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Old 29th November 2012, 01:29 AM   #51
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Originally Posted by buzzforb View Post
Ha. You make it sound so easy.
Your difficult and unpleasant experience is an important lesson to us. You practiced a logical and successful approach to managing fakes, and beat the culprit at its game. Unfortunately, the seller was collateral damage. I would aspire to do what you did when faced with a similar situation. Why be cheated and feel bad [or helpless] about doing nothing about it?
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Old 29th November 2012, 01:43 AM   #52
Bigun is online now Bigun  Canada
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For solid state, I pretty much buy only from a reputable source such as Digikey. Buying cheap parts online fuels the fake-part industry.
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Old 29th November 2012, 03:14 PM   #53
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Originally Posted by Bigun View Post
For solid state, I pretty much buy only from a reputable source such as Digikey. Buying cheap parts online fuels the fake-part industry.
I fully agree with you. You'll be in a position to return the misbehaving part for a replacement or a refund.

Here's an excerpt from a brochure by THRESHOLD Corp. for its Model S/150 Series II power amplifier. I am going back to the early 1980's and quote the extensive testing it did to qualify semiconductors. "To assure reliable operation, even under severe conditions, each power semiconductor of the S/150 [bjt] is tested to its secondary breakdown point at 125 volts before being placed in parts inventory". Also, from another Technical Brochure; "Every transistor undergoes individual testing and characterization, as necessary, for transconductance, matching, noise, saturation, and voltage breakdown prior to entering parts inventory."

In another publication, Mr. Pass emphasized the importance of the reverse-biased Collector to Base breakdown voltage. I do not have the exact language for it. Threshold prevented "off-spec" from its inventory.

Collectively, we can generate a general Quality Control procedure to qualify semiconductors for DIY use. I believe the first step is :
  • Buy from a reputable source as Bigun said above
  • Reputable or not, push it through key electrical tests for confidence building.
Let's generate such tests [in addition to flg's] to qualify the hot one SJEP120R100.
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Old 3rd December 2012, 08:03 AM   #54
qusp is offline qusp  Australia
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Originally Posted by Antoinel View Post
The bjts were destined to fuse. In hind sight, what will you do today different to ensure the avalanche of damage past will never occur?
I dont know what you mean? I followed the BOM and super regulators are high dropout regulators, I used them within recommended operating conditions and they failed because they were Fakes and not the part they were supposed to be, which is a 150W 230V part.

they should have been operating well within their SOA.

what I will do to avoid it next time is to not buy anything ever again from dodgy EBAY sellers, or buy any transistor from ebay unless recommended by someone I know who has experience with the seller and the exact part.

Last edited by qusp; 3rd December 2012 at 08:06 AM.
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Old 3rd December 2012, 11:44 AM   #55
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Originally Posted by qusp View Post
I dont know what you mean? I followed the BOM and super regulators are high dropout regulators, I used them within recommended operating conditions and they failed because they were Fakes and not the part they were supposed to be, which is a 150W 230V part.

they should have been operating well within their SOA.

what I will do to avoid it next time is to not buy anything ever again from dodgy EBAY sellers, or buy any transistor from ebay unless recommended by someone I know who has experience with the seller and the exact part.
qusp: I agree with you. The bjts were Fakes, and thus their fate was already preset to fail.
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Old 3rd December 2012, 12:24 PM   #56
qusp is offline qusp  Australia
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ah OK, all good I was just confused. yep, poor little..erm whatever they were didnt stand a chance
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Old 31st December 2012, 03:33 AM   #57
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Originally Posted by Tea-Bag View Post
dont go by just the lettering differences. The original R100's and some R100As used the more 'white' letter printing. They also used a more 'shiny' legs and drain substrate backing.

That being said, I've had a couple of parts searchers seek these out lately. They are saying any offer right now are from seedy sources and likely fake. So really buyer beware.
The IC district of China can unfortuntely produce whatever you want for a part in printing in a couple of days notice.

