The VMS4 variable μ screened tetrode dates from 1931. It was designed for RF and IF amplification in broadcast superhet receivers.
This M-OV valve is badged as Marconi suggesting it was made for professional and not domestic use. The narrow tube before the flare would allow for a horizontal mounting with a chassis screen in just the same was as the original S625. Our other examples of the glass VMS4 and VMS4 lack this feature. We also have the 1933 Catkin version VMS4.
The Marconi branding.
Looking down into the valve the mesh of the screen grid can be seen. Also as the anode connects to the top cap the stout wire from the cap can be seen to go to small vertical plates placed either side of the central column.
The balloon envelope is 45 mm in diameter and, excluding the B5 base pins, is 120 mm tall.
References: Datasheet & 1005 Type VMS4 was first introduced in 1931.