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How hard is it to change caps?

Discussion in 'DIY' started by EricC, Dec 14, 2006.

  1. EricC

    EricC AK Subscriber Subscriber

    Messages:
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    PA
    I have disassemble receivers and changed pots but never a capacitor. Is it the same process or much different? I am sure sourceing parts and direction of the cap make it more of a challenge.
     
  2. rulerboyz

    rulerboyz AK Member

    Messages:
    2,474
    Location:
    Cornwall Ontario Canada
    Since pots have leads that are soldered into a circuit board, it would be very similar to replacing caps. The basic idea is you melt the solder joint to the point at which the component can be easily pulled out. Then drop in the new capacitors and form new solder joints to make the new ones continuous with the circuit. There are of course a lot of little steps I'm omitting. These are the steps that make it "challenging" and requires a certain amount of practise. Having a good quality, reliable solder iron helps a great deal.
     
  3. hpsenicka

    hpsenicka Moderator Subscriber

    Messages:
    5,604
    Location:
    west of Toronto, Ontario
    One of the challenges will be that modern electrolytic capacitors are physically a great deal smaller than their 30 year old counterparts... not just a simple swap out exercise.
     
  4. rulerboyz

    rulerboyz AK Member

    Messages:
    2,474
    Location:
    Cornwall Ontario Canada
    If you are talking about capacitors before 1975, that can be a slight issue. Sometimes if you pick a bit higher voltage rating than the original, for example 50V instead of 25V, the difference in size won't be as much. But it definitely varies from one value to another. Another thing you can do is to add a short length of wire sleeving to capacitor leads when the lead spacing of the original cap was signifcantly wider.
     
  5. markn2wae

    markn2wae Mark T N2WAE

    Messages:
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    Location:
    Scotch Plains, New Jersey
    Cap\part replacement in tube gear.

    A majority of tube gear is point to point wiring using terminal strips\tube socket\component lugs to support the wiring, if a PCB is used, go with the procedures for that.

    Two ways you can use to replace the caps. with point to point wiring.

    First way gets the cap. connected and is electrically secure, but not as "nice" or original looking.

    You just cut the leads close to the old\bad\changed out cap. and form a hook in the wire ends left in the set, then place your new cap in position and hook its leads to the ones you just made, crimp the loops so they don't move, solder the joint and cut off the excess lead.:thmbsp:

    Second way is a little more "elegant\professional" what ever you want to call it, but take a little more time, care and patience.

    Cut the old cap. free as before, then use your favorite solder removal tool and get as much solder off the old connection as you can.

    Once you have a nearly "naked" joint, grasp the old cap. lead and try and wiggle it loose in the joint (apply a little heat if needed)

    When the lead is loose when the joint is cold, gently pick\pry\cut\pull the old lead free from the terminal.

    Then position the new cap\part in place, feed the new lead(s) into the terminal(s) and re-solder the whole joint.

    I feel this second method looks less like a "hack job" then just the "cut and hook" method, and feel it preserves the "vintage" style of wiring present, but because you are working closer to the terminals, the danger of breaking them is greater, so more care needs to be taken here.:scratch2:

    Mark T.:music:
     
  6. pustelniakr

    pustelniakr Silver Miner at Large Subscriber

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    Tucson, AZ
  7. jaymanaa

    jaymanaa AK Subscriber Subscriber

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    OZ
  8. rmunson

    rmunson console destructor

    applogies for the noob nature of this question -

    I would like to recap my project amp but don't know how to search web sites like mouser or partsexpress for the replacement caps.

    could someone help me out?

    the values off the old caps are:

    25 MFD 50 V.D.C. (2 paper caps)
    5 MFD 150 V.D.C. (1 paper cap)

    metal can capacitor on chassis is:
    Dry Electrolytic
    40 MFD 450 VDC
    40 MFD 400 VDC
    30 MFD 350 VDC
     
  9. jcmjrt

    jcmjrt Addicted Member

    Messages:
    6,204
    Location:
    S.F. Bay
    It's probably easier to search www.tubesandmore.com and they have a small sale right now. The metal can cap is called multisection. It's OK if you have an extra section that you aren't using, and you can combine sections to get needed values.

    As far as replacing the other caps - you haven't said whether this is a high buck amp or not, and I don't know what purpose these caps are serving in the circuit. That said from those values, I'm guessing that high audio quality probably isn't all that important - maybe just replace with some other electrolytics. The values should be plus or minus 20% so for example the 25uf cap could be replaced with a 22uf and be OK. Voltage should be same or higher but try not to go waaaaay too high - waste of money and some say not as good for the cirucit.

    Also, please keep in mind that these tube amps can and have killed before. This isn't low voltage, low current work so be careful, turn off the circuit, drain caps, and keep one hand for the work and one for yourself.
     
  10. PakProtector

    PakProtector AK member

    Messages:
    3,425
    Location:
    Ann Arbor, MI
    Hey-Hey!!!,
    It all depends on what you're after in changing a cap...or what kind of cap it is. Electrolytics come in a lot of sizes and flavours and usually it matters a great deal how they're connected( polarity-wise that is ).

    Is it for a re-build? return to stock? experiment with cap sonics in one of your creations? 'lytics or film?

    The short story is that it is quite easy, soldering is fairly simple, and the rest is just a matter of being careful with what you're heating up to melt the solder on.
    cheers,
    Douglas
     
  11. lorne

    lorne Sonic Lizard

    Maybe not so easy ...

    Hi Rich,

    I just wanted to comment on some of the posts that you have submitted in regards to electrolytic caps over the last couple of years. I have read them over several times, and I have referred back to them for specifics more often than that. Many thanks for effort.

