International projectionist (Jan-Dec 1936)

INTERNATIONAL PROJECTIONIST February 1936 FIGURE 1 wires, only as many are used as there are prongs on the tube being tested, or one more if it has a terminal on the top, as do the 262-A, 224 and some other tubes. The plug at the end of the cable is put into an adapter having as many prongs as this same tube has. With the four-prong adapter on the plug, we place it in a socket — say, in the 49 amplifier. The tube we took out of this socket is placed in the corresponding socket in the analyzer. The four socket contacts in the amplifier make connections to the four prongs of the adapter, while the other ends of these prongs connect to four of the prongs in the plug. All the other prongs in the plug go into "blind" holes in the adapter, and the wires connected to these plugs are not used in this case. A similar condition exists at the analyzer, where the four wires go to the socket in which we have placed the tube, but these wires also go to all the other sockets, as in Fig. 2. The other wires go to some or all of the remaining sockets. At A in Fig. 1 we see the socket in the analyzer; B is the plug, and the two are connected by the cable. In this drawing there is nothing else shown, although, actually, arrangements are made to open some or all of these connecting wires; also, other wires are hooked to them for different purposes. Notice that the main idea is to provide a means of placing the tube in the analyzer and yet have it connected just as though it were still in the amplifier. Having accomplished this, we are in a position to manipulate these circuits at will, something that could not be conveniently done in the amplifier itself. Elementary Analyzer Form Figure 3 shows the circuit of a very elementary form of analyzer, which was kept as simple as possible in order that the principle of the unit would become clear. It is easy to trace these circuits. In an actual analyzer there is a maze of wiring that makes one think of a telephone switchboard. While the average analyzer that you might buy operates about the same as the one shown in Fig. 3, unless you were quite familiar with the circuits, it would serve only to confuse matters. Wires Nos. 1, 2, 3 and 4 are in the cable, the end of which, extending to the right, having been plugged into the 49 amplifier. Tracing No. 4 to the left and then down to A, the socket in which the 264 tube has been placed, it is seen that this wire connects to one of the large prongs, a filament prong, and therefore carries filament current. Following this wire in the upward direction, it leads to B, a switch which makes connections allowing voltage or current measurements. At the moment, B is in the voltage A FIGURE 3 position, so the circuit goes up to C, a polarity switch. If the meter reads in the correct direction, all is well. Should it read the wrong way, C is thrown in the other direction, and by studying this part of the diagram it can be seen that the meter will now read as it should. As far as wire No. 4 is concerned, our circuit has been completed to make a voltage reading. This is the negative filament wire, and is left just as it is for all voltage measurements. Number 3 is the positive filament wire, and makes connection to that contact in the amplifier. We follow this wire to the left and down through switch D — which we disregard for the present, as it is closed — then to A, to the other filament contact. To read the filament voltage we now have to bring this wire up to the other terminal of the meter. Following No. 3 up, it goes to one of three points of th^ switch F. The knob has been turned so that contact has been made with this point. From here connection is made to two resistances in series, with taps going to two points on switch E. These resistances are multipliers. E is in the high-voltage position. To read filament voltage we need the low range, so E is moved to the lower contact. The circuit goes through B and C (which were explained in connection with the negative filament wire) and then to the meter. So far we have made connections to a tube that had been removed from an amplifier and placed in the analyzer. Also, a meter has been connected across the two filament wires, a multiplier resistance has been connected in series with it, and a means has been provided for correcting the polarity. This has all been done in less time than was required for the explanation. Multiplier Resistances In the actual analyzer there will be four or more multiplier resistances and as many positions on E. E may be combined with G and B, or B may be combined with F and H. E, F, G and H will have more positions, and there will be more of the switches shown at D and I, or they may be combined with H. Of course, the cable also has more wires. Number 2 is the plate wire, and the method of procedure will be similar to that for measuring filament voltage. F is moved to the point connected to No. 2: E is already in the high-voltage position, but must be checked to make sure, as the meter would be ruined if the plate FIGURE 2