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I www.americanradiohistory.com The 464 Radio News for November, 1928 o 110 VOLTS A. C. Q 2310 e 11111 CHOKE 2MF. 30 HENRIES 2MF. 11111 CHOKE 8MF. IMF B+ 90 ..*-100,000 OHMS oBFOET og- Connections of a simple electrolytic recttficr, which will furnish up to 90 volts "B" supply without the use of a step -up transformer. The variable resistor regulates the detector voltage to any desired amount. (A.) Yod will find the diagram of a power unit of this type in Fig. Q. 2310. Four electrolytic rectifier jars are used, and two 30 -henry chokes with three filter condensers comprise the filter system. The rectifier plates are made by cutting strips of pure aluminum and lead, 2 inches wide and 5 inches long. The aluminum plates are made of !e -inch extra pure or No. I commercial stock; you can obtain this from any good metal dealer or hardware company. Bend the plates over at a right angle, one inch from one end. Then hang them over the tops of the cells, which consist of four pint mason jars. Make the electrolyte by dissolving as much primary (acid) ammonium phosphate as possible in two quarts of distilled water. Add crystals until there is an excess which will not dissolve. Then pour off the liquid and place it in the jars. Next insert the aluminum and lead plates into the solution and connect them as shown in diagram Q. 2310. Before using the "B" power unit, the plates must be "formed." Connect a 25 -watt electric - light bulb across the rectifier, in place of the first 2 -mf. condenser, and leave the rest of the apparatus disconnected. This will place the bulb across the rectifier and will supply the necessary load. Next, connect the input or alternating current wires to the electric -light line and let the unit run for about 5 or 6 hours. This will be sufficient to "form" the plates and you can connect the condensers and chokes as shown in the diagram. High -voltage condensers are not required here. The output of the power unit will supply about 90 to 100 volts, depending on the resistance of the choke coils. This is usually too great for the detector tube, so that a variable resistor (a regular 100,000 -ohm carbon -type) is provided to reduce this voltage to the correct value. A 1 -mf. condenser is also connected between the detector tap and the "B-" terminal of the unit, to keep the output steady and by -pass any stray radio - frequency currents. In order to obtain satisfactory results with an electrolytic "B" power unit, you must use pure metal for the aluminum electrode and chemically pure ammonium phosphate for the electrolyte. Also use only distilled water, to be sure that it is pure. By pouring a layer of mineral oil over the surface of the electrolyte. evaporation will be reduced considerably; and this will also prevent sparking at the surface of the liquid to some extent. If the sparking is excessive, insulate the tops of the aluminum electrodes by placing rubber tubes over them or by coating them with celluloid dissolved in acetone. SIMPLE ONE -TUBE SET (2311) Mr. M. T. Lynch, Portland, :tlaine, writes: (Q.) "I am a beginner in radio and, although I have constructed several crystal sets, I have never attempted to build a tube set. I have been a reader of your publication for almost a year, so I am more or less familiar with the terms used in radio. I have looked over all the back issues that I have on hand, but I do not find a suitable set for my purpose. The receiver that I desire to build is one using a single tube. I do not like to make a set that would interfere with my neighbors, so I do not want a regenerative receiver: I want to get the greatest efficiency, though. Will you give me the diagram and specifications of a suitable set ?" (A.) We are printing the diagram of a single - tube reflex set, using a crystal detector, herewith. (See Figs. Q. 2311 A and B.) The parts required for the set are as follows: One 201 A- or 199 -type tube (VI); One tube socket; Two .0005 -mf. variable condensers (Cl, C2); One audio- frequency transformer, about 34 ratio (AFT); One crystal detector (CE); This one -tube reflex circuit furnishes the maximum amplification available without making a "blooper." One 20- or 30 -ohm rheostat, depending on whether a 201A or 199 tube is used (Rl); One .001 -mf. fixed condenser (C3); Eight binding posts; One 7 x 12 -inch panel; One 8 x 12 -inch baseboard, % -inch thick; Two 3 -inch tubes 3 inches long for coils; No. 22 D.C.C. wire; screws; wire for ccaneetions, etc. The first point in constructing the set is to make the coils. . aerial coupler is wound with 12 turns of No. 22 double -cotton -covered wire ftë the primary and 48 turns for the secondary. The primary is wound on one end of the coil and a space of %-inch is left before the secondary is wound on. Both of the coils are wound in the same direction. The second R. F. coil (L2) is made the same as the first coil (L1). except that the primary contains 15 turns. In the aerial coil, the end of the secondary -farthest away from the primary is connected to the grid of the tube. In the second coil, the outer end of the primary is connected to the plate of the tube. The next step in building the set is to drill the panel for the condensers and rheostat. Place the parts approximately in the positions shown in Fig. Q. 2311 B. The positions of the Lodes depend on the particular apparatus employed and will have to be determined when the parts have been bought. After the panel has been drilled and these parts have been mounted on it. mount the other apparatus on the baseboard in the