I have received a lot of 50 Toshiba 2SJ74 from a vendor in HK, unmatched, and this evening took the bunch of them to the bench to match them up. They were grade "BL" devices, and for the most part, with the exception of maybe 2 of them, they all fell within what I believe to be the range specified for the part. I was able to get 18 relatively well matched (within .1- .05mA) pair out of the bag of parts, ranging from about 7mA to 17mA in Idss.
I was somewhat surprised to see that much variation, but I'm betting I have received the remains of some cherry picked stock, because they didn't come on a tape strip or the like. I'm going to install them in my BA3 gain stage and see what happens. So far, they look good, and appear to be genuine.
Anything else I should be looking for in my anti counterfeit tests? If it turns out that these are real, I may want to order some more…
I was somewhat surprised to see that much variation, but I'm betting I have received the remains of some cherry picked stock, because they didn't come on a tape strip or the like. I'm going to install them in my BA3 gain stage and see what happens. So far, they look good, and appear to be genuine.
Anything else I should be looking for in my anti counterfeit tests? If it turns out that these are real, I may want to order some more…
They were probably cherry picked. The usual yield is the bulk of the parts
within 2 ma of average. Most of my BL's are 8 to 10 mA.
That said, put them to work.
They all have the same markings, and it looks as if I ended up with somebodies leftovers after they were done matching a bunch. Most of them are between 8 and 10 mA. I had them held down to a temperature controlled aluminum block, that was set for 78 degrees, and they had the power applied for exactly 3 seconds before the readings were taken. I rounded up my matches to the nearest .1 mA- I figured that was good enough for my amplifier experiments.
The outliers of the bunch measured a minimum of 5.5mA, and a max of 17. There was only 1 that high, but there were a couple more that measured 13- 14mA.
As soon as I get a chance to match up my 170s, I'm going to fire the gain stage up and see what happens…
The outliers of the bunch measured a minimum of 5.5mA, and a max of 17. There was only 1 that high, but there were a couple more that measured 13- 14mA.
As soon as I get a chance to match up my 170s, I'm going to fire the gain stage up and see what happens…
Funny that everyone thinks they are from a cherry picked batch... when 2SJ74 are (among) the most faked devices in Audio history....
Having so many off-specs (above 12mA).... especially with same date code !!! is enough for me to think they are not genuine
Where did you buy them from ? and at what price ? I'm sure that will tell us more about those parts
Having so many off-specs (above 12mA).... especially with same date code !!! is enough for me to think they are not genuine
Where did you buy them from ? and at what price ? I'm sure that will tell us more about those parts
Hi,
even when the sj74 was in production, I alway observed a distribution of idss values, that was not uniform. There were always "clusters" at one or two values. Those values varied in every bunch. Perhaps the properties depend on the production run, the wafer the sj74 came from or...
In greater bunches there were always one or two out of the spec.
I don't think that this must be an indication for fakes.
Regards
Flo
even when the sj74 was in production, I alway observed a distribution of idss values, that was not uniform. There were always "clusters" at one or two values. Those values varied in every bunch. Perhaps the properties depend on the production run, the wafer the sj74 came from or...
In greater bunches there were always one or two out of the spec.
I don't think that this must be an indication for fakes.
Regards
Flo
The consideration of whether they are fakes or not depends a lot on what
you will be using them for. I have lots of examples of high Idss Jfets,
mostly used for choppers and stuff. They work fine, but do not meet the
noise spec of the Toshiba 2SJ74 and 2SK170's, and of course differ in
other ways, but it is my experience that they usually work well enough in
things like a BA-3. Worst case you degenerate them a little more to get the
current down to where you want it.
you will be using them for. I have lots of examples of high Idss Jfets,
mostly used for choppers and stuff. They work fine, but do not meet the
noise spec of the Toshiba 2SJ74 and 2SK170's, and of course differ in
other ways, but it is my experience that they usually work well enough in
things like a BA-3. Worst case you degenerate them a little more to get the
current down to where you want it.
