Radio Broadcast (Nov 1926-Apr 1927)

304 RADIO BROADCAST ADVERTISER I ASK . . ANY . . RADIO . . ENGINEER The Crowning Adventure o/"Burgess Radio Batteries They Flew Over the North Pole <with Byrd 0N May 9, history was made . . . American history . . . World history . . . undying history. Lieut. Commander Byrd, in his fearless 1500'mile flight across the top of the world, adds another thrilling triumph to the long, proud list of American achievements. Radio went along, for radio has become vital to the lives and success of explorers and adveiv turers. Burgess Batteries went along, sharing the fate — sharing the hardships and the glory of Commander Byrd, the Detroit Arctic Expedition, and Capt. Donald MacMillan. It is eminently significant that in these glorious triumphs of American courage and American equipment where the test of men and their tools was the test of the survival of the fittest, that the standard products of the Burgess Battery Company were selected, used and "carried on" under extreme and unprecedented conditions. Burgess Battery Company General Sales Offices: Chicago Canadian Factories and Offices: Niagara Falls and Winnipeg BURGESS RADIO BATTERIES Now, I Have Found 9 A Department for the Exchange of Ideas and Suggestions of Value to the Radio Constructor and Operator eONTRI BUTIONS to this department are welcome and those used will be paid for at the usual rates, that is, from two to ten dollars each. Manuscripts intended for this department should not exceed about three hundred words in length, and should be typewritten. Little consideration can be given to manuscripts not typewritten. Envelopes should be addressed to this department, Radio Broadcast, Garden City, New York. Filter System for Cone Speaker I HAVE been reading with much interest, the various ways of revamping Western Electric cone speakers. I have seen several articles in Radio Broadcast and quite a number of methods have been described in other magazines, but none have worked satisfactorily for me. The Western Electric cone and RCA cone are somewhat alike, being made under the same patents and having the same mechanism. 1 borrowed an RCA impedance transformer, such as is used in a model 100 loud speaker, and put it in a Western Electric cone, and the results were wonderful. The way to build this transformer is very simple and cheap. Make an iron core with haywire, the size of a lead pencil, and cut the core 2§ inches long. Wind on this core a coil J inches in diameter, using No. 30 silk enameled wire. Connect this coil in series with the speaker and put a Dubilier condenser, capacity 0.0 1 mfd., across the speaker terminals, and one condenser of the same capacity or not. A shorted condenser will give no spark after the potential has been removed. A defective condenser may sometimes be repaired by connecting the terminals to a storage battery and allowing enough current to flow so that the short is burned out. , K. Blaine, Brooklyn, New York. s to To Receiver Iron Core% across the input the speaker. The diagram Fig. 1, shows clearly the method of wiring. This device, I have found, will match a Western Electric cone speaker perfectly, with an ux-120 tube, and give very good results with other tubes. The device is used by the Radio Corporation in all Model 100 speakers, and if properly made, will reproduce low and high notes perfectly with plenty of volume. W. C. Grasel, St. Louis, Missouri. Testing Fixed Condensers THE testing of small fixed condensers can best be accomplished by connecting an ordinary six-volt battery across them. If there is a "short" in the condenser, a good spark will be obtained whenever the connections are completed to the two terminals of the battery. The use of ear phones in series with a small battery for testing by the clicks heard is more or less deceptive unless the operator is thoroughly familiar with this type of testing. There is a distinct click, due to the discharge of the condenser, when there is no short present, which may easily be taken to indicate a short. In testing the larger sized fixed condensers, from 0.5 microfarad up, the best method for testing is to apply about 90 volts to the terminals. Then take the connections off and short the terminals with a screw driver or short piece of wire. A good strong spark indicates that the condenser is O. K. If the charge leaks off very rapidly after the battery voltage is removed, it indicates that there is a leak present whether it shows up ■ 0.01 Mfd. To Cone FIG. I Plate Current Burns Out Tubes EVERAL users of Browning-Drake receivers have reported that they are unable to make the 199 tube in the radio frequency stage last more than a few days before burning out. In a test run on one of them, the writer found that four tubes lasted a total of nine days, although a careful check-up showed that the tube was getting proper filament voltage and that there was no leakage through the neutralizing condenser. The trouble was found to lie not in the set, but in the diagram from which it was wired. This particular blue print (and a survey shows that many like it are in circulation) has the r.f. tube working on the same B voltage as the first audio tubes, which usually is 90 volts, or even more. Since the 199 is not biased with C battery, it is, therefore, being seriously overloaded. Inspection of the burned-out tubes showed that in every case the filament parted right at its base. It then became apparent that the plate current, which is added to the filament current on the side of the filament to which the B negative is connected, overloaded the filament and caused the trouble. The addition of, say, 12 milliamperes to the filament circuit of a large tube, makes little difference. In the case of the 199, with a normal filament current of 60 milliamperes, it represents a 20 per cent, overload. That this diagnosis is correct is attested by operation of the set in question for several months without trouble after the voltage on the radio frequency tube was lowered. In existing sets, to save adding binding posts, it is advisable to connect the r.f. tube plate circuit to the detector B tap and then run this, feeding both detector and r.f. tube, at 40 to 50 volts. No drop in volume is experienced, changes are easily made, and neutralization is simple. R. P. Worden, Cleveland, Ohio. Getting the Most from Your Milliammeter A Dl RECT-current milliammeter is a very desirable instrument to have about the home laboratory. It may be used for checking resistance units, testing tubes, adjusting the grid bias of an amplifier, testing battery elim •jr Examined and approved by Radio Broadcast -ir