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This consists of: the grid leak; the chopper; the choke coil, and the key. The grid leak is connected in the lead from the grid to the aerial to keep the voltage on the grid at the right potential. It has a resistance of 5000 ohms with a mid-tap at 2500 ohms as shown at C. It costs $2.00. The chopper is simply a rotary interrupter driven by a small motor.
The Filament Voltmeter. To get the best results it is necessary that the voltage of the current which heats the filament be kept at the same value all of the time. For this transmitter a direct current voltmeter reading from 0 to 15 volts is used. It is shown at F and costs $7.50. The Oscillation Choke Coil.
Or in a pinch you can use five standard B batteries to develop the plate voltage, but these will soon run down. But whatever you do, never use a current from a lighting circuit on a tube of any kind that has a rated plate potential of less than 100 volts. The Apparatus You Need.
Heating the Filament with Alternating Current. Where an alternating current power transformer is used to develop the necessary plate voltage a second secondary coil is generally provided for heating the filament of the oscillation tube. This is better than a direct current for it adds to the life of the filament.
The low voltage power supplied by the two flat sides of the ribbon was insufficient to have provided lethal contact, even if the person were there without the insulation of a spacesuit around him, a very unlikely occurrence.
Torreon muttered something and crossed himself. The arms seemed half to rise then suddenly to fall, flabby again. There was a light hiss like an inspiration and expiration of air, a ghastly sound. "Lungs react," muttered Kennedy, "but the heart doesn't. I must increase the voltage." Again he applied the electrodes. The face seemed a different shade of blue, I thought.
To make a spark coil step up the low voltage direct current into high potential alternating current the primary coil is wound with a couple of layers of thick insulated copper wire and the secondary is wound with a thousand, more or less, number of turns with very fine insulated copper wire.
Such a slight difference would not make an appreciable variation in the candle-power of the lamps. The feeders might be operated at any desired percentage of loss that would realize economy in copper, so long as they delivered current to the main conductors at the potential represented by the average voltage of the lamps. Thus the feeders could be made comparatively small in cross-section.
The resistance of a circuit to high-frequency currents is different from that for low voltage direct or alternating currents, as the former do not sink into the conductor to nearly so great an extent; in fact, they stick practically to the surface of it, and hence their flow is opposed to a very much greater extent.
The low voltage secondary coil which heats the filament develops 10.5 volts. This transformer will supply current for one or two 50-watt oscillator tubes and it costs about $40.00. Connecting Up the Apparatus. In time past the most difficult of all electrical apparatus for the amateur to make, install and work was the wireless telephone.
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