According to Old Christmas Lights, as long as your wiring is soft and flexible, and there is no fraying or exposed wires, your set is safe to use. If you are using the older lamps on an artificial tree, use caution as the heat generated could melt plasticized needles and cause a fire hazard. Modern lamps are of the cool burning type, and therefore do not present a problem. But the vintage lamps(any made before 1970 or so) burn much hotter and therefore must be used with caution.
Next Week’s Post: How Do I Make My Vintage Lights Last Longer?