What exactly is a capacitor, and how do we read theses things?   The basic unit of capacitance is the Farad, named after the Michael Faraday. Prior to the 1970's, capacitors were also called condensers. Same part, same function, different name. You'll still hear the old name used by some radio technicians. You will certainly see it in old schematics. Capacitance is usually measured in microfarads abbreviated uf, nano-farads (nf), or picofarads (pf). However, through the years "uf" had many other acronyms. For example, a 40 uf may be read as 40 mF, 40 MF, 40 mfd, or 40 MFD. The unit Farad is used in converting formulas and other calculations. A uf, (microfarad) is one millionth of a Farad (10-6 F) and a picofarad (pf) is one-millionth of a microfarad (10-12 F).   A capacitor is a device that stores an electrical charge or energy on its plates. These plates are placed very close together with an insulator in between to prevent the plates from touching each other, and a type of dielectric. Usually a capacitor has more than two plates depending on the capacitance or dielectric type. A capacitor can carry a voltage equal to the battery or input voltage. Once charged the discharge rate can be influenced by another source, such as a resistor. This action can create oscillation, or be used for electronic timing. The rate in which the capacitor charges and discharges can be used to create a filter, or limit unwanted noise, or used to prevent unwanted noise. There is lots more we can do with capacitors too. They can also allow AC to pass through, or be used in a DC circuit to eliminate AC, or AC noise. This would be called a ?bypass?. Capacitor Codes:   I guess you would really like to know how to read all those different codes. Not to worry, it is not as difficult as it appears. Some capacitors just tell you right out. Take your electrolytic and large body types of capacitors: These usually have the value printed on the body. For example: 100uf 250V, or something like that would be imprinted in plain text. It would also have marks pointing to the negative end of the capacitor. We cover more information about this further down. I have seen some pointing to the positive end, but only recently. That is not very common! So always pay attention, and use care.  Start here for the smaller non-polarized and old vintage and antique capacitors! It's mostly the smaller caps will have two or three numbers printed on them, some with one or two letters added to that value. Take a look at the table below. This is a visual example, but not for all of them.  As you can see it all looks very simple because its just number conversions. If a capacitor is marked with "105", it just means 10 + 5 zeros = 10 + 00000 = 1,000,000pF = 1000 nF = 1 uf. And that's exactly the way you would write it too, or figure it out. Value is always marked in pF (Picofarads). The letters added to the value is the tolerance, and in some cases a second letter is the temperature coefficient mostly only used in military applications, or industrial components. In most cases there is also a letter just after the numbers. This is a tolerance code. Most are 5 (J) to 10% (K), but certainly not limited to just these two.   So for example, it you have a capacitor with 474J printed on it: 47+4 zeros = 470000 = 470,000pF, J=5% tolerance. (470,000pF = 470nF = 0.47uf) The only major thing to remember here is to move the decimal point back six places for (uf) and three for (nf). Below in table A, is a simple version for direct conversions to make it easier for you. Now you know your capacitor is a 0.47uf 5% capacitor.  Now your looking or asking about voltage! This is pretty straight forward. They dont code that on most capacitors. The "bumble bee" type is coded with colors, but they used the standard electrical code colors. Same as resistors. This is covered later on on this page. The rest just print it on the body. In some cases the manufacturer will put ONLY their part number on the caps, like RCA. That should be obvious because they make no sense, and can not be decodes VIA electrical codes.  Other capacitors may just have 0.1 or 0.01 printed on them. If so, this represents the value in uf. Thus, 0.1 means just 0.1 uf. If you want this value in nanofarads (nf) just move the decimal three places to the right which makes it 100nF capacitor. Some caps will have a value then a letter. For example .068K. In this case its a .068uf 10% capacitor.   In few circumstances the capacitor may be marked in "pf" or "nf". However they should also in the letter "p" of "n" at a minimum.  The chart to the right is a simple conversion chart. It will help you understand how we convert uf to pf and nf.   