FLT CREW OF B732 DEVIATED FROM L30 DEP CTLR'S VECTOR WHEN THEY INTERCEPTED A RADIAL FROM LAS VICE INTO BTY AS CLEARED. A CONTRIBUTING FACTOR WAS THE SUBSTITUTION OF A NON GLASS ACFT FOR THE TRIP AND THE CONFUSION THAT ARISES AMONGST FLT CREWS WHEN SWITCHING BTWN ONE TYPE OF NAV AND THE OTHER.

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I WAS INFORMED OF A FLT ASSIGNMENT THAT WOULD HAVE ME DEADHEAD TO LAS VEGAS TO BEGIN A SERIES OF LEGS. BECAUSE OF THE NATURE OF THE ASSIGNMENT; I ARRIVED IN LAS VEGAS ONLY 25 MINS BEFORE SCHEDULED DEP TIME. I WENT TO OPS AND LEARNED THAT INSTEAD OF A 300 MODEL B737 SYS; I WOULD BE FLYING THE MORE BASIC 200 MODEL AIRPLANE. I ARRIVED AT THE AIRPLANE AND FOUND THE REST OF MY CREW ALREADY THERE. THE AIRPLANE HAD BEEN SITTING ON THE RAMP IN LAS VEGAS FOR QUITE SOME TIME AND WAS UNBEARABLY HOT INSIDE. OUTSIDE AIR TEMP WAS 109 DEGS F AND THE INTERIOR CABIN WAS AT LEAST THAT HOT. THE FLT ATTENDANTS WERE UNDERSTANDABLY RELUCTANT TO BOARD THE AIRPLANE; BUT WITH THE PACK RUNNING; WE MANAGED TO GET SOME AIR CIRCULATING IN THE AIRPLANE. SINCE THE EXPERIENCE OF GETTING TO THE AIRPLANE HAD BEEN SO HECTIC; I ASKED THE FO IF HE WOULD MIND FLYING THE FIRST LEG TO SFO. WE WERE CLRED BY ATL TO SFO; VIA THE MCCARRAN 1 VECTOR DEP; WITH THE BEATTY TRANSITION. OUR NAV RADIOS WERE SET TO THE LAS VEGAS VOR; SINCE OUR ENG FAILURE AFTER 'V.' PROC WAS PREDICATED ON THAT VOR. IN THE VOR STANDBY MODE THE FO HAD SET THE BEATTY VOR AND HE HAD SET THE CDI'S ON BOTH OUR HSI'S TO TRACK THE BEATTY 129 DEG RADIAL. WHEN WE DEPARTED THE GATE; WE DISCUSSED THE PROPER CONFIGN FOR A BLEEDS OFF TKOF NECESSITATED BY THE HOT CONDITIONS ON THE FIELD. EVENTUALLY; WE MADE AN UNEVENTFUL DEP FROM RWY 7L. BOTH OF US WERE DRENCHED IN SWEAT AND QUITE UNCOMFORTABLE AS WE CLBED IN THE VERY CHOPPY SUMMERTIME AIR. THE LAS VEGAS DEP CTLR EVENTUALLY TURNED US ON A 250 DEG HDG TO JOIN THE BEATTY 129 DEG RADIAL. WHEN WE WERE ISSUED THE INSTRUCTIONS; NEITHER ONE OF US NOTICED THAT WE HAD OUR RADIOS STILL TUNED TO THE LAS VOR AND NOT THE BEATTY VOR. THE RADIAL CAME ALIVE QUICKLY AND THE FO TURNED THE AIRPLANE TO JOIN IT. VERY SHORTLY; THE CTLR CALLED TO CONFIRM WE WERE ESTABLISHED ON THE 250 DEG HDG; AND I REPLIED WE WERE JOINING THE RADIAL. THE CTLR ISSUED A NEW VECTOR TO 230 DEGS AND POINTED OUT WE HAD JOINED THE LAS 129 DEG RADIAL! BOTH THE FO AND I FELT STUPID ABOUT OUR ERROR; BUT I THINK OUR PREOCCUPATION WITH ALL THE FACTORS WE'D EXPERIENCED BEFORE TKOF; PLUS OUR DISCOMFORT IN THE HOT CABIN CONTRIBUTED TO OUR OVERSIGHT; IN SWITCHING RADIOS AND THE SUBSEQUENT NAV ERROR THAT RESULTED. I REALIZE WHEN CONFRONTED BY SIMILAR CIRCUMSTANCES IN THE FUTURE; I MUST BE EXTRA VIGILANT.