The MS4 from Marconi is described as a general purpose screened-grid valve for use in RF amplification in receivers. The valve was available in both clear and metalised finishes.
The narrow waist above the base was there to allow for through chassis mounting where the chassis would be at the level of the lower screening shield. The latter can be seen below the silver of the gettering.
The envelope is a modification of the balloon shape as the top shoulder is not used to hold a mica sheet in place.
The MS4B is a 'maximum gain' improvement and dates from the early 1930's.
The Marconi paper label.
The classic envelope is 44 mm in diameter, and excluding the B5 base pins is 122 mm tall.
References: Datasheet & 1005 Type MS4 was first introduced in 1929.
Absolute Maximum Operating Conditions¶
Updated April 04, 2015. shape:classic construction:pinch type:tetrode age:1920.1930 base:b5 heater:4.0v pins:5 pin:1.g2 pin:2.g1 pin:3.h pin:4.h pin:5.k pin:tc.a