Devised, researched
 and written
  Peter King Smith BSc

                                                         The mid-1960s, German-built multi-track tape recorder with FM/AM/SW radio

Common Faults

Machine develops intermittent hum

Cause: The music center can produce two types of humming sounds: (i) a hum which in fact is a 'pilot tone' that is automatically recorded onto the tape during RECORD mode, and audible in PLAYBACK mode at the end of a recorded track, and (ii) an intermittent hum resulting from a failure of the head-switching mercury relay. It's the Type 2 hum that is relevant here.

Remedy: If one of the mercury relays fails, the only solution is to replace the failed mercury relay with a modern, conventional one. (See also 'Trouble with relays').