I can definitely tell the difference. A friend of mine has the AXE-FX. We tried testing its Mesa Boogie model against my actual Mesa Boogie amp -- and the difference was night and day.
Like one of the comments from above, part of the magic of tube guitar amplification is that it is much more responsive dynamically to inputs. You can turn the volume up a tick, or hit the strings harder or softer, or change your picking style, and the results are drastically different on a tube amp.
This gives the artist more space to express themselves -- which is why tube amps are still favoured amongst guitar players today -- decades after transistor's have taken over the rest of the electronic industry. You can't get the nuanced expressiveness in a crystal lattice that you can in the free space of a vacuum. [1]
[1] I'm paraphrasing from H. Alexander Dumble, one of the gurus of guitar amplification.
Like one of the comments from above, part of the magic of tube guitar amplification is that it is much more responsive dynamically to inputs. You can turn the volume up a tick, or hit the strings harder or softer, or change your picking style, and the results are drastically different on a tube amp.
This gives the artist more space to express themselves -- which is why tube amps are still favoured amongst guitar players today -- decades after transistor's have taken over the rest of the electronic industry. You can't get the nuanced expressiveness in a crystal lattice that you can in the free space of a vacuum. [1]
[1] I'm paraphrasing from H. Alexander Dumble, one of the gurus of guitar amplification.