The DK91 is a miniature B7G dry battery heptode, it was designed for frequency changer use in battery portable radio receivers for medium and long wave. The valve was designed for self oscillating service.
This exhibit was imported to the UK and is marked as Foreign made.
The octagon etched into the envelope has the Type as 1R5 - the American designation.
Some of the wire grids can be seen but the anode encloses almost all of the details.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Data-sheet & 1040. Type DK91 was first introduced in 1946. See also1946 adverts.
