Newbie Capacitor FAQ and Primer.
This seemed appropriate for the number of times I get asked these type of questions.
Help, my broken whatzit doesn't make sound?
Figure out how to fix it first. Don't recap any unit until it works. If you want to do a "recapair" 90% of the time you're just going to waste money, frustrate yourself, and make it a helluva lot harder for anyone on the boards to help you troubleshoot. Much of troubleshooting is the process of elimination, and if you add potential faults that process becomes exponentially more difficult.
Can you provide a BOM? or list of Caps?
If you're going to do a recap of something not well covered you'll have to learn how to do so independently of the few provided BOMs here. Think of those BOMs as a a guide only, and something of a luxury. Few have time or the desire to do what can best be done by someone with a unit in front of them. Changes over the course of the production of any unit lead to changes in components. You are the one who has the power to provide the best, most accurate list for your needs.
Does this list look right, should I place my order?
Find a service manual to use as a guide if you can. Check it against what's inside (if the unit is factory stock the unit takes precedence in discrepancies). Comparing to often errant service manuals there may be more or fewer caps, different values, incorrect board screening polarities, schematic errors, incorrect part IDs, IDs that are used multiple times, and a plethora of other hiccups that only you can uncover by doing your due diligence. Take pictures of the unit and boards from multiple angles, take notes, triple check polarities. Don't be in a rush to place your parts order, the likelihood of making a mistake or leaving something off is high. Once actually beginning the recap your best chance of success is breaking down the work into stages, doing a board at a time. Check for functionality between completing boards even if reassembly is required.
How do I know where to use what caps during a recap?
My advice is to study schematics and the internal layout of vintage amplifiers/receivers. In time you'll begin to digest and identify what all the symbols mean. As your familiarity grows you'll begin understanding which boards are which just by looking inside. For starters, it's not uncommon for at least one variation of the signal path (there are many depending on switch orientation) to be shown on the schematic for one channel, usually with a bold line. This will help you determine where and which type of caps should be used. Reading the forums and all relevant posts for any particular unit is encouraged and can help obviously, but in other ways it can also be a hindrance. Many differences in opinion on capacitor replacement exist and will lead someone new down different paths that can ultimately frustrate. For example, some claim to hear improvements using audio grade caps in the power supply over low impedance, but that comes at the expense of longevity. So you need to decide for yourself what your ultimate goals are in advance of trying to follow someones lead.
My basic, generalized recommendations for replacing electrolytic capacitors, with the understanding they will differ from others on AK, that there will be variables that cause exceptions, and that more specific applications exist than what I've detailed below.
Low Impedance, aka low ESR caps
When possible use 105°, low impedance caps in the power supply and with any local filtering caps. Identifying the power supply should be pretty obvious, local filtering may be a little more difficult, but are typically in line with a regulator or regulating diode providing voltage to a particular board. The main filtering caps will vary so much in size and mounting the choice becomes as much about availability than what's ideal to use. For example, if the unit uses clamp mounting the diameter of the cap becomes paramount, and the height must only be as tall as the case will allow. Be prepared to have to change the voltage and capacitance in a reasonable way and do the best you can with what's available. For main filter caps ideally look to specifications of 105°, low impedance, low ESR, and high ripple current.
Small value electrolytics
Any electrolytic cap 3.3uf and under can be swapped for a Wima MKS2 series polyester stacked film cap, where space allows. I do it whenever and wherever I can regardless of what circuit they are used. It's a simple matter of being a more reliable, better behaving, and in some circuits; better sounding capacitor than an electrolytic. In some circumstances where a signal cap uses 4.7uf or 10uf electrolytic I also find a way to make use of a Wima MKS2, again space dependent. If on the rare occasion the stock electrolytic cap is quite small say 0.22uf or smaller, you can possibly use a polypropylene substitute like the Wima MKP 2 series which is theoretically superior to polyester.
Understand that film caps will inherently be low leakage, so using them will automatically provide lower leakage than you can get from any electrolytic cap. Film caps are bi-polar (aka non polar) and are perfectly acceptable substitutes for polarized caps. This is NOT true in reverse however, because you CANNOT use a polar cap to replace a non-polar one. Because film caps are non-polar their orientation is not a concern. They have no positive or negative poles so can placed in the board in either direction.
Bi-Polars
If there happens to be a bi-polar electrolytic in the power supply, protection circuit or elsewhere that is larger in capacitance than 10uf I try to use a Nichicon ES series bi-polar electrolytic cap. The ES series is somewhat large in diameter for their relative capacitance and will sometimes not fit the available space. In this case I use whatever name brand bi-polar series I can find in an acceptable size.
