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

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

Dave A

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

Phil Nelson

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

jr

Best of luck - will be paying close attention!

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 !

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.

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

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. :o

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

---

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

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

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

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

...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...

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

OK... So long as the cat is out of the bag on this thread started by Jerome, I might as well put in my two cents.

First off, It is VERY HIGHLY likely that the leaks occur in the Ultor ring. John and I did the cross section cut away of the ultor ring that Jerome speaks of (we sent him photos).

The ring is composed of 2 glass to metal fusions (that you all are familiar with) and 4 layers of formed metal which are welded and fused together adding another 3 layers of joints around the entire circumference of the ultor ring.

In our cross section we could see that two of the metal to metal fusion joints are likely where the leaks occur.

IF the tube that RACS has in their possession was a leaker, it is not likely that the rebuild will succeed for very long. It will probably fill with air again. How long it will take is anyones guess.

John Folsom and I were ready to do a rebuild with Scotty at Hawkeye at the beginning of September. However Scotty injured his ankle in an athletic event and his foot is now in a cast. We are hoping that we will be able to make the first US attempt on a LEAK FREE dud that John owns, in the very near future (probably early November.) IF it works, then I will rebuild my LEAK FREE dud.

We appear to have the issue of cracking glass stems resolved with the design that John and I paid for and were manufactured for us by a US company out east. (This is the stem that Jerome mentions which John has sent to RACS in France) We sent the new stems to the Gun rebuilder and we now have 2 stems with rebuilt guns mounted and ready for the rebuild attempt. All we need is for Scotty to get better so he can perform the work for us.

After this attempt by John and I, we will then test out our leak sealing protocall which is top secret and proprietary. We believe it has a very good chance of sealing the leaks that are on the ultor ring, but only time will tell.

So that is where things stand on the US project that John and I are spearheading.

We will keep you all posted as to our progress as things develop.

Bob Galanter and John Folsom
The 15GP22 Project

Sorry to hear Scotty is in a cast, but also glad to hear he's still a part of this effort. And of course, if the super-secret sealant works on a 15G, I will be eager to have it tried on the 21AX that re-leaked on its first try.

Hi Guys,

John, Bob,

"We will then test out our leak sealing protocall which is top secret and proprietary. We believe it has a very good chance of sealing the leaks that are on the ultor ring, but only time will tell."

Not nice to not play ball, i've shared all info openly.

The common effort is to rebuild 15G's not become Maddoff-rich with proprietary secrets.

Good day

JH


Good evening Jerome,

I'm sure, when all is said and done, the "top secret" and "proprietary" protocall will be shown to be something quite "common" and "ordinary".

Bob & John, please tell us something about your top secret and proprietary protocall.

Kindest regards,

Terry Cheek

WOW Jerome!!!

Don't get your nose all bent out of shape. John and I BOTH agreed to send RACS that stem that we developed and it didn't cost RACS a stinking dime.

We have thousands of dollars invested in the R&D of that stem alone.

You have no right to critisize us. The fact is, that John and I have spent MANY THOUSANDS of dollars of our own money, and hundreds of hours in R&D, and nobody has contributed a single red cent to our effort.

John and I will keep the formula for sealing the tubes proprietary if it is successful.

How the hell do you expect us to recover even a small part of our investment if we give our trade secrets away.

This is not only an attempt, by John and myself, to do something that has been needed by members of our hobby for many many years, but it is also a business venture.

John and I are not a multi-millionires with deep pockets. And our efforts are not for the purposes of charity. We need to be able to possibly recover our costs of R&D by offering this service to other collectors at a small profit for each tube rebuilt.

If and when our process proves successful, and we have recovered our costs of developement, John and I will, no doubt, be happy to donate the technique to the public.

Until that time, you will just have to be patient and accept the fact that John and I deserve a fair shake, and some gratitude for all the time and huge amount of money we have invested.

