Re: 15GP22 Rebuild Attempt in France - Soon!

[jhalphen]

Good day Gentlemen,

15GP22 Rebuild Attempt Progress Report - 10/15/1009

A 15GP22 CRT kindly donated by Steve McVoy (ETF Museum) is currently at the RACS factory in the south of France awaiting imminent rebuild.

The CRT was broken and therefore down to air. The RACS team after careful UV exciting of the screen + close physical examination decided that the screen/Bulb/shadow mask assembly was sufficiently intact to be worth an attempt at rebuilding. In spite of being "down to air" for a considerable amount of time, the shadow-mask is not corroded, eaten by rust, nor by other contaminants. RCA made them tough!

Friend John Folsom Jr is very kindly donating one 15G stem assembly for the attempt. Thanks to him, we are advancing the rebuild schedule by 6-8 weeks, Big Thanks! John, and Kudos! to you.

Leakage detection is accomplished, not by Helium leakage detection (Thanks! to John Yurkon for describing the process/needed gear) but by a more mundane process developped from industrial practice:

The CRT is submitted to rough 1st stage vacuum pumping, using a centrifugal pump. The final anode & therefore internal Graphite layer is energized at a 30-40KV EHT. The operator, using thick EHT-Proof gloves has an array of fine "needle-point" search electrodes with which he searches on the outside of the glass enveloppe. At a leakage point, however small the hole may be, the EHT arcs over and pinpoints the hole. It it then covered with "chewing-gum" consistency Frit-Glass, which after baking at 400°C becomes tough as a bathroom/shower tile.

RACS has a Helium leakage detector, but Tech Manager François quoted "we never use it, our method is faster & hassle-free".

The gun has been rebuilt. We are awaiting John's Stem/Base to transfer the rebuilt gun to the new base. Glassworks are now complete. The new gun neck is ready and the broken bulb neck has been sealed to avoid further contamination.

I will travel to the RACS facilities to personally watch & photo-document this first historical attempt on European Soil. If the rebuild is successful, the RACS testing facilities will display a rectangular white raster on the 15GP22's screen.

The rebuilt CRT will be shipped back to the donator (ETF Museum) for incorporation into a test CT-100 operational chassis for the first pictures of a live video display.

Thanks! for bearing with me so far, will update this topic as time runs its course.

Best Regards

jhalphen
Paris/france

[Dave A]

The line forms behind me! Two of 'em ready to go.

Dave A

[Phil Nelson]

Very cool. Best wishes on the attempt. It will be interesting to hear the news and see photos.

Phil Nelson

[jr_tech]

The best of luck on this rebuild! I have a dead one also Has anybody accomplished a successful rebuild of a 15GP22 ?

jr

[old_tv_nut]

Best of luck - will be paying close attention!

[Sandy G]

Keepin' fingers crossed...I know I'll never have a CT-100, but HOPING that several more of 'em may "Live" again makes me very happy, indeed !

[Steve McVoy]

Originally Posted by jr_tech

The best of luck on this rebuild! I have a dead one also Has anybody accomplished a successful rebuild of a 15GP22 ?

jr

I have seen 15Gs that have been rebuilt with 21 inch guns. Apparently convergence assemblies from 21 inch round sets were installed, and only the static convergence magnets were used. Because the screens are so small, they probably looked Ok without dynamic convergence.

It is possible that 15Gs were rebuilt with 15G guns in the early days, but I have never seen one.

As for recent attempts, John Folsom and Bob Galanter have been working with Scotty at Hawkeye in an attempt to rebuild a tube. They are close, but no success so far.

[jeyurkon]

That's great progress and it's wonderful that they are taking on this project!

I'm embarrassed to say that I forgot about this leak testing technique even though I own a specialized HV probe used by glass blowers to search for leaks.

However, if the leak is at the ultor flange as Bob and John think, then I doubt that this technique will work because the metal is an equipotential surface. You wouldn't be able to pinpoint the leak. Also, since the flange penetrates the glass it would conduct even better than a pin hole in the glass.

Unless I'm overlooking something.

John

[andy]

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[kx250rider]

Originally Posted by jr_tech

Has anybody accomplished a successful rebuild of a 15GP22 ?

jr

Not for long. I had one re-evacuated by the owner of a tube rebuilding shop in SoCal in the early 80s, and it worked fine for about 6 months, then began to glow purple in the neck and arc internally. It was a leak around the anode ring, I'm sure. The trick was, at the time, to heat it up over a couple days, rather than the several hours they usually used. The owner of the shop was a retired engineer from Hoffman, and he had worked on a project there to build a proprietary tube for Hoffman color TVs so they wouldn't have to use an RCA or a CBS tube; both of which they tried in prototype sets. He also did the only true successful rebuild on an 8" Arvin metal tube for me, as well as several 21AXP22s for myself and others. He sold his equipment to a CRT rebuilder in Mexico and retired in the 80s, and I lost track of him. (Ron Richardson, Dunbar Picture Tube Company. Culver City, CA). If he's still with us, he'd have to be about 90 by now, I guess.

Charles

[jr_tech]

Originally Posted by jeyurkon

However, if the leak is at the ultor flange as Bob and John think, then I doubt that this technique will work because the metal is an equipotential surface. You wouldn't be able to pinpoint the leak. Also, since the flange penetrates the glass it would conduct even better than a pin hole in the glass.

Unless I'm overlooking something.

John

I think that is quite correct... and also suspect that the flange weld or the flange-to-glass seals are very likely leak areas. Perhaps a coating of Vacseal over the entire flange area would be helpful?

jr

[jhalphen]

Hi Guys,

John Yurkon, Thanks! for this input:
However, if the leak is at the ultor flange as Bob and John think, then I doubt that this technique will work because the metal is an equipotential surface. You wouldn't be able to pinpoint the leak. Also, since the flange penetrates the glass it would conduct even better than a pin hole in the glass.

Will translate ASAP & send to RACS, it's good forward thinking.

I did send them in August the set of Flange Cross-Section photos taken by John and Bob.

To everyone: Thanks for the encouragement.

A useful thing we can do right now: find some really "Lean and Mean" pricing quotes on USA to Europe shipping for a box containing a CRT the size of a 15G. We already got hit in the teeth with atrocious prices (US $1200.00 each way) for prospective DuMont 30 inch CRTs, as a result, none were sent.

Best Regards

jhalphen
Paris/France

[Eric H]

It would be really cool if someone could document this effort with video somehow.
Any chance they'd let you record any of this?

[kvflyer]

Originally Posted by jhalphen

...I will travel to the RACS facilities to personally watch & photo-document this first historical attempt on European Soil. If the rebuild is successful, the RACS testing facilities will display a rectangular white raster on the 15GP22's screen....

From the initial post...

[jhalphen]

Hi Eric,

Thanks! kvflyer,

Photos: Yes
Video: No

RACS will let me shoot what i want.

BUT, having sold Broadcast equipment for 27 years i know that 1 hour shot = 3-4-5-... hours of editing to make it look decent. I'm too lazy, besides, photographs have much better resolution for close examination of important technical details.

A bouncing, zoomed, in & out of focus picture, with constantly varying "Auto-Exposure" diaphragm aperture is my idea of hell!

You are however very welcome to come over, shoot, edit, title & sell the resulting DVD!

Best Regards

jhalphen
Paris/France