The purpose of this guide is to help novice tube enthusiasts understand the basic principles of tubes and valves. We all start somewhere, and I wanted to provide a first resource for absolute beginners. We will start at the very beginning of “What is a Vacuum Tube” and explore how valves operate. Finally, this guide will look at the basic different tube types. So get comfy with a cup of coffee or a beer, and enjoy “A Beginner’s Guide to Vacuum Tubes and Valves!”
What is a Vacuum Tube?
In its simplest form, a vacuum tube is an electronic device that allows one electrical signal to affect another. As you can imagine, there are many different ways an electrical signal can be changed, and tubes are capable of altering signal in different ways as well.
Typically, and especially in guitar amps, tubes are made of glass and you can find them by looking in the back of your amplifier. Tubes are round and cylindrical, and look like small bottles. They can vary in size and shape and your amp will likely have multiple tubes. It is also very possible that your amp may have no tubes at all! In this case your amp is a solid-state amplifier, and we will touch on what that means later in this article.
Tube vs. Valve
You may have heard another term for vacuum tubes, valves. Both terms are interchangeable and mean the same thing. Tube is an American term, while Valve is what our friends across the pond in Europe say. Much like “elevator and lift” or “hood and bonnet”, tube and valve are two separate terms that refer to the same thing.
Why are They Called Vacuum Tubes?
Even though valves look nothing like your vacuum cleaner at home, they do have something important in common. Under the glass covering, there is no air present. It has all been sucked out! This means that the internal components of tube operate in a vacuum. We will discuss later in this guide why a tube needs to operate in a vacuum.
What do Vacuum Tubes Do?
As I previously mentioned, tubes are capable of doing many different tasks. Here are some of their common duties inside a guitar amplifier.
- Tubes can change alternating current from your house into direct current like what’s produced from a battery.
- Tubes can amplify a signal, we perceive this as the signal becoming louder. If the tube amplifies a signal enough, it can create distortion.
- Tubes can mix different signals together and split signals into two separate signals. This is used to send signals to different parts of a circuit.
- Tubes can increase current delivery capabilities.
- Tubes can invert the polarity of a signal. This basically means it creates an exact opposite output signal from what is supplied at the input.
How do Vacuum Tubes Work?
Before we get in to how valves perform the above-mentioned tasks, we will need to cover common elements that most tubes share. Keep in mind that not all vacuum tubes contain the same components. I will do my best to keep these descriptions at a basic, high-level, that is still easy to understand for beginners.
The first component that truly is common to all tube types is the filament. This is also commonly referred to as the heater. The filament is the part of a vacuum tube that you see glow when the amplifier is powered on. It works very much like a light bulb or your toaster. As electrical current is allowed to flow through the filament, it creates both heat and light. We want the filament to create heat for the purpose of heating our next component, the cathode.
The cathode is an element located next to the filament. It has a special coating on it that when heated, releases electrons. That is the whole point of the cathode, to release free electrons into the vacuum tube. Electrons work like a magnet. A positively charged electron is attracted to a negatively charged electron and vice versa. After being released from the cathode, the electrons flow to the anode due to this charged attraction.
The next element is called the anode, commonly referred to as the plate. The purpose of the anode is simply to attract the free electrons released by the cathode after being heated by the filament. So far, so good right!
The next component is the grid, but before we get there we need to take a couple steps back and visualize what we have discussed so far. The easiest way to visualize electricity is to compare it to water. They are both amazingly similar in how they work.
Imagine water flowing out of your kitchen faucet and into the sink. In this analogy, the faucet represents the cathode, the sink represents the anode, and the water represents the flowing electrons. There is no filament in this comparison. Now while the water is running from the faucet into the sink, imagine taking your hand and placing it under the water.
What happens? Your hand changes how the water flows. By simply putting your hand under the water you can make it stop and start in a pattern. In this analogy, your hand is the grid. The grid is located between the cathode and the anode, and its purpose is to change how the electrons flow.
Electricity Doesn’t Work Like You Think It Does
Before we continue, I need to take one more step back. If you are new to electronics this will probably be easier to understand, but if you have been at it for a while this may be difficult to comprehend. Conventionally, we think of electricity flowing from a positive charge to a negative charge or from a high voltage to a lower voltage. While it is usually easier to understand electricity when explained this way, it actually functions in reverse. Electrons flow from negative to positive or from a low voltage to a higher one. It is important to understand this concept when talking about vacuum tubes.
