Vacuum tubes were fairly common before the solid-state semiconductors appeared. Vacuum tubes conquered the active electronic components in most instrument amplifier applications. Solid-state semiconductors, also known as transistor amps, took over since they are more affordable, easier to build and require less maintenance. These amplifiers are heat and shock-resistant, so they are able to reduce the weight of the amplifier. Tubes are not that resistant, and they require replacements and maintenance fairly often. Also, they can make amps impossible to operate when conflicts with the tubes evolve.
Many guitarists prefer the sound that the tube amplifiers provide because they consider that the sounds are warmer and more natural. Because of this, these amps remain fairly popular. Vacuum tube-based circuitry is technologically obsolete.
Vacuum tubes operate by controlling electrons. In the centre of the tubes glass envelope is a cathode which heats up and carries a small positive charge that releases a gazillion electrons. Near the cathode, you can find an anode, known as the plate in the guitar universe. The plate has a high positive charge that pulls negative electrons toward it. The cathode’s small positive charge seems negative compared to the highly charged positive plate.
Electrons tend to move towards the plate when they are located in a powered-up vacuum. When adding a grid, the flow of electrons might be controlled. When the grid is close to the cathode and linked through the plate, small voltages appear. When this happens, the signal releases a large number of electrons that begin to fly liberally. While this happens, the rush of electrons echoes the signal from the guitar intensifying it several times.
You can get a unique tube sound when the amplifier is activated, so, when talking about vacuum tube amplifiers, bigger is not always better. Experts recommend choosing a lower wattage amplifier and many professional guitarists agree, especially when they are recording and performing.