Multimeter to determine the good and bad method of composite tube
Use the multimeter to identify the good and bad composite tube. The multimeter will be placed in the R xlkΩ file, the red meter stick take over the gate of the tube G, the black meter stick connected to the source pole S. This time the head pointer should not move, at least should be greater than 500kΩ or more, then the gate is good. If less than 500KΩ, the tube gate leakage, not good. If the resistance value is close to zero, then the gate has broken down, the tube under test has been completely damaged.
After the above measurements, such as the gate resistance is good, then the multimeter will be two rods to adjust, that is, the black meter stick connected to the gate G, the red meter stick connected to the source S. If the resistance value measured at this time and the meter stick before the adjustment of the same, that is, the measured tube is not set up inside the gate to protect the diode, if the value of resistance is less than 10k Ω (generally around 2k Ω), that the tube has been set up inside the gate to protect the diode.
After connecting the line, close the switch K. This time, the normally closed contacts of the button switch will be shorted to the gate, source, that is, VGS = OV, the tube does not conduct, the line of light-emitting diodes do not light. Then press the pushbutton switch, this time the normally open contacts will gate and emitter short circuit, VGS is negative, the tube conducts, there is current flow through the light-emitting diode, light-emitting diode light. The 300Ω resistor in the figure is the current limiting resistor of the light-emitting diode. After measurement, to meet the above requirements, indicating that the measured high-impedance composite tube function properly.
If the light-emitting diode lights up after closing the switch K, it means that the source-emitter is penetrated or the source-drain of the MOS tube is penetrated and the tube is damaged. Conversely, if the light-emitting diode still does not light up after pressing the push-button switch; it means that the tube gate may be worn or the gate leakage is too large and the gate control is lost, and the tube cannot be used.
