The DE5 is a dull emitter triode designed to be used as an audio output valve to drive small loud speakers.
The DE5 was introduced in May 1924 and this exhibit carries the first BBC stamp etched into the glass. This has the words Type Approved by Postmaster General around the edge. This stamp was used from 1st November 1922 until September 1924. Thus we have good reason to believe that this form of the DE5 was the first to be introduced. The valve in the advert from May 28, 1924 has a metal skirt.
The base clearly carries the M-OV Co Ltd logo. We can say with certainty that M-OV were using the metal shell B4 base with the two part pins in May 1924.
The anode is just visible within the envelope. The etching of the Marconi identification is clear. the majority of the envelope has the familiar mirror of Magnesium gettering.
The size of the envelope is slightly larger in both diameter and height than later examples.