    I have to say that I admire your approach to the whole problem of turning a unit around as a stock piece. In particular, I was very impressed by your older thread that you cited above. The care that you take to replicate the original specification for each cap, as well as the data base that you use to do it has really called me to attention on a number of points.

    I have not been so diligent, and I am pretty sure that my acumen does not extend far enough to be so anyway. For example, I do not think that I can take a schematic and reverse engineer the design in order to select a cap from a selection of cap series specification tables. For the trouble you take, I am convinced that your restored 'Silver' must be the among the very best available. I am sure that the rest of your procedures receive the same attention.

    Sometimes I order FC's and other caps for projects. But lately I have been shopping in the parts bins of the three local suppliers. There are a number of brands available, and the series are usually pretty standard grade. I select 105 degree types whenever I can. I try very hard to stick exactly to the original value and the voltage rating whenever possible — in the mere hope that I come close to replication. Sometimes I have to use a higher voltage rating to avoid using what appears to be stale or NOS stock. Typical brands are TK, L-Tec (an offshore TK product), Nippon Chemicon, Marcon (which I think has been bought out by Nippon C.) and sometimes Nichicon and and Elna. (Of course, even as reduced as Akihabara has become, it is awash in caps. But that is a very expensive train ride from my burg).

    I guess I am taking a chance, and perhaps the optimum result will not be anything like a sure thing. For example, I am wondering (as I have done so before) exactly what those orange 4.7 uF 50 Volt LR series Nippon Chemicons are on my tone board. A few years ago I went on forums to inquire and search around for some sort of data base — or any info at all — in regards to obsolete/discontinued series. No one was able to come up with anything useful. For awhile I scoured downloaded spec sheets for ESR and ripple, leakage etc. But, in the end I said to myself, “Aw _ it” and faxed off to order FC’s. And now here I am using standard, readily available series for projects. (Oh, BTW, I’ve decided to use BP types to replace the 8 orange jobs — for better or worse).

    But one thing is for sure. Every cap change out I have done, regardless of what vintage piece it was, has resulted in dramatic sonic benefits — perhaps even allowing for the infamous ‘psycho-audio’ factor. But your articles have me thinking. Perhaps it was the new solder joints that most contributed difference!

    I have not usually reflowed boards because I have been shy about putting heat on old parts — unless I saw a suspicious joint (duh). But last night I found the volume board in my SA-8900 so suspect that I reflowed everything on the board. (I may have stressed the styrols). The other boards look better, yet I am thinking about reflowing them too — especially after reading your article for the nth time.

    Not all writers would agree with your conservative opinion on the subject of change-outs. Some argue that it is a priority that confers immediate sonic benefits in older gear, as opposed to it being the conservation measure that you have prescribed. After a lot of reflection, I think that YOU have the salient point. You have done the measurements on old caps. You have combed through the circuits, presumably watching wave forms and so on.

    Sometimes the change-out enthusiasts seem to be the same people who like using exotic caps. I may have gone too much in the other direction — using very common series. But the use of exotic parts in analogue circuits raises grave doubts about the wisdom of forgoing the expense, and moreover spurs on suspicion in regards to their opinions regarding the immediate benefit of replacing caps wholesale and out of hand.

    Perhaps I have to resist embracing the ‘pancea’ that you have cautioned against. Perhaps I am like many others in AK. Perhaps we have arrived at a point where we need to purchase an oscilloscope, a signal generator and prepare ourselves for knowing how to use these tools to diagnose any specific problems.

    I respect your detestation of the ‘shotgun’ approach. But there must be others like me who have found electronics to be fascinating and rewarding but, nevertheless, difficult, opaque and resistant to our understanding. Sometimes the shotgun seems like the best solution — crude, unscientific:stupid: :stupid: :sigh: .
     
  12. pustelniakr

    pustelniakr Silver Miner at Large Subscriber

    Messages:
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    Location:
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    The orange Chemicon LR series is replaceable by Xicon LLRL series. Both series are low leakage/low noise. The Xicons are even orange. It is not a big series, at least from Mouser where I get them. If I can't find Xicons in the right value/voltage, I use a film cap (Panasonic V series works well), physical size being the main limitation. Mouser does have 4.7, 50v in Xicon LLRL series.

    As for the styrol caps, I carefully examine the solder joints in close thermal proximity (the cap's joint and any others that that on on the same trace, within 1/2" or so). If the joints look OK, I mark them with a red sharpie, so I will stay off of them. The sharpie comes off when I cleanthe old flux off of the board.

    Enjoy,
    Rich P
     
  13. rmunson

    rmunson console destructor

  14. kalpol

    kalpol New Member

    Messages:
    31
    This is a damn good thread.

    I'm making a foray into recapping my Marantz 1090 and found this thread...great stuff. Thanks folks!
     
  15. ak_47_boy

    ak_47_boy Member

    Messages:
    64
    Finding the right cap is the hardest part, cap's on pcb's are easy to change. Case wired capacitors are a bit harder but still easy. SMD cap's are hard, takes time to get good at it..
     
  16. ericj

    ericj Well-Known Member

    Messages:
    613
    Location:
    Utah
    One more piece of advice - when desoldering capacitors from modern multi-layer boards, especially with solid groundplanes, it can sometimes be almost impossible to get the solder out of a plated through-hole.

    One method is to saturate some solder wick with a good mildly activated or just plain activated flux and see if you can draw it out with a good hot iron. You'd be surprised what a difference good flux can make. Note that when using activated flux it is critical to clean the board after you're done. With mildly activated flux, it's optional but suggested.

    Failing that, get a tiny carbide rasp and just drill the solder out of the hole by holding the rasp between thumb and forefinger and twisting. Harbor Freight Tools sells assortments of carbide rasps for a few dollars.
     

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