Radio Broadcast (May 1928-Apr 1929)

274 RADIO BROADCAST NORMAL PLATE AND FILAMENT CURRENT FOR VARIOUS TUBES T Filament Current (niA) Plate Current (mA) Grid volts 45 V. 67 V. 90 V. 135 V. 157 V. 180 V. 45 V. 67 V. 90 V. 135 V. 157 V. 180 V. 200A 250 0 201 A 250 1 7 2.0 2.5 -3.0 -4.5 -9.0 112 500 4.0 5.8 7.9 -4.5 -9.0 -10.5 112A 250 Same as 112 Same as 112 171 500 11.0 16.0 18.0 20.0 -16.5 -27.0 -33.0 -40.5 171 A 250 Same as 171 Same as 171 199 60 ] 0 1 7 2.5 -1.5 -3.0 -4.5 120 125 3.2 7.0 -16.5 -22.5 12 250 1 8 2.6 -3.0 -4.5 226 1050 a.c. 3.7 6.0 3.8 -6.0 -9.0 -16.5 227 1750 a.c. 3.0 5.0 6.0 -6.0 -9.0 -13.5 210 250 V. 350 V. 425 V. 250 V. 350 V. 425 V. 1250 12.0 16.0 18.5 -18.0 -27.0 -35 0 The operating currents and voltages of the standard tubes are given in the table above as helpful data for use with the trouble shooter. The table may be clipped and pasted on one of the panels of the instrument, thus making it handy for use in checking up on tubes. tester through a hole in the back of the cabinet. A d.p.d.t. switch, Sj, is used to reverse, when necessary, the direction of current flow through the filament milliammeter, A2. The filaments of various sets are not always wired alike as to polarity; hence, when some sets are tested you will find it necessary to have the switch to the right in order to have the filament meter read; with other sets the switch will have to be thrown to the left. A small short-circuiting switch, S2, is connected across the filament milliammeter, A->, for protective purposes. The meter should be shortcircuited when tubes with a filament consumption of more than 500 milliamperes, or tubes using A. C. on the filament, are tested. The placement of the parts is shown in the photograph, and Fig. 1 gives the wiring of the instrument, which is quite simple. TROUBLE SHOOTING TO TEST a set thoroughly with the "trouble shooter," take out the first radio-frequency tube and insert in its place the tube base of the tester. Place the tube in the tester socket, turn the set on, and note the readings of filament and plate current. If possible, adjust the filament current to its normal value. If the plate current is not near normal, replace the tube with one which is known to be good, and again note the plate current reading. If the reading is the same as the previous one, the defect probably lies in that part of the set which is connected to the tube circuit; or perhaps the B or C battery voltage is not of the proper value. Each tube socket in turn should be tested until the trouble is localized. It should not take more than a few minutes to test the entire set. Below is given a list of symptoms and a guide to where the trouble can probably be found. After becoming accustomed to using the tester you will find that with very little trouble you can completely analyze a set. [. Filament current — no reading (a) filament circuit open (b) defective rheostat or ballast resistance (c) A-battery dead (d) defective tube 2. Filament current — below normal SEPTEMBER, 1928 (a) too much rheostat resistance in the circuit (b) poor contacts in filament circuit (c) A-battery voltage low 3. Filament current — above normal (a) insufficient rheostat resistance in the circuit (b) A-battery voltage high 4. Plate current — no reading (a) plate circuit open (b) transformer primary open (c) B-battery dead (d) B-battery polarity reversed (e) defective tube 5. Plate current — below normal (a) C-battery voltage high (b) B-battery voltage low (c) tube defective or needs reactivation 6. Plate current — above normal (a) grid circuit open (b) transformer secondary open (c) C-battery voltage low (d) C-battery polarity reversed (e) B-battery voltage high (f) defective tube The table on this page, giving the normal plate and filament currents and grid biases, for the standard vacuum tubes, will also prove helpful in trouble-shooting. When testing B-batteries, be sure that the tester is not connected to the set. The terminals of the B-battery are connected to the proper binding posts, and the milliampere reading noted. The reading multiplied by the factor gives the voltage. It is wise to scratch the multiplication factor on the panel. Also mark the positive binding post, so that the battery may be connected with the correct polarity each time. The "trouble shooter" is not guaranteed to be a cure-all, but when used intelligently it will save the user much time, trouble, and