F. H. Richardson's bluebook of projection (1935)

660 RICHARDSON'S BLUEBOOK OF PROJECTION wire to a terminal post, and then soldering the splice, but this practice is dangerous in hands that are not thoroughly skilled. The novice at sound soldering should tin both terminals and solder them together, providing no physical bond except the solder itself. After the joint has cooled, tug hard at one of the wires. If the joint was properly made it will not yield. But this valuable test is useless if there is a physical splice aside from the solder. That is why such splices should never be used by the novice. Testing Sound Parts There are two reasons why sound parts are tested in the projection room. One is that such tests may be a necessary step in trouble-shooting. The other is equally important; no part should ever be stocked as a spare for use in emergency until tests have shown that it can be relied upon when needed. Testing Resistors (30) Resistors are tested by use of an ammeter, a voltmeter, and application of Ohm's law. Such tests, however, check only the continuity and resistance of the part, not its current-carrying capacity. The latter factor cannot readily be checked in the projection room. Testing Inductances (31) The inductance of coils is not usually measured in the projection room. They may be checked for shortcircuit with a. c. and an a. c. milliammeter. Inductance coils* show high impedance to a. c, which will be diminished or altogether absent if the coil is short-circuited internally. They are checked for open circuit with d. c. and a d. c. milliammeter, since direct current should pass through them with little loss unless the wire is broken inside. Testing Transformers (32) For projection room testing purposes the trans *Never test a speech choke coil with more current than it is intended to carry in actual use.