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I can recall perfectly that through my boyhood and young manhood every merchant and shopkeeper kept on his table what was called a ``bank-note detector, which, when any money was tendered him, he was obliged to consult in order to know, first, whether the bill was a counterfeit, as it frequently was; secondly, whether it was on a solvent bank; and thirdly, if good, what discount should be deducted from the face of it.
See, also, that all of the connections are tight and where you have to cross the wires keep them apart by an inch or so and always cross them at right angles. Adjusting the No. 1 Set The Detector. The first thing to do is to test the detector in order to find out if the point of the contact wire is on a sensitive spot of the crystal. To do this you need a buzzer, a switch and a dry cell.
If you are handy with tools, however, you can buy the galena and make your own detector. It will work with more or less satisfaction. Your next need will be the condenser. The condenser consists of a series of aluminum plates, some of which are movable and the rest stationary. Buy a small variable condenser.
A Simple Vacuum Tube Receiving Set. For this set you should use: a loose coupled tuning coil, a variable condenser, a vacuum tube detector, an A or storage battery giving 6 volts, a B or dry cell battery giving 22-1/2 volts, a rheostat for varying the storage battery current, and a pair of 2,000-ohm head telephone receivers. The Vacuum Tube Detector. With Two Electrodes.
The detector proper is a type of lamp, which gives a blue light at the ordinary intensity of such rays as would come from space or from an ordinary power plant, but gives a red light under strong excitation." "Uh-huh, I get that O. K.," said Seaton. "Rovol's great-great-great-grandfather had 'em I know all about 'em," Seaton encouraged Drasnik, who had paused, with a questioning glance.
"Nope, he's putting it on a tight beam that's fine, we can chase it up," and with a narrow detector beam he traced the invisible transmission beam into the council room. "'Sfunny.
From this you will see that any regenerative set can be used for autodyne, or self-heterodyne, reception. The Separate Heterodyne Receiving Set. The better way, however, is to use a separate vacuum tube for setting up the heterodyne oscillations. The latter then act on the oscillations that are produced by the incoming waves and which energize the grid of the detector tube.
Finally connect one end of the tickler coil of the tuner with the plate of the detector tube and connect the other end of the tickler to one end of the primary coil of the first audio frequency transformer and the other end of it to the wire that connects the two B batteries together.
Now connect one end of the secondary coil, or rotor, of the variocoupler with one post of the .0005 mfd. variable condenser and the other part to the grid of the detector tube. Connect the other end of the rotor of the variocoupler to one of the posts of the first variometer and the other post of this to one of the terminals of the detector filament.
A low exclamation from Craig attracted my attention from Winters. In a corner he had discovered a small box and had opened it. Inside was a dry battery and a most peculiar instrument, something like a little flat telephone transmitter yet attached by wires to earpieces that fitted over the head after the manner of those of a wireless detector.
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