SBT-11A GM tube

Very interesting. I don't think it is a case of one version being sensitive to alpha and the other not, perhaps more a case of a difference in sensitivity. That difference may be small or large and that is the part which is unclear. Alpha's barely penetrate through a layer of dead skin so naturally the mica window has to be very thin indeed and small differences in thickness could have a big effect on transparency to alphas. As I mentioned, of the two I ordered, if I receive one with the 'A' mark and one without I will be able to compare them using the radiactive sources I have, I will use the same detector for both tubes of course. It will be a fun experiment to do.

ChrisH

I decided to go for a walk. Unpacked another of my Sovtube SBT-11A tubes. Had two different sighted store clerks take a look.
On the back in black or dark blue this other tube has "S'B'T-11A", the 'B' being a syrilic combination of an S and 5. This tube has no designations on either side.
The previous tube I mentioned has no designations on the back, on the square block at one end of the SBT-11A. The "back" being the side opposite the mica window, where the 3 anode pins and 2 ground pins protrude. Yikes! Sometimes I get detailed like this because sighted people have often written me with connector directions or descriptions that become meaningless. Once, it was for connections to a detector: left to right, ground, positive VDC, signal out, signal ground. Now that looks/sounds fairly simple, however, it depends on which way is up and which way is right. As it turned out, he meant left to right with the pancake window facing up and on the right. So, signal ground was nearest to the pancake...

I digress. So, obviously, of the three currently intact SBT-11A tubes, two are different. One is inside a plastic project boxwith an SS mesh. If I feel ambitious, I'll open the box, and get somebody to look at the back of the tube. Right now, I'm going to relax and sip on the cream soda I bought at the corner store.

A good idea to protect these SBT-11A tubes in a box because they are very fragile and prone to their mica window being broken. There is a design on Thingiverse for a 3D printed external probe, I've printed that out in ABS but I'm not overly impressed with the result. I may either create my own design or simply mill one out of a billet of aluminium. I also have some fine phosphor bronze mesh which will do nicely for the front face. I also purchased from RH Electronics a high voltage geiger probe driver with TTL output and that will allow the tube to be mounted remotely using a long (>5 metre) wire. Using this the probe can sit outdoors with the detector staying indoors.

ChrisH