[powerdoc]

Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?

[Patrick Turner]

powerdoc wrote:

Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?

There is a HUGE POTENTIAL DANGER TO YOUR LIFE WHILE YOU WORK WITH VACUUM
TUBES!!!!

Some of us don't mind the serious health hazard that working constantly
with voltages brings.

We learn to not do a lot of things, and
its like traffic lights; most days we stop at red lights.
Maybe one day we make a mistake and run a red light. BOOM, life over.
**** happens.
I ride a bicycle 100Kms per week.
I have fallen off a few times. Maybe next time I am dead.

Working on solid state amps rarely killed anyone but now some
SS amps have +/- 240v rails, YEE - OOWW!!
In Oz we have 240Vrms mains, and most shocks I have got
is from mains sockets and wiring that I forgot were live.
Ive had the occasinal belt from 500Vdc in a cap et all, maybe
I'm lucky they were not to many shocks arm to arm, with the heart in the
circuit.

I'm lucky to be alive though, real lucky. I rode a BMW motorcycle for
100,000 miles
and survived unhurt. I attended plenty of funerals of friends who came
to grief on two wheels
in my 20s.

Take care,

Tell yourself to take care when you get outa bed in the morning, and
when you retire at night.

Shout to the rafters,
""You vacuum filled ****ers ain't gonna get me, OK!!!!!""

Maybe then your brain will stop you killing yourself.

If you don't tell yourself to be better, you won't get better,
and you might get worse.

Patrick Turner.

[Iain Churches]

"powerdoc" wrote in message
oups.com...
Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?


Are you serious? A current of only 10mA passing from one hand
to another through the chest cavity and across the heart,
can be fatal.

In addition, a 10 000µF cap of 15V holds enough charge to vapourise
a gold ring, or a dangling crucifix should you be foolish enough to
wear jewellery when working on your amp. The resultant molten
metal spurts in all directions.

A pal of mine, a former Army radar technician keeps a leather
glove pinned to the wall above his bench. The first finger of the
right hand is completely burned away. It's a useful reminder.

On of the most best gizmos that one can incorporate into a homebrew
amp is a power relay with its coil across the primary of the mains
transformer.
As soon as the power switch is off, the relay drops out, and a pair of
contacts
close to discharge the main reservoir cap through a high-wattage
10k resistor. By the time you have switched the amp off and removed the
cover,
it is safe to work on.

Iain

[David R Brooks]

Iain Churches wrote:

On of the most best gizmos that one can incorporate into a homebrew
amp is a power relay with its coil across the primary of the mains
transformer.
As soon as the power switch is off, the relay drops out, and a pair of
contacts
close to discharge the main reservoir cap through a high-wattage
10k resistor. By the time you have switched the amp off and removed the
cover,

Across the transformer (primary or secondary), it won't do much.
It wants downstream of the rectifiers, ie across the main HT caps.

[John Byrns]

In article
,
David R Brooks wrote:

Iain Churches wrote:

On of the most best gizmos that one can incorporate into a homebrew
amp is a power relay with its coil across the primary of the mains
transformer.
As soon as the power switch is off, the relay drops out, and a pair of
contacts
close to discharge the main reservoir cap through a high-wattage
10k resistor. By the time you have switched the amp off and removed the
cover,

Across the transformer (primary or secondary), it won't do much.
It wants downstream of the rectifiers, ie across the main HT caps.

Isn't that precisely what he said, or did I read it wrong?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[robert casey]

powerdoc wrote:

Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?


There are dangerous voltages used in tube amps, but following a few
basic safety rules helps manage the dangers to something we routinely
handle.

You really want to avoid causing a current across your heart. Thus the
"keep the other hand in your pocket" rule. Wear rubber soled shoes,
long sleeved shirts and long pants (the insulation value of clothing,
while not that great, does help you some from completing a circuit path
with your body. Ideally your body should be electrically "floating",
not grounded.

Use a set of voltmeter test leads that has an alligator clip you first
attach to chassis ground, and the other lead that has a small metal tip
on the end of a pencil shaped and sized plastic wand. Do not hold
both leads with both hands, your fingertips might poke a little too far
into something.

This is by no means complete. Others here can add to the safety rules.

Ideally you should find someone to help you, if nothing else someone who
can kill the power or pull you off if trouble does happen. Also someone
who knows tube circuits and can discuss troubleshooting strategies with
you as you proceed.

[west[_4_]]

"powerdoc" wrote in message
oups.com...
Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?

First, it would be nice to know your name. Despite some obnoxious flamers,
when this group perceives someone who is somewhat of a newbie, it concerns
them. I suppose deep down inside, no matter how caustic the persona mask we
wear, we do care ...shucks!

west

[powerdoc]

It's Dan. I realize that there are potentially lethal voltages
there. I have lots of insulated alligator clips and probes that I use
with the voltmeter and scope. I always am in touch with the plastic
parts of the probes and try to avoid shorting out things to ground.
As a surgeon I realize that current can cut human flesh but I doubt
that voltages inside an amp burned a guy's finger off, that takes a
lot more Joules and for more than a fraction of a second. I'm not
saying throw safety to the wind, just inquiring if anyone actually
knows someone who was killed by the voltages generated by their audio
equipment, not the mains or a commercial transmitter. I'm just a
little rabid this weekend as I had to see a man-hating chick flick
this w/e with the Mrs.

