The Champion 600 (now with  a 6" speaker) used circuit designation 5B1. It was rated at about 3 watts, and had a "T.V. Front" style cabinet with two-tone blonde & brown vinyl covering.

This style lasted until 1953, when Fender's cabinet style changed to the "Wide Panel" design with a tweed cloth covering. Fender also renamed the circuit the 5C1, 5 standing for the decade (1950s), C for the third circuit revision, and 1 was the Champ's circuit designation. The 5C1 circuit was extraordinarily simple, using one 6SJ7 pentode in the preamplifier section to provide a single stage of voltage amplification, one 6V6 beam power tetrode in the power amplifier section, and a single volume knob and no tone controls.

Sometime in 1954 the "Champion 600" designation was dropped and the control-plate logo changed to Champ-Amp.