3 prong power cord

[famous beagle]

Hey y'all,

I've got a '65 Gibson GA-5 Skylark that I love, and I need to replace the two-prong cord with a grounded 3-prong.

I know the green wire goes to ground (on the chassis), and I know the black wire is hot and the white wire is neutral, but how do I tell from looking at the schematic which is hot and which is neutral?

I've attached a pic of the schematic and then some pictures of the wires.

Can you tell me which one goes where, and how this is explained on the schematic?


Thanks so much for any help!

P.S. I have done some work on amps, and I know how to discharge the electricity from it and all that.

 

[famous beagle]

Here are some more pictures.

 

[Topcat53]

Is the 2 prong plug polarized? If it is then the wire that has the ribs on it that goes direct to the switch is the neutral (I think it is the neutral anyway, but if the plug is polarized than it is definite).

 

[Light]

The hot goes through the fuse, ALWAYS.


And remember to discharge those caps before you go mucking about in there.


Light

"Cowards can never be moral."
M.K. Gandhi

 

[Light]

Oh, and while you're in there, get rid of the "ground" switch. It's other common name is a Death Switch.


Light

"Cowards can never be moral."
M.K. Gandhi

 

[famous beagle]

There is no ground switch, and the 2-prong plug is not polarized.

Light: Ok, so you're saying, from looking at my photo (which shows, from left to right, fuse, lamp, power switch), that the hot wire is the one on the left that goes straight to the fuse first?

Thanks

 

[famous beagle]

If it were me in there with a soldering iron I'd rewire it so......

Black hot wire goes to fuse to switch to transformer

White neutral wire goes to transformer (ignore SW1B in diagram). The cap to ground could stay in this leg or be removed.

Green ground wire to chassis

Thanks for the suggestion, but could you explain the reasoning please? And where does the lamp fit in?

 

[famous beagle]

The switch should be in the hot leg. If left in the neutral, when the amp is switched off and left plugged in there will still be voltage going to the transformer and possibly to the chassis. The amp won't be powered up like this, but the chassis could be floating at the line voltage. Putting the switch in the hot leg isolates the voltage from getting in that far. The reason the fuse is before the switch is to protect if the switch should ever short to the chassis or elsewhere, which is generally not likely to occur. It will also help if you should miswire something and inadvertantly have a short circuit.

Sorry about missing the lamp, it wasn't in the schematic. It may have been an add-on later. See note below about the lamp.

The sketch below may clarify how it's put together better.

Edit: Looking closer at the picture of your switch, I don't see the cap that's shown in the schematic, so don't worry about the cap.

Also the schematic shows a lamp in the filament suppy voltage. This got rewired to a neon pilot on the 120vac supply side of the circuit.

Thanks for your help on this. Yeah the cap isn't there because I already removed it. (You can still see a tiny bit of the lead where I clipped it on the bottom right side of the tranny.)

So I know I'm reading this right (I'm still learning schematics): (All directions given are in relation to my "AC power cord full" picture)

1 The new black wire will go to the bottom post of the fuse.

2 Then a wire goes from the top post of the fuse to .. the top left post of the switch?

Aww crap ... I'm getting confused. I'm still learning how to read schematics, and without a layout, I still have trouble. Would it be an easy matter of telling me which wires need to be rewired to where? If it's too much trouble, don't worry about it. I appreciate the help you've given already.

Thanks

 

[famous beagle]

You will need an added point to tie the wires to the neutral. I don't know what you've got to do this. Ideally a terminal strip similiar to what I've got shown would be good and if it had a lug on it for the ground wire all the better. It would be preferable to solder the connection, but you might be able to use a twist on connector like electricians use for house wiring and make sure it's really secure.

Yes that helps tremendously. Thanks so much for the help!

 

[famous beagle]

You will need an added point to tie the wires to the neutral. I don't know what you've got to do this. Ideally a terminal strip similiar to what I've got shown would be good and if it had a lug on it for the ground wire all the better. It would be preferable to solder the connection, but you might be able to use a twist on connector like electricians use for house wiring and make sure it's really secure.

Could I just use a lug attached to a chassis bolt for the new tie point? That would take care of the ground as well, correct?

 

[famous beagle]

I wouldn't do that. If someone accidently used a three wire to two wire ground lift adapter and got the prongs reversed somehow, the chassis could end up hot and injure or kill a person.

Radio Shack might have this on the shelf http://www.radioshack.com/product/i...igkw=terminals&kw=terminals&parentPage=search

So ... where do I attach this? Or do I just leave it floating? If so, how do I assure that it won't touch the chassis or anything else? Is it just by the ridigity of the wires?

Thanks

 

[famous beagle]

Oh .. wait ...

How about just using a floating lug and covering it with electrical tape after everything's soldered to it?

 

[famous beagle]

Not pretty looking, but probably would work. A piece of heat shrink tubing over might be better.

I can do that. But that's the right concept, right? The connection will just be floating and not attached to anything?

 

[famous beagle]

Yup.... as long as it's floating and not touching anything else.


Can't talk you into making it look nice?

I'll use heat shrink tubing, but actually, I prefer to have it covered with something, just to provide peace of mind so I know it's not going to touch anything. And if it's gonna be covered, I think there's gonna be a bit of ugliness to it anyway.

 

[dementedchord]

hey if you want to go to all this trouble i have no real problem with it.... but actually it doesnt matter which way the voltage goes through the primary of that tranny... sorry... it doesn't... the fuse can be on the "send" or "return" side of the wiring and still do it's job just as well... BTW Never force a primary AC line to ground you're asking for problems... and possibly death... carry on...

 

[famous beagle]

Yup.... as long as it's floating and not touching anything else.


Can't talk you into making it look nice?

Wired it up last night, and it's working perfectly. Thanks again for the help!

 

[dgatwood]

What protection will clear this fault???? Granted this type of fault may not occur frequently, but if it could why not protect for it.

Yeah. Agreed. It should go through the fuse as soon as the hot side goes into the chassis. Then, it should ideally go into the switch followed by the transformer, but realistically, it doesn't make much difference whether it goes into the transformer first or the switch.

 

[dementedchord]

What protection will clear this fault???? Granted this type of fault may not occur frequently, but if it could why not protect for it.

is that scenario possible??? on a theoretical level i suppose... as a practicle matter??? i've seen lotsa amps with lotsa problems but i dont think i've ever even heard of a primary shorting like that... if it had there would have been deaths and fires before from 2 prong jobs... again i have no problem if you want to do it this way... just not "that much" of a problem.... ok??

 

[ggunn]

is that scenario possible??? on a theoretical level i suppose... as a practicle matter??? i've seen lotsa amps with lotsa problems but i dont think i've ever even heard of a primary shorting like that... if it had there would have been deaths and fires before from 2 prong jobs... again i have no problem if you want to do it this way... just not "that much" of a problem.... ok??

I think that it is good design practice for the first thing that the hot wire encounters when entering a device to be the fuse. It really doesn't make any difference what short could happen or how likely it would be if the fuse is upstream from everything.

 

[Alden_Sloe]

The cap to ground could stay in this leg or be removed.

I think the cap is to bypass voltage spikes to ground and should help reduce electrical interference conducted through the mains. If you're going to all the work of rewiring why not get an IEC receptical with a decent filter built in?