Questions and Problems

Author: N.H. Crowhurst

1. What are the advantages of working tubes in push-pull?

2. Explain how using tubes in push-pull enables them to be used (a) with less distortion, (b) to give more power (higher efficiency)?

3. Give the relative advantages of operating tubes in (a) class A, (b) class B, (c) class AB.

4. What is power drive, and how does it alter the requirements of the preceding stage?

5. What is the most informative way of displaying the distortion performance of an amplifier using an oscilloscope?

6. What is a phase splitter and when is it needed? Discuss the relative features of the following different types, with special reference for each to (a) accuracy of the two outputs, (b) uniformity of performance at different frequencies, (c) economical use of components: (i) Transformer type (ii) Split-load type (iii) Paraphase type (iv) Floating paraphase type (v) Long-tail type (vi) Paraphase from output transformer.

7. Compare different output circuits, using triode or pentode tubes, in various classes of operation, with regard to the power output that can be obtained for a given dissipation rating, to probable distortion content, to critical load requirements, and to the requirement of critical adjustment in operation.

8. In spite of the fact that it is evidently a good phase-splitting device, the transformer is very seldom used in modern amplifiers. Why?

9. The split-load circuit is criticized for not having any useful gain. Explain why this is. Why is its handling capacity less than some other types?

10. Describe, with numerical illustration to prove your point, why the floating paraphase maintains betters balance than the simple paraphase circuit.

11. In a floating paraphase circuit, the section of grid resistor common to both output tubes has one-half the average value of the other two, which are slightly unequal, so that when the gain of the phase-splitting tube is 20, both output tubes get equal drive. Using values to illustrate this condition, find how much error will result from the phase-splitter tube's losing working gain down to 15.