In the 60's and 70's, in general, how many minutes of commercials were there in an average hour on a big Top40 station on a daytime weekday? To my ears, it sounded like "a lot" of advertising. For morning and afternoon drive time shows, it seemed like a commercial was played after each song.
Every Top 40 station in L.A. advertised "more music" on their station, and that slogan was a staple of KHJ's identity. It seemed like maybe 8 or 9 songs an hour. Guess that one would have to go back and look at the station logs. ( Just my opinion). -D.
KFWB and KRLA maxed out at 18 minutes per hour, including commercials within newscasts. That was pretty much the industry standard, and the one followed by more established stations like KFI, KNX and KMPC.
Beginning in 1965, KHJ under Bill Drake had a firm commercial policy: No more than 14 minutes per hour, no commercial break lasting longer than 70 seconds and no commercial break with more than three commercials in it. So, you could have a 60-second and a ten-second spot, or two 30s and a 10, but not a 60 and a 30, and not a 30 and four 10s.
If you take 60 minutes and subtract those 14 minutes of commercials, you're at 46 minutes. If your songs are three minutes long, on average, and you allow for a little wiggle room for jingles, weather and the like, that's 15 records in an hour.
Mornings were a different animal on KHJ, with eight-minute newscasts at :40 and Robert W. or Charlie Tuna's phone bits. They were probably playing ten records an hour. Lohman and Barkley at KFI, Dick Whittinghill at KMPC and Dick Whittington at KGIL were probably playing six.
In an hour that had the limit---14 minutes of spots at no more than 70 seconds per break (and not all hours were always sold out), that required 12 commercial breaks.
In 1971, Ted Atkins, KHJ's Program Director, with Drake's approval, went to two-minute commercial breaks. Again, no more than three commercials in the break, so you could do two 60s, a 60 and two 30s, but not four 30s. The hourly maximum remained 14 minutes, so the number of commercial breaks in an hour dropped to seven from 12.
That worked for a while, but ultimately the lower spotloads of stations like KLOS and KMET forced top 40s (including KHJ and KKDJ) into a phase where they touted "Up to 52 minutes of music an hour")---meaning they'd cut the spot load to eight minutes, in four two-minute clusters.