The WD11 was designed by Westinghouse for use as a detector in the Westinghouse Aeriola Senior radio. Design work started at the Bloomfield, New Jersey labs in mid to late 1921.
Development over time: Initially an oxide coated filament, without getter then lime-gettered. The first base was a brass shell and the evacuation pip was at the top. The base was replaced by Bakelite. The third version was clear glass (no getter) and had the Bakelite base cap but the evacuation tube was mounted at the bottom. The final version of the WD11, as here, was gettered producing a mirror on the glass.
The WD11 replaced the earlier T88 and in 1923 was replaced by the WD12
The identification is etched into the dome. The reflection from the silvered inner surface makes reading the characters difficult.
The base has the same pin spacing as the B4 base but the pins have a larger diameter and one is both longer and thicker than the rest. The WD-11 is moulded into the base cap.
The electrodes: the folded bright anode is cylindrical and held on one side only. The helical control grid is fixed to a single side support. The filament is supported top and bottom but without a tensioning spring.
The wide glass tube envelope is 25 mm in diameter and, excluding the base pins, is 75 mm tall.
References: Data-sheet, 3001 & 1047. Type WD11 was first introduced in 1922.