And just to emphasize a point here, I don't suppose that RACS will be willing to rebuild 15GP22's for free, Will They??? Oh yes and as I recall; weren't those glass ringlets that RACS developed to rebuild Pyrex tubes also proprietary? So I guess this is tit for tat. Eh? And if they weren't proprietary maybe you should have RACS send a handfull of those rings to Scotty at Hawkeye in repayment for the stem that John and I sent them for free.

"The common effort is to rebuild 15G's not become Maddoff-rich with proprietary secrets." ..... Comparing me to the likes of Bernie Madoff has to be just about the most insulting thing anyone has ever said to me.

"The Common effort" ...... sounds pretty socialistic to me and make no mistake about it, I am a free market capitalist. God bless America and the Red White and Blue!

Seriously Jerome you were WAY out of line with your comments!!! and have really pised me off with your attitude. So much so that I may never agree to divulge what we have developed. This kind of attitude reminds me of how the European Unoin constantly picks upon U.S. coporations who have intellectual property to license. I am thinking of Microsoft and Qualcomm just to name a few.

I could go on and on but what's the point?

And please understand that I am speaking for myself. John Folsom had no part of this post, and should not reflect upon him.

Bob Galanter

Please, everyone, lets stop this badmouthing. I'm happy that John and Bob are close to success with Hawkeye, and I'm also happy that RACS may also be close. Remember that neither has succeeded yet, and having two companies trying it increases the chance of success greatly. If it turns out that RACS needs John and Bob's sealing method, they will probably work out a royalty arrangement with them that will allow RACS to rebuild tubes and allow John and Bob to recoup some of their investment.

I appreciate the effort (and money) that John and Bob have put into this venture, and I also appreciate Jerome's effort in getting RACS to look at rebuilding the 15G, and also the prewar tubes that have so far been impossible to rebuild.

OK, let's all calm down. Take a deep breath.

We are not in competition with RACS, if they can rebuild 15Gs more cost effectively than Scotty (factoring in shipping costs in either case), then I will be the first one in line to sign up for their services, regardless of how much $$ Bob and I have poured down the rat-hole :-).

As for the leak detection, here is a sketch and photo of the cross section of the 15G flange seal. There are 2 glass to metal seals, and 3 (!) metal to metal welds, any one of which can be the source of the leak.

Bob and I speculate that the leak is most likely at the metal-to-metal welds which join the flat metal pieces together, though we have no science to back this up.

It is not obvious to me that the HV needle probe technique would work here. As John Yurkon points out, the metal in the flange would be at the HV potential and attempting to needle probe would not work.

As for the top secret leak sealing protocol, it is not a secret, I have discussed it with others, and the materials used are common knowledge in the industry. It may work, it may not (I am not quite as optimistic as Bob, for reason I will not go into here). Certianly RACS would be aware of our approach, and has likely rejected it for the same reasons that make me a bit dubious. But it is worth a try, I may be wrong (I often am!)

And frit glass is another approach, and at some point we may attempt this as well.

But for any sealing protocol to work, what we really need a way to locate the leak so it can be addressed directly. If the HV method can be made to work, that would be optimum. Helium leak detection is another possibility, but it requires expensive equipment, vacuum pumps and mass spectrometer.

BTW, I am sure some of you are thinking "VACSEAL!" After discussions with several people in industry working with ultra high vacuum systems, there seems to be a consistent opinion that VACSEAL will not be useful in this appplication, so we have abandoned thoughts of attempting to seal leakers using this product.

When Scotty recovers and starts rebuilding tubes again, Bob and I are ready to make another attempt using a non-leaker tube and our new and improved stems.

Good luck to us all!

Yeah, come on, guys, snipin' amongst ourselves isn't productive at all. We're all supposed to be friends here...That's one of the things I like most about the old TV/Radio fraternity.

Well John, after seeing that diagram and cross section I gotta say it's a miracle there are any working 15G's at all.
So many potential trouble spots.

