The 7Y4 is a late 1930's American full wave rectifier design made in the UK by Cossor after 1945. The Marconiphone equivalent the U149 is basically identical.
The maximum reservoir capacitor is 40 µF and the minimum series resistance, for current limiting, is not given in the literature.
The main picture shows that the front to back thickness is small for each section. This image shows the face view of one of the two anodes. The second anode is above and connects to the left support rod. The cathode tube is common to both.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 55 mm tall.
References: Datasheet, 1040 & 1043. Type 7Y4 was first introduced in 1938.