The Plate and Grid Circuit Reactance Coils.--Where a single tube is used as an oscillator and a second tube is employed as a modulator, a reactor, which is a coil of wire wound on an iron core, is used in the plate circuit to keep the high voltage direct current of the motor-generator the same at all times. Likewise the grid circuit reactor is used to keep the voltage of the grid at a constant value. These reactors are made alike and a picture of one of them is shown in Fig. 91 and each one will cost you $5.75.
Connecting up the Apparatus.--All of the different pieces of apparatus are connected up as shown in Fig. 89. One of the ends of the secondary of the induction coil, or the microphone transformer, or the magnetic modulator is connected to the grid circuit and the other end to clip 3 of the tuning coil.
A 100 to 200 Mile Wireless Telephone Transmitter--With Direct Current Motor Generator.--By using the same connections shown in the wiring diagrams in Fig. 89 and a single 50 watt oscillator tube your transmitter will then have a range of 100 miles or so, while if you connect up the apparatus as shown in Fig. 90 and use two 50 watt tubes you can work up to 200 miles. Much of the apparatus for a 50 watt oscillator set where either one or two tubes are used is of the same size and design as that just described for the 5 watt oscillator sets, but, as in the C. W. telegraph sets, some of the parts must be proportionately larger. The required parts are (1) the 50 watt tube; (2) the grid leak resistance; (3) the filament rheostat; (4) the filament storage battery; and (5) the magnetic modulator. All of these parts, except the latter, are described in detail under the heading of a 500 Mile C. W. Telegraph Transmitting Set in [Chapter XVI], and are also pictured in that chapter.
It is not advisable to use an induction coil for the modulator for this set, but use, instead, either a telephone transformer, or better, a magnetic modulator of the second size which has an output of from 1-1/2 to 3-1/2 amperes. The magnetic modulator is described and pictured in this chapter.
A 50 to 100 Mile Wireless Telephone Transmitting Set--With 110 Volt Alternating Current.--If you have a 110 volt [Footnote: Alternating current for lighting purposes ranges from 102.5 volts to 115 volts, so we take the median and call it 110 volts.] alternating current available you can use it for the initial source of energy for your wireless telephone transmitter. The chief difference between a wireless telephone transmitting set that uses an alternating current and one that uses a direct current is that: (1) a power transformer is used for stepping up the voltage instead of a motor-generator, and (2) a vacuum tube rectifier must be used to convert the alternating current into direct current.
The Apparatus You Need.--For this telephone transmitting set you need: (1) one aerial ammeter; (2) one tuning coil; (3) one telephone modulator; (4) one aerial series condenser; (5) one 4 cell dry battery or a 6 volt storage battery; (6) one microphone transmitter; (7) one battery switch; (8) one grid condenser; (9) one grid leak; (10) two 5 watt oscillator tubes with sockets; (11) one blocking condenser; (12) one oscillation choke coil; (13) two filter condensers; (14) one filter reactance coil; (15) an alternating current power transformer, and (16) two 20 watt rectifier vacuum tubes.
All of the above pieces of apparatus are the same as those described for the 100 Mile C. W. Telegraph Transmitter in Chapter XVII, except: (a) the microphone modulator; (b) the microphone transmitter and (c) the dry or storage battery, all of which are described in this chapter; and the new parts which are: (d) the rectifier vacuum tubes; (e) the filter condensers; and (f) the filter reactance coil; further and finally, the power transformer has a third secondary coil on it and it is this that feeds the alternating current to the rectifier tubes, which in turn converts it into a pulsating direct current.
The Vacuum Tube Rectifier.--This rectifier has two electrodes, that is, it has a filament and a plate like the original vacuum tube detector, The smallest size rectifier tube requires a plate potential of 550 volts which is developed by one of the secondary coils of the power transformer. The filament terminal takes a current of 7.5 volts and this is supplied by another secondary coil of the transformer. This rectifier tube delivers a direct current of 20 watts at 350 volts. It looks exactly like the 5 watt oscillator tube which is pictured at E in Fig. 77. The price is $7.50.
The Filter Condensers.--These condensers are used in connection with the reactance coil to smooth out the pulsating direct current after it has passed through the rectifier tube. They have a capacitance of 1 mfd. and will stand 750 volts. These condensers cost about $2.00 each.