Strange 2sj74s

Atilla · 3rd December 2009, 08:06 AM

I received a batch of what are supposed to be 2sj74 transistors. They appear to have proper markings on them. It says BL grade.

However - I measured all of them, looking for some matches. They all appear to be GR grade, as the Idss varies between 2.7 and 4 mA.

I tested them the same way I tested a batch of 2sk170s - 9V regulated supply, just reversed the polarity accordingly.

Is it possible to have such low batch of Idss in BL grade? Are they marked incorrectly or simply fake? Is there any way to find that out?

That being said ... if they're the real deal, but just with low current, is there anything I can use them for except constant current sinks with that low Idss?

h_a · 3rd December 2009, 10:50 AM

Did you use a resistor to measure IDSS or set your DMM to current? If you used a resistor and by accident put it between Source and Gate, you got degeneration, ie. reduced IDSS.

If not, well...then they're not BL and then probably not 2SJ74. But at least jfets. You can test transconductance, but if these are not genuine J74 they are likely low transconductance and also not low noise parts.

In case you don't want/can't to send them back, you can use them for differential pairs as these are usually run at about 1mA.

Have fun, Hannes

Atilla · 3rd December 2009, 11:35 AM

No, DMM set to current. I don't think I did a mistake (this time, hehe)

Definitely not BL grade then. I can see about checking transconductance, if at least that is in the proper range there might be hope for them.

I'll try to talk with the supplier, IIRC I got them from a reliable place, but it was a while ago, so I don't know how that'll work out.

Oh well, I'm sure I could find some uses for them in the long run. I'll keep them out of critical applications though.

3rd December 2009, 08:06 AM	#1
Atilla Soldering Gun Fanatic diyAudio Member Join Date: Jul 2008	Strange 2sj74s I received a batch of what are supposed to be 2sj74 transistors. They appear to have proper markings on them. It says BL grade. However - I measured all of them, looking for some matches. They all appear to be GR grade, as the Idss varies between 2.7 and 4 mA. I tested them the same way I tested a batch of 2sk170s - 9V regulated supply, just reversed the polarity accordingly. Is it possible to have such low batch of Idss in BL grade? Are they marked incorrectly or simply fake? Is there any way to find that out? That being said ... if they're the real deal, but just with low current, is there anything I can use them for except constant current sinks with that low Idss?

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3rd December 2009, 10:50 AM	#2
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	Did you use a resistor to measure IDSS or set your DMM to current? If you used a resistor and by accident put it between Source and Gate, you got degeneration, ie. reduced IDSS. If not, well...then they're not BL and then probably not 2SJ74. But at least jfets. You can test transconductance, but if these are not genuine J74 they are likely low transconductance and also not low noise parts. In case you don't want/can't to send them back, you can use them for differential pairs as these are usually run at about 1mA. Have fun, Hannes

3rd December 2009, 11:35 AM	#3
Atilla Soldering Gun Fanatic diyAudio Member Join Date: Jul 2008	No, DMM set to current. I don't think I did a mistake (this time, hehe) Definitely not BL grade then. I can see about checking transconductance, if at least that is in the proper range there might be hope for them. I'll try to talk with the supplier, IIRC I got them from a reliable place, but it was a while ago, so I don't know how that'll work out. Oh well, I'm sure I could find some uses for them in the long run. I'll keep them out of critical applications though.

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