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 dome carries all of the identification. The arrangement of micas allows the electrodes to be a push fit to the shaped envelope.

The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 99 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type U4020 was first introduced^¶ in 1934.

 
Pin Connections

B5	1	2	3	4	5
	a	-	h	h	k

 
Absolute Maximum Operating Conditions^¶

Rectifier	Vh	Ah	Va	mAa
	40.0	0.2	250	120

Thanks to Frank Philipse for supplying the above PDF datasheet

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