The Birmingham age-herald., 1924-12-28

number of secondary turns are more , than the number of primary turns. Un. fortunately, the beneficial effect secured by increasing the turn ratio is limited by several considerations, and one of the first principles of correct transform CT design is to compromise between the efficiency of step-up potential and the distortion resulting from an excess ratio. The ratio between secondary and primary turns should be kept com paratively low-never higher than four | to one. There are other considerations that contribute to efficient simplifying trans former design, such as input and output | impedance, the amount and quality Of core iron, etc., and the writer has de- voted considerable time to the develop ing of a transformer conforming with the correct interpretation of these prin- ciples. In this particular transformer, especial regard has been paid to imped- ance characteristics, with the result that is equally efficient on dry-cell. and storage battery tubes.
 The Proper Transformer
 There are of course other excellent transformers available to the fan, and his selection of a reliable make need be governed only by consideration ot the secondary primary ratio.
 Efficiency in Construction Approved amplifier design is next carried to the actual construction of the set, where several, more definite princi- ples may be ventured. The use of many high inductance turns in simplifying transformers is necessarily accompanied x.&l, Aa; sD1n effects, which, when ignored, may result in undesirable feedback. Such feedback 1 is evidenced by lack of stability and is | the most common cause ot howllng. IL is rather obvious that if a second and illegitimate channel or connection ex- ists between two or more tubes, an lm- pulse started in either channel may be repeated back through the other, run ming the circle many times second. A howl is produced in much the same man. ner as the telephone squeal when the re- ceiver is held close to the transmitter.
 The principal and luckily the most remediable cause of such feedback IS the too close placing of the simplifying trans formers, thus permitting an interactlon of the comparatively dense magnetic fields. t 1 IranSIOrmer OpaCus
 The obvious correction is to mount the transformers at judicions distance from each other--a precaution that may be well carried out to advantage with other parts of the amplifier. The cou- bling between the transformers should be further decreased by positioning the cores at right angles to each other, as is shown in the working diagram and photograph illustrating this article.
 In General .
 The design and building of success full two-stage transformer coupled am plifier may be summarized in the fol lowing advice: Select a reliable make of low ratio transformer. Mount them with at least four inches between cen ters. with the cores at right angles. DC not crowd the sockets, being consistent! liberal in the spacing of all parts ana wires.
 The accompanying illustrations are descriptive of a two-stage amplltler de signed in observance of these principles and which, as a result, is as fool-prool las it is possible to make radio apparatus It is recommended as an efficient ano highly satisfactory amplifier to both tht beginner and sophisticated enthusiast.
 The Parts
 The following is a complete list or tn' required parts:
 One 7-inch by 10-inch panel.
 Two reliable low ratio audie ire quency simplifying transformers.
 Two rheostats.
 Two sockets.
 Two double circuit jacks.
 One single circuit jack.
 Six binding posts.
 These parts. including a drilled ant engraved panel, may be obtained com plete from most dealers. However, sucl readers who have parts on hand, or wh' are particularly adept in the art of pan el working, are referred to the layout figure ?.
 Construction
 The actual building of the amplifie is best described in the working sketch figure 3, and the back-of-panel photo graph, figure f. which are self-explana tory. The experimenter who desires U eliminate jacks may follow out the fun damental circuit as suggested. The ma terials used and recommended by the au thor are such as to permit the panel mounting of all parts. A baseboard ma be used if the reader is unable to obtall similar equipment. Should doubt exls in the mind of the builder as to any de tail, or a departure from the plan worked out by the author be desirable any original design may be resorted t permitted by the principles of efficien ampifier construction.
 Operation
 This amplifier was originally worke out for use in conjunction with the re generative receiver developed by tn writer (the Haynes circuit), and re gently described in this publication. Tn manner of combining these two units illustrated in the drawing figure 3.
 The amplifier, however, is equally ei ficient when imputed from any othe detector, and is easily connected to d
 receivers. The method of doing this V