Are these fake 2SK389?

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I hope this is the correct forum to post........so are these fakes? besides physical appearance , anyway to verify their authenicity?

P1010039.jpg


P1010033.jpg
 
it's usually power transistors that get faked. these look like maybe multiple jfets or jfet dual diff amps. actually checking the datasheet, they're dual jfets on a single substrate, for diff amps, etc...

i doubt they're fakes. you could measure Idss, but the datasheet says the Idss can be anywhere from 2.5 to 20 ma.

a better way would be to measure the differential Vgs. you apply 10 volts across the D-S on both transistors and meaure between the gates. the difference between the two gates should be 20mV or less.

that will be a more difficult characteristic to fake with two dicrete fets in the same package.
 
I bought the same Jfets from ebay (audiotek168 seller).. i received them last friday.

I havent tested them yet but their physical appeance tells me that they look geniune i think.. I've seen photos of the fakes 389 in the last groupbuy.

the pins of this jefts are very different from the groupbuy..they dont have solder and all pins are square not rounded..
 
hi folks,

This is what i did. I short the Gate and Source to ground, attached a 20ohm resistor to the drain, then applied a 9V battery. Current drawn 6.77mA ~ 7.5mA for all 4 pieces. is this the correct way to get IDSS or am i doing it incorrectly? i attached a multimeter to measure the current drawn for easy viewing in picture form :
An externally hosted image should be here but it was not working when we last tested it.
 
so should i go ahead to order more of these or should i throw them into the bin ? some expert here in singapore who sold lot of transistors in this forum in the past told me that they are fakes from the physical look of the legs...:D , and that he has a small lot of the originals which look differently...
 
commstech said:
hi folks,

This is what i did. I short the Gate and Source to ground, attached a 20ohm resistor to the drain, then applied a 9V battery. Current drawn 6.77mA ~ 7.5mA for all 4 pieces. is this the correct way to get IDSS or am i doing it incorrectly?
Check the voltage drop across the drain resistor (20r) It should be between 135mV and 150mV if the ammeter reading is correct.

Check also the match between the two FETs on the same die.
 
AndrewT said:
Check the voltage drop across the drain resistor (20r) It should be between 135mV and 150mV if the ammeter reading is correct.

Check also the match between the two FETs on the same die.
Hi Andrew,

the voltage drop is absolutely correct. hmm, i did not check the match though. i merely tested one FETs per chip. no problem, can do that easily. will report. but is my way of obtaining IDSS correct?
 
commstech said:

Hi Andrew,

the voltage drop is absolutely correct. hmm, i did not check the match though. i merely tested one FETs per chip. no problem, can do that easily. will report. but is my way of obtaining IDSS correct?

your method is very close now that you have confirmed that the ammeter readings are correct.
Idss is usually measured at a fixed Vds. Your test starts with ~9V and loses 135 to 150mV.
So I guess your Vds is ~8V to 8.5V.
The spec Idss for the 389 is @ 10Vdc.
Matching is guaranteed to better than 0.9:1 i.e. <11%
 
The fakes in the group buy were easily detected as they were bipolar transistors and not jfets. So measuring IDSS gave insane currents as the forward current of a diode was measured.

Further the fakes had differently long legs (the front row shorter than the back row) that were slightly roundish due to being tinned. The argument was that the fakes were simply not fakes per se, but relabeled dualbjts from Toshiba desoldered from old gear.

If IDSS is fine and about equal for both jfets in the duals, I would say you're fine.

Unless they have differently long legs which could mean they are used parts ripped from old gear.

Have fun, Hannes
 
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