The 12J5GT is a single triode with a heater designed for possible use with vehicle supplies.
The electrical characteristics of each half of the 6SN7 match those of the 12J5.
The base also carries the VT-135 identification and the fact that this valve was made for the military. The anode can be seen to have a small depth from front to back.
The carbonised anode is held together with stitches. The grid has a heat radiating fin across the supports.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 65 mm tall.