Question 6A218

In a Class B audio amplifier, the active device (transistor or vacuum tube) is biased at or near cutoff. This means that with no input signal, there is very little to no plate (or collector/drain) current flowing. When an audio signal is applied, the device conducts for approximately 180 degrees (one half-cycle) of the input waveform. As the input signal's voltage swings into the conductive region, the device turns on, causing plate current to flow. This current then decreases as the signal voltage drops back towards cutoff. Since an audio signal is a continuously varying AC waveform, the plate current will constantly increase and decrease in magnitude, following the shape of the amplified half-cycles. Therefore, the plate current must fluctuate in response to the varying input signal to accurately amplify the audio. Remaining steady (B) would indicate no signal amplification. A continuous increase (C) is not how an AC audio signal is processed, as the current must rise and fall with the waveform.