Even as technology has given us cheaper, more efficient forms of amplification, most guitarists still prefer the tried and true vacuum tube amp. The reason is simple – tone. While solid state amps have come a long way, tube amps and the century-old tech that powers them remain in heavy use thanks to the warmer and richer qualities they give to our sound. Below, we take a look at the how an important component of these amps work – their vacuum tubes.
How Vacuum Tubes Work
A basic vacuum tube is essentially an acting diode, meaning it consists of two electrodes – one negative and one positive, known as a cathode and anode, respectively. When current travels through the tube, it first passes to the cathode, causing it to heat up (which gives tubes their famous glow). As the cathode heats up, electrons begin to gather nearby. While the cathode itself stays at zero volts, the anode begins to increase in voltage. As the voltage increases, the positively charged anode begins to attract all of the electrons, flowing in a current from the cathode.
As far as the vacuum tubes used in amps go, they consist of a third electrode knows as the grid (making these tubes triodes), found between the cathode in anode. The grid consists of a negative charge that reacts to the input signal coming through, becoming less negative as the voltage increases. Because magnetic charges repel each other, the grid sends electrons back to the cathode, keeping them from flowing to the positively charged anode. But as the grid becomes less negative, it allows more and more electrons to pass through, creating the output that is then sent to the speakers. In a sense, the grid acts as a valve that controls the amount of electrons that can flow to the anode (hence the name “valve amp”).
Check out the video below for a more thorough look at how vacuum tube amps work:
The Importance Of Tube Amp Biasing
As more electrons cross through the grid of the vacuum tube, the more it heats up. If this is let unchecked, the grid would eventually heat up to the point where it completely breaks down. In order to counteract this, a “bias voltage” is applied on the grid. The bias voltage is a negatively charged current that is constantly applied to the grid in order to keep it more negative than the cathode. As for “tube amp biasing,” it simply means setting the correct bias voltage for an optimal idle current, which depends on the type of tubes and amp class (you can read more about amp classes in our Amplifier Classes Explained article).
Despite being comparatively more expensive and fragile than solid-state amplifiers, the rich, warm natural tone created by vacuum tube amps is well worth the price and maintenance responsibilities for many players. The way in which vacuum tubes create output might be relatively simple, but the smooth compression and gradual distortion they are known for is just something that can't be completely replicated by a transistor or digital amp. For that reason, it is likely that tube amps will remain the king of tone for years to come.
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