Fakes are definitely in the market!
My genuine J74s looks similar to your genuine one.
I can offer to measure and curve trace your JFETs if we are not talking about hundreds of JFETs... and send you the data (via e-mail) and JFETs back. PM me.
And you certainly take good care of it with hard box and anti-static padding
Yeeeeeeesss.... my precious... for the photo session was put in the hard box with anti static padding.
I handle these parts with great care and respect. They are NOS after all...
The few hundreds of genuine jets I've are stuck into anti static padding after being measured and curved traced. Just waiting for their purpose in life.
I handle these parts with great care and respect. They are NOS after all...
The few hundreds of genuine jets I've are stuck into anti static padding after being measured and curved traced. Just waiting for their purpose in life.
Try The beast with a thousand Jfets if you have way to many
Otherwise hold on to them as they will certainly not loose in value
Anyway, as a strange hobby I have been "collecting" samples of cheap J74 of eBay and I still have to find just one seller of genuine devices. There are several vendors of genuine J74, but they are never cheap.
Otherwise hold on to them as they will certainly not loose in value
Anyway, as a strange hobby I have been "collecting" samples of cheap J74 of eBay and I still have to find just one seller of genuine devices. There are several vendors of genuine J74, but they are never cheap.
Well, time runs fast sometimes, but some measurments have been done.
At first I had no current diodes for the Borbely rig. But I hope that I got this right anyway.
The result are as follows (10% measured=4psc each N/P). 10V.
For transconductance 0,1Vpp 1kHz sine was applied and output was measured with Rd 1k at Idss. Gm calculated as in Borbely papers.
"2Sk170BL"
Vp 1,304-1,350 V
Idss 15,27-16,92 mA
Out 1,32-1,34 V
Gm 23,42-25,18
V-grade should have higher Gm so what may they be ?
"2SJ74BL"
Vp 1,929-2,098 V
Idss 7,30-8,20 mA
Out 0,200-0,270 V
Gm 7,51-7,81
One intresting thing is that the current goes down when they get warmer. On my genuine parts the current goes up a bit before stabilizing...
They were bought at Banzai music. I will contact them
But the SJ103Y and SK246 GR they sent seem to fit the specs. Sadley they didn't send the same grade, but one can't get it all
Regards
Figge
At first I had no current diodes for the Borbely rig. But I hope that I got this right anyway.
The result are as follows (10% measured=4psc each N/P). 10V.
For transconductance 0,1Vpp 1kHz sine was applied and output was measured with Rd 1k at Idss. Gm calculated as in Borbely papers.
"2Sk170BL"
Vp 1,304-1,350 V
Idss 15,27-16,92 mA
Out 1,32-1,34 V
Gm 23,42-25,18
V-grade should have higher Gm so what may they be ?
"2SJ74BL"
Vp 1,929-2,098 V
Idss 7,30-8,20 mA
Out 0,200-0,270 V
Gm 7,51-7,81
One intresting thing is that the current goes down when they get warmer. On my genuine parts the current goes up a bit before stabilizing...
They were bought at Banzai music. I will contact them
But the SJ103Y and SK246 GR they sent seem to fit the specs. Sadley they didn't send the same grade, but one can't get it all
Regards
Figge
the first group of 2sk170BL have too high an Idss.
That makes the markings = fake
The second group of 2sj74BL
have too high Vpinchoff (for that range of Idss) and that leads to a calaculation of the gm that is too low.
That makes the markings = fake.
That makes the markings = fake
The second group of 2sj74BL
have too high Vpinchoff (for that range of Idss) and that leads to a calaculation of the gm that is too low.
That makes the markings = fake.
What is this?
Borbely tests are carried out at constant DC, not at 1kHz.
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More than 10000 of J74 came through my hands, so I just want to share my experience.
Most of 2SK74/2SK170 has laser marking and the font all the time is the same, marking
is very sharp - I saw some fake J74 with very similiar font and laser marking, but the lines were not so well-done, although most of fakes has printed marking with color similiar to laser, but this making easy removable by acetone. Some items of old production (I had a box of 2SJ74BL 1998 production) has white print marking - but is is impossible to remove it with acetone, alchohol, etc - fake marking usually easy removable.