Plastic or Bakelite round capacitors (bumble bee) < font color = #000000 >  T he color code is pretty universal with electrical and electronics. Decoding may change from device to device, but colors always represents the same number. These read a lot like resistors. Keep in mind, like before, this decodes to MMF and is equal to PF.   I find most of these in televisions and amplifiers. Sometimes in foreign radios. However, the format is always the same. Other round plastic or bakelite capacitors may have the value printed right on the body. I am sure we have all seen these, and there is no need decoding them. Some have a band on one end only, and that defines the negative or outside foil connection. For the bumble bee types there is no white band to designate the outside foil. They do have a square end molded into the body on one side. That designates the outside foil. The picture below shows an example for this.  The color code comes from the standard electrical color codes. One exception is the tolerance values. The chart below shows the values and colors associated.   The first group of four bands is your starting point, and this will decode to the value and tolerance. The second set of two bands will decode the voltage level. Using the color code and tolerance code you can calculate what the bands equate to. This equates to a 0.68uf 1600 volt 2.5 - 3% capacitor. First band = blue = 6 Second band = grey = 8 Third band = yellow = 4 or 0000 (4 zero's) Put these together 6 8 0000 = 680000pf = 0.68uf. You have seen all the charts, so this should make sense. pf to uf just go back 6 places! Forth band = orange = 4, this is the tolerance and equals 2.5-3% according to the tolerance chart. Fifth band = first voltage digit = brown = 1 Sixth band = second voltage digit = blue = 6 Take these two numbers 16 x 100 = 1600 volts This would have been a very expensive capacitor back in the day. Decoding Old Mica Capacitors:  This chart below will help figure out those codes on the Mica molded type capacitors. However, they rarely go bad. I don't think I ever found a bad one myself. Keep in mind this translates them to "pf" or "MMF". Don't worry they both mean the same thing. This example below would translate to 47pf, or 47MMF. The example below shows two methods. These are all I am aware of, and all I have ever seen. You must use logic to figure out the starting point. If your capacitor value starts off with 9 and a multiplier of 7, then there is an issue. Most of these are basic value capacitors.   Please note the "N/A" positions may have no color, and this goes for any spots that mean nothing or does not apply. Identify Capacitor Polarity:  Lets start with two of the most common: Radial (wires coming out the bottom) and Axial (wires coming out the sides). Also note the shorter lead coming from a radial capacitor is the negative end. So if there are no markings, then you will know the shorter lead is the negative end. In the examples below you will notice five different ways to show polarity. There are more, but I think this will be enough to get the point. The arrows and stripes are "almost always" present. You will find many variations of this as well. They always depict the negative lead.  What is almost always: Good question............In rare cases, long before there was a standard format you may find that positive end is marked. With multi-caps the information is on the body either by wire color, or a basic shapes imprinted by the leads. Shapes are usually a square, or triangle. In these examples below you will find an added way to figure out the polarity for axial capacitors. Remember these are marked with arrows and strips just like the radial caps. Almost always pointing to the negative end. On axial caps though, we can find the polarity just by looking for the aluminum housing. The aluminum housing is almost always the negative end. The other end will have a rubber seal, sometimes epoxy or glass, but always insulated from the housing. If you see no marks, or both sides are insulated, then you may have a non-polarized electrolytic capacitor. You would find these in crossover networks, speakers, and some amplifier circuit boards. Other than that, this should help for 99% of them.             NOW, a couple things about capacitors with out a polarity!   