The 2D4B is a pair of indirectly heated signal diodes with separate cathodes. The 2D4A has the same ratings but a single cathode and a B5 base cap.
The balloon envelope is 41 mm in diameter, and excluding the B7 base pins is 74 mm tall.
References: Data-sheet & 1043. Type 2D4B was first introduced in 1937.
Absolute Maximum Operating Conditions¶
Updated December14, 2012. shape:balloon construction:pinch type:double.diode age:1930.1940 base:b7 heater:4.0v pins:7 pin:1.m pin:2.a pin:3.k pin:4.h pin:5.h pin:6.k pin:7.a