WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Instrument amplifiers get "voiced" a lot to arrive at a wanted sound. Bumblebee capacitors and CC resistors are much in vogue. Mr Blencowe has a pretty site probably covering most of the topics you are looking for.