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west[_2_] west[_2_] is offline
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Default Variac as a Troubleshooting Aid

For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.

Cordially,
west


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Eeyore Eeyore is offline
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Default Variac as a Troubleshooting Aid



west wrote:

For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.


Is that so ?

Could you explain what you mean by a 'pc clad' btw ?

Graham

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Default Variac as a Troubleshooting Aid


"Eeyore" wrote in message
...


west wrote:

For intermittent problems possibly caused by a microscopic fracture in a

pc
clad, try lowering the AC input voltage with a variac. Lower the AC

until
the circuit just starts working, then clad fractures and often cold

solder
connections will manifest themselves.


Is that so ?

Could you explain what you mean by a 'pc clad' btw ?

Graham


Traces.
west


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Peter Wieck Peter Wieck is offline
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Default Variac as a Troubleshooting Aid

On Apr 24, 2:31 pm, "west" wrote:
For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.

Cordially,
west


West:

With all straightforwardness here, please look up some of my rants on
Variacs. You are looking for thermal effects based on low voltage,
with the (mostly mistaken) belief that if a circuit runs cool it will
be less likely to "open up" than if it runs hot. Right.

The rant below was written against vintage equipment of all sorts, and
in the case you cite, it is even more critical to have meaningful
metering. If there actually is an intermittent in the circuit, traces
or connections, that will manifest as significant movement in the
meter. Furthermore, the general current draw of any device is easily
calculated, so any variations above or below should be viewed with
great suspicion with diagnosis not being valid until the cause is
found and verified.
__________________________________________

1. A Variac *can* be useful. But only if used properly and with the
proper
metering. Otherwise it will serve merely to slow down whatever awful
discovery
(or success) you would have found by plugging it in and "letting her
rip".

2. In any case, DON'T justplugitinandletitrip.......

I am continuously surprised by the almost mythical status variable
autotransformers have achieved in the hobby to somehow diagnose the
condition
of vintage equipment, reform caps, and do all sorts of other magical
things.....
without any reference to the required peripherals for the variac to
achieve
these ends.

First, unless you have a current measuring device on the variac that
indicates
in meaningful increments exactly how much current the Item Under Test
(hereinafter IUT) is drawing as current is applied, then you have no
way of
knowing whether you are heading to operation or destruction as you
apply
current. Sure, you can use a dim-bulb device to approximate current,
but being
within the 20-30% (at best) that can be gleaned from this process is
way too
innacurate for trust. Example: You have a typical 7-tube PP-type 25wpc
amp on the bench. Nameplate is usually around 100 watts, actual
usually around
60-70 watts. As you have no meter, you bring it up on the variac, all
seems
well... it may even play. BUT, you are drawing, unbeknownst to you 85
watts.
You are a happy camper. The Unit plays. You bring it down(up)stairs
and say:
Hey, Hon, the Unit plays... let's listen to some chamber music on it.
About 20
minutes into the disc, there is this funny smell, and a small (or
large)
*POP*.... maybe even some smoke.

That 15-25-or-so extra watts was going somewhere. Typically heat. So
something
had to give.

Second, there are "dim-bulb" devices that insert standard wattage
lightbulbs in
series with the IUT. These will indicate VERY ROUGHLY whether there
are any
spectacular shorts in an item, but again the margin of error is pretty
immense
for the long haul. They are minimally useful when used with a variac,
but only
because they are better than nothing.

Cutting to the chase, before applying current to ANY item under any
conditions, one should have a direct method in place to measure
current drawn. There are several methods, the most "elegant" of which
is to have meaningful meters built into the variac (together with an
Isolation Transformer (to be saved for another rant). The other method
is to measure across a resistor (in series) of a specific value.
The drop across the resistor will indicate current thereby utilizing a
common VOM instead of hard-to-find and calibrate AC ammeters, or the
rare units with it all built in.

In this way, one can REALLY determine what a IUT is doing, and REALLY
get a
decent idea where to begin troubleshooting (if necessary).

Without meaningful information, one is entirely flying blind.
Meaningful information includes accurate measurements of Voltage and
Amperage, using meaningful increments. In the realm of equipment
mostly discussed here, increments of 0.01 or at worst 0.02 A on a
difference-scale of 0-1A must be clearly discernable, with ranges up
to 5A being useful.

Peter Wieck
Wyncote, PA



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Default Variac as a Troubleshooting Aid

On Apr 24, 2:31 pm, "west" wrote:
For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.

Cordially,
west


One mo
_____________________________________________

Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.

Variacs, on the other hand are either very handy diagnostic tools or
worse-than-useless anchors fit only to let the magic smoke out of an
otherwise
salvageable item. I am not really sure if there is an in-between other
than
their original function as light dimmers.

Without both current and voltage metering, they are worse-than-
useless. With
the proper metering, they can be very handy tools.

Myths: A variac will help reform caps (with specific reference to tube/
valve
equipment).

