This 6V6GT is from Sylvania and also carries the US Government code of VT-107A.
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. With the revival of interest in valve hi-fi the 6V6 has again found popularity and a pair in push-pull will deliver 10 Watts with low distortion.
The inner coating obscures the electrodes but the connections from the pinch are visible
On test this exhibit exhibited 104% of specified performance.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 70 mm tall.
References: Data-sheet, 1040 & 1043. Type 6V6GT was first introduced in 1937.