The DE3 is a general-purpose dull emitter triode that has a very delicate thoriated tungsten filament rated at 2.8V 0.06A. This exhibit is not from the early production batches, the base pins are split and not of the earlier two part construction as outer other examples.
The anode is mounted vertically and this allows the use of the wide glass tube envelope. Note the A for anode that has been moulded into the base and filled with white paint.
This image of the electrodes shows the spiral wire grid extending beyond the anode.
The DE3 was one of the first British valves intended for operation from dry batteries but the battery required was a 4.5V 'bell' battery. This was used with a series rheostat adjusted by the user to provide approximately the correct running voltage across the filament terminals.
1.5 V cells made in the 1920s soon dropped to 1.0 to 1.1 volts, due to polarization, when used continuously as in a radio.
The wide glass tube envelope is 25 mm in diameter and excluding the B4 base pins, is 78 mm tall.
References: Datasheet, 4051 & 1003 Type DE3 was first introduced in 1924.