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PostPosted: 06 Nov 2010, 23:22 
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sampleaccurate, that wall wart in the lower right corner of the second picture is kinda scaring the daylights out-a-me. ;) As far as your 3D wiring.... I've seen commercially built systems that were far worse than either of your examples.

A suggestion I would like to add to this thread is the employment of a good variable mains-transformer (variac). This will allow you to bring the mains up slowly. It's a great way to ease in to your first power on test and will generally limit the amount of damage that could occur as opposed to just throwing the full mains in to the circuit. They're not very expensive and one rated for 5 to 10 amps should suffice. MinuteMan Electronics sells these for ~$130 for the 10amp version, 5amp ~ $70 (http://www.minute-man.com/acatalog/Onli ... rs_58.html). An isolation transformer would be a good idea if you’re going to be playing around with direct mains power supplies. With transformer based power supplies, the power transformer acts as your isolation. Transformer less power supplies really should be tested using an isolation transformer. A variac does not normally do this function! You can find variable transformers that do have isolation, but they are very expensive.

For safety's sake always include a fuse. I suggest one in the mains and one in the HV after the rectifier at minimum.

A lesson I learned was when using test equipment like DMM or oscilloscope or otherwise probing around a live circuit: Whenever possible, keep one hand behind your back. This lessens the likelihood you'll lay that "unused" hand on something hot (physically or electrically). Also provides another layer of electronic safety by lessening the chance of completing a circuit across your heart should your probe hand touch something that is electrified and your "unused" hand happens to be touching something else, like a ground.

Never let your attention wane! If you are tired, STOP! Put the project aside and go get some rest. When troubleshooting a problem and you're becoming frustrated, take a break. Get away from the project, clear your mind and come back when you've settled. If something is keeping you from focusing on your project, put it aside a go take care of the other. Impatience, fatigue, anger and distractions are killers when dealing with high voltages. Take it from someone who’s had their share of picture tube discharges, bare wires, small power cap discharges and HV zaps. They all had two things in common; 1.) I wasn't paying attention. 2.) They all HURT! Anyone of those could have been more serious - I was lucky. Stay alert!

__
A simple first build would be a capacitor discharge tool. I built/used one when I was regularly servicing TVs to discharge the picture tube prior to handling. Other techs would just use a screwdriver between the anode pit and the ground mask, but I always hated the loud pop and the nasty arc pits in my screw driver shaft. Here’s what you need:
1.) A length of wire, say 24inches, about 18ga.
2.) 2 insulated gator clips
3.) A 33Kohm 1 watt resistor
4.) 47nF disc capacitor rated to about 600v (higher if dealing with higher voltages)
5.) An SPST rocker or push button switch.
6.) The provided schematic.
7.) A small plastic enclosure

Make sure the main power switch is off and the mains line is disconnected! Apply the gator clips to capacitor leads; throw the switch for about 30 seconds. Measure and remeasure the capacitor voltage to confirm complete discharge. Disconnect the leads.
:thumbsup:


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PostPosted: 25 Nov 2010, 22:35 
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Location: Lilburn, Georgia USA
hello, I was just browsing on E-bay and there was this old Variac with two gauges on the top of the face of it. One was for volts and the other was for amps drawn through the variac. It was advertised as a guitar amplifier booster. I bid on the thing just because it looked cool. I went up to $100.00 and was quickly outbid. The darn thing went for $200.00 and was only good for 5 amps! In one of my mail order catalogs you can buy one that goes up to 15 amps for $104.00 plus reasonable shipping. I say reasonable because anything on E bay will be a minimum $20.00 no matter if it is 5 miles from you. I bet whoever bid 200.00 plus shipping thought it was a tube guitar amplifier the way it was described. I never knew guitar players always had a variac hooked to their amplifier. Has anyone ever heard of such?


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PostPosted: 27 Nov 2010, 10:55 
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I'm guessing they do that to set the voltage to the amp. I guess it could also be used to run the voltage a little higher! :hot:

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PostPosted: 05 Dec 2010, 08:49 
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Just another safety reminder, that some people are not thinking about !

Personal safety:
Be aware while measuring DCR of transformers with a multimeter, don't touch primary and/or secondary vs. secondary and/or primary coil with your fingers. The voltage from a ( Ohm measuring field ) multimeter are able to transforme, an even low voltage, to a high voltage spike of the opposite site of the transformer, while measuring. :!:

Material safety:
Don't have a multimeter (1) connected to a transformer secondary and/or primary, while measuring with another multimeter (2) of the primary and/or secondary coil, it's possible to destroy the multimeter (1) by doing so.

