fixing am radio?
i admire the attitude of fix it yourself .....if they can build it ...i can fix it.
i have done what your talking about and it is a lot harder than it looks but if you have time you can figure it out....
the hardest thing about these old radios is that some of the mechanical parts with the tuner are plastic and often cracked and dry rotted .....parts like this are not available anywhere, so plan on re-casting your own plastic parts with panel bond or some kind of resin.
do yourself a favor and google the definitions of each part and understand what a transistor, resistor, capacitor, transformer and so on is and what it does before proceeding .......electronics 101 is good stuff
http://en.wikipedia.org/wiki/Transistor