I'm new in tube amp and i'm wondering what is the difference between 12AT7 tubes and 12AX7 tubes? Is the difference in sound very subtil or not?

If you're new to tube amps you probably won't notice much. The differences in tubes aren't necessarily subtle but they aren't red flags either. You have to develop you ear for tone a little bit to get a handle on what different tubes sound like.
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12AT7's normally have less gain than a 12ax7, you can substitute a 12at7 in a 12ax7 amp with no issues, You can also substitute it with a 12ay7, for minimal gain, but you also lose a small bit of volume with it.
Ibanez AFS75/Fender Strat Plus > Fulltone Deja' Vibe > Keeley TS808 MOD+ > Fulltone OCD > VanAmps SoleMate > Metro JTM45
Thank you. Fender sells Groove Tubes tubes but also USA Groove Tubes that are nearly two times more pricy. Does paying the double price will also double the quality of the tube sound or there is no difference except the fact of being made of US components?
Yeah I went in this post before posting this but it only describe difference between brands. Not between different tubes.