[ Björn Isebaert wrote in 120126 MMDigest --

> On the cylinder there are two raised metal strips which operate
> a key that no longer has a function. ... On the left side of the
> case there is a turnable knob which apparently had something
> attached to it, ...

The knob on the left is probably to turn off auxiliary instruments by
lifting the tracker bars.  On my cylinder piano the knob turns a long
shaft with cams that turn off the castanets, drum, and bells.

Marc Kaufman