Death cap and three-prong cord

[slidincharlie (Carlo P)]

Howdy,
I am doing a general maintenance job to my recently bought small Supro (Comet?) amp.
I bought it with a three-prong cord installed and the death cap (from the mains fuse to ground) still in place.
Should I leave it there or rather eliminate it?
TIA

[Gtr_tech]

We normally just snip them out.

[jrfrond]

Take it out ASAP.

[Chuck H]

+1
Remove it. If it's not too much trouble you should move the fuse from the nuetral to the hot side also.

[slidincharlie (Carlo P)]

Thank you guys!

[Enzo]

I think that will be the name for my next band -

Death Cap for Cutie.


Or maybe

Death Cap for Charlie.

[R.G.]

+1
Remove it. If it's not too much trouble you should move the fuse from the nuetral to the hot side also.

I have to disagree with this. If you don't move the fuse from the neutral to line side, you're building in a fair chance to electrocute yourself.

If a neutral-side fuse blows, the line side is still hot, and the power switch does not make the power lamp come on. Open it up to service, touch the wrong thing, and you're zapped if you don't happen to be holding something you can't let go of, and dead if you are holding the wrong place.

I disagree with the "if it's not too much trouble" part.

[Chuck H]

I have to disagree with this. If you don't move the fuse from the neutral to line side, you're building in a fair chance to electrocute yourself.

If a neutral-side fuse blows, the line side is still hot, and the power switch does not make the power lamp come on. Open it up to service, touch the wrong thing, and you're zapped if you don't happen to be holding something you can't let go of, and dead if you are holding the wrong place.

I disagree with the "if it's not too much trouble" part.

Maybe I worded it poorly. I said he SHOULD move the fuse to the hot side.

[R.G.]

Actually you worded it fine - he's more likely to respond to sugar than vinegar.

[slidincharlie (Carlo P)]

I have to disagree with this. If you don't move the fuse from the neutral to line side, you're building in a fair chance to electrocute yourself.
If a neutral-side fuse blows, the line side is still hot, and the power switch does not make the power lamp come on. Open it up to service, touch the wrong thing, and you're zapped if you don't happen to be holding something you can't let go of, and dead if you are holding the wrong place.
I disagree with the "if it's not too much trouble" part.

I have just checked the schematics of several Fender (from the tweed to the silverface era) and a few old Gibson amps, and all are wired like this Supro: mains fuse on the neutral side of the power supply. Is this a poor design that should be corrected?

[Jazz P Bass]

So look at a "modern" amp.
The black wire (hot) is always fused.

[R.G.]

I would say it is a dangerous design from an electrical safety point of view.

I think I know why they did it that way. With a two wire cord, either side may be the line/hot side, and more importantly, neither one is earth ground. All the fuse can do is open on an overcurrent. There is no reason to put the fuse on one side or the other. And it provides a convenient place to tie one side of the incoming line cord, the other side going to the switch. You save a terminal strip.

This changes with a third safety wire. In three-wire, the identity of the incoming wires is fixed. One is hot, one is neutral, and one is earth ground. In this situation, you *can* know which incoming wire is the hot one, and you *can* fuse the hot side. More importantly, you can fuse the hot side. If you fuse the neutral, an open fuse leaves the hot line still conducting, and if there is a short to chassis from the neutral wire (not fuse!) then the power still runs and its no longer fused. In addition, if the neutral is open, the hot side is still hot to the chassis and you can be killed by contact with the hot side and chassis when the fuse is blown.

Fusing one side and switching the other is a Bad Idea if you have a choice. All those older amp designs were done before three-wire was widely available or mandatory.

[slidincharlie (Carlo P)]

Should I just rewire the fuse and put it on the hot wire between the power switch and the PT primary wire (like in the attached schematic)? Is it as simple as that?

[Jazz P Bass]

With the addition of the third leg bonded to chassis ground, yes.

[Chuck H]

If I came across rude before I want to apologize for being so vinegary

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