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None of these coils is variable; all are wound to receive waves up to 360 meters in length when used with a variable condenser of .001 mfd. capacitance. In other words you slide the coils in and out to get the right amount of coupling and you tune by adjusting the variable condenser to get the exact wave length you want. With Compact Coils.
It has a diameter of 6-1/4 inches, a height of 7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00. The Aerial Condenser. This condenser is made up of three fixed condensers of different capacitances, namely .0003, .0004 and .0005 mfd., and these are made to stand a potential of 7500 volts.
Now connect the end of the tuning coil that leads to the ammeter with one end of the .001 mfd. grid condenser and the other end of this with the grid of the vacuum tube. Connect the telegraph key, the buzzer and the dry cell in series and then shunt them around the grid condenser.
This is the same kind of a hot-wire ammeter already described in connection with the experimental set, but it reads to 5 amperes. The Grid and Blocking Condensers. Each of these is a fixed condenser of .002 mfd. capacitance and is rated to stand 3,000 volts. It is made like the aerial condenser but has only two terminals. It costs $2.00. The Key Circuit Apparatus.
All of the apparatus for this C. W. telegraph transmitting set is the same as that described for the 100 and 200 mile sets but you will need: one or two 50 watt oscillator tubes with sockets; one key condenser that has a capacitance of 1 mfd., and a rated potential of 1,750 volts; one 0 to 500 milli-ammeter; one aerial ammeter reading to 5 amperes, and an A. C. power transformer for one or two 50 watt tubes.
Now connect one end of the secondary coil to one post of a .001 mfd. variable condenser and the other end of the secondary to the other post of the condenser. Shunt 1/2 to 2 megohm grid leak resistance around the fixed condenser and then connect the second post of the variable condenser to one terminal of the detector tube filament.
Now connect one end of the secondary coil, or rotor, to one post of a .0007 mfd. variable condenser, the other post of this to one end of the grid coil and the other end of this with the remaining end of the rotor of the variocoupler.
They have a capacitance of 1 mfd. and will stand 750 volts. These condensers cost about $2.00 each. The Filter Reactance Coil. It consists of a coil of wire wound on a soft iron core and has a large inductance, hence the capacitance of the filter condensers are proportionately smaller than where a small inductance is used which has been the general practice.
Shunt the potentiometer around the A battery and connect the sliding contact with the or zinc pole of the B battery and the + or carbon pole with one terminal of the headphone; connect the other terminal to one of the posts of the variometer and the other post of the variometer to the plate of the detector. Finally shunt a .001 mfd. fixed condenser around the headphones.
Intermediate Wave Set With Loading Coils. For this intermediate wave set you can use either of the short-wave sets described in the foregoing chapter. Approximate Wave Length in Meters in Millihenries Inductance .001 mfd. Variable Mounted Appx. Air Condenser. on Plug These and other kinds of compact coils can be bought at electrical supply houses that sell wireless goods.
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