at 50,000 watts). KPEN became the first station west of the Mississippi to broadcast in multiplex stereo, officially beginning August 10, 1961, after a series of field tests. KPEN's technological achievements were recognized by the Electronic Industry Association, the FCC, and President John F. Kennedy. "Excursions in Sound" was renamed "Excursions in Stereo"; hosted by James Gabbert, the show focused on recordings that made good use of stereo. Gabbert also had a Sunday afternoon show Anything Goes that played music, sound effects, and almost anything that dramatically demonstrated the stereo effect. In the 1960s, the station moved studios from Atherton to San Francisco, first in a SoMa location, then to Nob Hill in a luxurious penthouse atop 1001 California Street at the corner of Mason Street. With this move, the "PEN" in KPEN changed from representing "PENinsula" to representing "PENthouse". By the mid-1960s, KPEN played primarily orchestral and light vocal performances of pop songs and standards, in competition with similar FM station KFOG (owned by Kaiser Broadcasting). K-101 On December 1, 1968, KPEN changed its call letters to KIOI ("K-101"), considered an innovative matching of call letters to a dial position. Eventually, the station added pop and rock music to its MOR playlist, to compete with upstart freeform rock stations KMPX and KSAN. Gabbert aggressively began promoting the station via outdoor advertising, which was a first for the market. "K-101" is likely the first station in the country to develop what is now called the adult contemporary format. Even though KIOI's programming was mainly focused on music, it also featured many popular on-air personalities over the years including Don Kelly, Bill Keffury, Hoyt Smith and Jeff Serr. By 1970, K-101 advertised itself as being at 101 on the FM dial and had the address of 1001 California Street, with zip code 94101. During the 1970s, Gabbert developed another lasting technological achievement as KIOI became the first station in the country to develop circular polarization, which was a key element to FM reception in automobiles, which used to be difficult. Gabbert also experimented with quadraphonic sound (in association with RKO General's KFMS-FM). By the mid-1970s, Gabbert purchased KSAY-AM, changing its call letters to KIQI. Originally programmed as an oldies station, by the end of the decade, it was flipped to a Spanish language format. In September 1980, Gabbert sold KIOI to Charter Company for $12.5 million, then the highest price paid