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Replacement For Toshiba 2SK170/2SJ74
Replacement For Toshiba 2SK170/2SJ74
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Old 7th July 2018, 12:37 PM   #181
woofertester is offline woofertester  United States
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I have collated the test results of many 2SJ74 devices that I have purchased from several sources.

The Toshiba datasheet states that minimum gain for a 2SJ74 is 8 milli-Siemes. There is a range of Idss and gain for the 2SJ74 devices that I have measured.

The Idss and gain were measured "cold". No warm-up period.

The cold Idss varied from 7mA up to 14.5 mA. The cold gain varied from 1 milli-Siemes to about 5 milli-Siemens. To me, the results indicate that all of these devices are fake 2SJ74. They appear to be real JFETs but are likely some lesser device that is easily obtained for cheap and intentionally marked to mislead. The lowest Idss devices have the lowest gain and the highest Idss devices have the highest gain.

The number of device tested is well over 100 devices. They were tested on a keithley 2636B running a script that measures Idss then the Vgs at current points above and below 5mA and at 5mA to extract gain above and below 5mA.

Once the script is written, it is a rote exercise to test all of the parts. The most time consuming part is copying results to a text editor, printing the results and cutting up the paper to store with the device in a bag. A faster solution would be to have a printer spit out the test results immediately after the test.
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Old 7th July 2018, 04:33 PM   #182
NicMac is offline NicMac  Italy
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Replacement For Toshiba 2SK170/2SJ74
Quote:
Originally Posted by woofertester View Post
The Toshiba datasheet states that minimum gain for a 2SJ74 is 8 milli-Siemes.
The gain I calculate at Idss from the transfer functions of curved traced 2SK170BL and 2SJ74BL JFETs always exceeds 30 mS.
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File Type: pdf ToshibaFetscape.pdf (158.8 KB, 91 views)
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Old 8th July 2018, 04:28 PM   #183
woofertester is offline woofertester  United States
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Quote:
Originally Posted by NicMac View Post
The gain I calculate at Idss from the transfer functions of curved traced 2SK170BL and 2SJ74BL JFETs always exceeds 30 mS.

A picture is worth a thousand words. Thanks. That graph is enormously helpful.


Another helpful test result would be some measure of linearity at Idss and at some useful voltage excursion or a plot of distortion vs voltage excursion as seen in NP's write-ups. The final useful test result would be noise in nV per root hertz.
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Old 8th July 2018, 04:35 PM   #184
MEPER is online now MEPER  Denmark
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What are the applications for the highest grades versions (with lowest Idss)?
Is that for amplifying very small signals like from MC pickups?
Is there any Pass applications where this grade is the preferred?
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Old 8th July 2018, 05:05 PM   #185
jacco vermeulen is offline jacco vermeulen  Netherlands
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Quote:
Originally Posted by NicMac View Post
The gain I calculate at Idss from the transfer functions of curved traced 2SK170BL and 2SJ74BL JFETs always exceeds 30 mS.
Which corresponds with the transconductance graphs in the datasheets of both for an Idss>6.5mA
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