Take a look at these below. The first one has no markings at all. This is normal for non-polarized axial capacitors. This is the most common type found in early radios, and televisions. As well as most early electronic devices. They used paper and oil as a dielectric, then dipped them in wax. The new capacitors use a metalized poly film, and dip those in epoxy. AKA a dry capacitor. The new one will never dry out on you, will last your lifetime PLUS, and will perform just as good if not better than the original. The next capacitor is basically the same except they do have a mark for a polarity. Not necessarily for Positive and Negative. This mark denotes which side is connected to the outside foil. The mark will be a stripe running all around the body of the capacitor. The reasons for the marking has to do with coupling in Hi Fi amps. If you use these correctly they will cut down noise generated internally in the amp. You would want to connect the marked end in a special way so the out side foil doesn't interfere with another component, or send picked up noise to ground. Or can help eliminate interference from other components. Most people call these audio caps, because they are primarily used in critical, or high end amplifier circuits. However, the new caps and new technologies eliminated the need for this outer foil marking. Going forward you can replace a capacitor with a stripe with a capacitor that does not have one. WHAT ABOUT CAPACITOR VALUES   Electrolytic: Many questions about what values can be used when replacing an old capacitor. Actually, the exact replacement value should be close. In most circuits the value can be doubled, or half. For example, a 12uf (microfarad) capacitor can be replaced by a 10uf or 20uf. I would go with a higher value before a lower one though. However, in a power supply you do not want to go to high. The inrush current coming from the transformer may damage or burnout the transformer, or rectifier. This is more important as we go back in time when we used higher voltages and lower current. What most people dont realize, is capacitor tolerance back before the fifties was very high. As mush as 100%, or +/- 50/80% on many high value electrolytic filter caps. Although the original is marked 4uf, it could be 1-8uf when measured. Through the ages who knows what value it is 50 or 80 years later. Typically, your best bet would be to stay within + or - 20% of the original value. One thing you will find with values and time is the capacitance of the power supply caps. Radio's from the twenties used 600 volt 1-4 uf caps. In the thirties they used 10- 20 uf caps at 400 volts. The fifties they used 50-100uf at 150 volts. As time goes on the electronics got more efficient due to Engineering and technologies. The older sets used more voltage and less current. Thats why the caps were smaller. This could be due to cost too. The point I want to make is about the caps getting larger in value through time. When AC current is rectified VIA a diode the capacitor is used to take out the ripple and make the DC voltage as clean as possible. The less current you use the smaller the capacitor has to be. Yet not affected by voltage. Keep in mind that Ohms law is still in play. Less current but more voltage, as apposed to low voltage high current. Both of these power supplies can deliver the same power though. Just an FYI to keep you thinking.  Non-polarized: These are very much like the electrolytic with one exception. These should be closer matched. I would keep these within + or - 10%. I am sure 20% will work for most applications, but there are usually a few tighter tolerance caps in the device originally. As you go back in time those would be Mica caps because they are easier to manufacture with a tighter tolerance, and they are super stable, meaning the value is accurate as temperature, humidity, and other outside influences. So 10% should cover all of the paper type, and make it easier to adjust the device when done.  WHAT ABOUT VOLTAGE RATINGS?     Never replace a capacitor with one rated below the original capacitors voltage! HOWEVER, a replacement rated above the original value is acceptable. That's about it. If the original value is 350 volts, then any voltage rating higher is acceptable. The voltage rating on a capacitor is a maximum value. A 400-volt, 450-volt, or even 600-volt can be used to replace a 350 volt capacitor. Another thing to consider the new capacitors have a much higher tolerance to to over voltage spikes. Sometimes when you turn on a device the voltage may be higher for a short time period, then settle in the normal operating voltage. Just a point to make you realize its OK to use a 450 volt cap in a circuit the reaches 600 volts for a second or two as long as the device runs under 450 volts normally. Capacitors are designed to handle this.   WHAT ABOUT DUAL OR MULTIPLE CAPACITORS?   Dual or multiple capacitors are capacitors with more than one capacitor inside a single package. They are used to simplify the manufacturing of electronic devices. In fact it would be a better bet to replace these capacitors with single capacitors. Multiple capacitors cost more and are harder to find today. Sometimes you will find only one of the capacitors in the package is bad. If you do, replace them all anyway. These caps have a common foil and dielectric. In any case take a look at the example below. It would be a simple replacement to use axial caps in place of the multi-caps. This method is great when it comes to aesthetic. You can leave the originals in place and install these small axial caps under the chassis. Keeping the original look while enhancing performance. Just be sure to disconnect the old cap completely from the circuits. No one like the missing caps in the old thirties Philco radio's....................This way you shouldn't to pull them out.    