Radio Digest (July 1924-Apr 1925)

18 RADIO DIGES T— Illustrated November 29, 1924 SUPER-HETERODYNE (Continut'il from page 17) right of where you had it during this try out. Again revolve the oscillator condenser through Its scale and either signals or whistles should certainly be heard. If signals, adjust the neter until signals are at maximum strength without blurring; If whistles are heard, turn potentiometer to thte left With the right hand and swing the oscillator condenser bail ih with the left hand until the point is reached in the turning of the potentiometer where the whistles cease. Set the loop condenser at 70 and swing the oscillator condenser slowly through Its scale. Signals should be heard, hut jitney are not, get the loop condenser at 30 and swing the oscillator. Practice will familiarize the builder with the tuning of this s.t and it will lie found that once the potentiometer has been set for maximum signal strength on any one station it can be left in that position, as can the rheostat, and all tuning will he done with the two condensers. The loop tuning condenser will be found to be rather broad, the sharpness of a super-heterodyne being almost entirely in the oscillator condenser. If for any reason the Iver does not work at first, or refuses to work later, the following tests will quickly determine when tin error has been made in the wiring or the location of a detective piece of appartus. to Figure •"• it will be noted that the circuit diagram has again bee,, drawn, but this time certain points have been lettered as points to which to conwhen testing. Tests can be made with a single dry cell and a pair of head*' es. The batteries should he disconnected from the receiver when making , ,,f the phone terminals to one side of the dry cell and attach ;i piece of wire to the remaining dry cell terminal so that it will reach to any part of tic set. Touch the end of this i the unconnected phone cord terminal 2 or :; times so that you are accustomed to the click which results. To determine whether the pick-up coil of the oscillator coupler is O. K. touch the wire from the battery to the point nd the phone cord terminal to the plus A battery binding post. This should be done with the rheostat turned clear to the right to maximum. To test the loop co, meet the battery and phones to the points A and G. To test the grid coil of the oscillator coupler connect test terminals to point M and the negative A battery terminal with the filament switch in the "ON" position. To test the plate coil of the oscillator coupler, connect these terminals to the point N and the center B battery binding post. The primaries of the intermediate transformers may be tested by connecting one t( rminal of our test outfit to the plus 90 J; battery binding post and the other to the points C, D or E. To test the secondaries of the first two long wave transformers and the secondary of the filter coupler, connect the test terminals to the plus A battery binding post and points H, I or J. These tests on the secondaries should be made with the potentiometer turned toward the end of the potentiometer to wrhieh the plus A battery bus was connected. To test the upper jack and the primary of the audio frequency transformer connect the test terminals to point P and the plus 45 B battery binding post. The secondary of the audio frequency transformer may be tested by connecting to point L, and the negative side of the C battery. It will be noted by reference to Figure 5, that when any of the pairs of points 1 J Make Your Radio Joy A Sure Thing The quickest way to spend $20 is to accidentally make. a short circuit in a fivetube set. Zip, and your money is gone as well as your fun — until the radio store opens. Kit her style of KANT BLO means protection nst blowing out tubes. Kant-Blo <3* "Lights on any Short Circuit' The KANT-BT,D is not an extra accessory to your igned as a B battery Binding Post or as an A battery filament Switch Style— are at all the best radio stores. If r dealer is out of stock id us' $2 for a KANTBLO Binding Post Style, or $3 for the Switch Style, and we will ship any numof KANT-BLOS direct to you, charges prepaid. Manufactured by GANIO-KRAMER CO.. Inc. New York Sole Distributor! APEX RADIO CO. 503B Fifth Ave. New York mentioned in the foregoing test touched, a complete circuit should result and a click In the phones should be heard. Tf on touching the pairs of points mentioned the click is not heard it indicates either a defective connection to the instrument or a defective piece of apparatus. Even though the se, works and works exceedingly well at first, this should not be taken as the best that can be secured from it. The condenser across the primary of tin filter coupler which is of .0005 m I'd. capacity is very important and