The tube at left is a type 1626 rebranded "12J5GT" by an unknown rebrander. The center tube is a real 12J5GT, while the tube at right is a correctly branded type 1626. The "GT" suffix would indicate a tubular T-9 bulb and an 8 pin octal base.
The 1626 is not a good substitute for a 12J5GT. The most important difference is that the 1626 has a gain of 5 compared to a gain of 20 for the 12J5GT.