Fact: Only on those specific items with solid-state rectifiers that
pass B+ current at any voltage, and only if done over more time than
one cares
to consider.

In the case of a tube rectifier, most of them do not start to pass DC
until the
filament voltage reaches between 65% and 75% of rated voltage. If the B
+ on the
particular item is say.... 350V, that means that the first voltage
the
caps-to-be-reformed would see would be something between 227V and
263V... not
exactly a soft-start.

Myth: A variac will allow one to apply voltage gently to a item, so as
to
discover problems before they become fatal.

Fact: No, not at all. True, a variac does allow an item to see the
minimum
amount of current to trigger its functions... an item with bad filter
caps may
begin to hum at 80V rather than 120V but if the caps are not so bad as
to show audible hum, the variac ceases to be useful. And a variac will
*not* tell you whether a repaired item is OK or not.

However, if the proper meters are put on the Isovariac, then some
real
diagnosis can happen: An item which should, by calculation draw say...
65 watts
or so (0.55A), and draws 90 watts is dissipating 25 watts of heat
somewhere...
perhaps the output transformer(s).

Comes down to a current meter with fine enough increments to give
meaningful
information. Such a tool is useful right down the line from initial
diagnosis
to testing the completed results.
__________________________________

Peter Wieck
Wyncote, PA




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Phil Allison Phil Allison is offline
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Default Variac as a Troubleshooting Aid


"Peter Weeke the ****** "


Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.



** Totally false.

Isolation transformers need only be used when working on a live chassis
item.

Otherwise, you do NOT need one and using one INCREASES the electrocution
hazard for a technician.

See: http://sound.westhost.com/articles/electrocution.htm


a.. Do not assume that isolation or stepdown transformers are safe - they
are not. Isolation transformers will cheerfully kill you if you become
connected across the output - an isolation transformer has no active (live)
and neutral. Many stepdown transformers do not provide isolation. Isolation
transformers can lead to a complacent attitude, and one lead can connect to
chassis if there is an insulation failure - with no effect on the equipment
or transformer. The other lead is now a killer! Isolation transformers will
prevent an electrical safety switch from operating if a fault develops on
the isolated side!




....... Phil


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Default Variac as a Troubleshooting Aid

On Apr 25, 10:27 pm, "Phil Allison" wrote:
"Peter Weeke the ****** "



Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.


** Totally false.

Isolation transformers need only be used when working on a live chassis
item.

Otherwise, you do NOT need one and using one INCREASES the electrocution
hazard for a technician.

See:http://sound.westhost.com/articles/electrocution.htm

a.. Do not assume that isolation or stepdown transformers are safe - they
are not. Isolation transformers will cheerfully kill you if you become
connected across the output - an isolation transformer has no active (live)
and neutral. Many stepdown transformers do not provide isolation. Isolation
transformers can lead to a complacent attitude, and one lead can connect to
chassis if there is an insulation failure - with no effect on the equipment
or transformer. The other lead is now a killer! Isolation transformers will
prevent an electrical safety switch from operating if a fault develops on
the isolated side!

...... Phil


Phil:

Other than being a not-half-bad tech, you have a strange view of the
world which arrests your understanding at the most basic level. Put
another way, you are almost entirely unencumbered by the thought
process. Accordingly, you give advice out of your ass rather than out
of your brain.

"Hot Chassis" items can happen for any number of reasons (as recent
posts here illustrate), from shorted bypass caps and similar failures
to errors on the part of a technician, assembler, kit-builder... or
even someone as perfect as you.

An isolation transformer is a simple precaution. It does NOT protect
anyone against all error, and it is *only* useful on a bench during
the diagnostic process. Certainly when an item leaves the bench it
also leaves that very special environment and needs to join polite
society...
Futhermore, I do not think I mentioned anything about step-down/up
transformers either. Mostly they are auto-transformers anyway. What I
do mean is a laboratory-grade isolation transformer designed for
exactly the purpose. Not silly little Radio-Shack 32VAC transformers
mounted back-to-back or other expedients.

The one I keep is: http://www.oaktreeent.com/web_photos...20_collage.jpg

Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.

Peter Wieck
Wyncote, PA

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Default Variac as a Troubleshooting Aid



Peter Wieck wrote:

Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.


What Phil is quite correctly pointing out is that the use of an isolation transformer means that
you will get no protection from an 'earth leakage current' breaker feeding it.

Your very life might depend on it. Do not use isolation transformers 'willy nilly'. They have their
dangers.


Graham

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Ian Iveson Ian Iveson is offline
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Default Variac as a Troubleshooting Aid

Phil Allison wrote

Isolation transformers are critical for any workbench, and after
good
hand-tools the first thing any electronic hobb7 person should
get...
perhaps even before said tools.



** Totally false.

Isolation transformers need only be used when working on a live
chassis item.

Otherwise, you do NOT need one and using one INCREASES the
electrocution hazard for a technician.

