Radio Digest (Oct 1923-July 1924)

RADIO DIGEST — Illustrated January 12, IO FOR EVERYBODY .uinued from page 15) -er and the end of the secondary eta a method of connecting the \oellent one. as the pri easily under control by means of the plate variometer. There are at least thirty methods generally in use of connecting: various units btain and control regeneration, but they are all based on the three methods *■ m 1— \vv\yiv '1+1 i • ■ « « • i ' » Figure 6*— A popular circuit which includes both selectivity and easy control of regeneration. and secondary circuits may be • ly coupled for selectivity, the grid it may be tuned to resonance with antenna circuit and regeneration is here described — electromagnetic coupling, capacity coupling or a combination of both. (TO BE CONTINUED.) H. C. COIL CIRCUITS ontinued from page 19) Inductance Comparisons The inductance data furnished in the table result from some tests on a few of Radio Frequency Transformer Radio fans will readily appreciate the distinct advantages possible in using these inductances for air core R. F. transformers. The low internal capacity and low resistance value are two distinct features that »wv\ «^llllp-" IdOOOHM POTENT. Figure 5. these units. The values will be found to be correct within a very close margin. In comparison, then, a 25-turn coil will have an inductance of .06 millihenry or 60 microhenrys. A honeycomb coil of the same number of turns has an inductance of 14 microhenrys. A 50-turn coil is probably a better example of a more often used type; an inductance of this size in the special type is 236 microhenrys, compared to 150 microhenrys in the honeycomb coil type. Due to the lower internal capacity, the wave length range will have a much lower minimum value, while the maximum will vary but slightly. Another interesting feature is the fact that if two 75-turn coils wound with number 24 gauge wire are coupled together, their inductance is as high or even higher, due to the coupling effect, than the 150turn coil, while the resistance of the two coils will be only two-thirds that of the single coil, which has smaller wire. The wave length range measurements are based on tests made with an .0005-mfd. variable condenser across the coils. do much towards insuring their efficiency far beyond the average. An illustration of the application to this purpose is shown in Figure 1. By varying the length of the clip used for mounting the coupling, the distance between the coils can be varied at will. The mounting is such that different size coils can be conveniently interchanged; consequently the circuit will operate over a wide band of wave lengths using values that give the best of efficiency at the desired point. Not merely can this unit be used for Radio frequency transformers, but also for fixed couplers and similar units. Efficient Condensers Much has been said of coil efficiency, but all of this becomes valueless unless the same care and selection is followed for condensers. Their resistance and low minimum capacity values must be carefully taken into consideration. Space is not available for elaboration on condensers in this series, but let it be said that Figure 2 presents a form of variable condenser that is universally known for effi CROSLEY Model ACE 3-B 3 Tube Regenerative set, will operate a loud speaker over a distance of a few thousand miles. sets One of the best made. Beautiful mahogany cabinets. List $50.00 *n nf SPECIAL . .-$44. ID EXPRESS PREPAID NEUTRODYNE Complete Parts for 5 Tube Set, a on ct\ Licensed and Guaranteed t)>«5Z. DU HOME CHARGER Gold Seal, new type battery charger. Alternating current. LIST $18.50. <fc1 C Afi SPECIAL J>10.4U I 1 I iPERFECTION RADIO CORP., 59 Cortland St., N. Y. City g ciency. Losses have been reduced to a minimum, due to Its design and construction, and the minimum capacity value has been decidedly reduced. Three Coil Unit A three coil unit at present on the market, using a very similar form of winding, is shown in Figure 3. This unit is equivalent to a triple honeycomb coil mounting with a better coupling arrangement and using coils that are much better than honeycombs. When mounted in the rear of a panel, two rotating dials vary the coupling distance between the outer and inner coils by means of the geared shafting. Although possibly a little more expensive, the efficiency of the coils and advantages of the units make it well worth the difference in cost. Two Three Coil Circuits Two three coil circuits are shown in The Stars Are Out Price $1.25 THE STAR is a FIXT CRYSTAL DETECTOR for REFLEX OR CRYSTAL SETS. It is a marvel of efficiency and its gold tipped filament is so secured that it may be thrown against a wall without danger of dislocation. Try it with a horn on any good crystal sA and you will have a crystal loud talker, if within five miles of any broadcasting station. Sent on ten days' approval, postage paid, and you pay us when satisfied. All we ask that you send us the name of your dealer with your request. PERPKTrAL GUARANTEE For Reflex and Crystal Sets Star Crystal Company 525 Woodward Avenue, Detroit, Michigan 53 West Jackson Boulevard, Chicago, Illinois Figures 4 and 5. In Figure 4 the coils on the left are both 35-turn coils, while the one on the right is a 75-turn coil. A soft tube is used in conjunction with a 22%-volt B battery. In the second circuit the coils should be 35, 50 and 50 turns, respectively. An 1,800-ohm potentiometer permits a more uniform adjustment of the plate potential, while the variable grid leak insures maximum efficiency of tube operation. Here likewise a soft tube with 22 y2 -volt B battery is recommended. (THE END.) FAHNESTOCK'S LATEST RADIO HELP Antenna Connector Price 10c Snap larger connector over Antenna Wire; insert Lead-in Wire into smaller clip and a perfect connection is the result. At Your Dealers Fahnestock Elec. Co. LONG ISLAND CITY, NEW YORK SAVES YOU ON EVERY TUBE Vacuum tube prices smashed. Radio costs reduced. VOLTRON tubes give perfect reception for a dollar less than other tubes. Satisfaction guaranteed. Money promptly refunded for any imperfect tube. ALL ONE PRICE 50 Type Volts O. H. 12 1% O. H. 501-A 5 O. H. 699 3 B. Battery Amp. Voltages .33 15 to 90 .85 13 to 90 .06 16 to 45 *5! Either from your dealer or send direct C. O. D. Begin saving now — order TODAY! | O. HERSCHKOWITZ, 92 Branford Place, Newark, N, J. 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