Explanation: In a Class A amplifier using a vacuum tube, the DC bias applied to the grid relative to the cathode is typically negative. This is crucial for several reasons pertaining to the tube's linear operation and signal amplification. A negative grid bias ensures that the grid remains negative with respect to the cathode for the entire 360-degree cycle of the input signal. This prevents grid current flow, which would otherwise load the input circuit, introduce distortion, and reduce efficiency. By keeping the grid slightly negative, the tube operates in its most linear region, allowing it to conduct plate current continuously and amplify the input signal faithfully without clipping or cutoff. This consistent conduction over the full signal cycle is the defining characteristic of Class A operation.