Replacing electrolytic cans with E-caps for 40-180?
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Just got a set of caps from JustRadio.
Unfortunately, the electrolytic cans were substituted with E-caps with 2 leads. As long as it works, I don't mind the looks too much. Anyway, these have the arrows for the leads. Which way are they supposed to go. Are the wires for the tips of the can type, soldered to the arrow side or vice versa?
Another dumb Q. One of the cans did not have any wires for the ground, ie, no wires soldered to the collar nut. What do I do with the second lead on the new cap?
Jun
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Jun, I believe you are talking about part 58 (16uf) and 61 (12uf) electrolytic cans. The schematic shows both to chassis gnd and (-) and the positive of 61 to the front side of field coil and the 58 to the rear side (front side being nearest to power xfmer). You can identify the polarity of electrolytic caps that you have by the arrow. The arrow points to the neg on the caps, as a matter of fact they usually alternate the arrow with a "-" sign. I have run into caps that had no arrow and it took me a while to figure out the polarity. If you look at the cans you will see that near the base of most of the caps they are flared out to accomodate the base and then rounded over the base sealing it in place, while the top is not flared.The only terminal(s) come out the base. The can itself is the negative terminal, leads out the base are positive. If you look at the smaller e-caps you will notice an indentation around the cap near one end, thats the base end and +, the other end -. I am assuming that you are going to put the new caps under the chassis rather than stuffing them in the cans. What you have to do is add a ground lug or terminal to the chassis for the neg. leads, unless you can find a ground point close to the caps to hook up to. The reason for the lack of terminals on the mounting nut is that when you tighten the nut that portion of the can crimped over the base comes into contact with the chassis and grounds the can. Also, make sure you disconect all the leads from the old cans, you cant use them as connecting point as the old caps will still be in the circuit.
Pat
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Wow!
Wonderfully detailed explaination. I really appreciate you taking the time to answer my novice question.
Jun
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Jun, your welcome. You might think about stuffing the caps, it leaves the cans on the chassis and you avoid having to add that negative terminal.
Pat
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Do I cut the can open and reseal it or is there a special way to open it?
Thanks Jun
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On the cans I use a fine (small) hacksaw and cut around the can. I put marker marks on various locations with 1-3 lines so that I can use these as re-alignment points. You can purchase metallic tape at most auto parts sorts and I use the to retape the can together. I usually make the cut toward the bottom so that in many cases the mount bracket covers the cut so it appears invisible to most people. On the nut base cans if you cut near the bottom one can see the tape but it really doesn't draw that much attention. On some cans I just tap into the existing leads that went to the old electro cap, you may have to use a heat gun on some because the inside was more a tar type composite, other cans just have liquid in them.
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Jun, basically you want to take them apart in such a way that when you put them back they will not look like they were done. With some cans that use a mounting band you can cut them up from the bottom between a 1/2 to 1 inch. The height will depend on where the the band is located. You want to have the cut fall right in the middle of the band so when you remount them the band covers the cut. Having said that, your caps, I believe, are the type that have a base with a protruding threaded bolt which fits through a hole in the chassis and a nut is threaded on which pulls the cap down and snug to the chassis. If you look at the base of the caps you have you will see that the can flares out near the bottom, the base is placed into the flared portion and the sides of the flare are wrapped around and under the base for maybe a little less than a 1/8". You can now visualize that when you tighten that nut on the bottom of the chassis the part of the can now wrapped over the bottom edges of the base are going to be pulled up tight to the chassis making physical and electrical contact with the chassis, your negative lead. The problem you run into in stuffing the caps is providing a contact point to the can. It's aluminum and therefore cannot be soldered (there are method that are claimed to be used to solder to aluminum but I have not done it and I believe it is difficult). I've given the problem with your type caps some thought and believe the following will work:
Grind or file off the 1/8" aluminum that rolls over the sides to the bottom of the base. In other words that portion that is on the bottom of the base, not the sides. This has to be done carefully so as not to damage the base. A little scratching or even small gouges can be tolerated.
With the bottom of can that was rolled over the bottom (which was basically the only thing holding the base up in the can) gone you should be able to twist out the entire base with the contents attached. You may have to play with it a little to get the flange away from the sides but if you take your time and don't force it it will come out.
What you will now have is the base out along with (possibly) some fluid and the rolled foil cap. From the foil cap you will have two leads (not necessarily wire) going to the base. The positive will be attached to the center lead exiting the center of the base. It is usually attached to a rivet which goes all the way through the base and on the outside is another terminal under the other rivet head for wiring into the curcuit of the radio. The rivet holds both terminals together physically and electrically. It could also be a aluminum rod with the foil lead welded to it and on the outside a crimped on terminal made of sheet metal or copper on the rod. Again, these are only two possibilities but they overcome the problem of not being able to solder on aluminum. The negative lead will be attached to the can usually by pressure, not necessarily welded, riveted or bolted. I believe on your type cap the negative lead may be widened at the end and draped over the edge of the base so when the base is pushed into the can it is pressed between the can and the base thus physical and electrical contact is made.