See: http://sound.westhost.com/articles/electrocution.htm


a.. Do not assume that isolation or stepdown transformers are safe -
they are not. Isolation transformers will cheerfully kill you if you
become connected across the output - an isolation transformer has no
active (live) and neutral. Many stepdown transformers do not provide
isolation. Isolation transformers can lead to a complacent attitude,
and one lead can connect to chassis if there is an insulation
failure - with no effect on the equipment or transformer. The other
lead is now a killer! Isolation transformers will prevent an
electrical safety switch from operating if a fault develops on the
isolated side!


Seems to me you are both right, or wrong, depending on how you work.

As long as you are both aware of the dangers, one way or the other,
which I am sure you both are, then you are both right. You have both
done lots of work on dangerous equipment. You are both still alive.

Why should either of you insist that your way is better?

cheers, Ian


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Default Variac as a Troubleshooting Aid

On Apr 26, 8:10 am, Eeyore
wrote:
Peter Wieck wrote:
Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.


What Phil is quite correctly pointing out is that the use of an isolation transformer means that
you will get no protection from an 'earth leakage current' breaker feeding it.

Your very life might depend on it. Do not use isolation transformers 'willy nilly'. They have their
dangers.


Graham

I have no clue as to what sorts of GFIC devices you use, and how they
are configured, but in this country (USA), based on NEC requirements
the Device measures any deviations between input and output and will
trip on any leakage to ground.

Let's look at the nature of a GFIC device: It is designed to trip when
the current goes anywhere other than from hot to neutral. Can we agree
on that?

If that is the case, and you insert yourself into a circuit *between
the hot and the neutral*, whether there is a GFIC device or not, you
will get zapped, as it cannot differentiate between you and a 1/4 watt
10,000 ohm resistor put in the same location.. or a 25 what
incandescent lamp, for that matter.

Assume no isolation transformer. Assume a properly functioning GFIC
Device. Assume that you insert yourself into a ground path. Assume
that the GFIC Device trips properly. *You* are still subjected to a
momentary surge at whatever voltage is happening at that moment.

What an Isolation Transformer does is isolate you from said ground
paths. It does not obviate any protection from any additional outboard
devices, and it does not take the place of them either. Nor does it do
any better (or worse) than any other device if you insist on inserting
yourself into the *designed* current path.

Lastly, a properly designed isolation system does have a ground-path
through it to prevent test probes and/or attached devices to test-
equipment from setting up a potential hot-chassis situation outside
the Isolated Circuit. In this case, the GFIC device will trip as in
any other similar case. If you do not believe me, set it up for
yourself and try it. Mine trips just as it should under that scenario
when I go through the monthly tests.

NO piece of equipment rates "willy-nilly" use. All have their
limitations and dangers, and lack of wit and understanding will
overcome even the most carefully designed safety systems. At the same
time just because problem or fault *is* possible, that does not mean
one should discard all precautions as meaningless. Airbags can kill
under certain conditions. Seatbelts can trap one in a vehicle under
certain conditions, Anti-Lock brakes and/or ESP can cause problems
over no such systems under certain conditions.

You appear to fall into that logical trap that requires believing that
the opposite of Black is only and necessarily White. When, in fact,
the opposite of Black is anything that is simply *Not Black*. Just ask
the question: Is it black or not? Anything that is not black rates the
NOT. Whether it is the polar opposite of White, or merely Puce, it is
still NOT BLACK.

Peter Wieck
Wyncote, PA




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Default Variac as a Troubleshooting Aid

On Apr 26, 8:36 am, "Ian Iveson"
wrote:
Phil Allison wrote





Isolation transformers are critical for any workbench, and after
good
hand-tools the first thing any electronic hobb7 person should
get...
perhaps even before said tools.


** Totally false.


Isolation transformers need only be used when working on a live
chassis item.


Otherwise, you do NOT need one and using one INCREASES the
electrocution hazard for a technician.


See:http://sound.westhost.com/articles/electrocution.htm


a.. Do not assume that isolation or stepdown transformers are safe -
they are not. Isolation transformers will cheerfully kill you if you
become connected across the output - an isolation transformer has no
active (live) and neutral. Many stepdown transformers do not provide
isolation. Isolation transformers can lead to a complacent attitude,
and one lead can connect to chassis if there is an insulation
failure - with no effect on the equipment or transformer. The other
lead is now a killer! Isolation transformers will prevent an
electrical safety switch from operating if a fault develops on the
isolated side!


Seems to me you are both right, or wrong, depending on how you work.

As long as you are both aware of the dangers, one way or the other,
which I am sure you both are, then you are both right. You have both
done lots of work on dangerous equipment. You are both still alive.

Why should either of you insist that your way is better?

cheers, Ian- Hide quoted text -

- Show quoted text -


Depends on how one defines "life"... Phil may be the way he is due to
too many shocks? He certainly does have an electric personality...

In any case, I have come to the conclusion that electricity must
behave differently in the Antipodes and all the strictures and
standards of the NEC, NEMA UL and ANSI are relatively meaningless in
that environment.

