Hi Bob, Pianocorder pedal solenoids do indeed operate from the 170 VDC
supply, though never at full duty cycle. The playback logic board uses
pulse width modulation to provide a stronger initial surge followed by
a reduced hold force.
In stock Pianocorder systems, the surge lasts about one second, which
is too long and causes the dampers to float during passages with fast
pedaling. The late Carl Meyer devised a simple modification which
reduces the surge duration to about 1/5 second, improving the pedaling
response, but Superscope/Marantz never adopted this improvement.
Complete Pianocorder schematics and other service documentation are
available in PDF format at http://www.pianocorder.info/