When I was growing up, we had a Sears Silvertone 17" b&w portable with the same type of coaxial UHF tuner as your Emerson set. The only problem with the Silvertone's UHF selector was that the mechanism wore out within a very short period of time. Don't know why it wore out so soon, as there was only one UHF TV station in Cleveland when the set was new; the station was so weak we couldn't watch it. As much as we did watch the commercial networks, however, I would have expected the VHF tuner to wear out before the UHF, not the other way around.
BTW, just out of curiosity, how do you know your "Emerson" TV is a rebadged Admiral? My best guess is that there are Admiral components on the PC board or chassis; perhaps there is a rubber stamp somewhere on the chassis as well stating "Manufactured by Admiral Chicago" or similar wording.
I didn't realize that Emerson had taken over Dumont at any time. I do know the DuMont name was slapped on a few cheap offshore-made CRT TVs in, I believe, the 1980s or so--probably a cheap attempt to keep the DuMont name alive, even though the company itself had gone out of business decades earlier. Even DuMont's operated TV station in New York, while still on the air today on channel 5, is now known as WNYW-TV and is, IIRC, a FOX affiliate. The station's test pattern (when it was operated by DuMont and was known as WABD-TV) was often used in TV repair books of the 1950s to illustrate common TV picture problems. I used to have a few of those manuals, but lost them in a move.