Peter Wieck
Wyncote, PA

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Eeyore Eeyore is offline
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Default Variac as a Troubleshooting Aid



Peter Wieck wrote:

Eeyore wrote:
Peter Wieck wrote:
Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.


What Phil is quite correctly pointing out is that the use of an isolation transformer means that

you will get no protection from an 'earth leakage current' breaker feeding it.

Your very life might depend on it. Do not use isolation transformers 'willy nilly'. They have their

dangers.


I have no clue as to what sorts of GFIC devices you use, and how they
are configured, but in this country (USA), based on NEC requirements
the Device measures any deviations between input and output and will
trip on any leakage to ground.


It works bt detecting any line-neutral imbalance.


Let's look at the nature of a GFIC device: It is designed to trip when
the current goes anywhere other than from hot to neutral. Can we agree
on that?


Yes.


If that is the case, and you insert yourself into a circuit *between
the hot and the neutral*, whether there is a GFIC device or not, you
will get zapped, as it cannot differentiate between you and a 1/4 watt
10,000 ohm resistor put in the same location.. or a 25 what
incandescent lamp, for that matter.


Which is exactly what happens when you use an isoaltion transformer if you're touching the live and
ground say and the neutral is also grounded. You become a perfectly valid load and get electrocuted
whilst the breaker sees no problem with that. Remove the isolating transformer and the breaker will trip.

Graham

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Default Variac as a Troubleshooting Aid

On 25 Apr 2007 18:09:34 -0700, Peter Wieck wrote:

On Apr 24, 2:31 pm, "west" wrote:
For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.

Cordially,
west


One mo
_____________________________________________

Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.

Variacs, on the other hand are either very handy diagnostic tools or
worse-than-useless anchors fit only to let the magic smoke out of an
otherwise
salvageable item. I am not really sure if there is an in-between other
than
their original function as light dimmers.

Without both current and voltage metering, they are worse-than-
useless. With
the proper metering, they can be very handy tools.

Myths: A variac will help reform caps (with specific reference to tube/
valve
equipment).

Fact: Only on those specific items with solid-state rectifiers that
pass B+ current at any voltage, and only if done over more time than
one cares
to consider.

In the case of a tube rectifier, most of them do not start to pass DC
until the
filament voltage reaches between 65% and 75% of rated voltage. If the B
+ on the
particular item is say.... 350V, that means that the first voltage
the
caps-to-be-reformed would see would be something between 227V and
263V... not
exactly a soft-start.

Myth: A variac will allow one to apply voltage gently to a item, so as
to
discover problems before they become fatal.

Fact: No, not at all. True, a variac does allow an item to see the
minimum
amount of current to trigger its functions... an item with bad filter
caps may
begin to hum at 80V rather than 120V but if the caps are not so bad as
to show audible hum, the variac ceases to be useful. And a variac will
*not* tell you whether a repaired item is OK or not.

However, if the proper meters are put on the Isovariac, then some
real
diagnosis can happen: An item which should, by calculation draw say...
65 watts
or so (0.55A), and draws 90 watts is dissipating 25 watts of heat
somewhere...
perhaps the output transformer(s).

Comes down to a current meter with fine enough increments to give
meaningful
information. Such a tool is useful right down the line from initial
diagnosis
to testing the completed results.
__________________________________

Peter Wieck
Wyncote, PA

Why not just plug it into a watt meter? J.P.
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On Apr 26, 1:39 pm, Eeyore
wrote:
Peter Wieck wrote:
Eeyore wrote:
Peter Wieck wrote:
Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.


What Phil is quite correctly pointing out is that the use of an isolation transformer means that

you will get no protection from an 'earth leakage current' breaker feeding it.


Your very life might depend on it. Do not use isolation transformers 'willy nilly'. They have their

dangers.


I have no clue as to what sorts of GFIC devices you use, and how they
are configured, but in this country (USA), based on NEC requirements
the Device measures any deviations between input and output and will
trip on any leakage to ground.


It works bt detecting any line-neutral imbalance.

Let's look at the nature of a GFIC device: It is designed to trip when
the current goes anywhere other than from hot to neutral. Can we agree
on that?


Yes.

If that is the case, and you insert yourself into a circuit *between
the hot and the neutral*, whether there is a GFIC device or not, you
will get zapped, as it cannot differentiate between you and a 1/4 watt
10,000 ohm resistor put in the same location.. or a 25 what
incandescent lamp, for that matter.


Which is exactly what happens when you use an isoaltion transformer if you're touching the live and
ground say and the neutral is also grounded. You become a perfectly valid load and get electrocuted
whilst the breaker sees no problem with that. Remove the isolating transformer and the breaker will trip.

Graham- Hide quoted text -

- Show quoted text -


Clearly you do not understand the nature of lab-grade isolation
transformers. ALL power through them is 'above ground', the only valid
path is hot-to-neutral. There is no ground path from the isolated hot
side. Whether the neutral is grounded or not. There is still no path
except between hot and neutral... same as there would (should) be
anyway.

