Are these "bulging"? How much bulge is too much? Or is _any_ bulging to much? "If you can see that it's not flat, it's too much"?
Thanks, Bob
Are these "bulging"? How much bulge is too much? Or is _any_ bulging to much? "If you can see that it's not flat, it's too much"?
Thanks, Bob
Bulging is not an indication of the condition of a capacitor. I've seen many physically large capacitors in power supplies show some bulge and be dead on for value and ESR, and others that looked brand new and were decidedly low in value and high in ESR.
Either pull them and test them or at least scope across them (watch for hot ground with your scope).
In this case (I checked the photo) the bulging is certainly indicative of a dying capacitor. Another clue is the black plastic sleeve has pulled away from the top of the cap. As a matter of course we replace any caps where the sleeve has shrunk - that is an indication of the cap overheating or simply being in too hot an environment. A new cap has the sleeve covering around 25% of the top of the cap, if you can see signs of shrinkage then time to test and likely replace the cap.
As an aside, it is interesting that early amplifiers put all the transistors in sockets (pretty reliable devices actually) and yet soldered in the most failure prone part of all - the caps! Only on the odd rare tube equipment did you see electrolytic cans that had an octal style plug. Of course if the caps were in sockets then you would have one more junction to fail (OK two junctions per cap) but at least you could replace them more easily.
Ducking.
John ;-#(#
-- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd.
In general, capacitors are relatively inexpensive such that if one is in any doubt at all, replace them. All and at the same time, an ESR meter is a helpful - but NOT absolute - screening tool.
Yes, those caps appear to be bulging Further, the shrink covering on them has pulled down from the top. A typical cap has that covering turning onto the top by some amount greater than what you show.
My guess is that they have gotten very hot, one or more times. Which would explain both the shrinkage of the covering and the bulge.
Peter Wieck Melrose Park, PA
Thanks for all the prompt and helpful replies.
This is my step son's amp and I have decided that I'm not going to do any repair that might not be perfect in his eyes. So I'm going to return it and let him know that the caps should be replaced.
The shrinkage looks pretty mild to me. I've seen caps that got so hot (heat and electrolytics don't go together well) that the plastic casing had formed puckered-up 'crowns' on top. All the caps I found in that state have turned out to be f***ed, basically.
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_ bulging
"not going to do any repair that might not be perfect in his eyes" Hmmm strange choice of words? How are you quantifying a 'perfect repair'? Would 'perfect' mean replacing all components that may have been degraded? hence these caps are the first step. Do you suspect others? Carbon resist ors change resistance with age...going to replace all of them? How old is the amp? Is it experiencing any other abnormalities? J
r'?
ed? hence these caps are the first step. Do you suspect others? Carbon resistors change resistance with age...going to replace all of them?
This might be the level of restoration where you hollow out the old part
and put the new part inside and then seal it back up... early vintage (1920s) radio collectors enjoy doing that!
John :-#)#
-- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd.
That doesn't look like a problem at all. The "X" dents in the top of the capacitor are a pressure-relief scheme, intended to rupture if steam forms inside the capacitor, and there's no sign those are under stress.
A must-replace scenario is when the "X" has ruptured and fluid is seen leaking, or (sometimes) the rubber seal on the other end of the capacitor has failed, which sometimes lifts the entire aluminum shell. A significant bulge but NO leaking means that there has been some overheating, which can mean a rectifier has shorted and the capacitor is not the main problem.
Many low-ESR capacitor failures have occurred in recent decades, but these look like general-purpose capacitors, not known for high failure rates. If they are forty years old, replacement might be a good idea regardless.
The best answer is to test them for C & ESR. Or replace, bulging caps are usually bad.
NT
...
The key part is the "in his eyes". I don't want to do work that _he_ might not find perfect. It's really annoying to do a favor and have it criticized.
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