if its the old silverface mv then its not great, not terrible but not great compared to more modern designs. if it is the old style and you dont like it, its pretty easy to bypass it, and if its a more modern mv then it might sound great. part of the issue is there just isnt a lot of gain in the non-reverb ab763 circuit, two stages with a good amount of loss and scoop due to the eq, so you wont get a ton of dirt without pedals or slamming the pi tube.