Tube amplifiers were invented at the beginning of the 20th century and declined in popularity in the 1970’s in favor of transistors, and yet rose again to popularity due to their wonderful warm sound. But you may be wondering how do these interesting vintage pieces work?
A tube consists of a cathode, anode, and grid that generates a magnetic field. Tube amplifiers use transformers to convert AC voltage, and capacitors that result in a steady current. The output transformer converts the signal to a high current that drives the speaker, giving in a warm tube sound.
If some of that went over your head, don’t worry, we got your back. In the rest of this article we’ll go into a deeper explanation into how these work.
How Does a Tube Amp Work: explained
Throughout the history of music, there’s an uncountable number of guitar players, and more will certainly come. But even considering that tube amplifiers are almost a century-old technology, very few guitar players actually know how they work. It’s, of course, needless to say that this lack of knowledge isn’t even remotely a setback for someone who wants to be a stellar guitarist or even an acclaimed audio engineer. Actually, not much theoretical knowledge is needed in order to achieve acclaim in both professions, but nonetheless, knowledge is never a burden but something that can inspire you or help you to be more efficient. And when it comes to tube amps, a little bit of history doesn’t hurt also.
A little bit of history
In 1904, John Ambrose Flemming invented the first valve with two electrodes. In 1906, Lee de Forest added a third electrode and thus invented the first electronic amplifier. At first, valve amplifiers were used in long-distance telephones, but in the early 30’s, various audio devices and televisions were built using this technology. This technology had a lot of setbacks and imperfections, but technical progress that started after World War 2 led to a lot of advancements.
The existence of high fidelity audio equipment became possible in the early 60’s, which led to an undisputed dominance of valve technology in audio markets across the globe. But with the invention of silicon transistors in the 70’s, the usage of valve technology in consumer audio electronics was greatly reduced to the point when it became almost entirely obsolete. That being said, this technology is still highly regarded in guitar amplification and various hi-fi audio devices.
Why do we love tubes?
Although using tubes is relatively more expensive than solid-state transistors and is less convenient than its digital equivalents, we still prefer this outdated technology and enjoy it greatly. Even with a significant leap in the development of amp modeling technologies, most guitar players still prefer tube amps over any other alternative.
The reason for that is very simple, even a person with an untrained ear can say that transistor and digital amplifiers sound too perfect. And, we, humans, love imperfections, especially when it comes to sound. And tube amplifiers are as imperfect as it gets since they present tons of non-linear behavior and harmonic distortion.
And considering that the more you push the tubes, the more distortion you get, it’s unbelievably hard to find something more rock-n-roll than tube amplifiers.
A bit of science
As we all probably know, electricity doesn’t travel through the air, and we all would be in a bit of a pickle if it did. But it turns out that electricity happily travels through space if there’s no air or any other matter. And as you already guessed, the only space free of any matter is a vacuum.
So at the beginning of the 20th century, scientists established that electrons can fly through the vacuum, and in addition to that, they also can be directed. An electron is a negatively charged subatomic particle, and it can be attracted to a positively charged element that is called the anode. A heated metal element that is used as a starting point for the electrons is called the cathode. Scientists also discovered that a magnetic field can deflect electrons.
How does tube amp actually work
Now, imagine your favorite guitar amplifier. Inside of it, you can find a highly sophisticated electric circuitry where a tube, or as it is often called a valve, stands out the most. There are some amplifiers with just one valve, but in most cases, you can find up to 4 of those in your amplifier, depending on the power of amplification.
Usually, tubes look like a less spherical glass light bulb, and right in the center of it is a cathode. The anode is presented by the plate that surrounds the cathode. The cathode carries a negative charge, and the anode carries a high positive charge that pulls negative electrons towards it.
Up to this point, everything seems pretty simple, and the science pretty much adds up, except for one thing. In order for electricity to work for our benefit, we still need the magnetic field. That’s why there’s a grid between the cathode and the anode inside of a tube. That grid is connected directly to the pickups of your guitar, and despite that the guitar pickups generate an insignificant amount of voltage, it still is enough to change the flow of electrons inside of a tube. Since the flow of electrons directly mirrors the signal that is coming from the guitar, said signal gets amplified.
A bit of relativity
Earlier, when we said that the cathode inside the tube carries a negative charge, that wasn’t entirely true. The thing is, it happens that this charge isn’t negative but, in all actuality, is positive. It’s just significantly less positive than the charge on the anode. And knowing that voltages are relative, we can safely presume that the same charges are repelled from one another.
Since the grid that surrounds the cathode is negative, electrons will stay in place until the guitar signal comes through to make the grid positive. In other words, the only thing that you can hear from the speaker of your amplifier is complete silence until you actually start to play the guitar.
Other components of the amp
Of course, guitar amplifying couldn’t be as simple as sending a bit of electricity through the bulb. So naturally, besides the tubes, there’re a few very crucial components inside the amp.
First of all, there’s a power transformer that transforms an alternating current from the socket into a current more suitable for the tube. Alternating current is a sinewave of electricity that cycles through positive and negative charges. Tubes generate a DC voltage which stands for “direct current,” and is way more steady than AC voltage. As we’ve mentioned earlier, in order to work properly, a metal that serves as a cathode needs to be heated. So power transformers also supply the heaters inside the tubes with electricity.
Secondly, there are capacitors. Those are large cylindrical things inside of your amp that serve to hold a charge of electricity. They’re needed in order to make AC voltage that flows to tubes more stable and steady. If you have the need to poke around inside of your tube amplifier, be very careful since capacitors hold the charge even when the amp isn’t plugged in. This could be very dangerous if you don’t know how to discharge them properly.
And finally, there’s an output transformer. And one might argue that this is the most important part of the amplifier. Since along with the tubes, it shapes the sound of the amp. In the circuit, it stands between the tubes and the speaker. Output transformer doesn’t let the DC voltage from the tubes pass through and lets the AC voltage from the guitar pickups run past.
In order to drive the speaker, the output transformer converts the high voltage signal from the tubes that have low current to a low voltage signal with a high current. Depending on the impedance and the resistance of the output transformer, you can drive different speakers with different power output.
Some amplifiers can have an additional tube preamplifier. And if the main amplifier uses triode tubes, the preamplifier uses tubes with two additional elements. They’re called the screen and the suppressor and are presented by a very simple wire wrap inside the tube. The preamp tubes serve the purpose of supplying the main power tubes with a stronger and steadier signal.
