The current situation on GM tubes - Some thoughts. Fake tubes?

It seems of late that getting hold of good GM tubes, for reasonable money is a thing of the past. A single SBM-20 on eBay is going for in excess of £150 ($182) and there are hardly any suppliers left for them. Some years back I paid about £13 for a NOS SBM-20. I wish I had the nous back then to buy a large stock of them. I'd have made good money these days! eBay used to be awash with good GM tubes. Lots of regular types, SBM-20, STS-5, LND-712, SBT10A, SBT11A, pancakes, a bunch of Mullard and then a load of quite exotic tubes. Today there is hardly any of those and is covered with cheap Chinese glass walled tubes. The cheapest SBM-20 I can find now is £52 ($63) from Amazon with just 15 left in stock. I think the Russia/Ukraine war has most certainly had an impact on the GM tube market. Not necessarily all due to people buying them up but I heard on the grape vine that people just can't get to their stocks in Ukraine due to the war. With low supply and demand high the price for the remaining stocks has skyrocketed. Brexit in the UK also had an impact on the UK supply, but despite having to pay a little more for parts, I never really had an issue with getting parts from Europe/Ukraine/Russia until the war. Some people simply refused to ship to the UK after Brexit, such as BroHogan, which is a shame, but completely understandable for small suppliers.

There are some new(?) SBM-20-1 on eBay for between £30 and £40 each, but I could only count 3 available. I have never seen these until recently. They look like the SBM-20-U with a missing end cap. There are also some SI-22G tubes left for around £38 on eBay . I have three of these (one on test right now) and they are excellent gamma (a bit of hard beta too) tubes that suit background monitoring. If anyone knows of a good supply of decent tubes for decent money, please let us know.

It's not like there are no tubes at all left though. The Chinese are busy flooding the market with glass walled tubes. It looks like going forward these are going to become a lot more prevalent in the future. The J305y is all over the place. This tube is OK, I guess, but for me it just doesn't quite compare to a SBM-20. Some, but not all(?) have issues with UV light. I have one that is labelled J305yb. I don't know if this has more sensitivity on the J305y, or if it is just a labelling thing. In my testing of my J305yb I found that was a bit more erratic than the SBM-20, and slightly less sensitive. It would tend to spike up a few CPM when other tube nearby wouldn't. This could be interference or some kind as I do have a lot of (electronic) stuff going on. My J305yb also suffers with UV light interference. I think these may be better with a very very thin layer of aluminium foil over them. I think that would be worth testing. I also have a M4011 glass walled tube. Very similar to the J305, but slightly better I think as my M4011 is not affected by UV light. If these types of glass walled tubes are what we have to use, for cheap, then we may have to get used to their quirks.

It also seems the are some fake/counterfeit GM tubes starting to hit the markets. I noticed this first hand when I bought a FS2011 counter from AliExpress. The tube had no markings on it whatsoever. The tube was soldered in to the clips in the counter with big globs of solder and took some heat to remove it. In doing so both end caps came off really easily. Too easy. The tube still works, but is a pain to connect up now. I don't know if this is actually counterfeit, but a side by side comparison with a J305yb shows some differences inside. The anode is longer in the counterfeit (I'm going to assume it is, for the sake of writing) and the glass holder is smaller than the proper one. The counterfeit is also about 0.5mm thicker. I can't measure the length as the caps fell off.

You can see some subtle differences inside the tubes. A full res image is here.

Today I fell across what appears to be a fake/counterfeit LND-712 for around £100 on AliExpress . It looks like a proper LND-712, but has no markings on the tube. This is what prompted me to write this post.

And this was the first image I saw of it in the search list (I was searching for 'geiger tubes')

I have a couple of these tubes. One in my Gamma Scout and one loose. Both have good prominent markings on the tube. This is my loose tube:

The proper manufacturers website for the LND-712 is here: https://www.lndinc.com/products/geiger-mueller-tubes/712/ It is worth noting the image on LND Inc's page is the same as the search listing image on AliExpress, and seems the specs are images captured from LND's website. The seller on Ali Express is called 'GM World'. If these were from LND themselves, I'm pretty sure the seller would be something along the lines of 'LND Inc.' There is some good info about this tube on the PocketMagic website here: https://www.pocketmagic.net/tube-lnd-712-end-window-alpha-beta-gamma-detector/ .

I would be very very interested to get my hands on one of these counterfeit LND-712s, but I'm simply not paying £100 for it. I paid around £70 for my LND-712 some years back. I had intended on building a Gamma Scout type counter but never got around to it, then bought a Gamma Scout, so never really used the tube.

Its a shame it has come to this where there appears to be fake/counterfeit GM tubes on the market. Probably due to the low supply and high demand of GM tubes and the demand is probably down to the Russia/Ukraine war, and the fact that when the Chinese see an opportunity to copy something and make some money, they will.

I guess you can only piss with the dick you got! 😂

Archived from radmon.org - originally posted 14/10/2023