This 6V6GT is from Mullard and does not feature a Mullard type number. This shows the degree to which the 6V6 was regarded as a standard. Unlike most 6V6’s this valve has a glass disc base, like the all glass valves, and not a pinch. It is interesting to note that the original metal 6V6 also had a glass disc base, and only the glass valves that followed the original metal valve used the older pinch construction. The EL34 introduced in 1954 also has the same style of glass disc base with lead-out wires going into the IO plastic base rather than directly to pins. It is probable that this valve was designed in the late 1940s or early 1950s.
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 one of the first valves on an IO base.
The valves were capable of push pull use but the normal environment was as a single end output stage.