The CV0511 is the equivalent of the 6V6GT audio output valve.
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 and the little brother of the 6L6, the world's first aligned-grid beam tetrode to achieve quantity production.
The valves were capable of push pull use but the normal environment was as a single end output stage.
The internal coating is thinner near the top showing the oval anode within.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 68 mm tall.
References: Datasheet, 1040 & 1043. Type CV511 was first introduced in 1937.