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This is the Fotos horned type. This French valve dates from 1916 and has a hard vacuum. It was the development of the hard vacuum valves in France that commenced the explosive development of the valve and equipment that could be used by relatively unskilled operators. The hard vacuum valves of the day had a lower gain, but a more stable gain, than the soft valves used by the Marconi company. The valve can dissipate 15 W and was designed for both transmitting as well as receiving use. The construction of the triode is conventional for the period, being co-axial. The anode cylinder contains a helical wire grid supported at both ends, and running through the centre of the anode is a single strand tungsten filament.

The balloon envelope is 52 mm in diameter and, excluding the B4 base pins, is 88 mm tall.

Reference: ¹⁰⁰³ & private communication. Type Horned was first introduced in 1916. See also 1916 adverts.