Since 1993 Copyright Notice

It is advised to mount a capacitor if 50..100uF across the meter. This protects the meter best way. Though it's a robust meter, it stays a 150uA meter, and that is by default a sensitive device. At overload of more than a factor 10, it hammers in the corner, and bends the needle itself. You would not notice this as a problem, just re adjust the zero setting, and do not remember it later. But you may have introduced some unlinearity by this, when this also deformed the moving coil.

It is advised to mount a capacitor if 50..100uF across the meter. This protects the meter best way we can. Though it's a robust meter, it stays a 150uA meter, and that is by default a sensitive device. At overload of more than a factor 10, it hammers in the corner, and bends the needle itself. You would not notice this as a problem, just re adjust the zero setting, and you think that was it. But you may have introduced some unlinearity by this, when this also deformed the moving coil.

The meter is 150uA, and we do not want any capacitor leakage causing difficulties. This is not guaranteed with a plain electrolytic capacitor, since the voltage over it will be just a few millivolts. In such conditions, the cap will not regenerate chemically (as it will in a normal circuit), and develop problems. You may use a 100uF foil cap but they are quite bulky. So to take the best, I choose for a special kind of capacitor, the so called "SEALED WET TANTALIUM". These are expensive, but can be found on Ebay as USA or Russian NOS. These caps have lowest leakage possible, long life time, no storage problems, and tight tolerance. So all problems of aluminum electrolytic caps, these don't have. These are real diamonds, because with the older ones there were no limitations for chemicals used, and their original use was for stability. I cannot prove it, but I think specially the Russian types are the strongest of all. You do need to re-format them before use or before first testing. For this, connect the cap with a 1Meg Ohms resistor to a voltage source which equals it's working voltage. Forming is finished, when the cap must have reached this voltage. Now you can first time use the cap, like test it with a meter, or put it in a circuit. Sealed Tantalum caps should be close to their rated capacitance, because they're finest quality products. You may want to test this, but probably their is no need anyway if you don't have a tester. On the picture here, you see where the cap can be mounted, just put in in parallel with the meter protection diodes. Some L3-3 have these diodes close to the banana jacks on the stabilizer board. Just look for them, you can't miss it. So on that case, the caps are mounted there.

Now the meter will move gently.

VERY Important: Check with a sensitive voltmeter if you have polarized the cap correctly!