Hey folks, this list sure has been quiet lately.
I'm restoring an Amray 1200 bench-top SEM, and my attention has turned to the vacuum system. The instrument has been down to air and stored in a garage for 20+ years.
I have some experience with vacuum, but not much.
With all of the valves closed, pumping with a rotary pump against about half a meter of the internal plumbing, I can get down to about 20 millitorr repeatably, if the TC gauge is to be believed. It took about a day to reach that point, but now I can get there from atmospheric pressure in a minute or so. I presume that was adsorbed water.
Now I'm opening the roughing valve and trying to pump down the column and chamber. This significantly increases the volume of the system that's being pumped, so I'm expecting days of getting rid of the water. But, leaving it running overnight last night, it didn't budge from ~220 millitorr. I assume there's a leak.
Hunting around with my cheap-but-functional ultrasonic leak detector, I've found that there's a big ugly wax seal at the top of the column where the filament and HV leads enter the electron gun assembly. See attached photo. (if this mailing list is set up to allow such attachments) There's a significant leak right there, which changes as I massage that gloopy waxy stuff around.
I think that wax may have deteriorated with age. It's pliable, but it doesn't seem to adhere very well to anything, including the wires it's supposed to create a seal around.
Does anyone know what this stuff is, where I can get more (that I can afford), or in general have any other thoughts or advice about this?
This is a stately instrument that's in really good shape, all things considered, and I'd love to get it running again.
Thanks,
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
Dave McGuire
