B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 162
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
We were just leveling at FL 380 when the 'A' autopilot disengaged and we noticed we had lost the Number One Engine Generator. The First Officer had noticed the #1 Drive light illuminated; accompanied by the #1 Source Off light. I was the pilot flying and maintained aircraft control. I then engaged the 'B' autopilot and re-engaged the autothrottle. We then ran the Drive Light and Source Off Light Checklists per the QRH. Since the APU had been deferred we decided to return to our departure airport; due to having only one electrical power source remaining.  We coordinated our return with ATC; then notified Dispatch; the flight attendants; and our customers of the situation. We also ran the Diversion Checklist. The weather remained VMC throughout the flight. We flew an uneventful approach and landing. We were not overweight upon landing; and Maintenance personnel met us at the gate. We did not declare an emergency.
The weather remained VMC throughout the flight.
Dispatched with an inoperative APU the flight crew of a B737NG was forced to return to their departure airport when the left generator drive and source off lights illuminated thus rendering them with only a single AC electrical source.