The 1D5 is a half wave rectifier designed for 200 mA series connected heaters as found in AC/DC radio receivers.

The maximum reservoir capacitor is 16 µF and the effective minimum series resistance has to be 50 Ohms.

The literature gives the UR1C as an equivalent to the 1D5, and most respects it is, but the UR1C has a 20 Volt heater at 200 mA.

The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 100 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type 1D5 was first introduced^¶ in 1935.

 
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	100

Thanks to Frank Philipse for supplying the above PDF datasheet