it has been found that even when carefully tested by the fixed condenser manufacturers there is likely to be. considerable variation in condensers. If two or three fixed condensers rated at .000!) pifd. are available it would be well to try inserting each of these, one after the other, to determine whether there is any difference in the results considering both yolume and clearness. While UV-201A tubes are not, as a rule, critical as to the amount of grid leak to he inserted iii the grid lead when they are used as detectors, it would be well to try other values than that specified in the grid leak mountings. The tubes will function and function very well with two megohms in use. but since there is varia-i lion in tubes it might be well to try values as lc/w as one megohm and as high as four. The third and final possible change that might be made is the C battery. C batteries are usually constructed with a tap at three volts as well as at the 4%-volt point. Try the 3-volt point and see whether any difference is noted in the clearness of signals. If a friend has a C battery that you can borrow try connecting it in series with the one which you already have, as occasionally a tube is found which requires 6, 7V2 or 9 volts grid bias. -Dealers Need This~ 200% Profit The new FAHNESTOCK Display Case Will stimulate your sales of Fahnestock Radio correct place tor his set. A constant Invitation to are Included. Shows the purchaser instantly the correct piece for his Bet. A constant invitation to buy Fahnestock Products. Dealers are offered 200% profit on each case, an unusual offer on standard merchandise. Price to Dealer $17.50 West of Mississippi 18.50 Transportation prepaid when money order or check accompanies order. Contents Retail for $51.50 Refills will be supplied at the regular 100 lot prices, shown in catalogue, which comes with case, less discount shown on enclosed sheet. Send check or money order, today. FAHNESTOCK ELEC. CO. LONG ISLAND CITY HEW YORK For Low-Loss Receivers Use the Most Efficient Inductances VARIOMETER and VARIOCOUPLER Pat. Pending Pfanstiehl Variometer, P-301 $4.75 Pfanstiehl Variocoupler, P-300 5.00 Pfanstiehl "Three-Circuit" Tuner, P-302...... 5.00 Pfanstiehl Super-heterodyne Oscillator. P-600.... 6.00 Pfanstiehl Coils: List Wave Turns Price Lenoth P-201 25 $ .55 100 340 P-202 35 .59 125 470 P-203 50 .65 170 650 P.204 75 .74 220 960 P-205 100 .90 300-1300 P-206 150 1. 10 470-1980 Pfanstiehl UltraAudion. P-225 95 Pfanstiehl Reinartz 1.75 PFANSTIEHL RADIO CO. Highland Park, 111. Chicago: 1001 W. Washington St. Haymarket 8010 As a last injunction do not be too impartient to get the 3,00Q mile stations. This super-heterodyne will positively work well, even though the wiring is but mediocre and the apparatus is but average quality. It is efficient because it's simple and there is no shielding or other materials put in this set, which while they may cause a theoretical improvement, may also broaden the tuning and decrease the efficiency. The writer does not say that shielding is a bad thing, but as a rule it will be found that shielding is unnecessary and likely to lcrwer the efficiency. The chief point that attracted the attention of Radio Digest was the sharpness and the way it would pull in DX stations through the 9 or 10 locals in and around Chicago. This was not the case on but one model, but proved true with six models which were constructed. Different makes of apparatus were used in these sets, but the general layout and the wiring diagram were the same in all the models. (Radio Digest is preparing a special booklet telling how to build "The Simplest Possible Super-Het," which includes full size panel and baseboard blueprint layouts. This should be ready for distribution by December 10. The cost will be fifty cents. Next week Mr. Ryan will answer a number of questions asked about the super-het. — Editor's Note.) Switch Points Common brass upholstering tacks make good switch points when used on wood panels. It saves time as you do not have to drill the panel, because you can hammer the tacks in the wood panel. If one tack should be misplaced it can easily SPECIAL INTRODUCTORY PRICE For a limited time only, and to introduce this new and superior Storage "B" Radio Battery to the Public, we are selling it for $3.50. Regular RetailPriceis$5.50. Yousave $2.00 byordering \OVf. A. finer battery cannot be built than the World Storage "B" Battery (12 CELLS-24 VOLTS) To tell million homes with Radio Sets— and to countless millions of oroapectlvo buyers-this WORLD Storage "U" Battery brings o new coi.c«i»tion of battery economy ami performance. Here is a battery that pays for itself in a few weekn— will la«t for years and can be recharged at a negligible coat. 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