Radio and Television Today (Jan-Nov 1941)

Permeability Tuner on BC and SW Spread Band Permeability tuning is used on the battery operated Silvertone model 7110. This five-tube set uses a 1P5GT tuned RF stage and a 1A7GT converter. The set tunes four bands, 540 to 1700 kc, 9.45 to 9.75 ma, 11.62 to 11.95 ma, and 15.01 to 15.5 mc. These four bands are covered with a same moveable core tuner in the oscillator circuit. The diagram for the mixer stage is shown in the accompanying cut. The permeability tuner coil has only a shunt trimmer on the broadcast band, but as the short-wave ranges are switched-in, a fixed tuned coil is connected across the main coil. This auxiliary coil is not inductively coupled to the main coil and serves only to reduce the total inductance to that required for the range. Additional trimmers are also switched in to allow adjustment. The tickler on the main coil is shorted out when the set is operating on the short-wave bands. NEUTRALIZING CAPACITY Note the small capacity coupling from the oscillator grid to the injection grid. This small capacity is to neutralize the effect of space charge coupling on the short-wave bands. The electron space charge near the signal grid may cause a positive grid current to flow with loss of sensitivity if the neutral Permeability tuner is used on shortwave bands with additional shunt coil in oscillator. ization is omitted. This small capacity is adjusted for maximum sensitivity on the highest frequency range. The antenna circuit is fixed tuned on the short wave ranges, and the RF plate circuit uses a separate permeability tuner on SW. Clearing the Air If the noise is "on the line" it can be filtered out, either at the source, or at the set. Not every filter, of course, will remove all noise, but any power line noise can be removed by some filter. Get the right combination of chokes, and capacitance, and you "run the noise into the ground." But very often it is a loose lamp bulb, or a defective socket, plug, cord, or connection that is causing the trouble. You will do your customer, and _ your own reputation, a greater service if you can locate the source of the noise, and correct it there, than by just slapping a filter across the line and forgetting the cause. BOOK REVIEWS Radio Servicing Course Book 5th Edition N. N. Beitman Supreme Publications, 328 S. Jefferson St., Chicago Radio servicing from fundamentals to business methods is included in twenty-two lessons in this enlarged fifth edition of a popular text. Designed primarily for the beginner, there are many chapters which will find use in nearly every shop. The lesson on radio servicing techniques includes a full treatment of signal tracing methods as well as other types. Alignment and cathode ray oscilloscopes are also fea Replace Wi*lheBe«| ALLIANCE "EVEN. SPEED" PHONO 'MOTORS EASY TO INSTALL . . Fit 95% of all makes f%gSSS» # The low cost and quick, easy installation of "Even-Speed" Motors make it more practical and profitable to replace the entire unit when trouble occurs. The "Even-Speed" line of only four phono-motors provides a unit for 95% of all replacement requirements. Carry a few in stock. Each motor and turntable comes in an attractive carton for your greater convenience. Ask your jobber or write direct for complete information and low prices. ALLIANCE MFG. CO. • ALLIANCE, OHIO eadu/ tAfow CHIME RECORDINGS for the HOLIDAY TRADE For extra profits, sell these new high fidelity recordings of traditional Xmas music. Universally used to create the Holiday feeling. Our fourth series in this prime Christmas field. Big waiting market among homes, churches, schools, stores, institutions and community celebrations. 10" Discs — 2 selections each. 1006 HARK! THE HERALD ANGELS SING SILENT NIGHT, HOLY NIGHT 1007 ANGELS FROM THE REALMS OF GLORY IT CAME UPON THE MIDNIGHT CLEAR 1008 JOY TO THE WORLD O COME, ALL YE FAITHFUL 1009 O LITTLE TOWN OF BETHLEHEM WHILE SHEPHERDS WATCHED THEIR FLOCKS 1010 THE FIRST NOEL WE THREE KINGS OF ORIENT Start now to make money in this new field of musical recordings. To play them is to sell them. Wire or write at once LIST PRICE $2.00 each; the set for $9.00 TVNGERTONEJnc. ** 73 WINTHROP ST., NEWARK, N. J. 50 RADIO TODAY