Why tubes—subjective reasons

The three areas of tube audio tend to be mutually exclusive and appear not to influence each other, even though all three directly involve the production or reproduction of music. It is common to see the same tube types, such as the popular EL34 power pentode, in electric-guitar amplifiers and in high-end stereo amplifiers. Often, too, these disparate products employ similar circuit topologies.

Electric-guitar amplifiers, it is estimated, consume as many as three out of four of the world's production of audio tubes. This is hardly surprising, since the tubed guitar amp seems unshakably enthroned at the top of the rock 'n' roll world. In this case, the use of tubed amplifiers in the early rock of the 1950s and '60s caused their distinctive distortions to become the standard tonal effect for the electric guitarist. A cultural bias formed during those years among U.S. and British musicians in favor of the particular nonlinearities of those amps, which typically were quite simple and had little or no negative feedback to improve their linearity.[see sidebar, "Defining tubes"].

As documented in many books on electric-guitar technique; in magazines such as Guitar Player, Guitar World, Vintage Guitar, and others; and on Usenet news groups such as alt.guitar.amps, the clipping distortion and other sonic artifacts of '50s-designed tubed amplifiers supply the sonic signature required for a successful guitar amp.

Discussion of an amp's merit frequently hinges on the clipping effect, which is often described as yielding a sound like a brass wind instrument. The saturation distortion of the output transformer, which couples the power tubes to the speaker, also plays a key role in determining an amplifier's sound. Another amplifier parameter—its touch sensitivity—is affected by circuit nonlinearities and loose regulation of the plate-power supply.

Tubes have also been cited, albeit not without controversy, as facilitating a controlled so-called infinite sustain effect because of the way their signal compression interacts with acoustic feedback from speaker to guitar string. These effects are well-known among musicians, yet seem difficult to reproduce accurately with solid-state equipment. The many designers who have tried to build tube simulators over the past 30 years have achieved varying levels of musical and financial success. Such equipment has its supporters, but most amateur and professional guitarists remain faithful to tubed amplifiers.

As Ritchie Fliegler, vice president of marketing at Fender Musical Instruments Corp., Corona, Calif., said in a private letter last year, "This is not even a topic for discussion as far as I'm concerned...there is no substitute for tube electronics in the hearts and minds of pros."

This kind of thinking has influenced the professional-audio world of recording and mixing equipment. Since 1985, some studio engineers have been attracted by what they perceive as the "soft" and "euphonic" sound of vacuum-tube electronics—probably because of their experiences with vintage tubed amps, since modern tubed amps can be and are made without these characteristics. Tube enthusiasts usually contrast the soft sound of tubes with the harsh sound of modern digital recording and mixing, which may have more to do with the use of electrolytic coupling capacitors and inexpensive op-amp ICs than with solid-state devices in themselves. Regardless of the validity of their reasoning, studio engineers began experimenting with old tube-equipped condenser microphones, preamps, limiters, and equalizers from the 1946-70 era. The result has been twofold: street prices for vintage tube equipment have skyrocketed, and numerous small companies have sprung up to manufacture tube-equipped devices, following a variety of design practices.