I have read in old posts a way to set the transistors bias without the transistors in the circuit (for testing propose), the trick is to replace the transistor by a 220 ohms resistor. (by putting the resistor between the base and emiter goes in the circuit) , in this case the output stage has 2 transistors, one in the positive side and another in the negative side (class AB amplifier), the questions are.
In the case that we have more than one transistor in the final stage we have to replace all of them by the resistors or only one?
2 . Can i do the same trick in any stage?
If a amplifier has more than 1 transistor per side, it can work with only one per side?
I have read in old posts a way to set the transistors bias without the transistors in the circuit (for testing propose), the trick is to replace the transistor by a 220 ohms resistor.
I've never heard of that and it would only be an approximation. (I've never made an amp with discrete transistors since IC amplifier chips have been available for a long-long time... I did once add a discrete "boost stage" to an IC amplifier, but IIRC the transistors were inside the feedback loop and I used some "tricks" to avoid bias current.)
Maybe you could put a temporary "current-limiting" resistor in series with the transistor so you don't fry the transistors during testing. Or, you might use a temporary series resistor to measure the bias current (by measuring the voltage drop across the resistor).
...In the end, you'll probably have to trust your calculations or make actual measurements/adjustments.
If a amplifier has more than 1 transistor per side, it can work with only one per side?
Yes, that would be a class-A amplifier. But it's extremely inefficient (with a ship-load of quiescent "bias" current) so it's virtually never used in the output-stage of a power amplifier.