This valve is a Mullard experimental half wave rectifier with the cathode connected to the top cap. This configuration is typical of television efficiency diodes that return scan energy back to the HT capacitors during flyback. The heater is insulated and further held away from the cathode wall by spacers.
The anode is longer and of greater area than the production types we hold in the museum and it is possible that this never acquired a commercial Type designation.
On test it looks to have a 300 mA heater.
The stitched anode has a cross or + shape with four side wings
The inner anode surface is here seen connected to pins seven and eight.
The top of the cathode and emerging from the centre are the two heater spacers. These rods are linked together by a thin wire wrapped round them.
The two top micas. Almost visible is the bright structure that links the thin tape connection to the cathode tube to the top cap.
The base end with the insulated heater sitting between the spacer rods.
The top of the cathode with the bulge below the mica disc preventing it rising too high. The thin tape connecting the cathode to the top cap connects behind the left support.
The wide glass tube envelope is 28 mm in diameter and, excluding the B9D base pins, is 101 mm tall.
