Pathos In Power - Tubes????

The 12AX7 was the most common member of what eventually became a large family of twin-triode vacuum tubes, manufactured all over the world, all sharing the same pinout (EIA 9A). Most used heaters which could be optionally wired in series (12.6V) or parallel (6.3V), with respective current requirements of 150 mA or 300 mA. Other tubes, which in some cases could be interchangeable, include the 12AT7, 12AU7, 12AV7, and the low-voltage 12U7, plus many 4-digit EIA series dual triodes. They span a wide range of voltage gain, ruggedness, and transconductance.

I am guessing since they are interchangeable according to the above information. I would think you will not do any harm to the amp if placed in the wrong socket. I would still wait until someone with more knowledge can guide you in the right direction.

I did some "Googling" and found a comment on "thefind.com"" regarding the tube complement for your amp, listing 4 EL 34's, TWO 12ax7's, and one 6n6. That makes more sense to me, anyway. Probably some prior owner just stuck in a different tube and when it seemed to work: VOILA! Check with the manufacturer if you can, but it sounds like your in the market for a PAIR of 12ax7's (NOS Mullards sound warm and smooth, the european tubes (Siemans, WEST GERMAN Telefunkens, Mazda Chrome plates sound "accurate"). My personal favorite 12ax7 is a WEST GERMAN Telefunken, and I recommend that if you can find a good testing used pair of MacIntosh, Fisher, Eico, or Dyanaco labelled Teles', you have scored! Anyway, FWIW, that's what I found on your present dilema. Happy Listenting, as it sounds like you've found a very nice integrated amp.

The first owner may have had a source device that had a higher voltage output than he appreciated. The 12AU7 would have exhibited a slightly lower gain than the 12AX7. He may have preferred the sound of that tube, to what was provided by the designer. As mentioned: no harm will come to the amp, if you insert the tube(either as the input or driver tube), as it is interchangable with any of the 12AX7 family. Happy listening!