I might stick in my two cents to answer Robbie's question here:

>[ In my (American) Aeolian Themodist the accomp regulator vacuum is
>[ fixed with a spring, and the slide valves are a crude variable bleed
>[ to the theme supply.  I'd much rather the accomp vacuum were a
>[ _regulated percentage_ of the main reservoir vacuum.  A slide lever
>[ won't do this.  Have you ever seen a regulating mechanism which could
>[ maintain a constant proportion?

The perfect proportional regulator is the regulating Hickman curtain
regulator.  With a simple adjustment and no springs at all, it will
regulate an instrument perfectly at whatever percentage of the pedal
power you wish to generate momentarily.  Then your theme can simply
bypass it for accents, or, it can go through a cutout setup which in
effect adds more vacuum under the regulator curtain, opening the
effective supply to the stack momentarily, without the need for a
bypass.  All this happens to be in my Orchestrion Book, too.  See
Chapter 8 -- Designing Expression Regulators.

Craig Brougher