A deadly exit:
I don't have any argumentation, could this short spike bring a deadly chock ( i don't think know ), but anyway, be aware of this issue ..don't be affraid. As always, handle all kind of high voltage with care and respect. :ugeek:

Something else to think about:
It's actually possible to die :tombstone: of putting the tongue to a 9V battery ....weird but the truth. :(

DIY:
Means "Do It Youself" ...not "Die Ignorant Young".


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PostPosted: 05 Dec 2010, 12:47 
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KrammeAcoustics wrote:
It's actually possible to die :tombstone: of putting the tongue to a 9V battery

:confused: :confused: :eek:
I always did that when I was a kid. Enjoyed the sharp "lemony" taste LOL.

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PostPosted: 08 Dec 2010, 16:55 
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dtsup1 wrote:
:confused: :confused: :eek:
I always did that when I was a kid.


It's not easy to find statements, to conclude it's truth ...but i've found this:
http://www.theregister.co.uk/2006/07/28 ... y_battery/

I guess Dr. Quincy :geek: wonders, when finding dead people, with open mouth and a 9V battery in their hand !
Hmm, maybe those people just died of disconnecting the 9V battery, from their pacemakers. :?

dtsup1 wrote:
Enjoyed the sharp "lemony" taste LOL.


Lemony taste :mrgreen: ...yeah right. Not to mention Duracell with strawberry flavour. :yumcoffee:


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PostPosted: 08 Dec 2010, 23:03 
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Kramme, that article is scary...
When I get married and have kids, I'll teach them the right thing! :mrgreen:

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PostPosted: 17 Jan 2011, 17:50 
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Gio wrote:
I'm guessing they do that to set the voltage to the amp. I guess it could also be used to run the voltage a little higher! :hot:


Some guitarists will use a Variac and run their amp a little low on voltage. They claim that this was one of the ways Eddie Van Halen achieved his unique tone known as "the brown sound". NOT to be confused with the brown note!.

I think it's a great way to damage your amp, personally, because, if I'm thinking correctly, lowering the voltage means an increase in current. This practise probably keeps amp repair techs pretty happy due to increased repairs.

Using the wrong type of transformer can, I believe, also lead to a lethal zap when touching the guitar strings and then touching the mic.

Don't take any of this as gospel- I've spent my life working with 12vdc gear for the most part and I'm only now cutting my teeth on tubes.

_________________________________

Now on-topic: My Pop taught me as a kid to always put one hand in my pocket when working on high voltage. Wise advice. The unused hand in the pocket prevents inadvertantly grabbing onto anything conductive to ground. Prevents a current path through the heart.

Lets say I'm taking a voltmeter reading with my right hand. My left is literally in my back pocket. I also tend to lay my right wrist (the hand with the probe in it) on the chassis so that if I DO get a poke it will flow into my hand and out my wrist to the chassis rather than through my entire body. Perhaps this is bad advice but I'd rather take it through my hand than through my heart.

-Generic1964


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PostPosted: 21 Mar 2011, 11:46 
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Hi.
Generic1964 wrote:
Some guitarists will use a Variac and run their amp a little low on voltage. ...unique tone known as "the brown sound".

Yes, higher & lower supply voltage can change the amp sound. I tried with 8V B+ voltage higher than the 440V designated voltage for my 1-tube 1-stage MM phonostage, the sound gets tighter & more pushy.
I tried starving the tube heater voltage from 6.3V down to 4.8V. The sound gets very soft & backward. "Brown" or what not to me is terminology.
Generic1964 wrote:
I think it's a great way to damage your amp, personally, because, if I'm thinking correctly, lowering the voltage means an increase in current. This practise probably keeps amp repair techs pretty happy due to increased repairs.

Lower the supply voltage, less will be the supply current. Less will be the O/P audio voltage/power delivered by the amp. Noway current will go against the voltage & blow the the amp with lower supply voltage. The amp works cooler & will last longer instead.

c-J .

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PostPosted: 15 Apr 2011, 14:45 
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Hi Everyone, lots of good information. I'll be honest, I didn't check it out until today. :bawling: However, I would like to emphasize the comments about charged capacitors in equipment. I frequenly use poly caps as a last element in a high voltage supply. There are lots of reasons for this, but they have very low leakage and can maintain a charge for a long time. In one recent project I used them in the last two stages and they were isolated from other parts of the PS by a voltage regulator and there was no bleeder resistor. The regulator was effectively a complete DC blockage so that the caps could not discharge back through the earlier PS stages which contained electrolytic caps (that always have some leakage). The net result was nearly two days after shutting off the unit there was still a substantial charge on the polys. When I accidentally shorted one with a test probe the spark was impressive. :eek: I repeated the test with a meter after turning it on and waiting the same time period, the charge was still 195 volts. True both stages were 10uf polys charged to 475 volts, but the charge left after two days was probably in the lethal range. :tombstone:

Good listening
Bruce

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