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Old 2nd Nov 2017, 7:39 pm   #1
Top Cap
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Default How CRT re-gun was done

A fascinating insight into how re-gunning was done, I had no idea it was such a work of art. Scotty the Master. Shame that the facility no longer exists as I am sure there are members who have a CRT they would love to have re-gunned. Skip the first couple of minutes if you like then sit back for nearly 2 hours to be enthralled.
I can never get these videos to start from the beginning after copying the URL.
https://www.youtube.com/watch?v=W3G7b-DcOO4&t=3069
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Old 2nd Nov 2017, 8:09 pm   #2
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Default Re: How CRT re-gun was done

Link from the beginning.

https://youtu.be/W3G7b-DcOO4

The &t=3069 in te url is the number of seconds into the video i.e 51 mins plus a few seconds.
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Old 2nd Nov 2017, 8:14 pm   #3
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Default Re: How CRT re-gun was done

I get "this video is not available".
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Old 2nd Nov 2017, 8:23 pm   #4
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Default Re: How CRT re-gun was done

I get the same message on my iPad, OK on the computer, I thought it may be that it requires Flash but I don't have Flash on my computer and it works. Not tried to find out why the iPad doesn't work.
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Old 3rd Nov 2017, 1:22 am   #5
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Default Re: How CRT re-gun was done

Lots of parts of that facility exist, as do parts of RACS France,
at the Early Television Foundation.

The problem is time, logistics, and practice.
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Old 3rd Nov 2017, 9:56 am   #6
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Default Re: How CRT re-gun was done

The CRT re-gun is one big set of problems. It is particularly difficult for old Pyrex electrostatic tubes, though it has been done in the past using grades of glass with different expansion coefficients.

The problem gets amplified if the old CRT's phosphor is damaged, often it is either with ion burns or other degradation. Often when a non aluminised CRT is let down, even very slowly by making a very small hole in the exhaust tip, the high velocity gas molecules can take the central screen phosphor off.

Some years ago I re-screened a 12LP4 television CRT in my workshop with the method of letting the P4 phosphor settle out of suspension. I had about 10 goes at it. The trick was to decant it slowly enough to avoid ripples. I couldn't get a new gun so I fitted a new heater cathode assembly to the old gun. With the help of a (now non existent CRT rebuilder in NZ) we had a go at rebuilding the tube, it was unsuccessful. In the end it got rebuilt by Thomas Electronics in the USA. I still have it, they aluminised it, turning it into a 12KP4.

It's interesting that Thomas Tube's website in the USA says they still rebuild CRT's, I sent them an email to see if it was still true, but I got no reply.

It is good that Steve McVoy is making an effort in this area at the ETF.
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Old 3rd Nov 2017, 9:15 pm   #7
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Default Re: How CRT re-gun was done

Many years ago I used to work for Mullard's factory in Lancashire. Iworked on the colour tube repair section, it was a very interesting if somewhat dodgy job .......
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Old 3rd Nov 2017, 9:40 pm   #8
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Default Re: How CRT re-gun was done

If these were the rebuilt tubes I used to get from the Heywood depot as replacements for those under the 4 year guarantee they were excellent replacements.
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Old 7th Nov 2017, 5:05 pm   #9
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Default Re: How CRT re-gun was done

Quote:
Originally Posted by Argus25 View Post
Often when a non aluminised CRT is let down, even very slowly by making a very small hole in the exhaust tip, the high velocity gas molecules can take the central screen phosphor off.
Are the tubes typically 'let down' at atmospheric pressure? Would it be posisble to do this inside a pressurised compartment which is then slowly de-pressurised over a longer period with the tube inside?

I know very little about re-gunning but it's a very interesting process.

I'm also curious as to how 60 year old glass responds when the neck is cut off and replaced.

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Old 7th Nov 2017, 6:28 pm   #10
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Default Re: How CRT re-gun was done

In the early 60's when I was working for Rediffusion in East London, there was a re-gun company called Mildmay Tubes.

I know this may sound crazy in todays Health & Safety concious world, but they used to cut the necks off (before colour, & these were mostly 90deg CRT's) by using a 12v car battery and a piece of nichrome wire wrapped around the neck at a suitable point!

There was a young lad doing this he was probably about age 15, next to him was an older guy who would clip the youngster around the ear if he failed to make a clean break on the neck.

The place was fairly Heath-Robinson, and some of the asbestos-clad ovens had holes blown in the side, where a CRT had previously imploded.
To seal the new short neck to the flare again there was a fascinating rotary gas burner inside the oven which gradually brought the glass up to the correct temperature.