Don't take my word for it. Set it up and test it for yourself. You can
ground the test piece to a good direct ground. And then measure a VOM
from the hot side to it. No current will flow. And you can short the
neutral to the ground and do the same. It still won't go through the
ground. Or, measure current from neutral to ground. Nothing. Connect
your GFIC device. Use a leaky test-probe from a signal generator or
scope not isolated to the test piece... *POP* goes the breaker. As it
should. Lots-O-Speculation here, little actual experience testing from
appearances. It ain't nohow black magic.

This is an unique condition, and isolated (pun intended) to test-bench
conditions, to be used by someone who clearly understands the
limitations of the device with great specificity to what it does NOT
do.

Now, of course, consider your scenario under hospital conditions where
all sorts of wet stuff, machines, needles and monitors are operated
through isolation transformers to protect the patient (and the
machinery) from stray currents that could be anything from life-
threatening to causing the machines to malfunction. If your scenario
obtained, there would be no benefit to their use... which, of course,
is not the case.

http://www.reo.co.uk/files/kbase/Saf...ansformers.pdf

http://www.mhennessy.f9.co.uk/isolating/index.htm

http://www.sussex.ac.uk/Units/safety/sgn/sgn08.pdf

http://www.reo.co.uk/news_article/71/0

http://jobfunctions.bnet.com/whitepa...px?docid=58852

http://www.freelists.org/archives/pc.../msg00012.html

http://www.trft.org/TRFTPix/CHRSSafety.pdf

http://www.wireless-workshop.com/safety.htm

And on and on...

Peter Wieck
Wyncote, PA

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Default Variac as a Troubleshooting Aid

On Apr 26, 1:47 pm, J.P. wrote:
On 25 Apr 2007 18:09:34 -0700, Peter Wieck wrote:





On Apr 24, 2:31 pm, "west" wrote:
For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.


Cordially,
west


One mo
_____________________________________________


Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.


Variacs, on the other hand are either very handy diagnostic tools or
worse-than-useless anchors fit only to let the magic smoke out of an
otherwise
salvageable item. I am not really sure if there is an in-between other
than
their original function as light dimmers.


Without both current and voltage metering, they are worse-than-
useless. With
the proper metering, they can be very handy tools.


Myths: A variac will help reform caps (with specific reference to tube/
valve
equipment).


Fact: Only on those specific items with solid-state rectifiers that
pass B+ current at any voltage, and only if done over more time than
one cares
to consider.


In the case of a tube rectifier, most of them do not start to pass DC
until the
filament voltage reaches between 65% and 75% of rated voltage. If the B
+ on the
particular item is say.... 350V, that means that the first voltage
the
caps-to-be-reformed would see would be something between 227V and
263V... not
exactly a soft-start.


Myth: A variac will allow one to apply voltage gently to a item, so as
to
discover problems before they become fatal.


Fact: No, not at all. True, a variac does allow an item to see the
minimum
amount of current to trigger its functions... an item with bad filter
caps may
begin to hum at 80V rather than 120V but if the caps are not so bad as
to show audible hum, the variac ceases to be useful. And a variac will
*not* tell you whether a repaired item is OK or not.


However, if the proper meters are put on the Isovariac, then some
real
diagnosis can happen: An item which should, by calculation draw say...
65 watts
or so (0.55A), and draws 90 watts is dissipating 25 watts of heat
somewhere...
perhaps the output transformer(s).


Comes down to a current meter with fine enough increments to give
meaningful
information. Such a tool is useful right down the line from initial
diagnosis
to testing the completed results.
__________________________________


Peter Wieck
Wyncote, PA


Why not just plug it into a watt meter? J.P.- Hide quoted text -

- Show quoted text -


For a couple of reasons.

a) Most watt-meters are not very fine-reading. For them to be
effective, they must be able to divide into meaningful 1-2 watt
increments.
b) There is no isolation or voltage control.

For starters.

Peter Wieck
Wyncote, PA



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Phil Allison Phil Allison is offline
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Default Variac as a Troubleshooting Aid

"Peter Weeke the CRIMINAL ****WIT ****** "


Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.


** Totally false.


Isolation transformers need only be used when working on a live chassis
item.

Otherwise, you do NOT need one and using one INCREASES the
electrocution
hazard for a technician.



See: http://sound.westhost.com/articles/electrocution.htm


a.. Do not assume that isolation or stepdown transformers are safe - they
are not. Isolation transformers will cheerfully kill you if you become
connected across the output - an isolation transformer has no active
(live)
and neutral. Many stepdown transformers do not provide isolation.
Isolation
transformers can lead to a complacent attitude, and one lead can connect
to
chassis if there is an insulation failure - with no effect on the
equipment
or transformer. The other lead is now a killer! Isolation transformers
will
prevent an electrical safety switch from operating if a fault develops on
the isolated side!



