The 1807 rectifier is a directly heated device from the early 1930s. The construction looks very similar to the Mullard DW3 & DW30, the DW30 is rated for 500 Volts.
The filament supports are held in glass rods.
The identification is etched into the top of the envelope.
Thanks to Mike Edwards for the pictures and information that this valve came from a 1932 Kolster Brandes KB321 wireless set.
The balloon envelope is mm in diameter, and excluding the B4 base pins is mm tall.
Reference: Data-sheet. Type 1807 was first introduced in 1932. See also1932 adverts.
