Rebuilt 15GP22's?

[Tom_Ryan]

Charles,

Glass frit (you spelled it correctly) is essentially an extremely fine ground glass that flows into the microstructure of any adjacent surface (metal or glass). The frit is usually a lower temperature glass that has the ability to flow so that coalescence occurs during heating and bonds chemically to the adjacent surfaces. Temperatures as high as 500 degF (371 degC) not only helps the frit to flow but allows for rapid outgassing of the tube (mainly drive off water vapor - which sticks like hell to everything!). During manufacture high temperatures also help to anneal the glass structure. However, it could warp or buckle internal metal parts. As I recall, excess sealant exists during manufacture, so that during high temperature baking the sealant does not all pump out of the joint. However, reheating an old 15GP22 to extremely high temps would not be necessary since the original structure is already outgassed and frit seal created. If only the electron gun is replaced then outgassing may be accomplished at a lower temp, 392 degF (200 degC), within the limits even of any externally applied sealants, e.g. Varian 'Torr Seal'. The trick is to pump the tube for a long time!

'73
Tom Ryan

[3Guncolor]

Did RCA or anybody else rebuild the 15GP22 back in the 50's or 60's? I think we are also reaching the day when even 21FJP22 and 21FBP22's and other delta tubes will not be able to be rebuilt. But there are a lot more of them around so it will be a long long time before they rare and they don't seem to have the vacume loss problem as the 15G does. The way things are going in the CRT field there is a small window left for the rebuild to happen or the sad fact is there won't much of a chance in a few years. I hope people are able to rebuild some of the tubes before the art is gone.
Steve

[andy]

---

[Steve D.]

Originally Posted by Charlie

Has anyone (with a little bit of CRT knowledge) thought to call Western Micronics and inquire about the 15gp22 rebuild process? Hell... it couldn't hurt to ask... and it would shed some light on whether or not these yahoos got all of their marbles!

There is always the possiblity (although unlikely) that they might actually have an "all-wise all-knowing big giant head" with the secret to this tube.

I e-mailed these folks after reading this thread. No reply yet, but the disconnected phone probably tells the story.

-Steve D.

[Chad Hauris]

I would think that bad 15GP22's in the 50's and 60's did not get rebuilt...since those sets were fairly rare there probably was enough new replacement tubes in RCA's stock to cover the need for replacements.

[frenchy]

Originally Posted by Chad Hauris

I would think that bad 15GP22's in the 50's and 60's did not get rebuilt...since those sets were fairly rare there probably was enough new replacement tubes in RCA's stock to cover the need for replacements.

Plus the 21 inchers came out very soon after the 15s were introduced so by the time they needed rebuilt, it was probably a pretty good proposition for a customer to just dump the set and buy a lower priced brand new set with a MUCH bigger screen to boot.

[rca2000]

What would a skid (10 or so) of 15gp22's NOS and PERFECT, in emissions and seal, be worth? (NO, I do NOT know where one is... sorry!!)

I am guessing, between 30 and 40k?

[Chad Hauris]

There may be such a cache of 15GP22's somewhere so it always pays for all of us to check out old TV shops, etc. before it's too late.
Whenever I'm traveling through little towns in Texas and NM and I come across any TV shops I ask if they have any old round tubes.

[Pete Deksnis]

Originally Posted by Chad Hauris

There may be such a cache of 15GP22's somewhere ....

In case you haven't seen this story:

In the fifties, for the motion picture industry, the Hazeltine Company developed a system for viewing motion picture internegatives as a positive on a tricolor CRT. It is known as a color film analyzer, and the first one used a 15GP22.

The tube-type color film analyzers are now all gone -- the last all-tube survivor was a model made in the late fifties that ultimately used a 21FJP22. It was in India, still running in 1995.

About 1996, a Mexican company traded in an old analyzer that used the 15GP22. It was totally inoperable, but had been used up to around 1975.

