Early Television Museum
15GP22 Rebuild by RACS
This is the 15GP22 that was in the museum's warehouse for several years. Since it was in such bad shape, it was assumed that it could never be rebuilt and no effort was made to protect the interior of the tube.
The tube after rebuild, before the base was installed
The frit glass
A photo from the screen. Though there is some minor damage to the phosphor due to the way in which the tube was stored, the large spots in the picture are because the safety glass was not cleaned before the tube was installed.
Here is a description of the installation of the tube at the 2010 Convention by Dave Abramson:
The RACS tube has been working for almost 18 months now. John Folsom and Bob Galanter have decided to send three additional tubes to RACS for rebuilding. However, there is still a problem to be solved before the tubes can be sent. RACS solved one of the leak problems using frit glass. However, there are still leaks between the pieces of the metal ultor ring. At the 2011 convention Bob demonstrated a helium gas leak detector, which he has been using to test tubes. Here is his latest report on progress (August, 2011):
As of a couple months back John and I have had specially designed cartons for holding the 15GP22, fabricated by a local container company. We have also had a specially designed wooden crate built, that complies with international shipping regulations for wooden crates, and which will hold 4 of the tubes in their inner corregated cartons. The crate weighs 280# and is about 38" by 38" by 35" Roughly one cubic meter. We intend to probably send the crate via ocean vessel for cost effectivness.
About 6 weeks ago John Folsom came up to my place in Milwaukee for a week's visit. Before he came up, he shipped 4, 15GP22 duds from his hoard, up to my place via Grayhound bus. They were shipped in the specially designed corregated continers we had made up and they all arrived in great shape.
So when John got up here the goal was to do some leak testing of the 15G duds we have laying around just to see where the leaks are located, prior sending them off to RACS in France. We prepared the tubes by using our home brew rubbber masking technique and sand blasted the ultor ring and about a half inch of the glass adjcent to the ring. Then we used our mass spectromenter helium leak detector to test the duds and locate the leaks. We expected to find that most of the leaks occured where the glass is fused to the ultor ring. We expected that because you can see fractures in the glass in that area on almost all of the tubes. That is NOT what we discovered. What we discovered was that every tube had at least one leak on the weld of the ultor ring, and most tubes had two or more leaks on the weld. We only found 1 or 2 leaks that were caused by fractures in the glass, in the entire batch of tubes we tested.
This presents a big problem. If we send the tubes off to RACS to be rebuilt, and they apply frit glass where we suspected the leaks occured in the glass to ultor ring fusion area, it would do no good with respect to sealing the leaks that are in the weld. The question was, "what do we do now"
During the process of doing the leak detection we also encountered the same phenomena that we experienced at the convention, to be specific, we found that if you rub your finger over the leak in the weld, the grease on your finger will seal the leak temproarly. That got me to thinking about what we could use to seal the leaks on the weld. At one time I was in the electroplating business. We had a pretty good sized opperation. One of our processes was Nickel plating. Nickel plating is a very interesting process. It is "self leveling" and very smooth and even and shiny. It is used under almost all decorative plating process because of this. I thought nickel plating may be a good way to seal the weld leaks. We contacted John Yurkon as MSU and bounced the idea of of him. John thought it would probably work.
What we needed was a small plating shop with a highly experienced plater who could do nickel plating. I know of such a shop, and last week I stopped by with a 15GP22 and spoke to Tony about what we needed to do. We went back into the shop and measured up his nickel tank. We are in luck, his tank is large enough to accomodate the 15G. Tony will need to devise a larger tank to "activate" the surface of the ultor ring, prior to doing the nickel plating. The activation is sort of like electro plating in reverse, in that you etch the surface of the metal with electrical current and sort of "de-plate" it. Prior to activating the surface of the ring it is in a state known as passive, and it will return to the passive state in about 30 seconds after it is removed from the activation tank. So you have to move from the activation tank to the nickel plating tank quickly. If you try to plate a passive metal surface, the plating will not adhere properly and it will flake off.
In order to do the plating, I am going to have to design and fabicate a special plating rack that will hold the 15GP22 while it is in the tanks. The rack will be fabricated from 3/8" hot rolled steel rod welded into the proper configuration, and then coated with plastisol, which is the type of plastic coating you find on the handles of good quality pliers, wire cutters etc. It is a hot dip process. We coat the rack with plastisol because it has to be insulated electrically from the current in the plating tank.
So the next step is the fabrication of the plating rack. After the rack is completed Tony will give one of our 15G's a trial run and atttempt to plate it. We will only be plating the outermost 1/4" of the ring. The rest of the ring will be coated with a "masking" compound that you paint on to the surfaces that are not to be plated. After the plating is finished, a solvent is used to disolve and wash away the "Masking" compound. If the plating is successful, we will leak test the trial tube and if it no longer has leaks along the weld, we will plate 3 more tubes and then send them off to RACS for rebuilding.
I figure this phase of the project will probably take about 8 more weeks. If nickel plating dosen't resolve the weld leaks, we are back to square one.
The obvious question everyone is asking at this point is probably "why not just re-weld the leaks" We thought about that too. We are of the opinion that there is no way to be certain that we have located all the leaks on the weld. In order to be certain that we have located all the leaks it would be necessary to re-weld the entire circumference of the ultor ring. John Yurkon has a highly skilled welder at MSU that can do this type of work. However that introduces another issue. The heating of the ultor ring during welding, risks introducing additional fractures in the glass due to the heat of the welding process. Additionally, there is no guarantee that welding the entire ring, won't actually introduce more leaks than we started with. At best it is an iffy proposition to try and re-weld the ring.
From what we can tell, it looks like RCA started out welding the ring with some sort of manual process. Some of the tubes have very uneven welds that look as if they may have been welded by hand. Later on RCA used an automatic welding apparatus that most of us have seen in the photograph of the 15G being welded. That process produced a nice even uniform weld that we see on most of the tubes. But still those tubes welded with the automated process also leak.
So keep you fingers crossed that our latest concept for sealing the weld leaks is a success. We will update the group after we find out how it all works out.
I think this whole saga of the 15GP22 can be best summed up by the phrase, " if you throw enough crap against the wall, sooner or later something is bound to stick" we are hopeful that we are getting near the "sticking point"