the freakiest thing just happened:
after finishing the VCF and non-succesfully testing it, i went to check the voltages you wrote about.
at first pin2 of q26 was like 2 times it should be but after probing it 3 times it went down to 5.33 so all was good. all other votages too. more or less. then i tried hooking up the phones to the saw again and it was there! a clear saw!
then a loose wire on my desk made a shor-circuit on the x0xb0x psu and loud sparks went out of it.
i quickly disconnected everything and removed the loose wire. after turning it back on the PSU output voltages on J4 were exactly 2 times they should be. i disconnected everything, also the main board from the psu board. i waited a little and said to myself FROM NOW ON ALWAYS CLEAN THE DESK!!!
then i checked again the psu alone and it was outputting okay voltages again. i hooked up the main board and... EVERYTHING WORKS!
the tuning pot, the filter section, everything works...