The 4102D is a telephone repeater triode. The original Western Electric 102D design dates from 1925 and the 4 prefix denotes that manufacture was by STC. In this exhibit the maker was STC in Australia and carries the prefix SY.
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 3A/142A as a replacement for the 4102D.
The electrodes are distorted because a shock has broken the supporting glass rod at the base.
The grid is of ladder construction with thin wire welded to the two main supports. The finished grid has been folded at the top to make the two sided structure we see. In this way the valve is essentially two triodes in parallel. The flat plate anode can be seen to have the supports spot welded to it. The coated filament can be seen to have become detached from the tension spring. The latter is fixed into the top of the glass support rod.
The locating pin to guide the valve into the holder with the bayonet twist connections.
The balloon envelope is 58 mm in diameter, and excluding the UV base pins is 96 mm tall.
Reference: Data-sheet. Type 4102D was first introduced in 1925. See also1925 adverts.
