Valve amps are widely held to be the foundation of great electric guitar tone, but why would you want one?
If you’re a beginner guitarist, or just a guitarist who tends to just play without getting too embroiled in debates about gear, you might have noticed that the vast majority of your favourite players ply their trade through a valve amp (referred to as tube amps in the US).
Given that these are based on technology that is essentially archaic, and both heavier and less reliable than modern equivalents, you’d be forgiven for wondering why they remain so popular.
Here’s a mini-guide to valves, and why you would want a valve amp to play through.
What is a valve?
The valves at the heart of the valve amp are often referred to as thermionic valves, vacuum tubes or just ‘tubes’ in the US. Based on theories developed by Thomas Edison amongst others, in the 19th century, the valve is similar in principle to the common light bulb. In essence, it controls an electrical current through a vacuum in a sealed, glass tube.
When heated, the filament inside glows white-hot, and the electrons on the surface are freed into the vacuum. In a simple valve, an extra electrode is placed in the vacuum, and made more positive. This results in a current flowing through it. This type of valve is the simplest, known as a diode, and can be used to convert AC to DC.
The important type of valve in a guitar amp is the triode. Here, a third electrode is introduced. This is a grid that sits between the other two, which, modulates the current and acts as an electronic amplifier. Thus, the valve revolutionised the development of electronics, which included amplifier technology.
Why are they still around?
In the vast majority of electronic devices solid-state transistors take the place of the valve. Why, then, do valve amps still exist? Simple: like a great many things in the guitar world, it’s all about tone.
You’ll hear many guitarists praising valve ‘warmth’ and the ‘singing’ tone they produce. And, unlike many things that said about guitar tone, this is actually based on fact. Without getting too bogged down in the technicalities, valves behave in a way that is non-linear.
The result is a tone that enhances low frequency harmonics, and introduces a mild distortion when driven that results in compression. This means that with judicious gain adjustment, the amp can be set so that it is clean when played softly, and breaks into distortion when played harder. In this way, it becomes a dynamic extension of the guitar.
If the valve amp is driven harder (i.e. overdriven) it has a ‘broken up’ sound continually. Unlike solid-state amps, the non-linear response means that this distortion is less even, and generally less ‘fizzy’ sounding than transistor based amplifiers.
In addition, this non-linear response is also the reason that valve amps are perceived to be louder to the human ear than their solid-state equivalent.
Put simply, the reason that valve amps are still around is because their tone and idiosyncratic dynamic behaviour makes them an expressive extension of the guitar.
So, what are the drawbacks?
If valve amps are so good, you may question why all amps are not valve-based? This is a good question. Really, it all boils down to practicality. Valve-amps are generally heavy. So, for the gigging performer who transports all of their gear, ‘lighter’ is often better.
The other major issue is that valve-amps are far less reliable than solid-state equivalents. Valves have to be replaced intermittently, plus they need biasing and maintenance. Solid state amps tend to be far more ‘maintenance-free’.
The advent of modelling technology has meant that now, a non-valve amp can provide a wide variety of different amp tones, some based on classic valve amps from Marshall, Fender and more. If you buy a valve amp, you’ll be pretty much stuck with its tone (which isn’t necessarily a bad thing…)
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