The CV511 makes no secret of the fact that it is the equivalent of the commercial 6V6GT. This looks like a Brimar supplied device.
The 6V6 family of beam tetrodes came in many constructions and were very popular as the final audio stage of broadcast receivers. The original 6V6 was an American metal can valve from the mid 1930s.
The valves were capable of push pull use but the normal environment was as a single end output stage.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 71 mm tall.
References: Data-sheet, 1040 & 1043. Type CV511 was first introduced in 1937. See also 1937 adverts.