Mains ground cap

[drhulsey]

The last chapter in Dan Torres' book, Inside Tube Amps, is devoted to building a Class A amplifier. He uses a "ground switch" before the power switch and says to place a .047µF/400-600V cap in the mains ground. He emphasizes this by saying, "Do not ground directly." He doesn't explain its purpose. Is this just to prevent the ground switch from popping or is there another purpose for this cap? I don't seem to see it on mains grounding in amps with no "ground switch."

[dartanion]

IIRC, that's the death cap. Not needed if you have a grounded mains plug. The ground switch was there on old amps to get the polarity correct since you could plug the amp in to the wall socket in either direction. I think a lot of us here have gotten zapped on the lips a few times while trying to sing through a PA while having the polarity wrong on their amp. Not fun and is quite dangerous.

[drhulsey]

Not needed if you have a grounded mains plug.

He actually DOES use a three conductor in his diagram.
Our lead singer got a little jolt last year. You could actually see the arc I don't think he saw it, but he sure felt it We were playing a gig where we didn't set up our gear.