Vacuum Tubes

21. For a conventional vacuum tube used in the UHF band

1. The electron transit time becomes critical
2. The distance between the control grid and the plate must be increased
3. The physical size of the tube must be increased
4. Only a pentode can be used because of noise effects

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22. For a given plate voltage, if negative potential on the control grid of triode is increased, the plate current

1. decreases
2. remains the same
3. increases
4. becomes zero

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23. For faithful amplification, the control grid should be _________ with respect to cathode.

1. positive
2. negative
3. at zero potential
4. at infinite potential

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24. For the same plate voltage, a gas diode can conduct _________ the equivalent vacuum diode.

1. less current than
2. same current as
3. more current than
4. one-half the current than

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25. For the sample plate dissipation, the output power of a Class B push-pull circuit is nearly _________ that of Class A operation.

1. 2 times
2. 4 times
3. 3 times
4. 5 times

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26. ln directly heated cathode, filament and cathode are

1. separated components
2. same components
3. made of metals
4. made of alloys

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27. lonization current which is a positive-ion current produced by collision between electrons and residual gas molecules in an electron tube is also called

1. gas current
2. gas discharge
3. plasma current
4. plasma discharge

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28. lonization of cold cathode diode takes place at _________ plate potential compared to hot cathode gas diode.

1. the same
2. much lower
3. much higher
4. zero

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29. Once a thyratron is fired, its control grid _________ over palate current.

1. loses all control
2. exercises rough control
3. exercises fine control
4. becomes helpless

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30. One advantage of a mercury vapor diode over the high rectifier is

1. its higher peak inverse voltage rating
2. its reduced RF interference effect
3. its lower voltage drop when the plate current is flowing
4. the elimination of the need for a warm up period

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