Means for selectively suppressing test voltages in motor component test equipment

Claim 1

IN APPARATUS FOR TESTING COMMUTATOR-TYPE ARMATURES IN A JIG HAVING A FIRST PAIR OF BRUSHES FOR APPLYING ALTERNATING CURRENT TEST VOLTAGES OF OPPOSITE POLARITY AT DIAMETRICALLY OPPOSITE LOCATIONS ON THE COMMUTATOR OF THE ARMATURE UNDER TEST, HAVING A SECOND PAIR OF BRUSHES EACH ADAPTED AT INTERVALS DURING THE ROTATION OF THE ARMATURE TO ENGAGE ONE OF TWO NEIGHBORING SEGMENTS OF SAID ARMATURE FOR COMPLETING A TEST CIRCUIT BETWEEN SAID SEGMENT AND ONE OF SAID FIRST PAIR OF BRUSHES, THE SAID ALTERNATING CURRENT VOLTAGES BEING PRODUCED BY AN ELECTRONIC POWER SYSTEM EMPLOYING A DRIVER TUBE HAVING A SCREEN GRID, INSTRUMENTALITIES FOR SUPPRESSING SAID TEST VOLTAGES DURING PREDETERMINED PORTIONS OF THE CYCLE OF ROTATION OF THE AMATURE UNDER TEST, SAID INSTRUMENTALITIES INCLUDING: A STEP-UP TRANSFORMER HAVING (A) A SECONDARY AND (B) A PRIMARY WHOSE TERMINALS ARE EACH CONNECTED TO A DIFFERENT ONE OF SAID SECOND PAIR OF BRUSHES; A TRIODE; A FULL-WAVE RECTIFIER INTERPOSED BETWEEN SAID SECONDARY AND THE GRID OF SAID TRIODE TO GIVE SAID GRID A NEGATIVE CHARGE, THE CATHODE OF SAID TRIODE BEING CONNECTED TO THE SCREEN GRID OF SAID DRIVER TUBE WHEREBY SAID DRIVER IS SO SCREEN-MODULATED THAT SAID TEST VOLTAGES WILL DROP WHEN THERE IS A DECREASE IN THE VOLTAGE APPLIED TO THE GRID OF SAID TRIODE BY SAID SECONDARY.