Rebuilding the 15gp22: A final report - Page 5 - Videokarma.org TV - Video

David Roper · #61 04-14-2010, 03:25 PM

For comparison, the 15HP22 is shown above the 15GP22

jr_tech · #62 04-14-2010, 09:04 PM

Quote:

Originally Posted by David Roper

For comparison, the 15HP22 is shown above the 15GP22

Interesting! I don't think that I have ever seen a picture of an early 15" set that did not have a CRT with an internal mask... Can someone perhaps post one?
A tube constructed in this manner (with the troublesome flanges designed out) might well be easier to fabricate today. I really like the funky looking internal mask, but having a tube that actually worked be great!

jr

***Eric H*** · #63 04-14-2010, 09:17 PM

The 15HP22 seems to still have the flanges, just fewer internal components.

jr_tech · #64 04-14-2010, 09:48 PM

Quote:

Originally Posted by Eric H

The 15HP22 seems to still have the flanges, just fewer internal components.

Sorry, I stated it poorly.... I mean a simplified tube like the 15HP22, which has fewer parts to deal with and in addition, join the panel and funnel together with a frit seal instead of the pesky flanges. Such a tube would contain much less metal inside the bottle (perhaps reducing gas), eliminate the leaky flange areas, and also provide a slightly larger picture area (about 116 sq inch instead of 88).

jr

John Folsom · #65 04-14-2010, 11:05 PM

It was not until the RCA 21CYP22 that the faceplate and funnel of the color CRT were joined using frit glass seal. Pity this technology was not available for the 15GP22, or the 15HP22.

miniman82 · #66 04-15-2010, 10:05 AM

Gotta be a way to incorporate it, though. I wonder what would be more cost effective: doing a complete redesign of the 15g, or making one from scratch?

NewVista · #67 04-15-2010, 12:06 PM

First generation color should have used simple RGB projection tubes like that 1st Mitsubitshi color TV did. Then RCA could have made all the demo sets they wanted - with a bigger picture too !

jr_tech · #68 04-15-2010, 06:16 PM

Quote:

Originally Posted by John Folsom

It was not until the RCA 21CYP22 that the faceplate and funnel of the color CRT were joined using frit glass seal. Pity this technology was not available for the 15GP22, or the 15HP22.

Yes! If only Corning had developed devitrifying frit earlier our CRTs would likely be in better shape today. The first use in the 21CYP22 would appear to be in 1958.
This brings up a question... the 22EP22 was produced by Westinghouse in 1956.. Unpublished pix courtesy of CRT historian Peter Keller show the CRT and panel/funnel seal area...there is no frit bead! Anybody know how the seal was made?

jr

John Folsom · #69 04-15-2010, 06:26 PM

I may have been incorrect, that tube looks like an all-glass CRT, in which case it would have to be a firt glass seal. I was thinking that tube had a metal flange at the face, similar to the 21AXP2. Steve K should be able to give us the story.

jr_tech · #70 04-15-2010, 06:37 PM

Quote:

Originally Posted by John Folsom

I may have been incorrect, that tube looks like an all-glass CRT, in which case it would have to be a firt glass seal. I was thinking that tube had a metal flange at the face, similar to the 21AXP2. Steve K should be able to give us the story.

But there is absolutely no sign of the usual cream colored frit bead on the tube... perhaps they used some early solder glass type of material?...I don't think they could have done a flame seal, because of the thickness of the glass, and close proximity to the screen and shadow mask.

jr

eberts · #71 04-17-2010, 02:24 PM

That is a flame seal. It looks like a standard B&W bulb with a modified front panel to hold the shadow mask. It's unusual because it also is aluminized. Glass bulbs were thinner then, they used curved bulbs and safety issues were not the top priority. That's probably why it didn't make production, heat from the glass welding warped the shadow masks.

Steve K · #72 04-17-2010, 09:45 PM

John:

I cannot add much to this discussion, when I restored that Westinghouse I never pulled the tube out of the chassis or looked that closely at the seal. I too originally thought that it had a metal flange.

Eberts:

That CRT was in production. Westinghouse used it for one model year.

Steve

ohohyodafarted · #73 05-09-2010, 05:26 PM

AFter several weeks of preliminary preparation, I embarked on another phase of the 15GP22 project.

AFter doing some groundwork to find a skilled welder with the proper TIG welding equipment, I located Dave the welder. Dave has a very high tech and up to date shop with the latest in welding technology.

I brought Dave a Kovar ring from a broken 15G for him to practice on and the tig welds he made on the test ring looked wonderful.

So this Saturday I took a 15GP22 and a 21AXP22 To dave to be welded. We had previously tested these tubes with a Helium leak detector at the lab at MSU, and located leaks on the welded seam of both tubes, and marked their location. I had Dave re-weld these defective areas on both tubes. Then I drove from Milwaukee to EAst Lansing and John Yurkon re-tested the tubes for leaks again to see if Dave's welding cured the leaks.

I regret to report that of the 4 welds, that were performed, 3 of them still leaked when tested. Upon close examination under a microscope, we could see that there was some minor porisity and some irregularities in the welding. By comparison, the original RCA welds were done on an automated machine which produced very consistant welds. So it was to be expected that welding by hand would have some inconsistancy.

It is apparent that to cure the weld line leaks, it may take multiple trys, re-welding each leak, and then leak testing after each attempt, in order to seal the leaking welds.

Without a having a leak Helium leak detector to test and re-test at our immediate disposal, the sealing of the tubes is not going to move forward. It is far to inconvenient to drive 700 miles round trip to test welds, and besides, we don't want to out stay our Welcome at MSU.

However, it is encouraging to note that I had sealed the glass/kovar innterface of the 15G with the epoxy we had been testing, and it did indeed seal the glass to Kovar leaks, on the aforementioned 15G.

At this point we are pretty much at the end of the road for John and myself. We feel it's to much of a gamble to seal tubes and rebuild them, and then to just cross our fingers that we have sealed all the leaks. So until a Helium leak detector falls in our lap, rebuilding 15G's here in the US is on an indefinite hold.

Fortunately it seems that RACS in France will be able to take up where John and I have left off. Perhaps when the equipment from Hawkeye is installed and up and running at the ETF in Hilliard, we may be able to proceed with more attempts in rebuilding 15G's here in the U.S.

Bob and John

freakaftr8 · #74 05-10-2010, 01:38 AM

I do aerospace work, in my field there is certan epoxies that are used to withstand extreme heat and seal voids in vacuum seals. I wish I could find out what this substance is, and report. I will try to pick the minds of the engineers. Whoever it is makes this substance. Is there any way to remove the metal mask and install this stuff, and reinstall the mask?

*zenithfan1* · #75 05-10-2010, 08:40 AM

It would be great to get that equipment set up and running at the ETF. How much is a helium leak detector? I would imagine it's not cheap. That really sucks having to drive back and forth to test for leaks. No matter what, Bob and John deserve a huge thanks for working so hard to do what hasn't been done for 50 years. You guys worked harder on this than anyone ever has I think. You have success and screen shots to prove it, too bad that damn tube had to leak but that's RCA's fault for that crappy ultor ring design. I hope we can someday resume rebuilding here in the USA. Thanks again you guys for all your hard work and keeping us informed the entire time so we can follow your progress. My fingers are crossed on future rebuild attempts.