Ampico "Modify" switch connections: Only one tube from the modify
switch goes to the amplifier control box  (Illustration 10., elbow 1.,
in the service manual).

With the switch set at "Brilliant" it allows atmosphere to activate
the valve within the amplifier control box that supplies stack feedback
vacuum to the amplifier pneumatic.  As the stack pressure increases the
amplifier pneumatic increases the spill valve spring tension allowing
the pump pressure to escalate up to 30" when called for.

With the modify switch set at "Medium" no atmosphere is allowed to
enter elbow 1 on the amplifier control box, and the pump pressure will
not escalate beyond 20".  In effect, medium setting is not connected to
anything, it is simply blocking the amplifier pneumatic from being on.

With the modify switch set at "Subdued", two ports within the switch
are opened allowing atmosphere to enter both subdued valves on the
expression mechanism, which in turn close the re-regulators on both
expression units.

When one understands the above, it is quite clear that the most
important setting of the Ampico is the pump pressure spring when the
modify switch is set on "Medium", otherwise the Subdued and Brilliant
settings will be incorrect.

Bruce Clark