ACFT COMMENCED TAXI WITHOUT MARSHALLER GUIDANCE AND HIT TUG WITH R MAIN GEAR.

Narrative

WE WERE PICKING UP AN ACFT FROM A CONTRACT MAINT FACILITY. WE ACCOMPLISHED ALL PREFLT ACTIVITIES AND CHKLISTS. WE THEN PERFORMED A 4-ENG START AND COMPLETED THE AFTER START CHKLIST. THE MECH WAS CLRED OFF THE HEADSET AND I OBTAINED TAXI CLRNC FROM GND CTL. WE SAW THE ACFT AND SEVERAL PEOPLE DEPART THE AREA OF THE ACFT. THE RAMP AREA WAS AGAIN CLRED BY THE CAPT AND MYSELF. AS WE BEGAN OUR TAXI ROLL; WITHIN A SHORT DISTANCE WE FELT A SHUDDER AND CAME TO A STOP. COM WAS REESTABLISHED WITH THE MECH AND THE ACFT WAS SHUT DOWN. THE TUG THAT WAS TO MOVE THE ELECTRICAL PWR CART HAD STALLED AND THE R MAIN GEAR TIRES HAD IMPACTED THE TUG AND PWR CART. I BELIEVE THERE WERE SEVERAL FACTORS THAT CONTRIBUTED TO THIS INCIDENT: 1) THE PWR CART WAS POSITIONED SO CLOSE TO THE ACFT FUSELAGE IT WAS NOT VISIBLE FROM THE COCKPIT. 2) THERE WERE NO MARSHALLERS PRESENT. THIS DID NOT SURPRISE US SINCE THE ACFT WAS POSITIONED IN VERY CLOSE PROX TO THE ACTIVE TXWY (APPROX 100 FT FROM THE NOSE OF THE ACFT). 3) COM BEING TERMINATED PRIOR TO ALL EQUIP; (IE; STALLED TUG/PWR CART) BEING REMOVED FROM THE VICINITY OF THE ACFT.