Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

How to identify fake JFETs?
How to identify fake JFETs?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 16th June 2019, 12:57 AM   #71
808eengr is offline 808eengr
diyAudio Member
Join Date: Feb 2019
I don't doubt that there are fake parts all over the place out there. Was just trying to find out why the LCR-T4 tester was giving different results.

...Apparently my testing error is quite obvious. If anyone could point out what the obvious testing error is it would go a long way in making the criticism constructive.
  Reply With Quote
Old 16th June 2019, 09:32 PM   #72
PRR is offline PRR  United States
diyAudio Member
PRR's Avatar
Join Date: Jun 2003
Location: Maine USA
Originally Posted by scott wurcer View Post
I don't understand the continued mis-understanding here you CAN'T test and N channel JFET as an NPN transistor.
It's well known that these little totally automated testers do OK for 99% of parts, but sometimes go down the wrong path.

The tester does what you would do with unknown part and orientation: poke some juice at it and try to interpret it as some class of device, then measure like it was that class.

No, the user can't give the tester a clue.

These things were written by Programmers. Any transistor-man would know that hFE=99K is bogus, even 2K is dubious; but the programmers didn't know this.

I went into the notes and code once, it's all open-source. But too complicated for me. The algorithms and decision-points have been changed over the years, they are better. Maybe the one he has uses an older code; maybe so few people use high-Gm JFETs that this screw-up has not bubbled to the top of the bug-list.

IAC it is trivial to rig a battery and two meters (one is less convenient) and measure JFETs the right way.
  Reply With Quote
Old 17th June 2019, 07:24 AM   #73
DualTriode is offline DualTriode  United States
diyAudio Member
Join Date: Aug 2009
Location: Nor Cal
Yes, that is more than a bit harsh.

I too purchased a cheap $20.00 transistor tester it also incorrectly identified a bag of JFETs as NPN transistors.

The cheap $20.00 transistor tester was intended to do a quick screening. In this case it did not work out so well.

Thanks DT
  Reply With Quote
Old 17th June 2019, 01:34 PM   #74
adason is offline adason  United States
diyAudio Member
adason's Avatar
Join Date: Nov 2004
Location: Maryland
I too have that cheap tester, and I find it very useful. It never happened to me that it would identify jfet as npn transistor.
I use this guidelines (Fig 9) to construct curves to match jfets:
Biasing JFETS

The tester has limitations, but for quick Idss selections its ok. Plus it measures caps, resistor, diods, you name it. Not bad for $20.
  Reply With Quote
Old 17th June 2019, 02:17 PM   #75
Zung is offline Zung  Switzerland
diyAudio Member
Join Date: Apr 2005
Location: Geneva
It's more like $10 shipped: for that price, no complain, but it doesn't do FETs; for these, I use EUVL's jig. Next, I'll add Vp as per PMA.
  Reply With Quote
Old 17th June 2019, 02:44 PM   #76
Trollet is offline Trollet  Sweden
diyAudio Member
Trollet's Avatar
Join Date: Jul 2015
Location: Westcoast
How to identify fake JFETs?
I have a DCA-75 PRO and it works with Most component, but sometimes it fails with Lateral fets.
I don't match them with the DCA anyway, but had to check if it worked.
Hfe test for small signal BJT's seems to work fine with resonable tolerance.

  Reply With Quote
Old 17th June 2019, 05:51 PM   #77
w5jag is offline w5jag  United States
diyAudio Member
Join Date: Feb 2007
Location: Arkansas
I love the convenience of the Mega328 tester.

Mine has also mistakenly auto detected JFET's as bipolar transistors.

They are terrific considering the cost, but some user intuition is still required. It has never gotten an EBC pinout wrong on a bipolar device, and when it detects a JFET, it gets that right also.
  Reply With Quote
Old 17th June 2019, 11:15 PM   #78
808eengr is offline 808eengr
diyAudio Member
Join Date: Feb 2019
Seeing how many of the diy circuits measure values at certain steps only gets me thinking... maybe it would be nice to have an Arduino based curve tracer. Could always start with a simple breakout/hat, and can be written in C.

Matlab simulink has lots of interesting features. Last semester there was a guy in one of my project classes using Matlab Simulink and an Arduino DUE as as DAQ for a marine thruster. The sample rate is low but seems like there is potential for much more analysis once the data is in Matlab.

That said the cheap tester is convenient for identifying most parts plug it in push the button. Beyond that it seems like there might be room for another solution once the device type and pinout are known and one is trying to find the device parameters.

C code easily generates a Matlab best fit line graph, it was one of my lab homework problems last semester. Maybe I'll break down and get an arduino after all. And try to figure out to make the code generate excel best fit line.
  Reply With Quote
Old 18th June 2019, 01:55 AM   #79
davidsrsb is offline davidsrsb  Malaysia
diyAudio Member
Join Date: Dec 2005
Location: Kuala Lumpur
Most cheap tracers sense source current by voltage drop measurement across a source resistor. When Vgs is very low as in laterals and high Gm jfets, this does not work unless there is a gain stage after a low value sense resistor before the ADC
  Reply With Quote
Old 20th June 2019, 03:41 PM   #80
stereohifi is offline stereohifi  Canada
diyAudio Member
Join Date: Nov 2012
Location: Repentigny, QC, CND
About thoses? I haven't tested or tried them!
Attached Images
File Type: jpg P1010220.jpg (261.3 KB, 58 views)
File Type: jpg P1010221.jpg (254.6 KB, 59 views)
  Reply With Quote


How to identify fake JFETs?Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
How to identify Fake Transistors? Jrp27 Parts 20 22nd July 2019 07:18 AM
2SA1215 2SC2921, identify genuine and fake Sunmansli Solid State 10 15th May 2018 03:51 PM
How to identify a fake Toshiba transistor? Audio Maniac Parts 1 7th July 2012 08:06 PM
Is there ANY way to identify a fake LM3886 before buying one ??? MrAdel1984 Chip Amps 9 4th April 2012 07:55 PM
how to identify fake transistors Wagener Solid State 4 6th May 2004 01:46 PM

New To Site? Need Help?

All times are GMT. The time now is 12:41 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio