Which tube does my amp use? 12AU7 12BH7 12AX7 6CG7 others?

[SY]

Thanks- my memory failed me, the second hole is also a 12A*7. The third hole is a cathode follower, and that's likely to be 6CG7/6FQ7.

 

[HP8903B]

The third hole is a cathode follower, and that's likely to be 6CG7/6FQ7.

Yeah I think you had this one right the whole time as this socket only lights up the 6CG7.