Sorry for the non-stop questions but I am trying to get a better understanding of how everything works in these amps. Today I was poking around inside my amp and found that there is high voltage on the exterior cans of c6 and c7. Those are the caps in the bias supply. I measured and c6 shows -400v and c7 shows -200v. Is it normal? I double checked and the caps are installed with correct polarity.
Yes, the bias supply is a negative voltage wrt ground. This means that the electrolytic capacitor's can,
which is its negative terminal, will be "hot," and the positive terminal on its bottom will be grounded.
If these cans are bare, you might want to insulate them for safety.
which is its negative terminal, will be "hot," and the positive terminal on its bottom will be grounded.
If these cans are bare, you might want to insulate them for safety.
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In many cases this is normal. Electrolytic caps are made of rolled up aluminum foil and paper soaked in a conductive electrolyte (hence the name). There is some leakage current from the outer layer of this foil to the outer metal shell.
The outer foil is the negative connection which is grounded in 99% of the usual applications, so this current is not noticed.
In a bias supply the negative terminal is part of the output circuit, so there is a leakage path from the supply output to the can. The outer can is insulated for this reason. There used to be an insulator on the top of many electrolytics, but it went away when the top was scored to create a safety vent to prevent exploding capacitors in case of failure.
The leakage current should be too low to cause serious harm, but it can deliver an unpleasant shock. If your amp is exposed so that humans, or animals can touch the caps, put a piece of non conductive tape across the top.
The outer foil is the negative connection which is grounded in 99% of the usual applications, so this current is not noticed.
In a bias supply the negative terminal is part of the output circuit, so there is a leakage path from the supply output to the can. The outer can is insulated for this reason. There used to be an insulator on the top of many electrolytics, but it went away when the top was scored to create a safety vent to prevent exploding capacitors in case of failure.
The leakage current should be too low to cause serious harm, but it can deliver an unpleasant shock. If your amp is exposed so that humans, or animals can touch the caps, put a piece of non conductive tape across the top.