Seems logical to ME!!

[Pigyboy]

PRR and RG's anecdotes have reminded me of to HV lab incidents. We tested huge power supplies full of dielectric oil and when on one day I got a hand near one of the boxes and a spark jumped out about 4 inches and burned a pin hole through my finger nail and it scared me to death. About a week later while testing a batch of HV diodes I had very carefully performed my test, turned off the power and began to reach towards the diode submerged in dielectric oil when two of the engineers crept up behind me and flicked the center of a piece of paper with a finger producing a loud 'SNAP'. I can laugh about it now but I think that was the day my hair began to go grey....

[Bullet79]

my first tube overdrive project incident years ago still haunts me till today.....!!! the AC extention plug that i was using exploded just one second after i switch it on....  and i've built 3 tube overdrive already till now but still chicken to test it.. 

[petemoore]

  Slightly disoriented, picking myself off the floor, I said it's a good thing there were no sharp objects where I landed...I kinda 1/2 fell and 1/2 jumped out of the kitchen chair while quickly exiting an SLP's innards. Left hand started working again in about 15 minutes.
  The chassis IS a rail ! The amp just needed to have a bias pot wiper jiggled so it touched the wafer [probably needed cleaned and massaged and reset, but...I got up and soon was right back in there, this time being even more careful.
   While considering disorientation and motor control interference, a whole nuther batch of bags of trouble can be pondered. Don't let anyone who knows it happened hang around when you continue, or you may hear snapping noises [like RG referred to] which blow the mind, the adrenaline just refuses to subside.

[lowend]

True story about my mate, 25 years ago at highschool. We're doing experiments with DC to confirm Ohms Law, that sort of stuff, and something isn't right. He jumps to the conclusion that the fuse in the mains transformer must be blown and while I'm distracted he goes to get fuse out without disconnecting it from the power. 240V to one finger and probably back out the thumb onto the case of the transformer. He cataputed and slammed into the back wall. Funny as hell.

Us brainy guys got the back row as teacher didn't need to keep us under such close supervision. Mate is now the Director of Research at Google, yes you read that right, he's the Big Kahuna. I didn't catch the computer thing myself.

[served]

Well if you don't mind, I will add one more accident.

I build a tube amp on PCB, and so I used a lot of Soldering Grease. I didn't clean it off the board just plugged the amp in and switched it on. Lighting and smoke came out of the box. I digged for the problem for a long time and eventually I realised that it was the grease that burned, because I made it happen again.  

[wavley]

To be completely honest, I have given some of these warnings in the past.  I do so when I feel that the person that is asking has no idea what they are doing.  I replied to a thread a few days ago, no warning, why?  Because he listed the amps he had built, so I believe that he has already read up on this matter.  

Things I have learned...

1. Just because you are an EE doesn't mean you know how to work with tubes, my own school spent a total of 10 minutes on "Thermionic Devices"
2. Just because you have a job doing it doesn't make you good at it, I worked at a repair shop with a guy that shocked himself nearly daily, heck, one of the best techs I know had to go home one day because of a shock.
3. Most people are idiots, I'm sorry but they are.  "It's just a loose wire" "It keeps blowing fuses so I shoved tin foil in the hole" the list goes on and on, maybe we should have a thread where repair guys list all of the incredibly moronic and dangerous things customers have said and done.

I belong to a couple of yahoo groups about amps and I have seen people that are so stupid, there was one guy that got mad because nobody would post pictures of the part to change and how to do it and told everyone that he WOULD NOT read the safety, followed by a bunch of "Why are you guys suck jerks?"

Yes, chances are pretty small that you will blow a hole in your heart, but they are exponentially larger if you don't know it can happen.

[phector2004]

3. Most people are idiots, I'm sorry but they are.  "It's just a loose wire" "It keeps blowing fuses so I shoved tin foil in the hole" the list goes on and on, maybe we should have a thread where repair guys list all of the incredibly moronic and dangerous things customers have said and done.

