The VMP4/k or VMP4 is a variable μ screened amplifier pentode for RF and IF amplification in superhet receivers. This exhibit is the Catkin version and internally is totally different to the glass replacement the VMP4G.
This M-OV valve is branded Marconi by the paper label.
The outer screen is closed with a locked seam.
The original top cap was of the screw type. Here the later top-hat top cap is used but the top is threaded to allow it to be used in sets designed for the older connection method.
The envelope is 38 mm in diameter and, excluding the B7 base pins, is 113 mm tall.
References: Data-sheet & 1043. Type VMP4/K was first introduced in 1934.