Firing the getter was done by a very crude RF coil, held to the neck at the appropriate point. This operated by a young lady & I have it on good authority thet there had been problems with some of the girls having RF burns on their thighs! This was found to be due to them using suspender belts with metal clips. (ouch!) They soon changed to nylon types once the cause was found.

All good & dangerous fun. I wish there was someone still doing re-guns, but even if someone decided to try & make a go of it I doubt it would make a profit in todays high- labour cost market.

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Old 8th Nov 2017, 1:43 pm   #11
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Default Re: How CRT re-gun was done

Quote:
Originally Posted by Voxophone View Post
Are the tubes typically 'let down' at atmospheric pressure? Would it be posisble to do this inside a pressurised compartment which is then slowly de-pressurised over a longer period with the tube inside?
Yes that would work, but the re-gun people I saw doing it just made a small hole in the exhaust tip and let air in, that didn't seem to affect the more modern aluminized tubes, but it did for non aluminized ones. The adhesion of the phosphor to the faceplate may have been poorer in the earlier tubes than a more modern tube. Certainly if a modern tube has its neck snapped off, usually the inrush of air will shake the phosphor off the central screen area.
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Old 8th Nov 2017, 1:59 pm   #12
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Default Re: How CRT re-gun was done

Letting down is done by inducing a crack preferably in the pip, yes, with a hot wire, as small as possible. It may take an hour or more to get to air, to save the phosphor.
That description of a regun workshop sounds terribly like the R&D line I worked on at Ferranti and that was making new tubes!
Unknowingly we took terrible risks with tubes, asbestos ovens, RF heaters. Glass cuts were common, acid burns from cleaning glass with hydrofluoric too.
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Old 11th Nov 2017, 3:47 pm   #13
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Default Re: How CRT re-gun was done

Hydroflouric acid, now that brings back even more memories. There was an article in one of the '60s electronics magazines about missing type numbers on valves & crt's.
The idea was that you worked out what the valve was, either by recognising the electrode structure, or from the base code, & then etched the number into the envelope. Prior to the actual etching, one was supposed to melt candle wax on to the surface of the valve/tube, & then scratch the number through the wax resist, & gently brush the acid into the 'stencil'

They did warn you to store the acid (which you purchased from your local chemist) in a polyethelene container. That was the H&S bit!

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Old 11th Nov 2017, 6:46 pm   #14
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Default Re: How CRT re-gun was done

HF is very dangerous stuff, I lost all my finger nails with it. If it gets down to the bone, serious trouble, amputations to stop it.
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Old 12th Nov 2017, 10:05 pm   #15
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Default Re: How CRT re-gun was done

The mention of hydroflouric acid immediately (as was intended) brings to mind a photograph which was prominently on display in the electronic materials laboratory during my university days (late 60's). It was of the remains of a forearm and hand of a person who had been working with hydroflouric acid and wearing rubber gloves for protection. The trouble was that some acid got into the rubber glove. The photograph instilled in us the greatest respect for the chemical - and still does!
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Old 13th Nov 2017, 10:30 am   #16
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Default Re: How CRT re-gun was done

OT, but fluoropolymers, e.g. Viton as widely used in O-rings, gaskets and seals, can decompose under excess heat to produce hydrofluoric acid, so beware of handling items that may have come from e.g. fire-damaged cars. Washing down with plenty of water would at least be prudent- as mentioned, even a smear of HF could produce severe burn scarring, or worse.
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Old 13th Nov 2017, 11:17 am   #17
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Default Re: How CRT re-gun was done

The same goes for some of the gases commonly used in refrigerators, freeze sprays and air dusters. Also for some brake cleaner fluids. Especially if the can says non-flammable, don't spray freeze spray or air duster into an open flame.
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Old 13th Nov 2017, 1:30 pm   #18
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Default Re: How CRT re-gun was done

Quote:
Originally Posted by P.Pilcher View Post
The mention of hydroflouric acid immediately (as was intended) brings to mind a photograph which was prominently on display in the electronic materials laboratory during my university days (late 60's). It was of the remains of a forearm and hand of a person who had been working with hydroflouric acid and wearing rubber gloves for protection. The trouble was that some acid got into the rubber glove. The photograph instilled in us the greatest respect for the chemical - and still does!
I haven't seen that photo but I don't really think that I would want to. The ones in "Black Monday" were bad enough. The glove story illustrates perfectly why I don't like working with gloves, especially the disposable ones. They very easily get damaged and fill up with precisely the liquid you are trying to keep out. I prefer to take my chances without them. I sometimes handle nasty chemicals such as battery acid (H2SO4), HCl and NaOH but they're not as bad as all that. Keeping close to a tap or bucket of water to wash off any spills has saved me from any ill effects so far.
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