screw mount caps

[mike hadley]

my allwave fifteen power supply capacitors were broken and as this type of capacitor is impossible to get, I thought of this solution,

First a Modern cap is selected for physical size

after the plastic cover is removed, the cap is opened by filing the existing crimp,Stop when you see a thin dark line appear, this means the base can then be removed,once this is done the old capacitor can be extracted,you will then need a cable gland, for this cap we only need the center brass sectionthe coarse thread is then cut off, leaving a brass tube and threadthen a piece of steel or other flat material has a hole drilled to take the screw that will become the center terminal,this has a nut and solder tag to attach the replacement cap on to, the modified cable gland is then slipped over this and held in place with hot glue,this is then potted, you could use epoxy or even bondo,take the empty cap case and drill a hole in center of the closed endmake this hole big enough to slip over the brass threadthe brass gland then has copper wire twisted around the end for the other capacitor connection, this is how the case parts look, ready for stuffing, a closing disc is filed up out of some scrap alloywhen the cap is assembled it looks like thisNeat huh,

all that is needed is to roll the can edge over the disc, this should be done with a round plastic rod or screwdriver handle to avoid marring the finish,

work round the top using several turns to roll the top over, do this slowly or the can will dent and become really difficult to straighten,

this is how my psu looks

[David C. Poland]

Clever. 

[Joseph W Strickland]

Mike;

Good illustrations! This will work well for capacitors that need to be grounded directly to the chassis. If one is needed that is insulated from the chassis a PVC type cable gland could be used and then two screws brought out through the bottom, again insulated using some epoxy. If solder direct to the screws is desired, brass screws could be used. It would even be possible to use some heavy copper wire to attach to if desired instead of screws. There are lots of possibilities. Multi-section types could be made using this technique.

Thanks for sharing!

Joe

[Jon Ketron]

Thank you for sharing Mike.

Jon

[David C. Poland]

Mike - so cool, having reviewed your process again. 

For a dual cap, ought to be able to use 2 screws, sized small enough to share the brass passageway, maybe with shrink wrap insulation for good measure and then potted as you suggest.

Or instead of  screws, maybe just length(s) of hook-up wire potted in the brass piece.

Wonder how to adapt your method to  use an an early Scott filter cap lacking the the kind of crimped base your type had.

[mike hadley]

Thanks for the reply Dave,

I have just finished a Stromberg Carlson 82 radio, the caps were so badly corroded I had to resort to this method once again, here is another few photo's of the caps, these are made upside down compared to the earlier post.

The electrical fitting is 20mm, and a fairly close fit into the chassis hole, the thread size in the photo is m4, maybe a smaller thread could be used, along with suitable insulation, .It's  worth noting that using this method the original rubber seal is discarded as it's no longer necessary to seal the cap, this gives enough metal to roll over the bottom plate.

your suggestion of hookup wire is a good one, that would make a really neat finish.

the problem with the early screw mount caps is that the bouton is crimped around the insulation at assembly, I have tried to dismantle this type of cap but it's darn near impossible without causing damage.

Mike