We have selected observations of quiet K corona in maximum activity phase (1970 and 1972) and we have computed the corresponding density models. The density is found to be two times smaller than in average maximum coronal models (Newkirk, 1967) and nearly equal to that of minimum coronas (Saito, 1970). The research of quiet coronas between active periods has been extended to the three past solar cycles thanks to λ5303 A measurements: very low λ5303 A intensities, corresponding to very small densities, are found even in maximum activity phase. A short discussion about the values of average quiet coronal models is given.