• 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

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto

I've been looking for that listing. Thanks for that. I bought a few several years ago... It's good for running Nixies. Never tried a preamp with it. It's cheap though. All the cores are loose and I think the MOSFETs would melt if you asked it for 35W.
 
DC DC inverter designed for B+ power

I just found one Chinese DC DC inverter that is designed for B+ power:
DIY tube amplifier front stage tube DC12V boost inverter power board| | - AliExpress
It is used in this "Matisse" tube preamp:
breeze audio Matisse Fantasy Line Stage DC12V 1A Car / home 6N4 Tube preamp amplifier board|Amplifier| - AliExpress
It uses a TL494 switching controller, according to the photo.
Any thoughts on this, please?
Would it be possible to use it in a tube preamp that requires 20 mA high voltage?
 

jean-paul

diyAudio Moderator Emeritus
2002-09-20 7:20 am
Germany
Ultra high voltage 1000 - 1500V....

Yesterday I visited a 400 kV (400,000 Volt) distribution/coupling point. When I was standing at the safe distance of 6 meter I felt the field strength and current going through my feet. Cars had to be connected with chains to PE to prevent them from charging up (capacitively and inductively!) :) At that time only 32A was running per phase (that is 22 MW as in MegaWatt.....) The noise was terrifying though. Very impressive and scary at the same time.
 
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jean-paul

diyAudio Moderator Emeritus
2002-09-20 7:20 am
Germany
The hairs standing up was also experienced yesterday. Moving limbs gave the feeling an invisible tickling shell was around the limbs. Really a unique experience to walk around on such a terrain. I have the electrical handicap since I was very young but this is the first time it felt like my friends the electrons were clearly ready to devour me and they were all around me at ALL angles from ALL directions which makes one feel there is continuous threat/danger. I am used to very high power stuff but this was another level.
 
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Ultra high voltage 1000 - 1500V....

Yesterday I visited a 400 kV (400,000 Volt) distribution/coupling point. When I was standing at the safe distance of 6 meter I felt the field strength and current going through my feet. Cars had to be connected with chains to PE to prevent them from charging up (capacitively and inductively!) :) At that time only 32A was running per phase (that is 22 MW as in MegaWatt.....) The noise was terrifying though. Very impressive and scary at the same time.

From my days doing a bit of high voltage, I would expect 400 KV to be lethal at one meter distance. So six meters is a bit closer than I would consider safe.

One time there was a problem with a high voltage, high current pulse driver. It was connected via a very high voltage oscilloscope probe. The probe looked just like it should be on a science fiction movie set. A large diameter clear plastic tube with smooth rounded plates set about 50 cm apart and a series of high voltage resistors across the capacitor formed by the plates.

The whole apparatus was on a wood table. However it was not working properly. I suggest the issue was the metal edging on the table was acting as a shorted turn.

The professor running the project said “that was ridiculous and if that were the case when he lifted the probe ground wireeee!” The arc as he lifted the ground wire sparked for a good 30 cm in the air as his arm arced up. Fortunately the main current path was through the probe clip not the professor.

Next day the metal band was gone and the gizmo worked properly.

That lab only had a 60 KV AC power supply. Never ran into a current limit but based on the size, around an amp.

There also was a fellow who didn’t understand why a 15 KV PIV rectifier stack failed at less than 6,000 volts AC. He actually blew up two of them trying the thing out!

The research that came out of a nearby lab was the most fascinating. A fellow managed to photograph a spark originating. Turns out your eyes lie to you. The energy radiates outward as an expanding spherical shell. It is only when the shell reaches the other electrical pole that current begins to flow and an arc forms along the path concentrating the current flow. That is what you see.

So to my way of thinking you were inside the voltage spherical shell. Good thing you were far enough away that an arc didn’t form.
 
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Autocorrect on my cellphone. Need to fix that.

I prefer a 10/1 safety margin, but as it is distance squared the extra 5 is fine.

I am always amazed at how some folks get into hazardous situations without recognizing it. Obviously skin crawl from electric fields is a decent warning. Also fun to experience it. I suspect the folks at the facility have clear rules for keeping safe.

One tale of unknown truthfulness is of the fellow smoking a cigarette in a high voltage facility. Who knew smoke was an ionized path! Hard lesson to learn.

One case of unknown hazards was in college when an art student decided for a project he want to etch glass. I gave him a spray can of photo resist. He went to the chemical stores desk and because he used an in-house university purchase order, they sold him the hydrofluoric acid. He just put it in a tray in the darkroom and submersed the glass plate into it. No real ventilation. Surprisingly that wasn't actually the dangerous part! It seems the printed circuit board photo resist was developed by rinsing with trichloroethylene. Turns out exposure to those fumes damages your kidneys.
 
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jean-paul

diyAudio Moderator Emeritus
2002-09-20 7:20 am
Germany
This was at a representative company with strictest regulations (hence the extra meter). I think it was even more in the direction of more than 7 meter in total and we were standing in the middle of the "path" with everything clearly indicated and it was about work to be done in that particular field. People over there tend to underestimate distances as a habit was my thought. If one has no business to be done one does not even think to go there. I was at no moment in a hazardous situation but I happen to feel it while the others did not feel a thing. Well I don't mind as it maybe is better when one feels voltage without being in the dangerous zone! When I work with high voltage rectifier/DC systems I also feel field strength when I am in the vicinity of the dangerous areas. They call it electrosensibility which I ignore to believe in but nevertheless I am able to feel it.

The things that can go wrong by plain ignorance are breath taking indeed. After I saw a 7000 kg transformer being lifted in a building and a shingle broke while someone was sticking out his head two stocks below it to see it I thought I had seen it all :) Ended well for the person, less good for the transformer and the building.
 
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An interesting issue may be with Tesla coils. A number of folks who have worked with them have neurological issues. One friend after playing with one of the largest had his visual perspective turn sideway. Doctors exams could find nothing wrong, but he was quite incapacitated. After a few months things returned to normal. There are other similar tales of woe from folks who have been exposed to high voltage and high frequency AC fields.

I am not aware of such an issue with normal AC power systems even at high voltages.

Glad to see you haven't suffered from any direct or side effects.

I did fire one fellow who stuck his fingers in a steel beam joint that was not touching as it should have been. Idiot was trying to wiggle it to see if it would move. Had it moved with the forces involved it would have taken his fingers off quite quickly.

Stay safe.
 

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
While maybe not strictly allowed here (line powered), I would like a consensus.

If I build a tube amp in an insulated/isolated box, and I use input and output transformers, do I still need a power transformer?

My electrician friend and I both feel that the isolation is still there, it's just provided in a different place. I/P transformer is much less money than a PT.

Has anyone ever considered it? No I have not done it - just a mental exercise.

Koda
 

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
Yes, that makes sense for safety.

I couldn't do it anyway. I like to ground the chassis. That would mean either 240V split supply (possible but would be a kludge - tapped from upper and lower kitchen receptacles...) or a half wave supply.

My electrician friend even played with the idea of using the 240 split supply as +- 150V rails in a power amp. When he realized he'd need a much larger output transformer than he thought, and two of them to boot, he figured isolation PT is cheaper LOL
 
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