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The LS5 is a triode designed in 1923 especially for driving a loudspeaker and featured many developments in valve design. The LS5 had, for its day, a high anode dissipation of 10 Watts.

This exhibit has etched lettering branding it an Osram valve. It carries on the glass the type two BBC stamp and thus dates to between September 1924 and 1927.

The LS5 was of the early dull emitter valves to be introduced by M-OV who were the first manufacturer to introduce thoriated tungsten filaments. This introduction followed intensive research from 1919 onwards. The use of the V shaped filament with tension spring was new as was the flattening of the anode cylinder and grid helix.

Unlike our other LS5 this exhibit retains its paper label.

Under the etched Osram Valve can be seen the grid and flattened nickel cylinder anode. The upper filament support has a short length of filament attached, whereas the lower support ends without any filament. The slightly blackened inside to the glass testifies to a hard life before failure.

The balloon envelope is 56 mm in diameter and, excluding the B4 base pins, is 108 mm tall.

References: ⁴⁰⁵¹ & ¹⁰⁰⁴ Type LS5 was first introduced in 1923. See also 1923 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

PDF scanned from an original document held by the museum