Hubbard became the merged station's general manager, acquiring controlling interest in 1941. A month after the merger, KSTP became an affiliate for the NBC radio network, which it remained for 46 years. On November 11, 1928, under the provisions of the FRC's General Order 40, KSTP was assigned to a "high-powered regional" frequency of 1460 kHz. The only other station assigned to this frequency was WTFF in Mount Vernon Hills, Virginia (later WJSV, now WFED, Washington, D.C.). On February 7, 1933, the FRC authorized KSTP to increase its daytime power to 25 KW. In 1938 and 1939 KSTP also operated a high-fidelity AM "experimental audio broadcasting station" Apex station, W9XUP, originally on 25,950 kHz and later on 26,150 kHz. In 1941, as part of the implementation of the North American Regional Broadcasting Agreement, KSTP was assigned to its current "clear channel" frequency of 1500 kHz, with the provision that it and WJSV, as "Class I-B" stations, had to maintain directional antennas at night in order to mutually protect each other from interference. An FM station, KSTP-FM, was founded in 1946 but shut down in 1952.