( snip this totally ASD ****ed CRIMINAL IDIOT's brain dead abuse )

See: http://sound.westhost.com/articles/electrocution.htm


"Hot Chassis" items can happen for any number of reasons



** In which case the item is faulty and will trip a breaker or ELCB

....... INSTANTLY !!

Only a INTENTIONAL hot chassis items need an Iso Tranny for use with
scopes etc.


An isolation transformer is a simple precaution.




** WRONG !!!!!!!!!!!!!!!!!!!!!

It is a lethal POS that kill technicians.

God , how I hope YOU are the next one


See: http://sound.westhost.com/articles/electrocution.htm



....... Phil



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Eeyore Eeyore is offline
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Default Variac as a Troubleshooting Aid



Bret Ludwig wrote:

Brit practice is very different


In what way exactly ?


and will confuse people badly.


I fail to see any reason for confusion. Please elaborate.

Graham


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Phil Allison Phil Allison is offline
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Default Variac as a Troubleshooting Aid


"Bret Ludwig ****ing Mental Retard. "

"Peter Weeke the CRIMINAL ****WIT ****** "


Phil, you are a ****.



** I am simply trying to prevent innocent folk from being electrocuted by
the INSANE advice dished out by that arrogant, autistic **** called Weeke.

No way exists to do that WITHOUT discrediting the incorrigible, asshole as
much as possible.

YOU are just as mentally defective as Weeke.

So drop ****ing dead.




........ Phil





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WindsorFox WindsorFox is offline
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Default Variac as a Troubleshooting Aid

Bret Ludwig wrote:
On Apr 26, 5:49 pm, "Phil Allison" wrote:
"Peter Weeke the CRIMINAL ****WIT ****** "


Phil, you are a ****. Wieck is basically sane, he just hasn't worked
in service shops and electronics facilities. If you were to learn to
communicate better you wouldn't be such a **** then, would you??


Yeah he would.... P

--
"Yes, it is a good thing you are handy, as
you clearly suck at being smart." - Herb
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Peter Wieck Peter Wieck is offline
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Default Variac as a Troubleshooting Aid

On Apr 27, 7:37 pm, Bret Ludwig wrote:
On Apr 26, 5:49 pm, "Phil Allison" wrote:

"Peter Weeke the CRIMINAL ****WIT ****** "


Phil, you are a ****. Wieck is basically sane, he just hasn't worked
in service shops and electronics facilities. If you were to learn to
communicate better you wouldn't be such a **** then, would you??


Bret:

I have observed four (4) electronics "service shops" in my time, two
are still extant. ALL of them use(d) isolation transformers. ALL of
them *when they became commonplace in the 1970s* used dedicated GFIC
Breakers on the workbenches.

And, yeah, I have a very good ground at my workbench.

Peter Wieck
Wyncote, PA



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Phil Allison Phil Allison is offline
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Default Variac as a Troubleshooting Aid


"Windsor Fox ****wit TROLL Idiot "



** Drop dead, ****.




........ Phil


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west[_3_] west[_3_] is offline
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Default Variac as a Troubleshooting Aid


"Ian Iveson" wrote in message
. uk...
Phil Allison wrote

Isolation transformers are critical for any workbench, and after
good
hand-tools the first thing any electronic hobb7 person should
get...
perhaps even before said tools.



** Totally false.

Isolation transformers need only be used when working on a live
chassis item.

Otherwise, you do NOT need one and using one INCREASES the
electrocution hazard for a technician.

See: http://sound.westhost.com/articles/electrocution.htm


a.. Do not assume that isolation or stepdown transformers are safe -
they are not. Isolation transformers will cheerfully kill you if you
become connected across the output - an isolation transformer has no
active (live) and neutral. Many stepdown transformers do not provide
isolation. Isolation transformers can lead to a complacent attitude,
and one lead can connect to chassis if there is an insulation
failure - with no effect on the equipment or transformer. The other
lead is now a killer! Isolation transformers will prevent an
electrical safety switch from operating if a fault develops on the
isolated side!


Seems to me you are both right, or wrong, depending on how you work.

As long as you are both aware of the dangers, one way or the other,
which I am sure you both are, then you are both right. You have both
done lots of work on dangerous equipment. You are both still alive.

Why should either of you insist that your way is better?

cheers, Ian


The vexing question, Iverson, is ... why are YOU still alive?

west




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Peter Wieck Peter Wieck is offline
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Posts: 2,418
Default Variac as a Troubleshooting Aid

On Apr 27, 7:34 pm, Bret Ludwig wrote:
On Apr 26, 3:49 pm, Peter Wieck wrote:





On Apr 26, 1:47 pm, J.P. wrote:


On 25 Apr 2007 18:09:34 -0700, Peter Wieck wrote:


On Apr 24, 2:31 pm, "west" wrote:
For intermittent problems possibly caused by a microscopic fracture in a pc
clad, try lowering the AC input voltage with a variac. Lower the AC until
the circuit just starts working, then clad fractures and often cold solder
connections will manifest themselves.


