URGENT-Get Your CRT Tubes Rebuilt Soon!

[TubeType]

Dear Jhalphen,
Thank you for acting as our intermediary with the folks at RACS. I find the Q&A about metal-glass monochrome CRTs very interesting.
Here are my questions for the engineers at RACS.

Can they successfully rebuild a 15GP22 CRT?
If yes, what is their price?

Kindest regards,

Terry Cheek

[John Marinello]

jhalphen,

Thank-you very much for your speedy replies!
RACS is doing some fine work, lets hope they will be around
for a long time!

-John

[jhalphen]

Hi! to All,

Follow-up answers from RACS on various inquiries:

Photo of CRT during aluminization operation:
The tube was indeed vertically mounted, screen at the top.

For John/Jeyurkon: P4 phosphors with/without Cadmium.
RACS comments that "you have one hell of an eyesight" to perceive such minute variations in P4 White qualities.
Just curious (me) what is the nature of your vision deficiency, Daltonism for instance?

To come back to the topic:
- Sure we still have Cadmium phosphors, for instance Yellow phosphors used in monochrome computer monitors are Cadmium based.
As for vintage P4 Cadmium phosphors, NOS inventories aren't kept for no good reason...

For Vintagecollect:
RACS confirms they routinely rebuild video projector CRTs.
Please supply data on your specific Red tube:
Tube type, maker, screen size, EHT (if known), base type...

For Terry Cheek:
Ah! the 15G, the Holy Grail of CRTs!

RACS is not ready yet, although would like to do this in the future. The ETF (Thanks! Steve) supplied a 15G gun assy from a broken tube for preliminary assesment. To go any further, RACS will need a complete dud tube, still under vacuum, if possible, and maybe more than one.

I had long discussions with RACS about the 15G's major plague, i.e. the leaking glass/metal junction. They have good experience in this domain, having encountered the same problem on other tubes they were asked to rebuild. We didn't go in depth about the details of resealing, but i understood that in general terms Frit glass is applied around the rim of the leaky glass/metal junction then hardened by baking. Afterwards, the CRT is evacuated, etc.

My friend John Folsom Jr is doing pioneering work in this domain along with Pete Deksnis and Bob Galanter. One tough questions remains on both sides of the Atlantic: as no CRT rebuilder can make a new tricolor screen, are the 15G phosphors still usable on a tube which has gone to air, usually for decades.

just FYI, a new gun, any gun, on which a new cathode has been installed and activated, is instantly destroyed by contact with air, even if brand new and never used. Are phosphors as vulnerable? no one knows until a rebuild is attempted.

To finish on a more positive note, RACS is also interested in rebuilding "easier" tubes than the 15G such as 21xxP22, the 21" roundies which ruled supreme for a decade between 1955-1965. Providing the tubes are still under vacuum, no major theoretical stumbling block is anticipated as RACS has the expertise to rebuild B&W and Color electrons guns in-house

Best Regards

jhalphen
Paris/France

[electroking]

Dear jhalpern,

Please note that the term 'daltonism' is not usually understood in English.
They just call it 'color blindness'. One of those instances where our French
language is more concise than English...

[jeyurkon]

Dear jhalpern,

I'm PM you about this since it's way off topic. But interesting to me...

John

[andy]

---

[jeyurkon]

At least some recent CRT color phosphors are applied with a chromated hydroxycellulose. That's a water based photosensitive material. I would find it difficult to believe that any phosphor that stands up to water would be bothered by exposure to air. Once baked on moisture shouldn't bother them much either.

Prolonged exposure to moist air could damage the aluminization. Aluminum is a fairly reactive metal when not protected by its oxide layer. Particles of carbon, or possibly the phosphor, could cause corrosion in moist air.

So, I think you're right to worry about air, but the phosphors themselves should be stable. IMHO.

I use the red CRT phosphor that is used in color CRTs to make beam viewers. The phosphor is applied as a water solution and we bake them in air with no ill effects. However, we don't aluminize them.

