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 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.
This example features the Cossor Paper label whereas our other 202DDT example is later and has the identification printed on the external metalisation. Cossor adverts show the diamond paper label present in 1935 and this Type was introduced in 1936. We have a gap in the advert record but post WWII the label has been replaced by lettering on the bulb.
The reverse was made as plain zinc paint.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 108 mm tall.
References: 1043. Type 202DDT was first introduced in 1936. See also 1936 adverts.
Absolute Maximum Operating Conditions¶
Updated January 10, 2017.