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Restuffing Multi-section Can Capacitors

Discussion in 'Shock Brother's DIY Amps' started by Crawfish, May 28, 2013.

  1. Crawfish

    Crawfish Tele-Afflicted Silver Supporter

    Apr 21, 2008
    Maryland, USA
    There's been some discussion on the TDPRI about the Mallory multi-section filter can caps and how to replace them. I dislike the use of discrete caps on top of or alongside the can connections inside the chassis. I also don't like to drill a chassis or add terminal strips if I can avoid it.

    Now, you can get new cans from CE Engineering (they use the old Mallory tooling), or JJ and F&T. They are all high quality parts and will work well. However, they cost a bunch of money. The CE can with the filter cap values for the amp I'm working on here runs about $35 US.

    I wanted to share a method I use for restoring old radios. On most radio chassis, there is a lot of wiring, lead dress is critical, and the chassis are generally pretty cramped. Many times there just isn't space to put discrete caps in as a replacement for a multi-section can. Instead, I cut the can open and put modern radial caps in it. I also do this for amps that use this style of filter cap.

    Here's our victim...er....patient. A 40/20/20uf 450 volt can from a 1978 Vibro Champ.

    [​IMG]

    First step is to open the can.

    You *may* be able to open the crimp at the bottom and peel back the edge that's crimped down and remove the innards from the bottom. I've done this in the past, but this particular can was crimped down to the point that I couldn't get a tool into the seam to open it up.

    However, this is actually what I wind up doing 8 out of 10 times: cut the can open along the rim. You can use a hacksaw, or, as I did here, a Dremel or other rotary tool with a heavy-duty cutting disc. The can is light aluminum and will cut easily. Try not to hack it up too much. You'll soon see why.

    [​IMG]

    Well, goll-lee.

    The top of the can slides right off, exposing the innards.

    Snip off the aluminum strips that connect the tabs on the bottom to the caps. The long strip you see is the ground. Unfortunately, it's hard to solder to, otherwise I'd reuse it. I just snip them all off.

    [​IMG]

    I have these super duper, high performance Panasonic caps I'm using as replacements. If you think these are too expensive, you can save $5 and get more generic caps.

    With a little trial-and-error, I come up with a configuration that will leave me with all of the grounds tied to one point, and the three positive sides laid out so they'll contact the appropriate tab on the can for its value, and fit easily into the can. Depending on your can, you may have 2, 3, or 4 caps inside it. Radial lead caps tend to be easier to work with for restuffing than axials.

    In this case, the grounds are tied together in the middle. The two caps on the bottom are 22uF - the second and third sections of the can, and the cap on top is the first section. The older Champs used a 20uF cap; the later ones like this used a 40uF. I decided to split the difference and use a 33uF.

    [​IMG]

    More below.
     
  2. Crawfish

    Crawfish Tele-Afflicted Silver Supporter

    Apr 21, 2008
    Maryland, USA
    (Continued from above)

    Drill holes through the bottom of the can near each of the tabs, and also a hole for the ground.

    You can see what I mean by trial-and-error. I had to arrange the caps so that each positive lead would wind up near the appropriate tab.

    Just run the leads through the holes you drilled, and solder them to their terminal and trim the leads.

    You probably see where this is going now.

    [​IMG]

    Another angle of the tabs on the bottom of the can. You can see how I ran the ground lead through a mounting tab. I'll bend that tab down and solder the ground one it's back in the amp.

    [​IMG]

    Next, we mix up a batch of J-B Weld epoxy. Spread some around the rim of the can and cut edge on the bottom of the can.

    [​IMG]

    Stick it together and...

    [​IMG]

    ...voila!

    We have a newly restuffed can cap ready to go back in our Vibro Champ.

    I like doing this because it more or less keeps the original appearance. You will see a lot of these amps where new filter caps have been cobbled together above the cap inside the amp. I just don't like that look at all. Sure, with this method, if you look closely, you can tell the can has been redone, but I think it's a far better thing than using discrete caps.

    As an aside, I also 'restuff' paper capacitors in some radios and amps too - the ones that are rare enough where I want to preserve the look of the old caps.

    Hope this is helpful.

    -Kevin
     
  3. jimmy74

    jimmy74 TDPRI Member

    68
    Sep 8, 2011
    Italy
    Wow... I once tried doing this but I know see why it didn't work... I peeled back the rim of the alluminium can but the plastic base practically fell out and left all the innards and muck trapped inside the can. I've tried just about everything, sticking a screw driver into the muck and trying to pull the whole thing out... but nothing works. I think it would have been wiser if I did slice the base off. Thanks for this precious information Kevin!
     
  4. telex76

    telex76 Doctor of Teleocity Silver Supporter

    Age:
    67
    Jun 24, 2006
    Fort Worth,Tx.
    If I couldn't afford $35 for the proper replacement, I'd get another hobby.

