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Thread: Powering up unused SS amps periodically?

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    Powering up unused SS amps periodically?

    So I have a few SS amps that don't see much use. Will just plugging them in and turning them on every few weeks (no load, no input) keep the caps in better shape? Ive googled it and come up with lots of other stuff but not an answer to this simple question. TIA Bob

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    Supporting Member mozz's Avatar
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    Yes.

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    Bent Member Chuck H's Avatar
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    I've recognized that the nefarious syndrom of electrolytic cap death is somewhat ignored WRT solid state amps. Probably because it's so commonly discussed about tube amps? But IMHumbleE it's even more an issue with SS amps because of their greater numbers. Unused caps dry out and stop taking a charge the way they should. The lower voltage environment of SS amps might make less of an acute issue compared to the power supply in tube amps, but still an issue for all electrolytics none the less.

    To be clear, age is the biggest factor. Disuse makes it worse. It can be surprising how much time an electrolytic cap of some quality can give when it's charged regularly though. So I definitely vote for powering up once in a while just for this reason.

    JM2C

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Thanks! I have a lot of tube guitar amps -11 actually . Most are 25+ years old and none have had cap issues but they get used regularly. The last couple weeks I went thru all of them- deoxit, biasing, etc. Anyways got me thinking after I looked at a few SS amps Ive neglected and thought it probably would be a good idea to to make sure I turn them on periodically.

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    Old Timer J M Fahey's Avatar
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    I think itīs a good idea.
    Maybe not "every few weeks" but 2 to 4 times a year might be fine.

    That said, my oldest amplifier I know still in regular use is a 200W power amp I made in 1972.

    Still working faithfully after 44 years with its original "Brazilian made" (of course, assembled using 100% original German stuff) Siemens capacitors.

    But then itīs in an Evangelical Church and gets used every weekend since

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    Think about how sad those amps will be if you power them up a few times a year, with no speaker connected, and no signal run through them, and then shut down and put away without actually doing anything? Just because they don't have tubes doesn't mean they don't have feelings!

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    Well my old Sherwood S7100 is connected in the bedroom-just rarely gets turned on. To that end I just did!- classical station softly playing. If I can find a "nice" place for my Rotel I'll set it up in the garage and actually use it. My PA power amp will have to settled for being powered up occasionally as well as my PA head...

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    Got the Akai out while working on the Mackie 1604 , it hasn't been touched in years , the pic isn't fuzzy that's crud.Worked flawlessly ,and yes I did a thorough cleaning, gave it the TLC it needed. Check out the ribbon cable , made of 14ga. wire (exaggerated a bit, but thicker than the 1mil stuff now days.
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    Unused caps dry out and stop taking a charge the way they should.
    I agree that electrolytics suffer if not charged from time to time. That's why storage time is limited.

    But from my professional experience (and conversations with R&D and application experts of big E-cap manufacturers) I can state the following:

    E-caps don't typically dry out from long time storage. Rather the problem is that the liquid electrolyte starts to chemically dissolve the thin insulating aluminum oxide layer which acts as dielecric. The result is increasing leakage. Charging the cap leads to re-forming of the Al2O3 layer and can heal the cap if the amount of damage is not too big.

    Drying out, however, is accelerated by elevated temperature in operation. That's why lifetime reduces with operating temperature. Drying out primarily shows in decreased capacitance.

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    Bent Member Chuck H's Avatar
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    Good to have the clarification. The thing I remember is crystallization occurring with disuse. I took this for some kind of polymerization of the electrolyte itself, but more likely coagulate of aluminum oxide then? And, following this information...

    Is it actually true then that vintage caps can be resurrected by re-forming? Because I never had much luck with this and didn't believe it. Perhaps I was doing it wrong.

