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Help installing a 3-prong power cord

2/17/2001 10:08 PM
Help installing a 3-prong power cord
I've done a bit of electronic work...pickup installation and the like, but I'm not sure about this project. I want to install a 3-prong power cord on an old Premiere Reverb tank and my little Vibrochamp. A few basic questions that I have:  
1) My new 3-prong cords are black, white, and green. I know green is chassis ground. I'm not sure, when working with AC, which color is hot. My guess is: white is hot. How am I doing?  
2) On the reverb tank, one of the existing 2-prong leads goes to the on/off switch. The other goes to a black wire leading to the transformer. How do I tell which one is ground?  
3) What should I look for in the VC for hot and ground? I don't have the amp in front of me right now, as it is over at the rehearsal garage.  
Thanks much for any help you can give me.
2/17/2001 11:36 PM

Black is hot, white is neutral (not ground). The way the amps were wired originally, with two conductor cable, there wasn't any ground line coming in from the power socket. There never is a ground going into the power transformer.  
Solder the green line to the chassis, as you've said. You'll probably need a 100-watt or higher soldering iron, or else use a mechanical / bolted-down connection. The chassis absorbs so much heat away from the soldering iron, that you can't get anything hot enough using a 30-watt iron when you try to solder something to the chassis.  
Make sure the black line gets to a fuse early on. Assuming you don't have an outlet in the chassis, the black line would first go to a fuse, then to one of the leads into the pt. The white line would go to the power switch, then to the other lead into the pt. In the pt's I've worked with, both of those leads from the pt are black, but yours might vary.  
If your amp doesn't have a fuse holder, then put an inline fuse holder in the black line. You can get one at a car parts store, or probably at Radio Shack.  
Another thing you could do is get a dpst power switch, so that both lines are switched on and off at the same time. That seemed to become standard in the mid-70s or so.  
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2/18/2001 1:03 AM

Shea, thanks. I feel a little stupid, but not too stupid to ask questions. I'll put the ground on a mechanical bolted down connection. There's a machine screw with a star lock washer nearby that will be fine.  
I remember, neutral, and ground. Thanks for your patience.  
One question, just for clarification. I'm assuming that "pt" is "power transformer". Just a guess, but hopefully a good one.  
I don't understand the dpst switch. You recommend this so that both lines are "switched off at the same time". What two lines? Again, I apologize for my ignorance. Many thanks for your time and help.  
2/18/2001 5:15 AM

Hey, never feel stupid. I was learning this same stuff a few months ago. From this board, as a matter of fact.  
The dpst switch would break both the black line and the white line when it's turned off, and close them both when turned on. If you use one, you should put it after the fuse in the black line. I've never added one on. I'm not sure what the advantage is, but like I said it seems to have become the standard practice for amp manufacturers. If you're not sure how to do it, best to just forget about it rather than risk something else going wrong. When you change more than one thing at a time, and then the amp doesn't work, it can be confusing to track down where you made the mistake. Just like cars and motorcycles.  
I meant "power transformer" by "pt."  
2/18/2001 5:18 AM
I believe he means neutral (white) and hot (black).  
A DPST switch can do this because it has 2 separate switching mechanisms that are both thrown on/off with a flick of the switch. Therefore you can wire black on one side & white on the other...
2/18/2001 5:20 AM
Glen H.
Of course, DO NOT wire it so black throws onto white!  
You'll get a short circuit, and do some arc welding in the switch!
2/18/2001 5:23 AM
Glen H. Better reiterate...
I should say is wire black parallel to white.  
and continue the same on the other side of the switch...:)
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