OT - How to put 3 conductor AC cord on old amp?

[RDV]

I realize this is way off topic, but I've got an old Supro "Super" amp which is a single ended 6V6 amp(made in the mid 60's) with one control(an all in one volume/on-off switch), and I'd like to know the proper way to put a grounded AC line cord on there. I don't know if you just put the hot(hooked to the fuse) & common(one side of the switch) where they normally went before & then put the green wire to chassis ground or not. There's also a .01uF 1400v cap from the other side of the switch(the common going into the other side) to the chassis ground, does the cap stay or go? And if it does go, what would you hook to the switch in it's place? I know, I'm dumb.

Thanks in advance

RDV

[brett]

As far as I know, you just solder the green to a chassis lug.  The cap on my old, earthed amp was connected between active and neutral (it does some supply filtering at RF).  I presume it would do a similar job if connected to earth (ie conduct RF to ground while insulating at 60Hz).

But I did nearly electrocute myself the other day ( :oops: ), so maybe wait and see what others have to say, too...

[Peter Snowberg]

Just replace the existing wires with the new ones, connect up the green to the chassis, remove the 0.01uF cap, and you're done.

The job of the cap was to provide an AC path to the neutral which is then directly connected to a ground where the power enters the building. The ground wire eliminates the need for that cap.

Take care and welcome to safety,
-Peter

[Fret Wire]

You can get a three prong cord anywhere, but sometimes you can't find a strain relief bushing that fits the chassis hole. Then you have to use plastic ties on both sides of the chassis where the cord goes. Works, but not very pro looking. So if you buy locally, make sure they have a strain relief that fits both the cord and the chassis hole.

Here's a basic overview:

http://www1.korksoft.com/~schem/mods/3prongmod.htm

[RDV]

Just replace the existing wires with the new ones, connect up the green to the chassis, remove the 0.01uF cap, and you're done.

The job of the cap was to provide an AC path to the neutral which is then directly connected to a ground where the power enters the building. The ground wire eliminates the need for that cap.

Take care and welcome to safety,
-Peter

Thanks for replying as I know this is OT.

Thanks

RDV

[Paul Marossy]

The funny thing is, that even though amps are "off topic", you can actually get answers/replies quicker here than at the ampage forum. And intelligent ones, too.  :wink:

(Not to imply that anyone specific at ampage is incompetent, there are some very knowledgeable people there, but then there are those few...)

[RDV]

The funny thing is, that even though amps are "off topic", you can actually get answers/replies quicker here than at the ampage forum. And intelligent ones, too.  :wink:

(Not to imply that anyone specific at ampage is incompetent, there are some very knowledgeable people there, but then there are those few...)

I actually got a couple of replys there, but I'm more confident of the advice over here.

I got it done anyways, I attached the green wire to the place where the "deathcap" was attached on the end of the tag strip. Less hum now!

Thanks everybody!

RDV

[Paul Marossy]

Glad to hear it, RDV.  

[Fret Wire]

It's mandatory for safety and hum reduction. You still find used amps from even the eighties that have had the ground cut off the plug. Took a long time before a lot of homes were up to code, wiring wise.

[Lonestarjohnny]

I would like to add a few words to what Fretwire had to say, The wiring code in most clubs are on the most part addiquit, sometimes not, if the recepticle you plug your amp into has the hot and neutral wires reversed you will get a 60 cycle hum, the main reason for the phase switch on the Fender amp's, it lets you reverse the flow of electricty through the amps power transformer to get rid of the 60 cycle hum, in the Old days when most amps came with out a phase switch and only a 2 prong cord the trick was, unplug the cord, turn a half turn and plug it back in, that reversed the flow of electricity through the amp getting rid of the hum, when you put a 3 prong cord on a old amp with out the phase switch you can't turn the plug to change the flow, so you may get a hum occasionly when plugged into a recepticle that is wired incorrectly, the cure for this is a small addon plug you buy from your local electronic's store that goes between your plug and the recepticle, it has a phase reversing switch built in it with led's to let you know which way the voltage is flowing.
I hope this does not confuse to many of you but if you have any question's about this, feel free to E-mail me,
JD

[RDV]

What JD mentions is wwwaaayyyy safer than lifting the ground which is not good at all. When you lift the ground you're on a highwire without a safety net.

Regards

RDV

[Paul Marossy]

Lifting the ground is a bad, bad idea. Yet people do it all the time. I guess most people are ignorant about this sort of thing.  :?

The mouse only sees the cheese...

[Peter Snowberg]

To add a little more.....

It's not the phase of the transformer, but rather that a mains plug has two conductors.... a "hot" lead, and a "neutral" lead.

The neutral lead is hard-wired to a ground rod at the point where the power enters the building. This would make the neutral and a ground wire almost the same thing except that such a view would only apply if the receptacle was wired directly to the fuse (breaker) panel. If the power makes any kind of stop at another receptacle then you get the current used at that 2nd location superimposed on the "return" or neutral for the first receptacle. Because the wire has resistance, that causes the neutral to develop some voltage on it and it's no longer sitting at ground potential.

The big difference between a neutral and a ground is that you should NEVER have any current flowing on the ground conductor unless something is in the process of shorting out.

Three prongs is always better than two.

Take care,
-Peter