There call letter approval came though on September 19, 1935 but they did not launch the change till October 15 1935. During this time they were also making the change from 650Khz to 710Khz.
Link to letter from the FCC. A very young FCC they had only been un existence for 15 months when they sent out this letter to KPCB.
http://nwradiohistory.com/wp-content/pdf/kiro/kiro_call_change.pdf
From what I can tell they were operating on 710 on experimental authority till 1936 or 1937. Lots of interesting reading in the 1935-1940 FCC file. The one interesting thing in reading the early applications for the move from 650 to 710 and even the application for their 50KW power increase is that all the FCC rules are just 3 digit numbers. When they reference a rule it's rule 167 not the long number they are now.
Link to letter from the FCC. A very young FCC they had only been un existence for 15 months when they sent out this letter to KPCB.
http://nwradiohistory.com/wp-content/pdf/kiro/kiro_call_change.pdf
From what I can tell they were operating on 710 on experimental authority till 1936 or 1937. Lots of interesting reading in the 1935-1940 FCC file. The one interesting thing in reading the early applications for the move from 650 to 710 and even the application for their 50KW power increase is that all the FCC rules are just 3 digit numbers. When they reference a rule it's rule 167 not the long number they are now.