[powerdoc]

On the same subject this URL
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

[Sander deWaal]

powerdoc said:


Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?


Voltages don't kill, currents do.

In the "right" circumstances, a voltage source as little as 30V can be
lethal, as long as a current of 10.....30 mA can flow through the
chest (or better: the heart ).

So, caution is always needed when working on any electrical device.
A simple NAD with +/- 25V gave me an unpleasant surprise once.
My KT88 triode PP amp with 400V on the plates is always treated with
the respect she deserves, but since my NAD experience, I extend the
same courtesy to solid state stuff.

--

- Maggies are an addiction for life. -

[Iain Churches]

"David R Brooks" wrote in message
...
Iain Churches wrote:

On of the most best gizmos that one can incorporate into a homebrew
amp is a power relay with its coil across the primary of the mains
transformer.
As soon as the power switch is off, the relay drops out, and a pair of
contacts
close to discharge the main reservoir cap through a high-wattage
10k resistor. By the time you have switched the amp off and removed the
cover,

Across the transformer (primary or secondary), it won't do much.
It wants downstream of the rectifiers, ie across the main HT caps.

Hi David. The *coil* is across the mains transformer primary. The
NC *contacts* close to put a high wattage 10K resistor across
the reservoir cap, just as I wrote above.

Regards
Iain

[Chris Hornbeck]

On 28 May 2007 08:14:55 -0700, powerdoc
wrote:

Now I might be subjecting myself to some serious flaming here but does
anyone know someone who died or was seriously physically harmed by
working on a tube amp? I recently posted a question concerning a
problem with a Conrad-Johnson amp and everyone seems to be like my mom
telling me not to run with a stick. Granted, I've been on the wrong
end of a charged capacitor and even wall current but it just reminded
me that I'm human but never did any real damage except to my psyche.
Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?

For more than four decades (until pretty recently) I kept
the smashed remains of a Heathkit VTVM that followed me
backwards across a room and expired on the wall behind and
above me.

It'd been a good reminder of what *not* to do.

WRT bleeders and relays: don't. Relays cannot be trusted
if your skunky ass is at stake. Hard wire the bleeders or
don't bother pretending that you've made it "safe"; you'll
have only made it worse if you trust it to a relay.

All good fortune,

Chris Hornbeck

[David R Brooks]

Oops! That's what comes of reading Usenet late at night :-)
At least I was only reading, not fiddling with a tube power supply...


Iain Churches wrote:
"David R Brooks" wrote in message
...
Iain Churches wrote:
On of the most best gizmos that one can incorporate into a homebrew
amp is a power relay with its coil across the primary of the mains
transformer.
As soon as the power switch is off, the relay drops out, and a pair of
contacts
close to discharge the main reservoir cap through a high-wattage
10k resistor. By the time you have switched the amp off and removed the
cover,
Across the transformer (primary or secondary), it won't do much.
It wants downstream of the rectifiers, ie across the main HT caps.

Hi David. The *coil* is across the mains transformer primary. The
NC *contacts* close to put a high wattage 10K resistor across
the reservoir cap, just as I wrote above.

Regards
Iain

[Iain Churches]

"Chris Hornbeck" wrote in message
...
On 28 May 2007 08:14:55 -0700, powerdoc
wrote:

WRT bleeders and relays: don't. Relays cannot be trusted
if your skunky ass is at stake. Hard wire the bleeders or
don't bother pretending that you've made it "safe"; you'll
have only made it worse if you trust it to a relay.

Hi Chris. A bleeder, often not fitted even, is pretty slow.
They are generally about 220k. So the 10K relay-switched
power resistor is a lot better.

The ones I use are German octal power types, rated
at 10A. You can use two sets of contacts to split the
current flowing through them. These relays have a
neon indicator - they were regularly used in studio
amps in the 60's (that's where I got the idea) I have
never know one to fail, and if it did, the relay is used
in a fail=safe mode, in that the NC contact pair are
used.

But even this should not induce a false sense of
security. I still instinctively put a VM across the
reservoir cap:-)

Cheers
Iain

[robert casey]

Hi Chris. A bleeder, often not fitted even, is pretty slow.
They are generally about 220k. So the 10K relay-switched
power resistor is a lot better.


Use both. The relay with the 10K resistor, and the always in circuit
220K resistor. SO if the relay fails, you still get some bleeder
action, albeit slower. Think a little like NASA building spacecraft, a
little redundancy to improve safety helps the odds.

[David B.]

This may sound funny but, would wearing rubber gloves help?


"robert casey" wrote in message
link.net...
powerdoc wrote:

Yes, you should avoid fingerpoken in der elektrikelworken but is it in
actuality a danger?


