1969 kit first time build: fusing live or neutral??

[young flower]

Thanks a lot for your help julkke! Last thing I need to hunt down for my build is a chassis - when I have it, I´ll start a build thread.

Have a good day!
YF

[julkke]

No problem, this should be talked more! Also it is always good to use a residual current device with amps, just in case. A life saver circuit in guitar doesn't hurt either.

[young flower]

Since you are talking about residual current devices. There was one question you left unanswered, which is still bugging me. Maybe you could give it a try again:

Thinking about the whole topic - I´m asking myself how the safety situation is with all the other electrical equipment we use in Schuko countries, do these have fuses (or a comparable safety device) in live and neutral line? Or do they all rely on the FI safety switch (residual current device) in the house when they have an internal short? I guess, in contrast to amps, most equipment is simply designed in a way so you can´t touch parts that could potentially shock you.

And one more question: In the case of an internal short, what is it that makes the fuse blow - and do they really blow reliably? Is it the increased current draw from the mains (because current is leaking to ground) that causes the wire in the fuse to overheat and blow - or what mechanism is it electrically??

Thanks
YF

[julkke]

I never got this one either - I have read from many experienced and professonial electricians that one fuse is ok, at least in the EU. Also, I don't get how you could get shocked since the safety earth protects you by providing the path with least resistance to ground. In this case the house circuit breaker would trip. Maybe someone else will chime in..?

[young flower]

Also, I don't get how you could get shocked since the safety earth protects you by providing the path with least resistance to ground. In this case the house circuit breaker would trip.

I think there is not really a high risk of getting severely shocked in houses with fully functional residual current devices. However - there are some old buildings which lack such a device.
I also think the mains/neutral fuses are not primarily protecting the human user but rather the equipment. I guess the reaction (blow) time on those fuses is still too long to really protect a person who accidentally touches a live wire and a grounding point. Maybe the resistance of one person wouldn´t even be enough to blow a fuse...

The safest way to run amps would with no doubt be to use a plug-in-residual current device for your wall plug with the amp at any time - those are very cheap too, just about 20€. That in combination with fuses provides enough safety I´d say.
What I wrote in the beginning about the chassis carrying wall voltage when there´s an internal short with the neutral fused would only be a real problem if the building has no residual current device. If it has one - that would certainly trip the house circuit breaker.

At least that´s how I see the whole thing from my electrically unexperienced perspective .

I´m actually thinking about doing the TAD layout but without the additional neutral fuse now - and getting a 20€ plug-in residual current device to always use with the amp instead.

[julkke]

Yeah I guess two fuses aren't really needed. I'm a safety snob, in Finland houses have to have residual current devices (well, some do not, but new houses and gigging places do) but I use a plug in one too though. Then of course my amp is safety earthed and my guitars have a life saver circuit. I guess all shucko countries electrical equipment would have two fuses if it was really needed. I dont doubt John Suhr but seems a bit weird for him to say that he "has heard that you can flip the plug in some European countries".

I also believe novosibir uses only one fuse for his amps.

[young flower]

Haven´t heard of the guitar life safer circuit before - I have to look that up.

Another question: Looking at the TAD layout, that I´ll use now: Where should I best route the wire from the 120V pilot light to the 120V lug on the voltage selector for best noise suppression? Do you think it´s better to run it below the board directly to the voltage selector in a more or less straight line or along the corner of the chassis (I mean to the left and along both corners on the left side of the chassis, then next to the power tubes)- allllll.. the way to the voltage selector...??
Should I better use shielded cable for that connection?

[vh junkie]

Just run the pilot to the PT primary (common and 120v tap) that way it will work even if you do not use a voltage selector.

[julkke]

Here is what I posted about the life saver: http://forum.metroamp.com/viewtopic.php?f=23&t=41069" onclick="window.open(this.href);return false;

[young flower]

@vh junkie:

Just run the pilot to the PT primary (common and 120v tap) that way it will work even if you do not use a voltage selector.

