The DE3 is a dull emitter triode from 1924 and this exhibit is an early example. Later production used a moulded Bakelie base. M-OV sold the DE3 under both the Marconi and Osram brand names.
The filament is rated at 2.8 Volts at 0.06 Amps, this suggests two dry cells in series as the filament supply, but in fact a 4.5 Volt 'bell' battery would be used with a series rheostat. The filament could thus be maintained at the 'correct' voltage. The valve can be used at LF or HF or as a detector according to the label.
The obscured construction is of a vertical anode 18 mm long and 5 mm diameter, into which the grid and filament fit co-axially. The filament is a single strand, and the grid is a fine wire helix supported on a side rod through the whole length of the anode.
The base is stamped to identify the grid pin. The paper label is still clearly readable. The main DE3 identification is etched into the envelope.
The etched lettering appears double due to the reflection from the inside of the glass.
The Osram brand identification and the declaration that the DE3 was made in England.
The base shell covers a moulded disc that the pins fix to. The wires from the pinch pass through the moulded base and are then wrapped and soldered to the pin. In the centre is the M-OV logo.
The brass pins are of two part construction. An inner core fixes to the base disc and an outer sleeve is forced over the core. The sleeve is cut to allow four spring segments to open up as the two parts are forced together This provides a spring to retain the pin in the valve holder and maintain good contact.
The wide glass tube envelope is 25 mm in diameter and, excluding the B4 base pins, is 95 mm tall.
References: Datasheet, 4051 & 1003 Type DE3 was first introduced in 1924.