[ Bob Stewart posed this query in 030222 MMDigest. ]

Here is my theory: Many of post-1928 Ampicos I've worked on show signs
that the factory was using up leftover or surplus stock, which any
business would have done when things got tight.  I've seen many units
that have "A" and "B" parts mixed together.

The most common instance is a unit which has the "A" expression system
but the stack will have "B" valves.  A 1930 Haines grand I worked on
many years ago had a Welte Licensee drawer, pump and stack.  The
expression devices were typical Ampico.

I'm presently working on an Ampico A stack that has three different
valve types mixed throughout.  Most of the valve blocks are the later
"A" type, but with a wooden cap.  Two dozen have the common pressed
steel plate and eight of them are a design I have never seen before.

It is the same "A" style block but it has an inset steel plate which
looks like a Simplex plate only larger.  The valve is designed, and
sits on a simple brass grommet exactly like valves in a Western
Electric or Seeburg.  In this stack these valve blocks are "dummies"
substituting for the solid blocks that are used at the breaks.  Were
these experimental valves that flopped or infringed on somebody's
patents?

I have also seen mixing of "A" valve seats which have a larger inside
diameter than the "B" (they both fit in the same hole).  I have to say
however that I have only seen this done in units with the "A"
expression system.

Brian Thornton - Short Mountain Music Works
Woodbury, TN
http://www.shortmountainmusic.com/