the amp master volume effects distortion and tone. some amps do that in a good way, some don't.

plexi/marshall type amps benefit from master volume cranked. EL34 equipped amps get squishy/compressed and more mids when the volume is cranked.

others....not so much. rectifier is one such amp that is better when the master volume is below 3-4. 6L6 tubes don't distort in a good way in my opinion.