NEETS MODULE 6 CHAPTER 1 INTRODUCTION TO ELECTRON TUBES
Q1. How can a sheet of copper be made to emit electrons thermionically?
Q2. Why do electrons cross the gap in a vacuum tube?
Q3. Name the two series circuits that exist in a diode circuit.
Q4. Before a diode will conduct, the cathode must be what polarity relative to the plate?
Q5. An ac voltage is applied across a diode. The tube will conduct when what alternation of ac isapplied to the plate?
Q6. What would be the output of the circuit described in question 5?
Q7. Besides tungsten, what other materials are used for cathodes in vacuum tubes?
Q8. What is the advantage of directly heated cathodes?
Q9. Name two functions of the base of a vacuum tube
Q10. Vacuum tubes are designed to operate in what portion of the Ep - Ip curve?
Q11. What value can be calculated from the values found on an Ep - Ip curve?
Q12. A large negative voltage is applied to the plate of a diode, and a large positive voltage isapplied to the cathode. If the tube conducts, what tube parameter has been exceeded?
Q13. What is the primary difference between a diode and a triode?
Q14. Why does the grid have a greater effect than the plate on electron flow through a vacuum tube?
Q15. What component is used in a triode amplifier to convert variation in current flow to voltagevariation?
Q16. Why is the control grid of a triode amplifier negatively biased?
Q17. For a circuit to be considered to be in the quiescent condition, what normal operating voltagemust be zero?
Q18. A triode amplifier similar to the one shown in figure 1-19 has an Ebb -350 volts dc. The plateloadresistor is 50 N 8QGHUTXLHVFHQWFRQGLWLRQVPLOOLDPSHUHVRIFXUUHQWFRQGXFWVthrough the tube. What will be the plate voltage (Ep) under quiescent conditions?
Q19. A 2-volt, peak-to-peak, ac input signal is applied to the input of the circuit described in Q18.When the signal is at its maximum positive value, 2.5 milliamperes flows through the tube.When the input is at its maximum negative value, conduction through the tube decreases to .5milliamperes.a. What is the peak-to-peak voltage of the output signal?
Q19 b. What is the phase relationship between the input and output signals?
Q20. The waveforms shown below are the input and output of an overdriven triode
Q21. What type of bias requires constant current flow through the cathode circuit of a triode?
Q22. When a circuit uses cathode biasing, the input signal can cause variations in the biasing levelHow is this problem eliminated?
Q23. In a circuit using grid-leak biasing, the coupling capacitor (Cc) charges through a lowresistance path. What resistance is used in this charge path?
Q24. Grid-leak biasing in effect rectifies the input ac signal. What feature of the circuit is used to accomplish this rectification?
Q25. 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.
Q26. The plate voltage of a tube will vary 126 volts when a 3-volt ac signal is applied to the controlgrid. What is the gain of this tube?
Q27. If the mu of a tube is 85 and the signal at the control grid is 4 volts ac, the plate voltage willvary by what amount?
Q28. Transconductance is a measure of the relationship between what two factors?
Q29. A tube has a transconductance of 800 mhos and a load resistor of 50 kohms. When control gridvoltage varies by 6 volts, the plate voltage will vary by what amount?
Q30. How does the addition of a screen grid in a tetrode reduce interelectrode capacitance?
Q31. What undesirable effect does the screen grid in a tetrode create?
Q32. The suppressor grid is added to a tetrode to reduce what undesirable characteristic of tetrodeoperation?
Q33. On the diagram below, name the elements of the vacuum tube and their potentials relative to dcground.
NEETS MODULE 6
Q1. What is the major difference in grid construction between power pentodes and conventionalpentodes?
Q2. Beam-forming tubes and power tubes are similar except that power pentodes lack what element?
Q3. What effect does the shielding of the screen grid by the control grid have on plate current inbeam-forming tetrodes?
Q4. What effect does a large negative input signal applied to a variable-mu tube have on a. conduction through the control grid, and b. gain of the tube?
Q5. Identify the type of electron tube(s) that would be most suitable for the following applications.a. Power amplifier b. Voltage amplifier with small signal inputs c. Low distortion amplifiers for use with large signal inputs
Q6. What effect does transit time have on a conventional triode operated at uhf frequencies?
