[ Ref. Niels Berkers in 201215 MMDigest ]

Niels, your intention to built an interchangeable system with a
73-note Hupfeld and an 88-note tracker bar evokes another problem,
because the running direction of 72/73-note rolls from bottom to top
is just the opposite to 88-note rolls.

The rare original Hupfeld instruments with a 73/88-note tracker bar
have a special twin gear unit for the roll driving motor and a take-up
spool with movable flanges to place in the opposite position.

Hans Schmitz
Stuttgart