What do you guys think of the Hartke 4000? I've never tried it but it has a very good price. I know that the other Hartke heads (that have the tube preamp and graphic EQ) have problems with durability, but the 4000 is a completely different design that I haven't read any complaints about. It also includes a subharmonizer (like Ashdowns). Is this a good head? How would it compare to the Ampeg B-2r?