What amp settings do you need for John Mayer?
It depends on the song. On a generic five-knob amp, Slow Dancing in a Burning Room starts at Gain 2, Bass 5, Middle 6, Treble 6, Presence 5, Reverb 3; Gravity starts at Gain 4.5, Bass 5, Middle 7, Treble 6, Presence 5, Reverb 3. These are starting points, not the settings used on the records.
What gear did John Mayer use on these songs?
Slow Dancing in a Burning Room: Fender Stratocaster, Continuum era; Two-Rock, Dumble, Marshall or Fender. Gravity: The Black One, a black Fender Stratocaster; Not documented (his 2010 rig: a Dumble and a Two-Rock). Each song page lists the sources behind its rig.
Can you get the John Mayer tone without the original gear?
Yes. What carries these sounds is the gain structure, the EQ curve, the pickup position and the order of the effects, and all four can be rebuilt on other equipment. Tonelify rewrites each starting point for the amp and guitar you own.