I bought a Peavey Cab used from a store I really like it... But I'm not sure if it's 8 or 4 ohms. The guys at the store were clueless, the thing on the back is scratched off. How can I figure out what ohms it is? If it's 4 I need to take it back because I can't use it with my other cab... And I need to find this out quick! Thanks guys.