The 202DDT is an indirectly heated double diode triode. The envelope has a metallic screening paint on it. This paint was normally made conductive with metallic zinc. The box that the valve came in was dated 1948, but the design dates from 1936.
The 200 mA heater was designed for series heater powering across the mains supply in 'universal' or AC/DC sets. The double diode triode was extensively used in superhet receivers as signal detector, AGC rectifier and first audio amplifier stage.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 104 mm tall.
References: 1043. Type 202DDT was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated December13, 2012.