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The L610 is an early example of an audio output valve designed to drive a loudspeaker in a domestic radio receiver. It dates from 1929 and was for battery operation.

This specimen was manufactured for professional use (NB. MWTCo label & logo) during the later 1930s. The Marconi Company (then MWTCo.) favoured 6V filaments (large cathode area, lots of emission, longer life) for many purposes long after the domestic market had moved to the more economical 2V series. In particular, battery-operated low-impedance types such as the L610 were used in stable, low-drift RF oscillators for driving broadcasting transmitters and similar high-quality equipment.

The L610 was the lineal descendant of a series of similar valves including the DEL612 (thoriated tungsten filament) and the DEH610 (barium-coated filaments using the Azide process). Interestingly, although this exhibit definitely has oxide-coated filaments and was not made using the Azide process, its mica-less construction is an anachronistic hang-over from the Azide era.

The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 90 mm tall.

References: Data-sheet & ¹⁰⁴³. Type L610 was first introduced in 1929. See also 1929 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.