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Capacitor Rebuilding for Fun or Profit

Rebuilding older electrolytic caps can be cost effective, especially when 'original' parts counts....

Capacitor Rebuilding for Fun or Profit

I restore antique radios to make the cash I need to play with my toys. Audiophiles are happy, so is my wallet.

Mainly we do this simply because the ‘original’ parts are no longer available, or if they are, the price is exorbitant.

Steps

Step #1:

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Capacitor Rebuilding for Fun or Profit
  • When working in an old TV, Audio Amplifier, or Turntable, invariably I will run across capacitors of all types, Paper, mica, electrolytic, etc.... Generally when we run into caps that are of the electrolytic type they are mostly dry, or drying out. Some common practices have people just shotgunning the problem by swapping out all old caps with new technology.
  • Electrically equivalent.....but to some of my audiophile buds, it is blasphemy bordering on the obscene. It should also be noted... with times being what they are... You can command a little bit more for the units you choose to sell noting no new tech parts are there.

Step #2:

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Capacitor Rebuilding for Fun or Profit

Let's start off with the offending part. A dual cap 50uf@150wvdc in a waxen pressed board container.

Step #3:

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Capacitor Rebuilding for Fun or Profit
  • Nicely, notice I did not use the word gently... Smiley Take an old soldering iron and use it to liquefy the resin and waxen plug in the end of the cap. Some liquid will co-operate and gently flow out, the rest will become soft like putty, and easily manageable with the tip of a small flat screwdriver. NOW, gentle heating with a HAIR DRYER will loosen the material near the wall, and then clean it with the screwdriver. When you get to them, cut the cap leads at the rivets. (You will see them and feel them with the melting iron)
  • When you get deep enough, take soldering iron and press it into the center of the old cap material. This will make a pilot hole.

Step #4:

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Capacitor Rebuilding for Fun or Profit

Take a 3/8th's drill and while holding the cap shell by the side, measure (with the drill bit) how deep you can go, less about 3/4" just for safety, and mark it with some tape . Now, take the cap and hold it with gloves or whatever you feel comfortable with... and gently drill into the cap materials. If you go slowly, the drill SHOULD take a grab onto the whole core when it gets into the upper resin and the whole core SHOULD spin in the cap barrel. STOP drilling when you get to the tape mark or the core spins.

Step #5:

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Capacitor Rebuilding for Fun or Profit

Now grab the core with a hooked dental pick, o-ring tool, or even a small bit of wire with a slight hook in it. Pull out your prize.

Step #6:

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Capacitor Rebuilding for Fun or Profit

Here are your 5 constituent parts of the cap, less the plug material.

Step #7:

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Capacitor Rebuilding for Fun or Profit

Now, here comes the fun part. Take the replacement value caps, for ME, alone, I used three 25uf@250v caps per side of the cap. Remember, CAPS IN PARALLEL ARE ADDITIVE, while keeping the working voltages the same. Yes, I purposely chose 3 caps because they will form a triangular pattern for better centering. I put a large loop on these negatives, since this will be the common point for the cap.

Step #8:

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Capacitor Rebuilding for Fun or Profit

Cap bundle with the positives wired and the rest is now the pigtail for one of the positive leads.

Step #9:

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Capacitor Rebuilding for Fun or Profit

Needed to be done twice. Leave enough wire on the second bundle to hook them together.

Step #10:

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Capacitor Rebuilding for Fun or Profit

Take the negative lead from the second cap, and feed it through the center of the first cap, and cut it long enough to hook it to the first bundle's loop(remember that?)

Step #11:

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Capacitor Rebuilding for Fun or Profit

Remove the second cap bundle. Take some black tape and put a layer or two on the top of the first bundle. Poke a hole in it with the tip of a soldering iron.

Step #12:

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Capacitor Rebuilding for Fun or Profit

Reassemble the two cap bundles, soldering the negative lead from the second bundle, and the black(or whatever color it is) to the lug on the first bundle. Attach the remaining original wires to the positive leads.

Step #13:

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Capacitor Rebuilding for Fun or Profit
  • Now, insert the whole new stack 'o caps into the old shell. Take a moment to admire your work.
  • (no pics of the next 2 steps) Cut out a small piece of gray cardboard . The annoying fiberboard most things are shipped in or used as card material. Cut it down to the size of the inside of the cap shell. Poke 3 small holes for the leads. Feed the leads through the holes and press the fiber circle into the cap body, pushing it in about 1/2".
  • Take your melting iron, and using a small candle(unlit) preferably white, but not a brilliant white, melt the bottom of the candle filling in the bottom of the cap body. This is simply for aesthetics, but what the heck. Don't be lazy and burn the candle to drip. There is conductive carbon in the dripped wax.

Step #14:

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  • Tahdah! A brand new 'antique' cap. Take a second moment to chuckle.
  • Re-inserted into the radio/amplifier. Smile knowingly to yourself.

Comments

  1. David Rose says:

    I’d agree with that. This isn’t rebuilding a capacitor, it’s using an old capacitor to disguise new capacitors so you can claim the electronics are all original and charge more for it.

    1. Winston says:

      “so you can claim the electronics are all original and charge more for it”

      I do not believe that the intent of this is fraud, simply to retain an authentic period look and, frankly, if I was told that the ancient electrolytic caps HAD NOT been replaced with modern components, I would not buy the radio.

      1. Winston says:

        ‘I would not buy the radio”

        Or would replace them myself immediately after buying it.

      2. Brad says:

        The author clearly states in the article: “You can command a little bit more for the units you choose to sell noting no new tech parts are there.” How is this not fraud?

        1. Winston says:

          Didn’t see that comment. Yep, that would definitely be fraudulent.

  2. Mark Stout says:

    Replacing old capacitors with new (more so power cords) is a good thing and does not detract from the value. Using original parts shells to make it look retro is fine, but there is the legal and moral aspect of presentation; you have to tell the buyer that you put new parts inside the old capacitor shells. It doesn’t hurt the value to do this. Claiming original parts, the new owner is likely going to get those old capacitors replaced and he’s going to find out what’s happened; you could end up in court.

    1. Winston says:

      Agree 100% and, further, there is even this point to consider about using modern electrolytic caps:

      http://en.wikipedia.org/wiki/Capacitor_plague

      If you fraudulently claim that the caps are original vintage and a short and fire occurs because of one of your modern replacement caps, you are in even deeper trouble than just that caused by your fraudulent claim.

  3. Kris says:

    While I realize these are old caps and the likelihood of them retaining charge is very low, it’s still probably a good idea to put a disclaimer on this about properly draining high voltage capacitors before working on them. Though I’m sure most tube and vintage radio guys will already know this of course.

    Still a neat idea to retain a true vintage look.

  4. Wing Zing says:

    Why the heck would one want to spend the time to assemble a stack of capacitors when you can select a single that will substitute and fit into the old casing by just searching for the values and sizing criteria in an electronics parts site like newark?

  5. Bruce brown says:

    You guys are getting a little anal retentive. I restore vintage stereo and guitar amps. Not replacing 40 plus year old electrolytic caps is asking for destruction of a very hard to find transformer, or even a fire when the old cap explodes. When I work on very valuable equipment of the 60s or before, I discuss the situation with the customer and we decide if the want old caps rebuilt(more expensive) or newer replacements. I also ask about carbon film vs carbon comp resistors. people who think that not replacing an old electrolytic cap until it fails, find out,sadly, that a new power or output transformer is abou 50 to a 100 times more expensive. Would not replacing caps during a repair make you liable for the burned down house?
    Bruce

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