PrimaLuna EVO 100 Tube Power AmplifierBAD TUBE INDICATOR PrimaLuna engineers wanted to make owning a tube amp so simple you would have no excuse not to have your tube dreams come true. If a tube fails, Adaptive AutoBias will instantly put the amplifier into protection mode so no parts can get damaged. A red LED will light up in front of the tube that needs replacing. Simply plug in another tube, and listen. No guesswork. No smoking amp. No getting out the soldering iron or dropping your