Please have a look at the second layout I posted - then you´ll undestand why this doesn´t work for me: My PT has only PVC leads, no lugs, so 1 lead = 1 connection (I guess I could also splice together three wires but that would definitely look messy). I´m definitely going to use a voltage selector (although I´ll most probably never use anything other than 240V - but you never know, maybe I´ll need 120 or 220 too in the future), so the 120V tap from the PT will attach to the corresponding lug there, meaning one of the two pilot light wires has to connect to that voltage selector lug too. I´m just searching for the best way to route the wire.

@julkke:

VERY important - hadn´t considered the possibility of getting shocked through the strings before. But I remember all the posts of players talking about getting zapped from the microphone or "sparks shooting from the microphone" o.O (damn - that sounds as if somebody was really close to being electrocuted) now! I didn´t understand the problem before - now I get it. Thanks a lot for sharing that! I´ll definitely have a look at my strat´s insides soon and look into attaching one of these.

Do you happen to have some advice about that too?:

Another question: Looking at the TAD layout, that I´ll use now: Where should I best route the wire from the 120V pilot light to the 120V lug on the voltage selector for best noise suppression?

BTW:

You want to use 2A slow blow fuses for the mains and 1A slow blow for the b+.

Just to make sure - the HT fuse carries the b+ right?
And actually I can do all the wiring in the amp - except the IEC connector, mains fuse and mains switch - according to the Metro layout, right?

[julkke]

Better to solder the lamps another leg to 120v tap and heat shrink, leaving enough length to the 120v tap to be used in USA. Have you considered a 6V lamp? That just connects to the heaters, much easier to wire.

Yes, you can do everything but the mains wiring from the metro layout.

That guitar string ground thing is scary, isn't it? The life saver circuit should be a sticky thread in all guitar related forums..

[young flower]

Better to solder the lamps another leg to 120v tap and heat shrink, leaving enough length to the 120v tap to be used in USA. Have you considered a 6V lamp? That just connects to the heaters, much easier to wire.

I understand. Hmm - Could it possibly cause a lot of hum or why do you think it´s not a good idea? I´d prefer finishing all the wiring now, so I don´t have to modify anything in the future. Would it work in principle to solder the other leg to the voltage selector 120V lug together with the PT 120V tap?
I considered buying a 6V lamp - but I already bought a 120V lamp (and I also prefer the look of its plastic encasing to the 6,3V lamps ), so if possible I´d like to avoid paying for a new lamp+shipping if it´s not absolutely necessary. I´m sure you know how costly ordering is, if you have just one tiny part you need...

Yes, you can do everything but the mains wiring from the metro layout.

Thanks!

Yeah - the guitar string ground thing IS scary. I agree - the life saver circuit should definitely be a sticky thread everywhere.

[julkke]

Well then use the 120v lamp. The TAD layout shows clearly how to wire that too. If you are worried about hum just remember to keep AC wires away from DC wires, preferably tie the AC wires together as much as you can. Look into Larry grounding also.

[young flower]

Yes - I probably will use the 120V lamp. But if I happen to have to do a bigger order again before starting the build - I´ll get the 6,3V light (and swap the plastic encasing of course ).

Larry grounding (which basically is star grounding implemented as far as I understand it) basically reduces hum in the amp right?

I think this grounding method would be great. I´d really like to implement it on my build and I even found a very good thread about how to do that: http://forum.metroamp.com/viewtopic.php?f=45&t=31328" onclick="window.open(this.href);return false;

The refined (last) layout shows all the necessary connections for Larry grounding on a 69 SL type amp. Only thing missing in this thread is a clear and detailed listing+explanation of all the points connected to each of the five grounding points for paint-by-numbers builders like me who are not exactly shure what to connect where from just the layout whithout further explanation. And I would have to know which other grounding points listed/explained in the Metro instructions have to be changed or left out....

[julkke]

Search and find out about larry grounding, lots of info about it.