The DE5 is a dull emitter triode designed to be used as an audio output valve to drive small loud speakers. The DE5 developed into a family with DE5A and DE5B as well as the original DE5 valve. The valve is half silvered showing that the valve was magnesium gettered.
This trio of exhibits has Marconi valve and BVA on the envelope but not the BBC logo, suggesting these date from post 1928.
The electrodes and supports are visible to the right of the pinch. The filament is of the inverted V form and the top tensioning support has a support that originates from the centre of the pinch.
The base pins show the external attachment of the lead-out wires. The pin construction shows a central pin surrounded by an expanded sleeve.
The envelope dome has the type designation etched into the glass.
The balloon envelope is 55 mm in diameter, and excluding the B4 base pins, is 95 mm tall.
References: 4051 & 1003 Type DE5 was first introduced in 1924.