The spring adjustment on the crescendo mechanism has nothing to do
with the subdued setting.  The correct subdued setting is obtained by
adjusting the nuts on the springs of the bass and treble reregulating
pneumatics.

See Illustration 3A in the Ampico service manual.  The adjustment is
made at

  17. Leather nut under the spring of the reregulating valve.  Increase
  or decrease spring (16) tension.

Before this can be done, you must first check the pump pressure to see
that it is correct on Medium and Brilliant.  You must use an accurate
vacuum gauge to do this.

  Cover the tracker bar with masking tape.  Set the Tempo at 70.
Move the lever to Play, set lever to Repeat (to keep the motor on).
Turn on motor.

1. Attach the vacuum gauge at the stack, using any nipple on a unit
valve, while keeping in mind there is a division [mid-keyboard] between
bass and treble ends.

2. Set modify switch at Medium.

3. Disconnect hoses 1B and 1T on each crescendo mechanism.  (Both
crescendo pneumatics should close.)  This will raise the stack vacuum
to its highest level.

With the modify switch set at Medium, the stack pressure should read
20 inches.  Adjust this by slightly rotating the spring in or out,
#7 on the top of the pump nearest to the Amplifier pneumatic.  Ref.
Front Assembly Illustration 9 in service manual.

4. Next move the Modify switch to Brilliant.  The stack pressure reading
should be between 27 to 30 inches.  This is adjusted by turning the
screw in or out on the amplifier pneumatic, #8 of Front Assembly
Illustration.  If these readings are correct, proceed.

5. Move the Modify switch to Subdued and adjust the tension of the
spring on the reregulator by turning the leather nut up or down
The stack vacuum should be reduced to between 10" to 12" of vacuum.

6. Replace the hoses 1B and 1T on both crescendo units.

7. The spring adjustments on each crescendo units are for setting
the softest level of playing.  The factory specification is a vacuum
reading of not lower than 5" nor higher than 7" of vacuum.

Bruce Clark