International projectionist (Jan-Dec 1935)

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July 1935 INTERNATIONAL PROJECTIONIST 15 contact, but "look into" a full half of the fader regardless of the variable setting. The total impedance in ohms is: 146.5 18.5 101. 13.5 72.7 15.8 53.4 7.95 35.5 5.9 25.9 2. TOTAL: 498.65 Ohms In Figure 1 the fader is set at zero — that is, the long double arrowhead connects Zero Contact with the disc at the center of the potentiometer drawing. In the physical apparatus the control knob rotates a short brass bar with flexible pressure contacts at each end. One of these end contacts moves from point to point of the potentiometer contact studs 1 to 12, as the knob is rotated. The other end contact moves around a brass ring, but maintains unvarying pressure upon it. This bar with its two flexible pressure contacts is represented in the drawing by the slanting line with two arrowheads, one of which rests at Zero Point and the other upon the central disc, or brass ring. The D-86637 potentiometer is provided with four terminal studs, drawn in a horizontal line at its top center. The right-hand terminal runs directly to the upper end of the right-hand side of the fader. The second terminal from the right is wired down, right, down, left and down to the central point of the fader, and is common to both sides. The extreme left-hand terminal goes to the upper end of the left-hand side of the fader. The second terminal from the left is wired to the central brass ring, and therefore to the variable contact arm. There are two input circuits to the fader, one to each half. No. 1 inputs, whether film or disc, are run to the righthand half, that is, across the right-hand fader input terminal and the second terminal from the right. No. 2 inputs, whether film or disc, are connected to the second fader terminal from the right and the extreme left-hand terminal stud. The fader output also runs through the second terminal from the right and, therefore, from Fader Zero. The red-green wire may be traced from that terminal directly left to one of the two Output Terminals. This is grounded, therefore Fader Zero Point is grounded. And since one side of all the input lines to this fader run to Fader Point Zero, one side of all the input circuits must likewise be grounded through this same connection. The second fader terminal from the left, which internally connects to the brass ring and thence to the variable contact, may be traced externally to the other output binding post as follows: up and left along the red wire, down, left to and through the 100-ohm I-L resistor, and thence left, up and right to the lower of the two output terminals. The addition of the I-L resistor converts the circuit into an "L" pad, the purpose of which is to improve the impedance match between the fader output and the input of the system amplifier, as will be seen. Change in Code Seal Set For August 1 Beginning August 1 the seal of approval of the Production Code Administration, which now appears at the start of all feature picture releases, will appear in the same manner as is now employed on short subjects. At present the feature release seal is carried on a separate frame preceding the title frame. Under the new policy it will appear as part of an introductory frame, the proportionate size of the seal and code number to be uniform at all times. Many projectionists will welcome this change, inasmuch as the code seal often has not appeared at all on the screen, many projectionists, especially in de luxe theatres, considering the seal as a "cold" opening. Producers and distributors, hearing of this skipping practice, raised vigorous complaints because of the danger of running counter to the wishes of the morality groups, whose demands were responsible for the seal in the first instance. That portion of the potentiometer windings which may be included at any moment between the variable contact and Zero Point, plus the 100-ohm I-L resistor in series, constitutes the output impedane of Figure 1 — in other words, the impedance that "looks into" the 200-ohm amplifier input impedance. This potentiometer, unlike the 702-B Cabinet analyzed elsewhere in this issue, is not equipped with supplementary resistors in series with its contact studs. It is a simple potentiometer and not a T-pad, consequently its output impedances are not as precisely matched as in the case of the other fader. The 100-ohm resistor in series with the line helps, however, by converting the overall circuit of Figure 1 into an L pad, and thus secures a better output impedance characteristic. For example, assuming the fader to be set at Point No. 2, 102 ohms "look out" into the system amplifier's 200 ohms. If the I-L resistor were not included, only 2 ohms would look into 200 ohms and the mismatch would be decidedly serious. With the variable fader contact at its maximum setting (Point No. 12) the full 498.65 ohms of the potentiometer winding, plus the 100 ohms of the I-L resistor, or 598.65 ohms in all, "look into" the system amplifier. However, such moderately large mismatches occur only at the highest fader settings, where the resultant loss of volume can be tolerated and any distortion is less noticeable. At all middle settings the output impedance is, because of the 100-ohm output resistor, relatively accurate. But the figures involved, when compared with those of the 702-B Cabinet diagrammed elsewhere in this issue, illustrate very distinctly the advantage of T-pad arrangements whenever volume controls are used in low-impedance transmission lines. The output impedances of Figure 1, at the middle fader settings, which are those most often used, are shown in the following table: Fader Output Setting Impedance Impedance (plus 100J 9 178.45 278.45 ohms 8 125.05 225.05 ohms 7 89.55 189.55 ohms 6 63.65 163.65 ohms 5 45.15 145.15 ohms Any of the above will give substantially satisfactory impedance match to a 200ohm amplifier input. Consequently, wherever the fader-switching panel of Figure 1 is installed, the amplifier gain control should be pre-set to keep the fader position, under all normal circumstances, roughly within the range given just above. Australian Projectionists Seek Better Conditions PROJECTIONISTS have their troubles with exhibitors the world over, according to advices reaching I. P. from Australia. Work conditions in Australia and New Zealand are reported on by the film publication Everyones as follows: Elevation of the pay of assistant-operators in continuous shows throughout Australia to the basic wage will be the subject of a Federal court application unless conferences between Union representatives and employers result in an amicable arrangement. Assistant operators claimed working hours were excessive and the rate of pay out of all proportion. Ventilation of bioboxes was bad, they claimed, due to lack of supervision by health officials. Another allegation was that unlicensed operators were employed on country circuits ; so it was proposed that police be appointed as inspectors in such places, with authority to prosecute for breaches. In making assistant operators in continuous houses the special subject of an industrial application, the Union's case is that nine-tenths of them are adults, and the majority married. Yet they must exist on £2/15/ (approx. $13) a week. The executive asks that this be lifted to the basic wage at least. It is more than probable that the parties will confer with a view to a settlement without the aid of the court being evoked. The move affects assistant operators in continuous shows throughout the whole of Australia. That conditions are no better in New Zealand is indicated by the appended dispatch from there: Operators are moving for a Dominion award and the licensing of operators in New Zealand. For some time discontent has existed among them. So serious has the position become that they are taking steps to protect themselves against unfair treatment by certain proprietors and managers. In many theatres they are compelled to work excessive hours in a vitiated atmosphere without adequate time off for meals, and for wages barely sufficient to support a single man, far less a married man with a family.