The company from whom I got this information had an inventory of six NIB 15GP22's in stock until 1997, when management decided to toss all the tube-based analyzer inventory to make room. So along with all the other spare parts, there are six 15GP22's buried somewhere in a Los Angles landfill.

So yes, chances are good that somewhere there are undiscovered NIB 15G's.

[kx250rider]

The six spares in a landfill is a dreadful thought, but here is the flipside: Gary Hough (SoCal TV collector who passed away in '89) found two NOS 15GP22s back East. He bought them for a couple dollars, but found great disappointment in the fact that they had lost vacuum still new in the boxes. I had a similar experience with one that was in a working set, then the next time I fired it up it had failed to lost vacuum. The vacuum loss has nothing to do with how much if any time is logged through usage, so NOS is not applicable in the condition of a 15GP22.

I was told by someone that the manufacturing process involved some kind of procedure whereby the tube was cooked in a vacuum chamber without the front lens on it. Then the front lens and mask were assembled to the tube after cooking, still while inside a vacuum chamber. Zenith, not wanting to pay RCA, had to put visible screws in the mask of their 15GP22 clone because they couldn't figure out how to do it the same way RCA did... But the two known Zeniths still have full vacuum (KNOCK ON WOOD!!!) And one of the Zenith 43M20s with that tube survived being slammed repeatedly against a wall in the Northridge Earthquake... Enough to knock all the knobs off and break one of the wheels and still no glass-to-metal seal cracks! I was terrified to pull the back off that set for MONTHS after the quake, as I was convinced the tube had probably been wrecked. Finally I did and What a relief!

I met one of the 15GP22 assemblyline girls about 10 years ago, and she did recall some strange details. I hate to admit that I can't remember her name. She lives (or lived) in Westwood, CA near UCLA. I did a TV repair housecall for her, and the subject came up. I will think hard to see if I can get a clue and try to pull her up on the database. But even if I find her, I think she was at least 80 then. She was a WWII widow who had originally started at RCA during the war and kept the job on due to loss of husband in war, as I recall her telling.

Charles

[Pete Deksnis]

Originally Posted by Kaye-Halbert TV

I met one of the 15GP22 assemblyline girls about 10 years ago, and she did recall some strange details. I hate to admit that I can't remember her name. She lives (or lived) in Westwood, CA near UCLA. Charles

Intriguing, are there details you can share?

Also, there are tales about RCA attempting to manufacture the 15GP22 in Puerto Rica and even Brazil. Did you glean whether the line she worked on was in Lancaster PA or perhaps there in CA?

[andy]

---

[kx250rider]

Originally Posted by Pete Deksnis

Intriguing, are there details you can share?

Also, there are tales about RCA attempting to manufacture the 15GP22 in Puerto Rica and even Brazil. Did you glean whether the line she worked on was in Lancaster PA or perhaps there in CA?

It strikes me that this lady was from Back East. She remembered how they told her how "special" the tricolor tube was to be, and that she had to wear a space suit while working on it. That's about all the detail I can remember of the conversation, but I remember the type of TV it was that I repaired for her. So next time I visit the shop where that call came from, I will check their database to see if I can get her name & number from searching with the TV make and zipcode.

Charles

[Tom_Ryan]

Originally Posted by andy

I thought the whole problem with the 15GP22 was that it didn't use a frit seal. I thought they attached a metal ring to the bell and another to the screen, then welded the two metal pieces together after the screen was coated with phosphor. Could a bead of frit be added around the two metal to glass seals to seal and strenghten the CRT?

Does anyone know how much air it takes to ruin a CRT?

Yes, that problem is characteristic of all vacuum technology, in general. But, the 15PG22 is a bit of an exception because it so happens that there's a lot of iron inside this tube. 15GP22 would have been an outgassing nightmare for RCA during tube manufacture. For a rebuild there should be much less water vapor to pump out - if the tube is not initially up to air and the rebuilder is clean and pre-baked all parts in dry nitrogen gas prior to installation into the old 15GP22. The more residual gas that's removed the less electron scattering occurs from the gun assembly when cathodes reach emission temperature. Less scattering effectively means somewhat lower emission temperatures are required to create a space charge around the cathode.

