Complex sentence: Various manufacturers attempted to commercialize this concept but a major difficulty was getting sufficient playback time with the low-performance tapes of the time, though by the early 1960s, tape formulations had improved enough to make the concept viable.
Split into simpler sentences: Various manufacturers attempted to commercialize this concept but a major difficulty was getting sufficient playback time with the low-performance tapes of the time. It was not until the early 1960s that tape formulations had improved enough to make the concept viable.