Possible Clues:

• He maintains frequency by rescheduling one up train
• Wire worker
• Professional at pulling strings?
• One working with hammers
• You'll need one if someone's queered your pitch!
• Instrument adjuster
• Sound professional doing key work in the home occasionally?
• An eruption upsetting one with a fine ear?
• One who works on a grand scale?
• Worker with a fork