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April, 1952
CLARKE: MAGNETIC RECORDING
111
feet and embodies a footage counter operative in either direction of film travel, suitable film backing up and fast rewind facilities. There are two recording drums, each having a magnetic head closely adjacent and the unit uses off-drum scanning. The complete channel weighs some 300 pounds.
Fig. 5. PM.63 three track magnetic recording equipment, threaded to record or playback without erasing.
A Smaller Unit
The PM.64 (Fig. 4) is a much smaller version which is finding great favour in Hollywood. Where minimum weight is desirable it is very satisfactory. Again the recorder uses perforated film in either the 35 mm. or 17 J mm. gauges. It includes two recording drums, off-drum scanning, forward and re
verse counters and fast rewind and film back up facilities. The channel is made up of three cases — the mixer amplifier weighing some 28 pounds, the amplifier power supply unit weighing some 30 pounds, and the recorder complete weighing some 65 pounds. The film capacity is 500 feet with the transparent front door closed and 1,000 feet with the door removed. To use the larger reels the film centre spindles are pushed outwards and upwards to allow the spools to clear the film path assemblies. The bias amplifier and the pre-amplifier in this model are both mounted in the recorder itself so that the rest of the necessary amplification and power is housed in the mixer. Both these models are supplied as standard for two microphone mixing.
Triple Track Recording and Reproducing Assembly
The next equipment we shall make available here is a Triple Track recording and reproducing assembly. This is designed for studio use and will use 35 mm. magnetic film travelling at the standard motion picture speed of 90 ft. per min. The Triple Track model is known as PM.63 (Fig. 5) and is installed on two relay racks. The motor drive will usually be dual purpose — sync/selsyn or just selsyn, as most of its work will probably be in connection with final mixing, music recording, post-synchronising, foreign versions, and the like.
On the left hand panels reading from top to bottom, are seen the feed in film spool, triple erase heads and associated controls, film drive and two triple cluster recording and reproducing assemblies and finally, the film take up reel.
On the right hand panels are the amplifier units, gain controls, patch bay and test equipment. This is the only equipment to be fitted with erasing facilities and to avoid accidental erasure three distinct paths are provided for the film. The main functions of this channel are the recording of from one to three separate sound records across the active surface of a 35 mm. film. These multiple tracks may be simultaneous — comprising say the principal tracks of a re