The type VMS4B typifies the swansong of the screen-grid receiving valve with anode top cap. It is an improved, vari-mu RF/IF tetrode intended for domestic superhet receivers but it represents the final milestone on the road which started (barely 10 years earlier) with the Type S625.
The smudged Marconi name.
This exhibit looks to have been made right at the time that the screw top cap was replaced by the top hat. Here the valve was made to the old pattern and then fitted with a threaded top hat that offers the user a choice of connection.
The balloon envelope is 44 mm in diameter and, excluding the B5 base pins, is 127 mm tall.
References: Data-sheet & 1005 Type VMS4B was first introduced in 1933. See also1933 adverts.
