I think what Pat DeWitt is referring to [060203 MMDigest], is
the Ampico _Subdued_ re-regulator.  The Subdued setting can only
be adjusted _after_ readings on medium and brilliant are correctly
set.  The Ampico mechanism must be performing properly and have no
leaks in the system.  The correct settings cannot be accomplished
without the use of an accurate vacuum gauge:

  20" when the Modify switch is set at Medium;
  between 27" and 30" when the Modify switch is set at Brilliant.

To test these using a vacuum gauge, temporarily disconnect hose 1B
and 1T from the crescendo mechanisms (see Illustration 2., Crescendo,
in the service manual).  This will temporarily raise pump and stack
pressure settings to the upper limit, providing there are no major
leaks in the system.

First test the setting for Medium.  _This is the first and most important
setting._  If one does not obtain a reading of 20" the pump pressure spring
may require slight adjustment (see Illustration 9, Front Assembly).

Adjust Medium setting by slightly rotating spring (#7 on top of pump)
between thumb and forefinger, until a reading of exactly 20" is
obtained.  Once this has been accomplished, move the Modify switch to
Brilliant, and the reading should move upward to 27" or 30" but not
over 30".  If this reading is incorrect, it can be adjusted by slightly
turning the large screw #8 in the top of the amplifier pneumatic, until
the correct reading is obtained.

Readings are taken by attaching vacuum gauge to a nipple on a bass or
treble unit valve, and readings for both bass and treble should be the
same.  If not, check for leaks in the stack, unit valves or pump.

If both Medium and Brilliant readings are correct, set the Modify
switch to Subdued and proceed to adjust the leather nut (17) under the
spring (16), increasing or decreasing spring tension until the vacuum
gauge readings are equal on both treble and bass sides.  This reading
should between 10" to 12" according to softness desired (see
Illustration 3A in Inspector's Reference Book.)

Replace the hoses on the crescendo mechanisms and the expression system
should be correctly adjusted.

Bruce Clark