The electrodes are attached to leads which pass through the envelope via an air tight seal.
On most tubes, the leads are designed to plug into a tube socket for easy replacement.
Vacuum tubes, or thermionic valves, are arrangements of electrodes in a vacuum within an insulating, temperature-resistant envelope.
Although the envelope was classically glass, power tubes often use ceramic and metal.
This (a)(b)(c) sequence began in 1969 and was valid through 1983.
However, their low power, and limited control gave poor high treble and bass output.
In the 1960s, musicians began to experiment with distortion by overdriving guitar amps.
Most amplifiers are also able to modify the tone of an instrument by emphasizing or de-emphasizing certain frequencies, and by adding effects to create different sounds.
Amps were first used in the 1930s as a way to amplify the sound of acoustic guitars.