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Replacement For Toshiba 2SK170/2SJ74
Replacement For Toshiba 2SK170/2SJ74
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Old 25th March 2018, 05:39 PM   #81
WalterW is offline WalterW  Netherlands
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Replacement For Toshiba 2SK170/2SJ74
Quote:
Originally Posted by NicMac View Post
This is correct for the average FETs. In practice variation is quite big and to do the job well you will have to actually measure the FETs and find those where it works. But as I understand that is not your cup of tea as long as somebody else spoon feeds....

By the way, I did buy and test a couple of those Toshiba 2SJ74-GR you found at Reichelt.de and they are indeed fakes (way to low transconductance).
I have been measuring different JFET´s and found nice matching curves with a 2SK170 of 8.2 mA and a 2SJ74 of 9.0 mA and around 2.4 Ohm extra resistance for the 2SJ74, 5 Ohm was a bit too much. The higher Idss the JFETs are, the lower the difference between the two resistors can be.
But like NicMac said you have to measure them individually to get good results.
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Old 3rd April 2018, 05:19 PM   #82
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by WalterW View Post
But like NicMac said you have to measure them individually to get good results.
I think I posted it here, if you extract the beta parameter over a reasonable set of operating conditions the basic FET equations can give you good results even with equal degeneration resistors. I recently sorted 170/74 pairs for 0 offset with 25 Ohms in both sources, and still got 0.003% THD at line level. It's a no trim solution. By no trim I mean that zero offset and (near) minimum THD can be achieved without pots.

As for using trim pots I posted years ago the complimentary JFET input stage where the current ratios could be trimmed. You have two degrees of freedom you can trim offset and drift to 0 or offset and 2nd harmonic to 0 all with totally unmatched FET's.
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Old 3rd April 2018, 07:14 PM   #83
Soundhappy is offline Soundhappy  France
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I dream Linear Systems jfet's are available at Mouser , DigiKey , RS etc.
http://www.linearsystems.com/lsdata/...%2010%2006.pdf
http://www.linearsystems.com/lsdata/...%2008%2028.pdf
and indeed his duals version. Metal can package are handy
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Old 3rd April 2018, 09:03 PM   #84
NicMac is offline NicMac  Italy
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Replacement For Toshiba 2SK170/2SJ74
Dream that they will be available from main suppliers, AND that they will be as good as the Toshiba's
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Old 1st May 2018, 04:24 PM   #85
adason is offline adason  United States
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different question gents...those of you who received fake 2sk170, any one figured what actual jfets were used as donor to be relabeled?

even they are lower transconductance, they may be used with some mods to the circuits in active crossovers or phono preamps

anyone? are they easily identifiable by some parameters?
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Old 1st May 2018, 04:27 PM   #86
6L6 is offline 6L6  United States
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Replacement For Toshiba 2SK170/2SJ74
Very high noise compared to the real thing, and nowhere near as linear, leading to much higher distortion.

This seller is known by Nelson to have genuine Toshiba Jfets.

Toshiba 2SJ74 + 2SK170 LAB MATCHED QUAD to 0.03mA AND 4mV (7ma range) | eBay
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Old 1st May 2018, 06:39 PM   #87
adason is offline adason  United States
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thanks 6L6, but I was not looking for that info, I already know that, plus I only buy from diystore...
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Old 1st May 2018, 06:44 PM   #88
6L6 is offline 6L6  United States
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Replacement For Toshiba 2SK170/2SJ74
You’ll need to buy from him if you want Jfets. Linear isn’t able to make the J74s in any good quantity lately...
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Old 1st May 2018, 07:46 PM   #89
adason is offline adason  United States
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I got some in advance
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Old 1st May 2018, 07:50 PM   #90
adason is offline adason  United States
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btw, I got plenty of mpf102, long time ago from digikey, so I assume original

how bad are those? too noisy?
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