In the 70's, tape cartridge technology was good enough to record the music on endless loop carts, for airplay. Playing "records" on the air was beginning to give way to new technology. Records, after all, could get scratched, could develop noise resulting from dust and dirt in the grooves, and might even break if dropped or mis-handled. Frequently played records would have to be replaced, sometimes as frequently as once a day because of some sort of sonic defect. Tape cartridges would solve most of these problems.
The endless loop tape cartridge was a derivative of 8 track tape cartridges, except it used high quality studio grade lubricated tape, and specialized tape decks created specifically for broadcast use. That's what was done at ITC, International Tapetronics Corporation, where I went as service manager after my tour of duty at KAAY.
When carts were used on the air, there was always the danger that a cart would "die" on the air. The example KLPQ blooper was what it sounded like when a cart failed and the DJ was not in the room or otherwise not paying attention: Moments of nervous dead air, then the panicked scramble to get things corrected.
The ScotchCart was introduced that took tape cartridge recording and playback about as close to studio grade reel to reel performance as was possible with the technology of the time - direct A-B comparisons between the original material and the playback version of a ScotchCart were usually undistinguishable, even for the fabled "golden ears' always present in the studio.
(ITC Series 99 Professional analog audio tape cartridge record / playback deck)
The ScotchCart was the best analog audio tape cartridge we had ever seen. It was sonically transparent, mechanically rugged, and performed superbly in the often rough and tumble control room environment . And best of all it was a match for the ITC Series 99B analog audio tape cartridge machines that were our top or the line recorders and playback decks.
(ScotchCart audio tape cartridge)
But the ScotchCart had one very big problem. It would run for literally hundreds of plays beyond that of a traditional tape cartridge, and then without any warning whatsoever it would fail, usually at the worst possible moment. Since I ran the service department at ITC the telephone calls ultimately ended up on my desk. And there were a lot of P.O.'ed engineers I had to deal with.
We spent huge amounts of man-hours researching the cartridge failure mechanism. We discovered the failure mode, and from that we then developed a resolution strategy. We decided to develop the means to dynamically measure the cartridge playback performance in real-time, and display the cart performance in bar graph form. We used a "red-yellow-green" LED bar graph display that could be easily read at a distance. The idea was that if we could give the DJ an indication that the cartridge was beginning to fail, and how soon till disaster strike, he could pull the cart out of circulation until a new, replacement cart could be made and substituted.
Today, most radio playout is done from digital databases, and audio tape cartridges are used only on a limited basis, if at all.