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The U4020 is a half wave rectifier designed for 200 mA series connected heaters as found in AC/DC radio receivers.

The reservoir capacitor can be 16 µF with an effective minimum series resistance of 47 Ohms.

The special feature of this U4020 is the use of twin rectifier sections strapped together.

At first glance this looks to be a full wave rectifier, but look at the top and the ribbon joining the anodes can be seen.

Face view of one anode.

The three cylinder shape of the anode can be seen through the top mica. Only the centre one has a folded heater and cathode.

Here the ribbon strap joining the two anodes is plain to see.

The classic envelope is 38 mm in diameter and, excluding the B5 base pins, is 186 mm tall.

References: Data-sheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type U4020 was first introduced in 1934. See also 1934 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.