I have an ART Tube Channel, about two years old, that just stopped sending signal to the amp. I have checked/swapped all the cables and tested the amp which is working fine as well. The tube drive meter shows signal going in and the VU meter says it's sending signal but there's nothing coming out of the amp. The local shop wants $65 just to open it up but the Chief Financial Officer (wife) has signed off on a new pre. I'm open to suggestions.