Managed to find a 90's MIA Blues Deville 2x12 this week off craigslist. While playing, I noticed the "bass" pot really doesn't do much. If you turn it lower than "2" you lose all low end, but from 2-10, it's sounds about the same. There's low end but value doesn't seem to change. I have a Hot Rod version and the bass seems to be more responsive. Any idea what the issue is?