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Old 11th October 2012, 12:50 PM   #11
h_a is offline h_a  Europe
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Quote:
can approach 30kV
Heh? Air arcs way before that!

Also, we're talking here about voltage difference between the pins and not absolute to ground - because the fet doesn't see that.

I (don't) want to see somebody achieving 30kV between the pins, just by walking in dry air. A poor fellow!

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Old 11th October 2012, 01:39 PM   #12
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Please read it again.
And go to Wikipedia entry "Static electricity" and scroll down to "Energies involved." I'll find other supporting references if need be.
Quote:
The maximum potential is limited to about 35–40 kV, due to corona discharge dissipating the charge at higher potentials.
and
Quote:
Maximum potential commonly achieved on human body range between 1 and 10 kV, though in optimal conditions as high as 20–25 kV
And we're more precisely talking about the voltage difference between the external gate connection and the human hand.
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Old 11th October 2012, 02:22 PM   #13
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Originally Posted by sofaspud View Post
The "telephone cord like thing" should have a conductive wrist strap on one end, and the alligator clip connects to a ground point. NOT to your sleeve (and if you really want to get in-depth, don't wear synthetic fabrics while working with FETs). The cord should be made with a high-value resistor inline for safety purposes (else it wouldn't be pretty if you touched a live wire).
Both ends have an alligator clip (why I didn't differentiate between the ends, front end same as back end) and you try to clip the other end to something like your metal table leg (I just stick a rare earth magnet from a disk drive on said table leg and clip to there since the table leg is too thick). I don't know what is inside of it, maybe there is a resistor or small sand bar in there, but I'm not opening it up to find out. At the total cost of 12 RMB at the time (13 years ago), I believe I could have bargained lower.

Wouldn't my sleeve/shirt in contact with my skin/body/person carry the charge as opposed to my body (a bad conductor)?

I haven't had any problems yet wearing synthetics or cotton and I don't much like wool.
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Old 11th October 2012, 02:41 PM   #14
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Originally Posted by h_a View Post
I've build a fair number of amps and never had problems with static discharge. In fact I cannot remember any transistor failure during assembling. I also don't use any fancy sort of soldering station, just a cheap adjustable Weller.

IMHO it's the shorts that kill the amps
The problem with damage done by static discharge is that components might continue to work but might fail prematurely:

Basics of Electrostatic Discharge

see "Latent Defect" in the link above.
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Old 11th October 2012, 03:28 PM   #15
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Quote:
And go to Wikipedia
Thanks for your kind reference - however, I'm pretty happy with my knowledge that came with my phd in physics and from my experience that came with having worked in the research center of a rather large semiconductor manufacturer.

As long as nobody fears building amps as they could fail prematurely due to static discharge any second I won't stop anybody wearing wrist bands
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Old 11th October 2012, 03:39 PM   #16
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Ive seen electron microscope pictures of such static damages on semiconductors when I worked at Frequentis. They are real. If you want troublefree service from mosfets over years you have to take antistatic measures.
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Old 11th October 2012, 03:58 PM   #17
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I wonder what the Class Aand A/B amplifier builders did before the invention of wriststraps, tinfoil hats, and electrostatic discharge?


I am confident that somewhere along the line starting where everything starts out as a bucket of sand being melted to being packaged, shipped out, running roughshod down a very bumpy road, during a lightning storm, ending up at the a large dsitributor's warehouse only to be re-packaged by hourly paid unskilled labour, shipped out further afar in yet another lightning storm, marked up further, arriving either at the small electronics dealer an hour from my house, where it is parceled out and put into small ziplock baggies with labels, and repeating the process again going down the bumpy road to my house.

Or if it doesn't get to the the small electronics dealer down the road, the UPS guy decided to leave the 24 inch X 16 inch X 6 inch box of transistors, capacitors, vacuum tubes, and really cool looking sticker (that sticker in real life doesn't look all that cool, but pictures of the sticker on the website sure did) I bought on-line "hidden" underneath my front door mat in a light rainstorm where it ultimately got wet.

Then hearing from the lady across the road who saw the delivery and saying that the UPS guy dropped the box as he was trying to close the door to his truck and hoped that it wasn't anything breakable.

At times, I think that static electricity is the least of my worries.
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Old 11th October 2012, 05:31 PM   #18
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Does anyone now wonder why I said what I said in post #2? I could be wrong though. 45% relative Humidity could solve 99% of your problems? But, what about all the "statements" being put forth in this can of worms thread? Been there done that! Even the experts don't agree, so I'm not suprised. Buy a humidifier and do the silicon last! And enjoy your amp! Don't forget the protection diodes at the input. A big Zap right thru your pot knob, to the pot and #$%^&*!
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Old 11th October 2012, 05:35 PM   #19
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Originally Posted by flg View Post
Does anyone now wonder why I said what I said in post #2? I could be wrong though. 45% relative Humidity could solve 99% of your problems? But, what about all the "statements" being put forth in this can of worms thread? Been there done that! Even the experts don't agree, so I'm not suprised. Buy a humidifier and do the silicon last! And enjoy your amp! Don't forget the protection diodes at the input. A big Zap right thru your pot knob, to the pot and #$%^&*!
Well, actually you said 95% of your problems in your first post in #2, the last 5% were for the rest of the worms in the can.

Thank you also for that pointer about the protection diodes a the pot knob. Never thought about that until you brought it up.

Last edited by overtheairbroadcast; 11th October 2012 at 05:36 PM. Reason: added in your first post in #2
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Old 12th October 2012, 02:09 AM   #20
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Thanks all, as before. Reading between the lines, I see a lot of experience in the crowd. If I follow all these tips, I can't go wrong! I'll be wrapped up like the michelin man but my amp will work
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