Those Zenith converter boxes made by LG had very good tuners. Although Samsung tuners are normally good also. It may be the different antenna location of each TV that is the problem. Try connecting the Zenith box to the Samsung TV and see if it will get the same reception at that location.
I'm approximately 60 miles NW of Fordland and aim my antenna at 118 degrees. I have a cheap zenith digital tuner I use on an old tv in my basement (not HD) - it scans in 49.1 just fine. My high $ samsung HD tuner running off the same antenna won't scan it in. All other channels (3, 10, 21, 27, 33) are crystal clear on the samsung. Any ideas?
Actually, the "cheap zenith digital tuner" was one of the best government-subsidized CECBs, it had a very sensitive Generation 6 ATSC tuner. Unfortunately, as a condition of being in Uncle Sam's $40 coupon program, the Zenith DTT900/901 CECBs only display in SD 480i, but the picture quality is pretty good. You might look at several discussion threads on the "cheap" Zenith boxes in the Coupon Eligible Converter Box sub-forum.