If you’re an active participant in the music/audio production game, I’m sure you have come across the term “tube” before.
It is a widely used term and a common one at that.
In this post I’ll discuss how tubes are able to amplify sound because this is a question that I’ve gotten alot from people that work with tube amplifiers…but don’t really know what’s happening inside them.
I urge you to fully read and soak in this article because it will teach you almost all you need to know about tubes and how they’re able to amplify sound.
With that said, How do tubes amplify sound?
Tube amplification occurs when a tiny amount of electric charge controls a much bigger amount of electricity travelling through a vacuum in a tube. These tiny voltage swings make large voltage swings, which is a pretty good definition of amplification.
The Workings of tube Amplifiers
Most tube amplifiers have a simple design mainly consisting of four things I.e. Cathode, Anode, Filament and a Grid
The cathode is located in the centre of the tube and is a positively charged pole…
The cathode is an element with a slight positive charge which is able to emit a stream of negatively charged electrons under the right conditions…
One of these right conditions is simply the presence of an Anode. Which is basically a plate with a stronger positive charge.
Electrons emitted by the cathode pass through a vacuum to a second plate.
in order to ensure that the flow of electrons is heating, the cathode has to be heated in order for electrons to flow freely…
To facilitate this, the Filament is located next to the cathode.
In other designs, the element will act as a cathode and will coated with special material enabling it to provide the flow of electrons.
The anode is simply a plate that has a high positive charge and pretty much surrounds everything else in the vacuum tube.
It is called the anode because its mode of operation is attracting the negatively charged electrons towards itself within the vacuum tube.
The anode collects electrons collected by the cathode and also picks up the signal being run through the amplifier.
The fourth component is what is called the grid… it comes between the plate and the cathode.
You may be wondering why the cathode is not really negatively charged but rather has a slight positive charge …
Don’t worry you’ll understand why just now…
The grid is a piece of metal that is connected to the input from your guitar…
Which charges and gives it a tiny positive or negative charge…
It is for this reason that the cathode isn’t really negatively charged but has instead a slight positive charge… with no current flowing in it, the grid will be negative by comparison…this helps to repel the electrons in the anode and to keep them in place until voltage is applied in order to attract them..
What is a Tube Amplifier?
A Tube Amplifier is sometimes referred to as a valve Amplifier so don’t be confused when you encounter the term.
By definition, a tube amplifier is simply an electronic amplifier that uses vacuum tubes as a way to increase the amplitude or power level of an signal..
With regard to application tube amplifiers are still the go to equipment for most recording studios that utilize guitar amplifiers.
Some people are known to use these types of amplifiers at home because of other sonic qualities that come from running a signal through an amplifier.
Let’s look at some advantages of Tubes/Valve
They can be constructed on a scale that can dissipate huge amounts of heat …it is for this reason that valves remained preferable technology for very high power applications such as radios and TVs.
They are able to tolerate electrical over loads without being destroyed..
Another advantage of valves is that they can withstand high transient peak voltages without being damaged. Making them suitable for military and industrial application.
Their soft clipping abilities makes them highly preffered by many audiophiles..
Compared to solid state amplifiers, tube amplifiers require higher voltages for the anodes..
High impedance, low current
High impedance and low current output is not suitable for the direct loads of many real world loads like electroc motors.
Tubes have a shorter working life than solid state parts due to various failure mechanisms.
Components of Tube Amplifiers
Below are Components of Tube Amplifiers
The power transformers job is to supply electricity as required and send it to different circuits.
Rectifier or Diode
The role of the rectifier is to convert the AC Signal from the supply into a usable DC Signal for the tube.
Rectifiers were common in older amps but they have been mostly replaced by diodes that are present in most modern equipment.
The role of capacitors is to store the electric charge and then release it in a more steady form by straightening out the flow.
This is why it’s important that you take caution when trying to fix amplifiers because you can easily touch an exposed capacitor with stored power which can electrify you.
Capacitors are known to store what is called a “lethal” dose of charge even when the tube amplifier is switched off.
Resistors are used to control the amount of voltage in a system. This is their only role.
Pre-amp tubes are the first tubes that receive the audio signal. Their main role is to give character to the signal.
Power tubes are much larger than the Pre-amp tubes and their role is to take the signal from the pre-amp tube and amplify it.