Capacitor spec's, choosing replacements...

I saw something similar on some industrial equipment I was working on.

The batch of capacitors used was just plain defective...

Just get some made by a different manufacturer.

dpb,

The replacement capacitors, 2200uF 80v, should have been more than adequate. No idea what failed in your receiver. Replace the caps and then take some measurements to see if anything is wrong. These caps run $3-4 apiece and are very common. Brand new parts are sometimes bad.

Dave M.

Could the polarity of the replacement capacitors have been reversed by some reasonable situation?

Is the receiver solid state(transistor) or vacuum tube? I guess, solid state. Until you try another one(different brand) in there, it is hard to tell. Often cheap caps. are crap. Try to find a mil-spec. ones or name brand like Panasonic, Sony, etc.

Most likely - bad replacement caps (mentioned by other replies). Not likely but possible - your repairman accidentally reversed polarity. Additional consideration - both the original and replacements might have failed due to an additional problem in the amplifier's circuit - producing an abnormally high load on the caps. In that case, the circuit will continue to eat replacement caps unless/until the underlying defective parts are identified and replaced.

Then it will cause a short.

Capacitor is use in many different area for filtering for doubling Voltage for passing signal through. I will assume that this capacitor is in filtering circuit and as one gentlemen outlined it, I would say it was bad Cap. The higher voltage actually it should add reliability, but reversing polarity in the filter circuit, it will short out and that will happen almost immediately.

I know there are some electronics guys here; I'm a nukeE by training w/ not much other than a basic circuits kinda' electronics background so am outta' my knowledge area here...

Had an old ('69 vintage) receiver refurb'ed and the output coupling capacitors which were replaced failed after only a couple of months. The fella' who did the work has been doing this since '83 or so and says it's the first time in his experience he's ever seen such a failure.

The schematic calls for 2200 uf/50V; those installed were actually 63V instead of 50V. Per his usual practice, he replaced them with 2200 uF/80 V/(I don't know temp rating I realize).

The originals were ELNA CE-W but I have no idea what their actual spec's might have been.

Anyway, the question is, anybody have any insight on what would be a reliable replacement for the originals with a likelihood of surviving more than a few months?

I debated putting the originals back in as they weren't the actual failure point but electrolytics tending to degrade with time after 40 years seems that would be borrowed time, too...

Notice he said output coupling.

The polarity could have been backwards. It might have been good to look at the ESR of the capacitor. Also get a high temperature rating. A higher voltage should be fine. The installed capacitors could be defective or some very old stock.

That's why I suggested reversed polarity. If it had been in a filter circuit, then a reversed capacitor would most likely have generated a fair amount of heat as it shorted, with 4th of July sounds very frequently accompanying the short.

Sounds like transistor type circuitry using that high value caps. Vacuum tube circuitry does not have caps. with that high value. Looks like direct coupled OTL amp. section.

Fake caps of some sort ? Output coupling caps should be easy to handle the voltage specified. Output caps sit at 1/2 the rail voltage. They only peak at rail voltage at clipping of amp.they can push considerable current, and could get hot with high ESR specs.

Greg

Output cap short can result in speaker failure ?? I would want to test that type cap with constant voltage out of circuit. also test capacitance and esr. Order by digikey, etc., not eBay.

Greg

...

...

It is possible; just my luck maybe...

The caps used by the tech were from one of the west coast merchants 105C rated. I don't know what the ESR spec's were; more significant perhaps and what I was hoping beyond hope somebody might have a road to find out is what the originals' spec's/construction might have been for comparison. They've a manufacturer's code but nothing other than voltage/capacitance that is decipherable.

They seem to have failed open not as dead short; did no damage; the amplifier it self was still functioning excepting there was only the barest of output to the speakers...and they're ok with a replacement amp that's been driving them for a couple/three months now since the failure and trying to decide what to replace these with. It wouldn't be such a big deal if the tech was local and could just drop by and experiment but it's costing quite a lot to just ship the unit not to mention the hassle of packing it up so trying to ensure don't have to do that again...

Neither of which happened...actually it appears they essentially opened entirely to pass virtually no current. The amp was/is still functional in all operating modes; there was simply no output above a most minimal that was totally unaffected by volume controls, etc., ...

If they'd been reversed polarity, I'm certain they'd've gone poof! in a heartbeat; this failure occurred after a few months after the replacement....

On 07/01/2015 6:55 AM, dpb wrote: ...

For clarification, the second "they" above is referring to the speakers, not the coupling caps...

Sounds like transistor type circuitry using that high value caps. Vacuum tube circuitry does not have caps. with that high value. Looks like direct coupled OTL amp. section.

Sounds like transistor type circuitry using that high value caps. Vacuum tube circuitry does not have caps. with that high value. Looks like direct coupled OTL amp. section.

Use low esr 2200 65 or 75 volt name brand caps rated for 105C or better. Don't waste solder on 85C rated caps.