INSTRUCTOR PLT TOOK OFF WITHOUT TKOF CLRNC DURING A STUDENT NIGHT TRAINING FLT DUE TO MISSETTING THE AUDIO CTL PANEL TO THE RADIO SET FOR LCL TWR CTL.

Narrative

AT XA55; ON A TRAINING FLT FOR NIGHT FLYING; WE STARTED THE ENG OF THE KATANA; LISTENED TO ATIS; AND GOT A CLRNC TO TAXI TO THE ACTIVE RWY FROM GND CTL. WE TAXIED TO THE RUNUP AREA AND STARTED THE RUNUP. AT THAT TIME WE HEARD GND CTL ANNOUNCE THAT THE CTL TWR WOULD BE CLOSING IN 5 MINS; AND THEY STARTED CHKING THE PCL. SQL IS IN CLASS D AIRSPACE UNTIL XX00 AND THEN REVERTS TO CLASS G ACCORDING TO THE AFD. WE FINISHED THE RUN-UP; SET THE RADIOS FOR ALL UPCOMING FREQS; AND TAXIED TO THE HOLD SHORT LINES OF RWY 30. WE INITIATED A CALL TO THE TWR AND GOT NO RESPONSE. I CHKED MY WATCH; AND IT SAID XX02. WE CALLED ONCE MORE; AGAIN NO RESPONSE. A PLANE WAS WAITING BEHIND US. WE DECIDED THAT IT APPEARED THE TWR WAS CLOSED; AND CLASS G WAS IN EFFECT; EVEN THOUGH WE HAD NOT ACTUALLY HEARD THAT ANNOUNCED. WE ANNOUNCED ON CTAF THAT WE WERE TAKING THE RWY FOR A R DOWNWIND DEP; AND TOOK OFF ON RWY 30. ABOUT 5 MINS LATER; WHILE SWITCHING FREQS; I REALIZED THAT WE HAD FAILED TO CHANGE THE AUDIO CTL PANEL TO COM #1 BEFORE TKOF; AND HAD BEEN TRYING TO CONTACT THE TWR ON THE WRONG FREQ! CAUSES: 1) NOT DOUBLECHKING THE AUDIO PANEL. 2) ASSUMPTION THAT BECAUSE IT WAS AFTER XX00 THE TWR MUST BE CLOSED AND NOT RESPONDING. 3) VERY POOR LIGHTING IN THE KATANA -- DIFFICULT TO AUTOMATICALLY SEE. 4) FEELING THE NEED TO GET OUT OF THE NEXT ACFT'S WAY FOR TKOF.