Hello MMD again.  I have a couple of questions about the Half Duo-Art's
Temponamic controls.  I have sent Robbie a slightly blurry photo of the
external part of the control shaft, taken before I started any serious
dismantling.  I guess he will put it into the photo gallery.

Below is a statement of what I think all the external controls are for.
If anybody can find any errors in my ideas, I'll be very grateful to
find out about them.

There are four separate arms on this shaft.  The bottom one is the only
metal one.  It is clamped to the shaft and its motion controls the
position of the moving surface of the knife valve inside the box.
However this arm is not connected directly to the accordion pneumatics.
That connection is made to the wooden arm just above the metal one, via
the long wire rod running off to the right-hand side of the photo.

However, there is a long pin attached to the metal arm (the pin looks
vertical in the photo) and the wooden arm transfers motion to the metal
one because it presses against this pin. A by-product is that this
arrangement roughly doubles the torque and halves the angular shaft
motion caused by the collapse of an accordion pneumatic.  Perhaps more
importantly, this arrangement means that the metal arm can be
controlled by something other than the accordion pneumatics.

That something is the Temponamic control.  When the Duo-Art is switched
off, the accordion pneumatics are all pulled open and the Temponamic
comes into play.  As this control is rotated clockwise, the connecting
rod causes the top lever in the photo to rotate anti-clockwise.  As it
does so, it contacts the "vertical" pin on the metal arm and has the
same effect as do collapsing accordion pneumatics.  That is, the
accompaniment level is increased as the Temponamic is rotated clockwise.

But what if the Temponamic is rotated anti-clockwise?  As far as I can
tell, this affects only the third arm on the control shaft, counting
outwards from the box.  At the expression box end, about an inch of the
connecting rod between the Temponamic lever and the expression box
control shaft is bent through a right angle.  This end of the rod
passes through a bushed hole in the end of the outer (fourth) arm, and
controls its position.

But the bent over portion of the rod is much longer than necessary for
this task alone.  The excess protrudes out into the space occupied by
the third arm and contacts a pad at the end of this arm.  The arm
contains a pallet valve, which opens when the Temponamic lever is
rotated sufficiently anti-clockwise from its rest position.  Opening
this pallet actuates the Soft Pedal pneumatic, unless my back-tracking
of various small diameter tubes has gone wrong..

I don't think that the anti-clockwise rotation of the Temponamic lever
does anything else, and this worries me a bit.  If I'm correct, the
accompaniment will be at level zero (or whatever the lowest level is
called) and all the hammers will be resting in the Soft position.
It will certainly be a quiet performance.

I don't think I believe what I've written here.  Can anyone put me out
of my misery?

John Phillips in Hobart, Tasmania

 [ I'll place thephoto at http://www.mmdigest.com/Gallery/Tech 
 [ -- Robbie