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).
This exhibit has a blackened bulb typical of the Azide process. Our other L610 has a clearer bulb and was made using an oxide coated filament.
Side view showing a glimpse of the vertical anode within.
Here the mica-less construction is visible.
The dome carries the etched identification.
The balloon envelope is 46 mm in diameter and, excluding the B4 base pins, is 90 mm tall.
References: Datasheet & 1043. Type L610 was first introduced in 1929.