Yes, I've figured it out. Anyway I have another more complex problem.
Each 7490 has its own in-clock pulse, coming from the previous 7490. right? But if I want to add a second clock line, coming from a pushbutton, so when it is pressed, it also counts as a clock pulse (for manually advance the minutes or hour "hand"). I find a problem. If I connect both pushbutton and previous 7490 output into the same clock input, I need to do something for them both to work properly.. If not, when one of them is activated and the other one falls from 1 to 0, no transition will occur...
Any idea??