The POVT142 is a UK Post Office designation and is not to be confused with the American VT series. It is clearly a full wave rectifier and is indirectly heated. In CV specifications the UK GPO valves are referred to as POVT and by the GPO by the VT no. notation.
The pinch with evacuation hole, filament, cathode and anode plates.
The electrodes are rigidly held in the top mica that is an interference fit with the dome of the glass envelope.
The classic envelope is 45 mm in diameter, and excluding the B4 base pins is 102 mm tall.