How to determine the polarity of a crystal diode

The positive and negative poles of a crystal diode can be identified by the following methods:

1. Look at the symbol on the shell: The symbol of the diode is usually marked on the shell of the diode. (Refer to Figure 3), the end marked with a triangular arrow is the positive pole, and the other end is the negative pole.

2. Look at the color dot marked on the shell: On the shell of a point-contact diode, there is usually a color dot (white or red). Except for a few diodes (such as 2AP9, 2AP10, etc.), the end marked with the color dot is generally the positive pole.

3. Look at the contact pin through the glass: For a point-contact glass shell diode, if the mark has been worn off, you can gently scrape off a little of the paint layer (black or white) on the shell, and look through the glass to see which end is the metal contact pin and which end is the N-type germanium sheet. The end with the metal contact pin is the positive pole.

4. Use the multimeter R*100 or R*1K to measure the two leads of the diode at random. If the measured resistance is only a few hundred ohms (forward resistance), the lead connected to the black test lead (i.e. the positive pole of the battery in the multimeter) is the positive pole, and the lead connected to the red test lead (i.e. the negative pole of the power supply in the multimeter) is the negative pole. (See Figure 5)



Figure 5

5. Use batteries and speakers to determine the positive and negative poles of the diode: as shown in Figure 6. Connect a battery and a speaker (or headphones) in series with the diode to be tested. Then touch one end of the lead of the diode to the speaker intermittently, and then turn the diode upside down and measure it again. The lead with the loudest "click, click" sound is used as the standard. The lead connected to the positive pole of the battery is the positive pole, and the other is the negative pole.