M-O Valve

M-O Valve Company Limited grew out of an industrial agreement between the British General Electric Company and Marconi's Wireless Telegraph Company. Their joint company was established in 1919 as Marconi-Osram Valve Company and adopted the name M-O Valve in 1920. Its manufacturing centre was GEC's valve factory at Brook Green, Hammersmith, London W6: an identifiable manufacturing company stood behind several commercial names.

By 1922 Brook Green was carrying out the processes needed to manufacture valves. Products reached the market bearing Marconi, Osram and M.O.V. markings, later joined by GEC. From late 1925 GEC's sales channel used Osram, while Marconiphone retained Marconi. In 1929 Marconi's holding passed to the Gramophone Company together with Marconiphone; following the formation of EMI, EMI became GEC's partner. In 1956 GEC acquired EMI's share and took full control of M-O Valve.

The programme covered receiving valves, transmitting devices and audio power tubes. Types associated with this manufacturing organisation include KT66, KT77 and KT88; commercial designations, equivalents and military variants still require identification of the individual type and period. Ferrite isolators also appeared alongside valves in 1965. The range extended beyond domestic radio reception.

Most receiving-valve production ended in 1958, while professional lines continued. The 1969 reorganisation linked M-O Valve, GEC Electronic Tubes and English Electric Valve activities. This did not immediately end the M-O Valve name: the 1971 programme still identified the company at Brook Green Works, under the common management of GEC Electronic Tube Company, alongside English Electric Valve at Waterhouse Lane, Chelmsford.

In 1971 the industrial range included transmitting and pulse tubes, audio tubes, vacuum, mercury-vapour and xenon rectifiers, thyratrons, triggered inverse diodes, series, shunt and corona stabilisers, Geiger–Müller counters, photocells, noise diodes, low-noise and wideband-amplifier tubes, surge-protection devices and reed contacts. Instrument and radar cathode-ray tubes and microwave components formed additional programmes. Applications ranged from communications and telemetry to industrial heating, linear accelerators, nucleonics, ultrasonics and X-ray equipment.

One technical feature of the DET22 family was electrical selection of mechanically identical tubes. The basic DET22 had broader tolerances; D, E, G, R and S versions narrowed different characteristic ranges, useful when a circuit allowed limited adjustment. Q/DET22 and Q/DET24 versions were intended for shock and vibration conditions. Tube markings therefore identified selections and service requirements as well as a commercial name.