What was the purpose of the double wall of thin metal?

It looks like possibly it was to allow for different expansion rates between the bell and the face plate, is the corrugated washer welded to anything or just squeezed between the two pieces to provide some tension?

Would it be possible to pressurize the tube slightly with an inert gas and simply look for leaks with soapy water like you would a tire? I suppose it would have to be a pretty large leak to find it that way, also I don't imagine you could put much pressure inside without exploding the thing.

Eric,

I think you are right, the complex joint was made to allow for thermal expansion. Too bad they did not have frit glass.

I suspect most of the leaks we are looking for are microscopic in dimension, and would not produce any bubbles.

The corrugated washer isnot aattached, it is simply pinched between the 2 flat faces. Here is another photo highlighting the washer

Hi Eric,

The entire design of this tube and in particular the Ultor Ring Assembly, is predicated on a number of design constraints.

I will attempt to take the issues one at a time.

First RCA needed a method of making the envelope in two pieces. A front half and a rear half, so as to facilitate the instalation of a third assembly inside the tube. That third assembly is the phosphor dot plate/shadow mask assembly.

The technique of fusing glass to metal was well understood. So it was decided to make a glass front face assembly fused to a metal ring, and a rear glass funnel and neck assembly fused to a metal ring. Then the phosphor dot plate/shadow mask assembly would be mounted to the flange on the rear assembly, and the front half and rear half would be brought together and the two ultor ring halves would be heilarced together to form a complete crt assembly.

The phosphor dot plate/shadow mask assembly mounts to the light guage rear half of the ultor ring inner flange assembly with 3 bolts.

The reason for the two light guage metal rings with the bulge on the outer circumference, is that when the tube is evacuated, great amounts of mechanical force are exerted which squeeze the front and rear halves of the tube together exerting great amounts of pressure on the two light guage metal rings. The rings need to flex under the pressure. The pressure needs to be distributed evenly around the entire surface where the two halves of the ultor ring meet.

The corrugated metal washer that is sandwiched between the front and rear rings, is designed to act as a cushion to evenly distribute the tons of force squeezing the two rings together. If the corrugated washer was not there, the front and rear metal rings would squeeze together, and in the places where the rings would touch all of the force would be exerted in just those spots. That would cause huge stresses and probable breakage of the glass to metal bond on the front and rear rings. Even if the glass to metal joints survived, there would be pressure points that would make the tube vulnerable to implosion if bumped or jared.

The reason for the heavy metal rings which are the bonding surface for the glass is thought to be as follows. The light guage metal would likely melt under the high temperatures needed to fuse glass to metal. To solve this problem, heavy guage metal rings were bonded to the light guage sheet metal rings. Probably a rolling fusion weld under great force and very high current. This is the joint which probably leaks.

I had long suspected that the leaks were occuring in the metal to metal fusion jonts between the heaavy and light guage metal rings. So when John was in Milwaukee a couple months ago we decided to cut a cross section of an ultor ring that we had been using to experiment on. We used a 3 inch high speed carborundum disc to slice a section of the ultor ring away. We then ground and polished the cross section to a high finish so we could closely examine the integrity of metal to metal joint.

AS you can see from the cross section photo of the ultor ring in John's post, the heavy guage ring is not bonded uniformly to the light guage sheet metal ring. There is a very evident partial gap between the two components. This was only a random cross section and we found deficiencies in the metal to metal joint. I strongly suspect that some areas are joined better and some are joined much more poorly.

It is this metal to metal fusion weld between of the heavy guage ring and the sheet metal ring that will need to be sealed. We can't be sure, but we do not think the glass to metal bond is where the leaks occur.

Glass to metal bonds were well perfected and being used in metal funnel crt's for many years before the 15GP22 was put into production.

