The Mullard UY1N is a half wave rectifier designed to operate in AC/DC mains equipment. With this exhibit Mullard have written the Type designation as UY1(N) and the valve was made by Philips in Holland.
The 100 mA heater is designed for series heater chain use and can supply up to 140 mA of output current and is rated to work with a large maximum reservoir capacitor of 50μF.
The anode is blackened for better heat dissipation and shaped in X form with the two arms connected to the supports being longer than the others.
The cathode connection and through the hole in the anode can be seen the oxide coated cathode.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 79 mm tall.
References: Datasheet, 3002 & 1040. Type UY1N was first introduced in 1941.