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Old 10th Mar 2019, 4:40 pm   #1
Jolly 7
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Default Real versus fake 2N3819 JFETS

Here are two components both marked 2N3819. The one on the right is from a batch of a far eastern postal order and is a fake. It identifies as an NPN transistor.

The device on the left was from a UK seller and correctly identifies as a jfet with source, gate and drain being pins 1, 2 and 3 respectively from the left hand side.
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Old 10th Mar 2019, 6:01 pm   #2
paulsherwin
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Default Re: Real versus fake 2N3819 JFETS

I'm surprised it's worth anybody's while faking 2N3819s. The genuine ones are cheap enough, and fakes are obviously going to wreck any reputation the seller has.
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Old 10th Mar 2019, 6:12 pm   #3
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Default Re: Real versus fake 2N3819 JFETS

I recently bought 50 x j31xx fet devices from china and they were fakes-testing as high beta pnp. Markings were indistinguishable from o/e makers.

Like Paul,I am baffled as to why this is done,the profit is minimal and short lived. The ability to relabel devices is remarkable and looks genuine enough when viewed under a usb microscope.
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Old 10th Mar 2019, 6:22 pm   #4
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Default Re: Real versus fake 2N3819 JFETS

have you tried them in a circuit? Might it just be the component tester doesn't like particular batches?
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Old 10th Mar 2019, 7:05 pm   #5
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Default Re: Real versus fake 2N3819 JFETS

I don't know, if it tests as an NPN bipolar transistor with plausible hfe then it's very unlikely to be an FET. Very odd. I suppose some Chinese internet sellers are just criminals operating scams. I've not been caught out yet, but I suppose it's just a matter of time.
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Old 10th Mar 2019, 8:50 pm   #6
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Default Re: Real versus fake 2N3819 JFETS

Having been burnt a couple of times with semiconductors from China I now refuse to buy any at all from China.

The last time the devices were just blanks labelled up - nothing in the plastic moulding at all !

Supplier was UT Source.

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Old 10th Mar 2019, 8:53 pm   #7
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Default Re: Real versus fake 2N3819 JFETS

UT Source have bailed me out of commercial repair situations a couple of times where I couldn't find the components from anywhere else so I don't think they are all bad.
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Old 10th Mar 2019, 11:00 pm   #8
g4wim_tim
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Default Re: Real versus fake 2N3819 JFETS

Agreed UT Source have been useful in the past for me as well, but clearly they have not been able to filter out counterfeit parts coming into their warehouse supply chain.

Thus having been burnt once by them I'm now wary of using them again or indeed any other Chinese supplier.

That said if they are the only ones having stock then there's no choice but to take a chance.

BTW I did try and return the blank semiconductors but didn't get anywhere - lesson learned !
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Old 11th Mar 2019, 1:51 am   #9
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Default Re: Real versus fake 2N3819 JFETS

I also had some fake fets of a different type number. The devices supplied were NPN transistors, rather Nch junction fets. The explanation in that case was that there was one equivalents book that incorrectly listed the part as a transistor instead of a fet.

I wonder if that has happened here too. The reasoning being that re-labelled substitute parts or equivalent parts are just about as cheap as anything else, so the fact they made a blunder with the part being a transistor instead of a fet, suggests they might have one of the poor quality equivalents books and have got caught out this way.

If you had bought a fake transistor at least the fake would probably have been the correct polarity type and most likely have "worked" unless it was in some high stress application.I think the fakers try to please, where possible.
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Old 11th Mar 2019, 3:19 am   #10
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Default Re: Real versus fake 2N3819 JFETS

May be this is the same as I have experienced.

I bought at auction a large quantity of JFETs as clearance from a factory sale.

I was selling these on ebay, sold thousands.
I tested them before dispatch and discovered that though identical in every way, roughly one in four hundred or so tested as an NPN transistor.
And they worked as such!

The JFETs when passed on test also worked, I had one nasty complaint from a troll who bought 10 and found 1 to be a transistor. I sent him 20 f.o.c, hope he choked on them.

So perhaps if its a tolerance in manufacture, a JFET could be an NPN transistor or is that daft?
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Old 11th Mar 2019, 4:56 am   #11
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Default Re: Real versus fake 2N3819 JFETS

Contamination of the die during manufacture might possibly cause a JFET to act like a transistor I suppose.

Knowing this sort of stuff gets shipped out the factory back door could also explain how it ends up in the market.

