<P> From the earliest phonograph designs, many of which were powered by spring - wound mechanisms, a speed governor was essential . Most of these employed some type of flywheel - friction disc to control the speed of the rotating cylinder or turntable; as the speed increased, centrifugal force caused a brake--often a felt pad--to rub against a smooth metal surface, slowing rotation . Electrically powered turntables, whose rotational speed was governed by other means, eventually made their mechanical counterparts obsolete . The mechanical governor was, however, still employed in some toy phonographs (such as those found in talking dolls) until they were replaced by digital sound generators in the late 20th century . </P> <P> Many modern players have platters with a continuous series of strobe markings machined or printed around their edge . Viewing these markings in artificial light at mains frequency produces a stroboscopic effect, which can be used to verify proper rotational speed . Additionally, the edge of the turntable can contain magnetic markings to provide feedback pulses to an electronic speed - control system . </P> <P> Earlier designs used a rubberized idler - wheel drive system . However, wear and decomposition of the wheel, as well as the direct mechanical coupling to a vibrating motor, introduced low - frequency noise ("rumble") and speed variations ("wow and flutter") into the sound . These systems generally used a synchronous motor which ran at a speed synchronized to the frequency of the AC power supply . Portable record players typically used an inexpensive shaded - pole motor . At the end of the motor shaft there was a stepped driving capstan; to obtain different speeds, the rubber idler wheel was moved to contact different steps of this capstan . The idler was pinched against the bottom or inside edge of the platter to drive it . </P> <P> Until the 1970s, the idler - wheel drive was the most common on turntables, except for higher - end audiophile models . However, even some higher - end turntables, such as the Lenco, Garrard, EMT, and Dual turntables, used idler - wheel drive . </P>

When did the record player first become commercially available at an affordable price