202 



BELL SYSTEM TECHNICAL JOURNAL 



may be appreciable in comparison with the sound currents themselves; 

 (2) also the shunting effect of capacity between the electrical con- 

 ductors becomes noticeable, particularly at the higher frequencies. 



EXCITING LAMP 



PHOTOELECTRIC CELL 



FILM 



PICK-UP 



AMPLIFIER 



O 



MACHINE 1 1 



PROJECTION ROOM 



REPRODUCER 

 TURNTABLE 



SWITCHING PANEL 



yc 



DOUBLE 

 TURNTABLE 



41-A 

 AMPLIFIER 



42-A 

 AMPLIFIER 



o 



O 



MACHINE +2 



[r=r 



THEATRE 



TO 

 OTHER 

 UPPER 

 HORN |_r 



HORN 



CUTOUT 



BOX 



Fig. 7 — General layout of equipment. 



Hence a vacuum tube amplifier, which serves both to increase the 

 energy and to make that energy available across a low impedance 

 circuit, is closely associated with the cell upon the projector itself. 



MASTER POSITION 



AUXILIARY POSITION 



Fig. 8. 



The cell and amplifier are enclosed in a heavy metal box or shield 

 which is made fast to the frame of the projector and the projector 

 itself is carefully grounded. This amplifier is shown in Fig. 5. It is 

 designed to bring the level of the electric counterpart of the film sound 



