Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on August 16, 2014, 06:25:08 pm
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Hi Guys, Back on the Fi Sonic restore.
I noticed that these amps use a switch on the neutral for mains switching.
Is this a good practise?? Thanks
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Hi Guys, Back on the Fi Sonic restore.
I noticed that these amps use a switch on the neutral for mains switching.
Is this a good practise?? Thanks
I always thought that was a bad idea, because it could increase your chances of having a 'hot' chassis or even short circuits due to grounding issues, even when the amp is switched 'off'.
I tend to use a DPDT switch and just switch both the hot & neutral sides at once.
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This isn't wall-wiring.
In particular you do NOT know which wire is so-called "neutral". (Many wall outlets are wired wrong.)
If you have to work inside, you un-plug, right?
That's the difference from Building Wiring, where you can't un-plug a whole room (all conductors) readily and must trust that the White has very-low voltage on it.
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Hi guys, I hoping that here in OZ that our SPARKIES do wire the power points in the right polarity, power cable is RED active ,BLACK neutral, power leads BROWN active, BLUE neutral and GREEN/YELLOW, earth on both.
I don't see why they have the switch on the neutral only that it may have been the practice of the day.
I have rewired it so the switch is on the active. Thanks
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Here in Italy there is a tendency to use one color for live and one other for neutral (in building wiring) but you can't be sure it is wired on the outlet always at the same manner, however our outlet don't avoid in any way the reverse insertion of the plug
As far as I can know only in GB they have a special outlet on which a special plug (carrying also fuse) is used, this outlet and plug don't permit reverse connection, avoiding the presence of line in a wrong "place"
The problem, as said, can be easily bypassed using a DPDT switch, however without a fuse placed on the plug, the wires of the cord can short and the protection is send to the house wiring protection circuit
Some time ago the cord of my hair dryer shorted, the copper wire was fused and a jet of metal was sprayed on my fingers, not nice experience to do, it will be much better to have the British plug with their fuse
K
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Hi guys, This is how it is now. Thanks
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Hi dr, The switch being used is a 2P 3 position rotary. One half is switching the mains and the other breaks the ground connection of the PT CT.
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SERIOUS........................
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> Neutrals and secondary grounds are low voltage
The *power* switch still sees 120V. It isn't switching to-ground, it is (in this case) switching to-live.
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As further explanation:
Here in Italy now is obligatory installed (in building wiring) a differential switch
http://it.wikipedia.org/wiki/Interruttore_differenziale (http://it.wikipedia.org/wiki/Interruttore_differenziale)
At the time of my little accident there was not mandatory to have the differential switch installed
but his function isn't to protect against short, it protects only if there is a loss toward ground
Just curious in the US and in Australia and NZ do you have such protection (differential switch) on the wiring of buildings ?
K
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> do you have such protection (differential switch) on the wiring of buildings ?
In USA and Canada it is called "Ground Fault Circuit Interrupter", GFI or GFCI.
In the UK electrical systems the name is "Residual Current Device", something like that.
Wikipedia English article on RCD/GFI (http://en.wikipedia.org/wiki/Residual-current_device) is UK point of view with comments about US and other areas.
I like your name "Interruttore differenziale" better. The GFI does not need a ground to operate, and can trip even when current is leaking to someplace other than ground. These all operate on a *difference* in current in the two legs of the circuit.
In the USA, GFIs were required on bathroom outlets in the 1970s, then in many more places, but not in the whole house. Older units are outlets, which may power (and protect) additional outlets. Now it is common (in new-work) to put the GFI in the cellar fuse-box, built with the over-current protection in standard circuit-breaker format. This is also available on the UK market. Yours (in the Wikipedia pictures) appear to be 2-in-1 units with an over-current breaker permanently strapped to a GFI breaker, a bit more bulky. (I suspect that you can now get them all-in-one, narrower.)
One global difference. In the US market the trip current (after many milliSeconds) is 5mA. The UK market GFIs are marked 30mA (your pictures show 0.030A which is 30mA). While this sounds like a big difference, I once went through the details and decided it was not a BIG difference in protection, but a difference in the way they are tested and marked.
There are, in addition, in both markets, "equipment protection" GFIs with much higher leakage trip currents. A motor in a damp location may leak 10mA "normally", so a 6mA GFI would keep tripping. The "differential" is never perfect, so a 100 Amp starting-surge with 0.9999000 accuracy will trip a 6mA GFI. You can get 50ma and 100mA GFIs if you are only protecting equipment, not people.
I am shocked to learn that Germany did not require RCD until 2007?
In the UK, apparently you can have one RCD for the entire house. Better is to separate power and lights, and have at least two RCDs for the lighting circuits so the whole house won't go dark. This is never done in the US. We put GFI only where "needed". This can be a non-GFI circuit to bedroom and bathroom with a GFI outlet for the bathroom. Because of our smaller circuits (120V 20A vs 230V 16A) and large hair-dryers, we now favor a dedicated bathroom circuit with GFI preferably in fuse-box. I have 25 circuits in my house, four breakers (bathrooms and kitchen) are GFI, and one non-GFI breaker feeds GFI outlets on the outside of the house.
We put GFI in kitchens and bathrooms because water pipes were all metal, good way to get shocked. However as I was installing all those GFIs, I was also converting all plumbing (water and drain) to plastic pipe. So it is a bit silly.
Your next step, which you should resist, is "Arc Fault". The idea is that when there is a bad connection in a plug and outlet, and it heats-up, the AFCI should detect this and break power before a fire stars. These do not work!!, except in very severe cases, maybe. They trip for no reason, they give false hope of safety, and they cost way too much.
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> Neutrals and secondary grounds are low voltage
The *power* switch still sees 120V. It isn't switching to-ground, it is (in this case) switching to-live.
I believe TIMBO lives in an area where the electrical, is 240-0-240. The doubled voltage can cause a reduced life of contacts. The amp in question was originally wired to interrupt the neutral, and not the hot.
All RIGHT. The *power* switch still sees 120V or 240V or whatever the local flavor is.
The power switch does NOT know where the dirt is. It does not see to-ground voltage, but line-to-line voltage.
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Hi guys, did a bit of poking............
The first Fi Sonic I got it had the mains switch on the NEUTRAL as I have said.
I did not think that this was a good idea as the PT is live to the point of the switch contact.
So with the amp plugged in and turned on at the wall switch, I get 240v between the neutral on the PT and the neutral of the power cord as you would expect.
When turning the amp on to standby the voltage drops to 0 as you would expect also.
In theory I should be able to touch the neutral of the PT when the amp is truned on.
As I DON'T LIKE TO DO THIS so I used my MM and it told me that it was 0v so i'll agree with that.
It is an easy fix to change the switch from neutral to active. Thanks