Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frank57 on December 22, 2012, 12:14:34 pm
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The wire from the switch broke but now that I look at the whole fuse plug switch, it seems wrong.
They installed the plug upside down and maybe that's where the confusion is.
On the switch we have the neutral white from the Pt on one side with the brown wire going back to the plug.
On the other we have the black from the Pt and a black wire going to the fuse and then a black wire to the plug.
If the white is neutral then why is the brown hooked up to the Live?
On the other side from the fuse we're going to the neutral?
Should it not be vice versa?
What problems can arise ?
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The wires from the PT are interchangable, however the Live side must be fused not the neutral.
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I'm surprised that they sold the amp like this.
What is the worst case scenario with the fuse wired to the neutral?
Possibility of shock?
I'm thinking to flip the plug the other way around if I can and rewire it properly.
That way the live is right next to the fuse like in every amp out there.
How tough would it be to take out the plug?
It's a snap in type.
It's exactly like this one.
You can see in this shot that's exactly how they installed it with the N on the right and the L on the left.
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The wires from the PT are interchangable, however the Live side must be fused not the neutral.
Look at all most any Fender amp schemo, fuse is in the neutral line side.
Brad :icon_biggrin:
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The wires from the PT are interchangable, however the Live side must be fused not the neutral.
That's I do when I built amps, fuse on hot side, but boths are safe and do the same work as it protect primary of Power Transformer which is only a coil.
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I don't know about fender but on the Fender Blues junior they don't wire it to the neutral.
It's on the live side if you're looking at the inside of the amp.
The black wire in this schematic is the primary from the Pt right?
Almost every amp schematic has it on the live.
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Many older amps had the fuse on the neutral, and the death cap. After '72 NEMA Electric code called for neutral
with respect to ground. Henceforth, the 2 sized blades, and usually a ground pin, to insure polarity. The smaller blade is the hot, and should be the side to be fused. IE; the black wire.
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I think so too.
The blades are marked inside with L N and E so you can tell even more not to make a mistake.
It looks to me that all new fender amps with 3 prong plugs are wired to the black wire with the fuse
on the L.
Is there a possibility of getting shocked with the fuse on the neutral?
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Is there a possibility of getting shocked with the fuse on the neutral?
One component on the amp shorts to the chassis, the fuse blows
and your life is preserved only by the Earth connection via the 3 prong cable
if the earth connection fails you can be shocked touching the chassis or something connected to it like guitar cable
K
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The wires from the PT are interchangable, however the Live side must be fused not the neutral.
I don't know about fender but on the Fender Blues junior they don't wire it to the neutral.
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Almost every amp schematic has it on the live.
Every modern schematic. As Willabe says, on 50's-60's Fender schematics, and the amps themselves, the fuse was on the neutral side while the switch was on the hot side.
So what to do?
If your wall outlet is actually wired correctly and according to code (which may be a lot to assume), then you want the fuse on the hot side to insure that if the fuse blows that the wall voltage will not get any further into the amp than the fuse holder.
If the fuse is on the neutral side and the fuse blows, the PT primary can still be live even though no current flows through the circuit. That's a possible shock hazard.
But let's be real: if you or I poke in the amp, we would at least unplug it from the wall before grabbing things with our bare hands. And that probably subverts the only practical advantage of worrying about which side of the line the fuse is on.
Now if you plug into an incorrectly-wired wall outlet, all your obsessing over where the fuse is wired was for naught.
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Well if every new amp is wired this way you have to wonder why they did it to the neutral.
I think they just plain goofed.
Is there any harm in changing it to the hot?
Any possibility of adding noise to the power supply in any way wired to the neutral?
The neutral wire on the power switch is connected to the live on the plug.
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Wire it the right way.There is no noise from wiring it either way.I always fuse the black wire.
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The factory wiring IS correct.
Take the fuse out. Stick your finger inside. What do you touch?
All amps from the last few decades have been through Safety Certification by people with a LOT more incident-experience than anybody here. Don't change factory line wiring.
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It's somewhat unusual though.
You don't see any amps wired up like this much anymore.
I have to rewire it anyhow but I'll wait a bit more before deciding what to do.
I could just leave it like you said.
If some one had certified that it met some standard would there be a sticker or emblem somewhere?
I got this argument from one site:
Fuse has to go on the hot lead. Otherwise if you do end up with a hot short to ground, current has to flow through the house ground all the way back to the panel until it hits the bonding strap to become a short to neutral, then will blow the circuit breaker long before your mains fuse blows. Having it on the hot side blows the fuse before it has a chance to trip the breaker.
Having the fuse in the neutral line only protects in the event of a hot short to neutral, but won't protect in the event of a hot short to chassis ground. Having it in the hot line protects during both scenarios.
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Did I wire this up right?
I might just put it back the way they had it anyway.