positions shown. Fasten the binding posts either directly to the baseboard or to small strips of hard rubber or bakelite mounted on the baseboard. Then wire the set according to either diagram, Fig. Q. 2311 A or Fig. Q. 2311 B, as you find easiest, and check every connection. The connections to the audio -frequency transformer are indicated on both diagrams: although it may be found necessary to reverse the connections to the secondary coil in order to get the best results. The values of the "A" and "B" batteries depend on the type of tube used. If a 201A is employed, the "A" battery must be a 6 -volt storage battery; while, if a 199 is used, three dry cells connected in series will be sufficient. To put these batteries in series, connect the center terminal of the first battery to the outer terminal of the second. Then connect the center terminal of this bat - ery to the outer terminal of the third battery aml the two remaining terminals to the set. The center terminal of each cell is the positive ( " + ") and the outer one is the negative ("-") The "B" battery should have a voltage between 45 and 90, for either type of tube, and since the current consumption is rather low, the small dry - cell batteries can be used. Operation The set is now ready for operation. Adjust the rheostat R1 until the tube lights up with its normal brilliancy; in a 20IA tube, this will be quite bright, while only a dull red glow will be noticed (Continued on page 505) -r- --------- 12" ,. A- A+ B- B+ PHONES .001 MF 8' e i ¡ VUUUllIIIIIEIMM///p/p// Q23116 C AERIAL IN. mod Cl: : 44 a : O FIDP F AFT NM m : r. .1 =_ 1 - ' : aa m .= r. . . II®Q U///F - W®Il! S EMI= The single -tube reflex circuit of the diagram above is shown here in pictorial form; the simplicity of the hook -up can be seen. The crystal detector may be of any type preferred; a Carborundum unit gives excellent results and requires little adjustment. This unit works with phones only; but an amplifier such as the "Extension" may be added to operate a loud speaker.
www.americanradiohistory.com SJ Radio News for November, 1928 463 WONDERFUL RADIO! Super- Eight -100% Electric 8 TUBES- SINGLE DIAL Coast -to -Coast Shipped Direct from our Factory on 30 Days FreeTrial [ Battery or Electric I Now comes Metro's latest achievement -the world's greatest electric radio set -a powerful long distance eight tube receiver -clearness of tone that is astounding-ultra-selective--a set that expert radio engineers have pronounced as the ultimate for all around perfection. And to prove our claims, we will send this marvelous set to you direct from our factory on 30 days' free trial. Test it to your heart's content. <strong>Com</strong>pare its quality, beauty and price with any other radio on the market, and decide to keep it only after you are atisfied that the new 1929 Metrodyne super -eight is the peer ut them all. etrodyne SUPER-EIGHT ELECTRIC Save One -Half -Low Price a Big Feature! You will be amazed at the low price of these wonderful sets, in the console or table cabinet. Our low cost of distribution direct from our factory enables us to save you about half their regular value. Never before in radio history have you been offered such sets at such low prices. And we are so sure of their quality, beauty and performance pleasing you that we do not hesitate to let you try one for 30 days before deciding to keep or return it. SUPER QUALITY THROUGHOUT ! Eight powerful tubes. Highest quality low loss parts. Illuminated single dial. Positive switch control -simply turn a knob and it's on. Select your stations with accuracy at any desired volume. Beauty of tone that cannot he surpassed. Console and table cabinets are handsomely grained genuine walnut, hand rubbed, in two -tone effect - artistically carved trimmings. All metal parts finished in two -tone Sold. Seeing is believing. You will be the judge. Georgenns console with newest type, built -in sonorous loud speaker that reproduces the emir, range of vocal and instrnme -dal music. Amazingly clear and distinct. Lew, direct- from -factory price on 30 DAYS' FREE TRIAL! AGENTS and DEALERS The 1929 Super -Eight line offers great money staking opportunities. Nothing like them for high quality- nothing near them in price. Let us prove this by shipping you a Demonstration set on 30 days' free trial Test it- compare it- demonstrate it to prospective radio buyers. Get our liberal discounts -exclusive territory -newspaper and offer that will help you sell Metrodyne radios quickly. METRODYNE RADIO SETS Are Equipped For BATTERY or ELECTRIC OPERATION billboard advertising We are one of the pioneers of radio. t e success of Metrodyne sets is due to our Ii - end 30 days' free trial offer, which giv_s you the opportunity of trying before burin;. Thousands of Metrodymes have been bou.-.t on our liberal free trial basis. We will s 1 YOU hundreds f letters from owner: . acclaim the Metrodyne as the greatest r set in the world. A postal, letter or t 11, pon brings complete information. to - ntls. whole -ale price and our lib , days' free trial offer -WRITE TODAY: Send Coupon Today for Our 30 Days' Free Trial Offer -..i METRO ELECTRIC COMPANY 2161 -71 N. California Ave. Dept. 12 Chicago, Illinois Ple.nsr .cav c a w il in METRO ELETRIC COMPANY 2161 -71 N. California Ave., Dept. 12 Chicago, Illinois Gentlemen: Send me full particulars about Metro! ce Super -Eight sets and your 30 days' free trial offer Name ...- dc'dress- RADIO NEWS If you are interested in .4GE.1TS preposition, place an "S" in Ute squaw y a
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