Radio Broadcast (May 1928-Apr 1929)

-234 RADIO BROADCAST ADVERTISER OUT OF DATE Owing to the rapid advances in the radio science, a text or reference book on radio gets out of date unless revised every few months. We never have over 10,000 copies printed to an edition in order that we may issue a new and revised edition every few months, and keep our publication right up to date. The 4th Edition "Radio Theory and Operating" By Mary Texanna Lootnis is just off press, thoroughly revised with much new and valuable material never before published; contains nearly 900 pages and over 700 illustrations. The author is lecturer on radio in Loomis Radio College, member Institute of Radio Engineers, her long experience in handling radio makes her well fitted to know the needs of the radio student, engineer, amateur or fan. The book is used by practically all the leading radio schools in this country and Canada, universities, colleges and high schools, and all Government radio schools. For sale by nearly all bookdealers, or sent direct by the publishers. Price $3.50, postage paid. Loomis Publishing Company Dept. 10 Washington, D. C. FROSTRADIO A Complete Line of Radio Parts YOU can now obtain a complete line of radio parts from Frost, including many new items such as Variable High Resistance Units with A. C. Switch, I'anel Mount A. (' Switches, Hum Balancers. Center Tapped Resistances, Universal Resistance Kits, Hook-Up Wire, Panel Brackets, Filter and By-Pass Condensers, "B" Blocks, Moulded Mica Condensers, Cable Plugs and Radio Wall Outlets. These, with the Famous Frost Line of Parts, enable you to secure everything needed for your receiver from your nearest Frost dealer. See him to-day. Send 10c for New 16-Page Frost Radio Data Book A complete, valuable manual of hook-ups, radio tube data and fixed and variable resistance information. Write for your copy to-day. Inclose 10c to cover postage and mailing. HERBERT H. FROST, Inc. New York ELKHART, IND. Chicago HERBERT H. FROST, Inc! 160 North La Salle Street, Chicago Please send me your new 16-page Frost Radio Data Book by return mail. I enclose 10c to cover postage and mailing. N New Frost Variable Resistance with A. C. Switch ame . . Address City . . 214 Radio Broadcast Laboratory Information Sheet August, 1928 Measuring Instruments HOW THEY WORK 'THE drawing on this sheet shows in simple form the arrangement of the parts in an electrical measuring instrument such as might be used to measure the currents and voltages in a radio receiver. The instrument consists essentially of a very strong permanent magnet, M, a cylindrical soft iron core, C, a moving coil, L, the ends of which connect to the leads 1 and 2 which would be connected to the binding posts on the instrument. The space between the poles of the magnet, marked N and S, and the iron core, C, is made quite small so that an intense magnetic field will exist in the air space between the core and the pole pieces. The coil, L, is free to move in this gap. To the coil is fastened a small spring, G, and a pointer which is generally made of aluminum so that it will be very light in weight. The coil is pivoted at its center on jeweled bearings and the spring is adjusted so that with no current flowing through the instrument the pointer rests at zero 'on the scale. When current passes through the coil, it moves on its pivots. This motion is opposed by the spring and for each value of current there is some position of the coil at which the turning force produced by the current is exactly balanced by the force due to the spring; the pointer therefore comes to rest at a position on the scale corresponding to the point at which these two forces balance. The. scale can be marked off in values so as to indicate by its position on the scale the amount of current flowing through the instrument. With strong magnets, delicate parts, and accurate workmanship, instruments can be built which take only a very small fraction of an ampere to move the pointer over its entire range; the scale may be calibrated in thousandths of an ampere, or milltamperes; the instrument is then known as a milliammeter. Jo. 215 Radio Broadcast Laboratory Information Sheet August, 1928 The Hi-Q Six the parts used 'THE circuit diagram of the Hi-Q Six, the 1928 -1 model of the kit receiver produced by the Hammarlund-Roberts Corporation, is published on Laboratory Sheet No. 216. On this Sheet we give some details regarding the circuit and parts used so that readers who are keeping a file of these sheets may have on hand for ready reference the data on this kit. Other sheets to follow will give information on other popular kits. The circuit consists of three stages of r.f. amplification, followed by a non-regenerative detector and a two-stage transformer-coupled audio amplifier. The r.f. coils are arranged so that the coupling between the primary and secondary is varied automatically as the receiver is tuned. This feature helps to make the receiver perform equally well over the entire broadcast band. The first two tuning condensers are ganged to one tuning control and the other two condensers are ganged to the other control on the drum dial. Volume control is accomplished by means of a rheostat in the filament leads of the r.f. tubes. All of the r.f. stages are shielded. The following parts were specified for the official kit; the notation in this list refers to the diagram on the following Laboratory Sheet. Ti — Samson Symphonic Transformer. Ta — Samson Type HW-A3 Transformer (3-1 Ratio). Ci — 4 Hammarlund 0.0005-Mfd. Midline Condensers. Li — 4 Hammarlund "Hi-Q" Six AutoCouple Coils. L2 — 4 Hammarlund Type RFC-85 Radio-Frequency Chokes. C2 — Sangamo 0.00025Mfd. Mica Fixed Condenser. Ca — Sangamo 0.001Mfd. Mica Fixed Condenser. Ri — Carter 1R-6 "Imp" Rheostat, 6 Ohms. Si — Carter "Imp" Battery Switch. R2 — Durham Metallized Resistor, 2 Megohms. Ci— 3 Parvolt 0.5-Mfd. Series A Condenser. R3 — 4 Amperites No. 1-A. Rt — Amperite No. 112. Rs — 3 500-ohm grid resistors. Hammarlund illuminated Drum Dial. 1 Pr. of Sangamo Grid Leak Clips. 6 Benjamin No. 9040 Sockets. 3 Eby Engraved Binding Posts. 1 Yaxley No. 660 Cable Connector and Cable. 1 Hammarlund Roberts " HiQ" Six Foundation Unit (containing drilled and engraved Westinghouse Bakelite Micarta panel, completely finished Van Doom steel . chassis, four complete heavy aluminum shields, extension shafts, screws, cams, rocker arms, wire, nuts, and all special hardware required to complete receiver). . 2: OAnt. Radio Broadcast Laboratory Information Sheet The Circuit of the Hi-Q Six Shields August, 1928 l.s.OQ 1 J± 6 6 -A -B <-A +B i-B *-B -C -C *-C Gnd. 67 V. 90V.135V.4JiV. 9 V.