K-Line couplers are definitely different from Lionel couplers. The knuckle geometry is noticeably different if you have them side by side. The difference in required voltage has to be in the coil windings. I've standardized on Atlas electrocouplers (usually the ones that come on the Erie Built Diesels) for my steam and Diesel locomotives. All Lionel couplers get removed, tossed in a box and replaced by Atlas couplers.
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