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Old 9th April 2007, 08:02 PM   #121
Tweeker is offline Tweeker  United States
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Hi Gajanan,

Quote:
Good info,
But the birds don't DIY, if I am not wrong LOL
You are wrong, the birds around here make lots of diy audio.
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Old 10th April 2007, 05:13 AM   #122
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Yes, I know, but the majority here is crows with scratching driver. Even the peacock in my neighbburhood has a damaged audio driver although the cabinate is good looking.

Gajanan Phadte
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Old 14th June 2007, 06:41 PM   #123
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In response to everything-

All of these safety precautions are good; I don't have a problem with observing any of them. But, are the dangers spoken of a little... exaggerated? I am fully aware of the dangers of electricty, but some of these posts make it seem as though death is iminent if they are not folllowed.

I know that tube amps use high voltages, but by the same token aren't we also talking about current in the milliamps range? I've BEEN shocked with 1500V at an ultra-low current before(not only that, but the circuit was made from hand-to-hand through my body so that my heart was in circuit); it wasn't fun, and I don't plan on ever doing that again, so I take many precautions like the ones suggested in this thread. But- I didn't DIE. I was a little jolted, and the incident didn't stop me from working. It was more annoying than life threatening.

I'm not STATING that everyone here is wrong; I'm not nearly as experienced as everyone else here. This is only my limited experience with high voltage, and I just wanted to know whether these "threats of death" have any backing to them.
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Old 14th June 2007, 07:23 PM   #124
SY is offline SY  United States
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Yes. Any of us old-timers will have stories about people we once knew whom we know no longer. Note the demographics of the people with the most dire warnings- we've seen it.

If something is 99% safe, that means you've got a very significant chance of death. And even if you get away with it, if you do it enough times, the inevitable will happen. When I get into a plane, I do a preflight inspection and go through a checklist. I've never had an engine quit on me or flight controls break, but it DOES happen and the consequences are dire.

There are old guys who do high voltage work. There are careless guys who do high voltage work. There are no old, careless guys who do high voltage work.
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Old 14th June 2007, 08:19 PM   #125
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Quote:
Originally posted by SY


There are old guys who do high voltage work. There are careless guys who do high voltage work. There are no old, careless guys who do high voltage work.
Risks.. what's this ??? Wait a minute SY, as a offshore d'r, I'm still working on the last bit. I've always managed to sly away seconds before she blows off.

Your old HV salt,

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Old 15th June 2007, 04:42 AM   #126
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U should see one of my colleague at work. Mostly works on motors and electrical items. If he does not find a line tester or a meter, he will not hesitate to try other method. I suspect he must be jolted atleast once a fortnight. He does not need any type of connecting accesories for wiring anything to anything. The bare wire-ends are always used.
I am scared of even standing nearby him when he works.
He has survived and still going strong, in his fifties, without any hesitation to his practices.

He SHOULD NOT be a motivation.

Gajanan phadte
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Old 15th June 2007, 06:22 AM   #127
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Default Safety and shocks

I use a lot of the ideas mentioned in this thread. I also use an isolation transformer of limited power when testing offline equipment. If there is a fault, it limits current to keep from major destruction! I build phase converters for motors up to 20hp and I test them with a 300 va toroid until I trust them. Have not had any major malfunctions to date, but there is always the first time.

Another favorite from the old T.V. days: put a light bulb in series with the power input. If something goes wrong, it limits current AND gives you a visual warning!
Worst shock for me: I have a 350kv Tesla coil I exhibit at Science nights at local schools. One night my grounded rod had a broken wire I did not see. A four foot arc jumped to my arm and I was doing my best to keep the explicatives down in front of a gym full of grade schoolers! I now have redundant grounds and double check them each exhibit.

I wear glasses and take that protection for granted. They have saved my eyes from many a solder splatter and also a few small electrolytic cans blown off boards.

Remember: don't try this at home, We are proffesionals!
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Old 15th June 2007, 06:47 AM   #128
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Default Re: Safety and shocks

Quote:
Originally posted by gearheaddruid


Another favorite from the old T.V. days: put a light bulb in series with the power input. If something goes wrong, it limits current

Remember: don't try this at home, We are proffesionals!

Wait.....My good old days with British made TV's and Radio's had live chassis. One worked with a bench isolating transformer where isolated windings were wound on the otherside of the primary limb to avoid capacitive coupling through to primary.
All these little things made sense. Note the max winding coupling capacitance from primary to sec on most E&I isolating transformers is quite high, i.e 1-5nF. That's why it's often best to feed the mains live to winding start closer to the core which is by regulation sep earthed.
However this doesn't work in someplaces in Europe where bi phase 115 0-115 AC is used.
One uses logistical commonsense.

richj
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Old 29th June 2007, 12:02 AM   #129
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Default voltage vs current

Hi everyone, I am new here and just wondered about some commens on "ultra low current" and high vlotages.
As far as I know Omh's law is valid also for the human body, hence a certain voltage will give a certain current through a fixed resistance (your body in this case)
As I see it, a high voltage source that gives "ultra low current" is probably an "ultra high impedance" source. That means that that when you actually touch such a source the voltage will drop and the current through your body will be correspondingly low.
BUT this is normally quite the opposite of what we are trying to acheive in the power supply of a tube power amp, low output impedance is really the goal. This means that from such a supply you WILL apply almost the full voltage over your body and the resulting current will be high.

Quote:
Posted by Sir Trefor

I know that tube amps use high voltages, but by the same token aren't we also talking about current in the milliamps range? I've BEEN shocked with 1500V at an ultra-low current before(not only that, but the circuit was made from hand-to-hand through my body so that my heart was in circuit); it wasn't fun, and I don't plan on ever doing that again, so I take many precautions like the ones suggested in this thread. But- I didn't DIE. I was a little jolted, and the incident didn't stop me from working. It was more annoying than life threatening.
If our friend here had tried this with a power supply for a transmitter tube power amp with solid state rectification and a substantial amount of capacitance he would surely no longer be with us.
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Old 29th June 2007, 06:35 AM   #130
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Default Re: voltage vs current

Quote:
Originally posted by hemgjord


If our friend here had tried this with a power supply for a transmitter tube power amp with solid state rectification and a substantial amount of capacitance he would surely no longer be with us.
Wrong: One forgets that in the Agri domain, the cattle electric fence using CD capacitive discharge SS techniques is capable of a massive sharp jolt of joules which uses combination of high voltage and low Z to overcome effects of damp. Alot of fences here border the public domain. Anything different ?
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