The piano Andy describes is a Baldwin Electropiano, designed for use in
a piano lab classroom setup.  Fortunately, they did not make them very
long.  They were a bear to tune.  The early ones used three-string
unisons, later went to one string per note.  The actions were not
conventional spinet drop action, but with the hammers hanging down.
There was some sort of pickup bar (electrostatic?) that crossed the
strings to provide the input to the amplifier.  Baldwin finally went
to an all-electronic instrument.

Bill Maxim