[John Folsom]

OK, let's all calm down. Take a deep breath.

We are not in competition with RACS, if they can rebuild 15Gs more cost effectively than Scotty (factoring in shipping costs in either case), then I will be the first one in line to sign up for their services, regardless of how much $$ Bob and I have poured down the rat-hole :-).

As for the leak detection, here is a sketch and photo of the cross section of the 15G flange seal. There are 2 glass to metal seals, and 3 (!) metal to metal welds, any one of which can be the source of the leak.

Bob and I speculate that the leak is most likely at the metal-to-metal welds which join the flat metal pieces together, though we have no science to back this up.

It is not obvious to me that the HV needle probe technique would work here. As John Yurkon points out, the metal in the flange would be at the HV potential and attempting to needle probe would not work.

As for the top secret leak sealing protocol, it is not a secret, I have discussed it with others, and the materials used are common knowledge in the industry. It may work, it may not (I am not quite as optimistic as Bob, for reason I will not go into here). Certianly RACS would be aware of our approach, and has likely rejected it for the same reasons that make me a bit dubious. But it is worth a try, I may be wrong (I often am!)

And frit glass is another approach, and at some point we may attempt this as well.

But for any sealing protocol to work, what we really need a way to locate the leak so it can be addressed directly. If the HV method can be made to work, that would be optimum. Helium leak detection is another possibility, but it requires expensive equipment, vacuum pumps and mass spectrometer.

BTW, I am sure some of you are thinking "VACSEAL!" After discussions with several people in industry working with ultra high vacuum systems, there seems to be a consistent opinion that VACSEAL will not be useful in this appplication, so we have abandoned thoughts of attempting to seal leakers using this product.

When Scotty recovers and starts rebuilding tubes again, Bob and I are ready to make another attempt using a non-leaker tube and our new and improved stems.

Good luck to us all!