Radio Broadcast (May 1929-Apr 1930)

RADIO BROADCAST Input The frequency calibration curve is given in Fig. 3. It is practically flat from 60 to 8000 cycles — which we considered the useful range of the device. The fact that a high resistance, R7, is in the grid circuit of the second tube introduces a rather unusual characteristic. It has been found that as soon as an a.c. voltage, sufficient to swing the grid positive so that grid current flows, is impressed across the grid of the second tube, the reading of the plate meter, M, begins to decrease instead of increase. This characteristic prevents damage to the meter in case excessive a.c. input is applied to the voltmeter — this is certainly an advantage. The disadvantage of this arrangement is that false readings may be obtained unless it is realized that the meter is being overloaded. The decrease in plate current produced by overloading can be prevented by using a choke coil in place of R7, but the coil must have a very high inductance to prevent a decrease in gain at the low frequencies. A coil with an inductance of between 100 to 200 henries will probably be found satisfactory. The coupling con 45 Volts 6 Fig. 4 — Schematic diagram of the v.t. voltmeter pictured on page 107. denser, when using a choke, may have to be increased to about 0.5 or 1 mfd. The Laboratory's meter has been constructed on a baseboard as indicated in the picture. There is nothing unusual about either the parts or their arrangement on the board — except possibly that we would suggest that a Pacent or G.R. rheostat be used for B2, since these are the only rheostats we know of that can be fastened directly to the baseboard. A wood screw should also be passed through the center hole which normally holds the shaft. When the correct adjustment of R-2 has been determined, this screw will serve to hold securely the arm of the rheostat at the correct adjustment. List of Parts The following is a complete list of the apparatus selected for the construction of the v.t.voltmeter described in this article: Ci One Sangamo fixed condenser,!). 01-mfd. ; Ri One Ward-Leonard fixed resistor, type 507-93, 300-ohm; R.2 One rheostat, 2-ohm; R3 OneCentralab power rheostat,150-ohm ; R40neFrostfixed filament resistor,20-ohm; Rs Three Frost fixed filament resistors connected in parallel, two 20-ohm and one 25-ohm units; Rs One Durham Metallized resistor, 50,000-ohm; R7 One Durham Metallized resistor, 2 -megohm; Rs One Ward Leonard fixed resistor, type 507-29. 4000-ohm; R9 One Durham Metallized resistor, 0.25-megohm; Rio One Durham Metallized resistor, 0.1 megohm; R11 One Durham Metallized resistor, 50,000 ohm; R12 One Durham Metallized resistor, 1-megohm; R13 Two sockets; Fahnestock clips, etc. NEW 227-TYPE TUBE OF IMPROVED CONSTRUCTION By F. X. RETTENMEYER Chief Engineer, F. A. D. Andrea, Inc. During the past season dealers may have received quite a few complaints from purchasers of a.c. -operated radio receivers. The owners of these sets state that they frequently hear an annoying hiss and buzzing noise in the loud speaker. The cause of this noise has been traced by tube engineers to the 227-type detector tube. Fortunately, this trouble is not caused by the new tubes which are now available, but many of the old type are still in use. If a 227-type tube is examined, it will be noticed that the heater and its insulation extends above the cathode by a small amount and it has been found that the noise described above is due to the fact that the exposed portion of the insulating material collects a charge which builds up to a certain potential and then discharges to the cathode. This discharge, which is identical in action to that found in a leaky condenser, causes a buzzing type of interference which may occur at more or less regular intervals and which sounds not unlike radio-telegraph interference. In addition, the exposed portion of the heater sometimes introduces a certain amount of noise into the radio circuits by virtue of its effect on the tube space current. Both of these defects have been eliminated in the 227-type tubes now being manufactured. The cathode has been extended in the new tubes to the end of the insulation on the heater and it acts to shield the entire heater circuit from such interference. The type of interference mentioned above is, of