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Even with regular use, electrolytics fail with age by drying out or leaking electrolyte following internal corrosion. If the electrolytic bulges, shows obvious loss of electrolyte, or simply can't be reformed you must replace it. Note there are two types of leakage; physical and electrical. Since the electrolyte is a liquid or paste, when an electrolytic catastrophically fails it usually oozes some corrosive goop: physical leakage.
Unlike an ideal capacitor, electrolytics slightly conduct when there's voltage across the plates: electrical leakage. Other than being a deviation from ideal behavior, the small leakage in a new electrolytic causes no major problems; as the electrolytic ages, the leakage increases.
The leakage generates heat, which ages the electrolytic and increases leakage, causing more heat, and so forth. With enough leakage, the electrolyte boils, and the steam bursts the safety plug of the container causing physical leakage and signaling the demise of the capacitor.
Note also that there are other forms of terminal failure, including complete loss of capacitance open or bridging of the conducting plates short. While you may be able to reform your 30 to 50 year old original electrolytics, they may not perform as well as when new. There may be a partial loss of capacitance, or there may be excessive leakage the caps get really warm , or both.
It is sometimes possible to order replacement multi-unit capacitors that exactly match the original values. However, new multi-unit caps can be quite expensive and it may be hard to find the right value assortment in one container one supplier of such caps is Hayweed Hamfest. It is economical to replace a multi-unit capacitor with individual capacitors of the desired values. For instance, if your original can contained capacitors of 20 mfd, 20 mfd, and 30 mfd, you can replace it with two new mfd capacitors and one mfd unit.
Your radio will work exactly the same whether you use a multi-unit can or individual caps. The next photo shows typical new electrolytics, ranging in size from 5 mfd to mfd. If you plan to fix many radios, you can save money by buying an assortment of capacitors of common values.
Some merchants, such as Antique Electronic Supply , offer a "kit" of common caps at a good discount. You can usually save money by ordering 10 or more of a given value, as well. The most common values needed in old radio repair are. You will use many more small non-electrolytic capacitors than large electrolytics. For a typical five-tube radio, you might replace a couple of electrolytics and half a dozen of the smaller capacitors.
Capacitors are not expensive. The electrolytics that you'll need will usually cost from one to five dollars each. Most non-electrolytics cost less than a dollar. Recapping the Grundig radio shown at the beginning of this article cost me about ten bucks. Now that you have the parts you need, let's install the new ones!
Replacing small capacitors is the simplest operation, so we'll look at that first, then turn to the electrolytics. Note, however, that in practice it's preferable to replace the large electrolytics first.
That will help eliminate power-supply problems and simplify testing the radio while later replacing the small caps. Replacing a capacitor requires a wire cutter, small pliers, and a soldering iron. Another nice thing to have is a "solder sucker," a small rubber bulb with a heat-resistant tube at one end, or a metal tube with a spring-loaded sucking mechanism. I'll illustrate this section with photos from the restoration of my Clavioline.
The basic method is the same for every vintage tube device. I strongly recommend that you replace only one capacitor at a time and doublecheck the wiring of each replacement against the schematic. That way, if you make a mistake, it will be easy to correct. If you replace several capacitors at a time, it could be much harder to figure out where you went wrong! I often take notes, as well, writing down each capacitor's value and part number when it is replaced, or checking off the capacitor on the schematic and parts list.
Before replacing anything, of course you must unplug the radio from the wall and remove the chassis from the cabinet.
Use a small plastic bag to hold the chassis mounting screws, knobs, and any other parts. Turn the chassis on its side or back so that it will lie still while you work. Be careful not to damage delicate parts when you turn it over.
Don't rest the radio upside down on its tubes. If necessary, you can prop up one side of the chassis with a book, small block of wood, etc. My Midwest DD article describes a simple holder for large and heavy chassis. Some purists go so far as to hide new capacitors inside the shells of the small non-electrolytic paper capacitors.
This preserves the original appearance, but it is rather tedious. I have done this only in a few cases, for my most valuable radios. If you are interested in doing this, read the restoration articles for my Sparton Bluebird or Colonial Globe. Using your wire cutters, snip the leads of the old capacitor about one-half inch from the terminals where they are connected.
Leaving a little "tail" on the snipped wire makes it easier to remove. Set the old capacitor aside. Use your soldering iron to melt the solder on the terminal, suck the excess solder from the terminal, and use your thin pliers to remove the snipped wire tail from the terminal. You may need to unbend the tail a bit to work it free. If it is very firmly crimped onto the terminal, try snipping the bent portion to free it in two pieces.
Sometimes, a thin implement such as a nut pick or dental pick is handy for nudging the snipped tail out of its lair. A round wooden toothpick may help to clean out little circular holes in a terminals, since melted solder doesn't stick to wood.
If the snipped tail is attached to a pin of a tube socket, avoid using too much force to pull it loose. You might yank the pin right out of the socket or even tear it in two. The same goes for other components that are attached to the same terminal. Old carbon resistors are brittle and will break if handled too roughly. Once in a while, a capacitor will be mounted in cramped quarters, so that you need to unsolder another lead or component to gain access. In such a case, make a note or draw a picture so that you can reconnect everything correctly.
