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Cardboard cover on can capacitior.
Cardboard cover on can capacitior.
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Old 20th November 2019, 06:54 PM   #1
charnich74 is offline charnich74  United States
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Default Cardboard cover on can capacitior.

Hi all, I'm in the process of restuffing the cans in my Sherwood. One of the cans appeared to be a cardboard cylinder and when I opened it I realized that there was actually a metal can inside of the cardboard. The thing is that the metal can looks very good once it's polished and the cardboard cover looks pretty lame. My question is whether or not the cardboard cover serves some sort of function perhaps shielding etc. There are three other cans in the amp all of which are exposed metal. The question is if I am safe to leave the cardboard cover off and expose the beautiful shiny can or will doing so cause other problems? I'll include a photograph of the Black cover on the right and the actual can on the left.
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Old 20th November 2019, 07:02 PM   #2
rayma is offline rayma  United States
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This capacitor was likely not designed to have the case grounded, or connected in any way. That's why
there was an insulated covering on the can. It also could present a safety hazard if touched when charged.

If the metal case continues around the bottom and there are grounding lugs there as part of the case,
then it would be safe to leave bare. Do you have a photo of the bottom?

Last edited by rayma; 20th November 2019 at 07:16 PM.
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Old 20th November 2019, 07:52 PM   #3
charnich74 is offline charnich74  United States
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Quote:
Originally Posted by rayma View Post
This capacitor was likely not designed to have the case grounded, or connected in any way. That's why
there was an insulated covering on the can. It also could present a safety hazard if touched when charged.

If the metal case continues around the bottom and there are grounding lugs there as part of the case,
then it would be safe to leave bare. Do you have a photo of the bottom?
Yep sure do.
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Old 20th November 2019, 08:56 PM   #4
maxhifi is offline maxhifi  Canada
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The cardboard cover is typically used when the can of the capacitor is operated at high voltage, and creates a shock hazard. The base of the capacitor is probably mounted on a phenolic wafer rather than directly to the chassis, to provide electrical isolation between the can and the chassis. This sort of capacitor is usually used in voltage doubler power supplies.

If you rebuild the capacitor, you can insulate the negative terminal of the new capacitor from the can, and avoid the cardboard cover this way.

Myself I would leave it stock, because it will look less like someone messed with the amp.

Last edited by maxhifi; 20th November 2019 at 08:58 PM.
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Old 20th November 2019, 09:09 PM   #5
charnich74 is offline charnich74  United States
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Quote:
Originally Posted by maxhifi View Post
The cardboard cover is typically used when the can of the capacitor is operated at high voltage, and creates a shock hazard. The base of the capacitor is probably mounted on a phenolic wafer rather than directly to the chassis, to provide electrical isolation between the can and the chassis. This sort of capacitor is usually used in voltage doubler power supplies.

If you rebuild the capacitor, you can insulate the negative terminal of the new capacitor from the can, and avoid the cardboard cover this way.

Myself I would leave it stock, because it will look less like someone messed with the amp.
Yes it is mounted on a non metallic wafer. I think I'll leave it on for safety. Thank you to those who replied.
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Old 20th November 2019, 10:10 PM   #6
rayma is offline rayma  United States
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No problem, the can is grounded. Sometimes this "twist-lock" style can is mounted on an insulating wafer,
and a wire is connected between ground and one of the lugs on the rim of the can, to allow more control
of the grounding connections. But the can will always be grounded even if it is on a wafer.
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Old 20th November 2019, 10:43 PM   #7
maxhifi is offline maxhifi  Canada
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The can is the negative terminal of the capacitor. This does not mean it is grounded - in a voltage doubler power supply, it will certainly not be grounded, but will be sitting at about 1/2 of the B+ value, or hundreds of volts.

This sort of can is also used when capacitors are used in series, and in this case the can will also be at 1/2 of B+ potential.

A quick examination of the circuit diagram will make it easy to figure out what potential the can is at.
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Old 20th November 2019, 11:10 PM   #8
Galu is offline Galu  Scotland
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Quote:
Originally Posted by maxhifi View Post
The can is the negative terminal of the capacitor. This does not mean it is grounded - in a voltage doubler power supply, it will certainly not be grounded, but will be sitting at about 1/2 of the B+ value, or hundreds of volts.
That was certainly the case in my Rogers amplifier.

One of the voltage doubler capacitors was fully insulated, while the other had a bare metal case.
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Old 20th November 2019, 11:14 PM   #9
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by Galu View Post
That was certainly the case in my Rogers amplifier.

One of the voltage doubler capacitors was fully insulated, while the other had a bare metal case.
What kind of Rogers do you have?
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Old 20th November 2019, 11:23 PM   #10
Galu is offline Galu  Scotland
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Quote:
Originally Posted by maxhifi View Post
What kind of Rogers do you have?
It's a Rogers HG88 Mk3 - new caps and going strong after 50 years of ownership!
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