Questions and Problems

Author: N.H. Crowhurst

1. Why is grounded-cathode operation referred to in this book as the basic method of connecting a tube?

2. How does a grounded-grid amplifier differ from a grounded-cathode amplifier? Does the load resistance in the plate circuit affect the performance of either circuit?

3. Why is it advantageous to bypass the bias resistor in a grounded-grid amplifier? Illustrate with numerical example.

4. What is a cathode follower, and why is it so called? Explain how the cathode follower provides a form of amplification.

5. A certain tube, operated at a grid bias of - 1 volt, with a plate load resistor of 220,000 ohms, has a gain of 60. Calculate (a) its input resistance, operated grounded grid, and (b) its voltage gain, operated as a cathode follower.

6. Compare the essential control properties of a tube and transistor. What would you regard as the basic mode of operating each of them?

7. How can a transistor be operated to give characteristics very similar to a tube; with what essential difference?

8. Why is some form of coupling circuit necessary in an amplifier using two or more stages? What is the most common form of coupling?

9. How would you explain the concept of the time constant? Why is it not the full time taken for a capacitor to reach its final charge?

10. What properties of amplifier circuits in general are responsible for (a) low-frequency response, (b) high-frequency response?

11. How does an a-c load line differ from a d-c load line? A tube with a plate resistance of 60,000 ohms using a load resistor of 120,000 ohms gives a gain of 54, Calculate (a) its amplification factor; (b) its gain when coupled by a capacitor to an additional resistance of 200,000 ohms.

12. What is direct coupling? Describe two possible ways of using it.