Once a capacitor is wound we have no way of knowing inner & outer turns of a capacitor unless we were asked to identify at the time of manufacture.
This is what I have suspected for years. The theory that the outer foil going to the lower potential connection is plausible, but FWIW I don't recall hearing of any one trying a cap both ways and hearing a difference. If someone has a reference I'd like to see it. I can imagine that every cap may not go into the labeling part of the manufacturing process in the same orientation.
Hey Peebs, remember that guitar amp input circuit we were talking about? Might be a place to try it.