R100's of any sort will have a much lower VgS test then any IRF240.
Tea Bag is right, the "hard to read" lettering is not by itself an indication of anything. SemiSouth used a couple of Asian packaging firms. I have both types of package markings in my inventory, all of which was walked out of the SemiSouth building in Starkville, Mississippi by me. No fakes in my inventory.

I have neither seen nor tested a fake, but I don't think the counterfeiters are trying to put a device inside the package that is intended to survive scrutiny. My guess is they just wanted to shovel something out the door during the first buying frenzy. In that case, it should be rather easy to tell a genuine SemiSouth enhancement mode JFET from any likely fake. The forward current of the gate source diode (or the gate drain diode) will look like a pn diode. And then the rather high transconductance of the R100 or equivalents is easy to spot beginning around Vgs = 1 V. No MOSFET will duplicate both terminal characteristics.

Over the past two weeks I have tested literally hundreds of these parts as I sorted through my inventory that I acquired from a 12 year relationship with the company beginning at the beginning. I will post a few curve tracer images in the next couple of days that will illustrate what the real thing looks like if you have access to a decent quality curve tracer. As for genuine inventory, it is all in the hands of former customers supporting their own products or "hoarders." I can assure you that the company's inventory shelves are now bare and production is firmly stopped. SemiSouth had its own fab. No other fab anywhere in the world made SemiSouth JFETs. I had access to the inventory room during the last couple of months as the company unwound operations. They sold off the sell-able inventory quickly to raise cash, as you might imagine.

I have to thank all of you as a community (DIY Audio) for discovering the unique properties of SemiSouth JFETs in high-end Class A audio amps, and Nelson Pass in particular for giving the discovery a voice. The founders of the company were all thinking power switching because that is our professional background. Jeff Casady developed SiC SITs for radar at Northrop Grumman before joining me in starting SemiSouth. We never thought about linear as a motivation for SemiSouth's products. You all just made it happen.

I've enjoyed reading all about it. In my power electronics class this Spring semester at Mississippi State University, a Pass F2J amp is going to be one of our early analysis assignments. Cool stuff like this they will love!

Regards,

Mike Mazzola
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Old 30th January 2013, 04:10 PM   #58
amp_guy is offline amp_guy  United States
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first of all I feel safe in expressing a hearty thanks from all of us fanatics here at DIY to Mike Mazzola for providing his first hand knowledge.
One of the great things about DIYAudio is that the real great contributors to the art are willing to share knowledge and experience freely here.

As one who stood on the sidelines and have not obtained a single SIC device, where does that leave those who are looking.
Are the devices from CREE at all suitable?

Last edited by amp_guy; 30th January 2013 at 04:14 PM. Reason: poor spelling
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Old 30th January 2013, 04:31 PM   #59
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Quote:
Originally Posted by Antoinel View Post
Here's an excerpt from a brochure by THRESHOLD Corp. for its Model S/150 Series II power amplifier. I am going back to the early 1980's and quote the extensive testing it did to qualify semiconductors. "To assure reliable operation, even under severe conditions, each power semiconductor of the S/150 [bjt] is tested to its secondary breakdown point at 125 volts before being placed in parts inventory". Also, from another Technical Brochure; "Every transistor undergoes individual testing and characterization, as necessary, for transconductance, matching, noise, saturation, and voltage breakdown prior to entering parts inventory."
Here's a story for you. We were buying BJT output devices from a major semi
manufacturer (you can guess who, but they no longer make transistors and
it was forty years ago). We paid a premium to have all devices tested for
secondary breakdown as we had seen some problems with that, and we also
tested them in-house. We found a significant percentage breaking down
at voltages way below spec, so clearly they were either not testing them or
shipping them anyway. We called in the factory rep who was a real d**k
and after much discussion they agreed to replace them. We shipped the
bad parts back.

Later we received a batch of replacements, and found that they had our
felt pen test marks on them.

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Old 30th January 2013, 04:45 PM   #60
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Reminds the customer dissatisfied with the steak, complains that is hard and unpalatable, the waiter takes the steak to the the kitchen, and the cook strip the wooden clogs and gives you the steak with enough force, sends redeliver the same steak the client. And the customer says, "will now good, is too soft."

He had not felt pen to mark the steak!
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