Retro Tech: This 1960s BGM Machine played the Biggest Cassettes ever made

A look at the largest music cartridge format ever made
....and the machine that played it, the 3M Cantata 700.
Launched in the 1960s but still used in some places until the 1990s.
You can download a poorly recorded sample of the music here:
The problems with dubbing -
I've spooled one cartridge onto my reel to reel machine and there is a lot of leakage between tracks (the sound of the mono music recorded on the left output can be heard on the separate mono music played from the right). Also the sound is very low when played at 3.75ips and then slowed 50% in editing. A number of people said they used to record their own tapes at home...but given the fact the mono tracks aren't in line with the tracks on a home 4-track reel to reel I feel this may be mis-remembered.
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