ABSTRACT
This chapter covers vacuum tube power amplifiers design. Since a power amplifier directly drives the loudspeaker to produce sound, the output power, stability, distortion, and bandwidth are primary design factors. There are single-ended and push–pull vacuum tube power amplifiers. In this chapter, emphasis is given to push–pull type vacuum tube power amplifiers design. A typical push–pull power amplifier contains a phase splitter, voltage gain stage, and an output stage with at least one pair of power tubes connected to the output transformer. Commonly used phase splitters such as split-load, cathode-coupled, floating paraphrase, and cross-coupled are fully discussed. How the fixed-bias, self-bias, and self-balanced bias techniques apply to the output power tubes is covered. How the ultra-linear output transformer connects to the power tubes is explained. Some classic power amplifiers, such as Leak TL-12, Quad II, Williamson, Dynaco ST70, and cross-coupled power amplifiers are also covered. Finally, design examples of fully balanced vacuum tube power amplifiers are given.
