Questions and Problems

Author: N.H. Crowhurst

1. Why is an a-c power supply more convenient for many purposes than a d-c? What kinds of rectifier can be used for converting a-c to d-c for operating tubes or transistors?

2. Explain how (a) a choke and (b) a capacitor may be used to smooth out the large fluctuations in rectified a-c.

3. Distinguish between the inherent characteristics of smoothing filters utilizing (a) capacitor input and (b) choke input. Also, show how a "swinging choke" combines features of both and for what purpose.

4. Additional filtering is often provided for various supply points in an amplifier, but is usually called "decoupling." Explain the significance of this term.

5. Distinguish between self or automatic bias and fixed bias for tube operation. In what way is the former automatic?

6. Why should a bypass capacitor be used with an automatic bias circuit? Under what circumstances does automatic bias work better without this bypass, and why?

7. What is crossover distortion, and what causes it? How can it be avoided?

8. What two methods of supplying screens are used? If a screen is to be operated at 150 volts from a 250-volt supply, what resistors should be used so that change of screen current from 0.5 milliampere to 1.5 milli-amperes only changes the voltage from 155 to 145 volts?

9. Why is a capacitor necessary with a screen supply circuit? Explain why a cathode bypass capacitor may be as much as 50 microfarads or more, while a screen capacitor can be only about 0.1 microfarad.

10. What two principal methods of connection are used for tube heaters?

11. For what reasons may equipment be designed to work without a transformer in the power supply? What particular precautions are necessary in this kind of equipment?

12. What remedies would you try if an amplifier or other piece of audio equipment developed hum?