15GP22 needs a ride Indy to Windy City

[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.

[Combwork]

[QUOTE=ohohyodafarted;2069653]Greg,





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.


I'm fascinated by this but have zero knowledge so please don't jump up and down on me too hard if the following question makes no sense. If it can take years for a minute leak to let in enough air for the tube to go bad, are there any chemicals or metals that could be introduced into the tube during the rebuild that would react with any oxygen that finds its way into the tube and bind it? OK; I'll put this in to save you the trouble