Spencer Chase writes in 040301 MMDigest:

> The theme system does not seem to be operating properly although
> the theme primaries do open and switch the secondary pouches between
> vacuum and atmosphere as they should.  However, the theme accenting
> is unpredictable and the sound of the theme secondaries switching
> is feeble.
>
> In the Duo-Art, the theme primaries are operated from unregulated
> vacuum so as to always be as high as the theme regulator vacuum.
> The way this piano was tubed, the theme primaries are supplied from
> the regulator that serves the sustain pedal and the note primaries.
> Is this correct?  From the fittings in the piano there is really no
> other way to connect it, but someone has definitely gone to great
> trouble to make other things not work by substituting and modifying
> parts.
>
> How could the theme secondary operate if the suction to pull the
> pouch down is less than the suction pulling it up?

Absolutely right.  The theme action cannot operate properly as connected,
except when the Theme vacuum level is at or below the regulated output
of the pedal modulator.  You should find reliable theming at low
levels, but not at high, where the feeble switching you observe is what
should be expected.

Now you have a choice, between restoring the piano as it was
originally, mistakes and all, or redoing it to play properly (i.e.,
supplying theme primaries from the raw pump vacuum).  It may be heresy
to say so, but analogous to early radios, we can expect really early
music machines to have some design errors and misconceptions.

I'd say in this case the engineers hadn't quite yet figured out how
their creation worked, they were working around others' patents, and
were under pressure to get a product out the door, so they went with
something that sort of, mostly, worked.  Later they worked out the
bugs, as thousands of good Duo-Arts attest.

Given that you have other players, you may wish to restore this unit to
original, just to preserve the history of evolution (as in duck-billed
platypus :-) and man's groping towards perfection.  This player can
show viewers that early designs had flaws.

Mike Knudsen