The SU42 is an EHT rectifier with the pre-war 4.0V British standard heater.
The SU42 was made as a replacement type and requires an effective series resistance of 5,000 Ω and a maximum reservoir capacitor of 1.0 μF.
The anode has eight radial cooling fins and the ceramic at the top indicates high voltage and probably a valve designed for industrial use.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 100 mm tall.
Absolute Maximum Operating Conditions¶
Updated January 04, 2022.