How can a sheet of copper be made to emit electrons thermionically?
By heating it.
Why do electrons cross the gap in a vacuum tube?
Because the negatively charged electrons are attracted to the positively charged plate.
Name the two series circuits that exist in a diode circuit.
Filament and plate.
Before a diode will conduct, the cathode must be what polarity relative to the plate?
An ac voltage is applied across a diode. The tube will conduct when what alternation of ac is applied to the plate?
What would be the output of the circuit described in question 5?
Besides tungsten, what other materials are used for cathodes in vacuum tubes?
Thoriated-tungsten and oxide-coated metals.
What is the advantage of directly heated cathodes?
They reach operating temperatures quickly.
Name two functions of the base of a vacuum tube.
It serves as a mounting for the tube elements and as the terminal connection to the circuit.
Vacuum tubes are designed to operate in what portion of the Ep - Ip curve?
The linear portion.
What value can be calculated from the values found on an Ep - Ip curve?
Plate resistant Rp.
A large negative voltage is applied to the plate of a diode, and a large positive voltage is applied to the cathode. If the tube conducts, what tube parameter has been exceeded?
Peak Inverse Voltage (PIV).
What is the primary difference between a diode and a triode?
The triode contains a third element called the control rid.
Why does the grid have a greater effect than the plate on electron flow through a vacuum tube?
Because it is closer to the cathode.
What component is used in a triode amplifier to convert variation in current flow to voltage variation?
A plate load resistor RL
Why is the control grid of a triode amplifier negatively biased?
To prevent them from drawing grid current.
For a circuit to be considered to be in the quiescent condition, what normal operating voltage must be zero?
The input signal
What type of bias requires constant current flow through the cathode circuit of a triode?
When a circuit uses cathode biasing, the input signal can cause variations in the biasing level. How is this problem eliminated?
Through the use of a bypass capacitor
In a circuit using grid-leak biasing, the coupling capacitor (Cc) charges through a low resistance path. What resistance is used in this charge path?
rkg, the cathode to grid resistance.
Grid-leak biasing in effect rectifies the input ac signal. What feature of the circuit is used to accomplish this rectification?
Unequal charge and discharge paths of the coupling capacitor Cc.
Match each amplifier characteristic listed below with its class of amplification. (a.) Current flows through the tube for one-half cycle. (b.) Current flows through the tube for less than one-half cycle. (c.) Current flows through the tube for the entire cycle.
(a.) Class B.
(b.) Class C
(c.) Class A.
The plate voltage of a tube will vary 126 volts when a 3-volt ac signal is applied to the control grid. What is the gain of this tube?
If the mu of a tube is 85 and the signal at the control grid is 4 volts ac, the plate voltage will vary by what amount?
Transconductance is a measure of the relationship between what two factors?
The changes in plate current and grid voltage.
A tube has a transconductance of 800 mhos and a load resistor of 50 kohms. When control grid voltage varies by 6 volts, the plate voltage will vary by what amount?
How does the addition of a screen grid in a tetrode reduce interelectrode capacitance?
The interelectrode capacitance (cpg) is divided between two series capacitances; thus, cpg is greatly reduced.
What undesirable effect does the screen grid in a tetrode create?
Secondary emission, and noise.
The suppressor grid is added to a tetrode to reduce what undesirable characteristic of tetrode operation?
Name the elements of a vacuum tube and their potentials relative to dc ground.
Suppressor grid, negative.
Cathode, can be negative, positive, or at dc ground potential, depending on biasing type.