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800 HANDBOOK OF PROJECTION FOR
the edge of the base plate, while the positive feed shaft is parallel with the vertical alignment of the lamp. The feed shaft negative bearings, B1-B2 Fig. 304, are integral with the base plate, eliminating the support bearing brackets used on the G. E. type lamp, and the lower bearing of the positive feed shaft, B-3 Fig. 304, is fastened to the upper side of the base plate, so that it is readily removable without the necessity of knowing the lamp from the lamphouse. The new feed shaft bearing construction insures perfect alignment of the positive and negative feed shafts in their respective bearings, and considerably reduces the load on the motor.
The negative bevel pinions which were formerly used on the G. E. lamp to transmit the movement of the negative feed shaft to the negative feed screw, have been replaced with two helical gears, HT-26 Fig. 305. The new helical gears, because of their more generous size and the greater mechanical efficiency of this type of gear, will be found to have much better wearing qualities than the bevel pinions, heretofore used.
The design of the positive and negative carbon clamps had been changed. They are now so constructed that any size carbon may be used within the limits of sizes manufactured for the purpose. To illustrate : If the lamp has been operating at 75 amperes and it is desired to use 100 to 120 amperes, it is merely necessary to remove an insert from the positive carbon clamp, replacing it with a different size insert, in order to use a larger carbon. The negative carbon clamp rests in a V shaped slot and no change in this clamp is necessary when changing from a small to a larger size carbon. The negative carbon clamp, HT-29 Fig. 305, is provided with a hinged clamping block, HT-30 Fig. 305, on which pressure is applied by means of the thumb screw, HT-30 S Fig. 305. This thumb screw is easily tightened or loosened by gripping it with a pair of gas pliers and giving it a slight turn.
The negative pigtail connector which was used on the G. E. lamp to conduct the current from the negative cable clamp to the negative carbon clamp has been replaced with a number of crimped copper ribbon connectors, HT-294A Fig. 305. This change was made to eliminate the frequent trouble experienced with the pigtail connectors breaking off at a point where they enter the two lugs which fasten them to the lamp at each end. The new type of crimped ribbon connector is designed to stand up under the continuous bending action due to the up and clown movement of the negative carbon clamp.