During the 1970s, NSB started the process of finding a replacement for the El 9. New locomotives would cost NOK 20 million, and the company saw it as unrealistic to invest so much in a marginal branch line. NSB had also concluded its away-with-the-steam program, and therefore had a lack of locomotives in general. If a new class of locomotives was to be built, it would have to satisfy more than the requirements for the Flåm Line, so NSB instead started investigating whether any of the older models could be used. Tests were performed in 1971 and 1973 with El 11, built between 1951 and 1964, and El 13, built between 1957 and 1966. Neither was considered optimal: El 11 allowed the train weight to increase to , but the train had the steps for the voltage regulator and the commutation set for too high speeds. El 13 had rheostatic brakes, which were not suitable for the gradient; the locomotives were also better suited for mainline service and would therefore not be prioritized for branch lines.