The real question to ask is:

How much residual gas pressure does it take to ruin a CRT, i.e. make the tube too dim to watch?

Well, it seems to me that the question depends on both electron gun efficiency and ultor voltage field intensity accelerating the electrons towards the phosphor screen. Bright pictures require more energetic electrons, and more of them, with high kinetic energy to produce more photons as a result of slamming into the phosphor dots at high velocity, hence giving us a brighter picture. As pressure inside a 15GP22 rises to 10-6 torr the rate at which residual oxygen molecules inside the tube strikes the phosphor dot plate rises to 3.6 x 10 to the 11th power (molecules per square centimeter). That's a hell of a lot of garbage in the way of the electron stream trying to hit a group of phosphor dots while being scanned at horizontal line rates! As the pressure inside the tube gets higher towards the 10-5 torr range the picture begins to noticeably lose brightness. Above 10-4 torr the picture starts to get really dim. At higher pressure less than 10-3 torr you can expect the tube to arc over inside - especially when the ultor sits above 20KV. Now, the getter should be turning white too! Also, you don't have to be at room air pressure to internally arc the tube.

Let’s put pressure into perspective: a new two-stage Edwards EM8 rotary pump (pretty common in most labs) after an oil change should reach 10-3 torr after 24 hours of continuous outgassing. To reach lower pressures requires either a diffusion pump or turbo molecular pump on the system to reach up to 10-6 torr to 10-7 torr range or maybe less (if a turbo pump). To get pressures lower takes either ION pumps or cryogenic pumps to reach the 10-9 range. Passive chemi-absorption techniques - hence the use of a 'getter' inside vacuum tubes can get things down to less 10-9 if the tubes seals are really good and keep it there.

I recall one interesting incident as a graduate student; I once cranked the voltage up on an electron detector in a mass spectrometer quite high one day - just to see what would happen. Even at less than 10-9 torr I was able to strip enough electrons off a detector plate once it reached 40KV to create a massive arc inside the vacuum chamber! Ka-Boom!!! The SS chamber didn't implode - just made a heck of a loud crack ...I jumped, probably 5 feet and ducker under a table. Yet, it always amazes me how modern large CRTs can work at 35KV or higher and not cause severe ionization inside a tube over time - pressures must be very low and kept very stable inside these tubes - a definite a challenge for old tubes! ...of yes, I forgot to mention the 40KV supply I used could deliver over 100 milliamps of current ...several orders of magnitude higher than a TV chassis!!!

Tom

[RetroHacker]

I know this is a bit offtopic for this particular forum, but while we're on the subject of rebuilding tubes... I've heard of people that had set up shop for rebuilding black and white tubes in their houses - from what I'd heard, it seemed simple enough, a car battery and some nichrome wire to cut the neck off the tube, replace the gun and reseal the tube, and pump the air back out. But what kind of pressures are required for a black and white tube? And I'm only referring to all-glass tubes here - the metal cone kind would have the same sorts of sealing problems. But just how low does the pressure need to be in order to have a serviceable B&W tube?

Another thing that confused me about tube rebuilds (B&W tube) - did they replace the phosphors or only the gun assembly? I always thought that the phosphors in black and white tubes degraded with use too. Kinda like the screen burn on computer terminals where something would get burned into the tube if left long enough, and occasionally you'd see a really well used terminal with 24 rows of 80 fuzzy little boxes from where the characters lined up. Wouldn't a black and white tube eventually get the same sort of phosphor degredation over the entire tube? Or does the relatively rapidly changing content on television prevent this?

Basically, there's a lot that I don't know about picture tube rebuilds... Any insight?

-Ian