The MSPen (1933) had the anode connected to the top cap. In the 'B' variant of 1937, the same device had the control grid connected to the top cap. The signal isolation afforded by taking the control grid to the top cap became standard practice for most manufacturers.
The amplifier pentode would have been used in RF and IF stages of domestic radio receivers.
The classic envelope is 42 mm in diameter and, excluding the B7 base pins, is 107 mm tall.
References: Datasheet & 1043. Type MSPenB was first introduced in 1937.
Absolute Maximum Operating Conditions¶
Updated December14, 2012.