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Old 25th July 2003, 06:46 PM   #1
eduard is offline eduard  Netherlands
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Default Tension on chassis

Hello, A friend of mine allways has a measurable tension on his amplifiers. It will allways gradualy rise. When he will measure it it will be gone after that but it will return again. What can it be? A bad electrical system? Thanks a lot, Ed
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Old 25th July 2003, 09:02 PM   #2
dhaen is offline dhaen  Europe
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Hi,

Presumably you mean that there is voltage relative to earth.
This is one of my pet subjects, and one I've been meaning to expound on for some time.

There are 2 classes of equipment, known differently in different world area's, but nevertheless the classes remain the same:

Class 1: Equipment that can have conductive exterior, and single insulation. Any conductive surfaces must be connected to earth.

Class 2: Equipment that has double insulation and needs no earth. It may, in special cases, have limited conductive exterior parts.

In the case of valve amplifiers, it is hard to make one that conforms to Class 2*, so they must fall into Class 1.

*This is because even if full insulation is provided, the input and output connectors are a potential hazzard.
Also, there are many possibilities for faults developing that may cause the chassis to rise to a hazardous voltage.

In the UK and many country's, all mains outlets are provided with a safety earth. Where provided, this can be used to ensure safety.

However there are some European countries (and possibly others elsewhere) where no safety earth is available in the rooms where equipment is used.
It is my professional opinion that use of valve (tube) equipment in these places is potentially unsafe. My reasoning is this:

A fault. capacitive coupling, or leakage can cause the chassis or external parts to rise to a hazardous potential. Although the area might be designated as an earth free area, there are always earths. Examples are aerial (antenna) connections, central heating radiators, general plumbing, metal windows.

Bearing the above paragraph in mind, I would caution against the use of any high voltage equipment, valve/tube or SS unless a reliable earthing system can be guaranteed.

Right. I've said my piece Have a snigger, but it IS important.

Anyway, Eduard: check the earthing...


Cheers,
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Old 25th July 2003, 10:25 PM   #3
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Hi,

Quote:
However there are some European countries (and possibly others elsewhere) where no safety earth is available in the rooms where equipment is used.
As much as I hate to say it...most continental European countries only have dedicated earthing in kitchens or other places where washing machines and such are kept.

Living rooms in buildings older than, say, 20 years often don't have any three pronged earthed outlets.

Easy enough to solve as you pointed out.

And lucky me has split phase mains for free as does the better part of Belgium it would seem.

Ed,

The reason why it dissapears when measuring is probably because the meter itself drains it to earth.

As a little tweak, once you have a dedicated earth, you should remeasure the residual potential on the chassis referenced to earth with nothing else connected to that mains spur.
Compare residual chassis voltage depending on plug polarity and mark the plug for the lowest leakage current.
This is best done at the persons' home since mains polarity isn't necessarily the same.

Repeat for all the gear in the audio chain, one by one and enjoy the free lunch.


Cheers,
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Old 26th July 2003, 09:24 AM   #4
eduard is offline eduard  Netherlands
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Hello, I am not really sure about this but i think that my friend did tell me that if he uses a screwdriver with a light inside to find neutral and phase on the outlet. The neutral would also give a little light. Thanks, Ed
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Old 26th July 2003, 11:03 PM   #5
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Hi,

Quote:
Hello, I am not really sure about this but i think that my friend did tell me that if he uses a screwdriver with a light inside to find neutral and phase on the outlet.
That is one way to determine the polarity of the mains.

Now, it could very well be that the polarity at the powerXformer primary side is reversed.

Other causes could be leaky caps inside the amps amongst other things.

Ed, I remember you brought this same problem up about a year ago. Could you be more specific on how much voltage/current is measured with respect to ground?

Regards,
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Old 26th July 2003, 11:38 PM   #6
eduard is offline eduard  Netherlands
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Hallo Frank,
I don't remember asking it on this forum. I will ask my friend if he can measure the tension but i remember he did tell me it is really high. He uses a Hiraga 20 watt transistor amp and a Croft tube preamp. I think the problem is caused by the electrical system in his house. We will see. Maybe it is a good idea to connect everything in somebody's else house? Thanks so far. Ed P.s. maybe i will try to use some panasonic foil caps in my 600 hertz filter. I have enough others in stock to combine it to this value but i think it is better to use only one and not a combination.
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Old 26th July 2003, 11:50 PM   #7
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Hi,

Quote:
I don't remember asking it on this forum.
I do, not that it matters...

Quote:
He uses a Hiraga 20 watt transistor amp and a Croft tube preamp.
Well, well...I happen to know the JH 20W by heart and all of the Croft gear inside out..I used to distribute those.
A SuperMicro, I reckon? If it's a stock model I can offer a raft of things to modify...

Quote:
Maybe it is a good idea to connect everything in somebody's else house?
Yes.

Quote:
I have enough others in stock to combine it to this value but i think it is better to use only one and not a combination
I agree 100%.

Cheers Ed,
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Old 28th July 2003, 05:08 AM   #8
PassFan is offline PassFan  United States
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Quote:
Originally posted by eduard
Hallo Frank,
I don't remember asking it on this forum. I will ask my friend if he can measure the tension but i remember he did tell me it is really high. He uses a Hiraga 20 watt transistor amp and a Croft tube preamp. I think the problem is caused by the electrical system in his house. We will see. Maybe it is a good idea to connect everything in somebody's else house? Thanks so far. Ed P.s. maybe i will try to use some panasonic foil caps in my 600 hertz filter. I have enough others in stock to combine it to this value but i think it is better to use only one and not a combination.
Typically when one sees voltage on the neutral at the plug it is an indication of a floating Neutral. The bond is lost between neutral and ground at the pole transformer which causes the voltage to chase the load throughout the house. This can lead to backfeeding through the 2 pole devices in the home with dimming lights and fans running super fast or agonizingly slow. Have your friend seek a competent electrician to rectify this problem.
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Old 28th July 2003, 11:54 PM   #9
Morse is offline Morse  United States
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Hi Frank;

>>>...Now, it could very well be that the polarity at the powerXformer primary side is reversed...<<<

FWIW I had that happen with my last (in both senses of the word) storebought amp. And yes, that chassis would drift up quite a ways. The polarity of the cord was reversed; so much for quality control.

All the best,
Morse
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Old 29th July 2003, 09:51 AM   #10
dhaen is offline dhaen  Europe
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Default Mains polarity...

This should not be an issue. There should be equal insulation on both terminals, and the chassis should not be allowed to drift to any potential. Otherwise, what happens in installations where there are 2 pin reversable mains connectors?

I am sure no one would use an un-earthed electrical appliance in their kitchen. Well an un-earthed amplifier chassis is potentially much more dangerous. It's true that 2 pin outlets are generally fitted in "earth free" areas, but few will live up to that name nowdays.

I would seriously urge you to get a 3 pin outlet fitted, for safety reasons. There may well be sonic improvements to be had too
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