Elvis’s first guitar player Scooty Moore had a costum made amplifier in the 50s that had a built in echo unit, the cabinet of this very amp is now for auction at eBay.

quote from eBay page:

The original Echosonic guitar cabinet used on most all the live and studio guitar work during Elvis Presley’s career (1955-1957).

You can hear it on all the hits from the early years including: Mystery Train, That’s All Right, Heartbreak Hotel, Blue Suede Shoes, Hound Dog, Don’t Be Cruel, Love Me Tender, All Shook Up, and more.

The Echosonic was designed and hand-built by Ray Butts. While only 68 ever being built, the Echosonic found a unique place in history with a built-in tape echo (loop) unit. …