What eventually became KFMB-FM began testing in 1950 from the North Park Theater on Adams Avenue. It finally signed on as a commercial operation on 100.7 MHz on September 21, 1959, with a beautiful music format. In the late 1960s, the format was called "Music only for a woman." Station Manager Ed Peters bought the rights to syndicate the format. Soon after, Peters left and started his own company known as "Peters Productions" which syndicated the format on reel-to-reel tape to over 100 stations during the 1960s and 1970s, changing the name of the format to "Music just for the two of us."
San Diego in the early 1970s had three "beautiful music" stations and was about to gain a fourth, so KFMB AM program director Bobby Rich and station manager Paul Palmer put together a super high energy top 40 format to challenge market leader 1170 AM KCBQ. Rich wanted to change the call letters to something with a "Q" in them to become "the FM Q" but the owners refused to break up the KFMB AM/FM/TV matched set of call signs. Although 100.7 is closer to 101 than 100, 101.5 KGB-FM had already established itself as 101KGB, so KFMB-FM became "The all new B100 FM" in March 1975 with the slogan "Better boogie!", eventually knocking off longtime AM Top 40 powerhouse KCBQ in the Fall 1977 Arbitron ratings.
B-100 was the first major market FM top 40 station to achieve overall #1 Arbitron ratings for all listeners. The station's on air staff during its first two years included Phil Flowers, Rocket Man, Jimi Fox, Willie B. Goode, Rob Landree, Dave Conley, Bill Martin, Glen McCartney, "Shotgun" Tom Kelly, Gene Knight, Danny Wilde, Gary Kelley, Billy Pearl, Ken "Beaver Cleaver" Levine, "Just" Kevin (later Kevin Anderson), Cherie, Jimmy Rogers, Christopher Lance, Terri Lynne, Uncle Fred, and of course Bobby Rich using the on-air name "Dr. Boogie". Fox, Goode and Conley left to create Ten Q (KTNQ 1020 AM) in Los Angeles after the first year.
B100 had major success in the 1980s, reinventing itself as one of the nation's first hot adult contemporary stations. It melded top 40 hits (omitting some teen-oriented songs) with an adult delivery by its high-profile air staff. The day started with "The B-Morning Zoo" starring "The Rich Brothers (Bobby Rich, Scott Kenyon, Pat Gaffey, and Frank Anthony). Others included Gary Kelley, Gene Knight (now at Sunny 98.1), Danny Romero, Ellen K. Thomas, and John Fox.
Jeff and Jer became the new morning show hosts at B100 in 1991, but would leave in April 1993 for KKLQ. Replacing them were John Lander and Jools Brandt, followed by Larry Himmel, who had also succeeded Shotgun Tom in mornings on B100 in 1979. After Jeff and Jer departed, the station's ratings began to decline.