More on purchasing the SBT-11A

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4 years 10 months ago - 4 years 10 months ago #3470 by Sonarflash
This has been mentioned, but here goes again. Over the past few years, I've purchased 5 SBT (CNT) tubes from Sovtube. 4 were the SBT-11A as advertised. As it turns out, thanks to ChrisLX-200, 1 of the tubes is actually the SBT-11 (BG- beta gamma sensitive), not the 'A' alpha sensitive version.
These tubes looke identical, and both designations have the rectangular mica window. Perhaps the mica window is thicker on the non-alpha version? This SBT-11, not 'A', turns out to have four rods/wire anodes, not 3 as I previously thought. Perhaps it is the SBT-11A which has 3 anode wires. I'm just a bit bewildered.

If interested, look for a future post as I'm going to do a comparative alpha sensitivity test with the SBT-11A and SBT-11 tubes.

I Googled and John Giametti, Brohogan, has a post on the SBT-11A. He also mentions a caution when purchasing, as some of the non-alpha versions have been advertised and sold as SBT-11A's.
Last edit: 4 years 10 months ago by Sonarflash. Reason: I made a mistake about the number of anode wires.

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4 years 10 months ago #3472 by ChrisLX200
I'll look forward to seeing your results. I can't think of anything other than the thickness of the mica window that would affect sensitivity to alpha particles, the key will be differential sensitivity comparing the two different versions.

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4 years 10 months ago #3473 by Sonarflash
My apologies. When I hooked up the SBT-11 (not 'A'), it was immediately in avalanche. Somehow, without realizing it, I must have damaged the tube months ago. 400 VDC kept giving sporadic, high counts. So, since that was my only non-alpha tube, I can't run a comparison. Instead, I broke the mica window and cleaned it away. I'll get my son to measure the anode rods, their diameter and spacing. Also, the gap between rods and cathode sheet.
I'll also attempt to take photos and post them.
Brian

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4 years 10 months ago - 4 years 10 months ago #3474 by Sonarflash
This gets more and more confusing! I had my son examine the insides of the SBT-11 after deliberately rupturing the mica window. After all, the tube was unuseable. I cleaned away the mica. He said the three rods were not as I assumed. I used my talking multimeter and the rods seemed to be connected to the ground pins instead of the anode pins. So, I pulled up the rods from the end opposite the anode connection pins. Nope, they are connected to the anode pins. Go figure. For a while I was certain the arrangement was backwards. The three rods are actually three thin wires, about #18 or #20 gauge. There also appears to be other wires beside or below them that are cathode lines that that go to the ground pins. I'm not certain if this is only with the SBT-11, with cathodes being parallel wires.

Since I can't see it, or get a good feel with a probe, I'll leave it to others to figure out the structure.
Last edit: 4 years 10 months ago by Sonarflash. Reason: Change wire gauge

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4 years 10 months ago #3478 by Sonarflash
Did some editing. And, as I mention, I'm bewildered. A previously damaged SBT I'm certain, had 3 anode wires. Well, this SBT-11 non-alpha has 4 wires. I got confused until I pulled one end of the array up with pliers. Two of the wires seem to be common to the centre anode pin. About 6 to 8 megohm resistance between the others.
Maybe you can figure out what it looks like from the pictures? One seemed low-res, so I tried a second after getting my son to adjust the camera. On the web site it shows my first attachment as 25K, but on my computer, it is 450k. The second had a file size of 3000k.

My son says this SBT-11 has four channels of 1 piece of folded sheet metal. Near as I can figure, these four anode wires were slightly recessed in the channels. I'm pretty sure the other SBT that I ruptured a couple of months back had only 3 anode wires. Perhaps that one was an SBT-11A?
Regards
,

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4 years 10 months ago #3479 by Sonarflash
Addendum. The outside two channels seem wider than the inner, central two channels. Again, another curiosity in the design.

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