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Old 17th November 2012, 05:20 AM   #21
jeepy is offline jeepy  Switzerland
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DIY Curve Tracer for PC

Lockyz's device can be purchased on eBay
Got it. Brilliant!
Thanks a lot
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Old 17th November 2012, 08:07 PM   #22
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I ordered 40 2SK170GR. I was able to get 16 matched pairs but Idss values range within the valid GR range. See overlaid graph of curves for all 40 Jfets. Second picture is 2 pairs matched, 4 jfets. I did not paid much attention to the specific Idss (vertical not fine calibrated) but dividing the vertical by 3 gives the approximate Id values. On the pairs shown, there is roughly 1ma difference between the pairs.
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Old 18th November 2012, 09:45 AM   #23
Dzius is offline Dzius  Poland
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I odered 30 pieces of 2SK170BL from China several month ago. They are very consistent in Idds around 9,57mA. Are they fake or original then ? Should they have more random Idds ?
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Old 18th November 2012, 11:47 AM   #24
jeepy is offline jeepy  Switzerland
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I odered 30 pieces of 2SK170BL from China several month ago. They are very consistent in Idds around 9,57mA. Are they fake or original then ? Should they have more random Idds ?
You are lucky. Some Xtors from China are probably good. Who is the seller?
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Old 19th November 2012, 12:20 AM   #25
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Originally Posted by Dzius View Post
I odered 30 pieces of 2SK170BL from China several month ago. They are very consistent in Idds around 9,57mA. Are they fake or original then ? Should they have more random Idds ?
That's unclear.

merely having the requisite Idss doesn't tell us much about the device.

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Old 19th November 2012, 12:23 AM   #26
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Originally Posted by avincenty View Post
I ordered 40 2SK170GR. I was able to get 16 matched pairs but Idss values range within the valid GR range. See overlaid graph of curves for all 40 Jfets. Second picture is 2 pairs matched, 4 jfets. I did not paid much attention to the specific Idss (vertical not fine calibrated) but dividing the vertical by 3 gives the approximate Id values. On the pairs shown, there is roughly 1ma difference between the pairs.

Those curves don't say much because they are overlaid so much.

Maybe you could post just the "2SJ74s" like one typical, and one typical of the 170s?

Same settings...

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Old 21st November 2012, 10:49 PM   #27
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Those curves don't say much because they are overlaid so much.

Maybe you could post just the "2SJ74s" like one typical, and one typical of the 170s?

Same settings...

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That was the point, to show that the curves are all over the place (forming almost a solid forground) but still within spec for Idss. I was able to ger 16 pairs, but i doubt i can get more than a couple of quads.

I dont have 2sj74s, i am building a simetrical b1 buffers.
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Old 21st November 2012, 11:20 PM   #28
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I would expect the curves to not coincide.

What is most important is to see if they are genuine parts or not.
Based on the physical similarity between the currently available "170" and the "74" parts I am skeptical of the K170 parts. However, they appear to be much closer to the expected curves when I measured the ones I purchased.

Super matched (virtually identical curves) may not be terribly important in most buffers due to the feedback that is usually applied to get it to unity gain...

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Old 22nd November 2012, 06:13 AM   #29
h_a is offline h_a  Europe
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Why don't you simply check for transconductance?

I'm not aware of any part that offers the IDSS and the transconductance of the K170/J74, which is exactly the reason there is no 1:1 replacment. There are some parts that have the same IDSS (that could be relabeled), but much lower transconductance.

If the part meets IDSS and transconductance, then the only thing in question that remains is low noise and that is truly not easy to check with simple means. The fakes I've seen so far are very cheaply made with not much of an effort to hide it.

By the way, now and then it happens that one jfet is slightly out of spec, but that's more like 13-14mA at most. I haven't seen a 17mA BL part. Even big semiconductor factories are not perfect. Any case as long as transconductance is ok, use it!
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Old 22nd November 2012, 06:51 AM   #30
nr12 is offline nr12  Germany
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Hello Hannes,

do you have a tip for us how to determine the transconductance "on the kitchen table"?

thanks

Ulf
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