Opamps are wonderful little building blocks, but quickly building a test circuit is a real pain. Most people will use a breadboard, one of those plastic blocks with holes and connections, but I have found them to be a complete pain in the backside.
There may be differences depending on how the amp is fed: whether symmetrically or asymmetrically. These two main concepts are commonly called split supply and single supply, respectively.
It is not at all difficult to make an op-amp using transistors. This page shows you how and discusses how they work.
This is normal superheterodyne radio receiver. It does not use any coils. It uses a filter and oscillator made by OP-AMP. Converter is also constructed by a OP-AMP detector.
A band pass filter passes a range of frequencies while rejecting frequencies outside the upper and lower limits of the passband. The range of frequencies to be passed is called the passband and extends from a point below the center frequency to a point ab
The LM12 is a power op amp capable of driving ±25V at ±10A while operating from ±30V supplies.