Testing the Amplification Capability of JFET with a Multimeter
The 3DJ type with N-channel is commonly used in junction field-effect transistors, and its pin arrangement is shown in Figure 1-1. To test the amplification performance of this type of transistor, a circuit can be connected as shown in Figure 1-2. Set the multimeter to the DC voltage range of around 5V, and connect the red and black probes to the drain D and source S respectively. When the resistance of the potentiometer RP increases (as shown in the figure, the sliding contact slides upwards), the multimeter indicates that the voltage value should increase; Reduce the resistance value of RP, and the multimeter should indicate a decrease in voltage. During the process of adjusting RP, the greater the change in voltage value indicated by the multimeter, the stronger the amplification capability of the tube. If there is no change in the voltage indication of the multimeter during the adjustment of RP, it indicates that the amplification capability of the tube is very small or has been lost.
① To adjust the "zero point" (only available on mechanical watches), before using the watch, check that the pointer is pointing to the "zero position" on the left end. If not, slowly turn the "starting point zero position" correction screw in the center of the watch case with a small screwdriver to make the pointer point to the zero position
② When using a multimeter, it should be placed horizontally (only mechanical devices have it)
③ Before testing, it is necessary to determine the measurement content and turn the range conversion knob to the corresponding measurement gear shown to avoid burning the meter head. If the size of the measured physical quantity is unknown, the test should be started from the large range first
④ The probe should be inserted correctly into the corresponding socket
⑤ During the testing process, do not rotate the gear shift knob arbitrarily
⑥ After use, be sure to adjust the gear shift knob of the unused meter to the high range gear of the AC voltage
⑦ When measuring DC voltage and current, attention should be paid to the positive and negative poles of the voltage, the direction of the current, and the correct connection with the probe
