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Old 16th May 2014, 09:21 AM   #531
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Quote:
Originally Posted by davidsrsb View Post
Vgs of -1V should cut the part off completely. This is an unusually high Gm and will reveal if the supplier is genuine or packaging matched 2n3819 die
With Gate at 0 V ==> 10,3 mA; at - 0,9 V ==> 0 mA
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Old 16th May 2014, 06:00 PM   #532
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That looks right for the authentic part to me
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Old 17th May 2014, 02:20 PM   #533
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Quote:
Originally Posted by janegood View Post
With Gate at 0 V ==> 10,3 mA; at - 0,9 V ==> 0 mA
At $35/ea from that seller I would hope they are authentic, but if you have to have those parts then I guess they are worth the price. BTW The seller goes through great pains to tell people how to tell if they are buying fakes. Also, if you are going to buy any electronic parts on Ebay click on the sellers feedback and then click on the negative feedback. If you see multiple entries that say, counterfeit or fake transistor you can be virtually guaranteed that you are throwing your money away on a rare part like these dual Jfet's.

The Ebay seller you bought these parts from has a squeaky clean feedback record for someone with > 16000 feedbacks in the last year.
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Last edited by Chamberman; 17th May 2014 at 02:22 PM.
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Old 17th May 2014, 09:29 PM   #534
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btw, if anybody is interested, here's where you can find out what devices (the link shown is for bipolars) what devices are in current production by toshiba.....
Transistors | Products | TOSHIBA Semiconductor & Storage Products Company

their authorized distributors can be found here....
http://www.semicon.toshiba.co.jp/eng/buy/index.html
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Last edited by unclejed613; 17th May 2014 at 09:32 PM.
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Old 17th May 2014, 10:59 PM   #535
davada is offline davada  Canada
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A good test is to take some acetone or lacquer thinner on a Qtip and see if this removes the part number. If it does then it's fake. Breakdown voltage test is another good indicator. But do current limit the applied voltage or you'll have a small fire on you hands. A VI curvetrace test is tell all.
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Old 17th May 2014, 11:05 PM   #536
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Quote:
Originally Posted by davada View Post
A good test is to take some acetone or lacquer thinner on a Qtip and see if this removes the part number. If it does then it's fake. Breakdown voltage test is another good indicator. But do current limit the applied voltage or you'll have a small fire on you hands. A VI curvetrace test is tell all.
somewhere i have a schematic for a jfet curve tracer..... i think it came from a very old (1970) NatSemi app note book.... darn, now i have to go digging through my old data books.... there's so much good stuff in there i might get lost or sidetracked....

some jfet measurement methods can be found in the app note section of this data book... http://www.datasheetarchive.com/dl/S...cansUX9527.pdf
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Last edited by unclejed613; 17th May 2014 at 11:17 PM.
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Old 17th May 2014, 11:28 PM   #537
jcdrisc is offline jcdrisc  Australia
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Linear Systems make the LSK389 which is a current equivalent of the Toshiba part
No need for hand wringing about counterfeits
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Old 18th May 2014, 12:06 AM   #538
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found a schematic for a bjt curve tracer here: http://www.changpuak.ch/electronics/...Schematics.pdf

still looking for the jfet tracer.... i do remember it used a ramp generator and a cmos counter+resistor ladder with the counter driven from the ramp generator clock.....
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Old 18th May 2014, 12:30 AM   #539
davada is offline davada  Canada
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Quote:
Originally Posted by unclejed613 View Post
found a schematic for a bjt curve tracer here: http://www.changpuak.ch/electronics/...Schematics.pdf

still looking for the jfet tracer.... i do remember it used a ramp generator and a cmos counter+resistor ladder with the counter driven from the ramp generator clock.....
We used this one back in electronics school. Works pretty good to compare samples.

Curve Tracers
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Old 18th May 2014, 03:10 AM   #540
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well, i thought i'd take a chance and browse through TI's archive of app notes, hoping they had kept NatSemi's collection complete..... no such luck... looks like i need to make a trip out to the storage locker and pull my data book collection.....
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