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 American Government procurement code is VT-231.
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 anodes are 7 mm wide.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 67 mm tall.
References: Datasheet, 1040 & 1043. Type 6SN7GT was first introduced in 1941.