15GP22 needs a ride Indy to Windy City

[ohohyodafarted]

I'm still here KB.

During the summer time I spend as much vacation time as I can scrape together at our cottage in the last vestiges of the wilderness in the great northwoods of Wisconsin. Last week we heard wolves howling at the full moon at 2AM. That was a first for me.

I am going to test the 15gp22 I bought (the one under vacuum) tomorrow if time permits.

The 15g project is moving along. John Folsom and I have funded and ordered a new batch of stems to mount rebuilt 15G gun assemblies to.

I have perfected a method of removing the base sockets from the 15g without damaging the socket so that it can be reused on the rebuilt crt.

I have machined the tooling to EDM the old cathodes out of the 15g gun assembly using the EDM machine where I work. So now we can reliably remove the cathode assemblies from the 15g guns in preparation for sending the guns off to be rebuilt.

I have also been working (without much success) trying to develop a method to test the leaker 15g envelopes in an attempt to see if they can be sealed successfully with Vacseal compound. Early attempts have been a total failure using a laboratory grade vacuum pump and electronic vacuum meter I purchased for about $250.

I sopke to the former head of Rauland Picture Tube, and he told me that I needed to obtain a Helium leak dector if I wanted to test the envelopes for leaks. So it looks like we will have to obtain a Helium leak detector, which is a very expensive piece of scientific laboratory equipment. We need to pre-qualify leaker envelopes to make sure that they will hold a vacuum after we rebuild them. Because if they leak after they are rebuilt, we have wasted a lot of time, effort and BIG money if the rebuilt tubes fail to hold vacuum. So we need to be sure the envelopes are going to hold a vacuum before we attempt a rebuild. The envelopes have to be pumped down to a maximum of 10 to the minus 6 MM of Hg, and bathed in a shower of Helium while connected to the Helium leak detector. If there is a leak, the Helium atoms (because they are the second smallest atom known) will be sucked through the leak into the envelope of the crt and the Helium leak detector will be able to count the number of Helium atoms it finds in the vacuum stream flowing out of the crt. Essentially we are talking about a Helium mass spectrometer.

One of these units goes for about $25K to $30K new. I have located one in California that appears to be in relatively good condition, and at a reasonable price, but it still aint cheap.

Anyone have a couple thousand extra dollars they want to donate to the project to buy a Helium Leak Dector ???

That's all for now,
Bob

[ohohyodafarted]

OK KB here are the results of the test on the 15gp22 dud I bought.

On a scale of 0 to 1000 using a B&K 465 tester

Red gun is 20
Green gun is 10
Blue gun is 0 filiment is open.

Tube will need to be rebuilt as was suspected.

I bought it because it was under vacuum and was a possible candidate to rebuild. I already had 2 15gp22 duds that are full of air.

[andy]

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[kbmuri]

Agreed. Open blue filament means it's lost. 10-to-one says you could bring the red and green up to produce a bright picture though (albeit a yellowish one). While the tube is more valuable as another "Scotty run", in the meantime you could learn more about the 15GP22 and more about the Beltron restorer. I'd love to see it done...

[bgadow]

Very, very interesting!

I'm sure you've tried to get the blue gun to come back by tapping on the neck?

[ohohyodafarted]

Yes, tapping did not cause the filiment to re-connect.

I put it on the Beltron.

Cleaning method first.

Red gun came up to .20 ma cleaning light never came on
Green gun cam up to .75ma cleaning light came on very dimly at full voltage

Life test sucked big time on both guns.

Then I did the restoring method.

It acted very curious. Restoring current never came up as you usually expect to see but at full voltage I got the blue lights to flash and I hit the interupt button, and proceed with this 3 times as recomended in the manual. After the 3rd sequence I went back to test mode.

Red and Green guns both now reading about .25ma. I think the restoring method wiped out what little cathode material that was left.

So there you have it. This 15G is officially good for shit, and beyond all help except for a rebuild. This tube will be going into the oven on our next trip to Hawkeye along with one of John Folsoms bulbs. I am also going to rebuild an early production 21AXP22 which is still under vacuum, that goes into my 21ct55 at that time.

[andy]

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[kbmuri]

Yep, doesn't sound normal. I would never use the term "flash" when describing the blue-light action. If it had gone well, the blue lights would have slowly come up from dim to bright, over several seconds to several minutes. If they flashed, it suggests something arced over in the cathode-to-grid space. Catastrophically it sounds like. Oh, well, the Beltron can't fix everything. I'm very glad you tried, and thanks yoda for humoring us.

