Re: 230V to 110VAC isolation transformer

Phil screached like a gang-gang parot :-

Know nothing wankers like YOU Mr Crossley

can go drop dead.


Martin tied to get a parot to consider decorum.....

You similarly, Mr. Allison, though it would probably be more helpful for the
OP, and more interesting to me, for us all to have a reasoned discussion...
Martin.

And someone said something about flying pigs elsewhere, and sure,
when pigs have learnt aeronauticals, then decorum here may prevail.

Meanwhile, I make sure all metal chassis are definately earthed to the
earth wire from the power points
which have 3 contacts, active, with 240Vrms or perhaps 120Vrms if I use
my
step down auto tranny or variac, and neutral, which is the return path
for the
current from the active terminal, and the earth wire.

The neutral path wire from power points goes around the house/workshop
alongside the active wire
to the house distribution board where it is well connected to the green
yellow earth wire, and
an earthing wire is taken from this netral-earth common connection to
the copper waterpiping
running in the ground under the house.
So in effect, the neutral connection at the power point is connected to
ground and thus
one end of the primary on the power tranny is connected to earth
even if someone reverses the active and neutral terminals in a plug from
the amplifier.

BUT IT IS ESSENTIAL FOR THE METAL CASING OF THE AMP TO BE CONNECTED TO
EARTH
VIA A THIRD GREEN/YELLOW WIRE LEST THE ACTIVE BECOME CONNECTED TO IT
WITHOUT NEUTRAL OR EARTH PATHS FOR CURRENT.

Such a situtation could easily kill someone if they touched the chassis
and something
else that was earthy, such as test gear whose casing was earthed.

I once saved a man's life because I was quick enough to react.
The guy had a defective electric drill and we were working on a metal
framed building
to install gutters. he gave his mains lead to his old drill a pull along
to get slack
and the wires in the drill pulled away internally, but leaving the mains
atcive 240V
connected to the metal body of the drill.
Then he grabbed the adajacent metal purlin with his spare hand to get
force for the drill and copped
240V arm to arm, and he froze in position, barely able to speak.
I saw what was happening and yanked out the plug of the drill from the
socket of the supply lead.
If I had not been there, he would have been killed.

Guitar amps and all other tube amps and olf radios are potentially
terribly deadly.

The first thing I examine with old gear is the mains plug and earth
wiring
to make sure the chassis is earthed, so all old radios which very
commonly have unearthed
chassis in a bakelite cabinet with figure 8 two wire mains cables get
changed to earthed 3 wire
connection and a fuse included, for we do not want to read about dead
techs in this area
too soon, and don't want ppl's houses to burn down for lack of a fuse.

Having said all that, the commonest shock I have had over the last few
years is from the mains active to
chassis, 240vrms, and usually through a finger only, and not arm to arm,
which includes
through the heart. The "finger tingles" are not as bad as the
arm2armers.

So I try to place covering insulations over any active input wiring such
as the mains fuse and switch
terminals to prevent the mains shocks.

An occasional jolt from the B+ is always a possibility.
I have +700V, -500V rails in my latest 845 amps, reducing the shock
voltage
from a possible 1,200V from B+ to 0V or chassis, which people tell me is
all the more
"exciting" to experience compared to a mere +700V.
So far, no shocks from the 845 amps.

One is also supposed to have earth leakage detection which turns off the
mains
if there is earth current exceeding a tiny value below what would cause
the heart to fibrilate
or just stop.

But I don't have earth leakage, and it wouldn't help me if the B+ of an
amp is being discharged through me to the
0V rail or chassis of the amp/radio etc.

In most cases of dc shocks, I have jerked away from the live equipment.
One client of mine picked up a Leak amp chassis which
still had a charge in its rails, or was still turned on, to bring it to
me for a service check.
But being the clumsy type, he casually wraps his fingers around the
chassis bottom
edge and because Leak didn't supply a bottom cover, and he got a corker
of a shock.
Up in the air went the amp, and hit the ceiling with full unwanted force
as he could muster,
and two tubes smashed, and then the amp returned to his painted concrete
studio floor
with brute force and broke two more tubes.
The repair cost was larger than he expected; not just new OPT because of
the shorted turns...
It nearly cost him even more dearly.

Patrick Turner.
.