I think the statement that "no one knows until a rebuild is attempted" is still correct.

John

[TubeType]

Originally Posted by electroking

Dear jhalpern,

Please note that the term 'daltonism' is not usually understood in English.
They just call it 'color blindness'. One of those instances where our French
language is more concise than English...

The term "Daltonism" is derived from the name of the English chemist and physicist, John Dalton. Dalton was born in 1766, in Cumberland, England.

John Dalton described his and his brother's affliction of colorblindness with defective perception of red and green in the first scientific paper he published. It was entitled Extraordinary facts relating to the vision of colors, with observation. It is the first recognized account of red-green colorblindness.

Dalton's reputation largely rests upon his law of partial pressures and his Atomic Theory.

Terry Cheek

[jhalphen]

Hi Jeyurkon, John,

you wrote:
"I use the red CRT phosphor that is used in color CRTs to make beam viewers. The phosphor is applied as a water solution and we bake them in air with no ill effects. However, we don't aluminize them."

I'm interested! what sort of beam viewers?

Let me guess: IR laser beams? - Power?

Are you using Y2O2S:Eu, the standard P-22 Red phosphor?

A few years ago, Radio-Shack sold an IR viewer plastic strip to test remote controls. Works quite well in the dark, a few inches away.

Best Regards

jhalphen
Paris/France

[jeyurkon]

Yes, it's Nichia's NP-1154 Y2O2S:Eu Red crt phosphor.

I work at the National Superconducting Cyclotron Lab. The viewers are used to image the accelerated ion beams at various stations along the beam line.

The plastic IR strips are interesting. Another way that I found accidentally uses a CCD camcorder. I was using my Sony Handicam and was surprised to see how bright the IR led in my TV remote looked when I happened to catch it in use.

John

[jeyurkon]

In case I haven't already convinced everyone that I don't live in the real world these ideas probably will fix that.

It seems to me that metal ring that causes leaks in the 15GP22 actually might make it one of the easier color CRTs to attempt to re-phosphor. No doubt someone has probably already thought of this and why it won't work, but since I'm a newbie I want to bounce these ideas off of the forum.

Assuming that Bill Gates wanted a 15GP22 re-screened and said that money is no object, the procedure would go something like this:

Bring the CRT up to air, or verify that it is up to air.

Remove the weld on the metal ring. Machining or abrasive techniques would be a bit risky so the safest way would be to EDM the weld. We don't care about the electrolyte getting into the CRT since we're rebuilding it.

After separating the bell from the faceplate remove the decorative mask, phosphor-dot-plate and shadow mask.

Remove the gun from the bell. Clean the faceplate and bell removing all of the dag. Now would be the time to repair any problems with the glass-frit.

Clean the phosphor-dot-plate removing all of the phosphor.

Now we need some fixturing to accomplish the following. We also need some supplies and decide what type of phosphors to use. I had to purchase some CRT Red Phosphor for work. It was Nichia NP-1154 Y2O2S:Eu. The minimum was 1kg at a cost of $1.5K. You might want Phophors to match the original emission spectra though.

The first phosphor is mixed with a photosensitive polymer and appropriate binding agent. It is placed onto the phosphor dot-screen and spun to evenly distribute. After drying, the shadow-mask is assembled with screen. A UV point light source is positioned in the same position as the appropriate gun for the particular phosphor and the polymer is exposed. This hardens it. The screen is then washed and only the polymer and phosphor that was exposed remains. The original method involved a separate silk screen exposure but this method is more precise.

The screen is then baked. The process is repeated for the remaining two phosphors.

At this point you might want to apply a black coating to surround all the dots, but after getting this far I don't think it's worth the risk.

Now a lacquer is applied. Then the dot-screen is placed in an evaporator and a layer of aluminum is evaporated on to it. I would bake the screen again, probably in vacuum or inert gas to remove the lacquer at this stage. It would be easier to fix now if there is a problem rather than after the crt has been reassembled.

