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 Brimar branding.
A closer view of the construction. The heater is a fine insulated wire that passes through the cathode eight to ten times.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 100 mm tall.
References: Data-sheet, 1040 & 1043. Type 1D5 was first introduced in 1935.