Radio Broadcast (Nov. 1925-Apr 1926)

234 RADIO BROADCAST ADVERTISER A BRISTOL Loud Speaker will bring everlasting Christmas joy to the whole family. It has all the volume you will ever wish, but its fine point, — its outstanding claim for distinction, is its tone, a true, clear, natural reception of voice or instrumental music. This is because it is a true musical instrument not merely a phone unit in a horn. Bristol Loud Speakers have highly developed electromagnetic tone mechanisms, and non-metallic horns with long, freely vibrating sound chambers. The super S and super C models are equipped with the Super-Unit which contains a specially designed diaphragm of broad pitch range. It reproduces not only the low pitched notes but the high as well. There are four Bristol Speakers, horn or cabinet type, priced at $15.00 to $30.00. If not at your dealer's, send for our new booklet. "How to select your loud speaker." THE BRISTOL COMPANY, RadA°HDiv WATERBURY, CONN. For 5<5 Years Makers of highly accurate and sensitive Bristol Recording Instruments. BRISTOL AUDI^pNELoud Speaker R084. Tables. Charts. QST. Sept. 1925, pp. 16-17. Ind. Sr w. I. "Designing the Secondary Coil," G. H. Burchill. Using double cotton covered wire, the inductance and wavelength of cylindrical coils, closely wound, can readily be determined with the aid of the chart in the form of a graph. A simple description of coil design and method of procedure is given. R800 (535 3) Photoelectric Selenium Cells. Phenomena Radio Engineering. Sept. 1925, pp. 442-443. "Selenium and Photoelectric Cells," S. Wein. The third chapter on selenium cells gives the construction of different types of cells by various scientists: Tainter, Bell, Mercadier, Townsend, and Cherry. References are listed. R356. Transformers. Transformers. QST. Sept. 1925, pp. 21-24. "Transformers and Reactors in Radio Sets," R. H. Chadwick. 1 n the first article on transformers and reactors, the author takes up the general theory, regulation, and efficiency, and describes the construction and operating principles of various types of commercial transformers. The leakage reactance is a governing factor in proper transformer design. Useful information for users of these instruments. R342.15. Amplifier Transformer. Amplifying QST. Sept. 1925, pp. 27-29. Transformers. "High Ratio and High Amplification," R. S. Kruse. Some misunderstood principles about audio and radiofrequency transformers are cleared up by the author. Stage to stage amplification depends on the regeneration as well as the transformation ratio and the tube constants. When the transformer is largest, both regeneration and amplification are strongest. A 2:1 transformer may give much better amplification than a 6:1, depending upon design. Diagrams illustrate the points under consideration. R402. Short Wave Transmitters. Short wave QST. Sept. 1925, pp. 30-32. Transmitter. "A Power-Amplifier Transmitter for the Low Waves," W. H. Hoffman. The circuit arrangement in a Colpitts oscillator, using an added power amplifier, is described. The transmitter operates well on very short wavelengths. It transmits a very steady frequency and with the apparatus recommended, has a tuning range from 14990-3894 kc. (20-77 meters). Since the set uses uv-202 tubes it can be operated on storage or dry batteries, and used as an emergency layout. Operating adjustments and list of parts required, including circuit diagram, give complete construction data. R113.4. Ionization; Heaviside Layer. Heaviside QST. Sept. 1925, pp. 33-34. Layer Theory. "Is There a Heaviside Layer?" G. W. Pickard. A brief discussion concerning some of the transmission phenomena, with particular reference to various theories on reflection and refraction, is contained in a letter to QST by the writer. R512. Radio Beacons. Lighthouse, Radio Broadcast. Oct. 1925, pp. 719-724. Radio. "And Now — The Radio Lighthouse," J. C. Young. Radio service to ships at sea has become absolutely necessary. Radio signals help guide ships when near thecoast and give bearings when needed. What advances have been made in guarding against danger, what pleasure and: enjoyment has been derived through the use of radio tothose sailing the waters, is well pictured in this article. R140. Radio Circuits. RobertsRadio Broadcast. Oct. 1925, pp. 725-73 1 . Circuit. "New Developments and Experiments with Receiving Circuits," K. Henney. The Roberts Knockout receiver offers possibilities for development along many lines. In this article some of the experiments carried on at the Radio Broadcast Laboratory with this circuit, are discussed. How a fifth tube may be added, how the reflex stage may be eliminated, how the circuit is neutralized, how regeneration may be employed in either detector or amplifier, are changes that may be tried with success. R007. 2. U. S. Radio Inspection Service. RadioRadio Broadcast. Oct. 192;, pp. 743-744. Conditions. "Guiding the Good Ship Radio," D. K. Tripp. An interview with W. ID. Terrell. Chief Supervisor of Radio, concerning radio conditions in the U. S. at present, reveals his views about the department's attitude toward the amateur, the broadcaster, and the service both can render toward bettering conditions in radio. R132. Amplifying Action. Amplifying Radio Broadcast. Oct. 1925, pp. 745-750. Principles. "Some Remarks on Audio Amplification," G. C. Crom, Good radio reception depends upon proper amplifier design. The functions of each part in the amplifier circuit are discussed in detail. Good parts must be used for best reproduction. Distortion may be produced by any one of four things as stated. High plate voltages are recommended and are of advantagew-hen proper C batters' voltagesand by-pass condensers are inserted, as shown in Fig. 2. R373. 2. Microphones. Microphone RadioBroadcast. Oct. 1925, pp. 769-770. placing. " More About How to Place the Microphone." Methods of placing microphones for picking up band andi orchestra music in and out of the station studio, are shown. In particular, the placing of several microphones at the Lewisohn Stadium in New York City and on the campus of New York University, in order to broadcast music from large organizations, is of interest. R375.3 Electrolytic Rectifiers. Rectifiers, RadioBroadcast. Oct. 192;, pp. 774-780. Cbemical. "Notes On Chemical Plate Supply Units," J. Millen. The chemical rectifier here described, employs two or more jars in order to handle output voltages up to 1 50 voltsand enough current for the receiver, at the same time giving absolutely no line hum in the output circuit. The discussion covers all phases of construction and operation in a very thorough manner. List of parts and diagrams of circuits and complete unit are added. Tested and approved by Radio Broadcast