Obsolete touring and Broadway Lighting Control System. Twelve 6000W, or fourteen 3000W, resistance dimmer plates encased in a wooden crate the size and shape of an upright piano (hence the name). Weighed approx. 800 lbs., the same weight as a modern 96x2.4Kw Sensor Touring Rack. DL's Photobucket (Picture from Theatre Design & Technology, Spring 2008, page 22.) Notice the porcelain "stage plug" sockets at the top just above the numbers 1-12. A large musical could have up to six of these, run by three or four electricians. The mechanical master lever could be specified either on the the right or the left, allowing one man to run two boards. These boards were in use on Broadway until the late 1970s, primarily because they could run on DC current and Broadway theatre owners were reluctant to spend the capital required to convert the buildings to AC. I believe the original Broadway production of Grease, which opened in 1972 and closed in 1980, has the distinction of being the last show on Broadway to use them. See also http://www.controlbooth.com/forums/glossary/8583-dimmer-resistance.html.