Recently, I noticed my Model A Ampico was getting unusually louder on
some of the loud passages. The music seemed to be exaggerated. Upon
checking the pump pressures, I found that they had slowly increased
since I had carefully adjusted them during the winter months.
It is summer now, and the humidity has increased also. In spite of
attempts to reduce the humidity, I have notice for many years, that
pump pressure variations correspond to the percentage of humidity.
Upon checking the pump pressures, I found Medium to be 26" and
Brilliant up to 45". No wonder I thought Frank Milne was having
a bad day!
It is a simple matter to readjust these pressures, and I would like
to pass on a shortcut on this procedure.
Place a piece of masking tape over the port in the take up spool.
Place a roll on the piano, but do not connect the metal ring to the
hook in the take up spool. Set the tempo lever at 80, set the lever
at play, and turn on the motor. Make certain the tracker bar vacuum
holds the roll securely to the tracker bar. (The reason for setting
the tempo at 70, is the air motor uses air, and makes a difference in
the pump pressure setting)
Turn the modify switch to medium, connect a vacuum gauge to a bass or
treble unit valve (either one), and trip each intensity valve 2, 4 & 6,
by lifting the valve top slightly, for the section, bass or treble,
where the gauge is connected. The valves will lock to the on position.
Check the gauge. It should read 20" of vacuum. If not, remove the
spill box cover on the pump. Carefully and slowly rotate the larger
spring on the pump spill valve, until the reading is correct (20
inches). When it is correct, set the modify switch on Brilliant, and
the reading should be 27" to 30" of vacuum. If this is different, turn
the large screw in the top of the amplifier pneumatic until the correct
reading is obtained.
The first intensity usually is correct when the correct pump pressures
are set. If they are incorrect, they can be set by turning the adjust-
ing screws on each crescendo pneumatic. These should be set as low as
possible, but high enough that the softest notes do not drop out when
the soft pedal is on. Usually this setting is between 4.5" up to 7" of
water vacuum, *if* the gauge is correct on low settings. Most gauges
are not, so I suggest you use your ear to get this properly set.
My gauge came from the Ampico factory, and is correct on higher
readings, but incorrect on very low readings.