This is a more powerful audio valve than the 6V6GTY receiver type. The construction of this GTY variant is on a pressed glass foot base and housed in a tubular envelope. A flat cathode, zig-zag grids supported on notched rods, shaped beam plates and an anode cavity with side fins forms the electrode structure.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins, is 83 mm tall.
Reference: Datasheet. Type 6L6GTY was first introduced in 1946.