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Safety Practices, General and Ultra-High Voltage
Safety Practices, General and Ultra-High Voltage
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Old 31st August 2017, 08:31 PM   #361
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by rayma View Post
Why not use the parallel windings?
I guess I didn't write it clearly. The transformer in question is a guitar amp transformer that has extra secondary circuits of a different, unneeded voltage.

Quote:
Originally Posted by rayma View Post
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.
That's what I was thinking. Use a barrier terminal strip to terminate the unused wires. I was even thinking about potting the terminal after connecting the wires so that someone would have to cut the wires to get burned.
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Old 31st August 2017, 10:00 PM   #362
trobbins is offline trobbins  Australia
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I'm not averse to clean cutting the end of an unused tap wire, and then heatshrinking the end, and then coiling/securing (preferably under a bell-end to minimise stray coupling). That can free up terminal strips, and reduce risk of accidental touching or leakage or coupling.

If the tap wire comes from an internal solder tab (eg. Under a bell end) then better to remove the tap wire.

Future diy user can then use those taps if ever needed.

Last edited by trobbins; 31st August 2017 at 10:02 PM.
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Old 4th March 2018, 09:35 PM   #363
bluerooster is offline bluerooster
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Quote:
Originally Posted by Layberinthius View Post
Do you think a retired welfare guy has enough cash to afford all the equipment needed to fully and properly service your TV/VCR?
There are some retired welfare guys who made their living teaching the folks that built those TVs and VCRs how to build them, and how to repair them.
When it comes to tubes, and the HV supplies for them, I would only trust 100% the guy who graduated with a degree in electrical engineering, in the '40s or '50s, and then spent the better part of his career in that field. so that narrows it down just a tiny bit.
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Old 4th April 2018, 04:21 PM   #364
Hextejas is offline Hextejas
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Put a drain load across all significant charge-storage devices

I have no idea how to do this
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Old 4th April 2018, 04:57 PM   #365
GoatGuy is offline GoatGuy  United States
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Quote:
Originally Posted by Hextejas View Post
Put a drain load across all significant charge-storage devices

I have no idea how to do this
In simplest terms, its called “a resistor”. In my secret-squirrel engineering days, we just always specified that “large can capacitors” have hard-wired an appropriate resistor across their terminals. For instance:

C = 10,000 μF at 200 V (which is really large), and the target is to get it to discharge at more than 10 volts per second.

There's a relationship:

ΔV = it/C

or change-in-voltage ΔV is current (i) times interval time (t) over capacitance (C). We want:

10 = it/0.01 …
0.1 = it … where i is unknown and t = 1 sec
0.1 = i

Since we know Ohm's Law: (V = IR … R = V/I) then

R = V/i
R = 200 ÷ 0.1
R = 2,000 Ω.

Since we also know the power law (P = IV) then

P = IV
P = 0.1 × 200
P = 20 W

So now we know that it needs to be a 20 watt resistor. Is losing 20 watts continuously a problem? Too much? Not what you want? Well, work backward from the voltage and power, and accept a higher value resistor that'll drain away a lesser amount of power. Then calculate out the time-constant, and also accept that instead of 10 volts/second, your drain plug might only deliver 1 volt per second.

There is no free lunch here, either. You can optimize the drain-resistor idea by using a constant current device to maximize the total time to discharge the capacitor; you can even use a more sophisticated constant power device (which are hard to come by) to totally minimize the capacitor's retained charge time. But … compared to the bűtt-ordinary simplicity and utility of an ordinary power resistor, well … sometimes ordinary beats the competition.

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Old 4th April 2018, 05:06 PM   #366
GoatGuy is offline GoatGuy  United States
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Default Old, Bold Pilots

Quote:
Originally Posted by bluerooster View Post
There are some retired welfare guys who made their living teaching the folks that built those TVs and VCRs how to build them, and how to repair them.
When it comes to tubes, and the HV supplies for them, I would only trust 100% the guy who graduated with a degree in electrical engineering, in the '40s or '50s, and then spent the better part of his career in that field. so that narrows it down just a tiny bit.
OK, that was fun.
I “kind of agree” re: the need for an educated person to handle HV.

But I don't really agree that it has to be “degree in electrical engineering” plus “better part of career in field”. It certainly does take a mighty fear of self-electrocution and the safety of others to do HV safely. But its also a practical thing that only a year or two of apprenticing gives a life's worth of experience and expertise.

I — as a for-instance — am pretty dâhmned good at not self-immolation. I'm also 59, and have a life's worth of HV hacking. Wasn't my career, but just an avocation that never dissipated along with my bad teeth and gnarly knuckles. I don't trust very many people in doing HV at all. But the ones I meet that I do trust … gain that trust in only a few minutes of talking, and watching them work. You can tell a 'safe' HV guy (or gal!) in less than 5 minutes.

They don't TOUCH things.
They often have ONE HAND behind their back.
They LOOK DOWN at the floor often, and stand on a rubber mat.
They WEAR PROTECTION for the really HV stuff.
Their TOOLS are impeccably maintained.
And they LOVE thick layers of electrical tape.

Anyway - there you are.

As helicopter pilots say, “there are old pilots, and there are bold pilots. There aren't any old, bold pilots.” Same for HV expertise. Timid rules.

GoatGuy
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Old 11th April 2018, 02:14 PM   #367
krokkenoster is offline krokkenoster  South Africa
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I read all the stories and fighting about safe H. V. Working and I just wonder were we more careful when i started as apprentice in 1966 or did 400 volts became more dangerous today than then? I am more likely think that the more junior guys are so used to low voltage Solid State the t we want to scare dear life out of them working on Hi Fi in Vacuum Tubes? We must work safe but common sense and safety knowlege is what I was taught. Okay hi powered transmitters working with kilovolts and kilowatts is a different story and I hate insulation tape. I grew up with the old tar impregnated linen tape that after a while absorbed moisture and loose stickyness after some time. Shellac sleeving or called spaghetti we preferred ehere possible. ( I still wonder why we called it spaghetti and not macaroni?)
If live vo!tage chechecks have to be done I use crock clips and turn power off connecting my instruments.����

REMBER THE SAFEST MAINS SWITH IS PULL THAT MAINS PLUG OUT!!! It cannot climb into the socket and leak power due to faulty switch or accidentally turned on
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Old 1st September 2018, 05:44 PM   #368
MJ Sound Cubed is offline MJ Sound Cubed  Spain
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Worth reading this!
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