Radio Digest (Apr 1925-Jan 1926)

■April 18, 1925 RADIO DIGES T— Illustrated 15 Operating and Trouble Shooting For the Owner of Federal Models 141, 142, 143 and 144 THE Federal receiver, Model 141, is the basis for the other three models also marketed by the Federal Tel. and Tel. company, the difference between the four models being the cabinet in which the apparatus is contained. The discussion will, therefore, be based on Model 141 but the owner of any of the three models will find that it applies equally well to the apparatus in his set. Unlike most of the sets on the market, this receiver is neither regenerative, tuned radio frequency or super-heterodyne. It is a development of the Federal Tel. and Tel. company of which they may be justly proud, as the operation is readily grasped and very little trouble is encountered. The front view of this receiver with the doors open is shown in figure 1, while figure 2 shows the rear view of the panel and the apparatus mounted behind it. The schematic wiring diagram is shown in figure 3 and the numbers used to identify the various parts are the same in all three illustrations. There are five tubes in this receiver, two of which amplify or strengthen the incoming program at radio frequencies, one is the detector which changes the form of the incoming signals so that they will operate head receivers, and two are known as audio frequency amplifiers as they strengthen the current so that it will actuate a loud speaker. To briefly explain the above terms it should be stated that, when Radio waves strike the antenna of a receiving station, and traverse the coils connected to that antenna, the electrical current set up alternates in its direction of travel from 500,000 to 1,500,000 times per second and such rapid alternations of direction are known as radio freqeuncies. Energy alternating at these' frequencies can be strengthened or amplified by means of vacuum tubes but, before this energy can be applied to a reproducer, its form must be changed by another vacuum tube so operated that the energy which has been alternating at radio frequencies becomes a direct current traveling in one ion only and varying in intensity at audible frequencies, from 16 to 10,000 times per second. When in this form, if applied to a telephone receiver, the diaphragm of the receiver will be caused to vibrate at the audio frequencies meh Pigmre 1 tioned and sounds which can be heard will be produced. Audio frequency amplification, as accomplished by the last two tubes of the receiver, consists of strengthening this energy at these lower audio frequencies. The tubes used for these three purposes are identical in structure and are interchangeable as to use, and are called by different names only to identify the purpose to which they are being put. Tuning Operation. This receiver is tuned by dials 1 and 2 as shown in figure 1 and it is the purpose of this article to explain what goes on behind the panel when these dials are turned. Referring to figure 2, condenser 2B and coil 11 comprise an electrical circuit which can be tuned or adjusted to absorb any frequency desired. By means of condenser 2B this circuit, which is known as the antenna circuit, can be adjusted for all of the frequencies used by ffle Finer Side of Radio 5 MODELS The Cabinet shown hero li of beautifulb finished miiliHKiinv. 17 I in x 1014. I' hai .1 full wooden horn with lone expansion rhiimher and » hlgh-cradi prmlurer. Prlco (S I II i.ii" i 112, 125.00. Send for Bulletin AY-3022 Ask your dealer to demonstrate thorn on tho Bristol Coraparophon. A great baritone sang with uncommon fervor to his enraptured listeners. The melody seemed to string a golden chain of words for some responsive heart. It reached ten times a million hearts. For as the music faded into silence the singer said GOOD NIGHT MOTHER! And then we knew that song had gone straight and true to someone somewhere in that vast invisible audience. Someone whose tear-dimmed eye saw not the wonderful singer but a little boy whose tousled head lay on her breast. And in that spell of mother love which makes millions kin. All those listening hearts "tuned in" to one heart. A heart that must have felt the magic of ten million prayers unified in one "God bless her!" Our Bristol Loud Speaker had given its all the rich tonal quality of the singer's voice, it's natural sweetness, its pathos. It had been a wonderful evening. THE BRISTOL COMPANY Waterbury, Conn. BRISTOL'S -IHSTBUMIHTfl BRISTOL AUD'^0NE Loud Speaker broadcasting stations. When the reader turns dial 2 he is merely adjusting the antenna circuit for the frequency or wave length of a desired station. It is the purpose of coil 12 to absorb energy from coil 11, and coil 12 with variable condenser IB form another tuned circuit which is adjusted by condenser IB so that this circuit will be in resonance, or tuned to the same frequency as, the antenna circuit consisting of 2B and coil 11. From this tuned circuit, signals are passed to the first tube amplifying at radio frequencies which is the tube to be inserted in tube socket 13. It will be noticed that the five tube sockets are mounted directly above a brass box which is closed and sealed. From tube 13 the signals pass to what is known as an untuned radio frequency transformer contained within the brass box, and from this transformer the signals pass to tube 14. Here they are again amplified or strengthened at radio frequency and passed into the second radio frequency transformer, also within the brass box, from which they are passed to the tube which, in the foregoing explanation, we have called the detector. This is tube 15 in the illustrations. When the signals have passed tube 15 they are in the form of a varying direct current whose impulses occur at the audio frequencies and this energy is passed into a transformer known as an audio frequency transformer within the brass box. From this transformer signals pass to tube 16 which is the first of the two audio frequency amplifiers and from this tube the signals pass to a second transformer and finally to a second audio frequency amplifying tube which is tube 17. Separating1 Stations Going back now to coils 11 and 12, it is known that the selectivity or ability to separate stations operating on very similar wave lengths is greatly increased by turning coil 11 at an angle to coil 12. When coil 11 is turned by means of lever 4 so that its axis is horizontal there will be greater volume but there will be some difficulty in separating the programs from two stations whose wave lengths are very nearly the same. By turning coil 11 so that it is at approximately a right angle to coil 12 there will be some loss in volume but the user will find that by adjusting IB and 2B through dials 1 and 2, he will be able to completely separate the program and enjoy one or the other. Coil 11 can, of course, be set at various angles between horizontal and vertical depending on the amount of interference which exists. So, if the user finds that two powerful stations are spoiling each other's program when he tunes in, he need only vary the relation between 11 and 12 by means of knob 4 to enjoy either program. Knob 3 is attached to a device known as a potentiometer which is labeled 3B in figure 2. This piece of apparatus controls, to some extent, the sensitivity or range of the receiver and, in the case of nearby stations, it controls the volume. (Continued on page 18) THE Improved MARV-O-DYNE is the kind of a set you have always hoped to own some day, the ideal set of your dreams. Beauty of tone and of appearance, ability to get distance, well known units — all those features this MARV-O-DYNE has. The Improved MARV-O-DYNE, model 612-C, has more really useful improvements than any other set on the market. Take the Fil-a-meter, for instance, and the Antenna Tuning Compensator, and the push switch for reading B battery voltage. Those are only a few. The Improved MARV-O-DYNE will endear itself to you if you only give it half a chance. We would like to have you go to your dealer today for a demonstration. The price, by the way, is only $110. West of* the Rockies and Canada, $120. Amber Mfg. Corp., 115 W. Broadway, New York City CThe Xte^S^d Amber MHRVinDYNE 9*<? set With thi Fll ~a~ motor /