The STS-5 is almost identical in construction and function to the ever popular SBM-20 tube. It was made by a different Soviet factory and has nearly the same function and specifications. For more details about this tube, refer to the SBM-20. https://www.youtube.com/watch?v=__tjvi61nFM and http://cognito.me.uk/science/rh-electronics-myGeiger-review/ An industry standard, the STS-5 and the SBM-20 are used in a great many modern Geiger counters around the globe. These two tubes never go out of fashion.