Seeking info/docs: Pioneer Electric & Research Corp. (PER). Side band Selector. Model S-6 . Appears to be 455kc IF using crystal filters. AM, exalted carrier, USB, LSB, ISB. Appears to be the sort of thing that might have been used with radiotelephone. Rack mount. It's begging to be mated to a 1950's or 60's receiver. Thanks.