Revenue bonds authorized by section 23-3617 may be issued by resolution duly passed by the governing body of the county without any other authority. General obligation bonds authorized by section 23-3620 may be issued by resolution duly adopted by the county board without any other authority, unless the proposed sewer tax levy authorized by section 23-3616 exceeds three and five-tenths cents on each one hundred dollars of actual value, in which case the bonds may be issued only after (1) the question of their issuance has been submitted to the registered voters of the county at a general or special election, (2) three weeks' notice thereof has been published in a legal newspaper published in or of general circulation in the county, and (3) more than a majority of the registered voters voting at the election have voted in favor of the issuance of the bond.