The man behind Learjet was also the inventor of this early tape format that carried 4 pairs of stereo tracks
The 4-track cartridge or Stereo-Pak is an audio 
storage magnetic tape cartridge technology, inspired by ... George Eash [also of 
Toledo, OH], an inventor who had rented space in Cousino's building in the ... 
Earl Muntz's 4-track Stereo-Pak cartridge had four monaural or two pairs of stereo 
tracks.