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Marconi 'Osram' DE4
Marconi 'Osram' DE4 dull emitter (thoriated
tungsten) filament triode, probably from before 1925. A 1925 example at the
National Valve Museum
has a bakelite base. The valve bears a 'BBC' mark, (second picture above) of
the style used from 1924 to 1927 and the serial number
'W1512'.