Have to agree on that one 

Was trying to fix a fancy lamp at my brother's apartment suspended by its power cables. My brother's friend was scared to touch the exposed low voltage DC wires coming from the ceiling, yet proceeded to take apart the perfectly working dimmer switch with the power on... stopped him before he could "uncap that wire thing or whatever" 

[DougH]

I have seen someone who connected all of their offboard parts with bare copper wire - no insulation - with the wires all tangled up in a random mess and touching various areas of the board. In other words, shorting everything to everything else.

Circuit-bending! Kewl!!!

I agree with something I think that was at least strongly implied by R.G.'s first post (haven't had time to read the second or third):

I don't think we are doing anyone any favors by making it seem like this stuff is super easy, or that for the inexperienced it's merely like assembling a jigsaw puzzle on a lazy Sunday afternoon- especially when it concerns high voltage. That's one of the problems with the internet- it makes everything seem like it's as simple as "insert tab A into slot B".

It's not.

You want to work with high voltage? Work with someone who has experience that you can learn from. Spend some time in a classroom learning about electricity. Understand the pitfalls, which only come from understanding electricity and having some experience. Pay the same price everyone else did who successfully works on this stuff. Don't assume that if you read the right words on the internet that it's sufficient.

[okgb]

I dunno , it's like how they take away all the big slides and merry 'go'rounds from the playground
we got a trampoline and people say  " oh , you don't have a net ? "
the first time you jump close to the edge you go  " wow "
and figure it out , it's called learning
I hate the buzzing shocks of A.C. and the Zaps of D.C.
so i go like a lab and take my time to avoid them
[ can't seem to hold probes steady though ]
so scared that you never get anything done  ,
or cautious & prepared , knowing what to expect ?

[jasperoosthoek]

As I got more experienced I went from making beginner mistakes to making stupid mistakes. The 'I should have known better' ones.

I got my first shock when I was 12. I opened a argon light with some series resistor. My mother told be that it worked on a low voltage just like bicycle lights and that the little resistor was a transformer. I didn't really believe her because I knew that transformers were bigger but I didn't know what it was. So I planned not to tough it which eventually did happen. I don't know which side of the resistor I touched but I felt the 230 volts in my entire arm...

I did get some shocks later on from a disposable camera flash where I trippled the power caps. Also the Whimshurst electrostatic machine I built for my science project was powerful.

I built about four tube projects and never got shocked. I like to keep it that way. HV scares the hell out of me which is a good thing. That shock I got when I was 12 was a good learning experience even though it might have killed me.

[R.G.]

One of the jobs of any parent, whether they realize it or not, is to manipulate the child's experiences so that the child gets surprises - but that all the surprises are non-fatal ones.

[jasperoosthoek]

That's true. But I got my mother back when I built the electrostatic machine capable of producing 4cm sparks. The poor woman asked me pointing at a shiny doorknob, what's thaZAPPP. She did get the first shock although I got many later.

[served]

That's true. But I got my mother back when I built the electrostatic machine capable of producing 4cm sparks. The poor woman asked me pointing at a shiny doorknob, what's thaZAPPP. She did get the first shock although I got many later.

You are so evil 

But I have also been shocked by a photocam electronics. Its a nasty one!

[petemoore]

    Me. I introduced the idea of an LED on heavy duty wires and circuit that lights it...when B+ reaches or exceeds 30v, Wired solid and heavy, permanently in the amp, between Gnd. and the B+ rail.
  All the forum dudes were playing ping pong with my head and it's ideas until one dude helped me out, I had expected to recieve intelligent crotiqueing or critisism, and was amazed at the idiosynchratic nonsense the thread accrued.
  Seemed quite simple, a double check for the DMM, and a light that shines when potential danger appears. Dunno about you, but over the decades, it's my dmm probe wires that require the most maintainence and replacement, recieve the most abuse. Seemed pretty silly to purport that it is recommended to trust these wires to measure safety. Seemed like a good idea to have a little danger indicator.
  There's a sequence to charging and discharging the filtercaps that should be followed to the letter the 1rst, 2nd and every subsequent time. It's not terribly complicated...anyone else ever had a drain resistor get hot ? Forget to unplug AC for a second or two ? Started in and realized B+ is still hot ?...a simple little red light makes what is quite easy to misread [voltage-safety-condition of the filtercaps] exponentially harder to misread.
 

[amptramp]

One hobby I have had since the 1960's is restoring antique radios.  A lot of them in the late '30's or early '40's were wired with rubber-insulated wire which after about 70 years is just crumbling away.  Some of the earlier ones from the 1920's used no insulation - just solid wires bent to shape and self-supporting.  I have also restored old TV's which have a high voltage going to the CRT.  I would say I get a shock once a decade and minor tube burns once every two years - burns are more likely with power stages.

Check everything visually before turning power on.  Maybe that sound you heard when you were building it was a lockwasher falling on a switch terminal.

Bracing a hand against the chassis is a no-no when you are holding a probe.  Thick insulated gloves may be a good idea against both burns and shocks.

I always use a power bar because in the event of a short, the circuit breaker on the bar will open, even if the short is at the plug and there would be no way to unplug anything safely.  Even if the breaker does not open, you have another switch on the power bar in series with the power that you can open (but make sure the unit under test is plugged in at the end of the power bar away from the switch).

For the most part, the dangers can be easily avoided with some common sense and experimenters were working with tubes long before the legal liability lottery became so insane in the US.

Dsiclaimer:  This does not represent all of the steps needed to remain safe.  Just some things I have found useful.

[R.G.]

    Me. I introduced the idea of an LED on heavy duty wires and circuit that lights it...when B+ reaches or exceeds 30v, Wired solid and heavy, permanently in the amp, between Gnd. and the B+ rail.
  ...a simple little red light makes what is quite easy to misread [voltage-safety-condition of the filtercaps] exponentially harder to misread.
 

I used this in the Workhorse amps. Each B+ filter had a bleeder resistor which would bring it down to under 42Vdc (there's a story there) in ten seconds max. And since this was only a few ma, I put a red LED in series with the first few bleeders. By glancing at the PCB, you could not only tell there was B+ live if it was, but if part of the amp was dead, you could tell if B+ was getting to there or not.

[petemoore]

  All the hostility and discreditting I recieved at the amp forum...I decided to leave it there, but since this thread came up I figured the extreme heat had died down and the flames had subsided enough to give it another mention.
 Some amp guys get hit right in the nose with a fine concept and can't see it.
 Sardonic comedy says serves 'em right that they trust their old worn out DMM leads to measure for B+...what's it gonna say?..it's going to say 'nothing', or the same thing it says when the probes are floating !
 A little safety assurance [cost of an LED being the lions share]..right where it is important to have it is a good thing !
 It never hurts to double check these things.
 I'm glad you posted RG...
 An excellent feature for an amp !
  I hit the old amp tramps with it, right on the nose, they didn't want me there, poking their noses in their roses, fortunately we've been able to go right around them here.

[served]

But has anyone actually built somekind of Device that would disconnect the power if anything goes wrong? As much as I have learned from the school I can't find a way to build one that would fit in every situation.
Was thinking about stomp switch. Which will connect the power as long as you keep your leg on it. If you get shocked, then you will remove your leg. But it will not remove current from caps. But thats another thread, maybe some other day.

[phector2004]

Doesn't take long to mess yourself up...


A good nugget of advice I picked up from the guys here is to use the lightbulb test. Have a look at it!

[R.G.]

A little safety assurance [cost of an LED being the lions share]..right where it is important to have it is a good thing !

It's not perfect by any means, but better than an LED to check for high voltage is a neon bulb. An NE-2 neon sells at Mouser for $15.00 per hundred. It breaks over at 90Vdc and is current limited to under half a millliampere by a 150K to 470K resistor. It lights up when the voltage across it goes over the firing voltage, then drops back to the maintaining voltage, with the current limited by the resistor in series with it. This is probably back at about 60-80Vdc, but is not a precision voltage for the average neon bulb.

However, a resistor/neon across the B+ would light when B+ got above about 100V, and stay lit until it dropped under 60-80. That's not perfect, but it's sure a useful indicator of voltage across the B+, and probably better than current through the bleeder resistor, which is what an LED does.

Maybe I need to go mess with neons some more. ARGHHH!! So many circuits, so little time!!