Let’s tell you how to judge the quality of the transistor

Use an analog multimeter to measure a general triode. The triode can be regarded as two diodes connected "first to first" or "tail to tail". If "first" is positive and "tail" is negative, then the former is PNP type, the rear Those are NPN type. Can test the diode to judge the quality of the three-machine tube, how to test the diode? Use two test leads to connect the two ends of the diode respectively, and measure two resistance values, one is several K to tens of K, the other should be infinite. This is basically good. The triode can be measured as two diodes.