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Hmmm looking at your diagrams and waveforms, it seems that the 4.7u cap is being charged too quickly. TR20 is arranged as a constant current generator and this current should charge the 4.7u cap over the field period.
the dc voltage at tr20 emitter should be 5 volts LESS that the supply rail (15volts?) and the base voltage 5.6v less than the supply rail ( the zener voltage) These voltages should not change (much ) as the 5k pot is adjusted.
The actual current supplied to charge the cap is set by the 5k pot and hence the rate of voltage rise on the 4.7u cap.
If the circuit is correct check the zener voltage and the transistor is OK.
TR19 seems to be OK.
Brian S
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