Cap can insulation?

[Axtman]

How do you electrically insulate the multi-section capacitor metal exterior can?

I am currently working on an old Ampeg V4 amplifier where the outside metal of the cap can has high voltage. In the olden days they used cardboard tubes with cardboard lids.

[Helmholtz]

Usually the metal can of a multisection ecap is connected to the negative terminal and the can is grounded by the mounting clamp.

Can you post a schematic and pics?

[Axtman]

Here is the Ampeg V4 schematic diagram: V4 Schematic.pdf

[The Dude]

I suspect one of the upper caps in a totem pole arrangement (possibly?). Maybe cut a plastic cap for the top and large shrink tube/wrap for the rest?

[Helmholtz]

So which cap are we talking about?
Is the cap original?

[glebert]

This page has some good pics of a V4 (V22) with the cardboard cap housings, and also you can see in the chassis pics what they look like on the bases.

http://www.chambonino.com/work/ampeg/amp9.html

[The Dude]

Yep. My guess is that someone replaced one of those cardboard caps with a metal can and chassis mounting isolation. So, the can is not at ground potential if it's part of the totem pole. It's quite dangerous, but it wouldn't be the first time I've seen it done.

[glebert]

The cardboard cap housings remind me of mailing tubes, which can be gotten in multiple diameters and sometimes have plastic caps for ends.

[Axtman]

Yes the picture that glebert posted is what my chasis looks like..black cardboard tubes around the caps. I am going to recap this beast. Hopefully I can save the cardboard tubes but I think they are glued on.

I did not know they make shrink tubing that large. I guess I will go check out my electricians supply house.

[glebert]

If you can't get shrink tubing I would do electrical tape (for electrical insulation) then cardboard tube sprayed with a little flat black paint for the original look.

[Greg_L]

I've been "hit" with this before. I make a film coating of silicone goop across the exposed part.

[Tom Phillips]

It has been my experience that the cardboard tubes are salvageable. If they don't slide off with a reasonable pull then a little treatment with a heat gun loosens them up.
Other things to consider:
1. To re-use the existing sleeves the new can would need to be the same diameter.
2. A couple of years ago I looked into purchasing large diameter heat shrink which could be used along with an insulating top disk. The cost was very high to get suitable heat shrink from reputable sources that published the actual specifications and large diameter heat shrink from eBay & Amazon was ultra thin and I judged it unsuitable.
3. You could consider leaving the existing cans in place and mounting modern,physically smaller, caps to the side wall adjacent to the power transformer.

[Mick Bailey]

Did you check the replacement caps to see if the can is connected or not? I've had some where there's no connection between the terminals and case.

[Pixel]

3. You could consider leaving the existing cans in place and mounting modern,physically smaller, caps to the side wall adjacent to the power transformer.

On an old monoblock I disconnected the old cans and left them in place. Used the ground lugs of the cans like a terminal strip and hung the MUCH smaller new caps from them. It looked the same as before unless you looked under the chassis. One of the cans had a really neat looking rubber "sock" that went around the whole can.

[Axtman]

Just for laughs I checked the voltages on the cans. Two cans were at zero volts. One can, the closest to the back and easily reached by stray fingers, was 218 volts! That will certainly wake you up at the gig!