12 2-20. Which of the following is an advantage that an oilcan tube has over a lighthouse tube?   1.    The oilcan tube is smaller   2.    The oilcan tube has no filaments   3.    The oilcan tube can handle more power   4.    The oilcan tube can operate at hf and uhf frequencies 2-21. The plate potential at which ionization occurs is known as the ionization point. Which of the following is also a name for this process?   1.    Firing potential   2.    Saturation potential   3.    Extinction potential   4.    Deionization potential 2-22. What name is given to the value of plate voltage at which ionization stops?   1.    Firing potential   2.    Saturation potential   3.    Extinction potential   4.    High plate potential 2-23. When a gas-filled triode ionizes, the grid loses control and the tube then functions as what type of tube?   1.    Diode   2.    Triode   3.    Duo-diode   4.    Trigatron 2-24. After the gas-filled triode ionizes and the grid loses control, which of the following methods is used to stop the conduction of the tube?   1.    Increasing the plate potential   2.    Increasing the grid potential   3.    Removing the plate potential   4.    Removing the grid potential 2-25. What is the name given to the gas-filled triode?   1.    Variable triode 2.    Trigatron   3.    Thyristor   4.    Thyratron 2-26. For what minimum amount of time must the filaments of a mercury-vapor tube have voltage applied before the plate voltage is applied to the tube?   1.    0.5 minute   2.    1.5 minutes   3.    2.5 minutes   4.    3.0 minutes 2-27. Which of the following conditions is/are responsible for the soft, blue glow of the gas-filled triode?   1.    The tube is operating normally   2.    The tube is gassy   3.    The tube is saturated   4.    The tube is ionized   2-28. Which of the following types of tubes is normally used as a voltage regulator?   1.    Gas-filled triode   2.    Gas-filled diode   3.    Cold cathode   4.    Cold plate 2-29. For a cold-cathode tube, how does the voltage regulator maintain a constant voltage drop across the tube?   1.    By changing the current flow of the tube   2.    By changing the resistance of the tube as current flow varies   3.    By changing the plate potential of the tube as current varies   4.    By changing the source voltage of the tube