The 6SN7GT is a glass tubular version of the 6SN7 double triode valve. Each half of the 6SN7 is electrically equal to the 6J5 triode.
The construction uses a glass pinch and two separate electrode structures are visible through the envelope, the cathodes are separate.
The 6SN7 was designed for audio applications and is still used for valve hi-fi.
The anodes are 7 mm wide.
The triode sections are flat sided with rounded ends. For heat radiation and ease of support the anode is pressed with a side flange that also provides the place for the two halves to be stitched together.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 69 mm tall.
References: Datasheet, 1040 & 1043. Type 6SN7GT was first introduced in 1941.