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Original 2SK170 / 2SJ74 GB

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#21
Thanks Soundhappy!

I am not sad, at least, I have found out that these are not real 🙂
Sorry for anyone who got too hyped about the JFETs.
Just one more question. (As someone who doesn't know this JFET at all) If the Idss is within range, and it is a fake, what could be the difference?

Thanks again
 
#22
For sure not the same high audio quality , low noise etc.
 

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#27
Hi Sound happy, the pictures of the fakes look like the genuine parts I have. there are lots of threads on this site where someone has called fake on genuine parts. If you didn't have so many jfets, wouldn't you spend 3 dollars on a pair to test? Obisix, I am happy to pay for the test parts🙂
 
#28
Hi Luke,

A few dollars to test isn't such a bad thing. At least it would satisfy your curiosity.

That said, some of the Id figures Obisix measured do give me concern. For example,
the Idss for the '2sj74bl' sample is in the right range, but Id=1.8mA @ Vgs=1.2V is
quite a bit higher than what I expect. If you look at the Id-Vgs graph on page 2
here:

https://www.mouser.com/ds/2/408/6903-18063.pdf

you would expect the Vgs to be less than 0.4V for that current.

So that sample looks to me like a low transconductance part and not a 2sj74.

Cheers,
Dennis
 
#30
The problem with fakes tends to crop up more with power devices where a lower powered device has been substituted for the real device and has been remarked.
I bought some irffp9240 off ebay and when I unplugged my soldering the glitch on the mains blew it up. So I bought some from RS Components and despite trying very hard plugging and unplugging my soldering iron it wouldn't blow up. I can only guess the fake part blew up at a lower voltage than the real part.
 
#31
Dennis Hui said:
Hi Luke,

A few dollars to test isn't such a bad thing. At least it would satisfy your curiosity.

That said, some of the Id figures Obisix measured do give me concern. For example,
the Idss for the '2sj74bl' sample is in the right range, but Id=1.8mA @ Vgs=1.2V is
quite a bit higher than what I expect. If you look at the Id-Vgs graph on page 2
here:

https://www.mouser.com/ds/2/408/6903-18063.pdf

you would expect the Vgs to be less than 0.4V for that current.

So that sample looks to me like a low transconductance part and not a 2sj74.

Cheers,
Dennis
Click to expand...

hi Dennis, I didn't read that part. So if we know they are not real why are we all talking about them🙂 Its a pity, but its not always the case. I found a little stash of well priced jfets not long ago which I shared/swapped with a couple of local diy buddies. From what I have seen on this forum, photos can be deceiving.
 
#37
Soundhappy said:
Hi Dennis

This batch of jfet's from China was tested by mesurements many times by different Diyers in the old threads

Thx and best regards 🙂
Click to expand...

Did they check breakdown voltage ?

I bought some irfp9240 off ebay and they blew up from a spike on the mains. I replaced it with an RS Components part and tried hard to blow it up but couldn't. From that I have to assume the breakdown voltage was poor on the ebay part.
 
#40
jpr_pt said:
I saw at Reichelt they have the 2SK170 and 2SJ74. I got quite a few of 2SK170 bought at Mouser. But I need some genuine 2SJ74.
Does anybody has experience with the Reichelt and their 2SJ74?
Click to expand...

Hi,

my experience with Reichelt is, that if a manufacturer is shown, then the chances are very high that they are genuine.
If not, you don't know what you get. Could be anything from anywhere labeld SJ74.

But
Micha
 
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