Identifying the pure Ampico B has been a recent topic here.  I would
like to add my two cents to the discussion.

The following brands have the pure Ampico B installation: Mason &
Hamlin, Knabe, Chickering, Fischer.  These pianos have the expression
devices installed as part of the stack, as depicted in the "1929
Service Manual"

Two variants of the Ampico B are found in other brands, such as the
Marshall & Wendell.  The variation is in the stack construction.  These
stacks do not conform to those depicted in the "Service Manual".   They
are constructed as an Ampico "A" with the valves mounted directly on
the deck boards.

The expression devices are not part of the stack.  They are located
separately, but are identical in function to those mounted on the
stack.  These stacks lack either the lost motion compensation or the
individual note compensation adjustments.

Pianos made after 1932 have even more variations.  Piano brands former-
ly associated with Aeolian seem to have the most variants (the Weber
falls into this category).  The hybrid A/B piano has the B drawer, B
valves, and the A expression units with one A crescendo device.

Vertical pianos, such as the 1937 Baby Ampico spinet contain A
expression devices and may have either A or B valves.

The Ampico Service department in New York City installed the mechanism
in any piano on a custom basis.  AMICAn Alf Werolin, whose father ran
that department, worked in this retrofit area as a young college
student.

I have rebuilt an 1941 Steinway, model S,  Ampico B that was a product
of the Service Department efforts.  That particular piano has an
80-note, full B stack and a pump spill box that is located remotely
from the pump.

If the first intensity adjuster [slide] is present under the rim of the
piano, it is indeed an Ampico B with the B expression mechanisms.  If
the expression devices are an integral of the stack, all attributes of
the B are present in that instrument.   If the expression devices are
detached from the stack, the stack will be missing either the lost
motion compensation or individual note-compensation -- maybe both.

Bob Taylor

 [ Yep, that's a good description of my Weber as originally equipped.
 [ But I found the proper stack for it, for $25 (in 1958)! -- Robbie