Catalyzes the final step in the conversion of aurachin C to aurachin B. Catalyzes the reduction of 4-hydroxy-2-methyl-3-oxo-4-((2E,6E)-farnesyl)-3,4-dihydroquinoline-1-oxide to form 2-methyl-1-oxo-4-((2E,6E)-farnesyl)-3,4-dihydroquinoline-3,4-diol, which then undergoes a spontaneous dehydration to form aurachin B. Accepts both NADH and NADPH, but has a preference for NADH. aurachin B + H2O + NAD(+) = 4-hydroxy-2-methyl-3-oxo-[(2E,6E)-farnesyl]-3,4-dihydroquinoline 1-oxide + NADH Mutant accumulates aurachin D and aurachin C and does not produce aurachin B and aurachin A. Belongs to the 3-beta-HSD family.