Richardson's handbook of projection (1930)

1378 HANDBOOK OF PROJECTION FOR of amplification, and that is far too little. Most of the amplification is on the system occurring in the 41. In cutting out an amplifier there also is the problem of impedances at the input and the output of the devices. The difference of the impedance of the output of the fader and the input to the 42 is so great that almost no signal could be transferred from one to the other. The results would be very similar were an attempt made to cut out the 42 amplifier. The output impedance of the 41 being about 15,000 to 20,000 ohms and the input impedance to the 200A panel about 500 ohms. Again, only a very small portion of the signal would be transferred from one to the other. From what has been said it will be seen that the only amplifier that may be cut out with fairly satisfactory results, as the equipment now is made, is the 43A. In the output panel it frequently happens that one of the switch arms is left touching two of the contact studs. This may by some be considered as unimportant. However, it certainly does injure the quality of reproduction, hence it should be carefully guarded against. There are several places on this panel where a ground can occur, and such ground will usually kill all sound, though an open in most of these places will only kill the sound in one horn. An open in the autotrans former, or between this point and the output of the last stage will cause all sound to stop. The separate circuits involved may be tested at the panel in the rear, using a phone. A short in any of the speech circuits going to the horns will kill everything. The circuit at fault may be located by testing the individual horns, one at a time. All horns