The CV1402 is a half wave rectifier on an International Octal Base. The design dates from 1939 and the commercial Type is the CY31, itself a replacement for the UR1. This design was made with both Ct8 (CY1) and IO bases.
The maximum reservoir capacitor is 32 µF and the minimum series resistance to limit in-rush current is 125 Ohms.
The Mullard logo and Type CY31 on the other side of the glass. This was clearly made as a commercial valve and overprinted with the CV number.
The anode is 3 mm front to back.
The central cathode poking through the top mica. Note the fingers holding the electrodes firmly within the shoulder of the envelope.
The top of the original box showing that this was originally supplied to the UK Air Ministry.
The classic envelope is 40 mm in diameter and, excluding the IO base pins, is 85 mm tall.