A comparison of triodes and beam-tetrodes as power output valves in audio amplifiers

Power amplifiers have long been very important pieces of apparatus, but as long as the distortion introduced by primary and terminal apparatus such as microphones and loudspeakers has been considerable, it was pointless to devise amplifiers which were entirely free of distortion. However, in recent years with the advent of very high-grade microphone and improved loudspeakers, the demand for better power amplifiers has increased.