Radio broadcast .. (1922-30)

704 RADIO BROADCAST ADVERTISER Seven Years of Superiority KNOWN as the original HI-MU tubes before the days of BCL; Preferred by amateurs and experts be' fore the first popular receiving set was sold; Progressively improved in construction and performance; Made in the newest and best equipped plant in America. Get the World on Your Dial With Myers Tubes Low impedance, high amplification constant, high mutual conductance. Best results in any circuit —impedance, resistance or transformer coupled. cAt Your 'Dealer's Myers Radio Tube Corporation Cleveland, Ohio Attractive, compact, correct inside and out, no clumsy materials. Made by pioneer designers and builders of Radio Tubes. PUT Marvelous Clarity and Distance Use Myers Tubes in any set and get better results in volume, tone, range and ease of control. Made with standard four prong base, or double end, in types Myers 01 A, Myers 01 X, Myers 99, Myers 99 X. List Price Type 01 $2.00 Type 99 2.25 At Your Dealers SEND FOR New No. 739 Circular describing special voltmeters for Radiola, Victor and Brunswick sets Jewell Order from Dealer j^ Electrical Instrument Co. 1650 Walnut St. Chicago "26 Years Making Good Instruments" posts, the ends of a Belden battery cord being attached directly to various terminals, transformer, switch, etc., in the set. For experimental purposes, it is handier to use binding posts, however. Choke amplification may be used with either 90 or 120-135 volts of B battery. In case 90 volts of B battery is used, the 90 volts go to both r.f. and a.f. amplifiers, while the detector receives 45 volts. If, however, it is desired To coils & To Condensers Switch To Rheostat TO TOA.F. A.F. Resistances FIG. 3 to employ 120-135 volts of B battery on the last audio stage, then the r.f. amplifier and the first two stages of audio receive 90 volts. There are three separate units to be provided for, the r.f., ist and 2nd a.f. amplifiers, the detector, and the last a.f. amplifier stage. If three B plus binding posts are used, one for each unit, the a.f., r.f., or the detector may be quickly connected at the binding posts to facilitate the use of various values of B potential without tearing the set apart. The December, 1926, RADIO BROADCAST contained two very interesting articles on the use of high-mu tubes, one by Keith Henney and the other by Glenn H. Browning. The latter describes the use of Daven wood Mandrel with ISspokes Bushings with / set screws > - 2 .' HDia. Rod VM pr-ea tHi ;, Wood disc ' ' with nails (or counte Spike o rod 2i x r brass l*«Vii /Dasher , WOOd ; /Support! / -C---1S4--* i f Crank T — — ^ //H Small finishing nails % :l'lon( Baseboard FIG. 4 high-mu tubes in conjunction with National chokes, using 90 volts of B battery. When two Daven MU-2O and one Daven MU-6 (in the last stage) are used in the "Model 1926 Receiver" with Thordarson chokes on 90 volts, an appreciable gain in volume is experienced. When, however, 120-135 volts of B battery are used in the a.f. circuit, as suggested by Mr. Henney, the receiver talks right out. Furthermore, quality is not sacrificed. When Daven tubes are used, the rheostat lead to these tubes may be disconnected from the rheostat and connected directly to the current supply, as these tubes operate TesteH and approved by RADIO BROADCAST -f directly from a 6-volt battery. A switch of the midget type mounted inside the set makes this change simple. To care for added C battery (6 to ~j\ volts) to the a.f. circuit, an extra pair of C binding posts may be used to advantage, as indicated in Fig. 3. DAVENPORT HOOKER, Pittsburgh, Pennsylvania. A HOME-MADE COIL WINDER FOR DIAMONDWEAVE COILS THOSE preferring to "roll their own" will find in the accompanying sketches, Figs. 4, 5, and 6, sufficient instructions to build an efficient coil winder for diamondweave coils. It consists of a wood mandrel and metal spokes for a coil form, mounted on a shaft; also a counter and a wire guide made of small thread spools, and a small screw eye to give correct tension to the wire. Brassor Wood Bushing , Wood Spool ft '•* 4 r a ,,,,73, ft P 1~ Brass strip %" wide "-.4 %2 Threaded , — f a "* y^ " f\ ^3 Rod ~'*H dE" • t-i -*>-, Y Y J= f 1 I "^ FIG. 5 Care must be taken in marking and boring to the correct size, the holes in the mandrel to take the spokes. Place the spool or wire guide in an upright position, and far enough away from the winder proper to allow easy handling of the wire with the hand (about five inches from the shaft support). To wind, run the wire through the eye and under first spool, then between the two and over the top spool; set counter and begin winding. With a little practice one can soon learn the "swing" of "over two, under two," done with the left hand. After winding, remove the mandrel from the shaft, pull the spokes just out of the wood, but leave them engaged in the wire until sewn. About twenty nails in Wood Mandrel of diameterdesired , 2% *3/iJ Spike or Brass Rod FIG. 6