That's right, in late 1963 through 1964, as a great advertising gimmick, a local sale, booster of FM, and perhaps a desert topping, THE AUDITRON - "tuned especially to WGAY-FM." Above the radio is the "badge" from my real WGAY-FM Auditron (though I got it second-hand). Searching my memory banks, I cannot remember what the second knob was for (tone?) because surely they wouldn't have put a 'dummy' knob on there for tuning. As you can see, where the channel numbers might appear, there is a blank. I heard these advertised heavily and first encountered one at the District Grocery Store in Wheaton, Maryland (not far from WQMR/WGAY) in early 1964. I believe they sold for $29.95 or $39.95, can't remember which is the correct price. With a screwdriver, in the back you could tune to another station though that would be a terrible thing to do :)
So you have to use your imagination a little, and substitute the metal badge at top for the WRFY-FM badge shown in the picture. Sadly my Auditron is long gone. Yes, there WAS a time before multiplex stereo... then again there was a time before color television!
Thanks to Andy at Somerset.net for the picture! You can see other "FM Only" radios (in the days where most radios were AM-FM) at his page http://www.somerset.net/arm/fm_only_list.html