The 6GW8 was one of the last audio triode output pentode valves designed. Uses were in domestic radio and audio equipment. Normally in single ended output stages for radiograms and tape recorders. The design proved popular in low cost stereo systems and was made by several companies, this exhibit being labeled Sylvania but made in England, probably by Mullard.
The triode is on the left. At the right can be seen the top of the control grid support rods complete with radiator fins. The getter holder is at the extreme right.
The pentode with the triode in the top left corner. The ratings for the triode section are almost identical to one half of the ECC83.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 70 mm tall.
Reference: Datasheet. Type 6GW8 was first introduced in 1961.