The G120/1B/CV438 is a neon voltage stabiliser with open cylindrical electrodes. The central cylinder is the anode and the outer cylinder is the cathode and the orange glow forms round the anode.
The regulation of the voltage across the tube for variations of tube current between 2 mA to 30 mA is just three Volts.
The later G55/1K has the same specification and is a B7G based design.
The KB/F identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the F identifies the maker as STC, Paignton.
The CV Type designation. This exhibit is 9 mm shorter than other examples.
The geometry above the pinch.
The concentric cylinder electrodes.
The wide glass tube envelope is 29 mm in diameter, and excluding the B4 base pins is 60 mm tall.
References: Data-sheet. Type G120/1B was first introduced in 1945. See also1945 adverts.