[WA3WLJ]

Yoda ,

How did you leak check your tube?
Did you cut the stem and attach your pump there?
THANKS,
Greg

[old_tv_nut]

I've made contact with Scotty, and plan to go ahead with attempting rebuild of the aired 21AXP22A. I'll start a new thread when news develops.

[John Folsom]

Wayne, If you do decide to take the risk and rebuild a leaker 21AXP22, you should buy a 1.5 oz. bottle of VACSEAL and have Scotty apply a generous coating or two at the glass-to-metal frit seal before he puts it in the oven. And there is still a good chance that it may leak even so. Have you asked around to see if you could find a DUD 21AXP22 still under vacuum? That would be a better candidate for a rebuild.

Thanks for the follow-up on the R-Y/G-Y demodulation. Guess you can't believe everything you read, huh?

Keep us posted on any developments with Scotty. Yoda and I are still planning another attempt at the 15GP22 rebuild later in September or October if all goes well.

[ohohyodafarted]

Greg,

I removed the base socket, and made a 1/8" hole in the copper pinch off tube. I inserted a capilary tube into that hole and soldered the connection. The capilary was then attached to a larger copper tube that connected to a shut off valve and then to the vacuum pump. The problem is in creating a system that is leak free, so that any change in the vacuum level is atributed to the crt and not the plumbing. My pump is capable of pulling 19 millitorr (that is .019 of a millimeter of Hg) but at those levels we continue to see a degradation of vacuum even when the crt is isolated from the pumping system. We tried many things but could not maintain a leak free plumbing system.

Best method is to use a helium leak detector which can measure the infiltration rate of Helium into the pumping stream. This is the method that is used at a crt manufacturing plant. It is the only method that will acurately measure the size and location of a leak.

Presently we have decided that instead of droping a bundle of cash on a Helium leak detector, we are going to take a leaking 15G crt and spend the money to do a rebuild on it. We will treat it with the Vacseal and another compound that I am now aware of through my conversations with a fellow who is very knowledgeable about leaks in vacuum systems. If the products we use fail to seal the leaks on a known 15G leaker, then there is probably no hope for all the leaker 15G's out there.

One of the reasons I wanted to use a Helium leak detector was because using this method a person can determine if the leak is in the area of the metal flange at the front of the tube, or if the leak is in the neck end where the pinch off and lead wires exit. I am hoping that we will be successful in sealing the leaker 15G, but only time will tell. And it may take a long time. We are talking about very small leaks. The kind that may take years to let enough air ento the tube to make it go bad. My bet is that we will be successfull initially on the leaker tube, and that it may be a long time until, if and when, it takes on enough air to go bad.

All that said, if we had a helium leak detector, we could determine the exact location where the leak is. If the leaks are shown to be on the neck end of the tube, then we don't have a problem, because when a new gun is installed, everything on that end of the crt is replaced with known good components. If the leak is located at the metal flange, we must depend on Vacseal and another product, to hopefully seal the leak. But these compounds are a big unknown. We have no idea how effective these compounds may be in sealing a leak around the flange.

[bgadow]

Could there be somewhere that would let you use their equipment long enough for a test-maybe load everything up and take it to their facility. Just looking for ideas. I would love to see this as a success. What other types of industries might use this equipment?

[ohohyodafarted]

I gather that Helium leak detectors are used primarily in very high tech industries, such as semiconductor foundrys, where equipment that utilizes vacuum sputtering equipment needs to be tested for leaks.

There are companies that will rent them for a fee of about $600/week. The problem is that special fixturing and plumbing would need to be fabricated in addition to having access to a Helium leak detector. And then there is the issue of the fact that not all of the 15G tubes would be on hand at one time for testing all in one batch. So the detector may need to be rented on numerous occasions. So it would be more cost effective to have our own unit on site.

But in any event, if we aren't successfull in sealing our first experimental leaker tube with Vacseal and another sealant product, then I would suspect there is no hope at all for rebuilding leakers. And then having a Helium leak detector would be of no use anyhow.

However, if we are successful in sealing our first leaker, then it would be interesting to locate the actual leaks in other tubes to see if they exist in the flange or in the neck end of the tube.

Time will tell and there is much to be done before we make the jump to light speed. The important part is that after 6 years of slow progress, we now are moving at a pretty good pace, and it should only be a mater of a few months before the next attempt is made at rebuilding some more 15G crt's.

When we have more news you can be sure that you will hear it first here on AK.

Bob

[old_tv_nut]

I'll take up the report on the 21 AXP22A and the CTC-5 HERE:
http://www.audiokarma.org/forums/sho...=124126&page=3