat lamps and heat guns).

with a cover in place you could leave it under pressure for hours. The hard part would be to make a good contract with the glass.

I know it sounds like a lot of effort but with the scacity of these tubes (esp the roundies) I am just trying to take ever precaution possislbe. I would not even attempt it if the cat was mild, but that is not the case here.

[andy]

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[VintagePC]

Originally Posted by andy

Be careful not to use too much pressure because the safety glass will crack without warning. If you use a heat gun, play it safe any buy a temperature controlled one. That way you can dial in the minimum heat needed to separate the safety glass rather than hitting it with 1000 degree air.

The reason we're avoiding heat guns is to eliminate the thermal stress you get from heating the tube face without heating the rest of it. Too much of that and it goes bang. There've been some stories here recently about tubes going off with minimal stress, hence the move to using sunlight/heat.

The key is really an even temperature over the WHOLE tube. I suspect if you have a large enough convection oven that can do, say, around 40-50°C, you'd be well on your way.

[DaveWM]

yea thats why I am using the sun, and a long heat up time. the chop sticks in the sides allow for a very controlled application of pressure, just a very little at a time. I will report back on how it goes on the next one.

oh and yes I do have a face shield on all the time in the process.

Good to know I dont have to worry about the UV.

[DaveWM]

I have a email in to scotty about adding a tension band to a formally bonded CRT. I would not be suprised if he passes on answering due to all the legal BS but I figured it would not hurt to ask. the Question is should a band be added to a tube that was previouly a bonded face. I have floated this up a few times before, dont recall every getting a definative answer (are the CRT's the same, just one with a band and one with a bonded face).

[miniman82]

Think about it: how much 'tension' could a bonded faceplate even impart on a CRT? I had 2 tubes (now only 1) with the faceplate removed, neither of them had any sort of tension band. I also have a 21CYP22, no band. The only band I have ever seen on a tube was for mounting purposes, and had nothing to do with tension.

[DaveWM]

I know this has come up before but from what I gather there are 3 types of implosion protection

1) separate safety glass (I asssume the glass is true laminated safety glass not just a reg pane of glass. this just contains any of the damage from the front of the crt


2) bonded glass face plate (essentially safety glass made from the CRT face, plastic,second layer of glass), that is a tough plastic film that contaings the shards of broken glass in case of breakage, this would be the same stuff that is causing the cat to form as it breaks down). This does notthing to prevent an implosion, but if one were to occur then the screen would do like a patio door glass made the same way, lots of small broken pieces all stuck to the plastic, and not stuck to your body.


3) Tension ring, from what I have read this keeps the perimeter of a tube from expanding, which is the failure mode as a tube attempts to implode. The reason for tenison is to prestress the band so it can not expand, thereby keeping the perimeter size from expanding.

It would seem the bonded glass makes no real attempt to prevent the actual implosion, but is rather an attempt to containg the glass. Perhaps the mounting brackets/ring peform the function of perimeter containment on those.

again maybe it was determined that if the rim was contained by the mouniing hardware the implosion protection was sufficent to no longer warrent the need for the shatter protection afforded by the plastic lamination. By incorporating the tension band as a perm fixture to the tube the protection would stay with the CRT even when it was not installed in the set (where before the band was part of the TV mounting hardware).


I am not sure of all the above, just what I have been able to get after a lot of searching. there was talk of just the above over on a UK site as well.

[andy]

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[andy]

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[DaveWM]

I am looking forward to member CTC17's post about water tub removal, sounds like the safest if not quickest method. My kids had a old sand box (looks like a turtle) that was about 3' across (round) I think it would be ideal for a soaking pond for a large tube like a roundie. large enough to hold enough water so that evaporation would not be too big a problem. I was going to put mine in a location where no rain could get it (back covered porch), and I plan to seal the neck with a plastic bag (with a desecant bag inside) to keep any moisture from geting at the pins/wires in the neck socket. Not sure if I need to worry about the anode, maybe a small desecant bag and some packing tape. I want to keep it out of the rain to protect the dag (the one used in the subject of this thread lost a lot of its dag, It was just stored outside where rain could get on it.

[VintagePC]

I wonder if it would be as effective to carefully go in with a thin needle and force a bit of water water into the cataract? It would probably be quicker than waiting for it to soak in by itself.