possibly expense. For the laboratory, and for service and repair men, this instrument will be found invaluable. Book Review What Use Broadcasting? By William G. Shepherd, included in "Mirrors of the Year." Frederick A. Stokes Co., New York, 1928. Price $4.00 IT IS fitting that the current "Mirrors of the Year," among articles on aviation, the state of the nation, Messrs. Sacco and Vanzetti, feminism (U. S.), the fevers of journalism, the progress of science, art, literature and the movies in the United States, should include a treatise on broadcasting. Mr. Shepherd's discussion is reprinted from Collier's. It is not a depressingly serious effort, and will be remembered no longer than the paper on the theatre which precedes it or the article on the girls' clothes which follows, but it fits neatly into the jazzy although quite informative pages of the Messrs. Frederick A. Stokes Company's compendium. Mr. Shepherd's principal interest is in the political and sociological aspects of broadcasting, and he begins with a story about the Republican Convention at Cleveland, in June, 1924. He says he saw there a "puzzled looking young man fooling around with various gadgets," in a glass booth. The young man turned out to be Graham McNamee, then just beginning his career as perhaps the premier political reporter of the air, although already famous as a radio announcer in other fields. Mr. Shepherd may be romancing a little, because I do not believe that anybody ever saw McNamee puzzled, and the operators would kill him if he touched the gadgets — unless, of course, he first gave them a drink or other good and valuable consideration. Mr. Shepherd goes on to tell how, in contrast to the unknown functions and future of broadcasting in 1924 politics, in 1927 President Coolidge waited ten minutes before starting his speech at a United Press banquet, because the stations of the broadcast chain were not ready to go on when he was. In a considerable number of years of active broadcasting I never saw that happen, but probably the President would wait in such a contingency, because he knows that the audience along the network far exceeds that visibly present. The same thought, no doubt, emboldens the broadcast technicians to erect a rampart of microphones before the Executive so high and wide that most of the people in the hall where he is speaking can't see his face. "What Use Broadcasting" continues with some consideration of the delicate problem of free speech on the air. "There is more freedom of the air in 1928," says Mr. Shepherd, "than there was early in the broadcasting era." This is true, and I believe, as apparently Mr. Shepherd does, that it is due to the influence of a highly intelligent and tolerant conservative, Mr. M. H. Aylesworth. I am myself in the liberal and sometimes in the radical camp, and so I may be allowed to say without suspicion of bias that, in situations where amicable adjustment is possible, I would far rather deal with a sincere and fair minded Tory than with the average jumpy and querulous liberal. For an illustration on a large scale, just look at Dwight Morrow and Mexico. In broadcasting, Mr. Shepherd cites the case of Mr. Norman Thomas speaking over wjz without any censorship, and without pulling down the pillars of society. Since then, as a matter of fact, not only a few socialists, but even several communists, have agitated the 50-kilowatt transmitters, and what happened was precisely what my kind customers may recollect I have been predicting in our "As the Broadcaster Sees It" department for the last three years — nothing. The listeners were all tuned to the other channel, enjoying a jazz band. Of course the defenders of the downtrodden do not get a fifty-fifty break on the air, or anything like it. They have no more chance of that than Mr. Hughes would have of presenting the capitalist case in Russia. But in this country they are certainly getting a better break in broadcasting than in the domestic movies, for example. Can you imagine one of the news reels portraying the handsome countenances of Messrs. Foster and Gitlow, even once? The present regime of intelligent and unfrightened conservatism in the high seats of broadcasting is about all that can be expected while the stone angel on top of the Cathedral of Saint John the Divine stands mute with his trumpet raised to his lips, not yet ready to announce the Resurrection. — Carl Dreher.