KNBR started in 1921 as KPO. The original studios were in the Hale Brothers store at Fifth and Market. In 1929, the station moved to the Hale Brothers annex, seen behind the corner store. NBC acquired KPO in the 1930s and changed the call letters to KNBC. Later, they wanted to use KNBC for a Los Angeles station, and changed the San Francisco station to KNBR.
Radio history from John Schneider's wonderful site Voices Out of the Fog: http://www.sfradiomuseum.com/schneider/articles.shtml
This is my 100th post of the year and my 400th overall.