The THD BiValve-30 30W Class A Amplifier Head is a pure Class A design with 2 output tubes wired in parallel and combined through a special output transformer to deliver up to 30W. It accepts almost any type of output or preamp tube without bias adjustment-even in combination-for an astonishingly wide range of tone available for nearly any style of guitar playing. The standard of construction is absolutely top class, as you would expect for any handmade amplifier.Underneath its large, perforated steel lid you'll find large transformers and hi-fi style internal baffle plates to cut down on hum, as well as the tube sockets. On its front panel is a pair of input jacks labeled More and Less, followed by a Cut switch (high-cut filter), Volume, Treble, Bass, and Attitude (driver tube response control). In the center is a light bulb that glows as the amp distorts with a small switch to turn it off, a control for the built-in Hot Plate (output attenuator), and a defeat switch for the Hot Plate.The amp sports an acid-etched control plate with a delicate marine theme inspired by Glasgow artist Charles Rennie Mackintosh.