AN A300 CREW; DEPARTING IND; FOUND THAT THE CAPT'S VHF XMISSIONS WERE NOT BEING RECEIVED DUE TO WRONG SWITCH POS.

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THE CAPT'S AUDIO BOX XMIT BUTTON WAS LEFT IN INTERCOM. THE COPLT HANDLED THE RADIOS AS WE TAXIED. THIS WAS THE COPLT'S LEG. WHEN WE WERE 'CLRED FOR TKOF RWY 23R; FLY RWY HDG' I (PNF) RESPONDED WITH MY BOOM MIKE AND WE COMMENCED OUR TKOF. THE TWR MADE NO CALL OR QUERY AS TO WHETHER WE RECEIVED THE TKOF INSTRUCTION BECAUSE THEY SAW US ON THE ROLL. AS WE PASSED THROUGH 2000 FT; THE TWR CALLED AND INSTRUCTED US TO 'R TURN 050 DEGS; CONTACT DEP.' I (PNF) RESPONDED WITH MY BOOM MIKE AND PROCEEDED TO CHANGE THE HDG BUG AND SWITCH FREQ. THE TWR CALLED AGAIN (WITH A MORE URGENT TONE) WITH THE SAME INSTRUCTIONS; AND QUERIED IF WE HAD RECEIVED THEIR INSTRUCTIONS; I (PNF) THEN SWITCHED TO MY HAND MIKE AND REPLIED AGAIN. THE TWR; IN A MOST EXCITED TONE; CALLED AGAIN AND REPEATED THEIR LAST INSTRUCTION AND 'IDENT IF YOU CAN HEAR ME OR CONTACT DEP.' AT THIS TIME; I WAS LOOKING AT THE COM #1; AUDIO BOX (CAPT) AND THE XPONDER AND NOTICED THAT MY CAPT (PNF) AUDIO BOX WAS SET TO XMIT ON INTERCOM NOT COM #1; THE SECOND OFFICER SWITCHED XPONDERS AND ASKED IF ATC WAS RECEIVING OUR SQUAWK. I PRESSED THE IDENT BUTTON ON THE XPONDER AND SWITCHED TO COM #1 ON MY AUDIO BOX AND REPLIED TO ATC. AS I LOOKED UP FROM THE CTR CONSOLE AND SAW OUR ALT HAD BEEN EXCEEDED. I CALLED 'ALT' AND PULLED THE THRUST LEVERS BACK AND PUSHED ON THE YOKE. THE COPLT (PF) RESPONDED WITH 'SORRY' AND CONTINUED THE MANEUVER TO CORRECT BACK TO OUR ASSIGNED ALT (3000 FT). THE TWR CALLED; QUERIED OUR ALT AND GAVE US AN IMMEDIATE COMMAND OF 'FURTHER L TURN TO 090 DEGS FOR TFC SEPARATION.' I RESPONDED TO THE INSTRUCTIONS. THE TWR THEN ADVISED US TO CALL THEM WHEN WE REACHED OUR DEST AND HANDED US TO DEP. I BELIEVE THIS DEV OCCURRED BECAUSE THE COPLT (PF) WAS DISTR BY THE COM PROB CAUSED BY THE CAPT'S AUDIO PANEL NOT BEING IN THE PROPER POS AND THE EXCITED TONE AND NONSTANDARD TERMINOLOGY OF ATC. THE CALL FROM TWR TO 'IDENT IF YOU CAN HEAR ME OR CONTACT DEP' HAD US CONFUSED AS TO WHETHER OR NOT OUR XPONDER WAS WORKING OR OUR COM RADIO WAS INOP.