CRT implosion

[ionburn]

Originally Posted by kalee20

And yes, I've broken TV tubes in my teens, favourite method was throw a hammer at the screen from behind a door and then duck back while in flight.

That reminds me of when I was a child. I found a .303 bullet with its case in the garden and went into the farmyard at the bottom of the garden and threw it toward some stones several times while ducking back behind a wall. The casing split after a few times as it was rotted so I removed the bullet. No bang, which was probably good luck, but I still have the bullet in my collection. The things we do

[FERNSEH]

HKS wrote: "What a carry on, all over an oversize electric light bulb. I can't imagine that cloth bag doing much if it went pop! I thought all you guys up North were macho men."
Hi John,
how about this one then? This is the tube in the Cossor 137T. Now that the set needs servicing I've got to work out how to remove the tube in a safe manner.
The CRT is 14 inches diameter but the mask reduces the screen area to that of a 13" tube. The reason for doing that is to present a flat as possible picture viewing area.

DFWB.

[kalee20]

Originally Posted by FERNSEH

how about this one then? This is the tube in the Cossor 137T.

Now that - not only the tube, but the whole assembly - is a thing of beauty. Electrostatic deflection I presume?

[peter_scott]

Originally Posted by FERNSEH

Now that the set needs servicing I've got to work out how to remove the tube in a safe manner.
DFWB.

Just call in an expert.

Peter

[Lloyd 1985]

I see she has all the proper safety gear to handle that tube!

[FERNSEH]

Originally Posted by Lloyd 1985

I see she has all the proper safety gear to handle that tube!

She must have been one the works inspectors. It's most likely she is checking the glass bulb for manufacturing flaws. You can't be too careful with these things.

DFWB.

[FERNSEH]

Originally Posted by kalee20

Now that - not only the tube, but the whole assembly - is a thing of beauty. Electrostatic deflection I presume?

The CRT is indeed an electrostatic and deflection type. The Cossor 137T design was adopted by Dumont in the US and became the model 180. The CRT was modified with a 6.3 volt heater and designated as 14AP4.

http://www.earlytelevision.org/dumont_180.html

DFWB.

[turretslug]

It is absolutely a thing of beauty- I like things that combine science and art and making that lovely bulb must surely have been a highly skilled and refined art.

Possibly a dumb question- the phosphor appears to be a highly-separated "island", well away from that impressively even metallising deposit in Fernseh's #82 post- how does the charge building up on the phosphor "get back" circuit-wise to stop it just sitting up at many kV and repelling/distorting the incoming beam? Or is the beam current sufficiently minimal that screen charge can creep back across the glass surface to earth without accumulation? Maybe I'm not seeing something very basic here!

[Peter.N.]

I'm sure any of you who are near my age will remember the VCR97 ex MOD radar tube, for me they were my first introduction to a CRT and the basis of many a home built TV. I had to learn about magnetically deflected and focused tubes.

Peter

[FERNSEH]

From #72

Originally Posted by FERNSEH

The rather intimidating 15" CRT in the Baird T23. The tube has to come out so that the base connections can be examined.

A bad soldered joint to the cathode connection was found to be cause of the intermittent picture fault.
The bad connection has been put right and the CRT duly reinstalled into the cabinet.
All ready to test the units from the Baird T5? Well it would be so if I remembered to fit the line scanning coils to the CRT neck.

So the CRT must come out again.

DFWB..

[space_charged]

Originally Posted by TonyDuell

My late father, who worked on high vacuum systems in his day job as a research chemist, was very worried about implosions.

I too run a high vacuum system (see my profile for photos). The chamber is a 12" diameter 14" high borosilicate glass bell jar. The approximate weight sitting on it when its evacuated works out to be two tons. That is similar to a TV CRT and does represent a lot of potential energy. If a glass vacuum chamber or CRT implodes, it could send large super sharp fragments in all directions. It is potentially life threatening/changing without a doubt.

My vacuum bell jar is protected by an acrylic shield for that reason. I do not now operate it without that. I guess the risk from a CRT if properly handled is not that great. Modern tubes are safer and have to survive tests such as being struck in the face plate quite hard. I'd be increasingly nervous the older the CRT. This is for two reasons, glass can get brittle with age and the earlier CRTs weren't so robust.

When I first pumped my glass bell jar, I hadn't got the safety shield so I wore a motorcycle helmet an my Crowtree leathers! I also started the pump and backed off out the room. If a vacuum bell jar is going to implode during pumpdown is a high risk time.

[FERNSEH]

turretslug wrote: "Possibly a dumb question- the phosphor appears to be a highly-separated "island", well away from that impressively even metallising deposit in Fernseh's #82 post- how does the charge building up on the phosphor "get back" circuit-wise to stop it just sitting up at many kV and repelling/distorting the incoming beam? Or is the beam current sufficiently minimal that screen charge can creep back across the glass surface to earth without accumulation? Maybe I'm not seeing something very basic here!"

That's a good question. Perhaps much of the energy imparted by the electron beam impinging on the phosphor is dissipated as light. Makes sense?http://scienceline.ucsb.edu/getkey.php?key=512

Ref to #90: "So the CRT must come out again"
Today, the CRT in the Baird T23 was taken out, the line scanning coils fitted on the neck and then reinstalled on the metal cradle.

