Another situation would be where a pump is supplying a circuit with water, but in surges. On the outlet side of the pump, you can place a narrow piece of pipe. Prior to this you can install regular sized pipe that runs from the outlet to the inlet. Install a rubber diaphram on this pipe so that no water can actually flow through. The smaller pipe will act like a resistor, limiting the maximum amount of current flow. This will allow the rubber diaphram to have a better chance at "charging up." The rubber diaphram will build up a "charge" each time the pump puts out a surge, and the diaphram will release this charge whenever the pump isn't surging. This will smooth out the surges so that you have more of a smooth flow of water. This is how the filter system in your power supply works. Actually, the explanation I gave prior to this one, how a rubber diaphram is used to pass impulses from one circuit to another, is kind of how your amplifier works--sending audio information from one stage to the next without allowing the direct current in one stage to interfere with the current in the next stage. Explaining this more thoroughly with water would require a paper drawing. I'm sick and kind of dizzy right now, so I'm not up to explaining things in too much detail.

Anyway, so now that you understand that condensers charge up and all that, you should have a better understanding about what you are looking at when you test them on your multi-meter. Whenever you are going to test a condenser, remove all of its leads from the circuit. If the unit only has two leads, then removal of one lead is all that is necessary. When you connect your multi-meter to a condenser, depending upon its capacity, the needle will swing up to a greater or lesser degree. Then it will fall back down. It rises up as current rushes into the condenser (from the meter) to charge it. Once the condenser becomes "full," the needle swings back down. Condensers of smaller capacity will swing the needle up less than those with greater capacity. Generally, any condenser rated at 4 MFD or higher should swing the needle all the way up, or almost all the way up to zero ohms when concerning values right at 4 MFD. Smaller values may not swing the needle up much at all (as you move on to smaller values, deflection of the needle becomes less and less). When dealing with condensers around .05 MFD or .01 MFD, the needle will swing up a very small amount--almost unnoticeable. With values smaller than .001 MFD, you may not see any up-swing at all. When testing electrolytic condensers (those with polarity), if the value is above 4 MFD and the needle doesn't swing all the way up to zero ohms, then you can assume that the condenser has dried up (electrolytics have liquid in them) and is kind of useless. Since most electrolytics are larger in value than 4 MFD, you can pretty much use this as a testing method for all electrolytics regarding whether they have dried up or not. With values right around 4 MFD, if you are unsure, compare with a new condenser of the same value. They should be very similar in how far the needle swings up and how long it takes to fall back down. Some electrolytics that have sat for a long time may make the needle take longer to fall back down. These are electrolytics that need to be "reformed." This is explained a bit later. The process is complicated when dealing with good condensers in new condition, but the explanation I give below is good for old ones that probably need to be replaced anyway.

Now, regarding leakage--that is, when a condenser has a partial or total short, you want to watch the needle as it swings back down. Watch it until it stops moving. When the needle takes a while to fall down, it may simply be that the condenser needs reforming. The number that the needle stops at is your leakage. For electrolytics, leakage with a number lower than 1 MEG ohm is unacceptable. If you have an electrolytic that has 1 MEG leakage, you can try it in the radio for a while and see if it gets better--"reforming the condenser" (with the radio in series with a 100 watt bulb). If it doesn't get better (go to 10 meg or higher) after an hour of usage, replace the electrolytic. For continual electrolytic use, any leakage with a value less than 10 MEG is unacceptable. This means that the condenser is breaking down (usually), and could soon fail, damaging your power supply.

Now, with all other condensers (non-electrolytic), you do not want ANY leakage at all. Regardless of whether or not you normally can see the needle swing up (with values lower than .001 MFD, for instance), you will see the needle swing up when there's leakage. If the needle swings up, it must swing back down. As I said before, some condensers may only swing the needle up the thickness of a hair. If the needle stays up even just the thickness of a hair, the condenser has unacceptable leakage. Tube circuits are high impedance circuits, and are EXTREMELY sensitive. Leakage in the 10s of millions of ohms is enough to throw off AVC voltage and is enough to cause horrible distortion in the audio.

When testing condensers, use the X10,000 scale on your meter (the most sensitive one). Do not touch both meter terminals or both condenser terminals with your fingers at the same time. The moisture in your hands is enough to give false readings--you detect leakage even though there isn't any, because current is actually flowing through your fingers.

Whenever you acquire any radio, you should always test every condenser in the radio. Many radio repairmen just replace all of the condensers to be on the safe side. Modern condensers are far more reliable than old condensers (save mica condensers and air insulated tuning condensers). You can do many things to preserve the appearance of the chassis of your radio. You can stash the new condensers within the housings of the old condensers, and then seal them with hot glue or some more appropriately colored substance. Metalized film condensers fit nicely within the cardboard tubes of old paper condensers. Metalized film or ceramic condensers fit well in the bakelite condenser blocks found in Philco radios. Improvize. With electrolytics, sometimes you can figure out how to open the old ones in an inconspicuous way and stash new units inside (with all leads of new units well dressed--tape or spaghetti, so that no shorts occur). In other cases, simply stashing new units under the chassis and leaving the old units on top of the chassis (if this is where they are mounted) unwired, is the only option, especially when you can't figure out how to open up the old units.

Thomas