Frank writes from Kent: "I've been a gigging musician since the late seventies and have never came across a magnetized drum echo device before." He's just spotted this Fender Soundette from 1967/8, which used a spinning magentic disk, rather than a loop of tape, for delay effects (with a cool little orange window to watch the disk spinning.) There's a nice page about the Soundette here. Thanks, Frank!
Posted by Tom Whitwell. 
