Designing Power Amplifiers?

There are many power amplifier designs available from various magazine articles and other projects. However, each project has different input drive requirements.

I learned about BJT/FET power amplifiers at college 23 years ago. And promptly forgot about them. Well, I do not think I learned to "design" them. But I am re-reading some texts and some old memories are getting recharged for sure.

I have tons of open questions, most of them naive:

  • What determines the gain of the (large signal) amplifier? Is it just the β? For the same transistor, how do I change the gain knob?
  • Gain seem to be the wrong parameter for the PA. Usually, the output power is specified (eg: 20W PA). What parameters determine the power?
  • How is the transistor selected?
  • Most importantly what about the input drive level that is expected from the previous stage?
  • Matching the impedance of various stages? PAs usually have transmission line transformers (4:1 and 1:4) at the inputs and outputs.
  • How do we avoid race conditions because of rise in temperature?
  • ....

and many more. So, I am going to pour over the available books at my disposal. If anyone has hints, please leave a comment or email me.