You will now have to remove the rivet and replace it with a 4-40 or 6-32 machine screw and bolt. Both on the outside and inside you place a terminal lug, to the inside one you will later solder the new cap positive, to the outside you will solder the curcuit wire(s). You should use a lock nut or lock washer on the bolt so it will not loosen somewhere down the pike.
The negative terminal presents a problem since you no longer have the metal rolled over the bottom of the base so when you tighten the nut on to the base it would be iffy if the can would come into contact with the chassis. You can use a piece of aluminum flashing (very thin aluminum used in roofing) about a 1/4" wide by an inch long and drill a hole near one end through which you place a bolt with lock nut, you will attach the negative lead of new cap under the bolt (you might want to add a washer). Conform the aluminum strip to the base from the inside, and down the side of the base. leave at least a 1/2" to fold under the base.
Using a 1" long piece of 1" plastic water or electrical pipe cut a 1/2" wide piece out of the pipe down its side. On end it will look like a "C".
Slip the pipe into the upper part of the can leaving a 1/2" exposed. Test fit the pipe/can assembly to the base, the end of the pipe should rest on the base inside the flange. with the pipe still in the can push the can and base together, the flange should fit snugly over the base and the whole assemble should look like the original can. If everything fits take it apart and, using epoxy, cement the end of the pipe to the base making sure that you position it so the can flange will slip over it as it did before. TBC
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Jun, continuing:
If every thing has worked as outlined in the last "chapter" you can now do the final assembly. You should have the base with the piece of pipe cemented to it and the empty can.
Solder the positive lead of the new cap to the center terminal lug now bolted through the center of the inside of the base.
Bolt the negative lead of the new cap to the 1" strip of aluminum flashing that has been conformed to the base. Position the stripe in the center of the 1/2" opening in the pipe and down the side of the base.
Slide the can over the base and press it home. The aluminum strip should give some resistance as it gets pinched between the base and the can. Once the can is pressed home bend the exposed stripe under the base.
With an ohm meter check that you have continuity from the can to the strip on the bottom. If that checks out you can mount the can in the chassis and tighten the mounting nut. Again, check with an ohm meter that you now have continuity from the chassis to the can.
Notes: Use thin flashing. Watch that you do not allow the new cap leads to short to each other or the can (use sleeving). The pipe supports the can on the base snugly. I don't cement (epoxy) the can to the pipe as it fits snugly on its own and has the added advantage of allowing you to replace the cap by just pulling off the can. You can cement the can to the pipe but I don't. I'm sure I must have missed something but I,m getting tired and prone to mistakezzzzzzzzzzzzzzz. whops! Boy is a picture worth a thousand word? Pat
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I was able to cut the crimped top off. Easier than I thought. Again thanks for the great instructions.
Pat
You better get to work instead of writing a book a stuffing cans ;)
Jun
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Jun, I'm interested in the method you will use to connect the new caps to the leads in the can since you have opened the opposite end. Also, how will you mask the cut? Pat
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Hi Pat
I looked at the can I have and could not identify the area of the flare at the base you alluded to. I essentially cut the top off at the crimped sides. I have very good access to the internals now. I will lengthen the leads of the replacement cap by splicing some wire. The leads will be pushed out the bottom of the can which has been opened. The rubber plug was removed and the crimped hole enlarged.
Now to make the connections, I'll have to rig something up.
To close the top without making a mess, I was thinking maybe a plumbers cold solder, an epoxy or aluminum tape. The cut is maybe an 1/8" or less. I think it'll look good enough for my purposes.
What do you think?
Jun
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Jun, try using the 1" plastic pipe. If you align it right you can epoxy the top that you cut off to the end of the pipe and then slide it into the can and push down top, that should leave it stable and you can use the metal tape over it. If the bottom is aluminium (I thought it was plastic/bakelite/phenol) you could drill a hole innit and bolt a terminal lug through it to use as your ground, otherwise you will have to put the bolt through the side somewhere. You can't solder to the aluminium. Pat
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I can actually epoxy the top onto the can itself. There is plenty of surface area.
There is a metallic mesh inside the can. Can I solder the ground lead to this? The can will be ground to the chassis by the bottom threads as before.
Thanks Jun
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Jun, if that metal mesh was inside the can its aluminium and I don't think you can solder to it. If you can get a 4-40 bolt and nut through it you might be able to bolt a lug to it and then solder to the lug. Make sure you insulate positive lead so it doesn't short in there. Pat
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