Restuffing power supply multi cap cans?

[Tyrannocaster]

I have run into references to this but can't seem to find much with Google. These things are often expensive with respect to the value of the unit (ie, $30 for a cap can on an old junker that was free and never will be worth anything except a learning experience) and I have a few old amps with bad power supply caps that are also kind of crowded inside; restuffing a cap can becomes an attractive idea but maybe that's only because I don't understand what is involved. If you have a 40/20/20 (pretty common value) rated at (for instance) 500 volts, you can get three similarly rated electrolytics that appear as though they would fit into the can with suitable shielding between their leads. Am I wrong on this? Of course, I wouldn't have the faintest idea how to open one of these things up without totally destroying it...I'm hoping someone knows of an online tutorial, or at least better search terms for Google than the ones I have been using.

[stratele52]

This is what we call "re forming" a capacitor. Sometimes, it work sometimes not . In my experience it don't work most of the time and I don't do that anymore.
You have to supply low voltage and low current to your capacitor on test
I use variac to bring power to the amp . Starting at around 25 volts AC for fews hour . I put 25 volts more also for few hour  and going like that until I reach the maximum fiter voltage or amp operating voltage. It take a day.
I also use the Heatkit Capacitor Checker.

This is I read in a Gerald Weber book.

 You can find a lot of information on Google with " reforming capacitor "

I find that for you;
www.angelfire.com/electronic/funwithtubes/Restore_cap.html

 http://hhscott.com/cc/power_supply_caps.htm

[Willabe]

This is the one I tried.

http://www.electrojumble.org/reforming.htm

The key is _limiting the current_ so the cap does not over heat as you reform it.


                    Brad     

[Tyrannocaster]

I'm not talking about reforming a cap, I'm talking about replacing the innards of a can with new caps. Reforming doesn't work with really old caps anyway; they have to be replaced.

[sluckey]

See the little can next to the rectifier tube? I restuffed it for no reason other than to see if I could. Took me a couple hours. I'll never do that again!

[Willabe]

Gerald Weber said he used to do that but I think it was on single caps.  

IIRC, he said he would just cut off the bottom of the cardboard tube, very carefully and re-stuff it.

It might work in a multi cap can, get an old one thats getting thrown out and open it up and see what you think.

      
      
                             Brad                                      
 
                          

[Tyrannocaster]

I can see that it's a fair amount of work.

I finally found some info. It's not for the faint of heart.

http://www.boatanchors.org/filtercap.htm

And here is an interesting approach using tube sockets and plugs:

http://www.ea1ddo.es/r4b.html

[tonewood]

I finally found some info. It's not for the faint of heart.

That's what I thought. It's not really that bad if you have a dremel and epoxy. It's nice because you can separate the grounds for star grounding. Just drill extra holes in the bottom of the can for the separate ground wires.
I used the instructions on page 8 of the following doc:

http://www.classicspeakerpages.net/library/klh/klh_8_klh_model_eight/restoring_the_klh_model_eig.pdf

[HotBluePlates]

Gerald Weber said he used to do that but I think it was on single caps.  

IIRC, he said he would just cut off the bottom of the cardboard tube, very carefully and re-stuff it.

I can only imagine Weber was talking about something like this:


I can easily imagine restuffing those cardboard-wrapped Mallory's with new caps. The cardboard is just a label cover over the metal can of the electrolytic.

I think I read the same thing in the late 90's. I tried cutting open exactly 1 can cap. There is a mass of nasty mess in there which will take a LOT of work to get out. Even once you do, it's hard to clean out, and a lot of work is required to ensure your new caps inside don't short to the case (which is grounded by virtue of contact to the chassis in most cases).

If you want the amp to look authentic, you can buy a replacement can (expensive, but not terrible). Or, you leave the original can, but unhook everything from it, and mount new electrolytics in its place inside.

[Tyrannocaster]

Well, I took an old can apart to see. I used a Dremel but in retrospect I don't think you need one at all; a hacksaw would do just as well since you aren't going to save anything inside except the tabs at the base. It wasn't that bad to get the stuff out but maybe this one was atypical. I don't see why it wouldn't be possible and it would sure be a lot cheaper. Mouser has Nichicon Elytics 22 uF/450 V for from $1.50 to $3.00 (depending on things I can't figure out) and they would fit so you'd be out from five to nine bucks for a three cap can. Versus $30 most places. If I had discretionary money would I buy the new ones? Of course, but I have to do this on the cheap so I look for ways to cut costs.

[stratele52]

I'm not talking about reforming a cap, I'm talking about replacing the innards of a can with new caps. Reforming doesn't work with really old caps anyway; they have to be replaced.

Ok I understand ,

You loose your time IMO

[tonewood]

Ok I understand ,

You loose your time IMO

It really doesn't take that much time.  If you need to keep a can for looks or space, it's a great (the only?) way to have individual grounds from a can.

[SoundmasterG]

I just keep the can cap in place if someone is concerned about the vintage correct look and use discrete caps inside the chassis. Today's caps are super small compared with old stuff and are cheap too. Another approach is to replace it with a custom can cap that you can get from Ted Weber. They can even make them with seperate grounds. They work well, though the glue to cap joint is pretty flimsy so care has to be taken with them. Of course if they come unglued you can just reglue them anyway so its not a big deal. I've used the Webers on a space limited chassis and it worked great.

Greg

[Tyrannocaster]

From what I can see, re-stuffing one isn't worthwhile if the can has only two sections; you can buy most of the common ones (or something that will work) for not too much money. But when you get to three sections the price shoots way up. As you say, the modern caps are so small they fit easily inside the old cans. I'm working on a really tight budget, so for me it makes sense to try to replace some of them; for instance, I have this old Regency hifi amp that I've been redoing and it has two four section caps in it. The amp isn't worth much and there is no way I would spend $60 for a couple of cans that would only take care of six of the ones in the amp. (Each can has three 20s and a smaller cathode bypass cap in it - I already replaced the latter inside the chassis.) Then there's the issue of fitting the discrete caps into the point to point wiring inside the amp and that's a PITA. Plus, my workmanship is scary to look at, LOL, and the cans are just neater.

[jjasilli]

Re-stuffing of metal cap cans, and of cardboard tubes, is usually done by restorers of antique radios, to preserve the vintage look. 

Antique (tubesandmore.com) has lots of cap cans and values.  You can almost certainly get the values you need there.  You may have to get creative: 

* put some caps in the new can in parallel with one another: 20uF + 10uF = 30uF (or just use 40uF; close enough); 3X 40uF = 120uF.
* or use a cap external to the can to put in series, or in parallel with, an internal cap to get your value.  This should still save enough space inside the chassis. 

It does take time and planning for values & layout, but this method has worked for me.