I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?

:I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?
yes use your ohmmeter they should go up to 5or 10 megs then charge up and go back to zero if they do nothing they are open if they don't go back down they are leaky at least thats what i do. butch

::I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?
:yes use your ohmmeter they should go up to 5or 10 megs then charge up and go back to zero if they do nothing they are open if they don't go back down they are leaky at least thats what i do. butch

HI Butch,
I think you may have that bassacwards. When you first apply the probes the meter may deflect towards zero ohms then the readig should increase towards infinity.
Gary

:::I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?
::yes use your ohmmeter they should go up to 5or 10 megs then charge up and go back to zero if they do nothing they are open if they don't go back down they are leaky at least thats what i do. butch
:
:HI Butch,
:I think you may have that bassacwards. When you first apply the probes the meter may deflect towards zero ohms then the readig should increase towards infinity.
:Gary
your right gary sorry i shouldn't answer ques. at 3 30 in the morning when i should be sleeping.butch

Bob,
The problem with checking leakage with a multimeter is that it does not subject the capacitor to actual (higher)circuit voltages. Many "good" meter-tested caps will leak badly, or just plain fail in real circuit conditions. A good cap testing device performs the testing while subjecting the capacitor to these higher voltages.
Jim

As Jim says, an old, dedicated cap checker that applies a high voltage is the way to go.

Some modern multimeters have a capacitance measuring mode. If your cap measures high on such a tester, it's likely due to unacceptable leakage.

If any of those are paper caps, do yourself a favor and pitch them - NOS or not. I would also throw out any electrolytic caps that are more than, say, 15+ years old.

:I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?

::I have many new and old stock capacitors non-electrolytic. Is there a way to check these with a multi-meter for leakage or possible use in restoration of radios?

Bob, I don't have a leakage tester. This what I do. Method 1. For new caps. Connect one end of .5 meg resistor to 200 v DC and connect a meter to the free end. Measure the voltage. Connect the cap from the free end to the neg side of the supply. The voltage should go down for a few moments while the cap charges. Higher value caps take longer times. After about ten seconds if the voltage has not come back to the original voltage without the cap then the cap is leaky.
Method 2. In the radio. If I suspect a cap. If it is a coupling cap from a plate to the next stage grid measure the voltage from the grid of the tube to ground. Clip the cap and if the voltage becomes less positve then the cap is bad. If it is a bypass cap maesure the volage across the point that is being bypassed. When you clip the lead of the cap if the voltage goes up then that cap is leaky.

As far as measuring leakage using high voltage, the method just described does not give accurate measurements. Leakage in the millions of ohms will not drop the voltage across a .5 meg resistor appreciably. What should be done is to place the condenser in question in series with the multi-meter and the power source. With the meter set on 200 volts (200 volt DC supply being used), the needle should swing up when the condenser is first connected and then swing back down to zero. If it lingers at all above zero, then the condenser is leaky. If the needle jumps around, then the condenser is arcing. I have used this method for finding arcing condensers that otherwise show up as fine on a resistance check. Using the method formerly described (placing a condenser across a .5 meg resistor), will not put enough voltage across the condenser for an accurate check. For most paper condensers (those rated over 300 volts), actually 300 volts should be used for testing, as it will reveal even more arcing condensers, but I have had much success with 200 volts.

Also, when doing the simple resistance leakage check with your multi-meter, the needle may or may not swing up and then back down. You want to use the most sensitive resistance setting--the one that checks in the millions of ohms (X10,000 on the Simpson 260). With most condensers over .001 MFD, the needle will swing up and then back down just slightly. With values over .1 MFD, it may swing up quite a bit. With values below .001 MFD, however, you might not see any movement at all unless the unit is leaky. Rule of thumb is, though, that if you see any movement to the right, the needle MUST fall back to EXACTLY where it started. Leakage even in the 10s of millions of ohms is enough to throw off grid biasing. Tube circuits are extremely sensitive. DO NOT USE LEAKY CONDENSERS IN YOUR RADIO. Consider the high resistances that maintain bias on the grids in the audio sections, or the high resistance that sends AVC voltage to the RF section. If the AVC resistor is 2.2 meg and the AVC condenser leaks about 10 meg, it is going to throw off the AVC voltage, and will not allow the AVC circuit to kick in fully for local stations, which will cause distortion in the audio.

Checking condensers is a very critical task and it must be done properly. Of course to be on the safe side, many repairmen simply replace all of the condensers with new ones. The learning experience had from testing condensers and replacing them one by one can be a good one, though.

Now that everyone knows this, we can keep this in mind whenever we come across a radio that has distortion in the audio, especially after operating for 20 minutes. This is extremely common with AC-DC-battery radios, and happens quite a bit with AC radios as well. AC-DC-battery (3-way) radios are more sensitive to condenser leakage, however, because they must use extremely high grid bias resistors in order to take full advantage of sensitivity of the audio amplifier that is operating from batteries. Replacing all of the condensers in the audio section corrects this problem.

Thomas