The U22 is an EHT rectifier used in mains derived EHT in early television sets. The ratings of 5,200 volts and 1 mA define it for small screen CRT service.
The series resistance of the feed circuit has to be at least 50,000 Ohms and the reservoir capacitor is specified as 0.1 &mu:F at most. In the 1960s I built an oscilloscope power supply and the 5000 Volt 0.1 μF capacitors were in aluminium tube cases about 25 mm diameter and 130 mm tall. The top was an insulated cone with a central connector. The case was the second connection. When a teenager I was given a vintage television set where a mains transformer had a several thousand volt secondary winding for the EHT supply, I never tried powering up the set.
Mazda had problems of reliability with their cathode coating in the early 1950s with a tendancy for it to flake off and destroy the valve. Mullard had a much better reputation for reliability.
Internally the valve has a wide bell anode that shields the cathode at its centre. The enclosed construction is to minimize the emission of X-rays.
The oxide coated cathode is threaded by the heater. They are connected together at the anode end. Note the rigid cathode support wire.
The wide glass tube envelope is 27 mm in diameter and, excluding the MO base pins, is 79 mm tall.
Reference: Datasheet. Type U22 was first introduced in 1939.