Recapping Audio Epuipment, amps, power supplies, etc.

[Pioneered]

I hope this is the right place to put this, I reckon if not I'll hear about it.
I have questions that hopefully someone can help answer in a way I may comprehend being that I'm not the sharpest pencil in the box anymore. Just so you'll know my short experience, I've recapped motherboards and vintage radios, even some vintage telephones , yes in the old phones there's at least one. But, all the recaps have been done were with the same that was removed except for dual capacitors naturally and some that just aren't made in the same values anymore.
So my question is how does one know when to replace one type (mainly electrolytic) with another and when might you want to change value and or voltage? (knowing that most the time a higher voltage rating doesn't matter)
One more question if I may, what does it really matter if you just recap with the same values or as close as you can get using in series or parallel?
Maybe I'm asking too much, I'm not sure really cause I look at replacing components as fairly simple procedure
done the way I've always done it. Thank you for any insight.

 

[Silentnet]

My understanding is that bigger higher rated reserve caps are better, generally speaking.

If you can go to film from electrolytics that seems to be considered better over all.

Beyond that I don't have the knowledge to contribute.

 

[z-adamson]

So my question is how does one know when to replace one type (mainly electrolytic) with another and when might you want to change value and or voltage? (knowing that most the time a higher voltage rating doesn't matter)
One more question if I may, what does it really matter if you just recap with the same values or as close as you can get using in series or parallel?

My basic understanding is this...

Film caps are preferred by some in the signal path. Some replace electrolytic with film in the signal path, some stick with electrolytic.

You can always increase voltage rating. No reason to decrease it.

Increasing uf value can be a good thing in the power supply section of an amp. Never heard of anyone decreasing the value. If you change the values in certain areas of a preamp or anywhere outside the power supply you can alter the tone quite a bit.

It is always safe to safe to stick with the same value cap.

 

[Pioneered]

My basic understanding is this...

Film caps are preferred by some in the signal path. Some replace electrolytic with film in the signal path, some stick with electrolytic.

You can always increase voltage rating. No reason to decrease it.

Increasing uf value can be a good thing in the power supply section of an amp. Never heard of anyone decreasing the value. If you change the values in certain areas of a preamp or anywhere outside the power supply you can alter the tone quite a bit.

It is always safe to safe to stick with the same value cap.

Okay, Thank you sir. Then recapping as I've always done, same with same is as I thought......not a problem.
I'm not one to experiment by changing values of anything being what I work on I can not replace. Better safe then sorry I figure.

 

[Powertech]

In general you can increase the cap value of reservoir filter caps to a point, and using a higher voltage replacement will give extended life. As you increase the value there will be a point where you also have to take account of the surge capacity of the rectifiers and the transformer. Also, there is a point of no real advantage in increasing it any further. When it comes to replacing with a different type of cap, it really depends upon the circuit requirements. Some applications require a polarised electrolytic capacitor even in applications other than reservoir duty. Sometimes an electrolytic cap is used in series with the signal when a preamp or tone control circuit develops (by it's design) a high DC offset. Quite often a film cap can be substituted, but be careful of the value as there may be a filtering effect involved and not all non-polarised caps like to have a sustained DC offset on them. Quite a few circuits use ceramic caps high frequency stability control or spike snubbing and should be retained because they are very good at it. Any X or Y type high voltage cap should only be replaced with the same type (for safety).

 

[Pioneered]

In general you can increase the cap value of reservoir filter caps to a point, and using a higher voltage replacement will give extended life. As you increase the value there will be a point where you also have to take account of the surge capacity of the rectifiers and the transformer. Also, there is a point of no real advantage in increasing it any further. When it comes to replacing with a different type of cap, it really depends upon the circuit requirements. Some applications require a polarised electrolytic capacitor even in applications other than reservoir duty. Sometimes an electrolytic cap is used in series with the signal when a preamp or tone control circuit develops (by it's design) a high DC offset. Quite often a film cap can be substituted, but be careful of the value as there may be a filtering effect involved and not all non-polarised caps like to have a sustained DC offset on them. Quite a few circuits use ceramic caps high frequency stability control or spike snubbing and should be retained because they are very good at it. Any X or Y type high voltage cap should only be replaced with the same type (for safety).

Thank you for your reply, although I didn't understand much I think that you said there times that you can use another type of cap and or value but, there's limits.
I believe the safest thing for me to do with my limited knowledge is to just stick to what the manufacturer put in and to only replace it with the same.

 

[z-adamson]

and using a higher voltage replacement will give extended life.