DFWB.

[Vintage Engr]

I worked in the industry, both domestic & broadcast, for nearly 60 years.
In all that time, I only had one 9" CRT from a Cossor spontaneously implode.

Luckily I was out of the room at the time! It made an incredible mess. There was a perfect circle cut out of the linoleum on the floor where it had been standing, face down.The rest of the room was covered in 'glass shrapnel', with shards embedded into the plaster in the wall.

I was glad not to have been there. There were all sorts of stories,in the early 60's, mostly fictional, of electron-guns hurtling through the front of the TV towards an un-suspecting viewer! I never saw it happen, or heard it from a reliable source, but it kept the customers from poking around in the back of the set.

As others have mentioned, in the early 60's there were various methods of protection employed. The Mullard Panorama' tube used a rim-band, whilst some manufacturers had a 'Twin-panel' version. There was also a Corneal Hood, which was a thin membrane of transparent plastics material (with 'pimples' on the inside) which had to be carefully stretched over the front of the CRT, using a hair-dry to keep the plastic supple & exclude the air. All good fun..

I did once trip over whilst carrying a 23" non-protected CRT, luckily, I had both hands/arms under the face-plate, so all I did was to graze my hands on the concrete workshop floor.

The reason for the trip, you couldn't make this up, - a Tarantula, or similar spider, a huge beast, emerged from behind a pile of CRT boxes! It frightened the life out of me at the time. It wasn't unusual to find such creatures, + mice etc in our workshop, as it was located in a busy East-end-of London fruit & veg market.

The only time I was involved in deliberately destroying old CRT's was when we used to have clear-out of a large amount of dud tubes. These were stored in a room above the T.V. show-room, and we (irresponsibly) used to throw them out of the window, into a large skip in the yard below...
Some imploded spectacularly, but most just went to air with just a minor 'whoosh'.

On a final note, when I worked for a supplier of Broadcast T.V. equipment, we had a customer who purchase a Sony 27" Trinitron monitor, for use in a T.V. advert, where they wanted just a picture showing, i.e. no tube surround, or cabinet mask.

So, they used an angle-grinder to cut off the rim-band & mounting 'ears', then Gaffer-taped the CRT to the monitor chassis. They then made the advert, & sent the complete chassis & cabinet back to me, - in a London black cab, and asked if I could put the monitor back together again!!
If only the cab-driver had known he was driving with a potential bomb on the back seat.

I remember talking to the chap who used the angle-grinder on the rim-band, after he's returned the monitor to me. He had no idea how dangerous it had been...

A little knowledge etc.

David.

[Maarten]

Sony tubes might be a bit safer in that regard than average, since they use a surplus of glass and a heavy internal steel support construction (that might or might not be keeping some pressure on the glass, I'm not sure). Still, a very bad idea.

[Vectamart]

As a 15 year-old, My friend and I used to take duff tubes to a local disused quarry where we used to throw concrete blocks at the face glass until they imploded from behind a rock at a safe distance.

[Vectamart]

A chap who once worked for me told me about when he was service manager at Telebank in Worcester. Someone accidentally knocked a colour CRT off a high shelf, whereupon it imploded sending large chunks of glass in all directions. Unfortinately, one shard embedded itself in the leg of one of the engineers, causing a serious injury.

[Heatercathodeshort]

Originally Posted by Vintage Engr

There was also a Corneal Hood, which was a thin membrane of transparent plastics material (with 'pimples' on the inside) which had to be carefully stretched over the front of the CRT, using a hair-dry to keep the plastic supple & exclude the air. All good fun..David.

Sounds exciting. Are you sure you are describing a tube protection device?
John.

[McMurdo]

One of your USA youtube vintage tv repairers had a colour (color?) tv tube implode while he was trying to remove the bonded safety glass to repair one of their 'cataract' problems. It's not really applicable to tubes we're likely to see in the UK but the damage was well documented and filmed. I can't remember the guys name but he's a friend of Shango066 which is how I found the clip.

[TonyDuell]

The 'cataract' problem (decay of the bonding layer between the 2 glass layers on the screen of the CRT) most certainly is a problem for people like me who restore vintage computers, many of them originating from the USA. But I've seen it in UK-built computers too (I guess using American CRTs).

I have always been horrified by the people who remove the outer glass and leave it off. I am sure the 2 glass sheets and the bonding act like a laminated car windscreen and provide some implosion protection (even if the rimband is the major item here). And I have never felt happy with some of the methods suggested for removing it. Looks like I was right to be a bit wary...

[Graham G3ZVT]

Originally Posted by Vintage Engr

There was also a Corneal Hood, which was a thin membrane of transparent plastics material (with 'pimples' on the inside) which had to be carefully stretched over the front of the CRT, using a hair-dry to keep the plastic supple & exclude the air. All good fun..

As A "Junior Improver" (tea-boy) at Granada Rentals I was taught to use a 2kW fan heater to soften the "skin", and a hammer to position the mounting lugs and steel band. You did this standing up because your bar-stool had its cushion removed to act as a precarious jig to hold the tube.
This was 1971. Goggles were available in the workshop, but I don't remember their use being enforced. Full face masks were not provided, I'm not sure about gloves.