Founded by Henry Auchey and Chester Albright in 1904, it is the oldest roller coaster manufacturing company still in existence. More than 145 coasters were designed and built by PTC, 82 of which are still currently in operation; the company has also built 94 carousels over the years and 32 are still operating today. They are currently better-known for creating the trains used on wooden coasters, and they also manufacture queue systems for amusement parks. (The company is currently known as Philadelphia Toboggan Coasters, but many people still use the old name.)

Sources
http://www.aimsintl.org/phtobcoa.htm
http://www.univox.com/~barmah/jmiller/ptc.html