Originally published August 1998.

Although solid-state technology overwhelmingly dominates today's world of electronics, vacuum tubes are holding out in two small but vibrant areas. They do so for entirely different reasons. Microwave technology relies on tubes for their power-handling capability at high frequencies ["Tubes: still vital after all these years," Robert S. Symons, IEEE Spectrum, April, 1998]. The other area--the creation and reproduction of music--is a more complicated and controversial story.

The complications and controversy stem from the fact that music is played to be heard by human beings, whose nonlinear ear-brain hearing systems are far from fully understood. Since no one knows exactly how to model the human auditory system, no one knows exactly what engineering measurements are appropriate to evaluating the performance of audio equipment. A smidgen of some kinds of distortion may sound worse to the ear than larger amounts of other kinds. So ultimately, the only way to judge audio equipment is by listening to it. Hence the controversy: subjective human perception--especially when flanked by questions of artistic merit--is made to order for arguments and disputation.

Briefly stated, a commercially viable number of people find that they prefer the sound produced by tubed equipment in three areas: musical-instrument (MI) amplifiers (mainly guitar amps), some processing devices used in recording studios, and a small but growing percentage of high-fidelity equipment at the high end of the audiophile market. These areas employ vacuum tubes of the type once known as receiving tubes, but now called simply tubes. Not only has the use of vacuum tubes in these fields defied the semiconductor tide elsewhere, but such use and demand has even surged in the course of the 1990s.

Today vacuum-thermionic devices hold sway over the US $100 million worldwide guitar amp business. One rough estimate shows a 10-percent-per-year growth in demand for tubes used in MI amplifiers and high-end audio since the late 1980s, with no apparent slackening--even during the U.S. recession of 1991-92.

Interestingly, much of the demand for audio tubes derives not from the United States, but from Asia. In Japan, Taiwan, and mainland China, tubed high-end equipment enjoys a powerful cult status, and vintage U.S. and European electric guitars and guitar amps are valued collectors' items.