I have few suggestions. There is one kit that goes into detail.  AM/FM 108CK SUPERHET RADIO KIT. It explains what each section does in detail. If willing to spend a little money on some testing equipment you will seeighly  what I am talking about. It is made by Elenco and you can go to there site and read through the manual. I highly recommend it if you want a kit that explains what all the components do. A good lesson in Audio Amplifiers and a lot fun to build.