The original idea was talked about late one night in early 1963 in a Wimpy bar in Ealing in West London.The first six production units were assembled in the garden sheds of Ken Bran, Dudley Craven,and Ken Underwood in the same year, in Heston, Hanwell and Hayes, all in West London.The size of the wall of Marshall stacks "soon became an indicator of the band's status", even when rendered obsolete by improved PA systems; indeed, many of the "ridiculously huge arrays of heads and cabs" included dummies.
Marshall entered into a 15-year distribution deal with British company Rose-Morris during 1965, which gave him the capital to expand his manufacturing operations, though it would prove to be costly.
In retrospect, Marshall admitted the Rose-Morris deal was "the biggest mistake I ever made. For export, they added 55% onto my price, which pretty much priced us out of the world market for a long time." The new contract had disenfranchised several of Marshall's former distributors, among them his old friend Johnny Jones.
They most liked the sound of the 4x10" Fender Bassman and made several prototypes using the Fender Bassman amplifier as a model.
The sixth prototype produced, in Jim's words, the "Marshall Sound".
They were almost copies of the Bassman circuit, with American military-surplus 5881 power valves, a relative of the 6L6.