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Author Topic: Advice on replacing capacitors  (Read 763 times)

Joseph D. Macry

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Advice on replacing capacitors
« on: November 06, 2018, 10:04:02 am »

I'm intending to replace some old electrolytic caps in old (1980s) audio gear. Specifically, the ones I'm looking at are not for audio path, but smoothing caps in power supply, right after full-wave bridge rectifier.
New caps of same uF, voltage, and temperature rating are generally somewhat smaller than the old ones.
Question: Okay to use smaller sized, modern  electrolytics of same rating, or search further for same physical size?

(If you care, this is part of TASCAM DX-8, an 8-channel dbx noise reducer for 8-track reel-2-reel deck. I will be getting to the power supply in the deck itself later, which has HUGE smoothing caps.)
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Joseph Macry, CTS-I
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Scott Helmke

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Re: Advice on replacing capacitors
« Reply #1 on: November 06, 2018, 10:08:44 am »

Smaller is totally fine. Just make sure the voltage rating is at least as high, and that the capacity (uF) is about the same or slightly higher.   If you have a choice, go for the higher temperature rating.

If you were doing something like a Fender amp then you could get exact replacements, but for anything else I wouldn't bother.
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TJ (Tom) Cornish

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Re: Advice on replacing capacitors
« Reply #2 on: November 06, 2018, 10:10:17 am »

I'm intending to replace some old electrolytic caps in old (1980s) audio gear. Specifically, the ones I'm looking at are not for audio path, but smoothing caps in power supply, right after full-wave bridge rectifier.
New caps of same uF, voltage, and temperature rating are generally somewhat smaller than the old ones.
Question: Okay to use smaller sized, modern  electrolytics of same rating, or search further for same physical size?

(If you care, this is part of TASCAM DX-8, an 8-channel dbx noise reducer for 8-track reel-2-reel deck. I will be getting to the power supply in the deck itself later, which has HUGE smoothing caps.)
You should be able to replace caps of the same rating as long as they are rated for at least the voltage of the original caps and are of the same type - e.g. electrolytic.  Physical size is not a factor as far as I'm aware, though changing cap families - tantalum vs ceramic, etc. can sometimes be problematic.
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John Roberts {JR}

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Re: Advice on replacing capacitors
« Reply #3 on: November 06, 2018, 10:14:24 am »

+1  no benefit from old (larger) technology, modern caps are better.

JR
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Chris Hindle

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Re: Advice on replacing capacitors
« Reply #4 on: November 06, 2018, 12:20:48 pm »

I'm intending to replace some old electrolytic caps in old (1980s) audio gear. Specifically, the ones I'm looking at are not for audio path, but smoothing caps in power supply, right after full-wave bridge rectifier.
New caps of same uF, voltage, and temperature rating are generally somewhat smaller than the old ones.
Question: Okay to use smaller sized, modern  electrolytics of same rating, or search further for same physical size?

(If you care, this is part of TASCAM DX-8, an 8-channel dbx noise reducer for 8-track reel-2-reel deck. I will be getting to the power supply in the deck itself later, which has HUGE smoothing caps.)
I'm sure you know this, but I'll say it anyways.
Make sure you discharge those puppies before you lay a hand (or tool) on them....
Chris.
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Dave Pluke

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Re: Advice on replacing capacitors
« Reply #5 on: November 06, 2018, 10:34:48 pm »

Okay to use smaller sized, modern  electrolytics of same rating, or search further for same physical size?

Agree with the consensus.  Two additional points:

1)  Be sure to check the physical size before ordering (intended for those reading, other than the OP).  In the case of filter caps for Fender amps, for example, the 600V versions are much larger than the 400V and won't fit inside the doghouse ("a friend" told me that...  ::) ).

2)  Don't sweat small value differences.  Some values are no longer in production.  Keep in mind that tolerances swing widely in some cases (eg. F&T can caps have -10% +30% tolerance).  So, a 20uf or 25uf cap should be fine in replacing a 22uf one.

Dave
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Mike Caldwell

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Re: Advice on replacing capacitors
« Reply #6 on: November 07, 2018, 08:43:54 am »

It may be a good idea to replace the electrolytic caps in the signal path as well on something that old that you intend to keep using.



Joseph D. Macry

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Re: Advice on replacing capacitors
« Reply #7 on: November 08, 2018, 09:38:53 am »

It may be a good idea to replace the electrolytic caps in the signal path as well on something that old that you intend to keep using.

Understood and agreed. However this particular unit (dbx noise reducer) has no electrolytics in the audio path.
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Joseph Macry, CTS-I
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Scott Helmke

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Re: Advice on replacing capacitors
« Reply #8 on: November 08, 2018, 09:59:25 am »

Understood and agreed. However this particular unit (dbx noise reducer) has no electrolytics in the audio path.

You might keep an eye out for tantalum caps - they tend to be spherical blobs, and can dry out over time like electrolytics.
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John Roberts {JR}

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Re: Advice on replacing capacitors
« Reply #9 on: November 08, 2018, 10:54:56 am »

You might keep an eye out for tantalum caps - they tend to be spherical blobs, and can dry out over time like electrolytics.
Tantalum caps generally age better than aluminum electrolytic (as long as they don't short out and start a fire).

In general do no harm, replace obvious tired capacitors. Maybe run a frequency response on the audio path. Tired DC blocking caps might express as weak LF. If it ain't broke don't fix it. 

JR 
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