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The U31 is an indirectly heated half wave rectifier and was designed for series heater use and a 300 mA heater chain.

The maximum reservoir capacitor specified is 32 µF and the minimum effective series resistance has to be 100 Ω.

See also U31.

The ribbed and stitched anode with rectangular cathode tube.

Side view.

The classic envelope is 44 mm in diameter, and excluding the IO base pins, is 103 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type U31 was first introduced in 1937. See also 1937 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.