Schwinn early postwar, just as bobcycles said. I learn something new all the time. I guessed the numbers started with "A" when they went to the forward facing dropouts after the war. I guessed that by estimating how many bikes were built and backing up the letters from the 1948-1952 known numbers. That idea works well if they started with "A" and progressed. But yours , being a "K", didn't fit that sequence. The serial number lookup looks at it as if the serial number is on the dropout, that's why it incorrectly says 1953. My frame is also a "K" but the number is on the dropout, so it's a 53.
I checked the paint schemes from 46 to 52. Your paint matched up with the 1946 illustrations I found, different from the later ones. Now I need to learn more about the frames. I thought they were all identical cantilever frames, except for the later middleweight and also the king size frames of the 60's.
From the 46 catalog: B-507 Autocycle Tourist
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