Measuring Tips for Analog Multimeters
1. Test speakers, headphones, and dynamic microphones: Use the R×1Ω setting, connect any test lead to one end, and touch the other test lead to the other end. Normally, a clear and loud "click" sound will be emitted. If there is no sound, the coil is broken. If the sound is small and sharp, there is a ring friction problem and it cannot be used. There are generally three methods, which we will introduce in detail below.
The first method: For meters without hFE measurement jacks, or if the tube is too large to be inserted into the jack, you can use this method: For NPN tubes, first measure the b pole (whether the tube is NPN or PNP and its b pin It’s easy to measure, right?), put the meter in the R C terminal, use your fingers to pinch the tip of the test lead and the pin at the same time, pick up the tube, lick the B terminal with the tip of your tongue, and see that the pointer on the meter head should deflect to a certain extent. If you connect the test leads correctly, the pointer deflection will be If it is larger, if it is not connected correctly, the pointer will deflect smaller, and the difference is obvious. Of course, the test leads need to be exchanged and measured twice during measurement. The final judgment can only be made after comparing the readings. This method is suitable for triodes of all shapes and is convenient and practical. According to the deflection amplitude of the watch hand, the amplification ability of the tube can also be estimated. Of course, this is based on experience.
The second method: For a pointer meter with a jack for measuring the hFE of a triode, first measure the b pole, then insert the triode into the jack at will (of course the b pole can be inserted accurately), measure the hFE value, and then Turn the tube upside down and measure it again. If the hFE value is larger, the insertion position of each pin is correct.
The third method: first determine the NPN or PNP type of the tube and its b pole, then put the meter in the R×10kΩ range. For NPN tubes, when the black test lead is connected to the e pole and the red test lead is connected to the c pole, the meter needle may have a certain Deflection, for PNP tubes, when the black test lead is connected to the c pole and the red test lead is connected to the e pole, the meter needle may deflect to a certain extent, but there will be no deflection in reverse. From this, the c and e poles of the triode can also be determined.
