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I missed the point about the saturation voltage of TR20, so, yes the peak sawtooth voltage should be about 9.7. I don't think you need to change the 4.7 microfarad, though, because this should be in the range of the rheostat. Setting the rheostat to max 5k should get you a sawtooth that is only 3.4 v peak.
So, I agree a shorted TR20 is most likely the cause, or maybe TR21.
Don't mean to talk down to you, but are you sure the transistors are the correct polarity (PNP/NPN) and the b-e-c connections are not interchanged? In the past I made a mistake like that and got some very strange results.
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