Power, standby and pilot switch wiring, jcm 800 build

endofall

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So I'm I'm building a valvestorm jcm 800 2203. After looking through several different wiring diagrams just gathering ideas I notice that how the stwitches, light and fuses are wired different in several different layouts. I have been comparing the mojotone British 100 layout, Ceriatone 2203hw layout, the valavestorm linked layout and then another alternate one in the metroamps build guide. I am using the 120v lamp from the valvestorm 1969 kit. Is there one that's better than the other, does it matter? Any help would be great!
 

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BlueX

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I'm no amp expert, but for electricity in general I prefer:
- IEC inlet socket with built in fuse holder (see pic). That way you don't need to wire anything in between inlet socket and mains switch.
- DPST (Double Pole/Single Throw) mains switch, to switch both live and neutral on/off. See Mojotone 1959 layout (1st). The other two seems to switch only one, live or neutral depening of what comes out off the wall.

IEC socket.jpg
 

paul-e-mann

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So I'm I'm building a valvestorm jcm 800 2203. After looking through several different wiring diagrams just gathering ideas I notice that how the stwitches, light and fuses are wired different in several different layouts. I have been comparing the mojotone British 100 layout, Ceriatone 2203hw layout, the valavestorm linked layout and then another alternate one in the metroamps build guide. I am using the 120v lamp from the valvestorm 1969 kit. Is there one that's better than the other, does it matter? Any help would be great!
I dont know anything about anything but the Mojo layout was the most obvious to me what went where when I built my 5E3 amp last summer, in the long run I ended up using a Weber layout it was closer to what I was doing.
 

StuC

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It appalls me that Valvestorm are instructing DIYers to fuse the neutral :eek:

I was surprised to see that. The Metroamp JTM45 kit PDF on the Valvestorm site also instructs the builder to fuse the neutral, so who knows how many are out there. I looked up a few gut shots of DIY builds and sure enough, fused neutral.

Seems the Metropoulos amps are wired that way too. :(

 

Ronquest

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Considering that the DIYer may have also wired his home, it's best to fuse everything,....you know, just in case!
 

BlueX

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In big parts of Europe socket and plug are not oriented, even when there is protective earth. You can turn the plug 180 degrees and it will still fit. Unless you measured and marked the socket yourself you usually don't know which is live and neutral.
 
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Gene Ballzz

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Non-grounded AC plugs/receptacles scare the livin' "bejeezus" out of me! Especially when they are not even effectively polarized!

This can provide some fodder for some horrific nightmares:


Just Pluggin'
Gene
 

Pete Farrington

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The massive issue with fusing neutral is that live can short to earth inside the chassis (eg PT breakdown) without the fuse blowing.

In big parts of Europe socket and plug are not oriented, even when there is protective earth
That isn’t a problem per se, provided that the electrical installation has a high sensitivity trip switch that actuates if any current flows to earth (eg >30mA).
Which is mandated for new installations for most regions anyway.
But even then though, I much prefer the ‘belt and braces’ additional layer of protection offered by polarised mains connectors.
 
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Pete Farrington

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I was surprised to see that. The Metroamp JTM45 kit PDF on the Valvestorm site also instructs the builder to fuse the neutral, so who knows how many are out there. I looked up a few gut shots of DIY builds and sure enough, fused neutral.

Seems the Metropoulos amps are wired that way too. :(
It’s inexcusable, outrageous even, that this crap is going on; people proving such info have an ethical duty to get this right.
People building / repairing amps professionally have surely got a legal responsibility and liability for the mains equipment they’re sending out to comply with relevant regulations. I think they need to consider how they’d explain to their insurers / a jury, why they chose to send out stuff whose safety critical protective features were compromised, if eg, it was found to have caused a fire, injury etc.
 
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mickeydg5

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I agree that the hot/live should have the fuse for the amplifier PT primary.

I do not think I ever saw a actual schematic by Marshall that indicated the mains fuse on the neutral line.

The schematic on the METROAMP kit is not good.
 
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PelliX

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I don't have a pic of it, as mobile phones and digital cameras weren't so abundant back then, but I've had a piece of homebrew gear on my old bench that literally had a fuse for each wire in the mains lead; live, neutral AND earth. I didn't get to ask the designer what the earth fuse was for, but I doubt there would have been much of a sensible answer. I can only speculate that it was his or her guess that this would protect the apparatus in case of lightning or similar....
 

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