Hi All,  In his most recent article, "Comparison of the Ampico A and B
in Concert Grands", Craig Brougher details the most basic differences
between the two systems, which are the crescendos, the crescendo
springs, and the pump spill.  While there are indeed many differences
between the systems, you will discover why the 'B' is actually limited
in its performance capabilities at the 'concert' level, whereas the 'A'
is not limited, and why the 'A' system was used instead of the 'B'
during the 'comparison performances' of the 1920's.

This is a very technical article which provides proof that the Ampico B
system was designed primarily for home use even when married with a
concert grand, and how the system was adapted to perform flawlessly in
smaller grands.  The article is located at

  http://www.player-care.com/comparison-a-b.pdf 

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA