• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Safety Practices, General and Ultra-High Voltage

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.
 
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.
 
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
 
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!:bigeyes: 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!
 
Re: Safety and shocks

gearheaddruid said:


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
 
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.

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.
 
Re: voltage vs current

hemgjord said:


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 ?
richj
 
Re: voltage vs current

Originally posted by richwalters



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 ?

I must say that I sometimes thought that this thread was a little inclined towards scaring people away but to compare a cattle fence with a high voltage, low Z amplifier power supply is really a little too much towards advocating suicide.

Anything different? Yes.
I do not know much about cattle fences more than that they are pretty harmless. Most people try to avoid touching them but they are probaly not very scared. However touching 230V mains is another thing. And if your power supply has reasonably sized transformer there is not much diffrence between the secondary and the mains, except that the voltage is 500, 1000 or even more volts. That is if your secondary is grounded or if you touch both leads as our friend that I was quoting referred to.

It would however be interesting to hear why the admittedly very high voltages present in cattle fences are not dangerus.
 
Despite equipment makers of electric fencers mandatory designing equipment not to endanger life, some people have to watch it, especially those who have heart pace makers or other devices fitted. This applies equally to us who regulary meddle on the bench with H.V capacitors and inductors. It's the same game...i.e staying alive.

For those who work in the medical side, the lowest equipment leakage currents are a myth to what some of us experience in wild bench practise.

richj
 
If you were to open up an electric fence power supply you would see a tiny transformer that would saturate at the smallest current draw from the secondary. But I still wouldn't want it flowing through my heart.


REMIMBER IT ONLY TAKE 15 MICRO AMP TO CAUSE VENTRICULAR ARRHYTHMIA or ventricular tachycardia not 15 milliamps
This does not stop your heart but it can still kill you.

It makes your heart stop pumping

Nick
 
PS don't tamper with lightning

So you lot wanna to live ? My darling spotted this in a heavy thunderstorm and grabbed a snap photo....my lab wall socket is somewhat overused.....
PS.. Don't tamper with the light switch ? It so happened my neighbour had a direct hit and the pulse rocketted through supply live to earth.

richj
 

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Okay, I have a quick question and I figured it'd be best to post it in the safety section. This is regarding electrolytic capacitors. Basically, I'm starting my first tube amp project. I'm rectifying 300v from the transformer and it'll be around 400v or so. Now for the first filtering capacitor, I have 10 47uf 250V rated electrolytic capacitors. I want to use these, however, I'd have to series two capacitors and then parallel these sets of 5 to get about 117uf. Theoretically this should get me 500V of power handling. I've read somewhere though that this isn't a good idea. Can someone advise me on what would be bad about this idea, any safety issues? I believe I'm supposed to use high value resistors in parallel with each capacitor to even the charge?

Thank You
 
Re: Re: voltage vs current

hemgjord said:



It would however be interesting to hear why the admittedly very high voltages present in cattle fences are not dangerus.
Because of short pulse width and limited energy. Static shock (ESD) from your fingertip to another person can have up to 35kV or so and tens of amps and its barely noticeable because of short time and low total energy/charge.

More powerfull cattle fences operate with 10 Joule pulses, peak currents are typically 2-10Amps, peak voltage abt 2-4kV.

In comparision to that 10J of cattle fence tube amp power supply (big)caps can hold more than 300J of energy.