Modern amplified guitar music is possible due to a combination of valve, or tube, based amplification, solid-state amplification and digital modeling. Amplified guitars solved the problem of how to integrate guitars in ensemble performances. Acoustic guitars had problems because of the comparatively low sound volumes they produced.
Early Amplification
The first attempts at increasing the volume of a guitar involved using steel strings to produce more intense vibrations and increasing the size of the guitar's body. In some cases, more strings were added and tuned to octaves, such as with the 12-string guitar.
Early Mechanical Amplification
The first solution to low volume in acoustic guitars was the development of mechanical amplification in Dobro guitars and hybrid guitars using steel and wood bodies, of which the National Guitar Company is likely the best known. These guitars captured physical vibrations and concentrated them in the front of the guitar using a mechanical system of vibrating cones.
Early Electrical Amplification
The very first electric guitar amplifiers were likely produced for people playing Hawaiian pedal steel guitars. These were probably either public address (PA) amps or modified PA amps. The names of the early builders have been forgotten, as many were likely simple one-off builds.
First Commercial Electrical Amplification
The first electric guitar amplifier was likely made by Leo Fender and was a modified valve-based public address amplifier. Fender's early guitar amplifiers had no controls and simply amplified the electric signal produced by early magnetic pickups. Although early prototypes exist, the first commercially produced guitar amplifier was made by Fender in 1947.
Uses of Early Guitar Amplifiers
Early guitar amplifiers were used primarily by pedal steel guitar players in Hawaii. The amplifier as an integral part of a guitarist specializing in playing electric guitar probably didn't begin until the late 1940s.