Alternative Name(s): Electronic Vacuum Tube; Thermionic Electron Valve

General purpose triode electronic valve. Type ORA, first introduced in 1922. Manufactured by The Mullard Radio Valve Co. Ltd, London, England, about 1923.
3.6 - 4 volt 0.65 amp-hour directly heated cathode. It was a bright emitter valve with an amplification factor, ? of 8.5.

The Mullard Type ORA valve was designed in 1922 as a development of the K valve, with the redesign prompted by the commencement of public radio broadcasting. The type name signifies 'Oscillates, Rectifies, Amplifies', which were the planed usages of the design.

This valve is believed to have previously been used or collected by Francis West Chambers (1861-1928), who from 1909 held the position of electrical inspector for the Public Works Department of Victoria, with responsibility for supervising municipal power supply undertakings, and later held a similar role with the State Electricity Commission of Victoria from 1921. During the early 1900s he had collaborated with Henry Walter Jenvey in the first experimental wireless telegraphy experiments in Australia.

Physical Description

Most of the original ballooon glass envelope or bulb has been removed to show a vertical cylindrical triode structure (somewhat damaged). In construction, the valve has a metal skirt and a tubular anode. The grid is a curved folded arrangement and the filament is a single strand, tensioned by the support arm. With a European style 4 pin base with plated metal shell. Originally mounted on a wooden display block with label. The thin glass tube envelope is 24 mm in diameter, and excluding the B4 base pins, the valve was originally 83 mm tall.

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