The U60 EHT rectifier is designed to work with a maximum input voltage of 10,000 Volts RMS. The white band on the envelope is probably to minimize X-ray emission passing through the glass.
The data book gives the wrong base diagram in the text, the anode to the top cap is easy to determine.
The construction uses a pressed glass base with wire leads soldered to the IO base. The design is probably mid 1960's and the GEC brand was used for industrial valves.
The GEC brand applied as a sticker. The valve would have been made by M-OV.
The base: the central spigot houses the evacuation pip.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 75 mm tall.
