He built fewer than seventy of those amplifiers; one of them was bought by Sam Phillips and then used by Scotty Moore on every recording he made with Elvis Presley, from the 1955 hit song "Mystery Train" to the 1968 TV program Comeback Special.
By this time, rockabilly and other guitar players (such as Les Paul) had discovered the "slapback" echo effect, which had become generally used but could, however, only be made in a studio setting.
Since the EchoSonic lacked power for large live venues, Butts later made a set of 50-watt "satellite" amplifiers and cabinets, "to enable Moore's lithe rockabilly riffs to be heard on a stage in front of thousands of screaming Elvis fans.
"[1] The combination of Moore's Gibson Super 400 with the Echosonic ("a jazz classic meets a rock'n'roll revolution"[10]) became legendary.
Soon, many seminal rock and roll players, including Carl Perkins, started using an EchoSonic, which in turn led to other manufacturers producing individual tape echo units that could be used in the studio as well as on stage.