The MS4 from M-OV is described as a general purpose screened-grid valve for use in RF amplification in receivers. The valve was available in both clear and metallised finishes.
The MS4B is a 'maximum gain' improvement and dates from the early 1930's.
This exhibit is an early version as can be seen from the screw top cap connection. The MS4 is of later manufacture and has the metal top cap stud. The shape of this early version shows a straight tube up to the metal skirt of the screen. This design allowed users to mount the valve between two compartments with a metal sheet between them thus keeping the grid and anode circuits as isolated as possible. SeeS625 for mounting arrangements.
The anode is formed from a pair of plates hung from the top cap and either side of the screen. The latter has an outer box with a metal mesh. The anode plates have ridges pressed into them to add rigidity.
The anodes either side of the screen and the etched identification on the left of the glass. The oval lozenge has the M set above the S4. Later designs of the M-OV identification lozenge had the letters horizontally along the long axis of the oval.
The screening skirt extends the screen close to the envelope wall.
The classic envelope is 43 mm in diameter, and excluding the B5 base pins is 120 mm tall.
References: Datasheet & 1005 Type MS4 was first introduced in 1929.