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My amp will last forever... well sort of...

Discussion in 'Amps and Cabs [BG]' started by Avezzano, Jan 13, 2012.


  1. So, in another thread I've read about a fellow TBer that had to replace caps on his Nemesis 2x10 combo (one of the very first, say ten/twelve years or so) because they poured stuff out of their envelope.

    I have my ten yrs old Nemesis 2x10, too but it seems to be as good as new. The question is: is one to expect anyway similar capacitors degradation before or after? Is this a specific weak point for some amps (Nemesis or others)? Or it could instead happen to any amp anyway in (say) five/ten/fifteen years, or never or God only knows when?

    In a few words: what about amps degradation?
     
  2. will33

    will33

    May 22, 2006
    austin,tx
    Well, nothing lasts forever but in the case of capacitors, it's better for them to play the amp frequently. They'll dry out, start to leak if they just sit and never see any juice. It's common in old tube amps that have been sitting a long time to have to replace capacitors. Use them regularly, and they can last a very long time. Kind of a use it or lose it deal.
     
  3. Really? I didn't know that. I'll have to do some reading on it. Any electrolytic capacitor will dry out with age and the values will fluctuate.
     
  4. This is why for the last 9 years I owned my V4B I would run it every 6 months. Yes it can and will happen to any electrolytic cap. They don't have to leak to go soft either, I have reformed degraded caps with good success (only had one in maybe 300 short out). Reforming can not be done with the amp in a operable configuration BTW.
     
  5. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I owned one of those Nemmy combos for about a month. Of all the Eden products, that combo was the only one I ever liked. But the same week I got it, I discovered micros, and that was it for that ;)
     
  6. So it was you Jimmy! But, I mean: is this degradation fact mathematical? It WILL eventually happen to all of them, period, and it's unavoidable as the winter after autumn? How is one supposed to realise that his amp's caps are going sour? I mean: my Nemesis works great (10 years) or at least it seems to my ears and my LMK II that I bought used recently works 100% as well..... how do I tell "ok it's caps replacing time"? Please comfort this humble, trembling and weak heart of mine.....
     
  7. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Caps usually let you know when they're going bad. Usually it's by a crackling that won't go away, at least it's been that way in two amps I've recently had to do cap jobs in. As always, the old saying "If it ain't broke, don't fix it" applies.
     
  8. It can happen at any time, but usually it's old ones that go boom. According to my electrical engineer friends, "Conditioning" caps by running the amp once in awhile doesn't help. They go when they want to, and nothing you do makes any difference.
    You will notice that most E caps have a large + stamped into the top surface- this weakens the top and allows the cap to blow in a semi-controlled manner, through the top of the cylinder, in order to minimize damage to surrounding components. You might infer from this that designers expect them to blow from time to time. Just the way it is.
    If you are worried about it, it really isn't expensive to simply replace them, now.
     
  9. WingKL

    WingKL

    May 12, 2007
    You can tell if a cap is bad or is going bad by measuring it's ESR (Equivalent Series Resistance) with a meter. The measurements can be taken with the caps still in circuit. These meters come with a chart showing what ESR a cap should have for it's given capacitance. Anything too much above that value is a clear indicator it's crapping out. There was a period where some Chinese capacitor manufacturers tried to steal some electrolyte formulas but got an incomplete formula and produced a bunch of bad caps. So if your amp had some of these it will fail.

    Transistors can also drift and go bad but I don't know how often that happens.
     
  10. Thanks everybody! :) V.
     
  11. The "if it ain't broke don't fix it" philosophy doesn't apply to aging electrolytic capacitors. And they often will not exhibit much (audible) warning.

    Electrolytic caps depend on a wet paste inside. However, since a cap is made in several pieces, assembled, and sealed up, there is an inherent weakness in that the cap depends on the seal to remain intact. If the seal leaks--and indeed it will eventually, no seal is perfect-- the paste in the cap will dry out As this paste dries up, ESR (as mentioned above) increases. Measured capacitance can change. However, depending on a meter alone to see if the cap is good can be misleading. The meter is measuring the cap using the voltage inside the meter, typically a few volts. A solid-state high-powered amp can have power supply rail voltages of 70 or 80 volts or even more. A tube amp can have a B+ well in excess of 500 volts. While there are a few cap meters around that can test at those voltages, the cap must be desoldered to test it...might as well just replace it if one is going to go that far!

    Now there are some known recent instances of poorly-manufactered caps hitting the market. But other than that, "modern" caps would IMHO be good for maybe 15 to 20 years. In other words, I'm not going to automatically recap a 1990-era amp. Getting into the early 80's though, it's time (IMHO) to think about a recap as a preventive measure. Into the 70's, a recap is pretty much due. 60's and 50's amps, the amp is living on borrowed time if it's still got the original caps.

    Many folks may still think their 60's era amp is "fine". A slight hum that's present at all times, though, would be a symptom of dried-up filter caps (though of course there are other causes for hum). Low B+ in a tube amp with high ripple is a definite indicator. Other symptoms may include mushy bass response or loss of frequency response, the problem is that these symptoms come on so gradually that the owner may not recognise them.

    Note that ALL capacitor manufacturers acknowledge the limited lifespan of wetted electrolytic caps. Whether being used or whether sitting in a pristine climate-controlled storage, the mechanical seal necessary for the cap's integrity will eventually fail. This failure mechanism is well-documented.
     
  12. seamonkey

    seamonkey

    Aug 6, 2004
    Yeah there were some counterfeit caps around that somehow even made it to computer motherboards. These blew up. Justice in other countries can be quite harsh and these are off the market. Counterfeits that affect high tech business are very harshly dealt with.

    Caps created in the last 15 - 20 years are fine, even though they still make improvements. A 1 farad cap was unheard of 50 years ago. Now people hook them up to their car stereos all the time.

    Caps used for Solid-State amps aren't generally going to have a problem or wear out unless they are defective. Or abused - like applying high voltage or high heat.

    High voltage caps like those used for tube amps, especially the older ones are prone to breakdown. The old ones sealed in wax dry out. Caps are two metal places separated with a dielectric. the more area and closer you can get these plates the better the capacitance. High voltage likes to jump from plate to plate. There is no such thing as low voltage lightening.

    If you got older caps you can change them out for new ones in clever ways
    rebuild_complete.
     

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