1942 ARMY RADIO TRAINING FILM

[Music] from the earliest development of the vacuum - to modern high power transmission with its great water cool - radio has shown constant progress 30 efficient tubes make possible our modern military set these tubes serve in both receiving and transmitting installations high above the earth the pilot keeps in radio communication with units of his squadrons and with his base radio is today playing a major military role on a worldwide front its effective utilization demands an understanding of the scientific principles made use of in the vacuum - some materials such as copper electricity and are known as conductors others glass for example do not readily conduct electricity and are known as insulators a conductor contains a relatively large number of free electrons all of which are constantly in motion when a voltage is applied electrons are forced through a conductor producing current flow the movement of free electrons in a conductor may be accelerated by the application of heat to the substance of which they are apart if the temperature of a metal is increased enough to cause the metal to blow some electrons will gain enough momentum to cause them to break away from the metal they return however due to molecular attraction in many radio tubes the same action takes place when a filament is heated by a current of electricity in the open filament type of tube when the wire filament begins to glow it gives off a cloud of electrons they swarm about the silliman leaving it and returning to it at high velocity although pictured here electrons actually are invisible many modern tubes have an indirectly heated source of electrons the heater made of tungsten wire is surrounded by a thin metal sleeve this sleeve or cathode is coated with oxides of barium and strontium when heated it becomes the source of electrons in the tube here we see the cathode of a tube after the glass bulb and other elements have been removed this oxide coated sleeve or cathode contains the heating element inside the heater is insulated from the sleep the heated cathode with its swarm of electrons is surrounded by a larger tube element called the plate these two parts the cathode and the plate are the principal elements of the diode - all tubes contain these two essential elements 32z twas cathode and plate serve our military transmitting and receiving six all types of radio tubes are designated by definite symbols a circle on the wiring diagram indicates the glass or metal envelope surrounding the two elements in the simplest form of view the filament cathode is represented by an inverted V the plate or anode is designated by a straight bar within the circle this symbol represents a diode our two electoral rectifying to it is equipped with an indirectly heated cathode wires connecting the tube with various parts of the circuit are represented here by straight lines drawn to the several two elements when the cathode of a diode tube is heated by an electric current passing through the heater electrons are driven out from the cathode with the plate uncharged or of minus potential these electrons stay near the cathode or returned to it however of the electrons the electrons being negative rushed to the positive plate at high velocity the electron flow from the cathode is largely controlled by the voltage on the plate some electrons lacking sufficient velocity do not reach the plate this is called space charge the electrons remain between cathode and plates hindering electron flow however increased plateful did your becomes much of the retarding effects of this space charge a strong negative charge on the plate may stop all electron flow vacuum tubes are made in a variety of sizes and corresponding capacities in an experimental circuit the heater of the tube is attached to a storage or a battery the cathode and plate are connected to a B battery so that the plate is positively charged the a battery current heats the cathode which in turn gives off electrons a current flows from cathode to plate and around through the B battery back to the cathode and across to the plate against this is plate current this current may be measured by placing an ammeter in the circuit if we increase the voltage on the plate the ammeter shows an increase in current increasing plate voltage by another step leads to another increase in plate turn however when the plate voltage is made still higher no change is seen inflate curves we have reached the limit of the tube this limit known as saturation is the point which all available electrons are attracted to the place the effect of plate voltage upon the number of electrons reaching the plate may be charged increasing the plate voltage results in an increasing number of electrons or flame currents this increase continues to the saturation the diode - furnishes direct current in many radio installations if an alternator is attached to the plate of the cathode of a diode - the plate will be charged first positive and then negative a rectified current results electrons are attracted from the cathode to the plate and not in the opposite direction the resulting plate current is direct current in such a circuit the current flowing from the plate is a pulsating current flowing when the plate is positive stopping when it is negative thus the diode tube may be used to supply direct pulsating curve when an alternating voltage is applied in a circuit having one or more resistances the current through the resistance is alternating the output voltage is also alternating if a crystal rectifier is substituted for the resistance only half of each wave can pass the output current and voltage are positive the diode tube is a rectifier in the circuit it results in waves of pulsating current and voltage electrons pass through the plate only during the positive half of the way a diode tube may be connected through a transformer to an alternating current line the plate is connected to one of the secondary windings the other end of which is led through a resistance to the cathode or filament of the tube the filament or heater is connected to another secondary winding of the transformer the tube is a part of two complete circuits the filament circuit and the plate circuit the external plate circuit extends from plate around to the filament with such a circuit in action electrons rush in the upper or filament circuit in first one direction and then the other the electrons in the plate circuit moved to the plate only when it is positive a unidirectional pulsating current flows in the plate circuit and a pulsating voltage drop appears across the resistor for full wave rectification a duo diode tube is use this tube in emissions of having heater and cathode or filaments is equipped with two plates in every other way this tube is similar to the diode - for full wave rectification the duo diode tube is attached to a transformer in much the same way as one's desires the two plates are attached to one of the transformer windings either plate of the tube is part of a circuit extending through a portion of one of the transformer windings out through a center tap and around to the filament let us illustrate the flow of electrons in these circuits first one plate of the tube is made positive and then the other the electrons always flowing to the positive place both halves of the cycles of applied voltage are utilized by the full wave rectifier in making a unidirectional current this direct current varies but is not interrupted the variations are known as ripple the voltage wave resulting from the voltage drop across the resistor is also a varying wave but not interrupted as in the case of the half wave rectifier filters are usually employed in both the half wave and full wave rectifiers to remove the voltage variation this filter is not shown in this circuit the principles that have been illustrated by the diode and duo diode tubes are basic and are incorporated in tubes of a wide variety of sizes and types simple tools multi-purpose to rugged transmitter tubes of great power small to giving to our military receiving sets they're great sensitivity the vacuum tube is the heart of every radio installation is back of every wave radiating from or to an antenna [Music]