The Ampico model A crescendo units are both the same for treble and
bass.  When both #1 and #5 signal tubes are closed, the crescendo
units flutter, in preparation of a signal from a perforation in the
roll passing over the tracker bar.

This fluttering point is the zero setting, or the lowest vacuum the
piano will play softly, with the soft pedal on, and not drop out
notes.  The zero setting is accomplished by adjusting the spring
tension on the crescendo unit.

#5 and #1 on each crescendo unit receive the signal from the tracker
bar.  #1 by itself is a slow crescendo, _but,_ #1 and #5 together are
a fast crescendo.  #5 by itself is a decrescendo.

Test the crescendo mechanism carefully.  Remove the #1 tube, and
the crescendo pneumatic should close very slowly, until it is closed
completely.  It will over-ride the intensities.

If your Ampico unit is functioning perfectly, when you remove #1B
and #1T from each crescendo unit, the stack vacuum should reach 20"
(if the modify switch is set on Medium) and about 30" if the modify
switch is set at Brilliant.  If your crescendo unit is not doing this,
then either there is a leak some place in the crescendo unit (check
the hinge ends and gaskets) or the valves within the units are not
seating properly.

After replacing the #1B and #1T hoses on the crescendo units, the
vacuum should decrease to between 5" and 7" of vacuum or to the zero
setting, unless an intensity valve has been tripped.  #7B and #7T
should cancel the intensities.

Bruce Clark