I just came home with a Fulltone '69 pedal, and I notice in the instructions it warns not to use a regular negative center pin AC adapter. This is news to me. What's this all about? Are adapters with positive tips widely available? I currently power my pedals with the built-in power supply in my PS-25 pedal board. Will I be able to adapt anything that will deliver the positive center pin, and still use the board power? Thanks!