When to Change Filter Caps ???

Discussion in 'The Workbench' started by NewReligion, Mar 28, 2010.

  1. NewReligion

    NewReligion Well-Known Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    9,631
    Likes Received:
    6,747
    Location:
    Wringing That Neck
    I have read so much about changeing the filter caps on amps since I have become a member here that it prompts the following question.

    When looking to buy an older head, or otherwise. How will I know that the filter caps need changed ?

    Thanks, David

    David C. Hopkins on MySpace Music - Free Streaming MP3s, Pictures & Music Downloads
     
  2. cudamax2343

    cudamax2343 New Member

    Joined:
    Mar 14, 2009
    Messages:
    772
    Likes Received:
    31
    Location:
    Outside of Chicago
    Good Question. I'd like to know too.
     
  3. cylon185

    cylon185 New Member

    Joined:
    Sep 23, 2009
    Messages:
    603
    Likes Received:
    29
    Location:
    Melbourne
  4. dbf909

    dbf909 New Member

    Joined:
    Mar 9, 2010
    Messages:
    157
    Likes Received:
    45
    If I buy an amp and the caps are over 20 years old, AND I plan to play the amp - I replace all of the electrolytics. This includes the power supply filter caps, the bias supply filter caps, and the cathode bypass caps. Although there are lots of caps out there made in the 60's and 70's that are working fine, the failure rate is very high. 20-25 years is pretty much where the failure curve goes significantly North...

    If an amp has sat in a closet or basement for many years and has not been powered on, the insulator in the caps can dry out and fail. On the other hand, if an amp has been played regularly, the caps will last longer as the warm-up/cool-down cycles actually keep them in good working condition.

    This seems counter-intuitive but is true.

    A lot of folks just wait and replace them when they go bad. I personally don't want to wait for them to go bad because that will surely happen at the most inopportune moment. And there's nothing worse that seeing smoke pouring out of your amp while it makes a fizzling sound and goes quiet in the middle of a gig.

    If we're talking about a "Collector" amp, I would try not to replace them unless they are visibly swollen or leaking. I will power it up slowly on a Variac (over a period of 3-4 hours) and watch them closely to make sure that they are OK.
     
  5. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    10 years is the average life expectancy of filter caps.
     
  6. cylon185

    cylon185 New Member

    Joined:
    Sep 23, 2009
    Messages:
    603
    Likes Received:
    29
    Location:
    Melbourne
    thx Jon!

    Btw, loved the DC 1st part :)
     
  7. PaoloJM

    PaoloJM New Member

    Joined:
    Jun 15, 2008
    Messages:
    1,514
    Likes Received:
    118
    Location:
    Cork, Ireland

    Yup, I'd agree, and preventitive maintenance is good guys.
    If your amp is coming up to it's 10nth, and you don't fancy weird shit happening during gig, then go ahead and have them replaced, even if the amp is working fine. You don't wait for your tyres to go thread-bare and skid into a ditch do you?

    However, I'd just advice people that if your amp gets a bit noisier than normal, is loosing a bit of punch, making stange noises as a note fades out etc. then don't rule out the filter capacitors simply because the amp is "less than 10 years old".
    Don't forget that if it looks like a duck, quacks like a duck and waddles like a duck, then it is probably is a duck!!
     
  8. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    Just to clarify what Paolo is saying regarding the "noisier than normal, loosing punch, making strange noises" statement (only because the way it was worded was way too easy to have it taken literally to the extreme)...this does NOT mean that this is ALWAYS indicative of filter caps. Valves going bad exert those same symptoms. However, if it's a situation where you've got known brand new valves that have been tested in another amp and the amp in question still has the above listed symtoms, then filter caps is another possible cause to consider at that point regardless of their age/actual service life.

    Sorry Paolo...just figured I'd "remove the blanket" from the blanket statement. ;) :D
     
  9. charveldan

    charveldan Well-Known Member

    Joined:
    Jan 31, 2010
    Messages:
    5,083
    Likes Received:
    2,240
    Location:
    Somewhere with a Friedman Marshall & Les Paul.
    Bias filters are electrolytic as well i always have them replaced too.:hmm:
     
  10. jcmjmp

    jcmjmp Well-Known Member

    Joined:
    Nov 20, 2008
    Messages:
    8,104
    Likes Received:
    1,096
    Location:
    Canada
    Filter cap life expectancy varies. Like a lightbulb, an electrolytic capacitor has a finite number of hours in it. Most of the larger can capacitors will last 10'000 hours.

    If you used you amp on a regular basis, you can estimate when your filter caps need changing based on the life expectancy of those caps.

    The smaller caps, Like in a DSL, will last 5000 to 7000 hours, depending on the model and how it was sized.

