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.

In contrast to our other U4020 this exhibit has a larger anode with a greater surface area. This suggests that the earlier production valves got very hot.

The anode is much wider than the front to back dimension. In practice the cathode is a central tube and the anode is formed into a central tube with side fins.

The dome carries the identification etched into its surface. The central bright cathode tube can be seen in the centre of the image.

A close-up of the lower part of the valve. The heater is a hairpin of coiled tungsten wire coated in ceramic and inserted into the cathode tube.

The classic envelope is 38 mm in diameter and, excluding the B5 base pins, is 102 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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