I managed to develop an astable multivibrator transistor square wave generator of ~710Hz. This generator will be used as sound for AM radio transmission. The sound must be amplified by external circuit. The simulation and realization of the generator works fine, but when I want to snatch voltage from this generator at a certain point, it is getting instable.

I tried capacitor across voltage source or impedance matching and I could still not figure out, why I could not make it work. I don't suppose the failure was just that. Below a picture of circuit.

How can I extend a basic circuit in junction with another one without having to many disadvantages?


[![circuit][1]][1]

Edit:
As demanded below an example:

[![preamp][2]][2]

Edit2:

The amplifier right from the square generator has the following example components: (The values can vary, I just tried with few ones, but had no luck.)

[![preamp][3]][3]


  [1]: https://i.sstatic.net/bmoz41pU.png
  [2]: https://i.sstatic.net/MBPXUxkp.png
  [3]: https://i.sstatic.net/4h3qbyZL.png