i try to stay neutral on these topics, but sometimes i get so hot that i need to get grounded, ;D
just a ref drawing for my own selfish needs because we do wire old amps for 3 prong whenever possible,
in that case, by all means do we remove the cap because it will be a moot point if the chassis actually gets tied to ground via a good cord, properly wired wall socket, and a good transformer on the pole, plus, in that situation, the cap does see a real 120 VAC when plugged in,
what happens with a two prong cord chassis that has that cap?
that cap takes the floating chassis (line cord goes directly to pwr xfmr primary) and connects it to either the hot or neutral of the wall socket, but from an AC standpoint only.
Reactance of the cap is 1/377 * .047uf = 56,436 ohms,
what is the potential between the floating chassis and either/or the power line neutral or hot?
hopefully zero. no wonder the caps don't fail.
so why bother with the cap?
i would hazzard to guess that sometimes the chassis picks up EMF and that can be shunted to ground via the cap/neutral wire of the cord,
but if the cord is plugged in so that the cap goes from the chassis to Hot, then more hum would be experienced, thus the switch for picking the lesser of the two,
what about a vibro champ with no gnd switch? Leo says flip the cord for least hum and/or shock from the SM58 grill,
once the chassis is grounded via 3 prong, all EMF should go to wall socket ground.
however, sometimes you might find that even with the 3 prong plug you still get a bad hum, maybe due to funky wiring at the club, in that case, and old school player with the tweed bassman might have the jump on you with his ability to choose which side of the line that chassis cap is connected to,
why do two players get a mild shock when using vintage amps?
one might have his cord plugged in 180 degrees different from the other guy, this one guy has a chassis tied to Hot via the cap and the other guy now has chassis tied to neutral(gnd) via the cap, so they have 120 V-ac between them, but are current limited by 56 k twice = 112K = about 1 ma between them, which is probably not enuff to cause refib/defib, unless drugs are involved, which is a safe bet for working musicians, hell half the people who come into the git shop are on something or boozed up or both,
personally, being tied to electrical ground via the git cord/chassis and line cord gives me the willys, i can handle the .047 tingle with the floating chassis, but getting across another ground that is 180 out while holding the git and being connected to that green wire scares the crap out of me,
120 VAC wall socket plus mutant cj at the Rhythm and Rye last Thursday on the J bass, $15 jar, $90 gate, /3>