This article introduces a physics-based real-time model of the output chain of a vacuum-tube amplifier. This output chain consists of a single-ended triode power amplifier stage, output transformer, and a loudspeaker. The simulation algorithm uses wave digital filters in digitizing the physical electric, mechanic, and acoustic circuits. Due to the bidirectional nature of wave digital filters, important coupling phenomena between the loudspeaker and the power amp stage can be simulated.

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