Replacement For Toshiba 2SK170/2SJ74

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.
 
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.
 
Purchase of matched pairs of SJ74/SK170's

Hello NicMac,

do I read the link at the bottom of your messages correctly saying, that one can order from you devices per the list behind the link? May I make use of this oppoturnity? If so I guess, we can continue on this specific subject by mail separately not to bore the rest of the community.
 
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Hello NicMac,

do I read the link at the bottom of your messages correctly saying, that one can order from you devices per the list behind the link? May I make use of this oppoturnity? If so I guess, we can continue on this specific subject by mail separately not to bore the rest of the community.
Yes - my signature contains links to lists of FETs up for sale.
Contact me by PM if interested, but as I'm currently traveling I will not be able to ship anything until August 16th. Sorry:(
 
I measured Idss according to this scheme. On the example of one sk170bl: I measured Idss 5.51mA and Vds 3.01v. The pdf states that the test condition is Vds = 10V. Is my measurement correct?
 

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I found such a simple calculator rjm/1326-matching-jfets.html to measure jfets and measured my jfets according to it using a 9v battery. For 2sj74 I reversed the power connection. Here are the results:
2sk170bl:
Vgs0=0,48V (0,54V)
Idss=6,5mA (8,2mA)
Ids= 3mA
g_m at Ids = 18,2mS (18,6mS)

2sj74bl
Vgs0= 2,42V(2,47V)
Idss=10mA(10,1mA)
Ids = 3mA
g_m at Ids =4,5mS(4,5mS)
Thera are not matched but sj74 are genuine?