It has a pair of 12AU7 tubes and does invert polarity.
Begin by taking out the screws that hold down the top plate. Be sure the unit is unplugged before you do this. To remove a tube, gently rock it a few degrees back and forth while pulling up. Some will tell you to wear gloves to keep oils off the tube but I don't think it makes any difference. The pins are not symmetrical so the tube can go back in only one way. Line up the pins in the holes and gently rock back and forth a few degrees while pushing down.
Begin by taking out the screws that hold down the top plate. Be sure the unit is unplugged before you do this. To remove a tube, gently rock it a few degrees back and forth while pulling up. Some will tell you to wear gloves to keep oils off the tube but I don't think it makes any difference. The pins are not symmetrical so the tube can go back in only one way. Line up the pins in the holes and gently rock back and forth a few degrees while pushing down.