The A864 is a M-OV special type output beam tetrode with a 13 Volt heater and anode brought out to a top cap. It is possible that this was for use with vehicle supplies.
The top cap anode suggests that this was used for line output duty in a vision receiver.
The Marconi paper label.
BBC Valve Section label. Two dates appear 28 April 1947 and 17 August 1951.
The B7 base Pins.
Thanks to Mark Mallison for sending the image.
The classic envelope is mm in diameter, and excluding the B7 base pins is mm tall.
