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The smallest size coils cost about $1.50 apiece and the mounting costs about $6 or $7 each. The A Battery Potentiometer. This device is simply a resistance like the rheostat described in connection with the preceding vacuum tube receiving sets but it is wound to 200 or 300 ohms resistance as against 1-1/2 to 6 ohms of the rheostat. It is, however, used as well as the rheostat.
If you are a beginner in wireless you will hear those who are experienced speak of a telephone receiver as having a resistance of 75 ohms, 1,000 ohms, 2,000 or 3,000 ohms, as the case may be; from this you will gather that the higher the resistance of the wire on the magnets the more sensitive the receiver is.
It has the same resistance, namely 5,000 ohms as the one used with the 5 watt tube transmitter, but it is a little larger. It is listed at $1.65. The Oscillation Choke Coil. The choke coil in the power circuit is made of about 260 turns of No. 30 B. & S. cotton covered magnet wire wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long. The Filament Rheostat.
If you are a beginner in wireless you will hear those who are experienced speak of a telephone receiver as having a resistance of 75 ohms, 1,000 ohms, 2,000 or 3,000 ohms, as the case may be; from this you will gather that the higher the resistance of the wire on the magnets the more sensitive the receiver is.
This coil usually has a resistance of about 75 ohms and the meaning of the ohmic resistance of a receiver and its bearing on the sensitiveness of it will be explained a little farther along. How a Wireless Headphone Is Made. For wireless work a receiver of the watch-case type is used and nearly always two such receivers are connected with a headband.
A single receiver can be used but a pair of receivers connected with a head-band gives far better results. Then again the higher the resistance of the receivers the more sensitive they often are and those wound to as high a resistance as 3,200 ohms are made for use with the best sets.
If the same wire be coiled in such a manner that but one-quarter of its surface radiates, its temperature will be increased four times with the same battery, or, one-quarter of this battery will bring it to the temperature of straight wire. Or the same given battery will bring a wire whose total resistance is 4 ohms to the same temperature as straight wire. "This was actually determined by trial.
It consists of a primary coil of No. 20 B. and S. gauge cotton covered magnet wire wound on a core of soft iron wires while around the primary coil is wound a secondary coil of No. 30 magnet wire. Get a standard telephone induction coil that has a resistance of 500 or 750 ohms and this will cost you a couple of dollars. The Microphone Transformer.
Let ten or fifteen ohms of any convenient-sized wire be wound upon the bend of a commercial U-magnet. Let this wire be connected to a telephone in its circuit. When the magnet is made to sound like a tuning-fork, the pitch will be reproduced in the telephone very loudly.
"Would you be so kind as tell me, sir, what's a ohm?" said the worthy Mr. Stiggins to me the other day. "It's a modern term used in electricity, which I am too ignorant to explain to you." He looked full at me for more than five seconds without a word then he said, "I'm thinking that this man was a fool to talk about ohms when not even you knew what a ohm means.
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