The 8013A was at one time a fairly common EHT rectifier for military and professional applications and made by several manufacturers.
The peak inverse voltage is 40 kV and the peak current is 150 mA. Typical output (around 250 W) would suit the requirements of a small airborne radar transmitter.
The electrodes are cylindrical and the anode bell is supported from the top of the envelope.
The anode top cap. The outer ring is probably to prevent corona discharge.
Like the later TV type EHT rectifiers the oxide coated filament is mounted inside the anode bell with a side rod that connects to the top of the filament.
The classic envelope is 51 mm in diameter and, excluding the UX4 base pins, is 137 mm tall.