This Cossor rectifier, 43-IU (43IU), is a full wave device with a directly heated oxide coated ribbon filament.
The construction is of two long anodes formed such that the connection to the support rod acts as an extra radiator.
The top of the envelope showing the shape of the anode pressing, the filament ribbons and their support springs.
This image clearly shows the ribbon filaments and the central support for the top mica. Without this support the spring tension would cause the mica to sag.
The balloon envelope is 54 mm in diameter, and excluding the B4 base pins is 110 mm tall.
References: 1040 & 1043. Type 43IU was first introduced in 1937.