The 15GP22 Rebuild Project

[ohohyodafarted]

As per the request of another member I am starting a new thread on the 15GP22 project here. I was not able to change the title of the previous thread, so if you havent been reading it here is the link to the thread that started this line of discussion........

http://www.audiokarma.org/forums/sho...d.php?t=173070

Combwork,
First off we are not sure of the leaks in the crt are small or large. Tha is to say we do not know if it takes a long time or if some tubes lose vacuum in a mater of days or hours.

A helium leak detector is used because helium atoms are very tiny. Much smaller than Oxygen or Nitrogen which compose the bulk of our atmosphere, and as a result the tiny helium atom can squeeze through a very small leak more easily.

As for introducing chemicals into the tube....that is essentially what a getter does. The barium getter flash attracts stray molecules left after the tube has been evacuated. This cleans up any stray atoms still floatiing around in the tube after it is evacuated and sealed.

The idea of having a chemical inside the tube to act like a sponge to abosrb the air that leaks in is a non starter. If there were such a chemical, when placed under vacuum the chemical itself would evaporate in the vacuum and the chemical molecules floating around in the tube would have the same effect as atoms of Oxygen or Nitrogen....IE: they would interfere with the flow of electrons from the electron gun and the electrons would never reach the phosphor coating on the screen of the tube.


CUlater:
The tube did get transported via the seller and another AK'r that both went to the same swap meet. The tube is now in my hands and we will attempt to rebuild it on the next trip to Hawkeye.

Bob

[MRX37]

It'd be sweet if the tube's design could be copied and new 15GP22's could be made.

Perhaps make the new 15GP22's out of glass. The most important thing is duplicating the wide gamut phosphors, right?

[Steve McVoy]

Such a project would be impossible. All we can hope for is to be able to rebuild the tubes, including the ones that leak.

[mr_fixer]

Hi, i posted this on the other thread before i saw that the topic had been moved to here, so here is a copy of it,

Somehow in the back of my mind i remember a device, that was a small handheld Tesla coil. It had a probe that you would move around the object you were leak testing. If there was a tiny leak the air rarefied would glow giving a indication of where the leak was located. I 'll look on google and see if i can find more information about the name of the machine and any pictures, Logan
P.S. I found it and the factory is located a few blocks down from the old E.H. Scott radio factory in Chicago, whodathunkit?
http://www.electrotechnicproduct.com/

[vintagecollect]

...

[MRX37]

Originally Posted by Steve McVoy

Such a project would be impossible. All we can hope for is to be able to rebuild the tubes, including the ones that leak.

With the computing power we have today, the technology we posess, you're going to sit there and tell me it's impossible to reverse engineer and clone a 15GP22? I say that's a load of BS. The only real obsticle I see is making the phosphors, but even that should be possible.

[mr_fixer]

making a precision shadow mask would be extremely difficult not to mention the glass faceplate with the alignment pins, the phosphors would easy compared to that, Logan "IMHO"

[MRX37]

If that stuff could be made in 1954, I think it wouldn't be too hard to recreate it today.

Scan an original shadow mask into a computer, and with a precise enough C&C machine, it could be duplicated. The same for the alignment pins

[mr_fixer]

IIRC shadow masks aren't made by machining but a photo etching system, remember RCA spent years and millions of dollars to make the machines capable of making 28800 tiny holes at a few microns accuracy. The face plates of crt's are cast glass with the alignment pegs cast in. You could check with Corning glass and see how much it would cost to have 1000 face plates and bells made on a low production run, but i would bet it would over 400 bucks apiece. In Huntsville Alabama, Western Electric is making new 300b electron tubes which are about 1/100 of the difficulty of a color crt. I think the cost is around 80 bucks per tube to make, before profit. I could be wrong, Logan

[ohohyodafarted]

Steve McVoy is correct. Making a new 15GP22 is out of the question. It would be cost prohibitive. And even if cost were no object, the formula of the old full gamut phosphors is problably long ago lost in some long forgoten RCA archive, and you would be forced to use current phosphor formulations, negating the mystique of the 15GP22 color dynamics.



On to another point just to illiustrate the issue of cost effectivness, I would like to take a pole.

I would like to get a feel from current 15gp22 owners on how much they would be willing to spend to have their current dud 15gp22 rebuilt.

I have started another thread to get input from all of you 15gp22 owners

Bob

[Tony V]

As we all know, to recreate an original 15GP22 would be too costly. But one thing to remember and concider is that the same new technology and compounds we have now can also be used to make a more leak proof bulb while still using the original crt's parts. It sounds like the guys have the gun replacement situation under control now which was a major undertaking on its own. Now its just the matter of getting the leak problem solved. I commend all who are envolved in this project and am glad there is at least some hope now to save the 15GP22. Not only will this benefit the 15GP22 owners but also help the owners of other metal/glass crt's in the future. Hopefully down the road, electrostatic crt's and other rare crt's like the DuMont 30 inch crt can also be looked into. Good work guys!
-Tony

[Sandy G]

Just because we're more "advanced" than they were in '54, doesn't mean we can easily duplicate what they did. Witness the new moon program-They're talking 10, 15 years to do it, when in the '60s, they did it in 8...& there were hardly any "computers" as we know them now to help. In fact, I think I read that if they tried to duplicate the Apollo program nut for nut, bolt for bolt, it would take even longer than "starting from scratch".

[eberts]

You guys are dreamers.
The tubes could be made if there was a high demand profitable market.
There aren't going to be any tubes in the future, the industry has evolved.

[old_tv_nut]

Originally Posted by mr_fixer

Hi, i posted this on the other thread before i saw that the topic had been moved to here, so here is a copy of it,

Somehow in the back of my mind i remember a device, that was a small handheld Tesla coil. It had a probe that you would move around the object you were leak testing. If there was a tiny leak the air rarefied would glow giving a indication of where the leak was located. I 'll look on google and see if i can find more information about the name of the machine and any pictures, Logan
P.S. I found it and the factory is located a few blocks down from the old E.H. Scott radio factory in Chicago, whodathunkit?
http://www.electrotechnicproduct.com/

This is the device I was trying to describe that Scotty used to examine the aired 21AXP22A.

[zenith2134]

Impossible's not the word. Its hard enough to manufacture small signal tubes the same way these days!

Rebuilds are the only route..... If I ever get a CT100 it would be amazing to have a good CRT at hand.