They were used for recording the commercials and show promos. Their maximum length was 10 minutes. In addition to the stereo tracks, they had a third track called a cue track. The tapes ran until they encounter a signal on the cue track and then they would stop. So much for the equipment, I really need to talk about the job itself.
Sound engineering is both an art and a science.
Besides the equipment, which is the science side of things, you have to learn how to use the equipment artistically. You have to learn how to get a good sound pickup and you have to know how to mix the sounds together to get a good mix. Recording rock and roll is a completely different ball game than recording other music. Rock and roll requires close micing. The microphine has to be within a foot of the instrument.