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The M-OV Type S215 was (we think) the very first 'upright' screen-grid valve to reach the British market. It may also have been a World First to achieve quantity production.

This exhibit looks an early example with the Bakelite top and screw top cap.

Although most domestic radio manufacturers didn't bother, professional users liked to mount these valves so that they poked through holes in the metal chassis in order to isolate the anode and grid circuits at the level of the internal metal 'skirt' connected to the screen grid. Because the S215 is an azide-process valve this skirt cannot be seen in the photo but an essentially similar skirt can be seen in the later Mazda version SG215. The wish to match external screening to the level of this skirt explains the slimline base cap and the characteristic bulb shape of these early screen grid types.

The azide process worked best with horizontal electrode assemblies and was not really suited to screen grid valves. Because of this the S215, although widely acclaimed and used, was not completely successful and was replaced by improved but otherwise similar oxide-coated types (eg, S23) once M-OV had developed the necessary processes.

See also S625 the worlds first screen grid valve.

The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 115 mm tall.

Reference: ¹⁰⁰⁵ Type S215 was first introduced in 1929. See also 1929 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