" (The unique echo sound of the Sun studio was achieved through the use of a tape-loop delay and a 7½-ips, instead of the more advanced 15-ips, two-track recorder. The added echo effect heard in Scotty Moore’s guitar relied on a custom-built amplifier, made in Cairo, Illinois, by a man named Ray Butts. Moore got the second amp that Butts built; the first went to Chet Atkins, the third to Carl Perkins, and the fourth to Roy Orbison. When he ceased working with Elvis in September 1957, Moore put the amp in a closet. Several closets later he withdrew it at Carl Perkins’s request and plugged it in for one of Carl’s Mercury sessions early in 1975.) "

― Nick Tosches , Country: The Twisted Roots Of Rock 'n' Roll