In article , Don Pearce
wrote:
On Sun, 03 Aug 2014 10:16:40 +0100, "Dave Plowman (News)"
wrote:

We now have the annual PAT test. In my lab once a year a chap comes
round and tests the integrity of the grounding of everything that has a
mains plug, from the 100 grand Network Analyser to the kettle in the
kitchen.

Once he has gone all the oscilloscopes get their grounds removed once
again so they can make floating voltage measurements and not introduce
ground loop mess into normal measurements.

It doesn't actually make anything safer, but the company lawyers like it.

Nice to see that people are maintaining the old traditions. :-)

FWIW When I used to install and use systems on the old UKIRT (Telescope)
they were always 'grounded'. But always gave you a multi-kV static shock if
you were the first to touch them after they'd been left un-touched for
about 10 mins or more. The ground connection was essentially dry rock in a
dry atmosphere. So was little more than a common reference. Certainly not a
way of ensuring no overall charge potential. 8-]

One trick was to send the newest PhD student to adjust the kit and the
watch to see if we could see the spark in the darkened dome. Usually
accompanied by a suitable noise from the student. :-) Rite of passage.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article ,
Phil Allison wrote:
"Dave Plowman (Criminal LIAR)"


If you think there's no point in using an isolating transformer (where
there are no other devices like an RCD) get hold of one of those old
valve guitar amps where the chassis is connected to neutral.


** Kindly post a schem of any such amplifier that could possibly be used
in the UK.

You stupid, ****ing pommy ****.


Which part of 'old' needs explaining to you?


** HUH ???????

Which part of "****ing pommy ****"needs explaining to YOU ???

Bowel cancer if far too refined a way to die for stinking human GARBAGE
like Plowman.


You really really really should seek professional help.

--
*They call it PMS because Mad Cow Disease was already taken.

Dave Plowman London SW
To e-mail, change noise into sound.

In article om,
mick wrote:
Sorry Dave, but Phil is right on this one. The fact that it's an
isolating transformer doesn't matter, it's the fact that it's in an
"earthed" metal enclosure (or it should be) and both plug and socket are
wired incorrectly.

I'm talking about many years ago. There was plenty of gear around with
metal parts - even cases - and no earth.

If a case is properly earthed the worst case fault will simply blow a
fuse. Assuming the cabling feeding the device is heavy enough. And you
couldn't even guarantee that once.

--
*They told me I had type-A blood, but it was a Type-O.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 03 Aug 2014 19:16:08 +0100, Dave Plowman (News) wrote:


I'm talking about many years ago. There was plenty of gear around with
metal parts - even cases - and no earth.

If a case is properly earthed the worst case fault will simply blow a
fuse. Assuming the cabling feeding the device is heavy enough. And you
couldn't even guarantee that once.


A lot of live chassis stuff appeared over here while some areas still had
DC mains. I worked (well, messed about with!) quite a few old AC/DC
radios as a lad. I think there was also quite a bit of that stuff
produced during WWII, when it was very difficult for anything other than
the war effort to get metal for transformers.

There are certainly one or two circuits on the web for cheap guitar amps
that are live chassis.
Kay 703: http://www.freeinfosociety.com/elect...ematics/audio/
kay703.pdf
Harmony H400: http://www.angelfire.com/vt/audio/harmonyh400sch.jpg
I doubt if either of these would have been sold in the UK though.

On 03/08/2014 19:11, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
Bowel cancer if far too refined a way to die for stinking human GARBAGE
like Plowman.


You really really really should seek professional help.

People have been telling him that for as long as I've been on usenet,
and, from what I read then, even before that.

Occasionally, he returns from limbo and infests a random group for a
while. I have, in the past, learnt some new words off him, but he seems
to just be re-using his old vocabulary nowadays.

--
Tciao for Now!

John.

"mick"


There are certainly one or two circuits on the web for cheap guitar amps
that are live chassis.
Kay 703: http://www.freeinfosociety.com/elect...ematics/audio/
kay703.pdf
Harmony H400: http://www.angelfire.com/vt/audio/harmonyh400sch.jpg

** Neither of the above are really *live* chassis - notice there is a RC
network in series with the chassis that has an impedance of well over
50kohms at 60Hz.

I know of NO guitar amp that ever was live chassis - cos it would be a
killer.


I doubt if either of these would have been sold in the UK though.

** Also they can only work with 117V mains unless a step-down tranny is
fitted inside.

All such amps were very low powered, mainly used as practise amps by
beginners.


..... Phil

"mick"
Phil Allison wrote:

FYI:

Supply earth goes direct to one side of the amp's AC tranny, then comes
the iso-tranny's 240V winding and back to the amp's chassis. The amp
will not run - but the chassis is 240AC live relative to earth.

You're looking at an equipment plug being plugged into a fixed ISO tranny
that's plugged into a correctly wired mains socket? Ah... I was looking
at the tranny primary-side plug being wrongly connected, sorry. Yep,
the chassis is connected to mains earth via the isolated supply and the
amp's supply tranny in series.

** Correct - the result is 100% lethal.

Yet *another* good reason NOT to use an iso tranny on a repair work bench
as the regular AC supply.



..... Phil

In article , Phil Allison
scribeth thus

"mick"
Phil Allison wrote:

FYI:

Supply earth goes direct to one side of the amp's AC tranny, then comes
the iso-tranny's 240V winding and back to the amp's chassis. The amp
will not run - but the chassis is 240AC live relative to earth.

You're looking at an equipment plug being plugged into a fixed ISO tranny
that's plugged into a correctly wired mains socket? Ah... I was looking
at the tranny primary-side plug being wrongly connected, sorry. Yep,
the chassis is connected to mains earth via the isolated supply and the
amp's supply tranny in series.

** Correct - the result is 100% lethal.

Yet *another* good reason NOT to use an iso tranny on a repair work bench
as the regular AC supply.



.... Phil



What do you use then Phil?..
--
Tony Sayer

In article ,
John Williamson wrote:
On 03/08/2014 19:11, Dave Plowman (News) wrote:
In article ,
Phil Allison wrote:
Bowel cancer if far too refined a way to die for stinking human
GARBAGE like Plowman.


You really really really should seek professional help.

People have been telling him that for as long as I've been on usenet,
and, from what I read then, even before that.

Occasionally, he returns from limbo and infests a random group for a
while. I have, in the past, learnt some new words off him, but he seems
to just be re-using his old vocabulary nowadays.

It's certainly odd behaviour.

Perhaps he thinks using a title to a thread like this one comes up on
Google or whatever. But most seeing such a thing would know it comes from
a seriously deranged person.

--
*A person who smiles in the face of adversity probably has a scapegoat *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Phil Allison wrote:
Bet the Beeb et alia stopped doing that when they nearly electrocuted the
first guitarist.

You, of course, know better than the engineers at both the BBC and ITV
companies *at that time* - before RCDs etc were available.

There were many occurrences of musos getting electric shocks at gigs where
their gear was mixed with house PA systems - as was once the norm. Even
fatalities.

This never once happened in a BBC studio. QED.

--
*Bills travel through the mail at twice the speed of cheques *

Dave Plowman London SW
To e-mail, change noise into sound.