B737-800 CAPT WAS MAKING A NIGHT VISUAL APCH TO SRQ. HE DID NOT HAVE THE RWY IN SIGHT. THE NAV DISPLAY WAS ON THE WRONG SCALE. THE CAPT WAS CORRECTED BY THE FO WHEN HE GOT LOW. THE CAPT GOT TOO CLOSE TO THE ARPT; AND FORGOT TO GET LNDG CLRNC FROM THE TWR LCL CTLR. THE ATCT LCL CTLR GAVE THE CREW A 'GREEN' LIGHT FOR LNDG.

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NIGHT VISUAL APCH INTO SRQ; APCH VECTORED US INTO R DOWNWIND FOR SRQ N RWY. CAPT (ME) FLYING. TOLD TO STAY 2600 FT UNTIL S OF SRQ EW RWY -- CAPT ON 10 MI SCALE (THOUGHT I WAS ON 5 MI). COPLT CALLED TURN AND SPACED DOWNWIND SINCE I DID NOT SEE RWY; THINKING I HAD A LOT OF ALT TO LOSE SO DIRTY UP AND LNDG CHKLIST DONE AT BASE TURN. I WAS FLYING 'BLIND'; BUT WAS USING MY MAP (WRONG SCALE) AND COPLT INPUTS. COPLT INFORMED ME I WAS GETTING LOW (I WAS). THEN HE TOLD ME HE LOST THE RWY (WHICH I HAVE YET TO SEE). AT THIS TIME I REALIZED I WAS ON THE WRONG SCALE; CHANGED IT; AND REALIZED I WAS REAL TIGHT AND BY NOW; JUST A LITTLE LOW. COPLT KEPT 'VECTORING' ME UNTIL I SAW RWY. A VERY TIGHT 35 DEG ANGLE OF BANK TURN TO FINAL AND LNDG ENSUED; BUT IN THE PRESSURE OF FLYING AND NAVING; WE FORGOT TO GET LNDG CLRNC FROM TWR. I BELIEVE HE WAS WATCHING OUR 'UNUSUAL' APCH; REALIZED WE HAD NOT VERBALLY TALKED TO HIM; AND HE GAVE US A GREEN LIGHT CLRNC TO LAND. I AM GLAD SOMEONE HAD THEIR ACT TOGETHER. IN RETROSPECT; ALTHOUGH I MADE THE PARAMETERS OF A STABILIZED APCH FOR LINE-UP AT 500 FT; I REALLY SHOULD HAVE JUST GONE AROUND WHEN I REALIZED HOW TIGHT WE WERE AND PARTICULARLY WHEN I 'FINALLY' SAW THE RWY. ALSO; ON A R DOWNWIND AT AN ARPT I HAVE NEVER BEEN IN; LET COPLT FLY -- HE HAD THE VISUAL; I DON'T.