Does anybody know where those fakes come from? Who produces the originals "behind" those fakes. As Nelson states, they are not the sj74 and have not nearly the specs. But there are many applications for p-cannel jets and not every application is a mc-preamp.
The available p-jfets I know have a rather low idss (1-5 mA) so it would be intersting to know a souce for parts like that.
Buying fakes (even if you would want them) is not a reliable source.
Regards
Flo
The available p-jfets I know have a rather low idss (1-5 mA) so it would be intersting to know a souce for parts like that.
Buying fakes (even if you would want them) is not a reliable source.
Regards
Flo
i recently did a swap meet sale of 200 factory packaged j74's
https://docs.google.com/spreadsheet...VFWlBjRmNzbFE&hl=en_US&authkey=CKLl9ZcG#gid=0
none were anywhere near your outside figures .
cheers Woody
https://docs.google.com/spreadsheet...VFWlBjRmNzbFE&hl=en_US&authkey=CKLl9ZcG#gid=0
none were anywhere near your outside figures .
cheers Woody
They can either be genuine (but cheaper) parts with similar "general" specs / lower "specific" specs -like noise level-, that are relabelled, or rejects from bad production batches that are "stolen" from subcontractors trash bins before they receive the laser etching ... maybe not the company itself, but some of it's employees... there are places where everything is possible (apparently even stealing a wafer!)
I recently bought 10 off in China for 25 cents, just for fun (knowing that there was 99.99% chance they would be fake), and when they arrived I had a big laugh... the parts were polished by sand paper and laser re-labelled... dirty work!
Yes if the goal is to light a diode or so that's acceptable, but when they are in audio circuit, it's just impossible for many of us to accept that there is even the slightest possibility of them being fake....
you could prove me that it's unimportant for such or such application, but you know that audio is all about subjectivity , and if I had such a device in the DIY Pass Amp that I spent so much time building and cherry picking components, I'm sure I would only "hear" how harsh, thin and fake the sound would be
!!!!Fred
They can either be genuine (but cheaper) parts with similar "general" specs / lower "specific" specs -like noise level-, that are relabelled, or rejects from bad production batches that are "stolen" from subcontractors trash bins before they receive the laser etching ... maybe not the company itself, but some of it's employees... there are places where everything is possible (apparently even stealing a wafer!)
I recently bought 10 off in China for 25 cents, just for fun (knowing that there was 99.99% chance they would be fake), and when they arrived I had a big laugh... the parts were polished by sand paper and laser re-labelled... dirty work!
Yes if the goal is to light a diode or so that's acceptable, but when they are in audio circuit, it's just impossible for many of us to accept that there is even the slightest possibility of them being fake....
you could prove me that it's unimportant for such or such application, but you know that audio is all about subjectivity , and if I had such a device in the DIY Pass Amp that I spent so much time building and cherry picking components, I'm sure I would only "hear" how harsh, thin and fake the sound would be
Fred
Hi Fred,
Old post but we never know?
I agree with you and I am also really upset with this growing fake market.
Do have any idea of good source? Do you know Electronique Diffusion in France? They seem to have all the transistors I need to resurect some circuits of l''Audiophile.'
Thanks,
Jean-Paul
Afaik, all of the alleged 2SJ74s coming from asia and distributed from asia at this time are fakes.
Someone has sent me pix that show they are re-badged Fairchild devices, and not similar at all to bona fide Toshibas.
The best first pass way to check is with a curve tracer.
See attached images.
Someone has sent me pix that show they are re-badged Fairchild devices, and not similar at all to bona fide Toshibas.
The best first pass way to check is with a curve tracer.
See attached images.
Attachments
I just sent a listing of japaneese transistors to a company in Europe by email aking them which of them they can garantee. I hope to receive an answer!
I have a 2 traces scope but no curve tracer. Do you have any idea if I can add a 'not too expensive' module?
Thanks,
http://www.diyaudio.com/forums/solid-state/151253-diy-curve-tracer-pc.html
Lockyz's device can be purchased on eBay
Lockyz's device can be purchased on eBay
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