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CRT Broken Wire a Suggested Solution

 
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CRT Broken Wire a Suggested Solution

Post by crustytv » Sun Jul 24, 2011 8:48 am

Hi all,

I thought I would share this as others who have a CRT with a similar problem and may benefit from giving it a try.

I had a 1950's 14" 90 degree Mullard CRT given to me FOC by a kind member of another forum. What type I do not have a clue as the sticker is gone but that another mystery to be solved later.

The main problem was the cathode lead-out wire had broken off right at the base, there was nothing poking up at all it was a flush break to the glass base.

As is often the case a plan was hatched in my sleep, yep dreams are great playgrounds for solutions (see pic 2). I contacted Trevor and ran the idea past him to see if it was madness to even attempt. Trevor thought it was worth a go nothing ventured nothing gained as such.

I placed the CRT in it's tightly packed small box and I wrapped a blanket around the whole thing just in case the worst happened.

As I said the wire had broken flush to the glass surface, so under the mag lamp I worked away all around where the wire tip could be seen with my Dremel. Using the finest engraver I removed glass creating a litle cup like an oil cup on a clock plate. Eventually a little bit of the wire became exposed. I cleaned the top of the wire so it would get a good bond.

I then applied RS conductive paint to the cup, theory being the exposed wire surface would bond and the cup would form the larger area conductive area.

When this had dried I found some thin wire, put a kink in one end so it would sit in the cup. I then taped the wire in place and coated the wire and the cup again in conductive paint. I then used felxible epoxy resin to cover the wire and cup to ensure a secure fix.

Once dried Success, the cathode lead out had made good contact and is conducting. My CRT tester could see the cathode. Bad news was the tube was low emission. All was not lost so I left the CRT connected and set the tester on the gentle ageing process to see what would happen. After a while the emission started to rise, eventually settling to 100% emission.

I'm one happy bunny a 1950's CRT saved from the tip. Now I just got to figure out what Mullard tube it is MWxx-xx and the put in the stores with the others.

Hope someone finds this of use, but I except no responsibilty when you go diging at the base should it go pop!

Chris


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Post by neil29 » Wed Aug 10, 2011 2:14 pm

Ive had a few tubes with this problem. but did not fancy the idea of filing away at it until i got enough wire to solder to. as i was constantly worrying whether the tube would go pop. but an excellent result and as you say another tube saved..cheers neil.

 
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Re: CRT Broken Wire a Suggested Solution

Post by Haerial » Fri Aug 23, 2013 10:27 pm

What an excellent idea. one to remember for the future.

Richard.

 
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Re: CRT Broken Wire a Suggested Solution

Post by Boater Sam » Sun Dec 14, 2014 8:44 am

Had a similar problem many years ago on a one off R&D tube specially produced for a government project at vast expense.
Before all the testing could be completed an accident in the dark room removed 2 of the base pins flush with the glass.
Time was pressing and to recover the gun and faceplate and cone and rebuild and re-pump would take 2 days.
We came up with a solution by removing the pin connectors from the base holes on the affected pins and fitting small pointed screws into the base. After fitting the base we secured it with 2 jubilee clips and a split plastic sleeve to the neck.
By screwing the screws down onto the broken pin ends we got good connections and were able to complete the analysis, saving time and the governments cash!
May even work long term though grinding the glass away would be a more elegant solution.
As an aside, we used to joint new bases onto some tubes which needed alternative guns without changing phosphors for research on occasions with pyroceramic cement, but it was fraught with problems.

Boater Sam

 
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Re: CRT Broken Wire a Suggested Solution

Post by Terrykc » Sun Dec 14, 2014 1:19 pm

CrustyTV wrote:... Now I just got to figure out what Mullard tube it is MWxx-xx and the put in the stores with the others ...

Chris, as you have suggested yourself, it is almost certainly an MW36-24 but there is also the possibility that it is a later MW36-44.

As far as I know, the only difference between them is that the later tube had a aluminized screen to reflect the 50% of the light that would otherwise be wasted illuminating the inside of the CRT back though the faceplate. This gave a considerable improvement in contrast and light output but the other characteristics are unchanged.


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