 A playback head can then pick up the changes in magnetic field from the tape and convert it into an electrical signal to be amplified and played back through a loudspeaker.The first wire recorder was the Telegraphone invented by Valdemar Poulsen in the late 1890s.Wire recorders for law and office dictation and telephone recording were made almost continuously by various companies (mainly the American Telegraphone Company) through the 1920s and 1930s.