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First of all, which is it? Is the glowing glass thing in your amp a tube or a valve? The answer is that it's both, but in terms of its function, the most operative thing to do is to call it a valve. Think about how the valves on your kitchen sink work. Basically, they regulate the flow of water from the faucet in the same way that a vacuum tube regulates the flow of electrical current through your amp. The louder you crank your amp, the more power is allowed to flow through your amp's valves.
While it's true that transistors (basically the solid-state version of valves) work the same way, the difference is that the flow of power in a solid state amp has two speeds: full-gale and stopped dead. But again, just as your sink's faucet can govern several different water flow rates, valves have the same effect on the power flow in your amp. This in turn gives you access to a wide range of clean, crunchy and overdriven tones.
You can also think of a valve as an off-center fulcrum on a lever. As you press down a few inches on the short end, the long end swings up several feet, but the process is gradual (if you consider a few microseconds gradual), revealing new tones along the way as the valve opens and closes. But when your fulcrum is a transistor—you guessed it—it instantly snaps all on or all off. This is certainly efficient, but very "cold" sounding.
But before we get too far into why valves make such incredible vessels for an electric current, let's take a look at how these curious cathode-filled oddities came about.
The evolution of the vacuum tube began more than 100 years ago. Shortly after inventing the light bulb, Thomas Edison noticed the inside of his bulbs were blackened over time as the filament released contaminants. To fix the problem, Edison inserted a metal plate inside the bulb and applied different voltages of different polarities to see if he could minimize or eliminate the blackening effect. The experiment failed, but he noticed that positive voltages between the plate and the filament conducted an electric current, while a negative voltage between the same two elements did not. Thus, Edison unintentionally invented the first tube diode.
Twenty years later, British scientist John Fleming used Edison’s failed experiment successfully as a radio detector. The electronic age began shortly afterwards in 1906 when American inventor Lee De Forest took Fleming’s valve and added a third element close to the filament. He noticed that small voltages applied to the third element (the control grid) would cause huge changes in plate current.
De Forest had invented the first valve (triode) amplifier, which was promptly put into use by AT&T to extend long-distance telephone services to fully traverse the entire continent from New York to San Francisco. Prior to the invention of the triode, long-distance telephone services were only possible midway through the United States.
Valve amplifiers in the 1920’s found a new widespread use in radio receivers. Meanwhile, further refinements occurred in valve technology in which additional elements (grids) were added to the basic triode. Greater performance in terms of power output and sensitivity was achieved.
The first electric guitar amplifiers were made in the 1930s. Early rock n’ roll performers of the 1950’s created a huge new demand for electric guitar amplifiers. Soon, musicians began demanding louder amps with special effects like reverb and tremolo.
Technology has come a long way since then, but the valve guitar amplifier remains a relatively simple device. An amplifier will consist of anywhere from three to six valve stages in cascade, amplifying the weak millivolt signal from an electric guitar or bass enough to drive the speaker(s). A typical valve amplifier will consist of anywhere from one to 10 preamp valves containing triodes used for straight-through amplification as well as for effects like overdrive, reverb and tremolo. Meanwhile, there are anywhere from two to six large power valves where the bulk of the amplifier power is developed.
During the 1960s, valve guitar amps were seen as just another tool of the trade. People expected that solid-state technology would quickly replace valves by the early 1970s, but when early transistor amps were introduced, they didn't gain the acceptance everyone predicted. That's mainly because young guitarists like Eric Clapton, Jeff Beck, Jimmy Page, Jimi Hendrix and Pete Townsend were exploiting the warm, harmonic distortion that only their overdriven valve amps could create. When you try the same trick with transistor amps, the result is a distortion whose harmonics are more like a bunch of drunk guys on Spring Break singing along to Jimmy Buffett. But with valve amps, the distortion's harmonic overtones always complement the fundamental note, like an unholy—yet beautifully voiced—choir.
Harmonic overtones are precisely why many top guitarists consider valve amps to be musical instruments unto themselves. Think about how your guitar is affected by the gauge of its strings, tuning, action and pickups. In the same way, valves have several dynamic qualities that dramatically affect their sound. They sound different as you drive them harder, they adopt different tonal shades throughout their life in your amp, and depending upon what kind of valves you use, they can completely change the personality of your amp. So, does this make valve amps superior to solid state? It's really just a matter of opinion. But remember: The sound you get from a valve amp can be changed by doing something as simple as playing more aggressively. A solid state amp will always sound the same.
Lee De Forest - Tube Pimp
Photo of a Triode (1906) - Invented by Lee De Forest
