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.
It 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.
The BBC stamp is the earliest type that was current from 1/11/1922 to September 1924, so this exhibit is from an early production batch. This is also evident from the presence of the metal base shell.
The side support is topped with a spring to both hold the fold of the filament and to tension it so that the filament did not sag as the heating expaned the wire..
The maker's name is faintly etched into the glass and reads Marconi Valve made at the Osram lamp works. Additionally are the words covered by various patents.
A close-up of the grid and the lower part of the broken filament.
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.