Radio Digest (Apr 1925-Jan 1926)

April 18, 1925 RADIO DIGES T— Illustrated 17 Four Filter Eight Tube Super-Heterodyne Part VII — Testing and Trouble Shooting By Jacques Fournier V •*. s WERE is one more possibility of improving: results. The tubes should be shifted around in the sockets and it will be found that two of the tubes work better as detectors while three of the remainingsix perform better as intermediate amplifiers than do the others. Of. the other three tubes, one will be found to be a better oscillator, which leaves two for the audio frequency amplification. Practically all tubes will give fair results as audio frequency amplifiers but care should be taken first to get the best detectors, second to get the best intermediate amplifiers, third the best possible oscillator and last the audio frequency amplifier. Testing the Circuits If, after carefully checking the wiring and shifting tubes, there is no response at the loud speaker when tuning is tried, it will be necessary to test the various circuits of this receiver to determine whether there is a break either in one of the instruments or in the wiring. For this purpose, either a single dry cell or three cell C battery may be used with the head telephone receivers. One of the cord tips from the head phones should be connected to one side of the battery and a wire about two feet long should be connected to the other side of the battery. When testing, all batteries should be disconnected from the set, and the loud speaker also. Figure 20 is shown with this article, with letters identifying various points in the circuit, so that the writer can tell you where to connect the testing leads. "We will start at the input end of the receiver and check through to the output which will enable us to catch every circuit in the process. To determine whether the secondary of the antenna coupler and the two circuit jack are O. K., touch one of the leads from our testing equipment to point C, as shown in figure 20, which is the connection to the rotor plates of the midget condenser, and connect the other to point B, which is one side of the grid leak in the grid circuit of our first detector. This will also include the pick-up coil of our oscillator coupler. If there is O45V."b"9OV.0 no click, when our circuit composed of head phones and battery is completed by connecting to points B and C, either the secondary of our antenna coupler, the two circuit jack or the pick-up coil is defective. Now turn the filament rheostat clear over toward maximum and, to test the grid circuit of the oscillator tube connect one of the test leads to point D, which is the grid terminal on the oscillator socket, and the other to the minus A battery binding post. This will show whether the grid circuit is complete as far as the inductance is concerned, -but will not, of course, give any indication whether the connections to the oscillator variable condenser are complete. To test the connections through the plate coil of the oscillator coupler touch the test leads to point L, and the plus 45-volt binding post. To test the connections from plate of the first detector, through the primary of the first intermediate transformer, connect the test terminals to the P binding post of the first detector socket and the plus 45 binding post of the set. The P terminal of the first detector socket is indicated in figure 20 as point K. Testing Transformers The secondary of the first intermediate transformer can be tested by connecting using your Ali/Amax Senior which will carry you farther and more rapidly than any airplane. All'Amax Sets are mounted at the factory but not wired, saving you half the price. Wire your All'Amax in one evening and take your first tour the same night. WIN an ALL-AMAX by submitting a SLOGAN -Ask at your favorite radio store. ALL-AMAX Sets a3 they come to you : Senior (3 Tubes and Detector) $42 Junior (1 Tube and Detector) $22 The New Radio Key Book, just off the press, contains a wealth of practical information for radio listeners and experimenters. It illustrates an eight-tube set which is the sensation of the year, and shows many other approved hook-ups. Send 10 cents, coin or stamps, for your copy. ALL-AMERICAN RADIO CORPORATION E. N. Rauland, President 2640 Coyne Street Chicago All-American ©A© ©B Figure 20 the test terminals, one to point E, which is the grid post on the first intermediate amplifier tube socket, and the other to the center binding post on th'e potentiometer P. The click on each of these tests should be clear and sharp, and almost as loud as the click produced when the terminals are connected together without any apparatus in the circuit. The grid circuits of the other two intermediate amplifiers may be tested by connecting one side of the test circuit to the center tap on the potentiometer and the other side of the test circuit to points F and G, as shown in figure 20. The secondary of the last intermediate transformer and the entire grid circuit of the second detector may be tested by turning the filament switch to the "On" position, connecting one side of the test circuit to point II and the other side of the test circuit to the plus A binding post of the receiver. The plate circuit of the second detector, which will include the two circuit jack and the primary of the input push pull transformers, may be tested by connecting to point P, which is the P terminal of the second detector tube socket, and to f THESILCNT F Trie oiulnt M^ RANCE n Knows No Equal TN DEPENDABLE performA ance, quietness, economy and freedom from trouble, the France SuperCharger is in a class by itself. No sticking or sparking contacts, no bulbs to break, no acids to spill, no fumes — it is truly the ideal charger for home use. The France SuperCharger charges up to 120 volts of "B" battery IN SERIES. It also charges 2, 4, 6 or 8 volt "A" or automobile batteries at a 5 to 7 ampere rate, tapering as the battery is charged. Price of SuperCharger, $22.00 ; West of the Rockies, $23.0C; Canadian prices furnished upon request. Write today for literature and name of nearest dealer. Dealers and Jobbers: Write today for discounts and details of eur co-operation in selling this charger. The FRANCE MFG. CO. 10329 Berea Rd. Cleveland, Ohio the plus 45 binding post of the receiver. The secondary of the input transformer of the push pull system is tested by connecting one side of the test circuit to the center tap of that transformer and touching the second terminal of the test system to either point I or joint J, as shown in figure 20. Another way of testing this same circuit would be to touch the test wires to points I and J only, as between these two points one has the entire secondary. In the first method one has only half the secondary under test at one time. The primary of the output transformer is tested by connecting one side of the test system to the center tap and the other to point Q, or point R: the second method would be to touch the terminals to points Q and R only. The secondary of the output transformer is tested for continuity by touching the test terminals to the frame and the spring of the open (Continued on page 20) SOMETHING WORTH KNOWING! One reason that leading builders of fine sets use more Thordarsons than all competitive transformers combined is because EVERY Thordarson amplifies evenly over the entire musical scale. Thordarsons run absolutely uniform; always "match up" perfectly. And why shouldn't they? 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