I think I read somewhere that the recommended/average life span for power supply filter caps is 10 years..Can anyone verifiy this??
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Jerry Wallace-2001 Zum: D-10,8+6, "98 Zum: D-10,8+8,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico
http://communities.msn.com/jerrywallacemusic
Filter Caps
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jerry wallace
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Donny Hinson
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Sorry, Jerry. There's just no way to "verify" this. A lot of factors come into play here. How much you use the amp, how hot the amp gets, how old they were when they were installed (shelf life on these is a few years, too.) I've seen them last 20 years, and then I've seen the go bad in 4 or 5 years. They will usually last longer when used regularly than they will when only powered up every couple of years, too. Generally, they give warning when they are going bad. The amp starts humming, just a little at first, and then it gets progressively louder with time. Sometimes, when they begin to dry out, you'll notice the amp will "drop out" on a heavy chord.
Also, the smaller "bypass caps", which are electrolytic too, need attention. They isolate the stages of the amp, and when they go bad, the amp makes crazy howling, or whistling noises...similar to feedback.
The sad part is that the high voltage types (used in tube amps) are starting to get scarce, just like tubes! In another 10 years, some types might be almost impossible to replace. Whereas tubes and other electronic components have an infinite shelf life, a very old electrolytic capacitor may fail when installed...even though it has never been used
Also, the smaller "bypass caps", which are electrolytic too, need attention. They isolate the stages of the amp, and when they go bad, the amp makes crazy howling, or whistling noises...similar to feedback.
The sad part is that the high voltage types (used in tube amps) are starting to get scarce, just like tubes! In another 10 years, some types might be almost impossible to replace. Whereas tubes and other electronic components have an infinite shelf life, a very old electrolytic capacitor may fail when installed...even though it has never been used
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Hamilton Barnard
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Two of my Marshalls still have all of the original 30 year old caps in them (except in the bias circuit), and these amps only see '10' at the volume knob.
In my experience, changing caps every 8 - 10 years is a myth, as foolish as a concrete floor draining a car battery.
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My Marshalls.
In my experience, changing caps every 8 - 10 years is a myth, as foolish as a concrete floor draining a car battery.
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My Marshalls.
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Jack Stoner
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Electrolytics will tend to deteriorate over time. But, like Donny said there's no particular time table.
Filter caps in power supplies will show up either as decreased power output or hum. Electrolytics used as coupling caps, etc will tend to get noisy or frequency response will drop slightly.
It's interesting to note - and goes along with this subject - that the Lemay mod for the older, discrete component model, Session 400 is to replace all the electrolytic caps on the preamp board, nothing else.
When I was doing amp repair I would only replace components as needed.
Filter caps in power supplies will show up either as decreased power output or hum. Electrolytics used as coupling caps, etc will tend to get noisy or frequency response will drop slightly.
It's interesting to note - and goes along with this subject - that the Lemay mod for the older, discrete component model, Session 400 is to replace all the electrolytic caps on the preamp board, nothing else.
When I was doing amp repair I would only replace components as needed.
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Bob Metzger
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Most capacitor manufacturers insist that the service life for most electrolytics is 8 to 10 years but in fact, most will last years longer, especially the better made units. I do tend to replace them when they reach 30 years old or greater, especially if the amp they're in has any great value, as they can cause other components, some very expensive, to fail simultaneously. Most have relief seals that raise and burst at or near the end of their service life. Very large uf caps with moderate voltages in solid state amps (5000uf@50volts, for example) tend to last a very long time and I seem to replace fewer of these than the high voltage/lower uf units found in tube amps. Electrolylic caps should be thought of as service items, not unlike tires or belts on an automobile, but with a very long service life. They will drift in value over time and replacing them is part of the key to restoring an amplifier to its sound qualities present when it was new. Very occasionally, the drift in value will enhance the sound of the amp, but not normally. This is a good reason to keep the older caps, just in case. You can always measure these older units and fit new ones with these values, if you prefer the sound that your ears have grown accustomed to over the years.
Bob
Bob
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Terry Downs
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Jerry,
Due to the ripple currents and capacitance required at a rather high voltage for audio power amps, aluminum electrolytics have been the practical choice for size and cost. However, their reliability is not as good as most electronic components. In fact, military programs require special waivers for their use.
The most basic reliability calculation of an aluminum electrolytic is the good old Arrhenius equation:
L = Lb x Mv x 2^((Tmax-Tcore)/10)
where Lb is the base life, Tmax is the maximum permitted core temperature, Mv is a voltage-derating multiplier and Tcore is the average core temperature over life. This is based on the activation energy of anodic aluminum oxide and the rate of decomposition of the electrolyte/paper construction.
