If we're talking strictly Seventies, I remember some things about the cable system in Fortuna, CA and I think the company was called Fortuna Cable. The other cities in Humboldt County, I believe, were served by a company called HB Cable TV, and I think what they offered was similar. There was no set-top box, the cable just hooked up to the back of the TV and was received on the twelve VHF channels. At that point, only channels 9, 10, and 13 were empty, and channel 11 for whatever reason was audio only. They later added things to fill up those empty channels, including I think a premium movie channel like HBO or Showtime, but not sure what was done to unscramble the signal if you were a subscriber, as even in that case there was no descrambler box. In Eureka, however, they did use a descrambler box for the premium channel. Just a box with a big knob on it. You'd turn your TV to channel 4 and turn the knob and KRON out of San Francisco would be replaced with HBO or whatever it was,although I could be wrong. Perhaps channel 4 was just static unless you subscribed and turned on your little box.
Now, in the Eighties, I lived in several different places with different cable arrangements. In 1983, Vancouver, WA, ahd what seemed to be fairly sophisticated cable boxes. They seemed digitally controlled, at least, and had remotes. When I moved to Fairfield CA, what we got was a box with one big knob on the front to change channels. I think it could receive 37 channels, and if you wanted to have a subscription channel or two, you had to take the box to the cable company. I guess they had to open it up and do things with it so it could receive those channels. Now, for me as a blind guy, I could actually enjoy any of the three premium channels, even if we didn't subscribe to them, because only the picture was scrambled. The audio was in the clear and my TV had a very tiny screen so nobody cared that I was watching scrambled programming.
In Rio Vista, CA, the cable boxes had pushbuttons on the front, the type where if you selected one it would go in and stay in. When you selected another, the new button would go in whilst the previous one returned to the out position, so strictly mechanical buttons, no digital interface. No idea if we had an A/B/C switch, although we might have had such, and I think they did scramble the audio of the two premium channels you could get on that little system.
The next time I got cable was in the mid-Nineties and at that point TV sets could receive cable channels so no need for a set-top box, and I believe we had up to 98 channels or so that could be filled.