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Old 7th Sep 2005, 1:38 pm   #1
DoctorWho
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Default CRT Final Anode Repair Tip

I had a problem with the final anode coming adrift on an old Emiscope CRT that I have. I found a solution which seems to work very well. Obviously with the very high voltages at the final anode on a CRT extreme care has to be taken, but I just thought I would share this incase someone else may find it useful in the future.

The CRT concerned was an old Emiscope tube, and the final anode cap had come off and there was no visible piece of wire to connect it back to.

I removed the CRT and files the glass away very gently, but the connector going through the CRT glass looked more like carbon than regular wire, it was powdery.

I thoroughly cleaned the whole area with a file - this obviously had to be done very gently and goggles were worn. Then I cleaned the inside of the final anode cap and filed it to give a good clean surface. Both the glass of the CRT and the inside of the final anode cap were then cleaned with white spirit and left to dry.

I went to Maplins website and found that they sell something called "Conductive Epoxy" which is quite expensive, but you don't need a lot. I ordered some and it duly arrived in 2 syringes labelled "Part A" and "Part B". It gives precise mixing directions and it has a metalic look.

I carefully applied it all over the glass pip where the final anode connection is, working it well in to avoid air bubbles, I then filled the inside of the final anode cap and carefuly pressed it in to place. The whole area was filled and the excess was easily wiped away.

The whole thing then had to be left for 4 hours, and it was a total success. The bond is as hard as rock and it's perectly conductive. The tube displays a very good picture.

I'm no professional, but this does seem to have solved what may otherwise have been a hopeless situation. I hope that it may be of use to others. I've been very pleased with the results, it has rejuvinated what would otherwise have been a useless CRT. I suspect the same method could be used with valve top caps if the usual soldering on to the piece of wire was not successful.

Peter.
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Old 8th Sep 2005, 11:42 am   #2
Nickthedentist
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Default Re: CRT Final Anode Repair Tip

Quote:
Originally Posted by Richard_Newman
You sound very brave!! I've been in the trade for 40 years and there is NO WAY I would file the glass of a CRT!!
If the worst were to happen and the vacuum be lost, I wonder whether the glass would implode catastrophically, or, whether there would be nothing more than a gradual ingress of air over a period of several seconds with a characteristic hiss - just like if you break off the glass pip under the plastic cover between the pins on a modern colour tube (as some repairers apparently do prior to disposal of a scrap set).

Any comments?

Either way, I'd wear a welding-type face mask, thick builders' gloves and my winter overcoat!
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Old 8th Sep 2005, 1:13 pm   #3
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Default Re: CRT Final Anode Repair Tip

Hi Nick,
If a stress fracture occured on the BOWL of the CRT this would almost certainly lead to catastrophic collapse of the tube. The neck can be broken off usually without a problem but the bowl is another story. If a tube should implode, the sound is incredible and the force will send fine shards of glass everywhere including your hands, face, eyes and anything that is around. I have seen bits of tube stuck in ceilings and light fittings smashed with the flying misiles. That was in my days working with John Brown [Central Tubes] Remember also as I have mentioned in previous threads that glass is basically a LIQUID. It becomes very hard and brittle with age and I have no doubt that these old tubes are under more stress now than they were 50 years ago. If you need proof of this try cutting a piece of 50 year old glass....!
TAKE GREAT CARE. Regards. JOHN.
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Old 8th Sep 2005, 1:25 pm   #4
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Default Re: CRT Final Anode Repair Tip

Nick - thanks for your thoughts. I have broken the pip off of the end of a CRT neck as you mention, but I've never smaded one in any other manner. I guess it's possible that what I have said above could result in gradual loss of vacuum, especially if the glass is not so well bonded to the wire connected to the fina,l anode, but after John,s comments I think I would be somewhat nervous of doing it again without perhaps using a sack as John suggests.


John - You obviously have the experience in this field, to be honest I was quite shocked when i read of what has haoppened with imploding CRT's in the past. Hopefully I'll never be confronted with this issue again, but if I am I think I'll just clean up the glass with white spirit and use the conductive epoxy without any filing.

How about soldering? Sometimes if the final anode comes adrift you can solder a piece of wire on to the remaining wire and then fix the anode cap back on. Is the heat of the soldering iron likely to cause a high implosion risk at the final anode?

I'm glad this repair is over and done with, I'm not sure I'd have the courage to do it now.

Peter.
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Old 8th Sep 2005, 7:14 pm   #5
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Default Re: CRT Final Anode Repair Tip

Hello again bomb squad,
I don't know what to do with the lot of you..........
If a CRT anode connector has become detached from the bulb LEAVING a short length of stiff wire I would suggest the following. It is a method I used many years ago when this used to happen to the COSSOR 108K and the Mazda triode range. Clean the inside of the metal cap clearing away old fixative and solder. This will leave a small hole in the cap where the wire passes through. Mix a small quantity of ARALDITE APOXY [Two tubes] and smear some around the rim of the metal connector. Clean the short length of wire sticking out of the crt 'PIP' with some fine abrasive paper and place the cap in position so that the wire 'fills the tiny hole'. DO NOT USE SUPERGLUE..THIS WILL IMPLODE THE TUBE WITH TEMPERATURE CHANGE.
Leave overnight and when the glue has 'gone off' apply a soldering iron and some good solder to the cap and form a neat but slightly domed pool to solder the wire to the cap. This should take no more than 5 secs if done with a hot iron. Job complete. If your nervous I suggest you place the tube in an old fashioned hessian sack as suggested in my earlier thread. This will contain the tube should it decide its had enough.. Peters suggestion of using conductive resin is first class but would suggest cleaning the 'pip' to ensure contact if very little or nothing remains of the wire. The imploding tube film was from TOMOROWS WORLD. The tube was a AW 53-88 21" and it was to demonstate what happened when a conventional tube was smashed. The RIMBAND tube was introduced in 1965 and it was that development that led to the film. Regards JOHN.
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