Easy modification for the "normal channel" of a Fender two channel amp made before 1980. Higher gain, easier distortion. A Marshall-like tone. Great punch and a warm tone.
The mod is changing parts in the tube circuit to get higher gain and a more agressive EQ from the channel. It makes an unused part of the amp into something really useful and sounding great.
You can use an AB box to switch between your two channels for some real good, cheap and EZ tone variations - cool.