The Rhodes piano was the brainchild of musician Harold Rhodes. While a flying instructor stationed in Greensboro, North Carolina, Rhodes designed his first portable acoustic piano for the U.S. Army Air Corps in 1942. Beginning with a pile of aluminum tubing salvaged from a B-17 bomber, Rhodes fashioned a sort of xylophone with a 29-note keyboard. Following World War II, Rhodes built a self-amplified, 38-note electric model called the Pre-Piano after taking apart a chiming clock that used spun-metal rods called tines. Introduced in 1970, the 132-pound Mark I is made of wood, covered in a fabric-reinforced vinyl called Tolex, and sized to fit into a box that measures 45.25 by 9.85 by 23.63 inches. A compartment in the top cover houses four telescoping tubular steel legs that screw into the instrument's underside at a splayed angle for sturdy setup. A long metal sustain pedal attaches to the keyboard mechanism through a small hole in the center of the piano's underside via interlocking rods. The Mark I was manufactured in 73- and 88-key models. On the early Mark Is, the hammers were made of felt-covered wood; they were replaced on later models by rubber-covered plastic. Sound is generated when the key action causes the hammers to strike the tines. Audible vibrations are picked up by a system of individual magnets positioned close to the tip of each tine.