Last month, a discussion about the mysterious Mason & Hamlin tension
resonator was in several issues of the MMD.  Jeffrey Wood shared his
vast experience and fairly well put the cap on that discussion (MMDs
060316 & 060317).

When I was first learning about pianos early in my career, I was
told by one of my mentors that some Mason & Hamlins appeared with no
resonators at all.  I never got to see an example but I believe the
story, as it came from a rebuilder of many pianos in Chicago.

It was hinted by Jeffery that some Mason's have the tension resonators
partially removed to accommodate the Ampico mechanism.  I have seen that
as well.  But the installation of the Ampico does not always result in
removal of the spokes of the resonator.  I have seen six spokes in the
RA, eight in the RAA, and ten spokes in the RBB and RCC.  So it seems
that these pianos have the same number as their non-player counterparts.

Bob Taylor
http://members.socket.net/~rtaylor/aeolian_pipe_organ.html