I am interested in perhaps getting a tube amp, though I'm not looking at spending much. I don't really know much about them, other than they are warm sounding. I currently have Paradigm monitor 7s powered by an Onkyo601. I really don't like the bright sound of the Onkyo and would love to hear them on a tube amp. My question is, how cheap might I be able to get one used for my 7s?