Homebrewing is as old as ham radio. For decades, most hams built their own transmitters as a matter of course, and quite a few built their own receivers as well. As manufacturing technologies advanced, it became harder and harder to homebrew gear equivalent to commercial equipment. Today, it is nearly impossible to build competitive gear, with one exception: amplifiers. Many hams use amplifiers, especially on the HF bands. Even with modern manufacturing techniques, it is still possible to build an amplifier that is fully competitive with commercial gear. With a little patience and skill, you can build yourself an amp that equals or exceeds the performance of the best commercial product.
Ham amplifiers typically feature a tuned input stage to match the exciter's output to the amplifier's input. Until now, these were almost always simple L-C circuits, hand adjusted by a slug-tuned coil. This was a compromise at best; common practice is to tune the input for the center of the band. At the band edges, the match is not nearly as good. Some amps have no tuned input at all; this is especially bad for solid-state exciters.