2SK170BL and 2SJ74BL

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Russellc

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Joined 2003
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#1
Just wondering, Surely there are other devices, but most of the Pass Items require these two J-fets. Obviously, they are slowly going away. Most of the Pass projects require them.

Once gone, what will be the standard replacement, or other complemetary pairs the will accomplish the same goal? I recall one company has a 2SK170BL replacement, but no 2SJ74BL replacement.

Just wondering,

Russellc
 
#2
Linear Systems is making the LSK170 and we hope to see production of their
LSJ74 soon.

There are some complementary parts (usually designed as switches) which
can serve in power amplifiers, and there still is significant stock on the
originals - you just have to pay a premium for them.

😎
 
#3
Yes Nelson there must be somewhere genuine parts but in past weeks i bought 2sj74BL from schuro, utsource and NIKKO and they all measure between 17ma and 20ma Idss......

i would like to buy genuine ones...but where ?
😕

PS: i did test my setup with other genuine ones i have , that i had previously tested and these confirmed the values.
 
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#5
CeeVee said:
Yes Nelson there must be somewhere genuine parts but in past weeks i bought 2sj74BL from schuro, utsource and NIKKO and they all measure between 17ma and 20ma Idss......

i would like to buy genuine ones...but where ?
😕

PS: i did test my setup with other genuine ones i have , that i had previously tested and these confirmed the values.
Click to expand...

Test them for transconductance. 2SJ74BL's shouldn't have Idss anywhere near that high.

You can use the GR rated devices.
 
#8
CeeVee said:
2sj74BL from .... and they all measure between 17ma and 20ma Idss......
Click to expand...

They would be most certainly fakes, I am afraid. I bought parts labeled as '2SJ74' from one HK supplier, as a trial. They also measured some 17 - 20 mA Idss. But have low transconductance AND noise higher about 20 - 30dB at low frequencies. I test the parts in my discrete preamps and noise spectrum + FFT distortion measurement are the best answer if the part is fake or not.

Regards,
 
#10
I also have quadruples from Spencer...genuine stuff, all measure as you say.

The 2SK170BL are not a problem it seems, i have plenty, all tested and matched.

It's the 2SJ74BL that are much more scarce that are the problem.
🙁
 
#13
masag1 said:
I've bought mine from a Chinese supplier at DH Gate webside.

Range is from 3mA to 22mA.
....
Click to expand...

Thanks for your image, masag1. The 2SJ74BLs bearing the code "7C" have already been described as fakes by @h_a here:

http://www.diyaudio.com/forums/pass-labs/121228-f5-power-amplifier-1033.html#post2476459

Now you can guess that these "High Idss 2SJ74BL" offered here

20 X 2SJ74BL (10 Matched pairs) - HIGH IDSS | eBay

are also fakes (Seller says: They were manufactured in Malaysia)
 
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#14
CeeVee said:
Yes Nelson there must be somewhere genuine parts but in past weeks i bought 2sj74BL from schuro, utsource and NIKKO and they all measure between 17ma and 20ma Idss......
....
Click to expand...

PMA said:
They would be most certainly fakes, I am afraid. I bought parts labeled as '2SJ74' from one HK supplier, as a trial. They also measured some 17 - 20 mA Idss. But have low transconductance AND noise higher about 20 - 30dB at low frequencies. I test the parts in my discrete preamps and noise spectrum + FFT distortion measurement are the best answer if the part is fake or not.

Regards,
Click to expand...

@CeeVee and PMA:

What's the batch code of your fake 2SJ74s?
Thanks for the information!
 
#16
I am attaching photos of genuine parts and fakes.
 

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