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Questions and Problems

Author: N.H. Crowhurst

1. Explain why a diode rectifies current, and how the geometry of a triode affects the way in which the plate and the grid control electron flow.

2. What is transconductance, and why is it so called? State the conditions defining it.

3. What two units are used for measuring transconductance? If a tube has an amplification factor of 100 and a plate resistance of 62,500 ohms, give its transconductance in both units.

4. What is the plate resistance of a tube, and why is it sometimes called a-c resistance?

5. What is the amplification factor of a tube? State the conditions defining it.

6. How can the amplification of a tube be increased by its internal design? Discuss the practical limitations in achieving higher amplification from a triode tube.

7. A tube has an amplification factor of 100, a plate resistance of 80,000 ohms, and is used with a load resistor of 100,000 ohms. Calculate the approximate amplification of the stage from the appropriate formula.

8. What steps were taken in the design of tubes to obtain higher amplification than is possible with a triode? Explain the function of each added electrode.

9. Why is the amplification factor of a pentode seldom quoted in tube data for this type of tube? What figure is used instead?

10. What would happen to a moving-coil meter connected in an a-c circuit, without the use of a rectifier?

11. Draw two different types of rectifier meters commonly used for measuring a-c. State the relationship between the reading obtained and the maximum current alternations causing it.

12. Why is it that rms values are the standard used for specifying alternating voltages and currents, although most meters measure average values? How does the relationship change when different waveforms are used?

13. What two graphical ways are there of presenting the characteristics of a tube? State the relative merits of each method.

14. What is a load line? Show how it can be applied and discuss the information that may be obtained from it.

15. How can plate resistance be obtained from a tube's characteristic curves? Is plate resistance constant as various tube voltages are changed?

Last Update: 2010-11-03