The 6SL7GT is a medium impedance double triode with a gain of 70. It was designed for voltage amplification in audio amplifiers and/or as a phase inverter.
The twin triodes each have a folded plate anode sealed to the support with a flange for greater heat dissipation.
Seen from the back the locking hooks in the anode plates can be seen.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 62 mm tall.
References: Data-sheet, 1043, 3002 & 1040. Type 6SL7GT was first introduced in 1942. See also1942 adverts.