However, other factors must be included. For instance, the effective series resistance (ESR) of aluminum electrolytics increase with age, which results in a higher power dissipation.
In order to have any reasonable accuracy on the reliabilty prediction, you must have an accurate finite element thermal model for the capacitor. Cornell-dubilier company has a nifty Java applet to calculate reliability of an electrolytic. Check it out at http://www.cornell-dubilier.com/myweb/snapplet/snapplet07-05-01/CDThermal_Single.html
Cooling and voltage derating is the best protection. I think this applet above generates high numbers. I'm not saying this applet is highly accurate. I only know that reliability engineering considers the parameters above to make their predictions. There are large books written for this topic back when it was necessary to design high rel electronics with aluminum electroyltics. They are not used in todays high rel applications.
The thing I always hated about capacitors is that the names of capacitors are not consistient with what part of the capacitor they are talking about. Ceramic, polyester, and polypropylene are dielectrics. Tantalum and aluminum are anodes. The electrolyte in an aluminum electrolytic is the conductive media to the cathode, not the dielectric. The actual dielectric is an aluminum oxide layer thinly grown on the anode. The aluminum foil anode is etched with tunnels to increase its surface area by as much as 100. The oxide is formed on the surface in nanometer thicknesses. Paper soaked with electrolyte conducts across all that oxide surface to the negative terminal foil.
When Donny talks about shelf life, he is referring to the electrolyte "drying out". This gives the part a wear out term unlike the constant failure rate of an tantalum electrolytic. You begin to loose conduction to the anode when this happens, resulting in a decrease in capacitance. Modern aluminum types don't have this problem for up to 20 years (they say). You can bet those old 50s and 60s amps had that dry out problem. With that said, if you run a modern 500V cap on 100V, chill it, and limit its transient and ripple current, maybe it will last 20 years. I think no such practical application exists.
As far as replacing the capacitor on a preventive neasure, use a capacitance meter and measure its value with the cap out of curcuit. If it has lost 20-30% of its capacitance, you may want to replace it. You never know if the filter capacitance is adequate for a design though. 120Hz will always appear in the output at max volume. It's usually undetectable with other high volume audio on top of it. If the fundamental ripple hum is detectable with no input (nothing plugged in) signal, obviously the capacitance is inadequate. Make sure you are not confusing it with reverb tank electromagnetic pickup. Interference is usually a "buzz" containing harmonics. An inadequate power filter will result in a very low smooth hum.
Like bubba said on Forrest Gump, "that's about all I know about aluminum electrolytics"
Regards,
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Terry Downs
http://nightshift.net]http://nightshift.net]http://nightshift.net
terry@nightshift.net
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Terry Downs on 17 August 2001 at 08:19 PM.]</p></FONT>
Due to the ripple currents and capacitance required at a rather high voltage for audio power amps, aluminum electrolytics have been the practical choice for size and cost. However, their reliability is not as good as most electronic components. In fact, military programs require special waivers for their use.
The most basic reliability calculation of an aluminum electrolytic is the good old Arrhenius equation:
L = Lb x Mv x 2^((Tmax-Tcore)/10)
where Lb is the base life, Tmax is the maximum permitted core temperature, Mv is a voltage-derating multiplier and Tcore is the average core temperature over life. This is based on the activation energy of anodic aluminum oxide and the rate of decomposition of the electrolyte/paper construction.
However, other factors must be included. For instance, the effective series resistance (ESR) of aluminum electrolytics increase with age, which results in a higher power dissipation.
In order to have any reasonable accuracy on the reliabilty prediction, you must have an accurate finite element thermal model for the capacitor. Cornell-dubilier company has a nifty Java applet to calculate reliability of an electrolytic. Check it out at http://www.cornell-dubilier.com/myweb/snapplet/snapplet07-05-01/CDThermal_Single.html
Cooling and voltage derating is the best protection. I think this applet above generates high numbers. I'm not saying this applet is highly accurate. I only know that reliability engineering considers the parameters above to make their predictions. There are large books written for this topic back when it was necessary to design high rel electronics with aluminum electroyltics. They are not used in todays high rel applications.
The thing I always hated about capacitors is that the names of capacitors are not consistient with what part of the capacitor they are talking about. Ceramic, polyester, and polypropylene are dielectrics. Tantalum and aluminum are anodes. The electrolyte in an aluminum electrolytic is the conductive media to the cathode, not the dielectric. The actual dielectric is an aluminum oxide layer thinly grown on the anode. The aluminum foil anode is etched with tunnels to increase its surface area by as much as 100. The oxide is formed on the surface in nanometer thicknesses. Paper soaked with electrolyte conducts across all that oxide surface to the negative terminal foil.
