In regard to Ampico B roll drive motor problems.  Many of these motors
have pot metal holders for the carbon brushes.  These pot metal holders
are prone to warp out of shape and hold the carbon brush so tightly,
that it cannot conduct power evenly to the armature.

A temporary remedy would be to remove the brushes, and carefully sand
or file the rough spots off the holder.  Then insert the brushes, and
it might work a few more years.

A better solution would be to replace the brush holders with new ones.
I believe these can be obtained from:

  Robert Streicher
  P.O. Box 39
  Pond Eddy, New York   12770

Bruce Clark