This is a vacuum tube booster purchased from an account that makes and sells handmade effects pedals. I used it on my effects board, but I'm selling it as part of a gear clear-out due to a recent move, as I haven't been using it lately. The back cover can be opened to replace the vacuum tube; it came with a 12AT7 installed when I bought it. I bought 12AX7 and 12AU7 tubes and compared their sounds. I preferred the 12AU7 and used it with my bass. This listing includes the effects pedal itself (with the original 12AT7 installed) and the Electro-Harmonix 12AU7 and 12AX7 tubes I was using. The vacuum tubes have some minor scratches, but they should still be usable. It runs on 9V center negative power, but the maker recommended using 12V. Sound has been tested and confirmed.