Ground Old Amp

[Otis]

Hi Guys,
I have a begginners question that I'm sure has been hashed over but my searches have come up empty. I have an old Epiphone Zephyr amp with the original 2 prong power cord with polarity switch that I'm changing to a 3 prong cord. My plan is to hook the green groung wire to the chassis ,likely to a transformer lug, the hot lead to the fuse, the white neutral to the polarity switch. Should I leave the switch as wired, or just make either position go to the neutral? Or just bypass the switch completely?

[Colas LeGrippa]

bypass the switch, it is not necessary now. green to ground ( chassis ) , mains to a DPST ( on/off ) , DPST from neutral to the fuse then to the PT, the other ( hot ) to the PT. This way, when the switch is thrown OFF, you can be sure no electricity enters the amp ( hot lead may be reversed in the wall outlet so with a SPST , you can't be sure the switch has put the hot lead out of the circuit .

Colas

[stingray_65]

Black hot wire to the fuse. the end lug, not the side lug. the side lug goes to the transformer lead.

Bypass the switch entirely, attach the white neutral wire directly to the transformer lead.

You could for simplicity's sake use any of the lugs on the switch as a landing point for both wires.

Most just splice the connection and use the polarity switch as a standby or some other mod.

do not use the "death cap" at all.

electronically speaking, landing your green wire on a transformer lug will work.

a better solution is to drill a hole near the cord grip on the chassis and use a dedicated screw and lock nut for the ground. attach nothing else to this point.

best construction practices state the green ground wire should be the longest lead. try to construct it in the unlikely event that the cord is ripped out of the chassis and is pulling the mains wiring out of the back, the ground wire will remain intact and connected so that any errant shorting of the hotwire to the chassis will shunt to ground and will not be passed along to the musician.

 

[sluckey]

The Epiphone Zephyr schematic I found shows a double pole 3 position rotary switch that is used for Power and polarity. Is this what you have? If so, just connect the green wire to chassis (PT bolt works fine) and connect the black and white wires to the same points your old power cord is presently connected, removing the old cord. Leave everything else as is.

If you have a separate power switch and polarity switch, I would connect the green to chassis, power cord black to tip of fuse, side of fuse to power switch, other side of power switch to one of the PT primary leads. Connect the power cord white wire directly to the other PT primary lead. If there is a 120V indicator lamp, it should be connected parallel to the PT primary leads. The separate polarity switch will have nothing connected except maybe the line filter cap.

[Colas LeGrippa]

There are many ways that will work and electricity wise, good,  but I prefer hooking up the neutral to the fuse holder because if it happens that you try to remove a good fuse from the socket  with the hot lead connected to it, even if the hot side of the fuse holder is connected to the chassis side of it, you mayl get shocked. But like Sluckey said, if you decide to hook up the hot side of mains to the fuse holder, solder it to the hot side of it ( to the side where power is ever present, even if the fuse has blown ).

Colas

[Otis]

Thanks guys, I was on the right track, just wanted to be sure. As a side note, it cut the hum way down after I connected new cord.

[Colas LeGrippa]

cool !

[birt]

am i the only one who always unplugs an amp when something is wrong? who would risk the amp starts smoking while you are checking the fuse that appears to be ok?

assuming the neutral and hot being wired the right way is dangerous anyway. if you know it can be wired the other way around, you'll be more careful.
"assumption is the mother ********"
(quote from a Steven Seagal movie. even those movies make sense sometimes.)

removed offensive quote... sluckey

[John]

It's probably good practice to build or repair the amp as if a not-very-bright alcoholic musician will be using it.

[Willabe]

Been zapped one too many times. including playing electric guitar barefooted on concrete.

Somebody was watching over you that day. 


                    Brad