course, present in all electric receivers but it is much more apparent in those sets which have good a.f. systems. That this must be the case is at once apparent when it is considered that a great many musical instruments produce characteristic tones of the same pitch as the interference (i.e., -cymbals, castinets, bells, triangles, and the overtones of the violin). Further, the s's and th's of speech are hissing sounds which are vitally necessary for good articulation and are very similar in character to the above types of interference. To limit the range of reproduced speech and music so that the crackling and hissing noises would not appear would mean that the quality would be seriously marred, and a receiver is good only when it faithfully reproduces all the audible frequencies broadcast. COMPLETE LIST OF R.C.A. LICENSEES The following is a complete list of the manufacturers licensed to operate under the patents of the Badio Corporation of America. RECEIVING SET LICENSEES The manufacturers listed below are licensed under the B.C. A. receiving set patents. Those manufacturers marked with an asterisk (*) are also licensed under the power supply and amplifier licenses, and those marked with a dagger (f) are licensed under the electric phonograph patents. Ail-American Mohawk Corp.,*t Chicago. III. American Bosch Magneto Corp., Springfield, Mass. Amrad Radio Corp.,t Medford Hillside, Mass. F.A.D. Andrea, Inc., Long Island City, N. Y. Atwalcr-Kent Mfg. Co., Philadelphia, Pa. Bremer-Tully Mfg. Co.,*t Chicago, 111. Buckingham Radio Corp.,*t Chicago, 111. Colonial Radio Corp..t Long Island City, N. Y. Columbia Phonograph Corp., Chicago, III. Consolidated Radio Corp.,*f (two Divisions) Wells-Gardner & Co., Chicago, 111. Arborphone Division, Ann Arbor, Mich. Crosley Radio Corporation,* Cincinnati, Ohio. Day-Fan Electric Co.. Dayton, Ohio. Guihransen Co.,*t Chicago, III. Klcrlrical Research Laboratories, Inc..*t Chicago, III. Federal Telephone Mfg. Co.,* Buffalo, N. Y. Freed-Eisemann Radio Corp., Brooklyn. N. Y. and Chas. Freshman, Inc., New York, N. Y. Gilfillan Bros. Inc.,*t Los Angeles, Cal. A. H. Grebe & Co. Inc.* Richmond Hill, N. Y. Grigsby-Grunow Co.,*t Chicago, III. Howard Radio Co., *t Chicago, 111. Kellogg Switchboard & Supply Co., Chicago. 111. Colin B. Kennedy Corp.,t Chicago, 111. King Manufacturing Corp.,* Buffalo, N. Y. Kolster Radio Corp.,* Newark, N. J. Philadelphia Storage Battery Co., *t Philadelphia, Pa. Silver-Marshall, Inct Chicago, 111. Splitdorf Radio Corp., *t Newark, N. J. Steinite Manufacturing Co.,* Atchison, Kansas. Stewart Warner Speedometer Corp.,* Chicago, 111. Stromberg Carlson Telephone Mfg. Co.,*t Rochester, N. Y. Temple Corp.*t Chicago. 111. United States Radio & Television Corp.,* Chicago. 111. (three divisions) Apex Electric Mfg. Co., Chicago, 111. Case Electric Company, Marion, Ind. Continental Radio Corp., Ft. Wayne, Ind. Walbert Radio Corp.,t Chicago, 111. Zenith Radio Corporation,* Chicago, 111. POWER SUPPLV AND AMPLIFIER LICENSEES The following list includes manufacturers licensed under the B.C. A. power supply and amplifier patents. Other manufacturers licensed under these patents arc the receiving set licensees (listed above) which have been marked with an asterisk (*). American Transformer Co.. Newark. N. J. Autorad Electric Corp., Detroit. Mich. H. H. Eby Mfg. Co.. Philadelphia, Pa. Electrad, Inc., New York City. Enterprise Mfg. Co. of Pa., Philadelphia. Pa. Farrand Mfg. Co. Inc., Longlsland City. N. Y. Federal Radio Corporation, Buffalo, N. Y. Ferranti Inc., New York, N. Y. General Radio Co., Cambridge, Mass. Gray Products, Inc., Poughkeepsie, N. Y. Kingston Products Corporation, Kokonio, Ind. Martin Copeland Company, Providence. R.I. National Company, Inc., Maiden, Mass. Radio Receptor Co.. New York, N. Y. Sterling Manufacturing Co., Cleveland, Ohio. Thordarson Electric Manufacturing Corp., Chicago, III. J. S. Timmons Co. Inc., Philadelphia, Pa. ELECTRIC PHONOGRAPH LICENSEES Manufacturers licensed under the electric phonograph patents are those marked with a dagger (f) in the above list of receiving set licensees. VACUUM-TUBE LICENSEES The Raytheon Manufacturing Company Cambridge, Mass., is the only tube manufacturer which has thus far been granted a license to operate under the R.C.A. vacuum-tube patents. 101! • • JUNK • 1929 •