Ampico Sustain Pedal Compensating Pneumatics
By Art Reblitz
Re "Enigmatic Pneumatics In Late Ampico A Actions"
The little pneumatics should be tubed to the sustaining pedal
valves. When the sustain pneumatic lifts the dampers off the
strings, there is less weight (in a grand) or spring tension (in
a vertical) counteracting the force of the stack pneumatics for the
notes that have dampers. Consequently, the stack plays the notes
which have dampers a little louder when the dampers are lifted than
when they are at rest. The compensator pneumatics lower the suction
by a tiny amount, counteracting this effect.
This is described and illustrated on pp. 159-160 of my book "Player
Piano Servicing and Rebuilding."
(Message sent Thu 11 Jul 2002, 02:10:44 GMT, from time zone GMT-0600.)