The main job of a guitar tech is to set up the backline gear, change strings, tune and intonate the guitars and make guitar changes during the show. You might be involved in the pedalboard design, amp rig, any switching that might be done, etc. Pretty standard tech stuff.
But another part of the gig is to be a critical listener. Not necessarily of the actual playing of the guy you are teching for (though I have been quizzed a few times by Music Directors and Band Leaders), but of the sound of the guitars and amps in context with the entire band, during the entire show.
It’s one thing to plug into a rig, blast a few power chords and call it ready to go…that’s fine. But in rehearsal or during the gig, it helps to keep an ear on the role the guitar is playing, whether it is in tune for the song, if the string gauge sounds heavy or light enough for the part, if the pick is light or heavy, if the part is strumming or picking. All of these factors matter to the player and the band. You might hear that a certain guitar could take a heavier string in dropped D tuning. You might catch an intonation problem that could be solved with a bridge height adjustment.
Both of those things happened to me recently, on the same guitar. There is a song in the set that calls for a dropped D Stratocaster, played cleanly on the rhythm parts and screaming in a harmony lead with the artist during the solo section…which then drops to a naked, clean Strat part again during a breakdown verse. Whew!
The clean part is arpeggiated and played in unison and I noticed that our guitar sounded a bit out with itself, a little sharp of the fretted G string (second fret). The guitar intonated nicely using octaves when setting it up, but a plain old D chord was funky sounding. This is usually the fault of a too-high nut, in my experience, so I considered getting the files out. Instead, because time was a factor, I dropped it down at the bridge since there was room to do so, and that cleared it up enough to get a solid D chord ringing.
There is also a Duane Eddy-like riff that utilizes the low D note with a deep tremolo on. That part is also played during a quiet section and I though a heavier set might work better and add some heft to the tone. I used the D’Addario EXL 116 a Medium/Heavy set with a .011 on top and a fat and twangy .052 on the bottom. Sounds great.
Keeping your ears open and anticipating the needs of the player are important aspects of the tech gig. Try listening to recorded music and notice what frequency ranges each instrument resides in. This will give you an insight into what the best guitar for any given job might be.