Just wanted to see if anyone else had the same issue and how they solved it. An intact model 206 was brought to me to fix the low volume and have the vibrato knob added. Replacing all the electrolytics did not solve the volume issue and the new vibrato knob did nothing. Seems like the preamp is not getting the voltage that it should - only 8.4V is coming from the emitter and 9V from the base of TR6, almost half less than the 15.5V and 16.5V I should be getting. There's 22V at the collector, which is in the ballpark of 24V, so everything upstream of TR6 should be fine. However, this is causing lower readings at TR1 and TR3 also, which I figure might be affecting the vibrato as well.
Before I go hunting down some replacement transistors, is there anything obvious I'm missing? I might check the resistors around TR6 to see if they're OK, since I did find the two right before the vibrato pot (52 and 34) had almost doubled in resistance.