Although I am not familiar with this particular model Zenith, it seems a lot of older CATV ready sets only received channels 02-36 or similiar. I had a VCR from as late as 1991 that only received channels 02-36, and 95-99. I have a 1985 SL-100 Super Betamax VCR that does 02-66 and 95-99 CATV. I also have an early 1985 model Magnavox that only goes up to channel 56 CATV.

If you can't get any channel above 44 or so on CATV, maybe using a cable box or a VCR will work fine instead.