Connecting the Valve to the Circuit
Now that we understand the basics of how a tube works, lets understand how it functions within the circuit. The filaments are connected to a voltage source to make them heat up. The cathode is connected to a very low, or non-existent voltage source. The grid is connected to your guitar signal. Finally, the anode is connected to both a high voltage source and the point where your guitar signal exits.
So let’s think about this. The filament heats up the cathode. The cathode releases electrons. Since the cathode is at a lower electrical potential than the anode, the electrons flow towards the anode. Before reaching their destination, the electrons are interrupted by the grid. The grid is connected to your guitar signal (which varies from positive to negative potential.) This variability alters how the electrons flow to the anode. At this stage, your guitar signal gets imprinted on the flowing electrons. Finally, the electrons reach the anode and signal is able to exit the tube.
Please keep in mind that this is a very simple explanation of what it is happening inside an amplifier valve. In reality, it is a bit more complicated, but this should demonstrate the basics for all beginners.
Different Types of Vacuum Tubes
Moving along in our beginner’s tube guide, let’s discuss some of the different types of tubes one finds in a guitar amp.
A diode is a two-element tube that does not contain a grid. The purpose of a diode is rectification. Rectification is the process of turning alternating current from your house supply into direct current like from a battery. In fact, almost all electronics work this way of turning AC into DC. A diode tube also needs the help of some capacitors to make this possible. If you are interested in learning more about electronics basics take a look at my article here. Also, I have a great write up on capacitors as well.
A triode is a three-element tube and contains all of the components listed above. Triodes are the most common amplifier tube, and perform many of the duties I previously referred to. They are capable of amplifying signals and creating distortion. Triodes can combine signals and split them into two separate signals. They can also invert the polarity or phase of a signal.
Tetrodes and Pentodes
I am sure you have noticed the pattern by now! Tetrodes are four-element tubes and pentodes are five-element tubes. Typically (but not always) these tubes work very similarly to triodes but have additional elements called screens. Screens are also in between the cathode and anode and alter the characteristics of the tube. Tetrodes are pentodes are commonly found in your power amp section as they are capable of amplifying your input signal much higher than a standard triode.
Why Are Different Vacuum Tube Used?
We now know there are different types of tubes and they are all used for different purposes. Individual tubes are not good at all the different tasks a guitar amp requires. Therefore, engineers rely on using different tube types for their specific application.
While there are many tube types, there are again many different models of vacuum tubes within each category. For example, there are many different types of triodes (which we discuss in this article here.) Some triodes work really well at amplifying signals, some work best at providing ample current, while others do a good job acting as a phase inverter. When it comes to designing tube circuits, it’s all about using the right tool (or tube) for the job.
Vacuum Tubes vs. Solid State
As I mentioned previously, not all guitar amplifiers are in fact tube amps. Many amplifiers are what we call solid-solid. These amps also utilize components that are diodes and triodes, but are made out of different materials. These components still work similarly to tubes.
Almost all modern electronic equipment utilizes solid-state components instead of tubes. First, they are much cheaper and easier to manufacture than valves. For the most part, they also operate very reliably with little variation from component to component. Only audio devices continue to utilize vacuum tubes. But why?
The answer has everything to do with sound. Even though modern solid-state components have many positive qualities, most musicians (especially guitarists) believe that they are sonically inferior to a vacuum tube. So even though tubes are more expensive and less consistent, they have been the go to choice for quality amplifiers because they simply sound so much better.
Why do Tubes Sound Better?
Sound quality is subjective, so this isn’t to say they there are not good sounding solid-state guitar amps because there are. But why is it that so many of us prefer tubes? It all comes down to harmonic content.
You see, when a signal distorts, harmonic frequencies are created as a result. Vacuum tubes tend to create even ordered harmonics while solid-state components create odd ordered harmonics. Even ordered harmonics are typically found to be more musically pleasing to the human brain than odd ordered harmonics. While many reasons are likely and possible, this is why I (and many other guitarists) believe that vacuum tubes sound better than solid-state components. For more info on harmonic distortion, check out this article here.
I hope you have enjoyed this brief, introduction to vacuum tubes! If you would like to learn more, I highly suggest reading my subsequent article on the specific kinds of tubes found in guitar amps and how the operate in the circuit. Also, if you are interested in learning more about general electronics, please read my intro guide to electronics here.
There are many great resources in print and on the web to learn more as well. Never be intimated as a beginner! There is always a lot to learn, but that is part of the fun. And hey, we all start somewhere, right? Thank you for reading!