Take a close look at the value and voltage ratings on the replacement capacitors. This is a prime example concerning values and voltages. If there were a forth wire, then you would add a third capacitor. See example 2.2 below. Save yourself the heartache and expense trying to find a replacement. USE UP THE CAPS YOU ALREADY HAVE   Here are a few other things you can do with capacitors. This is great if you have capacitors already and don't need to spend the extra money on more! In example 3.1 you will see how we can make a 50uf cap from two 25uf caps. Any of the values will add together, BUT not voltage. Notice the voltage values are different. In this case the total voltage can NOT be higher then the lowest voltage value. This is now a 50uf, 160 volt capacitor. Now take a look what happens when we add a third capacitor.  Example 3.2 is now a 100uf 160-volt capacitor. I guess you got the point by now. This is called a parallel design. Just remember capacitors add up in this configuration.    Now lets make a 12uf out of two 25uf capacitors. What we want now is a configuration that divides capacitor values. Simply put Series configuration. This can be used for the same reasons as the parellel version above, but also to double the voltage. In this configuration you should use the identicle caps and voltages. This way the internal resistance and other parasidics are equally matched, or at least close. Example 3.3 will show a 12uf 320 volt capacitor. So you lose capacitance, but you gain voltage.  I wouln't go further than two, and in delicate or sensative circuits i would stay away from this. For most situations this works perfectly. Now lets review. Always watch your voltage ratings! Always watch your polarity (notice the + on all my examples) these are called electrolytic capacitors because they have a polarity. Be sure you discharge your capacitors before you handel them. How They Work   Most antique radios failures are due to dried out CAPACITORS. Most capacitors are made with foil and a dielectric. As time goes by the material used as a dielectric can dissipate from the body of a capacitor, causing it to fail. Sometimes they short causing other failures, but most of them just OPEN-UP. The electronic circuit acts as though the capacitor isn't even in the circuit. Just replacing a couple capacitors can repair most antique radios. You may hear nothing, or you may experience a loss of selectivity and/or sensitivity. This will help to explain why for a couple bucks you can repair these problems yourself with a few capacitors!  The example below is an example of a simple bypass example in an ideal situation. This circuit will allow the DC to flow, but not the AC. In simple terms a capacitor will see AC as a short circuit.  The example below could be used as an input signal conditioner on an amplifier. Blocking DC, which can damage your speakers as well as your amp. However it will allow AC or audio (AC in many frequencies) to pass. If it were to open then nothing would get through. Or the output may sound weak and distorted. Remeber a capacitor sees AC as a short circuit, so DC sees a capacitor as an open. SOOOO, why use capacitors in a DC circuit? One reason we already know. To block AC and or noise. If we read the previous Tech Notes, we also know they are used to filter DC. With a couple more components we can use capacitors for oscillators, band pass filters, and so on. We won't go that far. I want to keep this simple to insure it could aid anyone. This circuit will allow the AC to go through, but not the DC. Just the opposite as the circuit above. Disclaimer:  The information contained within this website www.wjoe.com, or any affiliate, is derived from theoretical information based on experience and knowledge obtained in experiance. The reader "you", are ultimately responsible for any and all information used from this site. Any damage, or any consequences you experience from this information is solely your responsibility. This information is a free service, so please enjoy it! Any other use, retention, dissemination, editing, selling, or copying anything from this site, for any intent is strictly prohibited. Unless you obtain written permission by me at joe@wjoe.com. Any information on this web site is owned by myself and is intended to aid you in your research about Antique or Vintage capacitors. Please enjoy!!!!!! Written by WJOE Radio 08/10/96, LLC Edited 10/10/19