Guitar amp valves represent one of the oldest active technologies still used in modern music. Here we explain what they are, and why people love them.

Harmonic Generation 101

In the world of musical instruments and equipment, there’s a clear thrust towards new and exciting technology. We’ve seen in areas like production and DJ how technology is unlocking new ways of working which wouldn’t have been available previously.

So it’s quite unique, and not a little odd, that the prominent technology in guitar amplification is something that has been around for absolutely ages. And not ‘a modern take on old tech’ either. Nope. Guitar valves (or tubes, if you’re in the US) are exactly the same now as they were when they were used in military radar machines since the 1920s.

But what is a valve? What does is do? Let’s focus on amp valves and answer those questions.

Focus On Amp Valves

Basic Valve Science

We’ll just start out by saying this isn’t a scientific blog, nor do we claim to fully grasp the inner workings on a technical level. Thankfully, because the technology is so old, it’s relatively simple to grasp.

Basically, and this really is basic, there are three components to a valve. In the centre, sticking up, is what’s called a cathode. This is gently heated so it releases electrons – ie. tiny flying pieces of electricity. The electrons are naturally drawn towards the next component, the anode, and them completing this journey is what creates a circuit. Left to their own devices, electricity would flow from one source to another until the cows come home. Unfortunately, there’s a problem with that.

You see, electricity naturally gives off heat if there’s too much of it. So, a third component – a grid – was introduced to add in a bit of control. This grid is negatively charged, causing the barrage of positively charged electrons to be stopped in their tracks. Crucially, this element of control comes from you, the player, when you play your guitar.

The final element comes in the form of the load. In this case, the load is the speaker attached to the valve amp, where the sound comes out.

We know that’s extremely basic and anyone with an electrical mind will probably be tearing their hair out. Let’s move on quickly…

Focus On Amp Valves

Why Use Valves?

As anyone who plays guitar will testify, the single biggest differentiation in tone comes from the amplifier. You can play a classic vintage Les Paul, through a small army of guitar pedals, but it’ll still be the amp which has the biggest effect on your tone.

Valve amps have one single, defining characteristic which justifies their continued use, and that is harmonics. You see, when the load going into the valves increases, it can create clipping. Clipping, as any producers will know, is when the audio signal being received is slightly too high. In a DAW that will mean the sound pops or crackles, or distorts in a nasty way. For guitarists, it’s the opposite. It’s that clipping sound which makes this ancient technology so desirable.

Gently clipping (overdriving) a signal adds warmth. Really pushing a valve amp gives you all manner of wonderful distorted tones.

Focus On Amp Valves

Which Valves For Which Job?

Here’s where things get interesting. You see, there are two overall types of valves which do slightly different things. Pre-amp valves are smaller, and are used as the signal enters the amplifier. They typically alter the sound before it reaches the tone stack. On their own they sound pretty fizzy, and don’t do a great job of actually amplifying the sound. So, once the signal has worked its way through them it goes onto the power valves.

It’s here where the magic really happens, and where the user has the most choice. You see, different amps use different valves. Some famously so. Some are linked with a specific brand or style, and some are linked to a particular type of tone.

As a basic example, we’ve all heard before how Fender’s clean sounds are often recognised as the perfect clean sound. The Fender Custom Deluxe Reverb is a perfect example. Warm, chiming, bell-like. That’s down to a large number of their amps using a type of valve called a 6L6.

Alternatively, you may be familiar with Marshall and Orange amps giving players a typically ‘British’ sound. No coincidence both use EL84 power amp valves.


There is, it must be said, no small amount of debate about how vital valves are to an amp’s sound. After all, this is old technology and surely, SURELY someone would have come up with something better by now. After all, they are fragile, expensive, prone to breaking and can be hard to find replacements.

But when you play one for the first time, with a bit of volume behind you, you’ll just know. Modelling amps may have come a long way, and be infinitely more practical in some situations, but sometimes you just have to let a valve do its thing. Trust us.