Radio age (Jan 1927-Jan 1928)

to RADIO AGE for January, 192? way of checking up on the operation of this tube, and of determining when it is over-loaded. A 0-25 DC milliammeter inserted at X in Fig. 1 or Fig. 2, should show a steady reading when the receiver is in operation. If there is any fluctuation of this milliammeter needle, the tube is being overloaded, and the volume should be reduced. An overloaded audio tube is a prolific source of distortion, if nothing else. Right here is a good place to say something about loud speakers. An audio amplifier capable of reproducing such a wide range of frequencies as does the one in the Henry-Lyford, deserves nothing less than the best of loud speakers. In no other way can the rich low tones of the receiver be appreciated. Some sort of a cone type loud speaker should be used and the Western Electric is recommended for best results, though there are others which are nearly as good. At any rate, an effort should be made to use the best one that is available. Questions have been asked about the use of a loop antenna with this receiver. The answer is that this set was not designed for and is not suited to use with a loop. It will work on a short indoor antenna, however, with exceptionally good results. Almost any sort of an antenna which will work with any receiver will work with this one, as long as it is not too large. One of about 75 or 100 feet over-all length — including the leadin — is just about the right, wherever possible. The use of the rotary coil on the antenna coupling transformer, was explained in the previous article. It allows greatly ZOR4 \t1FD. different antennas to be used with equally good results. It will be found that there is one position of this coil which is best for general use, depending on the location and the antenna, and after this coil is once set, it need not again be changed. It is convenient, and often very useful, to have on hand a tuning chart of your receiver, and one may easily be made. A typical tuning curve is shown in Fig. 3. This, as may be seen, is a curve of dial settings against wave-length. To make one, first log the settings of as many stations on different wavelengths as possible. These settings should then be plotted on a piece of squared paper, such as may be Shown originally in the blueprint section of the November Radio Age the Henry-Lyford circuit has been quite well received by our readers, both the fan and the experimenter type. The use of a deliberately unbalanced circuit and a stage of untuned frequency amplification, makes this receiver very interesting to those who are constantly on the alert for something new or novel in radio. Using a stage of untuned radio permits having three stages of radio (two tuned) with only two dials and without necessity for using a tandem condenser. Quality is one of the main features of the audio end of this set, two of the larger transformers being used. Results on a cone type speaker are certainly worth while. — Editor. Figure 1 In the sketch above is shown the way to connect your loud speaker so as to isolate the DC component. The choke may be an old audio transformer secondary while the condenser is a 2 or 4 mfd condenser procured at any stationary store. After a sufficient number of points have been plotted, a smooth curve is drawn through them. The tuning curve for any Henry-Lyford, thus drawn, will correspond very closely to the one shown, both in appearance and position. In locating a station whose wavelength is known but which has not been logged, a reference to this curve will tell you, within a degree, where they should come in on the dials. The curve of Fig. 3 shows very plainly the advantages of combination type condensers for tuning, such as are used in this receiver. There is no undue "crowding" of stations on either end of the dial, but all of the The Magazine of the Hour transmission channels are evenly spaced, making for easy tuning. The tuning curve illustrated was made for the broadcast type coils, but curves made for the other two sets of plug-in coils for this receiver, for the lower wavelengths, will look the same. The range of these other coils is from 37 to 125 meters and from 75 to 225 meters, respectively, and the operation of the receiver is the same when using these coils as when using the broadcast type. IF you are building the HenryLyford particularly because of its exceptional distance-getting ability, the use of vernier dials on the tuning condensers is strongly recommended. When the fullest gain of the r. f. amplifier is used, the antenna dial particularly tunes very sharply, and it will be found difficult to tune the receiver properly with ordinary dials. For stations within the radius of 200 miles, tuning is easy, but for any distance work the vernier dials will be very helpful. The panel size of the receiver is 7x24", and the depth is 9", so that the completed receiver fits readily into any standard cabinet, many styles of which are available. The panel layout of the receiver is simple and dignified, and graces any cabinet. One final word, about the results which you may expect to obtain. The first hour's use of this receiver may be a little disappointing, as far as results on DX are concerned, but as soon as the proper use of the balancing condenser is learned, slight disappointment will turn to admiration. Radio receivers, like automobiles, are individual, and each one requires a little familiarity with it before the ultimate results are obtained. Figure 2 The loud speaker in this sketch is shown connected throngh an output transformer, several makes of which may be found on the market today