I've just acquired a D-180 but I think that channel one isn't working, plugging into 1 does nothing until the gain on channel 2 is turned up. I'll probably just take it to a tech for this but I thought I'd run here for a few ideas. Plus, I seem to remember the pre-amp tubes being 3 12ax7's and 1 12au7 - is that right? If so which slot does the au7 go in? Thanks alot!