My Pirani gauge tube (Fredericks brand Televac) burned out last week, so I went to eBay. A kind seller had "two." One was used and the other had no visible signs of use. The price was good, and I bit. The used tube worked fine. The "new" tube didn't. In fact, when tested for pinout, it was completely different. A slight twist of the brass end unscrewed. I had never seen a Fredericks Pirani gauge tube that could be opened. There was an O-ring seal, a ceramic PCB, what looked like an IC, and one pin was soldered to a brass tube (see attached picture).
My guess is that someone at Sandia (Albuquerque) used a new Fredericks Pirani body to make something different, like an ion gauge. I could find no evidence of a filament, though. The quality of the machining is very nice, so I am assuming a professional instrument shop did it. The seller is in Santa Fe, NM, and I have asked him whether he got it there.
Any ideas what it is?
John