An interesting (if useless) find

[Dave S]

[Dave S]

The guy I got it from thought that the blackening on the glass near the socket might be good getter indicating that only some air had gotten in. I'm not sure what that darkening is (Edison effect?) but that's not where I'd expect to see getter material and the condition of the "real" getter would indicate that the vacuum is completely gone.

[wkand]

I am assuming that this tube has a metal cone and glass face, similar to the 15G. Also, that this seal would be the likely cause of going to air.

Correct?

Forgive me for not remembering, but would this tube be a possible rebuild candidate, if that ever happens at ETF?

[Dave S]

Originally Posted by wkand

I am assuming that this tube has a metal cone and glass face, similar to the 15G. Also, that this seal would be the likely cause of going to air.

Correct?

Forgive me for not remembering, but would this tube be a possible rebuild candidate, if that ever happens at ETF?

John Folsom had said:

Originally Posted by John Folsom

The 15HP22 unfortunately has the same envelope construction as the 15GP22.

Therefore the big problem in dealing with the welded flange is the same on this tube.

The difference is the screen. The design of the 15G apparently makes it susceptible to problems during the rebuild process. According to miniman82, the mass of the screen inside the 15G makes the ramping of heat during the rebuild process a pretty ticklish affair. This tube has a conventional screen, so based on what I've heard from the experts, I'd guess the 15H would have a greater likelihood of a successful outcome. As long as the leak problem can be solved. Nick? Jerome? Bob? Steve? Please correct me if I'm wrong.

[miniman82]

Dave, I think that's correct. The internal design of the 15H shares more in common with the 19V and 21AX than it does with the 15G, though any rebuild attempt on any tube seems tenuous at best these days... I tell ya, these next 7 years can't go fast enough!

[Electronic M]

Originally Posted by wkand

I am assuming that this tube has a metal cone and glass face, similar to the 15G.
Correct?

Wrong, but close. The 15G has a glass cone(and I'd assume it is the same for the 15H). The face of any color tube is attached to the cone fairly late in the manufacturing process because the shadow mask has to be installed and before that the screen has to be coated in phosphor....Neither of which is practical with the screen bonded to the cone. It would be like building a ship in a bottle.
The thing is that if they heated the glass enough to fuse it would burn the phosphor and warp the shadow mask. To deal with that issue they built the cone and face with metal rings bonded to the glass where the two pieces of glass would have normally have been bonded to eachother in a monochrome CRT. They would then phosphor the screen, insert the the shadow mask then seal the face to the cone by using a special low temp welder to fuse the metal rings together.

The rings were soon done away with in favor of low melting temp 'frit glass' which was much less leak prone then the metal to metal and metal to glass bonds of the rings.

The only metal cone CRTs I'm aware of are the pre-15G developmental types (the 4 digit designations of which escape me at the moment), and the production type 21AXP22.

All metal cone(and tubes with metal to glass seals) CRTs were very leak prone and not long after they were developed they fell out of vogue because of that.

[earlyfilm]

Originally Posted by Electronic M

The face of any color tube is attached to the cone fairly late in the manufacturing process because the shadow mask has to be installed and before that the screen has to be coated in phosphor....Neither of which is practical with the screen bonded to the cone. It would be like building a ship in a bottle. to metal and metal to glass bonds of the rings.

You know, it is always easier to see someone else's mistake (RCA) than one you (CBS) made. I had always assumed that Goldmark's Laboratory made the first 15HP22's the RCA way and by doing so, quickly realized that there was a better way. However, looking at the patent, we can see that it was filed June 1, 1953 (and granted Sept 28, 1954), so Dave's April 24, 1954 tube is obviously manufactured well after the patent application.

http://www.freepatentsonline.com/2690518.pdf

The "engineering sample" notation may also have been for legal reasons to protect the CBS patent.

This difference probably explains why even though the 15GP22 and 15HP22 were mostly interchangeable, they got a new tube number.


This patent expired in 1971 and CBS thanked Goldmark, by shutting down his Laboratory in 1972.

James

[old_tv_nut]

Originally Posted by earlyfilm

This difference probably explains why even though the 15GP22 and 15HP22 were mostly interchangeable, they got a new tube number.

James

Might not be usable with the same bezel/safety glass, or with the same convergence circuits/components, therefore had to have a different number.