I repair guitar amps so voltages around 400V are common. I know a good many people in this business and I see them doing things I would never do. They get shocked now and then but do not seem to care. Why so call professionals would act in this manner; I have no idea.
I think for me, distraction is the biggest danger. Life get in the way at times...well..you know the phone rings, FedX is at the door, the client has a gig tonight and needs his amp ASAP, and on and on.
Ever plugged in a amp and the pilot light would not come on only to find you plugged in the wrong cord? Just as easy to unplug the wrong cord. Attention to detail is always needed but sometimes in short supply. lol
High voltage can and does kill people, set things on fire, and screw up otherwise good equipment.
I do my best to stay out of trouble. I buy good safety equipment or at least the best I can afford. I would love to have someone around all the time to help keep me safe but that is just not an option all the time.
I have sailed around the world alone in my sail boat. No way that is "safe". I have run my little 28 foot sports fish boat from Florida to the Bahamas a zillion times, also not "safe". I have over 10,000 hours flying small aircraft all over the world and that is not "safe".
Working on high voltage stuff is not "safe".
I think I have survived these "unsafe" activities for nearly 70 years because of a few things.
1. Good luck
2. Situational awareness
3. Learning what was needed to keep from killing myself
4. Oh, and did I mention a bit of good luck...lol
Good luck with your activities and be safe and if you can't be safe be careful.
Billy
I think for me, distraction is the biggest danger. Life get in the way at times...well..you know the phone rings, FedX is at the door, the client has a gig tonight and needs his amp ASAP, and on and on.
Ever plugged in a amp and the pilot light would not come on only to find you plugged in the wrong cord? Just as easy to unplug the wrong cord. Attention to detail is always needed but sometimes in short supply. lol
High voltage can and does kill people, set things on fire, and screw up otherwise good equipment.
I do my best to stay out of trouble. I buy good safety equipment or at least the best I can afford. I would love to have someone around all the time to help keep me safe but that is just not an option all the time.
I have sailed around the world alone in my sail boat. No way that is "safe". I have run my little 28 foot sports fish boat from Florida to the Bahamas a zillion times, also not "safe". I have over 10,000 hours flying small aircraft all over the world and that is not "safe".
Working on high voltage stuff is not "safe".
I think I have survived these "unsafe" activities for nearly 70 years because of a few things.
1. Good luck
2. Situational awareness
3. Learning what was needed to keep from killing myself
4. Oh, and did I mention a bit of good luck...lol
Good luck with your activities and be safe and if you can't be safe be careful.
Billy
Im am 71 now and worked more than 30 years in design of High power industrial transmitters and magnetrons. High voltages were never less than 5 kV, normally upto 10 kV delivering DC powers more than 50 kW. And I am still alive...
We had to measure normally at a working transmitter. Indeed, the former advice to keep one hand in your pocket is VERY good. Keep your LEFT hand in your pocket when you have to measure at voltages beyond 1 kV
When you have to measure at switched-off equipment, ALWAYS ground the HV to chassis, I saw accidents caused by people switching on equuipment not knowing that someone was testing!!
And learn from an OLD HV technician, bad HV technicians never grow old....
We had to measure normally at a working transmitter. Indeed, the former advice to keep one hand in your pocket is VERY good. Keep your LEFT hand in your pocket when you have to measure at voltages beyond 1 kV
When you have to measure at switched-off equipment, ALWAYS ground the HV to chassis, I saw accidents caused by people switching on equuipment not knowing that someone was testing!!
And learn from an OLD HV technician, bad HV technicians never grow old....
A couple years ago I was building a 1500W audio tube amplifier with a pair of transmitting tubes operating at 5000V !
Except all the safety precautions I have attached on the amplifier a warning label.
" Danger of Death. 5000V are present "
And always think twice before you touch the equipment !
Except all the safety precautions I have attached on the amplifier a warning label.
" Danger of Death. 5000V are present "
And always think twice before you touch the equipment !
You, no doubt, are less used to looking after imbeciles than I am. I shall never forget the time I was setting up to record a concert at school and trying out a transistor mic amp (with a 170 volt supply!) which I had just built in a very attractive biscuit tin. Well, there was a group of girls circling around like vultures. When I shooed them off like a bunch of cats there was much tutting and complaining that it wasn't fair etc. The myriad of wires coming out of the biscuit tin had not struck any of them as in any way unusual. Most of the girls at this school go to the best UK universities with 10-15 each year going to Oxford or Cambridge. Scary, no?
Yeah, I figured that might be the problem with GU-50. I should save them until I am feeling sufficiently courageous to use them in Schaded pentode with 650 or so volts. I have lots of high gm 10 watts or so pentodes but I really don't mind mosfet followers at all, particularly since I got the hang of not blowing them up.
