In response to Rob Buckingham's question regarding the tubing
connections to the modifying switch on a 1925 Ampico A:  The switch has
three positions controlling two mechanisms which affect the playing
volume of the piano.  These are the "re-regulators" and the "amplifier".

The re-regulators are secondary low-gain vacuum regulators, one for
the Bass and one for the Treble half of the piano, that are placed
after the expression regulators and serve to reduce the playing volume.
They reduce the dynamic range.  There are two tubes for this function
from the modifying switch, one tube to the Bass and one to the Treble
re-regulator.

The amplifier is a pneumatic that increases the tension on the spill
valve as it collapses, raising the maximum suction from the pump, thus
raising the loudness of the higher intensities.  It increases the
dynamic range.  There is one tube from the modifying switch to the
amplifier pneumatic control valve.

In the "Normal" position neither the re-regulators or the amplifier
are active (all three of the tubes connected to the modifying switch
are closed to atmosphere).  In the "Subdued" position the two tubes
going to the re-regulators are open to atmosphere and the one to the
amplifier is closed.  In the "Brilliant" position the amplifier tube is
open and the re-regulator tubes are closed.

Hope this explanation helps.

Bob Hunt
Kennebunk, Maine