Marshall JTM-45

The first ever production Marshall units were almost exactly the same as the Fender Bassman circuit, with US-origin transformers and military surplus 5881 power valves. The major difference was the cabinet used, as Marshall decided to build separate amplifiers and speaker cabinets, and as they were originally intended as bass amplifiers, Marshall chose to use four 12-inch Celestion speakers in a closed-back cabinet instead of the Bassman's four 10-inch Jensen speakers in an open-back cabinet. This new amplifier, tentatively called the "Mark II", was eventually named the "JTM45" after Jim and his son Terry Marshall, and "45" as, in theory, it produced 45W of power.