Not 100% sure how true this is, but what I have gathered reading around on this is that aluminum electrolytic caps should be run at near it's voltage rating much of the time. If, for example, the rating is 20times the voltage that the cap is operating at, then performance and longevity will suffer.

 

[mbz]

Not 100% sure how true this is, but what I have gathered reading around on this is that aluminum electrolytic caps should be run at near it's voltage rating much of the time. If, for example, the rating is 20times the voltage that the cap is operating at, then performance and longevity will suffer.

Not sure how true that is either, maybe others can chime in.

The voltage rating is for capacitor dielectric breakdown or a withstanding voltage. It is in no way an indication of when the cap begins to "work". Earlier caps were
marked with Working Voltage which I suspect was a short hand of Maximum Working Voltage. Recently used some 200V caps in the power supply since no suitable
50V caps at hand, expect they will work just as well.

When replacing caps you should try and identify the purpose/function of the cap and then identify a suitable replacement. Film caps tend to be more expensive, I don't
see any benifit in using them in the VU meter or protection circuit. Certainly should be considered for audio path.

 

[Silentnet]

^^^^
As I understand it (I am no EE) films are preferred over electrolytics in the signal path (when possible) because they tend to have tighter tolerances / less variance between them.

I believe they also tend to last longer?

 

[Pioneered]

Thank you all for your replies and helping me to try and understand this.
I will not try to do something I'm not capable of like determining what circuit I can use anything other then what the manufacturer has used.
I asked in hopes I might understand it but, as I can see my days as a CET are long behind me. At least I still remember how to solder and am
able to tell the differences between components. I know the components in a schematic but, I couldn't tell you which way the current flows through it anymore.
My best is just to look at how they are placed on the board and replace them the same way. Yes, what you don't use you lose. Again, thank you all for your help.

 

[mbz]

Films are generally better caps than electrolytics as measured by esr/tan delta (the non-ideal component of caps). Films also have much lower leakage current which
means lower background noise/hiss. These 2 factors make them suitable for audio path. Nichicon UKL series is probably the best electrolytic in the area of low
leakage.

Some schematics highlight the audio path (for 1 channel at least) which is helpful. From the schematic it's relatively easy to identify the phono, pre, power amp and
power supply stages. Low leakage caps should be used in audio path of pre and phono. Questionable benifit of using film in the power supply, eg, 1uf cap to GND
electrolytic would be fine.

 

[Pioneered]

Films are generally better caps than electrolytics as measured by esr/tan delta (the non-ideal component of caps). Films also have much lower leakage current which
means lower background noise/hiss. These 2 factors make them suitable for audio path. Nichicon UKL series is probably the best electrolytic in the area of low
leakage.

Some schematics highlight the audio path (for 1 channel at least) which is helpful. From the schematic it's relatively easy to identify the phono, pre, power amp and
power supply stages. Low leakage caps should be used in audio path of pre and phono. Questionable benifit of using film in the power supply, eg, 1uf cap to GND
electrolytic would be fine.

So, (and I know you all are trying to beat this into my head and I appreciate that), It's more suitable to use film caps in the audio path as you say.
Again, I won't depend on my comprehension of the audio path on a schem. and I won't bother you all to try to explain further, you've done much more then
I expected. Like I said before, I'll replace with the same but, I will take your advice to use better components like the Nichicon UKL series.
Thank you again, you've all been more then patient with me sharing your knowledge.

 

[triode17]

Not 100% sure how true this is, but what I have gathered reading around on this is that aluminum electrolytic caps should be run at near it's voltage rating much of the time. If, for example, the rating is 20times the voltage that the cap is operating at, then performance and longevity will suffer.

I go by the advice of Morgan Jones in the Valve Amps. book. He did a study and found that if you run an electrolytic cap at just 89% of it's rated voltage, that the cap life will be increased by 2 times. At , (I think) 70%, the life , theoretically is supped to increase by 10 times! I have also read that running a cap way below it's rated voltage will cause the insulation layer to become very thin and may not be adequate to prevent inrush current surges causing a short between foils. I run mine at about 80%.

 

[Pioneered]

I go by the advice of Morgan Jones in the Valve Amps. book. He did a study and found that if you run an electrolytic cap at just 89% of it's rated voltage, that the cap life will be increased by 2 times. At , (I think) 70%, the life , theoretically is supped to increase by 10 times! I have also read that running a cap way below it's rated voltage will cause the insulation layer to become very thin and may not be adequate to prevent inrush current surges causing a short between foils. I run mine at about 80%.

