No way to be accurate without the other side, unfortunately. Then we would need the values of the pots, caps, transistors, etc.
But the picture could give some clues as to the nature of the circuit. It is discrete, cascaded transistor stages with diode clipping. Switch is for the diodes.
Could be JFET based with those trimmers being used to bias each stage, think Fairfield Barbershop or SSBS Mini kind of thing. Tone controls can be anywhere in the circuit, together or separate, likely passive.
Anyone’s guess is as good as mine at this point, but I’m sure we’ll figure it out eventually!