Cordially,
west


One mo
_____________________________________________


Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any electronic hobb7 person should get...
perhaps even before said tools.


Variacs, on the other hand are either very handy diagnostic tools or
worse-than-useless anchors fit only to let the magic smoke out of an
otherwise
salvageable item. I am not really sure if there is an in-between other
than
their original function as light dimmers.


Without both current and voltage metering, they are worse-than-
useless. With
the proper metering, they can be very handy tools.


Myths: A variac will help reform caps (with specific reference to tube/
valve
equipment).


Fact: Only on those specific items with solid-state rectifiers that
pass B+ current at any voltage, and only if done over more time than
one cares
to consider.


In the case of a tube rectifier, most of them do not start to pass DC
until the
filament voltage reaches between 65% and 75% of rated voltage. If the B
+ on the
particular item is say.... 350V, that means that the first voltage
the
caps-to-be-reformed would see would be something between 227V and
263V... not
exactly a soft-start.


Myth: A variac will allow one to apply voltage gently to a item, so as
to
discover problems before they become fatal.


Fact: No, not at all. True, a variac does allow an item to see the
minimum
amount of current to trigger its functions... an item with bad filter
caps may
begin to hum at 80V rather than 120V but if the caps are not so bad as
to show audible hum, the variac ceases to be useful. And a variac will
*not* tell you whether a repaired item is OK or not.


However, if the proper meters are put on the Isovariac, then some
real
diagnosis can happen: An item which should, by calculation draw say...
65 watts
or so (0.55A), and draws 90 watts is dissipating 25 watts of heat
somewhere...
perhaps the output transformer(s).


Comes down to a current meter with fine enough increments to give
meaningful
information. Such a tool is useful right down the line from initial
diagnosis
to testing the completed results.
__________________________________


Peter Wieck
Wyncote, PA


Why not just plug it into a watt meter? J.P.- Hide quoted text -


- Show quoted text -


For a couple of reasons.


a) Most watt-meters are not very fine-reading. For them to be
effective, they must be able to divide into meaningful 1-2 watt
increments.
b) There is no isolation or voltage control.


The main purpose of a straight variac (for tube audio) IMO is to
serve as a variable source for outboard DC, high and low voltage power
supplies you build yourself. You will use it more in its pure AC
supply function for solid state audio and, should you still wish to,
TV repair.

I particularly liked the old Lab-Volt power panels that had a variac,
a HV variable AC outlet, a LV variable AC outlet from a transformer,
and a variable HV and/or LV DC output from transformers and rectifier-
filters. And some metering.

Today you would use an isoformer on occasion, simply because the old
standby of drilling and pounding your own ground rod in the basement
is illegal and would trip the guffer. In the old days that's what
shops and hobbyists in basements did. They had one hot wire to the
bench and their own good ground. They would tie their own good ground
to the main building ground with the web copper strap cars used for
the ground cable sometimes. Today, smart people have a high amperage
four wire range or dryer outlet installed so they know whare ground,
neutral, and each of the two hots are, though most people will only
use one of them.- Hide quoted text -

- Show quoted text -


Any hobbyist that runs an electronics shop in a basement more-or-less
deserves what he/she gets. There are far too many unknown grounds
(including the concrete slab) for that to be a fit place to have a
proper shop. Not that it cannot be done safely, but the amount of
planning and care required is considerable. Given the general amount
of ignorance displayed in this particular thread as examples there are
damned few individuals here who have that capacity. Starting with Mr.
Allison who clearly has no clue about this subject... at least as it
applies in the good old USA.

Peter Wieck
Wyncote. PA


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Posts: 111
Default Variac as a Troubleshooting Aid

On Apr 26, 4:47 pm, Peter Wieck wrote:
On Apr 26, 1:39 pm, Eeyore
wrote:



Peter Wieck wrote:
Eeyore wrote:
Peter Wieck wrote:
Repeat: You are entirely unencumbered by the thought process. When you
get your meds adjusted and learn to think clearly rather than like a
gerbil on PCP, please do come back and revisit this.


What Phil is quite correctly pointing out is that the use of an isolation transformer means that
you will get no protection from an 'earth leakage current' breaker feeding it.


Your very life might depend on it. Do not use isolation transformers 'willy nilly'. They have their
dangers.


I have no clue as to what sorts of GFIC devices you use, and how they
are configured, but in this country (USA), based on NEC requirements
the Device measures any deviations between input and output and will
trip on any leakage to ground.


It works bt detecting any line-neutral imbalance.


Let's look at the nature of a GFIC device: It is designed to trip when
the current goes anywhere other than from hot to neutral. Can we agree
on that?


Yes.


If that is the case, and you insert yourself into a circuit *between
the hot and the neutral*, whether there is a GFIC device or not, you
will get zapped, as it cannot differentiate between you and a 1/4 watt
10,000 ohm resistor put in the same location.. or a 25 what
incandescent lamp, for that matter.


