Operation without GND

[Strikkflypilot]

Hi!

I have recently found out that some homes here with older electricity only have two outputs for the AC current and no GND. However it would be entirely possible to plug in a Bottlehead amp.
Am I right in the assumption that it would be deadly, as in the operator would be GND?
Or would someone care to elaborate on what would happen?

[Grainger49]

That is the first time I remember this question being asked.  It is a good question.  The manual used to say not to use a "cheater" to convert the Bottlehead 3 wire cord to a two wire outlet.  I haven't read that part of the manual in a long time.  I just dig in.

The ground is there in case the high voltage winding shorts to the chassis.  The chassis is grounded, to the third wire at the plug.  That should blow the amp's fuse in a 3 wire grounded circuit. 

In a two wire circuit the chassis becomes HOT to ground.  If you touch a ground, a water pipe or radiator and the chassis at the same time you get a potentially deadly shock.

If you get an insured, licensed electrician to run a three wire, grounded circuit to your audio outlet you are safer.  You will probably have lower noise/hum in the system too.

[Strikkflypilot]

Thanks Grainger.

Fortunately, I have modern electrical wiring at home, with a ground on all sockets.
It might however be important to clarify if one were to sell off a build.

[Paul Birkeland]

Electronics made back in the days of 2 wire AC plugs were interestingly scary.  If you look at old radios, the metal chassis is generally connected to one of the AC wires, making "ground", and the other leg feeds the rectifier (the AA5 setup).  This means that, when plugged in correctly into a correctly wired outlet, the chassis is tied to neutral and everybody is happy.  If, on the other hand, you have an outlet improperly wired, or the radio was plugged in backwards, then AC line voltage is present on the chassis.

To cope with this, the metal chassis were buried in wood and bakelite enclosures, plastic knobs were used, etc. to protect the user.  For those who refurbish radios, simply adding a power transformer takes care of this problem.

In our gear, we use the chassis plate as a ground for shields, as well as a safety ground.  If it's left floating, well, those features don't work as well.  Luckily, in structures of this age, you'll often find a radiator in each room, and fashioning up a ground to a radiator is often an acceptable substitute.

-PB

[Strikkflypilot]

Very interesting reading, Paul.
I am right in the assumption that e.g. The Crack
Needs proper ground, like a radiator?

[Paul Birkeland]

The Crack will work better with a hard ground, but it will also work without it.

[Strikkflypilot]

Ok. Thanks.
Just wouldn't want to be cause of someones demise...