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    Last edited by Chuck H; 02-10-2019 at 03:55 PM.
    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Is is actually true then that vintage caps can be resurrected by re-forming? Because I never had much luck with this and didn't believe it.
    Yes, this sometimes works. It is essential the limit the current to avoid heating up of the cap, e.g. by a low wattage bulb limiter with the amp or wiring a 1K (some authors recommend higher values) resistor in series with the cap. May take some hours.

    But re-forming cannot restore full capacitance if volatile components of the electrolyte have evaporated through the seal. Decreased electrolyte volume means decreased active area and thus permanent loss of capacitance.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Helmholtz View Post
    But re-forming cannot restore full capacitance if volatile components of the electrolyte have evaporated through the seal.
    You mean, like drying out

    Just poking at you. I get it. I suppose both evaporation and a breakdown of the oxide layer are acting in tandem. Though the evaporation isn't exacerbated by disuse it can still be a factor of time. Pretty sure NOS capacitors are still off the market for me.

    And this might explain why some older caps seem to last longer than expected. Perhaps less evaporation. Either because of an older electrolyte formula that is less prone and/or better seal construction or material. Perhaps. I know that on a couple of occasions I've seen good quality Mallory caps in older amps that were still doing their job after 50+ years. And it seemed they nearly always lasted over twenty years. I haven't come across more contemporary caps that will do that yet. And some, like most Illinois caps used in many production amps since the early 90's are downright poor in life expectancy.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

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    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    You mean, like drying out

    Just poking at you. I get it. I suppose both evaporation and a breakdown of the oxide layer are acting in tandem. Though the evaporation isn't exacerbated by disuse it can still be a factor of time. Pretty sure NOS capacitors are still off the market for me.
    Right but drying out is induced by elevated operating temperatures and oxide layer breakdown by long time storage without charge.
    It's the charge that stops the chemical breakdown of the oxide layer and leads to constant re-forming.
    Longest lifetime would be achieved by constant charged operation at room temperature.

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    Last edited by Helmholtz; 02-10-2019 at 05:06 PM.
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    Senior Member nevetslab's Avatar
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    That thought of power supply caps failing from lack of use does make me nervous, having a good half-dozen or more aging SS power amps, all using 20,000uF/100V 2" dia x 5" long computer grade electrolytic caps. And, all mounted horizontally, one of which has it's vent valve not on the high side so as to make the cap buss bar convenient. That's NOT the approved method of installation if you read the app notes from any of the cap mfgr's when they must be mounted horizontally. I think Crown did the same thing in their MicroTech and MacroTech series, though I'd have to look again.

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    The GTC has been powered up recently, though my TRIAMP's haven't been.......not all of them, though I have a set of them in use with a drummer friend of mine's studio that does get used regularly. I think with the TRIAMP's that had been in use by Compact Monitor Systems since 1989 until a couple years ago, I can't recall any of them having the filter caps fail. I'd been using Mepco, United Chemicon, Nichicon brands in production. The thought of having to replace THOSE caps these days is financially frightening.

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    Old Timer Leo_Gnardo's Avatar
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    A recent case history for illustration. A customer put away his Gallien Krueger 200MB bass combo some 20 years ago when it failed to light up one day. When he finally brought it in a couple days ago, I found the 15V supplies weren't working at all, due to failure of their 220 uF filter caps. After replacing those, tried firing up the amp and roasted a couple of small resistors being used as fuses in the low voltage supply. More of those 220 uF caps in other locations powered by those 15V supplies. After replacing half a dozen of those 220uF caps, the amp works as well as it ever did.

    It was probably the failure of one of those 220 uF's that put this GK on the junkpile 20 years ago. Lack of being charged over the course of 2 decades damaged the others.

    Possibly this is a good quality amp for the most part, but the acoustic hum from its power transformer makes it annoying to use with any quiet live act, and for recording there's obviously no point in mic'ing up the speaker with all that racket going on. Strictly for loud rock. As loud as you can get with a dinky 1x12 combo...

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    Old Timer J M Fahey's Avatar
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    That transformer might deserve some vacuum varnish impregnation.

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