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 as in this exhibit.
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 base cap carries the Type designation, patent information and the maker's name as Western Electric.
The UV base is of the bayonet type and a locating pip can be seen on the base cap. Once inserted into the base the valve would be twisted to lock it into place.
The electrodes are supported by the pinch and an auxiliary glass rod - seen on the right. The anode is a pair of flat plates mounted either side of the central ladder grids and the filament can be seen in the centre as an inverted V of ribbon. The tensioning spring is attached to the glass rod.
The ladder grid is formed between two stiff rods. The wire looks to be held within notches in the supports. Each grid is single sided suggesting that one half of the original winding has been cut off.
The geometry of the valve seen from the side.
The glass rod with enclosed metal parts. The anode is welded to the support.
The base cap insert has the Type designation moulded into it. The pins are solid as the base has the springs.
The balloon envelope is 59 mm in diameter, and excluding the base pins is 100 mm tall.
Reference: Data-sheet. Type 4102D was first introduced in 1925. See also1925 adverts.