Yeah, I figured that might be the problem with GU-50. I should save them until I am feeling sufficiently courageous to use them in Schaded pentode with 650 or so volts. I have lots of high gm 10 watts or so pentodes but I really don't mind mosfet followers at all, particularly since I got the hang of not blowing them up.
"You, no doubt, are less used to looking after imbeciles than I am."
I recall working in a lab where the recent graduate PHD physicist kept trying to measure a 170V laser drive pulse with a Tek sampling scope directly. After a few expensive repairs, the scope sampling head specifications finally got looked at. Not just girls. Nothing like 1st hand experience.
------------
"How do we know how much current is passing through the screen?"
Many tube datasheets give screen current curves (dashed lines at bottom) on the plate or Vg2 curve sets. Just determine the operating plate V and I range for the driven load, and check the screen current curves for those conditions (assume grid 1 = 0V initially, using the stepped Vg2 graphs).
For Twin/Crazy drive, the screen voltage swing required will typically be about 25% less than pure g2 drive to get the same plate current, due to the positive grid 1 assistance. Helpfully making Twin/Crazy drive considerably safer for the tube's health. You generally don't want to pull the plate down below 50 or 60 Volts, due to the rapidly increasing screen current. Best way to limit that is to put in a series drain resistor for current limiting of the Mosfet follower driving g2 etc. (ie, make the drain run out of voltage headroom at max screen current allowed)
If one is playing around with the Rg2g1 value with a pot, be sure to put in a 1K Ohm series resistor (with like a 5K Ohm pot) so that grid 1 does not get over-currented. From what I have seen on the curve tracer, grid 1 current required for linearization of grid 2 is quite small.
The 6LG6 datasheet gives a typical set of curves on page 3:
https://frank.pocnet.net/sheets/123/6/6LG6.pdf
...
I recall working in a lab where the recent graduate PHD physicist kept trying to measure a 170V laser drive pulse with a Tek sampling scope directly. After a few expensive repairs, the scope sampling head specifications finally got looked at. Not just girls. Nothing like 1st hand experience.
------------
"How do we know how much current is passing through the screen?"
Many tube datasheets give screen current curves (dashed lines at bottom) on the plate or Vg2 curve sets. Just determine the operating plate V and I range for the driven load, and check the screen current curves for those conditions (assume grid 1 = 0V initially, using the stepped Vg2 graphs).
For Twin/Crazy drive, the screen voltage swing required will typically be about 25% less than pure g2 drive to get the same plate current, due to the positive grid 1 assistance. Helpfully making Twin/Crazy drive considerably safer for the tube's health. You generally don't want to pull the plate down below 50 or 60 Volts, due to the rapidly increasing screen current. Best way to limit that is to put in a series drain resistor for current limiting of the Mosfet follower driving g2 etc. (ie, make the drain run out of voltage headroom at max screen current allowed)
If one is playing around with the Rg2g1 value with a pot, be sure to put in a 1K Ohm series resistor (with like a 5K Ohm pot) so that grid 1 does not get over-currented. From what I have seen on the curve tracer, grid 1 current required for linearization of grid 2 is quite small.
The 6LG6 datasheet gives a typical set of curves on page 3:
https://frank.pocnet.net/sheets/123/6/6LG6.pdf
...
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Hmmmm. I have a suggestion to solve this problem, based on my experience. It's very simple: invite these girls to participate in your projects. Or start to commenting about them. It is guaranteed that they will run away in despair! Hardly girls will be interested in electronics or similar tech work (((unfortunately for me, because I have more chances to convince a girl to a meeting at work than in a ballad!
))).About Twin Drive, I didn't gave up. When I found some time for it (before I need to finish a... yuch... transistor amp), I return to tuning the PL509 for linear gm.
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Actually, surprisingly, when I brought a tube amp into school (not in a biscuit tin this time, you'll be pleased to hear) one of the girls pleaded with me to teach her how to make one. She was very disappointed when I told her it was really too dangerous and I could not take on that sort of responsibility.
I shocked my daughters chemistry teacher when I bemoaned how safe science classes are now. I am in the Heinz Wolff school of thought on this!
Screening out the danger | Personnel Today
Screening out the danger | Personnel Today
I maintained several factory assembly lines for about 10 years where the only employment requirements were a basic knowledge of the English language and punctual attendance. The plant employing about 2500 at the time had only been open for about 3 years. Accidents, fires, whole batches of bad boards or parts, and serious personal conflicts including physical violence were commonplace.
