The appeal of early Marshall amps was their sonic transparency and response, not to mention the prodigious power of a 100-watt EL34 head plugged into a 4x12 Celestion-powered cabinet. It was – and still is for many players – the archetypal rock guitar tone, a collision of components and voltages that created a unique voodoo. However, as guitarists grew into the new era of progressive rock powered by the likes of Jimi Hendrix and Cream-era Eric Clapton, the early Marshalls’ simplicity – and the unreliability of circuits pushed to the max – became more of a hindrance for some players, meaning there was a growing demand for modifications as well as repairs.
In the late 1960s and early 70s, the amp-modding industry hadn’t properly
