International projectionist (Oct 1931-Sept 1933)

INTERNATIONAL PROJECTIONIST June 1932 305 Filter Condensers AMfTiJ Vim 250 f 250 Bleeder Resistance Filter Condensers __/VvVVVV\_ FILTER RECTIFIER uUmmflMfiJ looooooppJ FIGURE 1 FIGURE 4 Fig. 1 shows the wiring of part of a W. E. amplifier; Fig. 4 shows the wiring of the corresponding parts of an RCA amplifier. Since there are but slight differences between those two equipments, the trouble testing and remedial m.easurei are the same for both. The only difference in the rectifier is the positive lead: In Fig. 1 it is connected to the central tap of the filament transformer ; in Fig. 4 it is connected to one end of the winding. Fig. 1 has a choke in the positive leg; in Fig. 4 this choke is in the negative leg. RCA outfits have a bleeder resistance across the output of the B supply. In the amplifier proper, W. E. has another choke and a meter in the plate circuit. scribed in the above paragraph, it is nearly positive proof that a filter condenser is punctured; no time need be wasted looking for trouble elsewhere. We must determine which is the defective condenser. Condenser Arrangement Figure 3 shows the arrangement of the condensers in the 43-A amplifier, and also shows the wires connecting them to the choke, LI in Figure 1. Wire No. 1 corresponds to the wire marked No. 1 in Figure 1. Wire No. 2 is also the same in both drawings. The negative wire. No. 3 in Figure 1, has not been included in Figure 3. To locate the faulty condenser, break wire No. 1 where it is soldered to the first condenser, thereby cutting out all 9 condensers connected in the circuit at this point. Wire No. 2 could have been unsoldered just as well. This would have cut out the 9 condensers to the right. After the wire has been disconnectid, bend it so that it does not touch anything, then turn on the amplifier to see if the trouble has been cleared. Assuming that the meter now shows normal plate current we know that the shorted condenser is in this group. Turn off the amplifier again and break wire No. 3 at Y. Reconnect wire No. 1 and try the set again. If everjrthing is normal, it shows that one of the condensers marked X is shorted, since these four were cut out when No. 3 wire was broken. Leave them out of the circuit and start the show. After the performance a little further testing will show just which condenser is shorted; and it should then be replaced by another and the wiring re-connected as it was in the first place. Should the trouble still exist after No. 3 wire has been opened, then open wire No. 4, also at point Y, leaving No. 3 disconnected. Turn on the set. Supposing that this cleared the trouble, we know that one of the three condensers in the center row is bad. Solder the loose ends of Nos. 3 and 4 together, but do not solder them to the condenser. This Left: Figure 2 Right: Figure 3 leaves the three center condensers out of the circuit but again puts the condensers marked X back in. Start the show and replace the bad condenser immediately after the show. If the trouble had still been present v/ith wires 3 and 4 disconnected, it would have indicated that one of the two top condensers was bad. Leave No. 4 wire loose, reconnect No. 3 at Y and also bring No. 1 over and connect it at Y. You may have to splice a wire onto the No. 1 wire to make it reach point Y. The procedure outlined above will locate the trouble and get the show going again in the shortest time possible. It can be done in as short a period of time as it would take to disconnect the 43-A and to connect the output of the 42-A to the 200-A panel. Should it happen that the "short" is still present after removing No. 1 wire ai; the start of the test, the trouble is in the group at the right. Reconnect wire No. 1 and then disconnect No. 5 at Z. Ill is not necessary to break lead No. 2, since we already are quite certain that the trouble is in this group. Now continue the test in a manner similar to that outlined for the group of condensers at the left. In the event that the trouble still exists after wires No. 1 and No. 2 have both been disconnected, it shows that the plus wire in Figure 1 or some of the parts connected to it are grounded. In the case of a system having three or more banks of filter condensers, they must all be disconnected before it can be decided that some other portion of the equipment is grounded. If your amplifier is of a different type, it would be a good idea to look over the wiring to see what the most rapid method of repair would be. The wires could be marked with small price tags numbered 1, 2, 3, etc. The numbers would show the order in which the various wires should be disconnected in testing. In Figure 3 the group to the left would be numbered 1, 2, 3. The group to the right would also be numbered 1, 2, 3. If there were a third bank of condensers, they would also be numbered starting at 1 and continuing. Of course, the numbering would be carried on beyond 3 if the wiring were such that more than three of them had to be removed to locate the faulty condenser. #1 ^ RECTiriER FILTER AITPLIFIER