Large-signal analysis of triode vacuum-tube amplifiers

A mathematical model for the input-output characteristic of a single-stage triode vacuum-tube amplifier is presented. The model, basically a cosine-series function, can easily yield closed-form series expressions for the amplitudes of the output components resulting from multisinusoidal input signals to-the amplifier. The special case of an equal-amplitude two-tone input signal is considered in detail. The results show that, similar to transistor-based amplifiers, the vacuum triode amplifier generates both even- and odd- order harmonic and intermodulation components. The results also show that the amplitudes of these components are strongly dependent on the tube parameters, the biasing voltage, and the amplitudes of the input tones and are not following a general pattern.