Q7. How do uhf tubes counter the effects of transit time?
Q8. Why can acorn and doorknob tubes NOT handle large amounts of power?
Q9. What type of uhf tube was developed to handle large amounts of power?
Q10. What are two advantages that gas-filled tubes have over conventional electron tubes?
Q11. Once ionization has occurred in a thyratron, what control does the control grid have over the tube’s operation?
Q12. What precautions should be exercised when using mercury-vapor thyratrons?
Q13. Cold-cathode tubes can be used as voltage regulators because of what characteristic?
Q14. What is the unique ability of the CRT?
Q15. What are the three main parts of CRT?
Q16. What term is used for the ability of a spot on a CRT screen to continue to glow after the electronbean has struck it and moved away?
Q17. The electron beam in a CRT is made to sweep from left to right across the screen. What tubeelement causes this sweeping motion?
Q18. In applications where electronic waveforms are displayed on a CRT screen, the input signal is normally applied to what CRT element?
NEETS MODULE 6 CHAPTER 3 POWER SUPPLIES
Q1. What are the four basic sections to a power supply?
Q2. What is the purpose of the regulator?
Q3. What are the purposes of the transformer in a power supply?
Q4. For what are the low voltage windings in a transformer used?
Q5. For what is the center tap on a transformer used?
Q6. Does a rectifier tube conduct on the positive or negative alternation of the input signal?
Q7. What term is used to describe the period when the diode is not conducting?
Q8. Current that flows in pulses in the same direction is called _____.
Q9. For a diode to act as a rectifier, should it be connected in series or parallel with the load?
Q10. What is the Ripple frequency of a half-wave rectifier if the input frequency is 60 Hz?
Q11. What is the equation for determining average voltage in a half-wave rectifier?
Q12. What is the ripple frequency of a full-wave rectifier with an input frequency of 60 Hz?
Q13. What is the average voltage (Eavg) output of a full-wave rectifier that has an output of 100 voltspeak?
Q14. What is the main disadvantage of the conventional full-wave rectifier?
Q15. What main advantage does a bridge rectifier have over a conventional full-wave rectifier?
Q16. If you increase the value of the capacitor will the XC increase or decrease? Why?
Q17. What is the most basic type of filter?
Q18. In a capacitor filter, is the capacitor in series or parallel with the load?
Q19. Is better filtering achieved at a high frequency or at a low frequency at the input of the filter?
Q20. Does a filter circuit increase or decrease the average output voltage?
Q21. What determines the rate of discharge of the capacitor in a filter circuit?
Q22. Does low ripple voltage indicate good or bad filtering?
Q23. Is a full-wave rectifier output easier to filter than that of a half-wave rectifier?
Q24. In an LC choke-input filter, what prevents the rapid charging of the capacitor?
Q25. What is the value usually chosen for a filter choke?
Q26. If the inductance of a choke-input filter is increased, will the output ripple voltage amplitude (Er)increase or decrease?
Q27. Is an RC filter used when a large current or a small current demand is required?
Q28. Why is the use of large value capacitors in filter circuits discouraged?
Q29. When is a second RC filter stage used?
Q30. What is the most commonly used filter in use today?
Q31. What are the two main disadvantages of an LC capacitor filter?
Q32. What two factors can cause output dc voltage to change?
Q33. What is the commonly used figure of merit for a power supply?
Q34. If a power supply produces 20 volts with no load and 15 volts under full load, what is the percentof regulation?
Q35. What percent of regulation would be ideal?
Q36. The purpose of a voltage regulator is to provide an output voltage with little or no ____.
Q37. The two basic types of voltage regulators are _______ and _______.
Q38. When a series voltage regulator is used to control output voltages, any increase in the inputvoltage results in an increase/a decrease in the resistance of the regulating device.
Q39. A shunt type voltage regulator is connected in series/parallel with the load resistance
Q40. In an electron tube regulator, the electron tube replaces what component?
Q41. What is the purpose of the amperite regulator?
Q42. As the tube filaments in the load heat up, will the circuit current increase or decrease?
Q43. What is the most important thing to remember when troubleshooting?
Q44. What is the main reason for grounding the return side of the transformer to the chassis?
Q45. What are two types of checks used in troubleshooting power supplies?
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