The UY41 is a half wave rectifier designed for universal domestic equipment and replaced the UY21. By universal we mean AC or DC mains input and therefore no mains transformer. The UY41 was aimed at line voltages from 110 to 240 Volts.
All valve rectifiers have a maximum current rating when charging a reservoir capacitor, this will be several times the average current. To limit the current to a safe value for the UY41 the series resistance needs to be at least 210 Ω. The maximum reservoir capacitor must be limited to 50 μF.
The UY89 was a UY41 updated for the B9A base in 1960.
The metal skirt with locating pip remains but the spigot has been omitted. Unlike the 1935 RCA metal valves the spigot on the B8A valves did not cover the evacuation tube.
The X shaped anode with oxide coated cathode at the centre.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 60 mm tall.
References: Data-sheet, 3002 & 1040. Type UY41 was first introduced in 1948.