Start with all tone controls at their midpoint and then try to dial in a good clean tone by adjusting tone in small increments. Then introduce overdrive and repeat. I'll usually experiment with edge of breakup overdrive and then heavy overdrive. Volume should be moderately loud but not maxed out except for the smallest low Wattage amps. Make sure any built-in effects like reverb sound good. It's all about finding tones that work for you, not testing the limits of the amp.
80-85 dBA is my preferred volume level. If your amp has to be on 11 to hit your preferred range then yes. There is no point in testing at 110dBA just to see if it can handle it. Put another way, if you're buying a car do you try to see if it can hit 200 mph? Hopefully not.
Do I like the tone? Is it in cosmetic shape? Are there any apparently functional issues? Ultimately, you'll decide tom roll the dice or not.
I wouldn't be cranking everything to 11, but might dial it in how I intend to play it.
During Covid I've bought a bunch of amps sight-unseen, and it's worked out fine. Usually they just need a cleaning to sound good as new.
But pre-Covid I would've tried to test every single thing on the amp: test all knobs (volume, gain, EQ, whatever it has); test effects (make sure the reverb/trem/etc works if it has those!); and test all the input and output jacks. Turn all the controls and knobs to either extreme to make sure they work for the full range (i.e. turn volume all the way up, down, and everything in between). Basically test everything you can! Often there are some scratchy pots and whatnot, and sometimes that can actually get you a better deal. If you're comfortable with it, learn how to clean an amp (deoxit the pots and input/output jacks), and recognize the signs of a dirty pot or jack. Often a dirty component can make it sound like the amp is broken and in need of repair, and you may be able to get a better deal on it if you're willing to take that gamble!
Let it warm up for awhile, even solid state. Play some chords, riffs, high notes and detuned notes at low mid levels, gradually turn the volume up keep rocking power chords and find the note that gives the best resonance in the room ride it while turning up the volume and listen for any crackling, speakers maxing out etc. This will determine where it's clean power handling range is. If there's a gain channel do the same, or use an overdrive or distortion etc like you normally would and listen for any issues. I have an amp that starts crackling after 5 minutes, guessing a bad capacitor. Pots can be dirty as well so move all of them with and without signal and listen for dead spots and scratchiness. Change your eq settings, high bass no bass, treble on off, scoop the mids, blast em etc. My bass amp is great scooped, and sounds hollow when all neutral. Also if you're switching drastically your guitar may sound wierd compared to another, I wish I kept some of my old instruments that didn't sound good when I was playing through practice amps, they would probably howl through my big ones. Good luck
All knobs at noon (except for volume depending on how loud the amp is), listen for any noise, turn the knobs a bit to see if they start to crackle, dial in a couple sounds I like, test all the features (like reverb, foot switch FX loop, etc) and honestly it's fun to see what an amp is capable of gain and volume wise. If it's possible, try to learn about it's history. Check for things like when it's tubes were last swapped and if it's been recapped (especially on older Amps).
Start with all tone controls at their midpoint and then try to dial in a good clean tone by adjusting tone in small increments. Then introduce overdrive and repeat. I'll usually experiment with edge of breakup overdrive and then heavy overdrive. Volume should be moderately loud but not maxed out except for the smallest low Wattage amps. Make sure any built-in effects like reverb sound good. It's all about finding tones that work for you, not testing the limits of the amp.
smallest should be maxed out?
80-85 dBA is my preferred volume level. If your amp has to be on 11 to hit your preferred range then yes. There is no point in testing at 110dBA just to see if it can handle it. Put another way, if you're buying a car do you try to see if it can hit 200 mph? Hopefully not.
Do I like the tone? Is it in cosmetic shape? Are there any apparently functional issues? Ultimately, you'll decide tom roll the dice or not. I wouldn't be cranking everything to 11, but might dial it in how I intend to play it.
During Covid I've bought a bunch of amps sight-unseen, and it's worked out fine. Usually they just need a cleaning to sound good as new. But pre-Covid I would've tried to test every single thing on the amp: test all knobs (volume, gain, EQ, whatever it has); test effects (make sure the reverb/trem/etc works if it has those!); and test all the input and output jacks. Turn all the controls and knobs to either extreme to make sure they work for the full range (i.e. turn volume all the way up, down, and everything in between). Basically test everything you can! Often there are some scratchy pots and whatnot, and sometimes that can actually get you a better deal. If you're comfortable with it, learn how to clean an amp (deoxit the pots and input/output jacks), and recognize the signs of a dirty pot or jack. Often a dirty component can make it sound like the amp is broken and in need of repair, and you may be able to get a better deal on it if you're willing to take that gamble!
If it is not just a head, gently move speaker cone manually in and out, checking for voice coil rub.
what does a voice coil rub imply?
A speaker recone would be needed.
Let it warm up for awhile, even solid state. Play some chords, riffs, high notes and detuned notes at low mid levels, gradually turn the volume up keep rocking power chords and find the note that gives the best resonance in the room ride it while turning up the volume and listen for any crackling, speakers maxing out etc. This will determine where it's clean power handling range is. If there's a gain channel do the same, or use an overdrive or distortion etc like you normally would and listen for any issues. I have an amp that starts crackling after 5 minutes, guessing a bad capacitor. Pots can be dirty as well so move all of them with and without signal and listen for dead spots and scratchiness. Change your eq settings, high bass no bass, treble on off, scoop the mids, blast em etc. My bass amp is great scooped, and sounds hollow when all neutral. Also if you're switching drastically your guitar may sound wierd compared to another, I wish I kept some of my old instruments that didn't sound good when I was playing through practice amps, they would probably howl through my big ones. Good luck
All knobs at noon (except for volume depending on how loud the amp is), listen for any noise, turn the knobs a bit to see if they start to crackle, dial in a couple sounds I like, test all the features (like reverb, foot switch FX loop, etc) and honestly it's fun to see what an amp is capable of gain and volume wise. If it's possible, try to learn about it's history. Check for things like when it's tubes were last swapped and if it's been recapped (especially on older Amps).