Radio Broadcast (May 1927-Apr 1928)

238 RADIO BROADCAST ADVERTISER JlfAGNAYOX Dynamic Power Speaker for new allelectric A-C Sets TR.1CHLECHAFLGER. SPEAK.EFL Hook it up like this sketch because the 6 volt rectified output of any standard trickle charger or "A" rectifier will energize the field of the Magnavox 6 volt Dynamic power speaker unit. Aristocrat Model speaker (complete unit), illustrated above, $85. Beverly Model table type complete, $65. Unit only, (type R-4, 6 volt) $50. Fits any standard cabinet. Only the Dynamic type speaker can bring out the full qualities of reproduction demanded today. Write for speaker bulletins THE MAGNA VOX CO. Oakland, California THE Radio Broadcast Laboratory Information Sheets are a regular feature of this magazine and have appeared since our June, 1926, issue. They cover a wide range of information of value to the experimenter and to the technical radioman. It is not our purpose always to include new information but to present concise and accurate facts in the most convenient form. The sheets are arranged so that they may be cut from the magazine and preserved for constant reference, and we suggest that each sheet be cut out with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should be arranged in numerical order. In July, 1927, an index to all Sheets appearing up to that time was printed. All of the 1926 issues of Radio Broadcast are out of print. A complete set of Sheets, Nos. 1 to 88, can be secured from the Circulation Department, Doubleday, Page & Company, Garden City, New York, for $1.00. Some readers have asked what provision is made to rectify possible errors in these Sheets. In the unfortunate event that any such errors do occur, a new Laboratory Sheet with the old number will appear. — The Editor. No. 153 Radio Broadcast Laboratory Information Sheet January, 1921 Standard and Constant-Frequency Stations broadcasters with accurate frequencies 'T'HE Radio Service Bulletin, published monthly by the Radio Division of the Department of Commerce, Washington, District of Columbia, contains a list of standard and constant frequency broadcasting stations as determined by the Bureau of Standards. This bureau makes measurements on an average of about three times a month on the transmissions of a small number of stations and as a result of these tests data are published in the Bulletin on those stations which have been found to maintain a sufficiently constant frequency to be useful as standards. These are known as "Standard Frequency Stations." The list of "standard, frequency stations" is supplemented with a list of "constant frequency stations." No regular tests ,are made on these latter stations but each station in the list employs a special device, such as a crystal, to maintain its frequency accurately so that they can be generally relied upon to maintain their correct frequency. standard frequency stations WBZ KDKA WBAL 900.00 950.00 1050.00 Constant Frequency Stations Call Letters WEAF WRC WJZ WGY Frequency Kc. 610.00 640.00 660.00 790.00 Call Letters WMAQ WJAD wcco WTAM ] WEAR J WBBM KGO KTHS WCAD WJJD WLS WSM WKAQ KOA KFAB WBAA WHK WMBI WABQ WEBJ KWUC KFVS Frequency Kc. 670 670 740 750 770 780 780 820 820 870 880 880 920 970 1100 1130 1140 1150 1170 1230 1340 154 Radio Broadcast Laboratory Information Sheet January, The 11 2A and 171A Type Tubes operating characteristics TWO new power tubes have recently become available; they are designed especially for use in the output of a receiver. These new tubes employ an improved type of filament which gives high emission at a filament current of 0.25 amperes at 5 volts. They are exactly similar to the older UX-112 and ux-171 type tubes with the exception that the filament consumption is only half that of the older types. The filament of the corresponding 112 and 171 type tubes is 0.5 amperes at 5 volts. The other characteristics of these new .tubes remain the same as those of the 0.5 ampere filament tubes. These characteristics are given below. The UX-112-A (cx-312-A) may be satisfactorily used as a detector, general -purpose tube, or as a power tube in the last stage of a receiver. When used as a detector, the plate voltage should be 45 volts. The ux-171-A (cx-371-A) must only be used in the last stage of a receiver, and a choke-condenser combination or output transformer should be used in the plate circuit to keep the plate current out of the loud speaker. The advantage of these new tubes is in their greater efficiency. Under the same condition of plate voltage they produce the same plate current as the corresponding 0.5-ampere tubes; with only half as much filament current. These tubes must not be substituted for the ux112 (cx-112 )or ux-171 (cx-171) types in a receiver without changing the values of fixed filament control resistances or rheostats if they are used. Since they take the same filament current as a 201-A type tube, it follows the filament control resistances designed for the latter tube may be used in conjunction with these new tubes. Type Filament Volts Filament Current Plate Voltage Negative Bias Plate Impedance Amp. Constant Plate Current Output Milliwatts UX-112-A 5 0.25 90 6 8800 8 2.5 40 (CX-312-A) 135 9 4800 6 120 157J 10.5 5500 8 195 UX-171-A 5 0. 25 90 16.5 2500 3 10 130 (CX-371-A) 135 27 2?00 16 330 180 40.5 2000 20 700