Replacement Geiger Mueller Tube Make your own geiger counter using this sensitive Russian geiger mueller tube (sensitive to beta and gamma). It is about 97mm L x 10mm Dia. The recommended operating voltage is 350-475 volts. The Russian tube# is SBM-20. These are new old stock so we test each one for operation before shipping. May have slight edge scratches, tarnish or cosmetic marks, however these will not effect the performance. See schematic pdf link below of a simple geiger counter that uses our inverter transformer, a 555 IC and common components (schematic only - you must supply the parts). The inverter transformer is sold under the stock number of G13599.