When did dylan start playing electric?

Johnston recalls, "I don't know how Tom Wilson recorded him, but when I did Dylan, we set up all of the musicians in the same room, with Bob behind a glass baffle so you could see him. With Dylan, you always had to keep your eye on him. He came in and played a song to the band once and that was how they learned it. He never counted off, just launched right into it, so you always had to keep the tape rolling. And that wasn't easy at Columbia; we were using 4-track for that record, 8-track on of Blonde on Blonde, and the machines were way down the hall. We had union engineers, so one would be in the control room at the console with me, and I'd say, 'Roll tape,' and he'd tell his assistant near the door, 'Roll tape,' and he'd yell down the hall to a guy at the other end, 'Roll tape,' and then they'd start all over again yelling, 'Is tape rolling?' God, it took 20 minutes to get those damned machines going. It was like a Three Stooges short. So I got in the habit of using several machines with Dylan so as not to lose anything. He would start a song on the piano, and if the musicians dropped out during it, he'd go to the guitar and start playing another one. I lost one song that way and said never again, so I always used multiple machines.