A BE90 IN DESCENT AT 3500 FT DECLARED AN EMERGENCY DUE TO LEFT AND RIGHT GENERATORS FAIL WITH NO WARNING INDICATION . GENERATOR RESET NO HELP. STARTED CLIMB TO GET ABOVE CLOUDS. LEFT GENERATOR RESET. LANDED AND RIGHT GENERATOR RESET.

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FLYING ALONG AT 15000 FT; NO INDICATION OF A PROBLEM. TOLD TO DESCEND TO 4500 FT. AT 5500 FT TURNED ON AUTOFEATHER. SAW GREEN INDICATORS FOR L R AUTOFEATHER. NO WARNING LIGHTS. WITHIN A FEW SECONDS THE RADAR APPEARED TO HAVE A PROBLEM. IT WAS STREAKING MUCH LIKE BAD WINDSHIELD WIPERS. THEN I NOTICED THE RADIO WAS GETTING SCRATCHY AND AT THE SAME TIME PLT'S SIDE ATTITUDE INDICATOR APPEARED TO BE GIVING FALSE INDICATIONS. IT SHOWED THE AIRPLANE TO BE DESCENDING BUT THE AIRSPEED WAS DECREASING. WITHIN A FEW MOMENTS SAW LOAD METERS AT ZERO AMPS. RESET GENERATORS WITH NO SUCCESS. SET TRANSPONDER TO 7700; TURNED AIRPLANE TO THE SOUTH; AND STARTED A CLB USING GYRO INSTRUMENTS ON COPLT SIDE. I KNEW VFR WX WAS SOUTH. CLBED TO 19000-20000 FT TO GET ON TOP OF CLOUDS. MADE SECOND ATTEMPT TO RESET RIGHT GENERATOR. GENERATOR COMES ON LINE THEN GOES OFF. TRY TO RESET LEFT GENERATOR. GENERATOR COMES ON LINE. I TURN ON ONLY THE RADIO AND TRANSPONDER. CONTACT APCH; INFORM HIM OF SITUATION. FLY UNEVENTFULLY TO DEST. AT THE RAMP I RESET THE RIGHT GENERATOR. OPS CHECKED OK. MAINT COULD FIND NO PROBS. I AM IN THE PROCESS OF SENDING THE AIRPLANE FOR FURTHER INSPECTION. AIRPLANE IS +/- ONE MONTH AND 10 HRS OUT OF AN ANNUAL. DURING THAT TIME; BOTH GENERATORS WERE REPLACED DUE TO CALENDAR TIME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THIS AIRPLANE HAD VACUUM INSTRUMENTS ON THE FIRST OFFICER PANEL AND WAS USED TO CONTROL THE AIRPLANE TO THE DIVERSION AIRPORT. ON THE GROUND WITH THE NORMAL ELECTRICAL LOAD THE RIGHT GENERATOR COULD BE RESET AND THE LEFT AND RIGHT ELECTRICAL SYSTEM OPERATED NORMALLY. THE AIRPLANE WITH A TWO MAN CREW WAS FLOWN TO A SERVICE CENTER WHERE THE ELECTRICAL SYSTEM WAS CHECKED AND NO FAULTS WERE FOUND. THE MANUFACTURER WAS ADVISED AND ASSISTED THE SERVICE CENTER TECHNICIANS AND CAME UP WITH ONLY ONE POSSIBILITY AND THAT BEING THE GENERATORS BEING OUT OF BALANCE TOLERANCE BY 10% WHICH IS A SMALL VOLTAGE. THE GENERATORS WERE BALANCED AND THE AIRPLANE HAS FLOWN 25 HOURS WITH NO ELECTRICAL PROBLEMS. THE MANUFACTURER HAD ONLY ONE OTHER SIMILAR REPORT OF LOSS OF GENERATOR POWER CAUSED BY GENERATORS BEING UNBALANCED.