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LSK389/LS4391 jfets
LSK389/LS4391 jfets
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Old 22nd April 2013, 04:11 PM   #1
rellum is offline rellum  France
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Default LSK389/LS4391 jfets

Today, I got hard to find JFETs ordered at MICROSS.com in through hole TO71/18 package.
I asked for LSK389C and LS4391. The bags containing the parts are labeled that way, but on the metal cans, I can read «LSK389» and «LS439».
There is no printing on the parts about IDSS range like Toshiba did.
Some quick testing gives an IDSS of 2.9 to 5.4mA for the LSK389 and a pinch-off voltage of 2.9 to 3.5V for the LS493.
It seems I got LSK389A+B and LS4392. Not exactly what I expected...

Is it usual at LINEAR SYSTEMS not to print IDSS ranking or did I got fakes ?

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Old 23rd April 2013, 01:22 PM   #2
bear is offline bear
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LSK389/LS4391 jfets
check the Linear Systems website, download the pdfs and see what the standard markings are supposed to be?

Also you could try a direct email to Linear Systems, I do not know if they reply or not.

That and contact your distributor and let them know that you did not get what you ordered.

Somebody else may have better information...
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 23rd April 2013, 02:21 PM   #3
rsavas is offline rsavas  Canada
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Location: Ontario
Default Markings

I bought some LSK389 a while back. They were bought as IDSS "B" ranking, from a distributor in Florida,USA. They are in the SOIC8 pkg. I have yet to test/use these.
You are correct, there is no way to tell by looking at the markings, if they are actually "B" ranked.
I remember when Dennis Colin wrote the article LP797, in AudioExpress that he said that some of his tested samples did not meet the noise specs as stated on the spec. The article stated that he contacted them in this regard.
Unless you require, the dual matching, suggest to use a BF862 instead, you can probably get 25 of them for the same price as LSK389, in a can pkg.
0739 F

Sounds like a QA issues to me!!
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Old 23rd April 2013, 02:34 PM   #4
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
we had a group buy for LSK jFETs a few years back.
All the A & B & C grade lsk170 To92 came with identical marking.
regards Andrew T.

Last edited by AndrewT; 23rd April 2013 at 02:47 PM.
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Old 24th April 2013, 05:21 AM   #5
rellum is offline rellum  France
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Location: ALSACE
Thanks for your replies,

Perfect temp tracking was what I had in mind with those LSK389.
I will try LSK170, should do the job for a compound buffer.

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Old 24th April 2013, 05:54 AM   #6
PBNAUDIO is offline PBNAUDIO  United States
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Having tested many thousands of the Toshiba 2SK170/2SJ74 and their dual siblings 2SK389/2SJ109 the pinch off voltage you describe is way to high, 0.4 to 0.5V is what you should expect.

Best of luck

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Old 24th April 2013, 05:26 PM   #7
rellum is offline rellum  France
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Join Date: Jul 2004
Location: ALSACE
Hi Peter,

You're right about that. 2SK389/170 are low pinch off devices.

I was speaking about LS4391 wich have a higher one and I expected at least 3V at 6mA.
It's a good candidate as cascode device.

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