Low Leakage cap above 3.3uf
Low leakage caps are frequently found in the tone amp, filtering, preamp, and phono amp circuits . If you find an orange jacketed cap in a 70's Kenwood it can be identified as a low leak cap. If that cap is not replaceable by a film cap per my recommendation above because either it's too large in capacitance or won't fit due to space then use a Nichicon UKL series replacement. The Nichicon UKL series come in both 85 degree and 105 degree versions. I try to use the higher temp version when I can find them, but don't sweat it if you can't and go with what's available.
Audio Caps
I use audio caps primarily in coupling stages and in locations in the signal path where a low leakage cap wasn't factory installed. Occasionally I might also use them when I don't have the correct value of a low impedance or UKL cap on hand as a bit of a compromise. I should also mention there is some research to suggest that using a good Bi-polar electrolytic like the Nichicon ES can have lower distortion than regular polar audio caps so feel free to experiment with that option.
Size Selection, Diameter vs.Voltage
Sizing of the caps is something I'm particular too. I don't see this get mentioned much. I try to make any recap I do look like it could have been factory done. In order to have a new cap have the same diameter as the one that came out, you'll almost always need to increase the voltage value. This is important for two reasons. Firstly, a vintage cap and a modern cap of the same diameter will almost always have the same lead spacing ensuring a proper original fit. Secondly, the specs of a 16V and even a 25V cap will be vastly inferior to one of the same capacitance of a slightly higher voltage, say 50V. For this reason I try never to use electrolytics below 25V. There are rare times I'm forced to use 16V for size reasons and then also occasions where an even lower voltage cap is called for due to the circuit function.
Some will argue that selecting a voltage increase beyond a certain percentage of the actual operating voltage will impair a caps ability to perform optimally. I would argue that while it may not be performing optimally, and I don't know that to be certain in any case, it will spec better from the start just on the basis of being superior to a low voltage counterpart.
Increasing capacitance
Increases in capacitance require a solid understanding of the circuit in which the capacitors you'd like to bump up reside. Therefore for beginners I'd recommend only increasing the value of main filter capacitors and nowhere else unless it has been so advised. In most cases, it is safe to increase the main caps value by up to 30% without cause for concern. With many exceptions, some modern capacitors even by top brands will tend to measure on the low side of their tolerance, particularly at certain value ranges. This was not the case 40 years ago when manufacturers attempted to provide the actual value. A small bump in value could in fact be required just to maintain the closest stock value. The only way to know for certain is to measure each new cap going in. Once you've done this long enough you'll begin to see a pattern of which caps measure a little low.
This seemed appropriate for the number of times I get asked these type of questions.
Help, my broken whatzit doesn't make sound?
Figure out how to fix it first. Don't recap any unit until it works. If you want to do a "recapair" 90% of the time you're just going to waste money, frustrate yourself, and make it a helluva lot harder for anyone on the boards to help you troubleshoot. Much of troubleshooting is the process of elimination, and if you add potential faults that process becomes exponentially more difficult.
Can you provide a BOM? or list of Caps?
If you're going to do a recap of something not well covered you'll have to learn how to do so independently of the few provided BOMs here. Think of those BOMs as a a guide only, and something of a luxury. Few have time or the desire to do what can best be done by someone with a unit in front of them. Changes over the course of the production of any unit lead to changes in components. You are the one who has the power to provide the best, most accurate list for your needs.
Does this list look right, should I place my order?
Find a service manual to use as a guide if you can. Check it against what's inside (if the unit is factory stock the unit takes precedence in discrepancies). Comparing to often errant service manuals there may be more or fewer caps, different values, incorrect board screening polarities, schematic errors, incorrect part IDs, IDs that are used multiple times, and a plethora of other hiccups that only you can uncover by doing your due diligence. Take pictures of the unit and boards from multiple angles, take notes, triple check polarities. Don't be in a rush to place your parts order, the likelihood of making a mistake or leaving something off is high. Once actually beginning the recap your best chance of success is breaking down the work into stages, doing a board at a time. Check for functionality between completing boards even if reassembly is required.
How do I know where to use what caps during a recap?
My advice is to study schematics and the internal layout of vintage amplifiers/receivers. In time you'll begin to digest and identify what all the symbols mean. As your familiarity grows you'll begin understanding which boards are which just by looking inside. For starters, it's not uncommon for at least one variation of the signal path (there are many depending on switch orientation) to be shown on the schematic for one channel, usually with a bold line. This will help you determine where and which type of caps should be used. Reading the forums and all relevant posts for any particular unit is encouraged and can help obviously, but in other ways it can also be a hindrance. Many differences in opinion on capacitor replacement exist and will lead someone new down different paths that can ultimately frustrate. For example, some claim to hear improvements using audio grade caps in the power supply over low impedance, but that comes at the expense of longevity. So you need to decide for yourself what your ultimate goals are in advance of trying to follow someones lead.
