I would like to have your opinion on this circuit :
The source voltage V12 is a feedback of an other loop hidden. So the operating point of the system is changing.
When the 47 Ohm resistor R1 is connected to the NPN, the system seems to be stable according to LTspice and it makes sense according to the theory :
Nevertheless, if the operating point is making working the PNP and not the NPN, the system is unstable as the resistor of 47 Ohm is "removed" from the open loop gain.
What I am asking is the following : if the circuit is working with the NPN, i.e with the stable part of the system, can the system be lightly unstable? I ask this question because I have a circuit which looks like to be unstable. Sometimes the output op amp seems to change completely of state and then go back to its value. It is particurlarly the case when the 47k5 resistor is not placed. But it has a low effect on the open loop gain and so on the stability ...