The decorative mask, dot-screen and shadow mask are now assembled with the faceplate.

In the meantime the bell has had aquadag reapplied to the inside.

The bell and faceplate are reassembled in the proper orientation. Then the metal rings are TIG welded again. This is a critical operation but can be done by hand by an experience welder. If it's done improperly the frit-glass may crack and leak.

I would then helium leak test the assembly and repair any leaks. A coating of solder-glass or frit glass painted on to the glass metal transitions would be a safety measure and then fused at the appropriate time.

The new or rebuilt gun would be added now and the CRT processed following normal re-gunning procedures.

Enough of my crazy ideas. But they're here for you to shoot holes in them.

I was amazed at how much information is available on the web for the 15GP22

John

[vintagecollect]

Quest International Inc.,, 65 Parker, Irvine, CA 92618

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[jhalphen]

Hello to All,

Jeyurkon, i love your project!

I offer to scan in the IRE's 1951 "Special Color TV issue" the article describing the step by step production of the 15GP22's screen & post it on PhotoBucket to ensure adequate size & readability.

Can only do this after March 8th as i am at the CABSAT Broadcast show all next week.

Best Regards

jhalphen
Paris/France

[jeyurkon]

I hope I didn't give the impression that this is a project that I'm working on. It's just that it seems that there are no places that rephosphor CRTs. Besides the cost I wondered if there were any other reasons it couldn't be done so I started to think about how I would do it.

There also needs to be a reason for doing it. If there are few color CRTs that need to be rephosphored, then there isn't much motivation to set up for it.

Having said that, it's pretty amazing what resources some hobbyists have. Though any one individual might not have all of the skills or equipment, some set of them might.

I'm still amazed every time I watch Claude Paillard's video where me makes a triode vacuum tube.

John

[jeyurkon]

I did a quick and dirty test of the slurry screening technique. I used Nichia's NP-1154 red phosphor. The phosphor was suspended in a dichromated polyvinyl alcohol solution. I used potassium dichromate instead of ammonium dichromate which the recipe called for. Sodium dichromate should also work.

I spread the slurry onto a glass slide and let it dry. I then placed a metal mask over it and exposed it with a UV lamp. It was then developed by letting hot water run over it.

The results can be seen in the attached image. In the center there is an array of dots partially surrounded by a circle. The dots are spaced with a 600 micron pitch and are about 150 microns wide.

You can see problems with it. I was surprised it worked this well. The main reason for the damaged areas is due to the thickness of the coating. The optimal coating thickness is 1.4 phosphor grains. I didn't want to set up a spin coater for this test because of the work involved in cleaning it up afterwards. A spin coater will give a very uniform easily controlled thickness.

When the coating is too thick, the UV light is completely absorbed by the phosphor before reaching the surface of the glass. The result is that there is a PVA layer that doesn't get hardened. This layer softens and releases the hardened layer above it when developed. With the correct thickness, the PVA would have been completely hardened down to the surface and the phosphor would have remained where the PVA was exposed. In this case, some of the areas floated away.

The difference in the horizontal and vertical resolution of the dots also has to do with the thickness. The water was flowing horizontally across the slide and was able to flow undisturbed between rows. The material between columns was protected by the height of the dot in the preceding column. If the coating was as thin as it should have been, then the features wouldn't disturb the flow nearly as much.

It would also have helped to treat the glass so that it was hydrophilic. The most effective means would have been to evaporate a coating of silicon dioxide on to the surface. Another method would have been to clean the glass in a solution of potassium hydroxide and isopropyl alcohol.

BTW, the plate was illuminated with UV light to cause the phosphor to fluoresce when the photograph was taken. Otherwise, the phosphor would have looked white.

It's a simple matter to improve the process to the point of being able to apply the three phosphors using the shadow mask. Whether it would be profitable for a company is another matter.

I had fun in any event.

John