Vox introduced the AC1/15, the production version of Dick Denney's original 15 watt tube guitar amp, in the spring of 1957. A second generation version of the AC1/15, the "AC/15 Amplifier Circuit No. 2" was introduced on Jennings schematic OS/005 dated December 5, 1959. This revised circuit was utilized on AC-15 amps produced from late fall 1959 through late spring 1960. Along with the circuit revisions documented in schematic OS/005, Vox introduced the “Contempo” chassis design, a revised control panel layout and a cabinet finished in two-tone vinyl on the second-gen AC/15. Summary of Changes Vox AC/15 Amplifier No. 2 ● Circuit is depicted on Jennings schematic OS/005 dated December 4, 1959 ● Introduction of the Contempo chassis ● First use of slider boards for chassis mounting ● Changes to the second generation circuit ● Vibravox reduced to a tremolo effect ● Cabinet Fig 1 -AC-15 "Contempo" chassis Contempo Chassis The chassis of the original AC1/15 was constructed on a rectangular steel pan. Vox engineer Derek Underdown developed the Contempo chassis (see Fig. 1) to overcome limitations of the original design. The new layout allowed the mains and power transformers to be mounted horizontally on the chassis base rather than suspended vertically, alleviated circuit overcrowding, improved weight distribution, and simplified access for servicing. The ingenious JMI Vox AC-15 Contempo chassis design combined a horizontal steel base, housing the power supply and output amplifier circuitry, with a vertical aluminum section that accommodated the preamp circuitry and control panel. Separating the power supply and output amp components from the preamp circuitry alleviated the overcrowding that had characterized the original AC1/15 chassis. The steel chassis base provided structural strength while helping to shield the preamp from electromagnetic interference generated by the high-voltage power supply and output amplifier sections. It also provided the opportunity to mount the mains and output transformers horizontally on opposite ends of the chassis to promote better weight distribution. Using aluminum for the vertical preamp section offered additional benefits. Aluminum is lighter in weight and generally less susceptible than steel to nterference from nearby power supply and output stage components. This helped reduce unwanted hum and oscillation while improving the electrical isolation of the preamp. Although aluminum is significantly lighter than steel, it is not as strong. Brackets mounted to the top of the power and output transformers strengthened and supported the upper area of the aluminum section of the chassis. The Contempo chassis was mounted on a plinth, or “slider board,” constructed from seven-ply 9 mm (3/8-inch) plywood. The board rested on rails fitted inside the amplifier cabinet, allowing the chassis to slide in and out like a drawer for convenient access to the tubes and preamp circuitry. While introduced for the AC/15, the Contempo chassis design was subsequently adapted by Vox for use in the AC-10, AC-15 Twin, AC-30, AC-50, and AC-100 models.