Radio mirror (Jan-Oct 1923)

<>< tol» r 6, 1923 K A I) I O 1)1 G EST Illustrated Reflex Circuit Works on Loop or Aerial Aerial Hook-Up Is Combination of Several Types By Dr. S. L. Kalinowski OUT of the many different types of receiving: sets the writer selected the reflex circuit for experimentation. After almost a month of this work the following hook-up was found to give best results: Beginning with the aerial, there is a 43 plate vernier condenser, A, of .001 mfd. capacity in series with the aerial and the primary of the variocoupler. M, the latter being of the ordinary type, having five taps of units to the aerial and rive taps of tens to the ground. Across the secondary, or the rotor of the variocoupler, is a 23 plate vernier condenser. B, of .0005 mfd. capacity. Between the secondary of the variocoupler and the 23 plate condenser a double circuit jack, J. is placed for the use of a loop aerial, the plugging in of which cuts out the large or outdoor aerial, the 43 plate condenser. variocoupler and ground. By using the outdoor aerial, the writer has obtained better results than with the loop, which was of the 3 foot square type with 13 turns wound solenoid fashion. The fixed condensers, C, .002 mfd.; D, .001 mfd., and E, .001 mfd., are mica type and must have correctly fixed and tested capacities, as they are very important, being the means of properly balancing the circuit, remembering that both Radio and audio frequencies are present. Also make sure that the 43 plate and 23 plate variable condensers have the proper capacities, as often they do not come up to their rating. The vernier condensers are also used separately. Several transformers were tried in the Radio frequency circuit, and nearly all of them worked well. Transformer, Amplifier and Wiring The Radio transformer in the diagram is marked G. Any good transformer will do well, and if the reader has one at hand and intends to build a reflex set, it will be best for him to try the one he has on hand. In the audio frequency, H, a ratio of three to one or four to one works best. Higher ratio transformers were tried, but the lower ratios proved better. The filament rheostat has a vernier, and is of the 6 ohm resistance type, to which a 25 ohm radio resistance unit is attached for the purpose of controlling the % ampere vacuum tubes if used. The filament rheostat, L, and its vernier are very important in the control of the filament current, as proper filament control not only adds to the life of the tube, but also aids greatly in tuning. It is not necessary to do away with the rheostat that one may have of the 6 ohm type if the % ampere tube is to be used, because a 25 ohm resistance unit may be attached to it to increase the resistance to about 30 ohms. The vacuum tube, K, is an amplifier. Any amplifying tube taking a voltage from 4 5 to 67J4 or more on the plate will do. "When the set is not in use, the current from the six volt battery is cut off by means of a switch, Q, while the plate voltage is controlled by means of switch points and lever, one of the points being dead and serving to cut off the B battery voltage. The minus binding posts on the B battery are connected to the contact points, Tuning In with Loop and Outdoor Aerials Tuning is not as difficult as some writers say it is. The outfit is critical and very sensitive, as has been found during experimentation and even more so when the set is completed. When the large or outdoor aerial is used, tuning is done by | 1 • ! 1 ! i ' ' — i' i ! l.^'J \LOOP while the lever which sweeps over these points is connected to the minus post of the A battery. The plus binding post on the B battery leads to the phones or loud speaker. The A and B batteries and their outputs are also controlled by a potentiometer, F, having a resistance of 200 ohms. Any crystal detector, I, will serve its purpose in this circuit. No advantage is gained by using a vacuum tube as a detector, at least none were noticed. All the wiring is bus bar insulated by tubing and as short as possible. The panel is 10 by 20 by 3/16 inch of hard fiber. (The writer uses all hard fiber panels in his experimental work prior to mounting a definitely -decided hook-up on bakelite.) B-BATTE/ZY 4-ST°67/i.\/OLTS means of the variocoupler and the 43 plate and 23 plate condensers. The crystal detector is adjusted to a very sensitive spot, and when the signal or broadcast YouDon'tNeed Tllllft!Eto get out of town. If you * •*M^awant new stations on your crystal set WRITE ME TODAY. Mine works 400 to 1,000 miles without tubes or batteries ! Thousands have bought my plans and now get results like mine. CHANGES OFTEN COST LESS THAN A DOLLAR. Send self-addressed envelope for further information. Leon Lambert, SOI South Volutsia, Wichita. Kansas. comes in, adjust by means of the variocoupler rotor, verniers, rheostat, potentiometer and B battery. When a small loop or indoor aerial is used it is plugged in by means of a plug into the jack, J, thus cutting out the variocoupler, 43 plate condenser and large aerial and ground, Tuning is done by rotating the loop aerial Into proper position, and by means of the 23 plate condenser. Clearing up for loudness and clearness is accomplished the same way as before. Distance, Clearness and Sharpness There are no claims as to originality or any great improvement for this outfit as it is merely something that other men have done, but I may say that of all the different hook-ups I have tried the reflex circuit is my first choice. For instance, clearness and sharpness is of the first order. On it Atlanta, Davenport, Chicago, Schenectady and other stations have been received. In combination with a Magnavox and a one tube power amplifier this one tube reflex is heard all over a three story building as clear as a bell, without hums, hisses or knocks. A hook-up of the outfit accompanies this article and anybody wishing to construct one like it will surely feel well paid for his trouble. Try it and judge for yourself. A beginner should learn the operation of a simple Radio set first before attempting complicated hook-ups. GENUINE EDISON ELEMENTS (new) (or making "B" Batteries, obtained from U. S. Government. A positive and negative element — 6c; glass tube— 3c; all other parts at reasonable prices. Postage, etc., 50c extra per order. Free instructions. TODD ELECTRIC COMPANY, 109 West 23rd Street, New York. — Of special interest to Radio Dealers! One of Chicago's oldest and largest exclusive radio stores sold more MuRad Receiving Sets in 1922-23 than all other types of Receivers combined ! Mu-Rad sells — and sells! 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