Introduction

An amplifier is a device for increasing voltage, current, or power in a circuit. The original wave form may or may not be maintained; the frequency usually is. An amplifier may be mechanical, electromechanical, electromagnetic, or electronic in form, or it may be a combination of these. In this chapter the transformer-coupled electronic amplifier is considered. The amplifier consists of a vacuum tube, or similar device, with transformers, capacitors, and resistors. Input voltage or current is impressed on some element of the tube; this causes higher voltage or current to appear in the output circuit.