Sometimes the line bosses and their bosses were line workers that had been promoted, and nobody had any idea what they were building (complex pc boards hand stuffed with leaded parts, electronic components like RF crystals and NiCad battery cells, and microelectronic modules) or how it worked.
We had to teach people that trading your dull looking grey parts for your neighbors shiny red ones will ruin a whole batch of boards. Engraving your name in things with the laser is a No-No, so is blasting a cockroach or a mouse (really stinks up the place).
Things like eating a hamburger with one hand and operating a machine that screened lead solder paste (or worse) were acceptable behavior.
The trash can would spontaneously burst into flame and nobody understood why. Workers were told to wipe down their work area with a paper towel and acetone at the end of their shift. The acetone soaked paper towels were tossed in the trash, which was next to the line of screen printers, each powered by a brushed DC motor. Acetone has a lower flash point and a wider combustible mixture range than gasoline. They switched to Freon which made people dizzy and sick, then some synthetic stuff that was worse.
I was told to put up a barrier whenever I worked on the big laser with the covers off. The barrier was 10 mil black plastic. A 200 watt laser will blow through that in milliseconds, but we had to comply. We tuned the laser up by burning holes in 1/4 inch thick asbestos......yeah that was good for us, but SOP.
It took several years of craziness before enough intelligence infiltrated the factory to make it a first class manufacturing operation.
Now, training engineers fresh out of college in basic soldering with SMD's, tool use, and yes, especially test equipment operation is a totally different story where I could fill several pages from recent memory.
Forgive me if this advice has already been posted- so far I haven't read each and every post.
One temption I sometimes gave in to years ago was this: I was almost there - the magnificient new amplifier - high-power MOS-FET og OTL or whatever - was just about to reveal its true potential. There's just a tiny little thing I wanted to try out - or a "last" power test - it was well after midnight and I'd been working the whole evening. And then: Boom! The problem is that your guards are down - you're a little tired and impatient. I have never had the nerve to figure out what that has cost me in burned components! Luckily, I have never suffered a real injury - but that is by no means down to me! That was pure luck. So the advice is: Impatience is your enemy - and don't test anything critical after say midnight - or if you are the least bit tired: Your mind will play tricks on you -it'll make you believe that you can do things that you can't at that time. In order to remind myself of my foolishness I started to collect blown components in a jar on my workbench. Every time I caught sight of it I was reminded ....
One temption I sometimes gave in to years ago was this: I was almost there - the magnificient new amplifier - high-power MOS-FET og OTL or whatever - was just about to reveal its true potential. There's just a tiny little thing I wanted to try out - or a "last" power test - it was well after midnight and I'd been working the whole evening. And then: Boom! The problem is that your guards are down - you're a little tired and impatient. I have never had the nerve to figure out what that has cost me in burned components! Luckily, I have never suffered a real injury - but that is by no means down to me! That was pure luck. So the advice is: Impatience is your enemy - and don't test anything critical after say midnight - or if you are the least bit tired: Your mind will play tricks on you -it'll make you believe that you can do things that you can't at that time. In order to remind myself of my foolishness I started to collect blown components in a jar on my workbench. Every time I caught sight of it I was reminded ....
Talking about explosions... 2 weeks ago I managed to destroy 12cm long of 10mm sized PCB track and a bunch of parts (2 resistors, one diode and a MJE350) when I accidentally made a short-circuit in a PNP CCS bias. These 12cm tracks instantly vapourized with the 320V charge of a 2700µF cap! But even after that, the capacitor holds a good amount of charge... The noise of this explosion was like a good-sized pistol After that, I put ceramic cased explosion-proof fuses in all output of this high-charge PSU, and reinforced the insulations.
After that, I put ceramic cased explosion-proof fuses in all output of this high-charge PSU, and reinforced the insulations.
This seems like the place for a specific question.
If you have a transformer with extra secondary circuits and taps that you don't plan to use, how do you terminate them safely? Some of these are parallel windings. Others are taps from a high voltage main secondary. Obviously, noise is of interest, but safety is the highest priority.
Naturally, at the end of the project, everything will be inside a nicely grounded case, but these wires could still be reached by removing the top.
If you have a transformer with extra secondary circuits and taps that you don't plan to use, how do you terminate them safely? Some of these are parallel windings. Others are taps from a high voltage main secondary. Obviously, noise is of interest, but safety is the highest priority.
Naturally, at the end of the project, everything will be inside a nicely grounded case, but these wires could still be reached by removing the top.
Why not use the parallel windings? Unused wires should go to an isolated terminal that is not
connected to anything else. Never use electrical tape or heat shrink tubing instead of a terminal.
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