How to find the sweet spot settings of a tube amp

[hurghanico]

Most tube amps sound at their best when their controls are set to their sweet spots.

But how to find the sweet spot settings of a tube amp?

To find the sweet spot of the amp controls you should move them up and down, going from min to max values and vice versa while hearing the guitar-amp signal of a sustained chord (taking advantage of the looper placed at the beginning of the chain to play back the chord could be handy),
Personally I play unfretted adjacent strings pairs, which pair it depends on the tone control I want to check: BASS, MID or TREBLE, for the DRIVE control I use the central pair of strings,
in doing so you will notice that the tone changes very slowly and gradually by moving the controls for most of their range excursion, but there is a threshold point from where a more drastic or distinctive change occurs, if you narrow the up and down movements of the control just around that point you will hear a sort of wah effect, and there is the sweet spot!

Once you found the sweet spots you can fine tune them as you prefer.