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PULSE AMP
Fig. 1. Circuitry of the Synchro-Lite.
1440-rpm motor and the intermittent movement. This Fritts described as tuned to produce a normal 57° pulldown adjustable to somewhat less than 50° for television. We have adjusted it to 52°. This produces a pulldown time of 6000 /zsec, which in turn allows a 9° phasing tolerance based on the maximum vertical blanking time of 8%.
A more drastic departure from the projector as described by Fritts is of course in the lamphouse, where an entirely different light source is used. The housing is cast aluminum with outside adjustments for the height of the flashtube and position of the reflector. The dual aspheric lens condensing system is of the slide type, readily removable for cleaning. This condensing system was specially designed to provide an even and high degree of illumination on the film aperture from the small light source of the tube. The standby projection lamp and provisions for its immediate substitution in case the lamp in operation fails, one of the features of the Fritts design, will not be found in this unit since the flashtube used, GE FT-231, fails gradually after hundreds of hours
of use and may be replaced at leisure. Two 5 J-in. diameter fans provide forced air cooling for this unit. The power chassis is vibration-insulated from the pedestal to protect the sound system against any iron core vibrations.
Circuit Analysis
Electrical arrangements of the circuit are indicated in block schematic in Fig. 1 . The circuitry there shown performs five functions: (1) triggers the flashtube in synchronism with the vertical driving pulse; (2) provides power for the flashtube; (3) controls the width of the resultant light pulse by extinguishing the flashtube after the predetermined interval of 830 ^sec; (4) protects the flashtube against damage that might otherwise result from severe noise on the pulse line or other synchronizing generator trouble; and (5) synchronizes the projector motors with the flashtube action.
There are two thyratrons in the circuit: a 2D21 which is part of the trigger; and a 5545 which extinguishes the pulse.
Trigger action begins at the upper left of Fig. 1, where the vertical driving
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April 1953 Journal of the SMPTE Vol. 60