Cracked outer glass on twin panel CRTs

[murphyv310]

Hi.
I went to my friend to collect a NOS CME2306 for Fernseh. This is for his HMV project. There are a number of NOS CRTs stored rather badly in an out side shed. I used to store them in my old work place but they had to move else where in 2012. Unfortunately the twin panel CRTs are all cracked on the outer faceplate. The CRTs though are not down to air. I've brought it away and will be taking it to Newcastle on Sunday. I'm wondering if there is a way to remove the faceplate safely and perhaps swap it with David's original faceplate?
Whats people's thoughts.

[Lloyd 1985]

They sound a bit scary! I've only ever seen the twin panel CRT's separated by Shango066 on YouTube, where he sticks them face up in a bin in the garden, with a black bag over it in the sun to soften the glue, then he separates the outer glass to clean out the adhesive when it's gotten a cataract. In one of his video's the CRT went off with a bang whilst doing this!

it would be worth looking at how the outer faceplate is fixed to the tube, if it's the same thick layer of glue then I did wonder about using wire to saw through it, instead of heating it and driving wedges under the glass, I have done some very tiny Apple watch screens using very thin steel wire, they were scary enough! One bad move and the screen is wrecked!

Regards,
Lloyd

[FERNSEH]

With regard to twin panel CRTs tubes like the 23SP4 and CME2306 re-gunning firms would separate the outer panel from the CRT before carrying out the re-gunning process.
These tubes became obsolete when reinforced faceplate tubes were introduced in 1964/5.

DFWB.

[Tractionist]

Could the front-only be soaked in an appropriate solvent bath i.e. rather than utilising 'mechanical' processes?

[murphyv310]

Hi.
I think the solvent idea is the best and safest IMHO. Trying to remove it by mechanical means is far too risky.

[PaulM]

What follows may be considered very risky, but with care it's seems to be OK.
I've separated several 7" broadcast camera viewfinder tubes using a technique described to me by a guy in the USA. He also supplied me with a 9" CRT reprocessed the same way. You can find demos on Youtube. I've never had any success with solvents.

I don't know about these specific domestic tubes but I would have thought that the same principle would apply. Cataracts and cracks are the big problems, of course.

This sounds scary, but it's probably what the reprocessing guys did back in the day.
The basic idea is to put the CRT face uppermost in an oven at gas Mark 5 for about 20 minutes letting it warm with the oven. This causes the glue to disintegrate and you can just lift off the outer glass when it's cooled. It's worked a treat for me and because the tube is in the oven and 'boxed in', it's fairly safe. However, if it did implode you would have to answer to the wife which may not be too safe in itself. Obviously, you need to be very careful and wear protection when handling the bare tube.

You must remove any plastic round the gun pins before heating it because that melts too!

I do not know what the score might be with larger tubes but I'm told that it works just the same given a large enough oven and suitable support for the bowl.

Clearly, this all comes with stern H&S warnings all over it, 'own risk' etc. etc. but it's probably safer than trying to cut through it mechanically.

Not sure that we should be discussing this - legal stuff etc. etc.

Best regards,

Paul M

[murphyv310]

Hi Paul.
It's very much doubtful that a 23 inch CRT would fit in a domestic oven.
Certainly it's not a job for anyone that has any doubts with the safety aspect. I'll not be doing it nor would I attempt it. The fact this one is cracked it could suggest it may be easier to remove.
The CRT that is low can of course be made safe by releasing the vacuum and the faceplate then removed in relative safety.
I'll leave it up to Fernseh and what he wants to do. Of course the CRT needs to be tested in the first instance.
I wonder if the likes of Autoglass could do an invisible repair?

[PaulM]

Hello Trevor,

I did say 'given a large enough oven'
Anything with handling CRTs can be viewed as dangerous, so the H&S issues always need to come first.

I'd forgotten that I did finish the job using this technique with a 14" RCA monitor tube with the worst cataract I've ever seen. The outer glass was already separating and I warmed it as described (only just fitted in the oven) and that lifted off well before the full temperature.

I think that what happens is that the plasticiser is giving up with time - not necessarily bad storage. I have several broadcast tubes that have been well stored throughout their life and this is still happening.

The guy in the USA who told me about this is well regarded over there and the 9" tube he sent to me as proof of principle is absolutely perfect (it's in a Conrac SNA9 mono monitor). I feel that it's safer (for the operator) than poking about with tools!

As these tubes become ever rarer, we may well be driven further down these roads.

Best regards,

Paul M

[murphyv310]

Good point Paul.
I have to admit I'm not that brave. Old glass seems to get more brittle the older it gets. The thought of an implosion at "close range" is terrifying, especially if you are not properly protected. For me I'd leave it to those that are brave enough to attempt it.

Tubes are getting more and more scarce. There is though a regunner still in operation in Russia but the costs are really big plus the logistics difficult to say the least.

