The picture above shows a variety of Geiger tubes that are commonly sold under the name “SBM-20″. This post is an attempt to clear up some of the confusion around these tubes and to share some information about the different tube styles I have encountered in the wild since I first started selling Geiger Counter kits in 2011.
This is my spotter’s guide to the SBM-20 Geiger counter tube.
This is the quintessential Soviet Geiger Counter tube. 400V operating voltage. 105mm overall length. Gold (brass?) color. Symmetric end caps. Positive terminal is usually marked ‘+’, but if not, it’s the end closest to the CBM-20 marking. Date codes are always four digit, but I have seen both MMYY and YYMM (assuming I am interpreting the numbers correctly). Year of manufacture varies widely but most are 1970s – 1990s.
Very common alternate version of the SBM-20. Shorter 95mm overall length. Positive terminal is exposed rod with no end cap. Soldering to this terminal can be a challenge as the plating is usually quite oxidized and the underlying metal is steel. I’ve also seen the internal glass seals fail after soldering. These are often sold as SBM-20 tubes, and unscrupulous eBay sellers will sell the SBM-20/SBM-20U interchangeably.
SBM-20 (alternative negative terminal style)
Slightly longer positive terminal. 105mm overall length. Negative terminal is formed from the tube body (cost saving design?). Tubes I have seen are marked ’77’, presumably date code for 1977. Rare.
STS-5 / CTC-5
Older version of the SBM-20. Slightly longer overall length, approx. 110mm. Silver color. Positive terminal is marked + and closest to the CTC-5 marking. Date codes I have seen are mid-1960s through 1970s. I haven’t confirmed this, but I suspect date code is roman numeral month followed by arabic numeral year, eg. VIII 65. Aside from longer overall length, properties and performance are very similar to SBM-20. Less common than SBM-20, presumably because they are older and were not manufactured in great numbers across as many years. Sometimes sold under the name SBM-20. They are generally interchangeable with “real” SBM-20 tubes, but given that they are significantly older, failure rate might be higher (unconfirmed).
My Geiger Counter kit will accommodate the STS-5 and all of the SBM-20 variants shown. The SBM-20U requires a short jumper wire to connect the positive terminal to the PCB. I recommend using an alligator clip or wrapping a wire around the terminal to avoid compromising the glass to metal seal with the heat of the solder.
Holiday sales are picking up and shipments of a few critical components are just now arriving. As of today I only have a few Geiger Counter kits left in stock. I expect to sell out within the next few days, but should have more kits ready within 2-3 weeks.
International customers – I recommend ordering now to guarantee delivery by Christmas.
PS: Rescue Shield kits are running low as well. Once I sell out I probably won’t have more before early 2015.
The Rescue Shield is a 100% open source, Arduino-based high voltage mode fuse programmer for AVR microcontrollers.
It allows you bring an otherwise “bricked” or misconfigured AVR back to life by editing the configuration fuses that control the operation of the RESET pin, the internal oscillator, and other features of the microcontroller. The Rescue Shield can talk to chips when ordinary ISP programmers can’t.