Fellas,
I used to own an AMX pre amp which I have now sold to one of our member friends. It had a pair of 12AU7 tubes and a sovtek brand that looked just about as tall but twice as fat behind and between the 2 smaller 12AU7s. Another member told me that the AMX was solid state rectified, and the last tube did not actually function. And it never did in fact work. When he tested it, apparently, it would not light up, yet had no perceived effects on the sound. I am unsure if he mentioned that you could even pull it out.
Interestingly, the newer AMX pre amps did not have the 3rd tube. Could this have something to do with the rectifier? Or could this have been made so that if you wish to upgrade the pre amp into a phono stage, you can do so without having to add an extra tube since it is already there? Hope someone can help. Our friend might have just bought more (or less) than he expected.
cheers
whipsaw