On Sept. 6, 1968, The Beatles' George Harrison was heading in to London for a recording session for "While My Guitar Gently Weeps". His neighbor, Eric Clapton needed a lift into London, so George offered to take him. George had a different idea though.
Harrison wasn't happy with his own guitar tracks on the song so while driving, he asked Eric to come to the session and do a track on.
Clapton at first refused, saying that "nobody (famous) ever plays on the Beatles records!" but George insisted. Clapton came in and the invitation has its intended effect: the band members were completely professional and Eric's solo sounded great.
As Clapton was listening to a playback, the thought his solo wasn't "Beatle-y enough," so the solo is run through an ADT circuit with "varispeed", with the session engineer manually 'waggling' the oscillator: Engineer Chris Thomas has recalled: "Eric said that he didn't want it to sound like him. So I was just sitting there wobbling the thing, they wanted it really extreme, so that's what I did." The effect sounded like the guitar was run through the Leslie rotating speaker of the Hammond B-3 organ cabinet.