    I reuse the cardboard surrounds from old capacitors to preserve a vintage look, but I don't call that re-stuffing since you aren't using the actual can.
     
  5. hackworth1

    hackworth1 Friend of Leo's Vendor Member

    Very clever and well done.
     
  6. Robster

    Robster Tele-Holic

    996
    Feb 14, 2009
    Marietta, GA
    Nice job! I will try that next time. Where do you get high performance Panasonic caps?
     
  7. andyfromdenver

    andyfromdenver Friend of Leo's

    Dec 21, 2011
    grandpa's
  8. andyfromdenver

    andyfromdenver Friend of Leo's

    Dec 21, 2011
    grandpa's
    If I may add since it's a crafty thread, you can also just put the first two in there. Then, where your 100k plate resistors meet HT, run a 20/450 to a ground off the jacks or something in the upper R corner by the inputs. That separates them from a single ground by the power section.
     
  9. BobbyZ

    BobbyZ Doctor of Teleocity

    Jan 12, 2011
    Snellman MN
    I did the can restuff one time on a 62 Ampeg Reverberocket. That can was full of some kind of nasty tar. I spent I don't know how long cussing and drilling the stuff till I got it cleaned out.
    After that 35 bucks seem cheap to me !
    (looks like the newer caps don't have the tar though)

    On the Ampegs with the multi caps inside wrapped in tolet paper rolls I've use the covers for new caps and fill them with RTV.
     
  10. hackworth1

    hackworth1 Friend of Leo's Vendor Member

    Good call.
     
  11. Robster

    Robster Tele-Holic

    996
    Feb 14, 2009
    Marietta, GA
    I would add a sticker on the side of the cap can with the replacement date on it and the cap values. Make it easier for the next one to work on it.
     
  12. andyfromdenver

    andyfromdenver Friend of Leo's

    Dec 21, 2011
    grandpa's
    This was shown to me by a friend as a hum reduction too for the oldies. He replaced all the caps and the cap can and was still chasing hum.
    Then when he did that it stopped!
     
  13. Rod Parsons

    Rod Parsons Friend of Leo's

    Age:
    71
    Sep 26, 2009
    Winchester, Va.
    Sure does seem silly to me if you can buy a high quality, made in USA can cap for $35.00. I don't see any benefit to going to all that trouble, unless the can caps were unavailable..... Are there real benefits? Are the caps that you are stuffing in the can actually 'better' in anyway... Then that would make sense. The 'stuffed can" might look authentic, but since it isn't, who would really care? It was a nice lesson, however, for someone, who couldn't get the can cap..
     
  14. TheRumRunner

    TheRumRunner Tele-Afflicted

    I might try this on a Traynor head that is in the que for a re-cap.

    I'll need to break out the BASI (big a$$ soldering iron) as the tabs are basically welded to the chassis. lol

    DW
     
  15. Crawfish

    Crawfish Tele-Afflicted Silver Supporter

    Apr 21, 2008
    Maryland, USA
    Wow. Go away for a day and look at all the comments.

    Thanks for all the kind words.

    I did this because I can. (Hee hee). I agree that new cans aren't that expensive - I've used them in other projects.

    The idea was to show that replacing the filter caps in gear that use them can be approached in a different way. It really only takes 30 minutes or so to do this. It's not so much about saving money. I'm not that much of a cheapskate.

    Robster: I put a tag in the amp with that info on it. Also, the caps I used are here: http://www.mouser.com/Search/Produc...Svirtualkey66720000virtualkey667-EEU-ED2W220S . Really good stuff and not that expensive.

    Hackworth: Thank you! Your threads are always great, and I appreciate the kind word.

    A couple folks mentioned tar in the caps. Some of them have it, some don't. Really old caps used in radios from the 1920s and 1930s may have been liquid filled. RCA and Philco used to make caps that were housed in a steel or bakelite block and then loaded with tar. You can melt some of the tar with a heat gun (or heat it in the oven) and then pop the whole thing out in one blob. Do it when the wife's not around!

    -Kevin
     
  16. muchxs

    muchxs Doctor of Teleocity

    Aug 14, 2004
    New England
    I'd be careful handling the crap inside old capacitors. PCBs doesn't just stand for "Printed Circuit Boards". Lotta this stuff was made back when sex was safe, motorcycles were dangerous and four outta five doctors recommended Camels for their patients who smoke.
     
  17. Telenut62

    Telenut62 Poster Extraordinaire

    Age:
    58
    Oct 29, 2008
    Eugowra, Australia
  18. Crawfish

    Crawfish Tele-Afflicted Silver Supporter

    Apr 21, 2008
    Maryland, USA
    Yes, excellent point, as always.

    I wear gloves and then drop the innards right into the trash.

    I think the worst offenders in this regard are the older ones - there were liquid in early electrolytics and who knows what else.

    -Kevin
     
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