Mark Williams asks about the Ampico A pump and spill valve.  His first
question asks about the spill valve on the pump: "When the spill valve
is closed should it be air tight?"

The answer is absolutely not.  Some air should be allowed into the
pump.  If not, the pump could become damaged, or the motor could stall
and burn out.

The spill valve is also an important part of the expression system, and
needs to be carefully regulated.  To accomplish this, a sensitive vacuum
gauge is required.  It cannot be done accurately without using a vacuum
gauge.

Cover the tracker bar with tape, set the repeat switch to on.  Set the
Tempo to 60, turn on the motor, and carefully prick holes in #2, #4, and
#6 on each end of the tracker bar.

With the modify switch set on Medium, and intensity holes 2, 4 & 6 in
the on position [open], the vacuum gauge reading at the stack should
read 20 inches.  This is adjusted by slightly rotating the longer
spring on the spill valve, and usually can be done by using the thumb
and forefinger.  (The hose to the vacuum gauge can be connected to a
nipple on a bass or treble unit valve.)

After the spill valve and amplifier pneumatic are properly adjusted,
there should be a muffler cover lined in felt, placed over the
amplifier pneumatic and spill valve, which quiets the sound of the air
entering the pump.

At this point it is important to adjust the amplifier setting.  Move
the Modify switch to "Brilliant".  The vacuum reading should be between
27" and 30", not more than 30".  This setting is adjusted by rotating
the large screw on the top side of the amplifier pneumatic.  Turn it
inward for less, and outward for higher.  Usually a half turn or so
will be sufficient, unless someone unfamiliar with the Ampico has
adjusted it improperly.

Mark's second question, "There is a distinct change in the repetition
around E above Middle C, with the bass section not functioning as
well".

The stack is divided in half, between these two notes.  Each half is
controlled by an identical system, Bass and Treble.

If there is a weakness in either the Bass or Treble section, it can
mean several things.  I would suspect air leaks.  Often the gaskets on
the ends of the stack, if not replaced, will leak atmosphere into the
stack and lower the vacuum to a point where there will not be good
repetition.

In addition there might be a bad unit valve or more.  Often unit valves
will crack on their sides, from the pressure of the clamp that holds
them in place.  Remove one or two valves and examine them for cracks in
their sides.  Slight cracks can be filled in with thick shellac.  There
is a possibility some of the valve seats may have loosened over the
years.

The other problem might be that the spring tension on the crescendo
units has been altered by someone unfamiliar with the settings.  To
adjust this, turn off the motor, remove the tape first placed on the
tracker bar that was perforated, and place new piece of tape over the
tracker bar.  This time, do not perforate it.

Turn on the motor, and take a vacuum reading from each end of the
stack.  Both Treble and Bass should be the same.  This setting should
be set low enough for repetition.  The factory specifications are
between 5" and 7" of vacuum.  The setting for this is done by
increasing or decreasing the tension of the spring on each of the
two crescendo units.

Bruce Clark