The SET enthusiast’s mantra, coined by reviewer Dick Olsher, is, “If the first watt of amplifier power doesn’t sound good, why would you want 199 more of them?
”One early audio-amplifier triode tube, the Western Electric 300B, was suddenly in such demand that audiophiles were paying as much as 0 apiece for it.
Because a loudspeaker’s impedance isn’t constant with frequency, the SET amplifier’s high output impedance reacts with the loudspeaker’s impedance variations to produce changes in frequency response.
That is, the SET amplifier will have a different frequency response with every loudspeaker it drives.
(A single-ended triode power amplifier using the 300B output tube is shown in Fig.1 The 300B is the bulbous tube in the middle.)The triode is the simplest of all vacuum tubes; its glass envelope encloses just three electrical elements rather than the five elements in the more common (and modern) pentode tube.
Triodes have much less output power than pentodes, but more benign distortion characteristics.
Most power amplifiers, and the amplifier sections within integrated amplifiers, are strikingly similar in operation.
These so-called “Class A/B, push-pull” amplifiers have been around for decades and are the staple technology of nearly every amplifier manufacturer.One of the most interesting trends in high-end audio over the past 25 years has been the return of the single-ended triode power amplifier.The single-ended triode (SET) amplifier was the first audio amplifier ever developed, dating back to Lee De Forest’s patent of the triode vacuum tube in 1907 and his triode amplifier patent of 1912.These variations can range from just 0.1d B with some loudspeakers that have a fairly constant impedance, to as much as 5d B with other loudspeakers.The SET amp’s sound will therefore be highly dependent on the loudspeaker with which it is matched.The movement back to SET amplifiers began in Japan in the 1970s, specifically with designer Nobu Shishido, who combined SET amplifiers with high-sensitivity horn-loaded loudspeakers.