Season 1 CBS , 1973 Season 2 CBS , 1973 - 1974 Watch now Season 3 CBS , 1974 - 1975 Watch now Season 4 CBS , 1975 - 1976 Watch now Season 5 CBS , 1976 - 1977 Season 6 CBS , 1977 - 1978 Season 7 CBS , 1978 - 1979 Season 8 CBS , 1979 - 1980