KYW has been the longest running format anyway, they started in 1965. But the long run of WKDN goes back to when FM was just starting to come into its own. At the time among FM stations were WWDB was jazz, WFLN & WFIL-FM classical, WQAL, WDVR, WPBS, WSTW, WJBR, WFMZ & others beautiful music, WIFI & WIBF suburban mixed programming stations, & WRCP country in mono. Within a couple years WMMR would be progressive rock, WIFI 'Hit Parade' MOR then top 40, WQAL became WWSH, WDAS-FM Hyski's Underground...and soon FM was taking away the audience from AM.