Sorry for the late reply, some screws were impossible to dismantle with a screwdriver!
Following your instructions I have:
- snipped out C31, I got a replacement (0.022 uF instead 0.02)
- looking for a replacement for C28, the tone corrector, looks very bad and greasy
- R21 reported 255 Ohm
- R22 reported 952 Ohm
- no resistance could be measured in R24, seems faulty
I could not check the valve heaters continuity, because I am not sure how it is done
Thanks for the advice! I got the service sheet, but it is still a bit tough for me anyway