The guitar amplifiers and keyboard amplifiers are made differently, and if you use guitar amp for keyboards, you run the risk of distortion. The keyboard amps are more complicated as keyboards have a wide range of frequencies. The guitar amps on the other side are designed for a specific range of frequencies. It does not work outside the frequency and can damage the sound of the keyboard. Most guitar amps are also single units and need separate speakers while the keyboard amps have the combos. Some keyboard amps can also contain compressors to protect the speaker circuits from high volumes. Guitar amps generally do not come with compressors which can cause damage to the speaker units. Check out Roaming Sound to know more about guitar.