The 6SL7GT is a medium impedance double triode with high gain and superseded the 6SC7. It featured separate cathodes and was designed for use as AF voltage amplifiers, phase splitters and where required as a cascade amplifier of very high gain.
Each anode is folded into a cylinder with a side flange for additional area and to allow fixing.
Looking along the grid axis. The separation between and grid and anode is large.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 67 mm tall.
References: Datasheet, 1043 & 1040. Type 6SL7GT was first introduced in 1942.