From the TCA Western web page
As Fred says, you can run an AC motor on both AC and DC. These motors in our older trains are more correctly termed a "Universal" motor for that reason. They have a wire wound field and wire wound armature. Your typical DC motor utilized a solid magnet in place of the field windings. On the AC universal, the juice flow goes through both the armature and the field windings in series. Reversing is accomplished by reversing the relative voltage potential two the brushes and armature. That's why these motors have the more complex reversing units like the Lionel E-unit for example. On the strictly DC or Permanent magnet motor, you just reverse the potential at the transformer so the motor does not need a reverser on the loco. The sin wave of AC does not play well with the permag motor and so they just sit and hum on AC. Bad juju. The Universal AC motor does not care. Many people will run these motors off of DC as well, no issues. Unless your train relies on a dc pulse to activate a whistle or reverse function. Then you better stick to AC for that motor.
