Hello and welcome!
If you purchased your TV within the last 5 years, then no, you should not need a converter box. Anything called a "TV" (as opposed to a "monitor") is required to have the correct type of tuner to watch over-the-air broadcasts without an external converter.
The issue is probably related to where you are relative to the broadcast towers and what kind of antenna you need to pick up the signals.
You can use the TV Fool signal analysis tool (located
here) to figure out where the stations are and how strong your signals should be. The tool will generate a "radar plot" report. When you get that report, you can copy the URL of that page (copy the content of the address bar in your browser) and post it here. That will help the rest of us understand your signal situation and provide more specific responses to your needs.
At 50 miles, most people need to use some kind of attic or rooftop antenna for reception. The exact needs depend on how high your elevation is and what the terrain around you is like, but that's where the tvfool report comes in. Your situation might be easier or harder than average, and the report will let us know.