Movie Makers (Jan-Dec 1953)

128 A new approach to an old problem . . . TRY SYNCHRO-TACH HERBERT H. REECH, ACL for controlled speeds in tape recording ONCE . . ." the man says glibly! "Once the synchronization problem is licked, tape (he believes) offers several advantages over magnetic stripe." (See Making the Most of Tape, January 1953— Ed.) This well may be so. I'm a tape man myself, and I am not disposed to argue in favor of a system which I do not yet use. But not so fast there, Brother ! Let's lick the synchro problem first. I am well aware that there have been outlined in this magazine a number of interesting and often ingenious systems for synchronizing one's tape recorder with one's projector — or vice versa. But it has seemed to me in each instance that too much confidence has been placed in the stroboscopic principle — regardless of whether that principle has been bodied forth in the familiar strobe disc or in the more recent Revere Synchro-Tape pattern. In either case, the strobe system does indeed tell you when the projector is running at the correct speed. But when that speed is incorrect, FIG. 1: Simplest use of tachometer to pace projector mounts it in place of turning knob. the strobe pattern does not indicate by how much it is fast or slow. This small but important problem I have solved recently by creating a system which I have designated "SynchroTach." Heart of Synchro-Tach's control mechanism is an ingenious and inexpensive gadget called a hand tachometer. It is precision-made by the StewartWarner Company (Chicago), reads clockwise or counterclockwise in units of 100 up to 4000 rpm, and sells for $10.45 at list. Common retail outlets should be all W. W. Grainger warehouses, the Wellworth Trading Company and most of the bigger tool and hardware stores. Fig. 1 shows this unit in use in a simple setup which requires the minimum amount of time for construction. The tachometer is held by an aircraft hose clamp which I happened to have lying around, and is then attached to an angle-shaped strip of aluminum. This assembly is then mounted on an old metal base with a dime-store corner FiG. 2: In de luxe version, tachometer is housed in cabinet, sports a pilot light and rheostat control. brace. A radio parts store supplied the )3-inch-long flexible shaft and a % by %. (inch brass coupling. The free end of 'this shaft is drilled, tapped and then /replaces the projector's hand-turning knob, as will be seen in Fig. 1. Very well. On the Keystone projector pictured, this hand-turning knob makes two revolutions in passing one frame of 8mm. film — or 32 revolutions per second and 1920 per minute. But to make for easier reading of the tachometer dial, let's run the projector at 2000 rpm, or only slightly faster than 16 frames per [Continued on page 137] SCHEMATIC WIRING FOR POLARIZED SOCKET AND METER CABINET LEGEND W WHITE WIRE G GREEN WIRE B BLACK WIRE PP AMPHENOL POLARIZED PLUG 3 POLE P AM PHENOL STD. AC RECEPTACLE R RHEOSTAT FIG. 4: Wiring diagram for polarized socket and cabinet installation is seen here. 'IOV. MODIFIED WIRING FOR PROJECTOR LEGEND FIG. 3: Three-pole, polarized Amphenol plug on left side of meter cabinet connects thru three-wire cable with projector. M P L S| S2 R W G B PROJECTOR MOTOR PILOT LIGHT PROJECTOR LAMP PROJECTOR SWITCH SPST 3 AMP SWITCH PROJECTOR RHEOSTAT WHITE WIRE GREEN WIRE BLACK WIRE FIG. 5: Modified wiring for adapting projector to tachometer control is diagramed herewith.