We talk of tubes as being the “amplifiers within our amplifiers”, but the fact is, while tubes do complete the vital mission of amplifying our guitar signals, they do a whole slew of other things at the same time that add up to so much more than that. Let’s take a quick look at why we really love tubes so much, and what they do for our tone.
These devices—vacuum tubes, to give them their full name, or thermionic valves in the UK (tubes or valves for short)—have enjoyed such longevity in the realm of guitar amplification not simply because they are capable of making an audio signal louder, but because of the way in which they make that signal louder. Most good electric guitar tones, and that includes virtually all of the legendary sounds recorded by myriad guitars heroes over the past six decades, rely to some extent on tube distortion to give them body and texture. Even amid guitar tones that we consider “clean”, there’s usually a modicum of natural tube distortion that adds thickness and increases the harmonic richness of each note. To hear an electric guitar played truly clean, plug into a very powerful amplifier such as a PA amp or a large hi-fi amp or a studio or PA mixer and play at a relatively low volume, monitoring yourself on large hi-fi speakers or headphones respectively. That thin, clinical sound your beloved instrument produces is the sound of a truly clean electric guitar. In order to give it the punch, sweetness, juiciness, and dynamics that we all love in great guitar tones, you need to process it with some distortion, and nothing distorts more sweetly, juicily, and dynamically than tubes—and the beautiful part is, they do it naturally.
The reason we love tube distortion, whether used very lightly, moderately, or slathered on like BBQ sauce at a Texas ribs joint, is because of the way these devices distort the audio signal when pushed into clipping. “Clipping” is a term used to describe how an amplifier responds when pushed beyond its ability to produce a clean signal. All clipping is a form of distortion, but the way in which different amplifiers clip defines the character, and thus the appeal (or lack thereof), of that distortion. When pushed past their limits, solid-state devices clip a signal suddenly, which results, in audio terms, in a harsh, jagged distortion, and one that is usually not very pleasant to the ear.
Tubes, on the other hand, clip relatively smoothly and gradually when pushed further and further toward their operational limits. The result is a rounder, warmer, fuller-bodied distortion that is also smoother and more “musical” than that produced by a solid-state device. View two different sound waves on a scope, one from a solid-state amplifier and one from a tube amp, and you can actually see the “squareness” and “roundness” of the respective signals. Also, in the process of distorting, even when distorting just a little, a tube also adds harmonics to the fundamental note or notes in the signal, which gives the guitar tone added texture and dimension.
When you’re playing through a tube amp with anything from a little to a lot of distortion, the extra harmonics that are added to each note layer up to build a sonic picture that is significantly bigger than the original, fundamental note. This is the enticing “ear candy” that any truly great guitar tone presents, the kind of sound that sucks you in and makes you beg for more—and we owe it all to the way in which tubes distort.
Of course, many guitarists today play through modern solid-state amps or digital “modeling” amps, and many of these are capable of creating some powerful tones these days, too (although the majority of professionals out there still use tube amps more often than not). When you dial up a juicy tone through one of these tube-less amps, however, you’re still benefiting—in a second-hand manner—from tube distortion. Digital amps come right out and say it in the amp selections on their preset menus, but analog solid-state amps have long “modeled” tube amps, too. In order replicate the desirable characteristics of tube-amp distortion, solid-state guitar amps incorporate a lot of extra processing to shape, smooth, fur up, and round off the signal… in short, to help them to sound less transistorized, and more tube-like. Many of the good ones do an excellent job of it, too, but by and large they are still chasing a tone that tube amps produce simply and naturally, and usually with far fewer components. Tubes… bless their dirty little souls.
Written by Dave Hunter for Gibson.com