SBT-11A GM tube

I've mentioned this tube in another post. Purchased from Sovtube, I have a few of these tiny, rectangular, mica window alpha detectors. Brohogan had one post that listed them operating at about 60% of the LND7317 pancake. That sounds pretty impressive. For those who haven't played with one, they operate well at the standard 400 VDC. I have tried different configurations when it comes to connecting anode resistors.
This tube has a group of 3 anod pins at one end of the rectangle, 2 ground pins in the middle, and a plastic/bakalite block at the other end.
I've tried using pin clips from a broken 9 pin vacuum tube socket and solid wire wraps. Either works. I've tried them with 3 separate 10 megohm anode resistors, one to each of the three pins. I've gotten the same results with all three anode pins wrapped common and connected to one (1) 10 megohm resistor. These tubes are very sensitive to alpha, beta and gamma radiation sources (sorry, no scientific specs).
At present, I have one on the bench with a simple SS mesh rectangle folded at the long edges to protect the rectangular mica window, held to the tube with a wrap of vinyl electrical tape. At present, I have 2 10 megohm resistors connected to each of the 2 ground pins, leads common, and connected to a GK+4 GC made by Atomic Dave. That configuration works just as well as having 1 or 3 anode resistors.

I've broken open a defective SBT-11A and torn out the guts. Inside are three separate anode rods parallel and lengthwise. Beneath them is an interesting, rectangular, curiously folded metal sheet to form a common ground/cathode. I don't know why the Russian engineers used two cathode/ground pins. Maybe to insure good connections if this unit went up in a satellite?

Each of the three anode rods is independent however. This may provide some means of comparing alpha particle strikes. Again, I don't know. Best to operate with all three connected to provide maximum sensitivity.
This tube is extremely robust, as with many of the Russian Soviet era tubes. One of the SBT-11A tubes I purchased from Sovtube was defective. They sent me a good replacement within a month without my having to ship the bad tube back. Another tube developed problems after I accidentally reversed-biased it at 400 V. Ouch. Strangely, it still works, but is hyper-sensitive and reads double the background of my LND7313-3 (Aware Electronics RM-80) pancake detector.
At $30. US, this tube is a bargain if you want an alpha sensitive mica window GM tube.

Interesting observation. I'm not entirely certain the tubes sold by Sovtube are the SBT-11A variant though, the ones that definitely are SBT-11A appear to have the 'A' printed on the back in the same dark-blue dye. Do you have a photo of the rear of yours? I do have one on order from them which I will check out when it finally turns up (after a week still no indication it's actually been posted to me!). Either way, these tubes are still good for beta & gamma monitoring.

ChrisH

Hi Chris
Thanks for the feedback on this.
I'll try to get somebody sighted to check my tubes for the letter 'A' you mentioned. I'll also get help making a decent photo and post it here ASAP.
Regardless of their designation, the rectangular mica window is quite thin and the tubes I have are extremely sensitive to alpha sources. The usual 241Am smoke detector buttonsmake the detector scream, until I interpose a sheet of printer paper. Then, I just get the usual gamma. They are, as you mentioned, also very sensitive to beta and gamma sources. One of these days I'll have to take some calibration readings with my 137Cs source. But, right now, I'm getting packed for a big move to a grandpa suite in my sons new house. That will occupy me most of August and September.
Regards, Brian, VA7BDG

Just an hour ago I received confirmation the tube from Sovtube has been posted to me so now I just have to wait for the postal service to get it to me.
Can you say what your Cs137 source consists of? I have heard some spark gap tubes contain a small amount ( less than 1 micro curie).

Thanks for your response Brian, and good luck with the house move.

ChrisH

Hi Chris,
My Cs-137 source is a small piece of glass that came from a TG-77 radar spark gap tube. It is about 30 years old, but still has a potent 662 keV spectroscopic signature. Can't remember how many CPM off the top. This one came from a rad science/geologist friend in New Mexico free+small shipping charge. The tube dropped, hit the floor and broke. So, I was busy picking up and vacuuming glass fragments for a while. Checked each part and particle for radioactivity. The spark gap metal was mildly contaminated, but the main hot spot was the 137Cs coating spot on the inside curve of the glass under the radiation symbol. That had been directly opposite the ball-shaped electrodes. My son helped me visually confirm the spot/symbol.
I've 'seen" (JAWS screen reader) some tubes listed on Ebay, but usually very expensive/overpriced.
If you find any, let me know. I'd like to get an intact tube.
Regards, Brian

Okay, I got a neighbour lady to look at one of my SBT-11A tubes (from Sovtube). It did not have a blue letter 'A' on the back. it had several letter designations. One was G'S'-11, the 's' likely a syrilic 'B' for beta.
Interpreting the 'S' as 'B', There was also what may have been BGT-11 stenciled on the side.
I find this lack of alpha designation curious, since these tubes are extremely alpha sensitive. No matter, so long as they work.

I don't have a small Braille ruler, so I'm guessing the mica window at 1.5" by .75", or approximately 1.1 square inch. There was also a manufacture date of 1981.
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