With regard to Bill Chapman's inquiry in MMD 160205, it sounds as if
he may not have observed the late Ampico "A" design with the so-called
Loud Pedal Compensation pneumatics.  Admittedly, these are not well
documented in the literature, however, as he observes, they act in a
direction to oppose the force of the "spring" pneumatic, resulting in
a slight reduction of the stack power.

These 1-inch square pneumatics should be teed together and thence
into the tube or valve supplying power to the loud (sustaining) pedal
pneumatic.  The quick and simple explanation of their purpose is this:
When the loud (sustain) pedal operates, it lifts _all_ of the dampers
away from the strings, thereby removing their weight from the "path"
of the individual striker pneumatic(s), resulting in a slightly louder
sound than was deemed appropriate by the Ampico engineers, had these
"compensating" pneumatics not been incorporated.

A more thorough discussion by Dave Saul, which references an even more
comprehensive discussion in an earlier AMICA Technicalities article,
may be found at

http://www.mmdigest.com/Archives/Digests/201303/2013.03.27.04.html 

The overall effect is quite subtle and may not even be noticeable in
an action that is not otherwise carefully restored and adjusted, but
in action, it anticipates the effects of the "Sub-intensity" found in
the Ampico "B" mechanism.  For the advanced restorer, these pneumatics
may be easily fabricated and added to earlier Ampico "A" mechanisms
not originally equipped with them; however, careful attention must be
paid to the exact dimensions and geometry of placement of any such
"retrofits".  Particularly important is the location of the pneumatics
"operating point" in terms of its distance from the hinge of the spring
pneumatic.

With regard to Bill's comments about his "blocked" intensity valves,
I can assure him that no drilling is necessary!  The purpose of the
factory installed "plugs" is to close off "construction" holes which
allow the creation of internal channels necessary for the lock and
cancel function.  This was a time and labor saving way to create these
channels which otherwise would have required (at least) two pieces of
wood to be machined separately, then glued together, a construction
that has its own possible failure modes.  A more thorough study and
understanding of the way the lock and cancel works is advised.

John Grant