Ok, do you know what that Op Amp in the center is, is it the CA3140?

The circuit I posted is the same and uses a very old CA3140. It is better than a 741 or LM358/LM324 opamp but there are many better newer ones.

 

Thanks for your help eh!
Do you think I could substitute the circled Square Wave circuit and use that as the clock signal ,and use the rest of yours.

The reason I ask is I already having a working version of the above circuit.

 

Ok, do you know what that Op Amp in the center is, is it the CA3140?

As shown in the diagram, it converts the sawtooth output of the R/C network on the 555 to a square wave. The adjustment changes the trigger level of the op amp, which changes the duty cycle.

 

So I can't use my circut, hmm OK then I 'll stick with that design. Thanks