In MMD 150428, Joe Osborne reported finding the source of the low
frequency vibration in an Ampico A piano.  In reading his report,
it occurred to me that there is another possible defect that may be
contributing to the problem.

The typical Ampico A pump has the stack cut-out pouch inside the
distribution block at the "top".  The actual pouch is glued to
a small, slightly rectangular wooden "dish" which has a 3/16" diameter
elbow tube that communicates with the underside of the pouch, coming
out of the edge of its approximate 1/2" thickness.

There is another 3/16" elbow that goes through the wall of the
distribution block that connects with the "output" of the cut-out
valve mounted on the bass rim.  The ends of these two elbows that are
_inside_ the distribution block are connected by a short segment of
3/16" rubber tubing.  In my experience, this short piece of tubing,
if still original, can fail by turning hard and developing hairline
cracks and/or losing its "grip" on the elbows.

The inside of this tube is subjected to either full vacuum or
atmosphere through the operation of the cut-out valve.  But it is also
subjected to, on its outside, by the pump vacuum which surrounds it.

If pump vacuum leaks into this tube when it should be pure atmospheric
pressure, the cut-out pouch (not its control valve) can flutter,
causing the sound Joe has heard, and probably in the area he reports,
but only during rewind.  If the noise is present only during play, then
the most likely cause is still the cut-out valve or leakage in its
pouch tube going to the transmission frame.

John Grant