Tube Amp

Many guitarists prefer a tube driven guitar amplifier. Why is that? How does a tube amplifier work?  How does it affect your tone?

On this page I will  explain it in a way that is easy to understand. I am not an electrician myself, so if I get it, you will probably get it too!

tube amp and tone

The harmonics of a tube driven amplifier are rich, they brake up nice and warm and soft sounding. Tubes give a great dynamic feel when you play.

But this are all words to describe something you have to experience yourself!

how does a tube amp work?

Vacuum tubes are used to make an electric signal strong enough so it could be heard through a speaker.

As mentioned before, a guitar amplifier has two power sections.

  1. the preamp  
  2. the power amp .

Your guitar delivers a small electric signal to the preamp part of your amp. In the preamp this signal is amplified in to a stronger signal. This signal can be shaped with the tone control knobs (mostly bass, treble, and mid).

From the preamp this stronger, tone shaped signal, is send to the the power amp. The power amp amplifies this signal into a powerful signal which can be send to your speakers.



If you have 3 minutes time to watch this small movie, you will get a good idea about the way tubes work (thanks to Rob Robinette).

A glass tube is vacuum and inside it are two electrodes: A cathode and a anode (plate).

The filament inside the tube heats up the cathode. When it is red hot, the cathode releases electrons into the vacuum. The anode (plate) attracts those electrons and because of the vacuum, the electrons are free to fly right into it and leave the tube as an electrical current.

But how do they amplify the guitar signal?

The anode and cathode are separated by a grid. The grid is connected with your guitar signal and controls the flow of electrons between the cathode and anode.

The harder you strike your strings, the stronger the electric signal (AC) from pick-ups to your amp will be. The grid responses to this electric  signal of your guitar by letting more (ore less) electrons fly  from cathode to anode (plate). It works like a gate. 

different tubes

In a guitar amplifier you find 2 main tubes:

  1. preamp tubes
  2. power amp tubes

Tubes are  also used for spring reverbs and effectsloops.

amplifier classifications

There are different classifications of a tube amp. The Class tells you something about the way the amp is designed:


Power tubes needs to be biased . What does that mean?

As mentioned above, a grid controls the flow of electrons between the cathode and plate of a tube. And there is a big stream of electrons in a tube!

As a matter of fact there are so much electrons flowing through the tube, that the tube will destroy it self. To avoid this a bias voltage is applied to the grid. This is a steady amount of DC voltage.

This amount of DC voltage wil reduce the stream of electrons passing through the grid.

The amount of bias voltage is adjustable so it can be set to the perfect point for the kind of tube you use, so they perform optimal.

Preamp tubes don't need to be biassed because they are part of a self biassing circuit.

If you want want to learn more about how amps work, you should check the site of Rob Robinette.