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The Siemens Type A was developed from the French hard valve during WWI. This exhibit is an experimental laboratory triode; a type 'A' fitted with a British B4 base. It is probable that this exhibit dates from about 1917.

It has been suggested that this standard German valve has been modified to work in captured Allied sets.

The wide glass tube envelope is 33 mm in diameter and, excluding the B4 base pins, is 110 mm tall.

Reference: Observation. Type Type A was first introduced in 1917. See also 1917 adverts.