Early sound transcription and reproduction was solely dependant on acoustical/mechanical means. The early 1920’s saw the vacuum-tube amplifier invented by the American Lee De Forest come into use. This marked the transition from mechanical to electrical recording. Microphones took over from acoustical horns, and lo and behold the development the modern 78-rpm electric phonographic amplified player, a motor-driven turntable that incorporated a record-changing device, a cartridge, and loudspeakers. These records were originally made of shellac and later of synthetic thermoplastic resins with a playing time of about 4 minutes, which became standard. ...... More on Lee De Forest in History of Vinyl Part 5 | 
