ADVISORY: Radial caps and electrocution danger

[CraigGa]

Thanks for that advice, it certainly explains why one of the filter caps had the end taped up in the chassis mounting clip.

Luckily the Nichicon replacements I used don't test the same, I've put a piece of insulating material - well a plectrum, in there for good measure anyway.

Craig

[Hifi_tech]

It is common knowledge for us technicians that all electrolytic capacitor cans usually is connected with the negative to the chassis of the can.
We learned that in one of the first classes in electronics back when I was going to school. I presume they still teach that today.
If you take a look at the negative end of an older axial capacitor you will normally see the lead is connected directly to the chassis.
On a radial capacitor this is not visible to the eye, but they are often connected from negative lead to the can.

But then again there are many cans of newer date that are not directly connected.
But that does not mean that they are safe to touch directly on the metal structure or the stud on chassis mounted types.
They have a potential from the negative lead to the chassis of the can.
That is why they sell mounting kits in plastic for them if there are high voltages or positive, ground and negative voltages in the circuit.

The latest FT 220uF caps I received here with mounting stud was meassuring 70 KOhm from negative to the stud and 8 MOhm from positive to the stud.
So if you put them in series between HT and ground and touches the chassis ground and the can of the capacitor connected to the HT, you will most likely get a new hairstyle.

[rooster]

Addressing the fear/safety concerns presented here, linking the radial pairs with 220K 1W resistors will negate the charge on the 2nd radial cap. Pretty simple fix. Fender did this in the 70s on their single axial pair and Dumble did this on his multiple pairs, as well, in his case before and after the standby and choke.

[xtian]

Addressing the fear/safety concerns presented here, linking the radial pairs with 220K 1W resistors will negate the charge on the 2nd radial cap. Pretty simple fix. Fender did this in the 70s on their single axial pair and Dumble did this on his multiple pairs, as well, in his case before and after the standby and choke.

I don't believe this is true. The balancing resistors will drain voltage after amp is shut down, but during operation, I see about 1/2 the B+ node voltage at the junction of the two stacked caps...and on the exposed case(s) of the radial caps.

[rooster]

Oh. I thought your post was talking about stored voltage on the caps after the amp was turned off....

FWIW, I've been 'trained' not to touch any cap, axial or radial, when the amp is on.