Here's a pretty interesting lower gain overdrive. There's a an opamp gain stage with soft clipping going into a JFET stage that pushes a modified BMP tone stack, followed by a BJT output buffer. One of the diodes in the opamp stage is unknown, so socket and experiment. I also took a few liberties from the original using a TL072 instead of a TL071 for layout purposes and using the second opamp to buffer the voltage reference. Should fit nicely in a 1590B. Schematic available on FSB.