However, one application of fixed bias is to achieve crude automatic gain control in the transistor by feeding the base resistor from a DC signal derived from the AC output of a later stage.
12.
In this era Fender experimented with different amplifier designs cathode vs . fixed bias, paraphase vs . cathodyne vs . long-tailed pair phase inverters, octal vs . 9-pin preamp tubes, feedback loops and filter chokes.
13.
Unlike many amplifiers marketed as " Class A ", the Prosonic truly functions as a Class AB mode, not all class A tube amplifiers are cathode-biased, and not all fixed biased amplifiers are Class AB . Fixed bias amps, however, require lower B + Voltages to stay within the Plate Dissipation of the power tubes used; Cathode biasing " throws away " this voltage using conventional Higher Voltage power supplies.
