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Old 27th Apr 2024, 3:48 pm   #1
TonyDuell
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Default Dripping CRT

The CRT in question is actually in a Beehive B601 computer terminal, but I've put this under 'vintage TV' as it relates to the CRT rather than to any part of the electronics of the terminal.

I have such a unit, and upon moving it today I noticed 2 things. One was that the laminated faceplate of the CRT was clearly delaminating, there were what are commonly called 'cataracts' on it. The second was a sticky brown substance that was leaking out the bottom of the unit and which had attacked the paint on the cabinet it was standing on.

So it went on the bench and I got it apart (which is not easy). The gunge was coming from the monitor section but not from the line output ('flyback' transformer or any capacitor. No, it was coming from the CRT itself and seems to be the remains of the laminating adhesive.

I am worried that not only is the screen unreadable but that the implosion protection of the CRT is no longer good and the thing could go up in a unpleasant manner.

Any comments/thoughts?
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Old 27th Apr 2024, 4:03 pm   #2
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Default Re: Dripping CRT

Balsam!

It's commonly used as a transparent, stays sticky, cement for glueing optical glasses together that can be done without trapping bubbles as the two parts are slid together.

It was commonly used in fancy camera lenses with compound elements.

It could be re-done.

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Old 27th Apr 2024, 4:04 pm   #3
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Default Re: Dripping CRT

I think you are right to be very wary about this.
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Old 27th Apr 2024, 6:40 pm   #4
TonyDuell
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Default Re: Dripping CRT

My late father was a physical chemist who did a lot of work with vacuum systems. He taught me to have a healthy respect for such things!

Anyway, I've extracted the CRT, removed the yoke, etc. I can investigate and repair the rest of the unit. The CRT is packed in a box surrounded with old T-shirts, that should stop it being lethal in the house. It doesn't take that much to contain the flying glass if it does implode, actually.

As regards re-cementing it. Yes, I know about balsam and the more modern UV-curing optical adhesives. But I would have to separate the glass panels at the front of the CRT to use either, probably have to remove the tension band. I am not sure how easy it would be to do that safely.
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Old 28th Apr 2024, 12:37 pm   #5
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Default Re: Dripping CRT

If there's a tension band, it's the actual implosion protection and should not be removed. In that case the screen in front is only for contrast or some such purpose and can be safely left out or attached loosely.

On the other hand, if there isn't a tension band but only some kind of mounting strap, it isn't integral to the implosion protection and can be safely removed to re-attach the actual implosion protection screen.

You could try to take a few pictures, but as a rule of thumb, a tension band is welded in place while a mounting strap is, at most, screwed on tightly.
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Old 29th Apr 2024, 4:02 pm   #6
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Default Re: Dripping CRT

It certainly looks like a tension band, the ends are spot-welded together. But the front glass doesn't seem to be tinted or anything like that, so it's not an optical filter. And it was clearly once bonded to the CRT glass envelope over the entire screen area.

The CRT has a label saying it was made by 'Clinton Electronics Corp' and has a type number CE434M15P42TE15. I can't find any reference to that number anywhere, does anyone have any ideas as to equivalents, data sheet, etc?
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Old 30th Apr 2024, 11:01 am   #7
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Default Re: Dripping CRT

Quote:
Originally Posted by TonyDuell View Post
It certainly looks like a tension band, the ends are spot-welded together. But the front glass doesn't seem to be tinted or anything like that, so it's not an optical filter. And it was clearly once bonded to the CRT glass envelope over the entire screen area.
Belt and braces?
Rimbands always struck me as a leap of faith
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Old 30th Apr 2024, 11:18 am   #8
Maarten
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Default Re: Dripping CRT

If ir's spot welded ir certainly seems like a tension band to me.

It being a terminal, it seems strange to me that there wouldn't be any optical purpose to the cover, but maybe it was extra protection since people would sit close to it. It's likely glued on because not doing so would affect the picture which is more important since it's a terminal.

@Graham not really a leap of faith. More like a revolution of the mid to late 1960's. Almost overnight most modern tube designs were adapted after the principle became known. It redirects the energy and the glass just doesn't gain speed upon implosion.
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Old 30th Apr 2024, 4:31 pm   #9
TonyDuell
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Default Re: Dripping CRT

I wish I could find a data sheet on the CRT, but a google search comes up blank. It's not even listed in the charts for my B&K 467 tester.

There is another number on the CRT label: 1-014-0875. That looks very much like a Ball Brothers part number. Ball Brothers were a well-known manufacturer of monitor subassemblies to use in computer terminals etc. It would not surprise me at all if the monitor PCB and associated bits in this Beehive terminal were made by them. Alas Ball Brothers service manuals simply tell you to order the CRT by the number on the label and give no other information.

I've been thinking some more about this CRT. CRT manufacture is not really my area so I am not sure, but... The screen layers are clearly separating. The gunge comes from the CRT, you can see the path it took on the inside of the case panels and there's no other unit that is leaking. But it may not come from the screen lamination adhexive. Could there be some glue/plastic/stuff associated with the tension band? Of course if the tension band should be bonded to the glass and no longer is then it is not going to do its job if the CRT implodes.
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Old 1st May 2024, 3:28 pm   #10
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Default Re: Dripping CRT

The tension band doesn't need to be bonded per se. It just needs some light tension (I think it was usually heated and then shoved on the tube) and to stay in place. It's often placed and then filled in with some kind of resin to keep it in place (or rather: keep the tube in place), but I've seen tar or something very similar being used, which actually did drip a little bit...

