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Simple Bulb Transmitters
325
that the experience of building even an unsuccessful rectifier is well worth the cost. If the experimenter is at present transmitting on a small B battery radiophone, such as has been previously described, he is advised to adapt it to electrolytic rectification, following out the
FIG. 5
principles demonstrated in applying this system to the originally direct-current Colpitts circuit. Indeed, it would be well to construct especially, a 5-watt set of simplified design, in order to become familiar with the characteristics of rectified operation, before attempting to build more complex apparatus.
AN EXPERIMENTAL 5-WATT SET
SUCH an installation is indicated diagrammatically in Fig. 6, and the cost of the various parts should not total more than twenty-five dollars! The apparatus has been
boiled down to essentials, and the set is operated altogether from power supplied by a single A. C. lamp socket.
Excepting for the rheostat, microphone, bulb, socket, the ^ooo-ohm grid-leak, Cj, C4 and C5, the set is home-made. If the amateur has facilities for the construction of any of these items, the cost of the set will be still further reduced. Inductance Li is wound with 40 turns of any convenient insulated wire under No. 22 and tapped every fourth turn. L2 is a single turn of wire wound over Li. Ci is a fixed capacity of three to eight plates (to be determined by experiment) of one by 3-inch tinfoil (two square inches active area) separated by mica. Gz is similar to Ci, using however, only two or three plates. X has already been described, and 03 may vary from two to ten microfarads, the higher capacities being desirable. C4 and C<=, will probably cost the experimenter nothing, but in advent of his inability to obtain the spark-coil vibrator condensers, telephone shunt capacities of .002 5 mfd . , used for receiving purposes, may be substituted. The only variation in the rectification transformer from that designed for the Heising modulation set exists in the secondary S, which is wound to 2500 turns, a reduction that permits the cutting down of the rectifier to sixteen jars. A radiation ammeter should be borrowed for tuning the set.
Tuning and operating is done as suggested for the D. C. installation in the January RADIO BROADCAST.
110 VOLTS
TRANSF.
FIG. 6 Diagram of a 5-watt set, operated by power from a single A. C. lamp socket