IDSS of genuine items always according datasheet - I have never seen even one outside the range. During IDSS measuring, the current of GR/BL slowly goes up (till some value, of course) - fake often has idss that reaches maximum at the beginning, then goes down - exception is "V" grade with high IDSS - it also goes down.
All things that people told about the item thickness is right - usually fakes are thinner.
I testednot a long time ago faked 2SK170GR, good laser marking, font a bit smaller than original - this was suspicious, and IDSS is in range(!!!), but curves were different - looked like J310 as I remember.
You can post pictures of your J74/K170, and usually I can say by picture, is it genuine or not.
Most of 2SK74/2SK170 has laser marking and the font all the time is the same, marking
is very sharp - I saw some fake J74 with very similiar font and laser marking, but the lines were not so well-done, although most of fakes has printed marking with color similiar to laser, but this making easy removable by acetone. Some items of old production (I had a box of 2SJ74BL 1998 production) has white print marking - but is is impossible to remove it with acetone, alchohol, etc - fake marking usually easy removable.
IDSS of genuine items always according datasheet - I have never seen even one outside the range. During IDSS measuring, the current of GR/BL slowly goes up (till some value, of course) - fake often has idss that reaches maximum at the beginning, then goes down - exception is "V" grade with high IDSS - it also goes down.
All things that people told about the item thickness is right - usually fakes are thinner.
I testednot a long time ago faked 2SK170GR, good laser marking, font a bit smaller than original - this was suspicious, and IDSS is in range(!!!), but curves were different - looked like J310 as I remember.
You can post pictures of your J74/K170, and usually I can say by picture, is it genuine or not.
Dear Alweit,
Thank you, that confirmed my observation about diametre!
Last batch SJ74BL I've bought, seemed to be original, according to Idss measurement.
Also it have a shining surface with laser marking, quite good font types and colour,
Although line of 7 is straight, rather than curved a little.
But they didn't behave well in my Sony VFET amp.
BTW, I would like to thank to you for 2SK2013/2SJ313 I've bought from you, at EBAY some time ago.
Also, I must ask, can I buy some 2SJ74BL?
Reguired Idss range is 8-11mA.
Kind regards,
Gyuri
Thank you, that confirmed my observation about diametre!
Last batch SJ74BL I've bought, seemed to be original, according to Idss measurement.
Also it have a shining surface with laser marking, quite good font types and colour,
Although line of 7 is straight, rather than curved a little.
But they didn't behave well in my Sony VFET amp.
BTW, I would like to thank to you for 2SK2013/2SJ313 I've bought from you, at EBAY some time ago.
Also, I must ask, can I buy some 2SJ74BL?
Reguired Idss range is 8-11mA.
Kind regards,
Gyuri
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I have now mailed Banzai support.
Waiting for their answer, but it has already been taking longer than when I contacted them about buying some parts, then the were fast as lightning
I will contatct Paypal tomorrow if there's no response, or wrong response
Anyone knows where to get ~8 matched J74/K170BL pairs ?
There seem to be a couple of reliable sources
Regards
Figge
Waiting for their answer, but it has already been taking longer than when I contacted them about buying some parts, then the were fast as lightning
I will contatct Paypal tomorrow if there's no response, or wrong response
Anyone knows where to get ~8 matched J74/K170BL pairs ?
There seem to be a couple of reliable sources
Regards
Figge
Anyone knows where to get ~8 matched J74/K170BL pairs ?
There seem to be a couple of reliable sources
Regards
Figge
Try In DiyAudio Store matched pairs of jfets from Linear Systems maybe ?
They are equivalents of old Toshibas and probably back in stock very soon.
Transistors – diyAudio Store
Best regards
I could ship a pair of 2sk170/2sj74 for anyone who would like to help me to test on curve tracer?
show us the top side, they look real for now
Hi WalterW
top side will be posted when I back home tonight!
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