This must be a very early one, word has it that Jimi Hendrix tried one of these boxes for its big muff-like forced sustain. It is one of the earliest electro harmonix effects.
It is powered by TWO 9v batteries and so much for it “being distortion free”, it is very hissy and noisy, and colours the tone. The compression is VERY apparent and squashed.
Transistors: FS36999, the same as early 70’s Big Muffs.
The tube version Black Finger is a much different, more reliable and usable item.