The VU72 is a half wave mercury vapour rectifier. The VU indicates a UK Air Ministry specification. The other side of the glass carries the M-OV ellipse with the Type GU50 inside.
The maximum reservoir capacitor is 4 µF. The filament is a twin horseshoe of corrugated tape. The anode is a short dustbin lid connected to, and supported by the top cap.
The M-OV etched ellipse. The valve needs to be operated vertically and after storage the filament needs to be run for 15 minutes before applying the HT.
The anode is secured only to the top cap.
The corrugated filament.
The classic envelope is 47 mm in diameter and, excluding the B4 base pins, is 123 mm tall.
References: Data-sheet & 1040. Type VU72 was first introduced in 1940. See also1940 adverts.