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This is another document unearthed by our friend, the late Frank Dubiel. I'm just providing an excerpt here. This is the original RCA theatre wiring diagram for a four track magnetic CinemaScope stereophonic sound system, also taken from the Dufree Theatre. Page 4 of the manual, describing the system, is shown here. The full document can be made available upon request.

View The Diagram

Page 4 of 10

Type PG-301 and 301A


General Description

These systems have been designed to reproduce sound from a four channel magnetic track motion picture film of the "CinemaScope Type".

The sound from the four magnetic tracks is fed through a four channel amplifier system which feeds the three sets of stage speakers and the sound effects speakers around the auditorium.

Through the use of a switching control system (MI-9716) the following combinations of film reproduction are available.

(1) With switches in "Magnetic" and "Single film system" position, the four tracks of a CinemaScope Type film will be connected to the stage and effects speakers.

(2) With switches in "Magnetic" and "multiple film system" position, the magnetic tracks of multiple films of the 3-D variety wil1 be connected to the stage speakers, the optical track will feed the effects speakers.

(3) Switches in "Optical" and "Single film system" position will place the sound from the standard optical sound track on the center stage speaker amplifier and all other amplifiers will be loaded with a 250 ohm resistor.

(4) With the switches in "Optical" and "Multiple film system" position, 3-D sound on the center stage speakers may be reproduced under emergency conditions.

Four Track Magnetic Soundhead

The MI-9010 (29500) four track magnetic soundhead provides the electrical and mechanical facilities to reproduce CinemaScope type composite prints having the sound recorded on four separate magnetic strips applied to the base side of the picture print.

Since both picture and sound are on the same film, there is no problem of synchronization between the two. The soundhead mounts directly on the top of the RCA (Brenkert) Projector without the use of adaptors. Detailed information on the installation is covered in a separate service note.


The output of the four track soundhead is fed to a four channel pre-amplifier through four special shielded cables (MI-9015/A).

The pre-amplifiers consist of two separate units for each channel. Four MI-9268 amplifiers, which are compensated electrically for optimum reproduction from a magnetic track, are mounted in the volume control (MI-9745) unit, and four MI-9362 amplifiers are mounted in the rack. The output level of each channel can be adjusted so that all channels will operate at the same relative level. Overall volume of all channels is controlled by the ganged volume control (MI-9745) mounted on the front wall.

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