My basic, generalized recommendations for replacing electrolytic capacitors, with the understanding they will differ from others on AK, that there will be variables that cause exceptions, and that more specific applications exist than what I've detailed below.
Low Impedance, aka low ESR caps
When possible use 105°, low impedance caps in the power supply and with any local filtering caps. Identifying the power supply should be pretty obvious, local filtering may be a little more difficult, but are typically in line with a regulator or regulating diode providing voltage to a particular board. The main filtering caps will vary so much in size and mounting the choice becomes as much about availability than what's ideal to use. For example, if the unit uses clamp mounting the diameter of the cap becomes paramount, and the height must only be as tall as the case will allow. Be prepared to have to change the voltage and capacitance in a reasonable way and do the best you can with what's available. For main filter caps ideally look to specifications of 105°, low impedance, low ESR, and high ripple current.
Small value electrolytics
Any electrolytic cap 3.3uf and under can be swapped for a Wima MKS2 series polyester stacked film cap, where space allows. I do it whenever and wherever I can regardless of what circuit they are used. It's a simple matter of being a more reliable, better behaving, and in some circuits; better sounding capacitor than an electrolytic. In some circumstances where a signal cap uses 4.7uf or 10uf electrolytic I also find a way to make use of a Wima MKS2, again space dependent. If on the rare occasion the stock electrolytic cap is quite small say 0.22uf or smaller, you can possibly use a polypropylene substitute like the Wima MKP 2 series which is theoretically superior to polyester.
Understand that film caps will inherently be low leakage, so using them will automatically provide lower leakage than you can get from any electrolytic cap. Film caps are bi-polar (aka non polar) and are perfectly acceptable substitutes for polarized caps. This is NOT true in reverse however, because you CANNOT use a polar cap to replace a non-polar one. Because film caps are non-polar their orientation is not a concern. They have no positive or negative poles so can placed in the board in either direction.
Bi-Polars
If there happens to be a bi-polar electrolytic in the power supply, protection circuit or elsewhere that is larger in capacitance than 10uf I try to use a Nichicon ES series bi-polar electrolytic cap. The ES series is somewhat large in diameter for their relative capacitance and will sometimes not fit the available space. In this case I use whatever name brand bi-polar series I can find in an acceptable size.
Low Leakage cap above 3.3uf
Low leakage caps are frequently found in the tone amp, filtering, preamp, and phono amp circuits . If you find an orange jacketed cap in a 70's Kenwood it can be identified as a low leak cap. If that cap is not replaceable by a film cap per my recommendation above because either it's too large in capacitance or won't fit due to space then use a Nichicon UKL series replacement. The Nichicon UKL series come in both 85 degree and 105 degree versions. I try to use the higher temp version when I can find them, but don't sweat it if you can't and go with what's available.
Audio Caps
I use audio caps primarily in coupling stages and in locations in the signal path where a low leakage cap wasn't factory installed. Occasionally I might also use them when I don't have the correct value of a low impedance or UKL cap on hand as a bit of a compromise. I should also mention there is some research to suggest that using a good Bi-polar electrolytic like the Nichicon ES can have lower distortion than regular polar audio caps so feel free to experiment with that option.
Size Selection, Diameter vs.Voltage
Sizing of the caps is something I'm particular too. I don't see this get mentioned much. I try to make any recap I do look like it could have been factory done. In order to have a new cap have the same diameter as the one that came out, you'll almost always need to increase the voltage value. This is important for two reasons. Firstly, a vintage cap and a modern cap of the same diameter will almost always have the same lead spacing ensuring a proper original fit. Secondly, the specs of a 16V and even a 25V cap will be vastly inferior to one of the same capacitance of a slightly higher voltage, say 50V. For this reason I try never to use electrolytics below 25V. There are rare times I'm forced to use 16V for size reasons and then also occasions where an even lower voltage cap is called for due to the circuit function.
Some will argue that selecting a voltage increase beyond a certain percentage of the actual operating voltage will impair a caps ability to perform optimally. I would argue that while it may not be performing optimally, and I don't know that to be certain in any case, it will spec better from the start just on the basis of being superior to a low voltage counterpart.
Increasing capacitance
Increases in capacitance require a solid understanding of the circuit in which the capacitors you'd like to bump up reside. Therefore for beginners I'd recommend only increasing the value of main filter capacitors and nowhere else unless it has been so advised. In most cases, it is safe to increase the main caps value by up to 30% without cause for concern. With many exceptions, some modern capacitors even by top brands will tend to measure on the low side of their tolerance, particularly at certain value ranges. This was not the case 40 years ago when manufacturers attempted to provide the actual value. A small bump in value could in fact be required just to maintain the closest stock value. The only way to know for certain is to measure each new cap going in. Once you've done this long enough you'll begin to see a pattern of which caps measure a little low.
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