I read a thread from a while back where Tombowlus was recommending that the tubes in this puppy be replaced with something better. I haven't popped the top yet but I assume that the 659 has the proverbial Sovtek cheapies in it? I believe Tom recommended Telefunkens. Anyone else have experience with upgrading the tubes in a DB659 and how much and what kind of difference in the tone did your upgrade make? Thanks!!