The 6K6GT is an audio output pentode designed for the final audio stage of television and radio receivers. Strapped as a triode it is also rated for service as a frame (vertical) output valve.
Electrically it is identical to type 41 it was also released in 1950 with a Loctal base under the type number of 7B5E.
The reverse shows no markings.
The top view reveals three sets of grid supports indicating that this is a pentode. The control grid copper supports are topped off with a horseshoe shaped head radiator.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 68 mm tall.
References: Data-sheet, 1040 & 1043. Type 6K6GT was first introduced in 1937. See also1937 adverts.