Why the preference of the SBM-20?

[NGinuity]

Hey Jeff,

Just wondering why you prefer the SBM-20 over the other tubes that might be used in your design. Any loss of functionality by using others? I notice they are glass in nature, but can't seem to figure out the differences otherwise besides form factor.

-Eric

[mightyohm]

Hi Eric!

The SBM-20 is quite sensitive, operates at a relatively low voltage, and is fairly inexpensive. So it was a logical choice.

Note that I designed the kit to work with other tubes as well. By moving the right clip, you can use the kit with the SI-1G and SI-3BG soviet tubes:

SI-1G: Roughly comparable to the SBM-20 in terms of sensitivity to the sources I have, same voltage, glass envelope.
SI-3BG: Very inexpensive tube that is very insensitive - it is intended for use in highly radioactive environments (up to 300R/hr!!)

Different tubes will have different characteristics. Small tubes will usually be less sensitive, since they have a smaller cross section. Some tubes have a mica window that makes them sensitive to alpha particles, but these are quite expensive (best example here in the US is the LND-712, which costs around $100). Some tubes require a very high bias voltage, around 1000V.

The kit should work with other tubes that operate between 300-500V, although I haven't experimented much, as my access to tubes is limited. In some cases, minor component changes might be needed in the tube bias and pulse detection circuits, but I encourage you to experiment and report back with your results.

Out of curiosity, what other tubes are you interested in using with the kit?

[NGinuity]

Well, really, I was just exploring the other tubes you've designated on the board in the course of learning. I want to build a few of the units as is, but I'd really like to design (or see one designed) a board that would fit inside of the footprint of an Altoids tin (I have a friend who shipped me 500 cans after realizing he was addicted, and I've been using them for everything since). The problem I am running into with my idea is that at over 4 inches, that SBM-20 doesn't really fit into that 3.5" side to side requirement for the Altoids tin. So this got me thinking about the length/usefulness tradeoff and what other alternatives I might be able to find.

By the way,that's a pretty cool idea of using the 555 timer to drive your switching power supply timing! I've never needed to do a small supply voltage that high, so it was a pretty refreshing deviation from the usual switching power supply designs I see.

[peterloron]

Altoids tin will be a bit tough, but there are some small tubes out there. Be sure to check the specs before you buy, though. Some of the small ones (like the SI-3BG are not very sensitive). May of the US geiger tubes operate at around 900V, so you'll probably want to focus on the Russian tubes as most of them seem to operate at about 400V.

This page points to specs on the SBM-20. The site has lots of specs for other Russian tubes as well.

http://www.gstube.com/data/2398/

-Pete

[NGinuity]

I had come across the GStube website already, and I agree, it's a excellent reference. I agree that the SBM-20 is the ideal candidate, but I was just hopeful

[peterloron]

There are some very small GM tubes out there. The SBM-10 is pretty small and may be a good choice for an Altoids build.

[mightyohm]

Electronics Goldmine carries the SBM-10.

http://www.goldmine-elec-products.com/p ... ber=G18400

It should work with the kit, but I haven't tried it. It would be perfect for an Altoids tin-sized version of the kit.

[NGinuity]

Awesome. Let me draw something up and get a dorkbot order in and I will report back my findings!

Question, I assume that the second contact goes on the large flat surface on the backside of that tube, correct?

[mightyohm]

Yep! That's the cathode (negative) terminal.

[atomic.dave]

If you don't mind, I'd like to chime in. I have experimented with quite a few tubes as I have built a few kits ranging from an arduino DIY from John G (Brohogan) which I think this kit is real similar to. And also a chaney kit- the C6981digital geiger kit with LCD. If you are looking for a smaller tube that is lower in voltage, and decent in sensitivity, might I recommend the Russian SI-29BG tube. Here are the specs:

Operating Voltage 360-440v
Intitial Voltage 250-320v
Recommended V 400v
Plateau Voltage 100v
Length 55mm
Diameter 11mm

They claim that it is more sensitive than the SBM-20, but with its small size, it didn't seem to be more to me. But It is definitely more sensitive than the SBM-10. Plus it has two prongs (anode and cathode) on the end for really easy hook up. Available on epay for around 20-30 bucks.