I heard literally everywhere that it is really important to let my amp warming up for some minutes before playing the guitar (or give some audio do the input).
Strange thing is that the recommended time is different everywhere ! I red between 30 sec and half an hour...
I did not find any other physical/electrical reasons than "the tubes have to warm". In my opinion there is a lack of true scientific explanations, it's seems more like a blindly believing. What are the risks if tubes are stimulate directly at startup ? And why these hypothetical risks even exists ?
Lot's of guitarist seems to don't care about it and directly play whithout reporting any issue.