The HVR2 is a half wave low current EHT rectifier from Mullard. It would have been designed for provision of EHT in such applications as Radar and Oscilloscopes where Cathode Ray Tube indicators were used.
The pinch and lower end of the cathode. The cathode tube has a tape connecting it to the central support rod. The insulated heater is wrapped around a central ceramic support. Both ends of the heater are connected to supports held in the glass pinch. The one on the right connects to a base pin. The left hand wire support is connected by a strap to the central vertical support.
The top of the cylindrical anode. The top of the cathode tube is connected to the two rod supports.
The classic envelope is 45 mm in diameter, and excluding the B4 base pins, is 109 mm tall.
References: Datasheet & 3002. Type HVR2 was first introduced in 1937.