[AdrianH]

There is a video with the guy removing a cataract screen by just leaving it to soak in water for several weeks getting into the PVA adhesive and , then the glass just slides off and smashes anyway, but shows that water may work.

https://www.youtube.com/watch?v=VeaiuHW0ges

Adrian

[murphyv310]

Interesting video Adrian.
It looks like a laminated type to me. The earlier twin panels are different though and as far as I know are not laminated. Certainly the other cracked one on a CME1906 that was particularly bad had no plastic sheeting between the two glass parts, CRT screen and external panel.

[AdrianH]

I thought the plastic sheeting was in fact the PVA adhesive used to bond between the glass and CRT?

Adrian

[murphyv310]

Are we sure this is a PVA adhesive? Normally on a twin panel CRT the glass is bonded at the sides, mind the older twin panel tubes are constructed differently. The glass has extrusions that hold the tube to the cabinet by brackets. Rimband tubes are precisely that with a metal band round the tube with steel mountings on each corner.
I've a picture of a CME1908 when I had them in mid 2000s I'll post up.

[AdrianH]

I am not sure of anything, just with the mention of Shango066 on youtube heating up faceplates, mention of ovens to heat them up I remembered he did try a long soak in water to remove one hence the link to that video as an possible alternative.

When he throws it down to the floor after the safety glass has smashed he calls it PVA, now that may have a different meaning to what I think.

My knowledge of old TV's is very limited, and what is used to secure safety glass to the front of a tube I do not know.

Adrian

[murphyv310]

Hi.
I've watched the video. It does and doesn't look like what we know as PVA if you get my drift.
So yes it probably isn't a laminate. I think his way is good and the end result is fine. Whether David can do this with his old tube and the one I have is debatable. Perhaps just a standard tube and fitting the face plate off his old CRT once down to air would be easiest and safest. Will see what he says tomorrow when I take it to Newcastle.

As a "cure" for cataracts in the tube maybe the old trick used for cameral lenses that have split a bit could be used. This is applying a drop of very thin oil to the gap and letting it fill it. A modern silicone oil won't evaporate.

[slidertogrid]

If the faceplate is the bonded type with mounting lugs on the corners you won't get it to come off without it cracking. The American tubes use just a piece of glass the same shape as the face of the tube, once the bonding gives it is removable . The bonded type with the mounting lugs wraps around the tube and is very strong as it has to hold the weight of the tube. The mounting lugs being part of the outer glass. Even if you could get the glass off without breaking it you would need a very strong bond to the replacement tube. I don't know how the re-gunners did it. I do know some didn't supply re-gunned twin panel tubes.

The original tube didn't look that bed on the pictures I saw, has it been given chance for the emission to pick up with a good run, possibly at a slightly increased heater voltage? The thought of necking a vintage tube fills me with horror, the poor thing has survived this long and now in the hands of an enthusiast where it should be safe it gets destroyed...!
If the bonded screen can be removed from the one with the cracked screen that tube may be ok as a replacement for a unprotected tube in a set that uses a different type of implosion method. But I wouldn't fancy doing it.. I did donkey's years ago. I removed a bonded faceplate from a 19" tube, it came off in chunks with bits of the outer glass still attached to the adhesive. I wouldn't attempt it now though! I was much less concerned of the dangers back then! I replaced tubes on a almost daily basis with no protective gear whatsoever and old tubes were often smashed with a brick just for fun! How I got this far without serious injury I don't know!

Rich

[murphyv310]

Hi.
I have to agree. I certainly wouldn't attempt it. I believe the picture David put up looked really good but as often as not the camera can lie.
I'd be inclined to give the original CRT a clean and Balance, as David did say it wasn't responding to a few hours running.
The Fenbridge cap could be the answer and there may be one in the "Set store". When I get the time I'll look.
The only issue would be a larger gap around the facia where the CRT is "pushed" through using the Fenbridge cap.

[murphyv310]

Hi.
The CRT is now with Fernseh. He like me is a bit reluctant to remove the outer panel. I do think a chat with a windscreen repairer may be an idea.

[Heatercathodeshort]

Central Tubes did not remove the faceplate when rebuilding bonded tubes or Rimband types including colour. They were very good tubes enjoying a very long life, the colour types were rebuilt for the BBC.
The faceplate is fixed to the CRT with a soft, what appears to be a clear Silicon compound.
If you check the point at the edge where it joins the CRT you will find it quite 'squishy.'

I think you will find it almost impossible to remove the faceplate and certainly refit it.
It may be possible to remove the plate and use it in conjunction with an ordinary tube such as the AW59-90/91 but some form of conventional mounting would have to be devised.

It would be extremely dangerous to heat the tube and the thought of ovens horrifies me! I recently experienced a spontaneous implosion of a 9" MW22-7 tube that was fortunately in a packing box. It had been brought over by the owner for testing and went pop about one hour after we had placed it back in the car in it's box and that was bad enough! He discovered the gun assembly under the driver's seat! Heating or stressing a 23" tube would not be recommended. You have been warned. Take care, John.