Which is exactly what happens when you use an isoaltion transformer if you're touching the live and
ground say and the neutral is also grounded. You become a perfectly valid load and get electrocuted
whilst the breaker sees no problem with that. Remove the isolating transformer and the breaker will trip.


Graham- Hide quoted text -


- Show quoted text -


Clearly you do not understand the nature of lab-grade isolation
transformers. ALL power through them is 'above ground', the only valid
path is hot-to-neutral. There is no ground path from the isolated hot
side. Whether the neutral is grounded or not. There is still no path
except between hot and neutral... same as there would (should) be
anyway.

Don't take my word for it. Set it up and test it for yourself. You can
ground the test piece to a good direct ground. And then measure a VOM
from the hot side to it. No current will flow. And you can short the
neutral to the ground and do the same. It still won't go through the
ground. Or, measure current from neutral to ground. Nothing. Connect
your GFIC device. Use a leaky test-probe from a signal generator or
scope not isolated to the test piece... *POP* goes the breaker. As it
should. Lots-O-Speculation here, little actual experience testing from
appearances. It ain't nohow black magic.

This is an unique condition, and isolated (pun intended) to test-bench
conditions, to be used by someone who clearly understands the
limitations of the device with great specificity to what it does NOT
do.

Now, of course, consider your scenario under hospital conditions where
all sorts of wet stuff, machines, needles and monitors are operated
through isolation transformers to protect the patient (and the
machinery) from stray currents that could be anything from life-
threatening to causing the machines to malfunction. If your scenario
obtained, there would be no benefit to their use... which, of course,
is not the case.

http://www.reo.co.uk/files/kbase/Saf...ansformers.pdf

http://www.mhennessy.f9.co.uk/isolating/index.htm

http://www.sussex.ac.uk/Units/safety/sgn/sgn08.pdf

http://www.reo.co.uk/news_article/71/0

http://jobfunctions.bnet.com/whitepa...px?docid=58852

http://www.freelists.org/archives/pc.../msg00012.html

http://www.trft.org/TRFTPix/CHRSSafety.pdf

http://www.wireless-workshop.com/safety.htm


I always see problems in if the people are not aware of what a regular
isolation does and is connected. I was reverifying how they are
connected. For servicing equipment, I make use of a transformer that
has the secondary completely isolated, which is not the case with
approved devices.
By the way, I use variacs, isolation transformers, and light bulbs, as
needed to control power.
According to rules, isolation transformers have one side of the
secondary tied to ground. The ground
goes from input to output. The secondary is ground referenced and can
be hazardous working
on equipment. An isolations transformer is designed to minimize common
mode leakage current from
primary to secondary. It also effectively filters common mode noise.
Drawn like this...............
http://zekfrivolous.com/iso/isozoom.JPG.

Like all these and the medical approved......................
http://www.tripplite.com/products/co...eneral_purpose
The medical units have the better plugs but are otherwise the same.
Operating rooms have a 100 ua limit but even that can be hazardous
with open
tissue.

I found some info from the original stuff from Mark Waller.

http://www.smartpowersystems.com/New...%20article.pdf

greg


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Default Variac as a Troubleshooting Aid

I use a lab-grade variable A/C supply with a current meter for basic
troubleshooting and other tasks.

It can reform electrolytic caps. This requires that you have SS
rectification or replace tube rectifiers with a SS equivalent.

I use it to look for dangerous conditions, e.g. excessive current draw,
before applying full line voltage to the device under test. Can't tell you
how many transistors, etc. this has saved.

It can determine transformer step-up / step-down ratios, or figure out taps
on unknown iron.

Often audio amplifiers powered through a regulated A/C supply sound worse.
Sometimes dramatically so. One wonders why . . . .

Jon



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Peter Wieck Peter Wieck is offline
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Default Variac as a Troubleshooting Aid

On May 2, 2:52 pm, Jon Yaeger wrote:
I use a lab-grade variable A/C supply with a current meter for basic
troubleshooting and other tasks.

It can reform electrolytic caps. This requires that you have SS
rectification or replace tube rectifiers with a SS equivalent.

I use it to look for dangerous conditions, e.g. excessive current draw,
before applying full line voltage to the device under test. Can't tell you
how many transistors, etc. this has saved.

It can determine transformer step-up / step-down ratios, or figure out taps
on unknown iron.

Often audio amplifiers powered through a regulated A/C supply sound worse.
Sometimes dramatically so. One wonders why . . . .

Jon


Chopped DC from minimal filtration... "regulated" supplies tend to be
designed against the lowest anticipated load. So when the amp is
pushing, the power-supply isn't up to it. There are always exceptions
as a well-designed power-supply of almost any type will put out clean
DC as needed. "Design" includes proper isolation (noise and other
artifcacts) as well as simple capacity.

For related reasons, running an amp from inverter power (unless a true
(pure) sine-wave type) can cause many otherwise good amps to sound
pretty wretched.

And yes, a lab-grade iso-variac can be quite versatile. But as you
note, not without proper metering.

Peter Wieck
Wyncote, PA

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