The ORA from Mullard was designed in 1922 as a development of the K valve and the redesign was prompted by the commencement of broadcasting. This exhibit is one of the early samples as later production had a balloon envelope.

The grid wire is held in a pair of wires twisted together.

The ORA stands for Oscillator, Rectifier, and Amplifier - its planed usages. It is a bright emitter valve and had a μ (amplification factor) of 8.5

In construction, the valve has a metal skirt and the familiar tubular anode. The grid is a curved folded arrangement as seen above and the filament is a single strand, tensioned by the support arm. See ORA for a version with a wire helix grid fixed to a rigid support.

The thin glass tube envelope is 24 mm in diameter, and excluding the B4 base pins, is 83 mm tall.

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	ra	gm
	3.8	0.65	30-90	27,000	0.32

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This exhibit was last updated on 02 December 2007