Found an interesting statement in a CD booklet from the Butterfield Elektra Years Anthology (1997). I had forgotten that Butterfield played at the same 1965 Newport Festival at which Dylan went electric, and I don't think I ever knew that Mike Bloomfield and Sam Lay, from Butterfield's band, backed Dylan in his electric set. In any case, the liner notes argue that, in tandem, Dylan's performance and the performance by Butterfield
"sounded the death knell for the folk music era and ushered in the age of amplification and rock".
Seems a bit over-blown of a claim, regarding both the death knell of folk and the ushering in of amplification (I seem to recall a few amplified pieces of music pre-dating 1965, but maybe my memory is going).
Gotta admit that I like the Butterfield tape, though. Great versions of "Born in Chicago" and "Song for Lee".