The Positron Preamp Drive is an adaptation of the Gorilla TC-35 Tube Cruncher amplifier that first appeared in 1986. The Gorilla amps were solid-state combo amps aimed at the budget market. They were not terribly well-regarded in their day, but they caught the eye of Josh Homme from Queens of the Stone Age who cranked them for their unique overdrive tone.
Interestingly, there are no clipping diodes present, and so all of the overdrive comes from overloading the opamp. Typically this is an undesirable characteristic that is avoided, but in this circuit it works.
The Positron is an adaptation of the TC-35’s preamp section. It’s a direct clone of the circuitry based on factory schematics, running on the same voltage as the original, but meant to be used as a standalone drive pedal instead of a true preamp.