multi section capacitors

[mike hadley]

After posting my method for stuffing screw mount caps, I thought I would post how I first started with multi section caps.

as in a previous post, use either the original cap or a suitable donorafter removing the cover, file the old crimp on the base of the cap, until you see a thin line appearwhen you get to this stage the crimp can be pulled off

and the old innards removed

the original cap and it's base will have to be discarded because the base is too thick and will not fit back in the new cap, so a new base is made from copper clad board,

First with a hot air gun catch the copper edge with a knifewhen a suitable edge is lifted the rest of the copper is heated and the copper pulled off with pliers, this is quicker than etching.

the board is then filed into a disc that is a tight fit in the cap tube, drilled with the correct number of holes to suit your applicationthe cap connections are made from solder tags rivets and washers, the new bottom plate now looks like thisand now the cap is ready for stuffingthe bottom edge is then gently rolled over using either a plastic dowel or the blade of a screwdriver,

if the metal is too hard it can be annealed by coating with soap and heating until the soap turns black, caution here as the annealing temperature is close to the melting point.

If the pcb material is too thick, it can be split like slate,

take a cut off knife and drive it into the edge of the board at the desired thickness, twist the blade and the board can then be peeled apartresulting in two pieces of thin boardFrom what I understand the multi caps with mounting tags on have a separate ring crimped in the housing, this ring is made from copper or steel for soldering and would have to be retained, and re instated in the bottom of the cap before crimping, if any one can verify this please tell me,

Thanks

[Joseph W Strickland]

Mike;

Good procedures! One thing I have always had trouble with is making nice circular parts. Lots of filing and rechecking is needed. I finally bought an adjustable hole cutting saw. I also have a number of hole cutting saws that can sometimes be used without using the center drill bit. Otherwise you wind up with a hole in the center. I am fortunate to have a drill press that is very useful in drilling and cutting circular parts.

You are correct about the separate ring shaped piece in multi-section caps with twist-tabs. It would have to be kept and used in a re-built cap. Or a suitable substitute from another cap with its tabs intact. This type cap is often difficult to remove and re-use due to the tendency for assembly people to solder the tabs to the chassis metal. Not all solder guns or irons are able to provide enough heat to remove the excess solder, straighten the tab such that it can be used again and remove the old cap intact. I have had success with many but often one of the tabs does not co-operate and part breaks off. The failure rate is significant with old twist-lock tab types. Again in a pinch, a new cap can be sacrificed if not needed and on hand. I have a number of NOS caps that I have kept which are way beyond their normal useful life and can be sacrificed for making a suitable replacement.

There are still a few companies that have the replacement metal plates that can permit the installation of a twist-tab type cap where just a large circular hole exists. Capacitor manufacturers used to always supply an insulating bakelite wafer for this type cap and some even included the metal plates as well. I always made a point of keeping them even if I did not need them at the time. Many power supplies with one cap isolated from ground (especially voltage doubler circuits) used these bakelite wafers for mounting and they often get damaged while changing defective caps. Availability of these wafers is not so great any more. They can be found, but there are not too many sources.

Joe

[mike hadley]

Joe;
I am rather fortunate that I work in the industrial repair business, the caps that I have used are all from scrap, we seem to have an endless supply, I often think it's a real shame to see them go for re cycling (scrap) I have been using this second method for quite a while now as radio's here in the uk have clips holding them on to the chassis, it's then easier to knock over the bottom edge in three places than crimp the whole can, this allows for a future restuff.
I think that it's best to assess each individual case as it occurs and hopefully do what is correct for that radio,
As you can imagine I have seen some real nightmares that people try to pass off as a repair.
Mike

[Joseph W Strickland]

Mike;

You are to be commended for your dedication to doing it right. Like you, I always hate to work on a unit that has been improperly repaired in the past - nightmares indeed!

Joe