After you remove the snipped tail from the terminal, look carefully to make sure that you didn't leave any bits of wire or solder crumbs in the chassis. Small bits of metal can cause problems if they lodge in between two connections and make a short circuit. Hint: if you do a great job of cleaning the old terminals, it may not be obvious to the eye where the new leads should go. If you are interrupted at this stage in the process, loosely stick the leads of the new capacitor into the terminals so that you won't be scratching your head with puzzlement when you return.
It's easy to forget exactly where things went, after an hour or two. You can also temporarily attach the ends of clip lead to the connection points as a reminder.
It is good practice to test every new capacitor before installing it in the radio. Modern capacitors are generally high quality, but every now and then a bad one slips through.
If you don't have a capacitor checker, you can at least test the capacitor's resistance using a multimeter. The ohmmeter should show infinite resistance on all scales. Any continuity is a sign of leakage and a leaky capacitor must be replaced.
New capacitors usually have wire leads somewhat longer than needed. Your first job is to trim these leads and bend them to fit the spot. Hold the new capacitor near the place where it is to go, bend the leads to fit, and then trim the excess wire from the end of each lead with the wire cutters.
Leave enough length on the lead to allow for crimping it around the terminal. Again, be sure to avoid leaving stray bits of wire inside the chassis.
If the terminal is the type with a hole, slip the end of each lead into the hole. If you did not clean all the old solder from the terminal, you may need to heat the terminal to soften the solder before slipping in the lead. After the lead is through the terminal, carefully bend it around the terminal. Before soldering the new capacitor in place, you want to make sure that it has a solid metal-to-metal connection with its terminal! When both leads are securely crimped onto the terminals, heat each joint with the soldering iron and apply new solder.
Apply solder to the joint , not to your soldering iron. If the solder doesn't melt when touching the joint, then the joint is not yet hot enough. Don't jiggle the connection while the solder is cooling. That can create a "cold" joint that is not reliable. Sometimes, when a delicate component is connected to a terminal, I'll temporarily clip a metal tweezer onto that component's lead, to act as a heat sink and prevent overheating damage.
After replacing the capacitor, doublecheck your work against the schematic to make sure that you connected the right component to the right places. If the radio or TV is in working order, I often turn it on for a quick test after replacing each capacitor. Even professionals make absent-minded mistakes from time to time, and this brief road test will reassure you that you haven't made things worse!
If your set doesn't work at all, you will obviously need to do some other diagnosis and remedy the problem before turning it on. The "test after each replacement" routine applies only to radios and TVs that are basically working in the first place.
Obviously, if you are testing the radio with the chassis exposed on your workbench, use extreme caution to avoid getting a shock. Temporarily put the knobs back on their shafts before turning it on. Don't touch anything except the knobs while the radio is plugged in. Unplug the radio before resuming your recapping. That's all it takes! If you can replace one capacitor, you can replace 'em all, so go to it. Replace the remaining paper or molded paper capacitors one by one until you reach the end of your list.
It's good practice to make a note of each replacement as you go along, to prevent confusion and to make sure that you haven't skipped anything. I usually check off each part on the schematic and parts list:. Digital photos are extremely useful, and since they're virtually free, why not take a lot of them?
I take detailed photos of every radio or TV chassis's underside before starting work. If confusion arises later, those photos will show you how things were connected before you started messing around. I take more photos from time to time as my work proceeds, whenever I want to record something important.
Starting in the s, manufacturers introduced printed circuit boards. Instead of wiring every component separately, the wiring was pre-applied to a board and the component leads were soldered into little holes in the board. Replacing caps on PC boards is usually not difficult, but you'll need to use slightly different techniques. The mechanics of disconnecting the old capacitor and soldering in the new one are the same for electrolytic capacitors, so refer to the previous section for those basics.
But I think you have to specially treat the resulting gasses, as dioxins can re-form when the gases are cooled to slowly, I think some fast quenching is necessary. Transformer oil, PCB containing or not, is normally based on mineral oil. This is in no case acceptable for human consumption like deep frying. Crazy People! These capacitors would not pass Mr. The capacitors are only reforming or seeming to because of low run time hours intermittent use on the power supply.
These Mallory capacitors are not wax type, nor do they have stamped rubber seals of traditional pcb mount caps. These caps have been mounted inverted so the seals have not been under constant attack from the internal acids. So whether or not the caps pass your test, they will be unreliable in constant use because they have gone past their shelf life. Electrolytics are inherently more leaky than other caps.
The current for reforming appears as leakage current. They copied it everywhere and probably still do in real crap. I have several old electrolytics in regular use from the s. One of them clocked 5. Completely reliable. Of course i have had several bad electrolytics. You notice that soon enough — tremendously high leakage or lost capacitance.
Sometimes the overpressure valve has already acted. Obviously those need to go. In my opinion many people are way too quick to just replace them. Thanks for this practical and almost obvious comment! It clearly states what engineers and technicians should go for — clear and measurable parameters as symptoms of failure.
Just one more thing. Measuring the capacitance with a good LC meter or even reliable universal instrument is a simple task. But what I have encountered up to now were only drastic examples of this, i. Have you measured some in-between states? Also, for the non-polar electrolytic capacitors, used in the signal path, how would you measure the leakage?
Well, the usual process to check for leakage is to take the capacitor out of circuit and apply a current limited voltage that is equal to the maximum rated voltage of the capacitor, and measure the leakage current. Usually, the voltage is brought up to the rated voltage. If you are fortunate enough to find an old Heathkit capacitor leakage tester, even better. They can test capacitors up to several hundred volts. I just rebuilt a Heathkit IT
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