A guitar amplifier is an electronic amplifier designed for use with an electric or 

electronic musical instrument, such as an electric guitar.

The first electronic instrument amplifiers were designed for use with electric guitars. 
The earliest examples appeared in the early 1930s when the introduction of 
electrolytic capacitors and rectifier tubes allowed for the production of economical 
built-in power supplies that could be plugged into wall sockets. Consequently portable 
vacuum tube amplification equipment was no longer dependent on heavy multiple 
battery packs for power. While guitar amplifiers from the beginning were used to 
amplify acoustic guitar, electronic amplification of guitar was first widely popularized 
by the 1930s and 1940s craze for Hawaiian music, which extensively employed the 
amplified lap steel Hawaiian guitar.

Tone controls on early guitar amplifiers were very simple and provided a great deal of 
treble boost but the controls, the loudspeakers used and the low power of the 
amplifiers (typically 15 watts or less prior to the mid-1950s) had poor high treble and 
bass response. Some better models also provided effects such as spring reverb and/or 
an electronic tremolo unit. Early Fender amps labeled tremolo as "vibrato" and 
labeled the vibrato arm of the Stratocaster guitar as a "tremolo bar"; see vibrato unit, 
electric guitar, and tremolo).