I got myself a little treat (10 Kg of scrap electronics) and inside I found, among other great stuff, a GDR board that was made by RFT. It seems to be some kind of stereo amp or Tone control circuitry because of its symmetric nature.
We have a 2761 Dual opamp and 4 E X3 C36 (?) transistors at work alongside 4 Styroflex(polystyrene) (you gotta love em) caps.
I asked around in my favorite forum where some old-timers hang out and that were in electronics back in the day, when there was the GDR. I’m hoping to find out some more soon and get this thing going!