Hi everyone, I've thought about building a combined Welte (Red) and
Hupfeld Solophonola Vorsetzer for a while now.  Forgetting the problem
of the different tracker bars for the moment, my problem is deciding
how to build the stack.

I've only seen Welte and Hupfeld stacks and they consist of primary
and secondary valves but, from what I've seen in books, Duo-Art stacks
have only one valve (as a separate unit).

Is this right?  If so, what are the advantages of each system?
Obviously, building half the valves would be easier if I was ever to
try and build such a thing, but would the notes not repeat as well or
something like that?

Cheers
James Senior

 [ In a nutshell, the double valve system is reliable, with un-critical
 [ tolerances, but it's expensive; the single valve system is simple but
 [ it has tight production tolerances.
 [
 [ Hupfeld and Welte-Mignon systems were very conservatively designed,
 [ and the reliable double-valve system added considerable expense.
 [ The Ampico B of 1929 eliminated the primary valves of the earlier
 [ Ampico.
 [
 [ New Ampico console pianos, designed in the 1970s and produced in
 [ limited quantities, used a single-valve design like the Duo-Art but
 [ with a very lightweight valve core.  The valve core consisted of
 [ a thin disc of Neoprene rubber supported by a fluted plastic guide,
 [ much like the Universal Piano design.  The valve travel was critical,
 [ though (as in the Duo-Art).  -- Robbie