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Old 24th May 2013, 01:54 AM   #11
Einric is offline Einric  United States
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I bought my JFET's from Spencer & he even had matching pairs.

I got my IRFP240/9240's from Alweit on Ebay, again matched sets. He is from Israel so it takes a bit longer for them to arrive.
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Old 24th May 2013, 05:21 PM   #12
RS232 is offline RS232  United Kingdom
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I would say "know the seller you buy from"
All Jfets I bought from this seller were tested and compared with other Jfets I got from diystore and all were within tolerance (BL grade) and worked perfectly on the F4.
My last purchase was from Spencer here in the forum.
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Old 27th May 2013, 10:11 PM   #13
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Be careful I bought " high IDSS " J74 from Isreal and they were fakes.
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Old 27th May 2013, 10:25 PM   #14
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The 2SJ74 may very well be perfectly within tolerance for IDSS.

NONE of the ones I got from ebay or from other asian sources are genuine, there is a thread here about fakes, look for it, there are examples of the JFET fakes. Also some USA suppliers are just passing along fakes from asia.

The problem is mostly going to be the 2SJ74. The 2SK170 being offered may or may not be a real 2SK170, but it is easier to make N ch JFETs and the ones being offered work and curve trace ok.

The J74s I have obtained DO NOT match at all when curve traced.
The gains are different, as is the linearity.
But it is a functioning JFet, just not a Toshiba that is anywhere near a compliment to the K170.

This is not a low noise circuit, or one where low noise is required, so that aspect does not matter.

The performance of the amp in terms of harmonic distortion will be altered by the difference between the P & Nch JFETs in the front end. The amp will function regardless.

Hannes probably has legit parts. Spencer I have no information about.

Beyond this, it is apparent that JFETs and through hole parts in general are becoming rare quickly, and may end up being more difficult to source than tubes! Ironic.

_-_-bear -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 28th May 2013, 11:23 PM   #15
alazira is offline alazira  United States
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I concur with Bear. The K170's and SJ74's I've purchased through eBay in the past couple years were revealed as fakes on a curve tracer, even if their Idss happened to be within spec. I can confirm that Spencer's product looks genuine when curve traced. Unfortunately, he has been raising prices as things become scarce (can't blame him, supply and demand). Maybe Linear systems will one day bring their sj74 to market, but don't hold your breath.
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Old 30th May 2013, 03:59 PM   #16
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I have "reliable" information that this will occur.

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Old 30th May 2013, 04:25 PM   #17
Zen Mod is offline Zen Mod  Serbia
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I'm always finding Pa's words as same "reliable" , at least when he's serious ;

1M$ question is - when he's serious

my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
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Old 4th June 2013, 12:27 AM   #18
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Originally Posted by Nelson Pass View Post
I have "reliable" information that this will occur.

Papa our question is not if but when ? I ask that with all due respect to you. Regards
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Old 4th June 2013, 01:07 AM   #19
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The only thing is... the LSK170s that I acquired recently had somewhat different curves than the genuine SK170s that I compared them with...

...just sayin'
_-_-bear -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 4th June 2013, 01:43 AM   #20
EUVL is offline EUVL  Europe
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This is also our finding.

A team member of XEN who has the best equipment in the Team (R&S UPV) did extensive measurements on LSK170 compared to 2SK170.
As a result of his measurements, we immediately bought a life time stock of Toshiba devices from Japan even at premium prices.
(This supplier is now also out of stock.)

While most of the LSK170s meet noise specs, their distortion in a typical circuit is higher than 2SK170.
And they also need to be operated at much higher Vds than the Toshiba's.

So even though we are fully aware of the possible (since 2005?) availability of the LSJ74s, we shall continue to want to use Toshiba's in our DIY lifetime.
You only need to compare the annual budget for process development at Toshiba, to say the total turnover of Linear, to understand why.

And look around in all Japanese (as well as elsewhere) semiconductor manufacturers.
Who else has ever managed to put out a low-noise, high-Yfs P-JFET ?
Only NEC, years and years ago (2SK163 / 2SJ44).

A few years from now, Toshiba FETs will just become like NOS tubes from Telefunken etc.
You can still get new equivalent tubes from Russia or China these days, but they are just not the same.

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