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MMD > Archives > January 2018 > 2018.01.20 > 04Prev  Next

Regulating the Ampico A
By Bill Luecht

There is an updated version of Bruce Clark's excellent article about
regulating the Ampico A at John Tuttle's Player-Care site: 

In the updated article Bruce recommends removing the 1B and 1T
tubes from the crescendo devices to cause the expression mechanisms
to go to maximum volume level (rather than poking holes in the tape
over the tracker bar).  This is much easier to do and undo, especially
if you are already lying on the floor under the piano to make the
other adjustments.

One important adjustments that is rarely mentioned is the initial
setting of the "at rest" suction level inside the crescendo units
(this is the suction level inside the crescendo and spring pneumatics,
not the stack suction level).

In his 1974 publication, "How to Rebuild the Model A Ampico", David
Saul says to set this to between 3 and 4 inches of water.  An AMICA
Technicalities article (that I can't locate now) specified the 3.7
inches setting that I use.

Do this for both bass and treble sides.  Remove the tube that connects
the crescendo to the spring pneumatic from the spring pneumatic, and
connect it to a vacuum gauge.  Tracker bar holes 1T and 5T (or 1B and
5B) should be closed, and the crescendo pneumatic should be open to the
zero setting equilibrium point. Adjust the crescendo spring tension
until the gauge shows 3.7 inches.

Now, re-connect the tubes to the spring pneumatics, connect the vacuum
gauge to the stack and adjust the pump spill valve and amplifier as in
Bruce Clark's article.  Then adjust the first intensity suction levels
by adjusting the leather nuts on the arms of the spring pneumatics where
they connect to the regulator stem.  Fine adjustments to the first
intensity can be made later by adjusting the crescendo spring nuts,
but the initial setting should be done as above to ensure that the
crescendo and spring pneumatic are operating within the correct range
of suction levels, so that the crescendo "ramps up" at the correct

It is important to calibrate your vacuum gauge to a water gauge
(manometer), particularly when measuring low suction levels.  I made
a water gauge from an 8-foot piece of 3/4" clear plastic tubing from
Lowe's, an old board and some nails. I have two vacuum gauges; I found
that the "new" gauge is off by 1-1/2 inches throughout its range and
the old one is off by varying amounts.

Bill Luecht

(Message sent Sat 20 Jan 2018, 20:44:55 GMT, from time zone GMT-0800.)

Key Words in Subject:  Ampico, Regulating

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