This exhibit is clearly of early-mid 1920s origin. The filament current of 60 mA indicates an oxide emitter rather than thoriated tungsten. However, there is no maker's name and the paper label describes the valve as a Beam Valve - so we have a mystery. The plated base cap looks much like the early Dutch valves rather than UK production. There is a slight remnant of lettering on the glass and with some imagination it suggests the Frelat logo but the base construction is different.
We would very much like to identify this valve correctly.
The operating details are printed on the paper label that wraps around the base cap.
The base pins are simple split pins that are secured within the composition base. The black plastic has a central hole but no indication of origin.
The anode is mounted horizontally and the grid is an open helix with a single strand filament.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 91 mm tall.
