Vacuum Tubes

61. Vacuum tube rectifiers are _________ affected by the changes in temperatures.

1. not
2. highly
3. greatly
4. severely

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62. Valves in a radio receiver generally employ _________ heated cathodes.

1. directly
2. indirectly
3. oxide
4. nickel

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63. Voltage amplifiers are operated as _________ amplifiers.

1. Class A
2. Class B
3. Class C
4. Class AB

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64. What are the two principal electrodes in every tube?

1. Plate and control grid
2. Cathode and screen grid
3. Plate and cathode
4. Screen grid and control grid

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65. What emitter is used in X-ray tubes?

1. Thoriated tungsten
2. Oxide-coated
3. Tungsten
4. Nickel

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66. What is one advantage of a pentode tube over a triode?

1. Lower input impedance
2. Lower output impedance
3. Less noise internally generated
4. Less control grid to plate capacitance

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67. What is provided by transformer coupling?

1. lmpedance matching
2. Step-up in voltage
3. Good frequency response
4. Stability of gain

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68. What is the amount of additional energy required to emit an electron from the surface of a metal?

1. Surface barrier
2. Threshold level
3. Work function
4. Potential

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69. What is the pentagrid converter?

1. A tube with a total of five electrodes
2. A tube with a total of five grids
3. A tube that can be used for frequency conversion
4. A tube that requires twice as such plate voltage as a single triode

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70. What is the phase difference of the output and input voltage of a grounded-cathode amplifier?

1. 90°
2. 360°
3. 270°
4. 180°

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