Loudspeaker (Jan-Aug 1931)

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GENERATOR TESTS by R. Van Slyker In testing for a ground, disconnect the output leads from the load. Take a 110 volt test lamp, or better still, a 110 volt voltmeter. Connect one leg or lead to the ungrounded or hot side of the current supply, and take the grounded side and fasten it to the frame of the generator. Touch the other lead of the voltmeter or lamp to each of the generator leads. If there is any deflection of the voltmeter or glow of the lamp, it is an indication of a ground. A voltmeter is more accurate in showing a partial ground, showing a feeble deflection that would pass unseen in a test lamp, due to the smaller current passing. If there is a deflection shown on the voltmeter, place pieces of paper or any other insulator under the brushes of the generator and apply test lead to the terminals. If a deflection is still apparent the next most likely cause is that the brush holders have (due to oil and carbon dust accumulating in them) shorted to the frame. Disconnect the leads to them and test the terminals again. If there is any deflection of the voltmeter the trouble is in either the field coils or the brush leads themselves. Check through to the brush leads and examine them closely to see if the insulation is chafed or cracked, thus causing a ground. If these are all right cut out the field coils by disconnecting them from each other until the faulty coil is located. In the event that raising the brushes from the commutator stops any deflection of the voltmeter, it is safe to assume that the armature is at fault. Take the test lead and place it against one of the commutator bars or segments, and rotate the armature by hand, marking the grounded bar with a grease pencil. F o r t\ Remove the armature and examine for loose binding, chafed wires, loose commutator bars or surplus solder. This routine should reveal any of the most common ills which develop in high voltage generators. Special stress should be made on the importance of making each test exactly as herein directed, making very sure that no detail is overlooked since any small item overlooked will render the test false and confuse the issue. GP. *'**■* ■» T T T T * * * '» . T T T * T T V -rig] | Season’s Greetings j f j ; H. J. RILEY H. T. CRAIG j FOX ADAMS THEATRE | LOS ANGELES. CALIFORNIA 1 ► Los Angeles, 1931 j [ j ; New Year Greetings EARL LIETER FILM ARTE THEATRE Home of Foreign Pictures LOS ANGELES, CALIFORNIA, 1931