The quality of the power amplifier block is the quality of the triple tube. There are many ways to judge the quality of the ordinary triode, mainly by using a multimeter. Hit the pointer multimeter to x1K ohm gear, now talk about the quality of NPN type triode. The black watch pen is connected to the triode base, and the resistance between the triode base and the emitter, and the base and the collector is measured respectively. The resistance value in both cases is thousand ohms (if the triode is a germanium tube, the resistance value is about 1k ohms; If it is a silicon tube, the resistance value is about 7k ohms). Adjust the marker, and then measure the resistance of the emission junction and the collector junction, and the resistance value is infinite. It can be preliminarily determined that the triode is good. Otherwise it means that the triode is bad.
The following can further judge the quality of the transistor. Set the multimeter to x10k gear, use the red and black pen to measure the resistance between the emitter and collector of the triode, and then adjust the pen to measure again. The resistance measured on both occasions should be infinite on one occasion, and hundreds to thousands of kilohm on the other. From the above, the triode can be judged to be good. If the resistance between the triode emitter and the collector is zero or infinite twice, it means that there is a short circuit or open circuit between the triode emitter and the collector, and the triode is no longer available. For PNP type triode, the red and black pen of the multimeter can be switched when judging by the above method.
1. There is no absolute way to judge its quality under amateur conditions. The amateur method to roughly judge its good or bad is to find a good integrated block, use a multimeter 1k ohm file red pen ground terminal, black pen respectively to measure the resistance value of each foot and write it down, and then the same method to measure the integrated block to judge, as long as there is more than one foot resistance value difference is too large, then the integrated block is bad.
2. This method is not 100% accurate, the most accurate method is direct replacement on the circuit, at a glance.