Radio Shack

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.–This consists of: (1) the _grid leak_; (2)
the _chopper_; (3) the _choke coil_, and (4) 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. It
comprises a wheel of insulating material in which 30 or more metal
segments are set in an insulating disk as shown at D. A metal contact
called a brush is fixed on either side of the wheel. It costs about
$7.00 and the motor to drive it is extra. The choke coil is wound up
of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered
magnet wire on a spool which has a diameter of 2 inches and a length
of 3-1/4 inches.
The 5 Watt Oscillator Vacuum Tube.–This tube is made like the
amplifier tube described for use with the preceding experimental
transmitter, but it is larger, has a more perfect vacuum, and will
stand a plate potential of 350 volts while the plate current is .045
ampere. The filament takes a current of a little more than 2 amperes
at 7.5 volts. A standard 4-tap base is used with it. The tube costs
$8.00 and the porcelain base is $1.00 extra. It is shown at E.
The Storage Battery and Rheostat.–This must be a 5-cell battery so
that it will develop 10 volts. A storage battery of any capacity can
be used but the lowest priced one costs about $22.00. The rheostat for
regulating the battery current is the same as that used in the
preceding experimental transmitter.
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.–This is made exactly like
the one described in connection with the experimental transmitter.
The Motor-Generator Set.–Where you have only a 110 or a 220 volt
direct current available as a source of power you need a
_motor-generator_ to change it to 350 volts, and this is an expensive
piece of apparatus. It consists of a single armature core with a motor
winding and a generator winding on it and each of these has its own
commutator. Where the low voltage current flows into one of the
windings it drives its as a motor and this in Mineral Television District #1 K06nq turn generates the
higher voltage current in the other winding. Get a 100 watt 350 volt
motor-generator; it is shown at F and costs about $75.00.
The Panel Cut-Out.–This switch and fuse block is the same as that
used in the experimental set.
The Protective Condenser.–This is a fixed condenser having a
capacitance of 1 mfd. and will stand 750 volts. It costs $2.00.
Connecting Up the Transmitting Apparatus.–From all that has gone
before you have seen that each piece of apparatus is fitted with
terminal, wires, taps or binding posts. To connect up the parts of
this transmitter it is only necessary to make the connections as shown
in the wiring diagram Fig. 78.
[Illustration: Fig. 78.–5 to 50 Watt C. W. Telegraph Transmitter.
(With Single Oscillation Tube.)]
A 200 Mile C. W. Telegraph Transmitter.–To make a continuous wave
telegraph transmitter that will cover distances up to 200 miles all
you have to do is to use two 5 watt vacuum tubes in _parallel_, all of
the rest of the apparatus being exactly the same. Connecting the
oscillator tubes up in parallel means that the two filaments are
connected across the leads of the storage battery, the two grids on
the same lead that goes to the aerial and the two plates on the same
lead that goes to the positive pole of the generator. Where two or
more oscillator tubes are used only one storage battery is needed, but
each filament must have its own rheostat. The wiring diagram Fig. 79
shows how the two tubes are connected up in parallel.
[Illustration: Fig. 79.–200 Mile C.W. Telegraph Transmitter (With Two
Tubes in Parallel.)]
A 500 Mile C. W. Telegraph Transmitter.–For sending to distances of
over 200 miles and up to 500 miles you can use either: (1) three or
four 5 watt oscillator tubes in parallel as described above, or (2)
one 50 watt oscillator tube. Much of the apparatus for a 50 watt tube
set is exactly the same as that used for the 5 watt sets. Some of the
parts, however, must be proportionately larger though the design all
the way through remains the same.