Distribution of Idss in a bunch of random 2SJ74? - Page 2 - diyAudio
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Old 11th December 2011, 04:40 PM   #11
dodo is offline dodo  Poland
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funny
I messured lately around 200 pices SJ74 BL grade
All were in range 6,6 - 10,8 mA

those sj74BL , which shows high ( more then 12 mA) idss are usually fakes
( make the test , apply to them some Id 2-3 mA and mesure Vgs )
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Old 11th December 2011, 05:07 PM   #12
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The consideration of whether they are fakes or not depends a lot on what
you will be using them for. I have lots of examples of high Idss Jfets,
mostly used for choppers and stuff. They work fine, but do not meet the
noise spec of the Toshiba 2SJ74 and 2SK170's, and of course differ in
other ways, but it is my experience that they usually work well enough in
things like a BA-3. Worst case you degenerate them a little more to get the
current down to where you want it.

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Old 11th December 2011, 10:37 PM   #13
Floric is offline Floric  Europe
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Does anybody know where those fakes come from? Who produces the originals "behind" those fakes. As Nelson states, they are not the sj74 and have not nearly the specs. But there are many applications for p-cannel jets and not every application is a mc-preamp.

The available p-jfets I know have a rather low idss (1-5 mA) so it would be intersting to know a souce for parts like that.

Buying fakes (even if you would want them) is not a reliable source.

Regards

Flo
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Old 11th December 2011, 10:48 PM   #14
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i recently did a swap meet sale of 200 factory packaged j74's

https://docs.google.com/spreadsheet/...CKLl9ZcG#gid=0

none were anywhere near your outside figures .

cheers Woody
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Old 12th December 2011, 09:07 AM   #15
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Quote:
Originally Posted by Floric View Post
Does anybody know where those fakes come from? Who produces the originals "behind" those fakes.
They can either be genuine (but cheaper) parts with similar "general" specs / lower "specific" specs -like noise level-, that are relabelled, or rejects from bad production batches that are "stolen" from subcontractors trash bins before they receive the laser etching ... maybe not the company itself, but some of it's employees... there are places where everything is possible (apparently even stealing a wafer!)

I recently bought 10 off in China for 25 cents, just for fun (knowing that there was 99.99% chance they would be fake), and when they arrived I had a big laugh... the parts were polished by sand paper and laser re-labelled... dirty work!


Quote:
Originally Posted by Floric View Post
As Nelson states, they are not the sj74 and have not nearly the specs. But there are many applications for p-cannel jets and not every application is a mc-preamp.

Flo
Yes if the goal is to light a diode or so that's acceptable, but when they are in audio circuit, it's just impossible for many of us to accept that there is even the slightest possibility of them being fake....

you could prove me that it's unimportant for such or such application, but you know that audio is all about subjectivity , and if I had such a device in the DIY Pass Amp that I spent so much time building and cherry picking components, I'm sure I would only "hear" how harsh, thin and fake the sound would be !!!!

Fred
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Old 16th November 2012, 01:09 PM   #16
jeepy is offline jeepy  Switzerland
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Quote:
Originally Posted by Lazybutt View Post
They can either be genuine (but cheaper) parts with similar "general" specs / lower "specific" specs -like noise level-, that are relabelled, or rejects from bad production batches that are "stolen" from subcontractors trash bins before they receive the laser etching ... maybe not the company itself, but some of it's employees... there are places where everything is possible (apparently even stealing a wafer!)

I recently bought 10 off in China for 25 cents, just for fun (knowing that there was 99.99% chance they would be fake), and when they arrived I had a big laugh... the parts were polished by sand paper and laser re-labelled... dirty work!




Yes if the goal is to light a diode or so that's acceptable, but when they are in audio circuit, it's just impossible for many of us to accept that there is even the slightest possibility of them being fake....

you could prove me that it's unimportant for such or such application, but you know that audio is all about subjectivity , and if I had such a device in the DIY Pass Amp that I spent so much time building and cherry picking components, I'm sure I would only "hear" how harsh, thin and fake the sound would be !!!!

Fred

Hi Fred,
Old post but we never know?
I agree with you and I am also really upset with this growing fake market.
Do have any idea of good source? Do you know Electronique Diffusion in France? They seem to have all the transistors I need to resurect some circuits of l''Audiophile.'
Thanks,
Jean-Paul
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Old 16th November 2012, 01:52 PM   #17
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Afaik, all of the alleged 2SJ74s coming from asia and distributed from asia at this time are fakes.

Someone has sent me pix that show they are re-badged Fairchild devices, and not similar at all to bona fide Toshibas.

The best first pass way to check is with a curve tracer.

See attached images.
Attached Images
File Type: jpg ASIA SOURCE-2SJ74.jpg (324.9 KB, 260 views)
File Type: jpg TOSHIBA-2SJ74-NOS.jpg (290.7 KB, 254 views)
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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
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Old 16th November 2012, 02:09 PM   #18
jeepy is offline jeepy  Switzerland
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Quote:
Originally Posted by bear View Post
Afaik, all of the alleged 2SJ74s coming from asia and distributed from asia at this time are fakes.

Someone has sent me pix that show they are re-badged Fairchild devices, and not similar at all to bona fide Toshibas.

The best first pass way to check is with a curve tracer.

See attached images.

I just sent a listing of japaneese transistors to a company in Europe by email aking them which of them they can garantee. I hope to receive an answer!

I have a 2 traces scope but no curve tracer. Do you have any idea if I can add a 'not too expensive' module?
Thanks,
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Old 16th November 2012, 09:32 PM   #19
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there's a thread here on a not too expensive PC based tracer, complete here...
__________________
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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
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Old 16th November 2012, 11:10 PM   #20
alazira is offline alazira  United States
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DIY Curve Tracer for PC

Lockyz's device can be purchased on eBay
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