What is a Vacuum Tube?
The tube is basically an electronic valve that controls the flow of electrons. It consists of an envelope (bulb, usually glass) from which most air and other gasses have been removed. Inside this near vacuum are two systems. One is called the heater. This is in the center of the tube and is the portion you will normally see glowing orange (some tubes may have more than one heater). The other system consists of the cathode, grid(s), and plate (also called the anode). The plate is the largest metal structure you see inside the bulb. All of this is held to correct locations by thin disc spacers made of mica or ceramic.
What's that Silver Stuff on the Glass?
The silver deposit is called the "getter" and is there to help increase the vacuum in the tube. Its color may vary slightly. Sometimes the getter will flow with use, even to the point of becoming evenly and thinly deposited over the entire envelope. The edge of this flow may have a brown color. None of this is important as long as the tube biases correctly and stability.
Why The Vacuum Tube?
Before we go further, someone undoubtedly will ask, “Why the vacuum tube?” A quick answer would be: “The tube looks cool!” But the real answer does not stop here; there are more legends about the tube that wait to be unveiled.
Why Vacuum Tubes Are Superior for Music Playback?
Why use the vacuum tube? Because the tone of the tube attracts listeners in a simple, basic way. There have been too many arguments between solid-state and tube technologies – many experiments and blind tests have been conducted. Even statistical gurus have contributed to the argument on the outcome of these tests.
Skepticism has argued that even an average solid-state amplification device is measurably superior to the best tube device, but the argument may not stand the trial of tonality. So let us make it simple here – We love what we hear regardless of harmonic distortion as well as the limited frequency response compared to a solid-state device. With tube technology, the music is more musical!
Jimmy Page strikes the guitar strings on "Stairway to Heaven" and Angus Young of AC/DC's "Back in Black" share one common attribute– It is the vacuum tube that powers their guitars’ souls that express what they want to sound like and what the listener likes to hear.
How The Vacuum Tube Works?
Let’s take a look at the fundamentals of how the vacuum tube works. In a modern vacuum tube, there are four principal elements that work together to make a tube work. The Filament (heater), Cathode, Grid and Anode (or plate). When the filament is connected with voltage that boils the cathode, the cathode then emits electrons that pass through the grid and hits the Anode. Through this electron flow, the tube will amplify a small AC signal into a larger AC voltage, thus amplifying it. By controlling the grid voltage, the current flow can be regulated and thus creates the desired electronic characteristics, while amplifying the signal (source)
Today, most electric guitar and bass amplifiers are tube-based. Professional audio equipment also deploys the tube as a preferred amplification device. One can even find tubes in digital-to-analog converter designs. The vacuum tube is a natural choice for these music-associated vehicles to depend on.