As said above, faking 2N3819's just wouldn't appear to be a profitable pastime.
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Old 11th Mar 2019, 9:43 am   #12
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Default Re: Real versus fake 2N3819 JFETS

I bought a bag of 50 BC550 from ebay a couple of years ago and they turned out to be PNP not NPN ( full refund from seller and I now have a bag of general purpose PNP transistors )
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Old 11th Mar 2019, 12:01 pm   #13
Maarten
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Default Re: Real versus fake 2N3819 JFETS

Quote:
Originally Posted by Boater Sam View Post
So perhaps if its a tolerance in manufacture, a JFET could be an NPN transistor or is that daft?
More likely to be a 'tolerance' in stamping or in sorting or stocking of the unstamped parts.
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Old 11th Mar 2019, 12:50 pm   #14
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Default Re: Real versus fake 2N3819 JFETS

Watch out for the chinese transistor testers too. Sometimes they identify parts wrong as well. Worth digging out DMM and doing junction / resistance test as well.

2n3819 is very widely specified. It can confuse them.
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Old 11th Mar 2019, 2:11 pm   #15
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Default Re: Real versus fake 2N3819 JFETS

Quote:
Originally Posted by Argus25 View Post
If you had bought a fake transistor at least the fake would probably have been the correct polarity type and most likely have "worked" unless it was in some high stress application.I think the fakers try to please, where possible.
I'd think so, too. A good faker wants to make money, so he'll supply parts which do most of the job but are cheaper. Maybe relabel BC108's as BC109's - except that there wouldn't be much money in this. So maybe use smaller die in the fakes. Maybe encapsulate them in scrap resin which has passed its use-by date. It'll work long enough for him to get paid, and maybe sell more.

Quote:
Originally Posted by Boater Sam View Post
So perhaps if its a tolerance in manufacture, a JFET could be an NPN transistor or is that daft?
An N-channel J-FET consists of a length of N-type material, with S and D connections to its ends. So it looks like a resistor. Then it's surrounded by P-type material which forms the gate.

If a P-type diffusion takes place to form the gate, but goes on too long and goes right through the N-type, you could I suppose end up with a NPN structure, but I can't see it having much gain. Happy for a semiconductor design or process engineer to put me right, though!
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Old 11th Mar 2019, 5:59 pm   #16
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Default Re: Real versus fake 2N3819 JFETS

With these low value parts, I dont think the issue is fakery, but more likely poor quality control. There just isnt the profit in faking parts that cost pennies. Fakes of more expensive parts are often as Angus says, workable up to a point, so long as the end user doesnt notice the problem until long after. But ultra common, 'universal' parts that are consumed in their hundreds of thousands by industry would get flagged almost instantly if they were trying to pass different devices off.

Far more likely I think is that millions of these parts are made, all packaged in identical unlabelled carriers, then get mixed up during the transfer from production to labeling. The labeling machines can probably handle a much greater throughput than the fab and encapsulation lines can, and so the products will be chopped and changed depending what is awaiting markings, and such mistakes occur in that incorrect batches get put through. And as anyone whos worked on a high speed production line knows - by the time a mistake is spotted, a good portion of the product is already packed and shipped!
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Old 11th Mar 2019, 6:48 pm   #17
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Default Re: Real versus fake 2N3819 JFETS

While eBay, AliBaba etc. generally deliver the goods there are always the chancers and scam-artists out there.

When I buy semiconductors (and capacitors, and resistors) I prefer to stick to mainstream suppliers with quality-accreditations to match. Yes, this can mean paying £15 for the likes of five humble BFY51 or 2N3053 transistors but they arrive next-day and I know that if they don't perform to-spec I have a good chance of geting my money-back.

Fitting "Bought-off-eBay" parts into gear where I'm billing the client £45/hour for my time and experience makes no sense. Hobbyists may be prepared to chance it because they're not paying for rework-time or loss-of-reputation.

I note that Surplectronics - a UK-based trader I trust - have 2N3819s at a sensible price: https://www.surplectronics.com/prodd...sp?prod=2N3819
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Old 11th Mar 2019, 7:17 pm   #18
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Default Re: Real versus fake 2N3819 JFETS

CVC are my go to for genuine parts plus you can usually haggle
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Old 11th Mar 2019, 7:30 pm   #19
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Default Re: Real versus fake 2N3819 JFETS

Chinese sourced parts certainly make more sense for the hobbyist than professional constructors and repairers, and should be tested before use in anything.
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Old 11th Mar 2019, 7:42 pm   #20
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Default Re: Real versus fake 2N3819 JFETS

The serious damage in hobby electronics is when dodgy parts get into the hands of a beginner. They can destroy someone's confidence. There are too many iffy designs out there that when you round in the risk of dodgy parts, it will probably take so,e serious experience to get things to work.

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