There are dangerous voltages used in tube amps, but following a few
basic safety rules helps manage the dangers to something we routinely
handle.

You really want to avoid causing a current across your heart. Thus the
"keep the other hand in your pocket" rule. Wear rubber soled shoes,
long sleeved shirts and long pants (the insulation value of clothing,
while not that great, does help you some from completing a circuit path
with your body. Ideally your body should be electrically "floating",
not grounded.

Use a set of voltmeter test leads that has an alligator clip you first
attach to chassis ground, and the other lead that has a small metal tip
on the end of a pencil shaped and sized plastic wand. Do not hold
both leads with both hands, your fingertips might poke a little too far
into something.

This is by no means complete. Others here can add to the safety rules.

Ideally you should find someone to help you, if nothing else someone who
can kill the power or pull you off if trouble does happen. Also someone
who knows tube circuits and can discuss troubleshooting strategies with
you as you proceed.

[robert casey]

David B. wrote:
This may sound funny but, would wearing rubber gloves help?



Not really, as something reasonably sharp could easily poke thru the
rubber. A chassis burr, or a small stub on a resistor lead wire. And
continue on into the juicy part of your hand.... Then you can really
get nailed. Or the sweat inside the gloves may do just as well to nail
you bad. It's a case of false sense of safety.

[Claudio Bonavolta]

On 29 mai, 17:42, "Iain Churches" wrote:
"Chris Hornbeck" wrote in message

...

On 28 May 2007 08:14:55 -0700, powerdoc
wrote:

WRT bleeders and relays: don't. Relays cannot be trusted
if your skunky ass is at stake. Hard wire the bleeders or
don't bother pretending that you've made it "safe"; you'll
have only made it worse if you trust it to a relay.

Hi Chris. A bleeder, often not fitted even, is pretty slow.
They are generally about 220k. So the 10K relay-switched
power resistor is a lot better.

The ones I use are German octal power types, rated
at 10A. You can use two sets of contacts to split the
current flowing through them. These relays have a
neon indicator - they were regularly used in studio
amps in the 60's (that's where I got the idea) I have
never know one to fail, and if it did, the relay is used
in a fail=safe mode, in that the NC contact pair are
used.

But even this should not induce a false sense of
security. I still instinctively put a VM across the
reservoir cap:-)

Cheers
Iain

Pretty late on this ...
I too use the relay approach:
http://www.bonavolta.ch/hobby/en/audio/discharg.htm

One good thing with relays is that they make a noise when they
switch ...
Which doesn't mean I'm not cautious afterwards as I'll always check
the remaining voltage on the caps before working on the device.

[Andre Jute]

On Jun 22, 7:43 am, Claudio Bonavolta wrote:
On 29 mai, 17:42, "Iain Churches" wrote:



"Chris Hornbeck" wrote in message

.. .

On 28 May 2007 08:14:55 -0700, powerdoc
wrote:

WRT bleeders and relays: don't. Relays cannot be trusted
if your skunky ass is at stake. Hard wire the bleeders or
don't bother pretending that you've made it "safe"; you'll
have only made it worse if you trust it to a relay.

Hi Chris. A bleeder, often not fitted even, is pretty slow.
They are generally about 220k. So the 10K relay-switched
power resistor is a lot better.

The ones I use are German octal power types, rated
at 10A. You can use two sets of contacts to split the
current flowing through them. These relays have a
neon indicator - they were regularly used in studio
amps in the 60's (that's where I got the idea) I have
never know one to fail, and if it did, the relay is used
in a fail=safe mode, in that the NC contact pair are
used.

But even this should not induce a false sense of
security. I still instinctively put a VM across the
reservoir cap:-)

Cheers
Iain

Pretty late on this ...
I too use the relay approach:http://www.bonavolta.ch/hobby/en/audio/discharg.htm

One good thing with relays is that they make a noise when they
switch ...
Which doesn't mean I'm not cautious afterwards as I'll always check
the remaining voltage on the caps before working on the device.

Nice to see you here again, Claudio.

I find relays too many components and the circuitry too complicated;
they raise the hackles of my paranoia.

Therefore I long ago decided that real designers permanently bleed 10
per cent of the current in every amp, preferably more, and gladly pay
the price for a hefty power bleeder in the range 10--22K. (Anyone who
fits a 220K bleeder should work in the advertising department: that
isn't a bleeder, it is a murder weapon in search of a victim.)

I also found that the extra current pulled through the power supply
stabilized it a little, though it isn't so easy to see when you
already have one or several chokes in the supply. Presumably the
mechanism is different from the ballast resistors which have a similar
calming result (1).

Once you grasp that mo' current is betta current, relays become
surplus to requirements.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

(1) It always amuses me when fools doubt the probity of the ballasts
in my designs, making obvious to all that they have never seen a
thermionic rectifier spec sheet in their lives. Worthless Wiecky is
only the last in a long line of undistinguished passing eejits to fall
into that trap.