The UY85 half wave rectifier was designed for use across the European mains, as the 100 mA heater suggests. The reservoir capacitor specified is 100 µF and the minimum effective series resistance in the circuit needed to be only 100 Ohms. The design use was in domestic broadcast receivers for the main HT rail.
The two halves of the blacken anode are stitched together.
The ends of the anode sheets are bent outwards to increase the radiating area. The inside of the anode is left bright.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 58 mm tall.
References: Datasheet & 1040. Type UY85 was first introduced in 1954.