UHF was an option for this set; as dieseljeep says, there is a hole under the logo and some other accommodation in the chassis for a control there. The SAMS schematic does include the optional UHF tuner. On my set, the second large knob is is power/volume.
That's fine with me as there are only a handful of mexico-based channels available on UHF around here anymore, nothing I'd ever miss watching
Interestingly, the schematic includes a channel indicator light, though I don't see any sign of there actually being one. I haven't looked into the tuner section yet for where it might have gone; although, it's a moot point because it's always on channel 4 now anyway.