The DD13 is a double signal diode with a common indirectly heated cathode. It has a 200 mA heater for use on series heater chains. Application would be as signal detection and AGC rectifier.
The anodes are mounted on support rods around the common cathode. Unusually for a signal diode the anode is blackened and fitted with substantial heat radiating fins.
Each anode connects to a single side support and a single middle support.
The classic envelope is 38 mm in diameter, and excluding the B5 base pins is 91 mm tall.
References: Data-sheet & 1043. Type DD13 was first introduced in 1936. See also1936 adverts.