. The Bell System technical journal . MASTER POSITION AUXILIARY POSITION Fig. 8. The cell and amplifier are enclosed in a heavy metal box or shieldwhich is made fast to the frame of the projector and the projectoritself is carefully grounded. This amplifier is shown in Fig. 5. It isdesigned to bring the level of the electric counterpart of the film sound A SOUND PROJECTOR SYSTEM 203 record up substantially to the same energy value as that obtained fromthe magnet coils of the disc reproducer. The filaments are heatedfrom a 12-volt storage battery. Small dry batteries supply its plate THEATRE HO
. The Bell System technical journal . MASTER POSITION AUXILIARY POSITION Fig. 8. The cell and amplifier are enclosed in a heavy metal box or shieldwhich is made fast to the frame of the projector and the projectoritself is carefully grounded. This amplifier is shown in Fig. 5. It isdesigned to bring the level of the electric counterpart of the film sound A SOUND PROJECTOR SYSTEM 203 record up substantially to the same energy value as that obtained fromthe magnet coils of the disc reproducer. The filaments are heatedfrom a 12-volt storage battery. Small dry batteries supply its plate THEATRE HORNCONTROLS THEATRE HORN KEYS OUTPUT CONTROLPANEL PLATE CURRENT METER-GAIN CONTROL SWITCH-; 41 -A AMPLIFIER* WESTERN ELECTRIC205 TYPE VACUUM -~TUBES (AMPLIFIER) 42-A AMPLIFIER-*- PLATE CURRENT METER-^ WESTERN ELECTRI211 TYPE VACUUMTUBES CAMPLIFIER) 43-A AMPLIFIER. MONITOR HORNCONTROL monitor, horn key-input key ^filament currentmeter -filament control _plate currentpush buttons -filament key western electric~~239 type vacuumtubescunder cover western electric205 type vacuumtubes (rectifier ) starting switch plate current METER WESTERN ELECTRIC211 TYPE VACUUMTUBES (RECTIFIER) STARTING SWITCH Fig. 9—Amplifier Panel. current and also the polarizing potential for the photo cell. Thesebatteries and the battery leads are shielded. Vibration of a vacuum tube often produces sufficient motion of itselements with respect to each other to effect changes in the stream 204 BELL SYSTEM TECHNICAL JOURNAL of electrons which appear when sufficiently amplified as noise from aloud speaker. In spite of all precautions there is a certain amount ofvibration of the projector when in operation and it has therefore beennecessary to design a rather elaborate shock-proof mounting for thephoto cell amplifier. It is evident from the relative location of apparatus as shown
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
