Distinguishing triode electrodes and tube types
(1) Visual inspection method
① Identification of tube type
Generally, whether the tube type is NPN or PNP should be identified from the model number marked on the tube shell. According to the ministerial standards, the second digit (letter) of the triode model, A and C represent PNP tubes, B and D represent NPN tubes, for example:
3AX is a PNP type low-frequency low-power tube. 3BX is an NPN-type low-frequency low-power tube.
3CG is a PNP type high frequency low power tube. 3DG is an NPN type high frequency low power tube.
3AD is a PNP type low-frequency high-power tube. 3DD is an NPN-type low-frequency high-power tube.
3CA is a PNP type high-frequency high-power tube. 3DA is an NPN-type high-frequency high-power tube.
In addition, there are internationally popular 9011~9018 series high-frequency low-power tubes. Except for 9012 and 9015, which are PNP tubes, the rest are NPN-type tubes.
② Identification of tubes
Commonly used small and medium-power transistors have shapes such as metal cylindrical shells and plastic packages (half-cylinder type). Figure T305 introduces three typical shapes and tube arrangements.
(2) Use the resistance range of a multimeter to determine
There are two PN junctions inside the transistor. You can use the resistance range of a multimeter to distinguish the three poles e, b, and c. This method can also be used to identify the tube type when the model label is unclear.
① Identification of base
When judging the tube, you should first confirm the base. For the NPN tube, use the black test lead to connect the assumed base, and use the red test lead to touch the other two poles respectively. If the measured resistance is small, it will be about a few hundred to several thousand ohms; and swap the black and red test leads to measure The resistances are all relatively large, above several hundred kiloohms. At this time, the black test lead is connected to the base. For PNP tubes, the situation is exactly the opposite. When both PN junctions are forward biased during measurement, the red test lead is connected to the base.
In fact, the base of the low-power tube is generally arranged in the middle of the three pins. You can use the above method to connect the black and red test leads to the base respectively, which can determine whether the two PN junctions of the triode are intact (and the PN junction of the diode). The measurement method is the same), and the tube type can be confirmed.
② Discrimination between collector and emitter
After determining the base, assume that one of the remaining pins is the collector c and the other is the emitter e. Use your fingers to hold the c and b electrodes respectively (that is, use your fingers to replace the base resistor Rb). At the same time, contact the two test leads of the multimeter with c and e respectively. If the tube under test is NPN, use the black test lead to touch the c pole and the red test lead to the e pole (opposite for the PNP tube), and observe the deflection angle of the pointer; then set another The pin is c pole. Repeat the above process and compare the deflection angles of the two measurement pointers. The larger one indicates that the IC is larger and the tube is in an amplified state. The corresponding assumed c and e poles are correct.
