I bought a tube powered reel to reel tape player at a thrift store. It has an input, amp out and speaker out. It sounds great for bass, not quit as good with guitar because it's voice too low. I has six tubes. two 12au7 one 12ax7 one 12ab5 one 12x4 and one crazy green eye type of thing that must be for looks. which one is the power tube and how much power could it be putting out?