Bottlehead Forum
General Category => Technical topics => Topic started by: Jamier on April 06, 2018, 09:42:10 AM
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I have an old SS amp from the late seventies that has begun to make intermittent "popping" noises.
I opened it up and tried my best to evaluate the condition and found several small caps that look like this(see picture below). They don't appear to be leaking and on first look I didn't notice that the plastic cover had shrunk back (these caps are really small). This must be a symptom of swelling and thus, failure, right? I don't have another cap that size in the amp that doesn't look like this, so I have no size comparison to determine if it is swelling.
Jamie
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The plastic usually shrinks because it gets hot, not because the can swells. If electrolytic the can almost always has a vent. But I can't really tell what that cap is.
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I can make out the label even with the distortion of the writing from the shrinkage, I think it is a 10uF, 50V.
Jamie
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If not vented it is possibly a tantalum, in which case they do often need replacing with age.
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Doc,
Here is another view of the cap in question.Is there any harm in changing it for a good quality electrolytic with the same values? I think it is an electrolytic but I'm no expert.I found some nichicons that are the same physical size/ lead separation.
Jamie
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Just a guess, but for me intermittent popping has been a potentiometer problem. There may also be some small ones located on the board. I heard good things about Caig Deoxit products.
Could very well be capacitors
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I know that some will disagree with me, but I don't trust electrolytic capacitors in any device that is from the 1970s. Caps tend to be the most likely component to fail and cause all kinds of problems, depending on where they are located in the circuit. Essentially, any electrolytic that is more than ~15 years old is not to be trusted, no matter what it looks like on the outside. Yank 'em and replace 'em.
I wrote up a web page about stuff like this a few years ago. Perhaps there is some useful insight here: http://www.facstaff.bucknell.edu/esantane/movies/DIYRepairs.html (http://www.facstaff.bucknell.edu/esantane/movies/DIYRepairs.html)
Eric
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In this case we have been asked to advise on some capacitor in some piece of gear, and have been given an image of a cap that looks normal and has otherwise not been tested. We really don't have a clue if changing this cap or any other cap out will fix the problem described. Yes, replacing all the caps will probably help - if the device has a bad cap. There are other factors to consider in choosing replacements besides capacitance and voltage ratings - temperature rating, ESR, leakage current, case dimensions, etc.
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Doc and Eric,
Thanks to both of you for your comments on this issue. To the extent that my limited expertise allows, I agree with both of you. I should not have asked Doc to advise me on the repair of an amp that is not a Bottlehead product. Doing so puts him in a bad spot and I apologize for that. I posted a couple of crappy images and asked for his opinion; that was pretty unreasonable of me. I do feel that
Eric is probably correct concerning his opinion on old electrolytics. These caps are about 40 years old and are probably at the end of their useable life. I'm going to replace all of them, including the power supply caps, while I have it apart. It's cheap and easy enough to do. At the end of the day,
DIY means making decisions for yourself, after properly researching the subject.
Jamie