I have a lot of amps and would love to know how to troubleshoot and repair them. I've done the BYOC pedal build and I change out pickups and pots in my guitars as well as bias my amps but that's as far as I've gone. So, I need to learn from step 1. What do you recommend? I found a dvd by Gerald Weber called "Tube Guitar Amplifier Servicing and Overhaul". Is that a good place to start? Thanks.