If you ran an amp with blistered filter caps, how long can it go before....

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Dr. Tweedbucket, Jan 28, 2008.


  1. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    ...... something very bad happens? :confused:


    Here is the pic of an amp that looks like the filter caps are on their last leg. See the big blisters at the base on each cap? I wonder if that would kill your power supply or power transformer if one of them blew up?

    [​IMG]
     
  2. Mickey Shane

    Mickey Shane Supporting Member

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    How do you know that those weren't manufactured that way? All 3 look identical.
     
  3. PRNDL

    PRNDL Member

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    That's actually a good question, since the photos show some bubbles, which may be very old.

    The real problem is when the electrolyte formula breaks down and melts, which can be pretty messy. The caps in my last vintage amp (circa 1960) looked and worked fine, but after a while I noticed the new cloth colored wire was discolored. It was from the electrolyte leaking.

    In answer to your question: most techs that have experience with old amps will replace the power supply electrolytics as standard practice because they have a limited shelf-life. IMHO, that's a good practice.

    The cathode bypass electrolytics (25 to 50 VDC ratings) sometimes last a lot longer, although some techs will replace them too, as they have an effect on tone.

    Replacing old coupling caps is controversial, since the quality can vary considerably. Some prefer the LoFi tone of old low-quality paper-in-oil caps, or the smooth sound of high-quality PIO caps that are broken in.
     
  4. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    Because that is what they do at near end of life and that's what to look for on worn out filter caps. That is an ebay amp btw. My own Hiwatt DR103 is just starting to do the same, although not as extreme as that. I've never heard what happens if one lets loose, but I don't imagine it would be pretty.
     
  5. Blue Strat

    Blue Strat Member

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    Question for you: Why would you risk a valued amp by not doing the right thing and replacing the caps?

    No one can predict how long they'll last because it's not possible. You may get "answers" (maybe even ones you like), but you should disregard them.
     
  6. callaway_1

    callaway_1 Member

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    Mike is right, it is impossible to predict how long they will last. But those pictured should definitely be replaced soon.
     
  7. slider313

    slider313 Silver Supporting Member

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    They may last a day a month or a year like that. But when they go, and they will, you will be wishing you replaced them. I'm sure the amp will sound much better when they're replaced also.
     
  8. Structo

    Structo Member

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    It's the m0jo trying to get out!
    One more power chord and that m0jo will be all over the inside of the chassis!
     
  9. Jon C

    Jon C Silver Supporting Member

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    buy it & let us know....
     
  10. Groovey Records

    Groovey Records Member

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    Please indulge me I am here to learn!

    Which are the 3 filter caps we are discussing?

    Do you actually own this Amp or is this thead simply for you own erudition?
     
  11. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    I don't risk my valued amps, in fact when I saw the condition ( which again were not as bad as the pictured amp above ) I quit playing it.
     
  12. Dr. Tweedbucket

    Dr. Tweedbucket Deluxe model available !!!11

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    I don't own it, it's just an extreme example. I thought maybe someone here may have experienced a filter cap blowing on them and wondered what ill effects it had on the rest of the amp. Doesn't look like anyone has. :)
     
  13. phsyconoodler

    phsyconoodler Member

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  14. Trout

    Trout Member

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    In That picture if you look closely, all 4 caps are venting/blistered.

    Chances are that they will not last long especially if the amp has been left idle of any length of time. To me it looks like it would be a high priority situation to replace them.

    The guy that has it listed claims is sounds great, but how long?

    Trout
     
  15. lannyhall

    lannyhall Member

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    The biggest concern is that a failed cap can take out a transformer, and that could really hurt the value of a vintage amp. If you are so unfortunate as to have that come about, you can get quality replacements from Mercury Magnetics. Their products are very good, but not cheap!
     
  16. SatelliteAmps

    SatelliteAmps Member

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    Usually when a cap goes, it actually pops, and breaks the electrical connection. So, when it goes, usually the amp won't work. Rarely will it kill a transformer, or cause any voltage spikes. They can be very messy, and there is potential anytime something explodes to cause other damage to other components in an amplifier.
     
  17. Groovey Records

    Groovey Records Member

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    So I can be better informed could someone point out the color and position of the caps above in question to me. I really don't know the difference between a Cap or a Resistor appearance wise only how they function (fundamentally.)

    Below we have the circuits from two different 59 Harvard Amps. The one on top claiming original condition down to the smallest detail. Is it Possible? that after almost fifty years this amp is going to have its unique character intact sonicly. Would it be wrong to "restore" this amp

    The other also a 59 Harvard has had work done in several areas but circuit wise has this amp been given an update or a restoration. Is it just as desirable as the all original because work will need to be done on it anyway ?

    [​IMG]

    [​IMG]

    Thanks

    Listening to Memphis Underground-Herbie Mann
    on Vinyl of course
     
  18. ScottR

    ScottR Member

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    the one on the bottom looks to have had almost ALL of its caps AND resistors replaced. I understand the reasoning for replacing caps but why resistors?
     
  19. Hacksaw

    Hacksaw Time Warped Gold Supporting Member

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    about 1980, I had an old Holmes amp that popped a cap like that.. like your experience, it went everywhere! this had no warning signs. Just the loud POP. it was like christmas.. Stuff everywhere! This was the only amp I have seen do this to this day..
     
  20. Groovey Records

    Groovey Records Member

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    Great advice John,

    I think the bottom amp may have even a few more restoration issues is was adapted for use by a harp player.

    We're looking at a differene of $1000.00 for original values to an amp with unknown generations of work, understandable after almost 50 years,.

    Alas someone else is going to get both of them. I couldn't raise those funds this week.

    Thanks
    Groovey Records

    PS The ePay buy it now price on the Matching serial number original Harvard is $2.5K. If anyone here snaps it up keep us informed on what you do.

    Listening to Every Picture Tells a Story(don't it) The Faces
    on original first pressing Vinyl of course
     

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