There has been much discussion betewen John and myself about the usability of frit glass to try sealing the metal to metal fusion joint. And John and I have differing opinions on the use of frit glass to seal 15GP22 leaks.

I had a very long and interesting discussion with one of the elderly engineers who worked at Rauland picture tube. I also spoke to a fellow that works for one of the companies that make frit glass. These fellows both told me that frit glass will not work for the metal to metal leak we are trying to fix. The problem is that the coefficient of expansion of the frit glass has to be matched to the metal very precisely. And even if we were able to match the expansion coefficients properly, due to the fact that the sheet metal ultor ring flexes when the the tube is evacuated, the frit glass would crack due to the flexing.

Frit glass is very useful to bond two glass surfaces of a crt together because the glass all moves at the same rate. When you get dissimilar rates of expansion or physical stresses such as the ultor ring flexing, then frit glass will fail. It will either crack or debond from the surface. Even in glass to glass joints, if the frit glass in not perfectly matched to the rate of expansion of the glass parts, the joint will fail.

As to your query on leak detection, as was discussed in another post the spark method is not going to work on the metal ring as it is electrically conductive throughout. As to pressurizing, you are correct the leak is too small to find this way and may explode the tube because it is not designed to be pressureized, it is designed to be under vacuum.

The only practical method of leak detection would be with a helium leak detector. IN this method a strong vacuum is pulled on the crt by a machine that is designed to count Helium atoms in the vacuum stream. Helium is used because the atom is so small it can squeeze through the smallest of leaks. So while the tube is under vacuum via the HE leak detector, the operator introduces small amounts of HE from a tiny supply tube into the areas where the leak is suspected. Almost instantily the HE leak detector will detect the HE atoms in the vacuum stream and a meter on the machine will register a large number of atoms. As soon as the meter registers, you know you have found the leak.

All this leak detecting is in my opinion not of much use. Even if were to find the exact pont of the leak, and seal it, additional leaks could crop up in other spots. The solution is to seal the entire metal to metal joint all around the tube to make sure that the leak is fixed and to prevent any possibility of future leaks occuring.

I hope this has shed some light on the subject of why the tube was built the way it was and where we suspect the leaks are.

Bob

Forget about pressurizing ANY crt for ANY reason. Glass is excellent under compression, but should NEVER be subjected to tension. A few pounds into a 15GP22 would cause the ultor flange to act as a bellows, thus ruining that. Add few more pounds, and the tube will explode & cut you to ribbons.

The corrugated crush washer appears to be a different metal than the other parts in the photograph. Is it aluminum by any chance?

John

Thanks Bob and John.

It was nice to read your detailed explanations of the 15G's construction. I counted five glass-metal or metal-metal junctions. That's ten bound surfaces. This is a mechanical engineer's nightmare.

Have you considered using a large molten glass band to completely encompasses the Ultor ring? This glass band would be fused to front and rear glass surfaces of the 15G. It would include a feed-through connection to the Ultor. If this technique is mechanically sound, wouldn't it eliminate most if not all of the sources for vacuum leaks?

Kind regards,

Terry Cheek

Thanks Bob and John for posting the construction details of the 15gp22. Wow! No wonder many of these crts leak. I suspect that percentage wise, more prototype metal cone 15" crts have survived!

I suspect that patching over the outside of the seal areas with frit (or glass) would not be a permanent solution. as flexing of the seal area is likely to fracture these brittle materials. Also, I suspect that pockets of air that could be trapped between the frit and the metal flange could be a source of a "virtual leak" that could over time cause the tube to become gassy even though there may be no detectable path to the outside...

Tough problem !:scratch2:

jr

jeyurkon:

The crush washer is of a different metal. I dont have it hear, but it is either aluminum or Stainless steel.



jr_tech:

Your asumptions are right on. We too are concerned about redidual gas entrapment after sealing the metal joints. Hopefully the amount of entraped air would be so minimal as to be absorbed by getter material.

