The maximum reservoir capacitor is not quoted, but at 60 mA maximum output current the U10 was clearly designed for broadcast radio reception in 1930s all mains sets. The 4.0 Volt heater is characteristic of the 1930s British heater standard.
The twin anodes are stitched together.
The top mica reveals that the cathode/ filament is an oxide coated ribbon held tight by a tension spring. Our other U10 has heated cathode tubes with the heater strapped to the cathode.
The classic envelope is 45 mm in diameter and, excluding the B4 base pins, is 104 mm tall.
References: Datasheet, 1040, 3002 & 1043. Type U10 was first introduced in 1930.