The DE4 is a rare valve, little used and not generally included in contemporary lists. This exhibit has the type two BBC stamp and dates from between 1924 and 1927, probably around 1925 when this type was introduced. The base pins are of two part construction.
The design purpose was for audio output applications in broadcast receivers.
The base and brass two part base pins.
The Marconi logo etched into the envelope.
The bright anode has two wires spot welded to the ends and these wires are then spot welded to the support rods that fix into the pinch.
The control grid can be seen as can the two lower filament supports. The top of the filament is held by a spring attached to the rod that can be seen to be passing outside of the the anode.
The etched lettering is very feint on this valve. The BBC stamp is of the second type and the wording is Entirely British Manufacture.
The Marconi logo and Made in England.
A closer view of the BBC stamp and the DE4.
The balloon envelope is 55 mm in diameter and, excluding the B4 base pins, is 105 mm tall.
References: 4051 & 1003 Type DE4 was first introduced in 1924.