    For most people, the electrolytic capacitors will last closer to 15 years, maybe more.

    There is a method for testing your capacitors but it involves taking them out. If they're already out, you might as well just replace 'em. You can also have a look at the waveforms on an Oscilloscope to get an idea as to how well they're doing their job.
     
  11. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    And that brings another interesting trait about practical electronics (as opposed to theoretical electronics) to light...

    Everyone wants "guidelines" to follow but at the same time doesn't wanna feel "locked in" to anything. Yet with electronics, two things hold true -

    * There are no absolutes

    * There are LOTS of exceptions

    It is for these two reasons alone that I am against the whole "power valve swapping movement" that seems to have become ever so popular these days. Unless you're well versed in theory and valve amps and really know what you're doing, there's no absolute guarantee that it will work in the short or long term, and there are way too many exceptions that come into play with each amp model and circuit. Even for those of use who ARE well versed in this field there's no 100% guarantee that things will work, but the odds do seem to be in favor of the tech types getting things to work a lot more consistently than those who just simply follow the advice of others. The difference is that when things go wrong, actual techs know where to look whereas the non-techs would be lost up shit creek without a paddle.
     
  12. jcmjmp

    jcmjmp Well-Known Member

    Joined:
    Nov 20, 2008
    Messages:
    8,104
    Likes Received:
    1,096
    Location:
    Canada
    Are you against the "Filter Cap Swapping Movement"? Its the new thing. You ain't cool if you're not doing it. :lol:
     
  13. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    Only if it involves swapping over to the magnetically formed type that use chrome dipped gold irradiated titanum foil plates with the space age cryogenic radiation treated dielectric. Only then will I ever buy into that. :lol:
     
  14. anthonyr

    anthonyr Member

    Joined:
    Jan 15, 2009
    Messages:
    249
    Likes Received:
    5
    Location:
    Clearwater Florida
    Can you still get brand new Daly or LCR caps for guys who want the original look? Or can someone suggest a comparable brand X for a standard 50 50 500?
     
  15. Wilder Amplification

    Wilder Amplification New Member

    Joined:
    Oct 12, 2009
    Messages:
    6,163
    Likes Received:
    700
    Location:
    Fresno, CA
    I'd use F&T. They look very much like the LCR 50x50s but are a little bit shorter.

    NOS filter caps are a moot point. Just like batteries, they have a shelf life and as such they're a crapshoot and there's no guarantee that they'll be any good.

    Unless you have a way to test/measure them prior to installing them it's never a good idea to use caps that are decades old even if they've been sitting in a box all their life.
     
  16. anthonyr

    anthonyr Member

    Joined:
    Jan 15, 2009
    Messages:
    249
    Likes Received:
    5
    Location:
    Clearwater Florida
    That makes sense to me. If we're replacing "old" caps, why replace them with "old" caps? Particularly ones that have been sitting unused, as I understand the dielectric goo dries out from non use. Anyway, thanks for the tip. I actually hate this topic because it starts me thinking that I should replace mine based on age alone. The performance isn't an issue but if it has faded over 28 years, you wouldn't know what you've been missing until you popped some new ones in.
     
  17. PaoloJM

    PaoloJM New Member

    Joined:
    Jun 15, 2008
    Messages:
    1,514
    Likes Received:
    118
    Location:
    Cork, Ireland

    Where can you buy those? I can usually only get standard TAD or F&Ts. :mad: :lol:

    No worries on the blanket clarification. I was just trying get to the people that say "my amp is only 5 years old, it can't be the caps". I've seen it mentioned here once or twice here.

    It does kinda seem like vintage collectors, weekend Dumble stock exchange guys, wanna-be internet gurus and people that listen to amps with their eyes and internet forums, have removed a lot of the science from amplifier electronics.
    Can you imagine if NASA or Formula 1 worked like that? :)
     
  18. NewReligion

    NewReligion Well-Known Member VIP Member

    Joined:
    Nov 17, 2009
    Messages:
    9,631
    Likes Received:
    6,747
    Location:
    Wringing That Neck
  19. LPMarshall hack

    LPMarshall hack Well-Known Member

    Joined:
    Nov 18, 2009
    Messages:
    8,251
    Likes Received:
    5,466
    Location:
    San Diego, CA
    How much can one expect to pay to replace caps?
     
  20. MM54

    MM54 New Member

    Joined:
    Feb 14, 2010
    Messages:
    4,113
    Likes Received:
    590
    Location:
    Erie, PA
    I don't know how much a tech would charge to do it, but for just the filter caps themselves, a good estimate (in my experience) is $10/each (really like $8 or $9, but this way you don't have to add shipping).
     

Share This Page