The ORA from Mullard was designed in 1922 as a development of the K valve. The design was prompted by the commencement of broadcasting. The exhibit is marked BBC as was the case in the early days when the BBC was founded from interested industry companies, and the participants had to use the stamp on their products.
The ORA stands for Oscillator, Rectifier, and Amplifier - its planed usages. For the time, a reasonable number were made.
In construction, the valve has a metal skirt and the familiar tubular anode. The grid is formed from a castellated wire curved into an open cylinder. The filament is a single strand, tensioned by the support arm.
Original 1922 samples of the ORA had a tubular envelope, the balloon shape ORA was introduced in 1923.
The balloon envelope is 33 mm in diameter and, excluding the B4 base pins, is 77 mm tall.
Reference: 1003. Type ORA was first introduced in 1922.