Another question

[gf]

Hi,

If you take some time to help this ignorant, it will be great !  

Here's a question that always confuses me and keeps me working with batteries only.

In almost every country you got the ac plug with a ground connection.
Here in Paraguay, we don't. So I would like to know how this affects a circuit, because I would like to work on a tube amp in the future.

Let's take for example a 9vdc power supply. It takes the 220v from the ac plug, the it uses a transformer to get ? volts, the it use diodes to separate positive and negative voltage, then it does some more stuff (regulate the voltage ?), and you get 9v positive, and 0 volts.

Ok, here you don't have a ground connection, so instead of 0 volts you will get -9v right ?

Can this damage a circuit ?

1- It's possible
2- A little damage
3- Big damage
4- Explosion
5- It would end the human race

And, also, will be safe to work with tube amps here ?

Thanks, Gabriel

[Joe Davisson]

The ground connection in the wall socket is to "earth ground". So if a wire comes loose in your toaster, and touches the metal chassis, it provides a separate conduction path to prevent you from getting shocked when you reach for the toast. It's a safety thing, and is not really part of the circuit.

Tube amps are extremely dangerous to work on, because of the charged HV filter capacitors. It only takes 20mA through your heart to kill you. I don't know how things work in Paraguay, but I would at least:

- understand electricity and HV, not just building circuits.
- find out how fast paramedics can bring a defibrillator. That's you're last hope if something goes wrong.
- work with a buddy, since you won't be likely to call for help.
- have a footpedal worked out that controls the AC -- one you have to hold down constantly while you work. Then if you're being shocked (or something blows up) you have a sporting chance to cut off the AC.
- research as much other safety information as you can.

I personally don't mess with tube amps. There's a lot of guys who talk about how they've been shocked and it's no big deal -- they're lucky. The power released by a charged HV cap is deadly under the right circumstances. This doesn't mean you shouldn't build them if you want to, but take the appropriate precautions, and don't take shortcuts on learning what you need to learn beforehand.

-Joe

[Nasse]

:? I live in an old house, and almost all wall sockets in my home are not "earthed". Only those that are outdoors or near water outlet or some damp environment like bathroom are "earthed". That was common practice in our country in "dry indoors and like" until only recent years, I think new buildings are equipped with earthed sockets only. Luckily (?) I dont own a tube amplifier. My computer manual says it should be connected to earthed supply, but I dont have suitable one yet.

But I believe you can quite easily convert a socket or two to earthed one. "You" here may mean an authorised repairman who has the knowledge how to do it. In Finland there is a rule if you change one socket in a room, you must change all sockets in that room to earthed model.

But I believe any professional repairman at your country can easily say if and how that can be done

[niftydog]

First, note that there's a distinction between "earth" and "ground".

Earth is literally the earth.  This planet has an insatiable appetite for electrons.  As stated previously, "earth" is used as a safety, to shunt excess electrons away.  You connect earth to the chassis so that if something goes wrong and the mains supply is connected to the case of your device, the enormous current going to earth trips the circuit breaker.

Earth is the connection in an AC plug/socket.

Ground is meerly a reference point in a circuit.  The two need not always be connected, although they often are.  Usually, ground is called zero volts, and all other voltage readings in the circuit are taken with respect to ground.

Ground is normally connected to one terminal of a battery.  If it's connected to the negative, you get +9V.  If it's connected to the positive, you get -9V.

Working without a ground can be dangerous, but there are ways around it.  Most non-grounded devices are "double insulated".  Meaning, there are TWO types of insulation between the exterior of the case and the mains wiring.

You can always MAKE yourself a ground.  Take a long conductive rod (copper is good) and drive it into the ground a metre or so.  (moist soil is best!)  Connect a nice, thick copper cable to it with a good electrical connection.  There's your ground.  Connect this cable to the chassis of the equipment you're working on and you'll have more protection.

Otherwise, normally a household tap (faucet for you yanks) provides a good ground connection point.  (That is if your pipes go into the ground!!)