I think the dripping gunge is most likely from the screen cover. It would have been glued with optically neutral material, which was fully transparent, filled al the gaps and had a compatible refraction index.

That said... I've been thinking.. If the tension band is constructed as an anti-implosion device, there should be no need to remove it to replace the screen protective cover. Are you sure it's in the way? Do you maybe have a few pictures of the construction?

Last edited by Maarten; 1st May 2024 at 3:34 pm.
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Old 1st May 2024, 3:49 pm   #11
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Default Re: Dripping CRT

The CRT is currently packed in a box well away from my workbench while I work on the electronic side of the terminal. When I get a chance I'll carefully unpack it again and take some photos.
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Old 1st May 2024, 3:49 pm   #12
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Default Re: Dripping CRT

Hi.

Clinton Electronics Corp. are still in business. They started in 1963 manufacturing CRTs but now specialise in CCTV equipment. https://www.clintonelectronics.com/about/

A long shot, but maybe email the company. They may have archived data on their products.

Regards,
Symon
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Old 9th May 2024, 9:46 am   #13
TonyDuell
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Default Re: Dripping CRT

Here are 5 photos of the CRT.

1 : Overall picture of the CRT face-down.

2 : Some of the leaked-out gunge collected on the CRT mounting bracket

3 : Ditto, for the middle of the CRT, showing the band

4 : Spot-welds to join the ends of the band

5 : The edge of the screen. I've pulled back what seems to be transparent plastic tape around the outside. The white stuff is the remains of the laminating adhesive.

Note the relatively large gaps between the band and the CRT glass.

My thoughts now is that it is not an implosion-protection tension band. It was bonded to the glass with some adhesive, that's what's dripping out. It holds the mounting brackets in place.

But, being stuck to the glass, could it also have some supporting function in the event of an implosion? My late father used to cover things with normal sellotape before pumping them down, even that relatively weak adhesive made a big difference.

I think the screen was laminated as an implosion protection. The adhesive is clearly failing with age.

So, where to go from here? Assuming I can get the rest of the thing working, do I need a replacement CRT to be safe?
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Old 10th May 2024, 8:56 pm   #14
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Default Re: Dripping CRT

The term integral implosion protection usually refers to the tension band, but it's not impossible that they used a combination of the tension band and screen lamination to be extra safe since the user sits closer by than by a tv set.

Unless the gunk is corrosive or severely impacts the fit of the tension band, I'd say the gunk and the tension band can be left alone.

Of course there's still the problem of the cataract. Can the laminated layer be removed intact? If not, I don't know what a suitable replacement would consist of.
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Old 10th May 2024, 10:06 pm   #15
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Default Re: Dripping CRT

Hi Tony,

If the implosion screen is delaminating from the CRT face, due to the polymer degrading, I could relay some experience that Frank (Hirschfelde) had on the I-Telex Forum.

He had, A Lorenz Lo3000 with a severe cataract, and managed to remove the implosion screen by disolving or softening the polymer, then cleaning the resulting glass sections, and assembling without the adhesive layer

https://telexforum.de/viewtopic.php?...atarakt#p36300

Hope this helps
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Old 10th May 2024, 11:18 pm   #16
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Default Re: Dripping CRT

Disclaimer: For entertainment purposes only, I'm not encouraging anyone to do this stuff, but on the other hand I'm surprised no one has invoked Shango's many videos on the subject.
Besides, we don't have the Californian sun.

https://www.youtube.com/watch?v=32_qMSWEdjc

https://www.youtube.com/watch?v=IuX2UkrKxeo
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Old 12th May 2024, 4:39 pm   #17
factory
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Default Re: Dripping CRT

If I remember correctly he has shown three different methods of dealing with the TV CRT cataracts, one seems to be heat, another water and the last was a hot wire, the method he used depended on the type of bonding material. Full body protection & face protection is a must for anyone that does decide to attempt removal.
Also don't think he's got much sun at the moment either.

I've been taking a interest in these methods for some time, as the oscilloscope CRTs HP used in the 1960s also suffer from the bonding material degrading, both round and rectangular CRTs, this picture shows a bit of the cataract in a HP 180 series CRT.
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If I ever decide to attempt removal & refitting, I have a dead HP 175A CRT (with no vacuum) to play with.

David
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Old 13th May 2024, 6:04 pm   #18
TonyDuell
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Default Re: Dripping CRT

Quote:
Originally Posted by factory View Post
If I remember correctly he has shown three different methods of dealing with the TV CRT cataracts, one seems to be heat, another water and the last was a hot wire, the method he used depended on the type of bonding material. Full body protection & face protection is a must for anyone that does decide to attempt removal.
Also don't think he's got much sun at the moment either.
I have never been able to learn things from videos, I much prefer books/manuals/text. And to be honest I am not at all happy about trying to remove the outer layer and/or the tension band from this CRT and putting them back. Even if I managed to do it, I don't think I'd trust that I'd done it well enough to provide satisfactory implosion protection

But anyway, when thinking about the dangers posed by a CRT breakage, the attached section, taken from the Whitechapel MG1 computer technical manual, always amuses me ...
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