I have a 16gp4 that has milky getters. Presumably from a leak. But it still produces a very good picture. So, it is possible that if the getter flashes are very large, we may be able to counteract the infiltration of any small amounts of gas that might get entraped in the ultor ring after it has been sealed.

Bob

So, I take it the reason there are so many dead 15GP22's is that they were a faulty design to begin with?

So, I take it the reason there are so many dead 15GP22's is that they were a faulty design to begin with?

But at that time (before Frit was developed) what other options did the CRT manufacturer have for joining the funnel to the panel? Metal tube, welded like the prototypes? other sealing methods?

I have never been able to determine the seal method used on my Westinghouse 22EP22. There is no visible frit bead (frit as we know it today had not yet been developed), and only a faint line can be seen where the funnel and panel join. Solder glass perhaps? Flame seal? Early experimental frit like substance from Corning?

jr

That would logically follow. Not only that, but I would surmise that they were extremely difficult to produce in any case, & prolly had high failure/scrappage rates. Must have been expensive, too. And everything I've read says RCA sold what relatively few the CT-100s they did at a loss-I'm sure somebody was jumping up & down over this, as well as screaming about coming up w/a cheaper, easier to make, better design. Since the CT-100 was only sold/made for a few short months, this may have been the case.

Just an idea, if RACS can find a glass replacement bell for the 15G with similiar size and dimensions, frit or glass weld it to the glass neck and CRT Face,--- wouldn't that eliminate most hassles common of a CRT made part metal and part glass.

Someone NEEDS to look at an Advent 1000A projection CRT as an example. A glass neck, glass bell, glass CRT face w/ phoshor on striking plate. All fritted together and mostly glass.

The alignment and distance between the shadow mask, phosphor dot plate, and the gun+neck makes this really difficult (~expensive) unless there was/is another tube that used a bell identical to what was used originally without provision for the flange.

The path of stabilizing the ultor flange seal is likely the best way to go.

The bottom line is that the designers at RCA had to make the best of what technology and methods they had at the time.

I'm sure the engineers at RCA would have never imagined that these tubes would be in use some 55 years on.

I'd be curious to see how many modern CRTs will survive 50 years with a vacuum intact.

Colorfixer has it right.

And on top of what he said will add that the inside flange of the ultor ring is used for mounting the Shadow mask/phosphor dot plate assembly and internal bezel mask.

Even in the extremely remote chance that you could find a 2 piece glass envelope with exactly the same geometry as the 15G, you would still have to figure out a way to mount the internal assemblies.

You need to remember that a 15G is the only color production tube ever made that did not have the phosphor dots deposited directly on the inside face of the envelope.

You would probably have a easier time making an all glass 15" roundie color crt from scratch. I suppose if you had millions to throw at the project you could find some chineese company to make one for you in limited quantities.

The sensible thing to do is follow the course we are already on. It will take time to solve all the issues, but in the the end we will be able to certainly rebuild tubes under vacuum. Leakers are another story. But I think with persistance, we will also be able to solve the issues of sealing the leaks too.

Bob

jeyurkon:
it is possible that if the getter flashes are very large, we may be able to counteract the infiltration of any small amounts of gas that might get entraped in the ultor ring after it has been sealed.

Bob

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

Nope, the getter only works on a singular molecular level on the surface it is deposited on. Surface area of getter flash is more important than amount of material in getter. You need a good hard vacuum for the tube to work.
Maybe you could rebuild a tube connected to a molecular ion pump continously, then you won't have to worry about a slow leaker.

I think Bob did mean "large" in terms of area and not thickness. I believe the getter flash does do better than a single mono-layer, but its pumping speed decreases.

John

So the problem seems to be sealing the thin metal ring to the thick metal parts.

It has a nice V shaped crevasse that something could be flowed into, seems like Vacuseal should work on something like that unless it can't survive the baking process.
Perhaps if it was a slow enough leak it could be applied after evacuation and cooling were done?

