The UY21 half wave rectifier dates from the early days of all glass construction in the early 1940s. The device was designed to operate as part of a series heater chain in universal sets. The 100 mA current allowed a few valves to run from 240 Volts, eg a domestic radio.

The maximum reservoir capacitor is 60 µF and the minimum series resistance has to be 175 Ohms. The design is quite efficient compared to octal valves of the same period.

The wide glass tube envelope is 26 mm in diameter and, excluding the B8B base pins and spigot is 75 mm tall.

References: Datasheet, ³⁰⁰² & ¹⁰⁴⁰. Type UY21 was first introduced^¶ in 1941.

 
Pin Connections

B8B	1	2	3	4	5	6	7	8
	h	a	-	a	-	ic	k	h

 
Absolute Maximum Operating Conditions^¶

Rectifier	Vh	Ah	Va	mAa
	50	0.1	250	140

Thanks to Frank Philipse for supplying the above PDF datasheet

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