When Al Pebworth asked (MMD 12.02.14) about identifying a stack
thought to be removed from a Steinway AR, he wrote directly to me as
well. My response had to be delayed until I returned home from a trip.
I just finished looking at the scale stick for the Steinway AR. From
the bass end, the stack follows this pattern: 16-31-17-16. This is
for the 80-note stack. Older large 88-note stacks would have four
notes added at each end.
The AR stack is always easy to identify as it has a huge section two
with 31 pneumatics. I think this feature is unique and no other stack
comes close to that number.
To repeat what has already been said, the Steinway XR and OR stacks
are interchangeable. Not counting the rare Model D or Duo-Art
Concertola style pianos, that means in the USA only two stack sizes
exist (within the 80-note group) for Steinway pianos. The XR/OR
pattern is 22-28-17-13, for the 80 note stack. Again, add four notes
to each end for the larger 88 note stack.
Another size Duo Art (7' 6") based on the Steinway model B was built
in England using Hamburg Steinways. Only one of those pianos has made
it to the USA and that is in my collection. The other five or so are
thought to be in the UK or Europe. It is believed that all were built
as Pedal/Electric pianos.