Visual neurophysiology: a field-effect amplifier designed and built by R. L. De Valois

In the middle of the last century, R. L. De Valois designed and built a unique and effective amplifier based on the newly developed field-effect transistor (FET). This amplifier has many beneficial qualities for amplifying the signals of neurons with minimal disturbance. We have used this amplifier successfully for more than three decades. We describe the circuitry of the De Valois amplifier and provide performance specifications. The FET amplifier is one of De Valois's contributions to visual neurophysiology; we share the design in his honor, with the hope that it might prove useful to others.