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Show (Edited by G. Douglas Wardrop, Editor of Radio Merchandising.) .. By G. L. INGRAHAM One of the unfortunate characteristics character-istics of a radio fan is his never-ending search for "the set." In conducting conduct-ing this search he tries many hookups, both freak and standard, and Invariably Invari-ably ends up by using one of the old standbys, such as the t'nree honeycomb honey-comb or the two variometer set. Still even then they are constantly being Improved by the fan, and it seems to be the chief desire of most fans to add a stage of radio frequency to J J fcjfrat$ing Condenser -a - o i r&i. Circuit Diagram to Be Used to Wire Up Amplifier Unit. their sets as soon as a good hookup for same can be found. To satisfy these radio frequency fans this simple amplifier that can' be added to any three honeycomb coil set is offered. The parts needed for the set are few and the results obtained ob-tained from the set are very good as to selectivity and distance reception. Stability of operation is one of its main selling points, so to speak. The parts necessary besides a three honeycomb coil tuner are one amplifier tube, socket and rheostat to fit tube used, one .0005 mfd. variable vari-able condenser, one 75-turn honeycomb honey-comb coil and one 100-turn honeycomb coll, one neutralizing condenser, a panel 7 by 10 inches and a baseboard. For the Amplifier. This circuit diagram is given In Fig. 1. This is the diagram for the amplifier, ampli-fier, while the circuit given in Fig. 2 is the diagram for the complete circuit amplifier and three honeycomb coil tuner. The circuit given in Fig. 1 is the circuit diagram that should be used to wire up the amplifier unit on the 7 by 10-lnch panel. Before preparing the panel the two honeycomb coils should be tapped in two places. The first tap is approximately approx-imately on the twenty-fifth turn, and the second tap at approximately the fifteenth turn. To do this take a turn that seems to be about one-third up from the inside of the coil and pull it out with a knife blade. Then scrape the Insulation from this turn at the point where it protrudes from the coil. The 50-turn tap is .prepared in the same manner. The 100-turn coil is tapped in the center. To find the exact center of this coil will be rather hard, and it Is therefore suggested that two taps are brought out, one each side of the coil at approximately the fiftieth turn. The correct one can then be found by test when the set is operating. The 75-turn coll is the aerial tuning inductance for the radio frequency amplifier. The two taps and the end fj?2. Complete Circuit Amplifier and Honeycomb Honey-comb Coil Tuner. of the coil are connected to the switch points on the panel and the Inside end of the coil Is connected directly to the aerial. The switch lever is connected to the ground, as shown in the diagram. dia-gram. On the rigiit-hnnd edge of the amplifier am-plifier panel three binding posts, are placed. One of these is connected to the plate, one to the "U" battery and one to the neutralising condenser. The battery binding posts should he brought out on the baseboard, the aerial and ground binding posts being at the left-'nand end of the panel. Switch May Be Added. In the three honeycomb coil receiver receiv-er a switch may be placed in the set to disconnect tne primary condenser when the radio frequency amplifier is in use or the condenser may be shortcircuited by a piece of wire when using the amplifier. Whichever Is done, remember that it is necessary to cut the primary condenser out of the circuit when using the amplifier. When the radio frequency amplifier Tins been wired up according to the diagram in Fig. 1. to test it, it should be connected to the throe honeycomb coil set by connecting the binding bind-ing posts on the amplifier that f.re Conner-red to the plate and the n-i-tralizing condensor 1o the aerial a::d ground posts of the three honeycomb coil set. The "I!" battery posts of file amplifier should be connected to a piece of flexible wire. Then the 1 1""-turn coil that was tapped in the rvnter is put in place of the cr.;l generally gen-erally user as the primary coil in the honeycomb coil tuner. The secondary and tickler coils are left on the tuner, -the same values being used with the amplifier as without with-out The flexible lead from the "B" battery post on the amplifier Is then connected to the center tap on the 100-turn coil. Light the radio frequency fre-quency amplifier tube and the detector tube. Cause the detector tube to oscillate os-cillate and set the secondary condenser conden-ser at about the setting generally used for whatever station is on the air at the time of testing. Then tune the aerial circuit with the taps and the 23-plate condenser. Adjust Neutralizing Condenser. When a whistle is picked up tune in the station and then adjust the neutralizing condenser until the radio frequency amplifier does not oscillate. Tne best method of doing that is to move the neutralizing condenser's brass or nickel-plated tube back and forth until a point is found wherein the tuning of a station is smooth and not by clicks. That Is when the aerial tuning condenser con-denser can be tuned past a station setting, set-ting, when the station Is tuned In on the detector tube without clicks being heard in the phones, then the tube is neutralized. If it is found that the tubss do not seem to neutralize perfectly shift the flexible lead to another tap and try again. If the four taps do not allow neutralization it will be necessary neces-sary to make new ones, though this will not be necessary in most cases. New York Sun. |