Hi Glen, Hmm, a mystery. The HX-50A that I owned back in 1970, if my = memory is correct, had the same style knob for 'Operations' and = 'Frequency'. I don't recall my HX-50A having a spinner knob. I'll send = a photo of my 'new' HX-50 to you directly and you can take a look at the = 'Frequency' knob and let me know your thoughts. Thanks! 73, Scott WA9WFA