When Donny talks about shelf life, he is referring to the electrolyte "drying out". This gives the part a wear out term unlike the constant failure rate of an tantalum electrolytic. You begin to loose conduction to the anode when this happens, resulting in a decrease in capacitance. Modern aluminum types don't have this problem for up to 20 years (they say). You can bet those old 50s and 60s amps had that dry out problem. With that said, if you run a modern 500V cap on 100V, chill it, and limit its transient and ripple current, maybe it will last 20 years. I think no such practical application exists.
As far as replacing the capacitor on a preventive neasure, use a capacitance meter and measure its value with the cap out of curcuit. If it has lost 20-30% of its capacitance, you may want to replace it. You never know if the filter capacitance is adequate for a design though. 120Hz will always appear in the output at max volume. It's usually undetectable with other high volume audio on top of it. If the fundamental ripple hum is detectable with no input (nothing plugged in) signal, obviously the capacitance is inadequate. Make sure you are not confusing it with reverb tank electromagnetic pickup. Interference is usually a "buzz" containing harmonics. An inadequate power filter will result in a very low smooth hum.
Like bubba said on Forrest Gump, "that's about all I know about aluminum electrolytics"
Regards,
------------------
Terry Downs
http://nightshift.net]http://nightshift.net]http://nightshift.net
terry@nightshift.net
<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Terry Downs on 17 August 2001 at 08:19 PM.]</p></FONT>
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Terry Downs
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One thing I forgot to point out in the Arrhenius equation is the 10 in the denominator of the 2^ part. This means that due to chemical reaction the life of the capacitor doubles for every 10 degrees C decrease in temperature. This means you should store your amp in the freezer when not in use. Just kidding.
Actually it is good idea to store your amplifier with aluminum electrolytics in your house. You may only heat up your tube amp for 3 hours on Saturday night, but for the rest of the week (186 hours) staying in a hot car or garage in a Texas summer would shorten the life of the capacitors.
After doing a little more checking, I found that the Illinois Capacitor Company uses the Arrhenius equation with an additional temperature term for heating due to ripple currents. The Cornell-Dubilier study just assumes ESR will degrade to 2X over its life, which is more conservative.
Actually it is good idea to store your amplifier with aluminum electrolytics in your house. You may only heat up your tube amp for 3 hours on Saturday night, but for the rest of the week (186 hours) staying in a hot car or garage in a Texas summer would shorten the life of the capacitors.
After doing a little more checking, I found that the Illinois Capacitor Company uses the Arrhenius equation with an additional temperature term for heating due to ripple currents. The Cornell-Dubilier study just assumes ESR will degrade to 2X over its life, which is more conservative.
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Steve Stallings
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I've got four older Evans amps. The two large cabinet amps both are getting kinda loud. One of them will drop out every once in a while. What should I expect to pay to get them recapped?
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Steve Stallings
Bremond, Texas
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Steve Stallings
Bremond, Texas
Carter D10/ Zum D10/Evans
Martin D35
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Steve Stallings
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any guesses? I'm just curious.
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Steve Stallings
Bremond, Texas
Carter/Emmons/Zum
Evans
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Steve Stallings
Bremond, Texas
Carter/Emmons/Zum
Evans
Martin D35
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jerry wallace
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Steve,I think there are 2 about 5000 uf filter caps in the Evans amps..I know there is in the Peaveys..The caps are about $10 each..I replace my own so I cant say about the labor charges but I would guess $50 to $100 for the labor..So thats a total of $75 to $120 dollars..I think thats in the ball park for the cost..
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Jerry Wallace-2001 Zum: D-10,8+6, "98 Zum: D-10,8+8,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico
http://communities.msn.com/jerrywallacemusic
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Jerry Wallace-2001 Zum: D-10,8+6, "98 Zum: D-10,8+8,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico
http://communities.msn.com/jerrywallacemusic
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Terry Downs
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Hi Steve,
You know the replacement of the main power supply capacitors of an Evans amp is not much more complicated than replacing the battery in your car. It has a + terminal and a - terminal. If you connect it backwards, you will not be happy with the results. Fire and smoke will result. There are not that many electrolytic manufacturers out there. If you could give the entire listing of text info on the capacitor, I could maybe help you find a source for buying the replacements.
Your friend,
Terry
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Terry Downs
http://nightshift.net
terry@nightshift.net
You know the replacement of the main power supply capacitors of an Evans amp is not much more complicated than replacing the battery in your car. It has a + terminal and a - terminal. If you connect it backwards, you will not be happy with the results. Fire and smoke will result. There are not that many electrolytic manufacturers out there. If you could give the entire listing of text info on the capacitor, I could maybe help you find a source for buying the replacements.
Your friend,
Terry
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Terry Downs
http://nightshift.net
terry@nightshift.net