Whatever is used it has to be impenetrable, flexible to some degree, capable of withstanding heat & so on.

I don't imagine there's any way to weld the thin metal to the thick metal without cracking the glass or destroying the seal there.

I knew a guy who could weld aluminum cans together using a Plasma Welder, there's still a lot of heat involved though.

You're right Eric,

the problem is between the thick metal ring and the thin metal ring which are fused together in some sort of fusion welding process.

Yes, we have taken advantage of the fact that you can "flow" a sealant into the area where the thick and thin metal meet. Vac seal is not the material of choice. Too thin to fill the voids between the metal layers. It does however seem to endure the heat of the evacuation oven very well. In our first trial, we used vacseal. When we took the crt out of the oven the Vacseal had left a very nice glassy coating on the surfaces that we applied it to. That tube was however not a leaker.

I also used Vacseal to seal some vacuum pumping lines that I was experimenting with and it did not seal the leaks.

Also, I spoke to a fellow in the business of working on UHV eqipment. He rapairs and services HE leak detectors. He had nothing good to say about Vacseal. He did however say that the material we are now using was very much favored by him for sealing leaks.

Oh yes, I almost forgot, one of the reasons that Vacseal is not the first choice, is that it is a solvent base material and it's curing hinges on the depletion of the solvent. This is a very big problem for sealing a CRT. The issue is that as we pull a vacuum on the crt, the Vacseal will have a tendency to outgas it's solvent into the crt. That could potentially contaminate the crt after pumpdown. The sealant we use is not solvent based.

Some amazing epoxies out these days. I really like 3M 8115.

You're right Eric,

the problem is between the thick metal ring and the thin metal ring which are fused together in some sort of fusion welding process.

Yes, we have taken advantage of the fact that you can "flow" a sealant into the area where the thick and thin metal meet. Vac seal is not the material of choice. Too thin to fill the voids between the metal layers. It does however seem to endure the heat of the evacuation oven very well. In our first trial, we used vacseal. When we took the crt out of the oven the Vacseal had left a very nice glassy coating on the surfaces that we applied it to. That tube was however not a leaker.

I also used Vacseal to seal some vacuum pumping lines that I was experimenting with and it did not seal the leaks.

Also, I spoke to a fellow in the business of working on UHV eqipment. He rapairs and services HE leak detectors. He had nothing good to say about Vacseal. He did however say that the material we are now using was very much favored by him for sealing leaks.

Oh yes, I almost forgot, one of the reasons that Vacseal is not the first choice, is that it is a solvent base material and it's curing hinges on the depletion of the solvent. This is a very big problem for sealing a CRT. The issue is that as we pull a vacuum on the crt, the Vacseal will have a tendency to outgas it's solvent into the crt. That could potentially contaminate the crt after pumpdown. The sealant we use is not solvent based.

I've only been able to use Vacseal on very small leaks. Even conformal coating works better. There are epoxies that use a reactive dilulent, but they're still not as good as the one that you plan to use. They are water thin though which might be an advantage.

John

So the problem seems to be sealing the thin metal ring to the thick metal parts.

...

I don't imagine there's any way to weld the thin metal to the thick metal without cracking the glass or destroying the seal there.

I knew a guy who could weld aluminum cans together using a Plasma Welder, there's still a lot of heat involved though.

One of our welders has TIG welded Coke cans too. It helps to have that level of skill, but it doesn't mean you can reduce the heat in other situations. Where you have to weld is too close to the glass and the rapid heating would be catastrophic.

I thought about suggesting brazing using preforms in a programmable vacuum furnace, but I don't know if the phosphors would survive. I've done similar brazing in a hydrogen atmosphere, but it might react with the phosphor. I don't know enough chemistry...

John

JB Weld! heh, heh.

Or 3M Weatherstripping glue, that stuff is the most evil crap ever invented, it never comes off! :D