The 4102D is a telephone repeater triode. The original Western Electric 102D design dates from 1925 and the 4 prefix denotes that manufacture was in the UK by STC.
Originally the spherical envelope was fitted with a metal skirted base. This exhibit is of much later manufacture but follows the original electrode construction.
See also the experimental M25 for similar construction that was also believed to be derived from Western Electric.
In 1946 STC produced the 31/142A as a replacement for the 4102D.
The British STC company (Standard Telephones and Cables) was, before the 1925 take over of the parent Western Electric company by International Telephone & Telegraph (ITT), a subsidiary office of Western Electric. For years after the separation STC relied on Western Electric technology.
The vertical glass rod holding the electrodes is normally found broken near the base but here it is intact.
The single inverted V filament of oxide coated ribbon has fractured and parted.
The anode plates are mounted either side and held at the top and bottom. The locating pin for the bayonet base can be seen on the right.
The filament is held at the top in a hook. The supports look rigid but the separation of the tape indicates that the top support with the bend at the right was holding the tape under tension.
The balloon envelope is 58 mm in diameter, and excluding the base UV pins is 97 mm tall.
Reference: Data-sheet. Type 4102D was first introduced in 1925. See also1925 adverts.
