Guitar amplifiers were at first used with bass guitars and electronic keyboards, but when broader-bandwidth sounds are needed, other instruments use a suitable full-range speaker system and different power level. Much more amplifier power is required to clearly reproduce low-frequency pitches produced by bass guitars and electronic keyboards, especially at high volumes.
Some guitar amplifiers used with electric guitars are solid state, because they are easy to repair, lighter-weight, and less expensive. Despite the drawbacks of vacuum tube amps, such as their heavy weight and the need to periodically pay to re-tube and re-bias the guitar amp (every year or two with moderate use), many guitarists prefer the sound of vacuum tube guitar amps, particularly in the genres of blues and rock. There are modern tube guitar amplifier companies that are designing fixed-biased guitar amps that require no tube biasing so long as the proper rating tube is used. There are also tube amps designed to make biasing very simple for the user.
Some modern guitar amps use a mixture of both tube and solid-state technologies, with 1960s vintage vacuum tubes next to integrated circuits. With the advent of microprocessors and digital signal processing in the late 1990s, modeling guitar amps were developed that can simulate a variety of well-known guitar amplifiers' vacuum tube sounds without necessarily using vacuum tubes. New guitar amplifiers with special processors and software can emulate the sound of a classic guitar amps almost perfectly, but due to the digital element of modeling the response of these amplifiers from the player's point of view is not quite the same. "Hard core" tube guitar amp fans may not be able to tell the difference, in a blind auditory test, but will most always choose to play a tube guitar amp because of its analog sensitivity.