cleeds,
thanks for the info about cartridges, I have read in several places over the years that 8 tracks were developed by Lear, for radio ads, so I am guilty of repeating bad info, it's good to know more.
consumer pre-recorded 8 tracks, bad as they are, were a revolution because of portability. the 1st time I took one apart, I couldn't believe the mechanism. how does tape come off the inner diameter and go on the much larger outer diameter? 1 revolution, very different lengths of tape on and off??? took me a while to understand the slip sheet and gradual tightening involved. then yanking the tape up and over the top of the spool of tape, OMG.