So what your saying if the circuit runs at let say 50v using a 60v rated cap would make it last longer. Of course one would have to know the exact voltage a circuit carries
with a maximum load to know what voltage and use a 11% give or take rated cap and you really can't rely on a schem. for that.. Sounds like I'd need to know much more then I'm capable of.
Besides my life time is nearing it's end so I really don't need anything to last longer then me.

 

[z-adamson]

So what your saying if the circuit runs at let say 50v using a 60v rated cap would make it last longer. Of course one would have to know the exact voltage a circuit carries
with a maximum load to know what voltage and use a 11% give or take rated cap and you really can't rely on a schem. for that.. Sounds like I'd need to know much more then I'm capable of.
Besides my life time is nearing it's end so I really don't need anything to last longer then me.

What I gather based on what I have read is replace the cap with a new cap that has the same voltage rating or bump it up a little bit.

Simple as that. No reason to make it more complicated.

If I have a bunch of 25uf caps in a device some at 30v, some at 35v and some at 40v......I will just replace them all with 40v, 25uf......get a bulk discount and keep my ordering process simpler. Thats how I approach it. I don't think to myself....."hmmm, I can increase voltage and uf by X amount and improve the design".

 

[Pioneered]

Oh! I misunderstood, certainly don't want to make ANYTHING complicated. K.I.S.S. is my motto.
Thank you sir.

 

[sssboa]

I go by the advice of Morgan Jones in the Valve Amps. book. He did a study and found that if you run an electrolytic cap at just 89% of it's rated voltage, that the cap life will be increased by 2 times. At , (I think) 70%, the life , theoretically is supped to increase by 10 times! I have also read that running a cap way below it's rated voltage will cause the insulation layer to become very thin and may not be adequate to prevent inrush current surges causing a short between foils. I run mine at about 80%.

The thing about running caps at too low voltage and insulation going thin to cause short sounds to me like caps are living organisms and their muscles will undergo atrophy if they don't exercise with enough weight

There is also the temperature rating. If a cap is rated 22uf/35v/105C/2000hrs then at temperature of say 30C it may take higher voltage than rated 35v or its life will be longer than rated life of 2000 hours.

I was restoring a 43 year old amp where many caps where working on their rated voltage +/- 1v, still the caps were in good condition. I replaced them with higher rated caps of course.

 

[triode17]

The thing about running caps at too low voltage and insulation going thin to cause short sounds to me like caps are living organisms and their muscles will undergo atrophy if they don't exercise with enough weight

Electrolytic Caps. are like living organisms in that they adapt to their 'climate'. For example, if a 400v cap. is run at 10v repeatedly , it's insulation layer will adapt to a 10v level. Then, if you put it in another device and run it at 350v, the thinned out insulation layer will have to reform back to 350v. There is a race created now between the insulation reforming and the temperature rise created by excessive leakage past the now thin insulator. If it reforms before the cap. bursts, you 've got it, if not.....Bang!

 

[gadget73]

I generally replace like with like unless I have a reason not to. If I'm pulling out parts that are 30+ years old that did not fail from over voltage or excess heat, chances are pretty good that a equivalent modern part will hold up just fine. I do tend to use parts rated for higher temperature, but usually thats just because they don't cost enough more to fuss over. Sometimes voltages get bumped for availability reasons, or the original ran too close to the margins for comfort. Usually really low voltage caps (sub-10v) or mains filter caps get that treatment. The filters in my Phase Linear were rated for 100v, it ran at 108v across them. The replacements are 160v rated.

 

[sssboa]

I generally replace like with like unless I have a reason not to. If I'm pulling out parts that are 30+ years old that did not fail from over voltage or excess heat, chances are pretty good that a equivalent modern part will hold up just fine. I do tend to use parts rated for higher temperature, but usually thats just because they don't cost enough more to fuss over. Sometimes voltages get bumped for availability reasons, or the original ran too close to the margins for comfort. Usually really low voltage caps (sub-10v) or mains filter caps get that treatment. The filters in my Phase Linear were rated for 100v, it ran at 108v across them. The replacements are 160v rated.

I didn't check at first and believed that they used some safety allowance in old amps but often they didn't so now I always go up a notch with voltage rating. I have a feeling that modern caps are not as durable to work well on their rated voltage after 40+ years as the old ones do. And there were no series even back then just Nippon had black caps, Nichicon blue and so on. Now every brand has like 50 different series of caps most measure quite bad comparing to the old caps I remove. Exceptions are Panasonic FM/FR, Nippon KZL, Nichicon HW and such, they call them ultra low esr caps, seems like they would be standard 40 years ago.