The Magic of Tube Amps

This article was originally published in The Loop Magazine. It’s reposted here by permission for your enjoyment.

The vacuum tube is a quirky, outdated, expensive, fragile technology. Long after the solid-state transistor replaced the vacuum tube, tone-chasing electric guitarists still treasure these relics of a bygone era. While designers flirted with solid-state amps in the 70’s and 80’s, they didn’t have the same feel and tone as those funny old glass tubes. As always, the tube amp is still the king of tone.

How the tube-amp rose to prominence is a case of fate and circumstance. It may seem that vacuum tubes are inherently magical and our forefathers were wise enough to harness them in their amp designs. In truth, they were the best tools available when the first amplifiers were built. But their unique characteristics have defined the sound of the electric guitar in popular music.

As musical groups grew in size, the guitar needed to compete with the volume of other instrumes. A traditional acoustic guitar was simply not up to the task of being heard with a horn section blasting away.

The solution was to amplify the guitar electrically. This is done by placing pickups under metal strings. When the strings are played, a tiny electrical signal is created from the movement of the strings within the pickup’s magnetic field. By itself this electrical signal is tiny and needs to be amplified thousands of times over to the point where the signal can push a magnet in a speaker, which moves air and creates soundwaves. When the first amplifiers were created, they used the technology of the time: vacuum tubes.

The remarkable thing about vacuum tubes is that, when pushed hard enough (driven with enough voltage), they start to effect the tone of the original signal. Depending on how hard they’re pushed, the way the guitar is played, the type of pickups and myriad other factors, they can dramatically change the character of the guitar’s tone. This coloration is something we find pleasing to listen to and will cause a “tone-chaser” to empty out their bank account to get a particular sound.

This mutation is called “distortion” and ranges from the warm and glassy, to crunchy or molten metal. From the standpoint of a pure engineer, this isn’t a desirable feature. Many original designs aimed to maximize head room (the amount of voltage you can drive a tube with before it breaks up). For example, many of the original Fender designs were built to actively avoid distortion.

In the hands of visionary players, tube amps were pushed to create previously unimagined tones. Players like Chuck Berry and Link Wray were some of the first players to find delight in cranked-up tube amps. As rock and roll emerged and the guitar took a more central role, tube amps got louder and crunchier.

In the mid-60’s Eric Clapton, Jeff Beck and Jimmy Page were taking cues from their American influences and inventing new tones and musical styles. At that time American amps were very expensive in the UK and quite rare. Home-grown manufacturers like Vox and Marshall emerged to meet local demand. While their original designs were simply copies of Fender amps, they evovled into their own unique sound.

By the time the late 60’s and 70’s rolled around, rock and roll had hit the big time. But, sound reinforcement of the day couldn’t match the venue size in which many acts played. The need for more volume gave birth to the archetypal image of the guitarist wailing away in front of a wall of Marshall stacks.

As amps grew, players like Jimi Hendrix, Angus Young and Tommy Iommi pushed the boundaries of tube coloration even further. The advent of hard rock and heavy metal came from bigger amps getting pushed harder and harder. This gave way to Eddie Van Halen and the legions of hard rock and metal guitarists that followed in his footsteps—all of them using tube amps.

When the solid-state transistor appeared, it was much cheaper to manufacture and did not wear out like vacuum tubes did. In less than a decade most tube-based electronics switched to solid-state transistors. Not only did it make TVs, radios, stereos and the like cheaper to make, they were more reliable than ever—a real win for the consumer.

It made sense to apply the same idea to guitar amplifiers but, for the most part, solid-state amps haven’t captured guitarists’ imagination like those old tube amps. When pushed hard, solid-state amps don’t color the signal in the same pleasing ways. Many guitarists feel transistor amps produce a harsh sounding distortion and are nowhere close to creating the same intoxicating shades of grit that tube amps create.

Another part of the tube amp mystique is its dynamic response. Tube amp enthusiasts will often talk as much about how a particular amp feels as they do about its sound. Compared to solid-state amps, the dynamics of tube amps can almost feel like playing another instrument.

Despite its age, the tube-amp has undergone a lot of change over the years as various amp designers influenced each other. The original UK manufacturers were copying US designs (chiefly Fender) only to later evolve into their own unique sounds. The classic British designs (e.g. the Marshall “Plexi”) influenced future generations of amp makers such as Mesa/Boogie. There would be no ENGL, Bogner, or 5150 amps without Randall Smith’s innovative Mesa/Boogie designs.

In the past decade there has been an explosion of “boutique” tube amp makers to suit every taste. Many are revisiting older designs and putting unique modern twists on them. Meanwhile the major amp makers (Fender, Vox, Marshall, etc.) still continue to crank out great-sounding amps. There has never been more choice in tone for electric guitarists.

While an engineer might view vacuum-tube powered designs as outdated, guitarists would call them timeless. One wonders what the sound of rock and roll would be if amplifier technology were different in 1959. If transistor amps were the weapon of choice, would the guitar have ascended to its premier position in rock and roll? Would we even have had rock and roll at all? I shudder to think of the possibilities.