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How to identify fake JFETs?
How to identify fake JFETs?
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Old 7th June 2019, 11:31 PM   #21
Bigun is offline Bigun  Canada
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How to identify fake JFETs?
Quote:
Originally Posted by andyr View Post
I'm wondering if anybody can advise me what tests I can do to determine whether a parcel of 500x 2SK170s I bought from a supposedly reputable source ... are genuine ... or fake.

Thanks,
Andy
if they came from eBay or equivalent and especially from China, very likely they’re fake
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Old 8th June 2019, 11:07 AM   #22
davidsrsb is offline davidsrsb  Malaysia
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Quote:
Originally Posted by stormsonic View Post
Sometimes fakes are damn good and close to original specs, even outside dimensions are within specifications. Measuring only Idss is not enough.
o2SK170 = original Toshiba
f2SK170 = fake
I would not call that fake, the difference is within typical fab spreads, let alone any official second source
The noise measuremnet would be interesting
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Old 8th June 2019, 12:25 PM   #23
kamis is offline kamis  Serbia
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Take a look at the top of TO92 package. Real Toshiba fets and bipolars have a 2mm wide line in center. If it is shorter line at the side, transistor is fake.
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Old 10th June 2019, 04:57 AM   #24
andyr is offline andyr  Australia
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Quote:
Originally Posted by kamis View Post
Take a look at the top of TO92 package. Real Toshiba fets and bipolars have a 2mm wide line in center. If it is shorter line at the side, transistor is fake.
Brilliant, kamis!

Yes, the few genuine Toshiba 2SK170s I have, all have this thin raised line on top, in the centre, about 2mm long.

Whereas all the "suspect fake" ones I have ... have a line which is:
a. at the side - not in the centre, and
b. 1m long, max!

So I think this confirms they are fakes!

Andy
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Old 10th June 2019, 05:49 AM   #25
meanie is offline meanie  Singapore
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I bought a brand new Marantz CD63SE player in the late 90's, it had been in storage till i recently brought it out to mod, while bypassing the HDAM circuit, i accidentally found 2 pairs of J74/K174 Jfets (V grade) in the circuit.
But the issue was they looked fakes, with straight 7 printings.

How can Marantz do that ? or are these really fakes ? Or are there another licensed OEM Jfets makers during the 90's ?

I m still confused !

Anyone doing this HDAM bypass mod please verify too.
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Old 10th June 2019, 06:10 AM   #26
EUVL is offline EUVL  Europe
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So what makes you think that a professional company the size of Marantz would not have a proper purchasing and incoming QC department ?
And why would they not purchase their components directly from the manufacturer or their official distributors ?


Cheers,
Patrick
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Old 10th June 2019, 12:07 PM   #27
meanie is offline meanie  Singapore
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I totally agreed with you, that's why i m so puzzled by what i extracted out of their flagship cd player model in that era.

I believed CD67SE also have the same Jfets used in their HDAM circuits.
To get to the bottom of this, i encourage others whom are going to remove the HDAM in these CD players to take some pictures or video and share.
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Old 10th June 2019, 12:29 PM   #28
EUVL is offline EUVL  Europe
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To get to the bottom of this, YOU can do the simple measurements suggested by PMA in #post 9.


Cheers,
Patrick
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Old 10th June 2019, 12:35 PM   #29
andyr is offline andyr  Australia
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Quote:
Originally Posted by EUVL View Post
To get to the bottom of this, YOU can do the simple measurements suggested by PMA in #post 9.


Cheers,
Patrick
And yet, Patrick, 'Stormsonic' in post 19 showed that measurements of fake units can actually be pretty close to genuine ones.

Andy
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Old 10th June 2019, 12:40 PM   #30
meanie is offline meanie  Singapore
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When i bought new then, my Marantz cd player sings well all those years, after which its laser suddenly can't read any disc and retired into my storeroom till recently...

I can do that for testing the Jfets taken out of the cd player, but that's not my point, i was hoping that someone with those Marantz flagship cd players in those era, to take a real look of what Jfets are in their set visually first, then idss and pinch test follows later.

Just to prove that whether they do came in with the straight 7 printing in another set or not.
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