I recently acquired a pair of KH 52 speakers. It looks like somebody has separated the AC power and added a jack at the bottom for the signal. I still have to open up the speakers to check this out to be certain , but if that is what they did, how do I connect them to a receiver? I am planning to check them out by connecting them to an AV stereo receiver made in the 90s. Also is it possible to connect them to a mid 70s receiver? If so, how would I do that? The cord that is pictured is the AC . I know that because it has a US adapter connected to the European plug. The speaker jack is in the center near the bottom . Thank you very much.