road crews may have their own catering crew. Guitar techs for the most famous international guitarists such as Jimmy Page or Tony Iommi can become minor celebrities within the guitar fan community because of their proximity to famous musicians and insider knowledge of how a certain guitarist's unique tone is created. Training and career path Guitar technicians must have a broad knowledge of the musical equipment used in the types of bands they work with. At a minimum, this must consist of familiarity with setting up and tuning guitars and making simple adjustments and repairs. As well, guitar techs are often expected to set up, repair, and adjust electronic effects, tuners, pre-amplifiers, amplifiers, and pedalboards. To do these tasks, guitar techs must know about a range of audio engineering and electronics concepts—such as impedance, signal phase (for speakers and microphone wiring), and input voltage for pre-amps and effects. To do simple repairs on electronic gear, a guitar tech may have to know how to use a soldering iron and a multitester, and how to do basic electronics troubleshooting. As well, since guitar techs need to soundcheck the instruments and amplifiers, they must have a knowledge of the way guitars and amplifiers are supposed to sound in the style of music of the band. This means that the guitar tech must have an ear for music, and for musical tones and sounds. A guitar tech for a heavy metal band must be able to tell whether distortion from a heavily over-driven tube amp is desirable tube clipping or distortion from a blown speaker or damaged power amp. The distinctions a guitar tech must make can be subtle. For example, a guitar tech replacing a blown tube with a new one may have to ensure that the tube amplifier still has the same "color" or "warmth" when chords are played through it. To check guitar tuning, a guitar tech must be able to play major, minor, and other chords in a variety of keys. Even if the guitar has been tuned with an electronic tuner, the tuning still must be checked by ear, because the equal tempered tuning of a guitar can involve compromise. Guitar tuning can be affected by fret placement and wear, the angle of bridge angle, string age, and other factors. Thus, even if an electronic tuner indicates that a guitar is 100% "in tune," it may still need