The DSB is a screen grid valve or tetrode for RF amplification. It is an improved version of the DS and both have 250 mA heaters at 16 Volts for use in series heater chains in radio receivers designed for use on DC mains. It is not vari-μ and was thus employed in TRF not superhet designs.
The Marconi brand label.
The missing top cap was of the large plastic type with screw connection as can be seen from the remains of the adhesive. The envelope is shaped so that the screen could be aligned with a hole in the chassis for extra screening. The image shows the screen grid as a large mesh cage.
The balloon envelope is 44 mm in diameter and, excluding the B5 base pins, is 113 mm tall.
References: Data-sheet & 1043. Type DSB was first introduced in 1933.