Rebuilding Can Caps

[loudthud]

I've heard of can caps (so called twist lock types) being rebuilt, but how do they get the existing caps open? The can itself looks like aluminum and the mounting tabs look like plated copper or brass. The aluminum is rolled over the mounting tab piece to hold it in place. The terminals stick through a phenolic insulator. This cap is from a Vox-Thomas amp so the mounting tabs are not connected to either side of the cap, plus and minus are on separate terminals. Is there some trick that is used to unroll the aluminum or do you just cut the cap open?

[Enzo]

Probably could saw off the top neatly with a Dremel, but I haven't opened one of those in decades. When I did, I used an old pair of dikes and peeled away the rolled edge all around to clear the phenolic and pull out the innards.

I have a few can cap ends in the shop. It is the phenolic puck with a few terminals staked onto it, and the rolled aluminum around it, but was never part of a can. Looks as if I sawed off the body of a can just below the fatter ring, and neatly rolled the under edge of the ring to look like the top.

That and I have a bag of the phenolic mounting plates, so one can mount standard twist tab caps to it and then mount the plate to the chassis for insulated can. If any of that might help?...


Your imaged ones are maybe easier to get into that some. I have a bunch of can caps with a narrower threaded neck to poke through a chassis, then one large nut and start washer mounts the thing. Those and of course the can caps with octal base ends, you plug then into a regular tube socket. Leslies used them a lot. I don't know HOW I'd get into those.

[g1]

I haven't seen any pictures of the rebuilds, but I had assumed they were not re-using the phenolic or the original terminals and got into them that way?
Of course then the work would be obvious from inside the chassis.

[olddawg]

There's this:
Capacitor Rebuilding for Fun or Profit | Make: DIY Projects, How-Tos, Electronics, Crafts and Ideas for Makers
Not sure why he uses candle wax when you can easily use 5 minute epoxy it latex. Guess it's easier to get apart again.

[52 Bill]

On the Vox insulated can types, I used to grind off the rolled edge so that all of the contents could slide right out the bottom of the can. Because the can didn't have to be grounded when the new caps were installed, I would epoxy in the phenolic and the tabbed ring into the can. Once the cap was remounted to the chassis, the opening and glued seam was hidden.

Lately I've just been disconnecting the original cans and soldering in replacements on the underside of the chassis where they can't be seen from the outside.

[Leo_Gnardo]

Lately I've just been disconnecting the original cans and soldering in replacements on the underside of the chassis where they can't be seen from the outside.

Big +1, my favorite method! Get ye some 105C rated caps and all will be good & preserve the all important "original equipment look." Also gives you the option of placing the lowest-voltage cap at the preamp location which can often provide some extra hum/buzz relief.

Second fave method, out with the multi cap, mount a 50+50uF/500V - your choice of brands JJ, F+T, I use Ruby - needs a mounting bracket but usually the capacitor hole and associated screw/rivet mounts in the chassis fit perfectly. Fit individual caps as necessary for the 3rd and 4th sections if needed. Many a 60's Ampeg has gone this route here, Princetons & Champs too, & lots of others besides.

On Audio Asylum maybe 5-6 years ago there was a demo of how to dissect & rebuild a typical twist-lok cap can. The poster started with a pipe cutter & applied the blade just above the expanded part of the can. There are long skinny electrolytics now which can be used to re fit multi cap cans but IIRC they top out at 450V. The worst part is clearing all the old goop out of the way. Drill a couple little holes in the phenolic end insulator, run the cap leads out & solder to terminals. Epoxy aluminum tube back onto base & bob's yer uncle.

[R.G.]

Shrug. It's phenolic. Drill and pluck. I've done several this way. It can be done in place so you don't have to un-twist the locks, which is often the hardest thing to do non-destructively if they're soldered to the chassis - which they often are.