Bunch of 2N5457 JFETs - fake or not?

[fripholm]

I've purchased a lot of 100 2N5457 JFETs from a chinese supplier on ebay for a 1176 project I'm currently working on. After trying about 20 of those to find matched pairs, I've  found that they all have about the same cutoff voltage of -0.45 Volts with one exception - this one had -0.53 Volts. According to the datasheet, Vgs(off) of the 2N5457 ranges from -0.5 to -6 Volts. What puzzles me, is that they all are the same. Usually, FETs are supposed to vary a lot more and the offer on ebay didn't imply they were MATCHED parts.

They - kinda - work in the circuit. Calibrating the unit is not as straightforward as I am used to from another 1176 I've built - maybe it's the lowish cutoff voltage giving me trouble. And as soon as the compression kicks in, the signal becomes pretty noisy. Again, I haven't seen this before.

My component tester thinks, these are NPNs with a HFE of 24.000 (24 thousand!!)  Is there anything else I can test to see if they are genuine parts?

 

[JohnRoberts]

Fets pinch off voltage depends on process consistency... a batch from a single production lot should and could be similar. (I would expect modern processes to be better than old days.)

To confirm if they are real 5457 maybe check other parameters from the spec sheet (breakdown voltage, etc).

Maybe compare against real 5457 not memory of in circuit behavior that could have several variables.

JR

 

[Bo Deadly]

One time I bought 2sk170 on Ebay from 4 different suppliers, plugged them into a simple amplifier circuit and analyzed the gain, distortion products and noise floor [1]. One supplier was from China. I found the China parts were noticeably different. And incidentally very close Vp / Idss.  They were different enough that I pretty much concluded that they were indeed fake. Although they where still pretty good transistors. In fact the noise floor was better (although they had less gain so ...).

Personally I'm not so pedantic about replicating circuits down to specific parts. There have to be JFETs that will work well in the 1176. No one would be able to tell the difference. Maybe something like J106? Just need to look at Vpp and Idss of course and then pick based on noise performance, transconductance, look at charts, ... etc.

[1]  https://groupdiy.com/index.php?topic=66423.0

 

[ruffrecords]

The 2N5457 is available from Mouser for instance. They have over 8000 in stock. Why buy crucial components from eBay?

Cheers

Ian

 

[fripholm]

Thanks guys!

Ian, I've seen those - but I paid less than half the price of what Mouser charges for 100 pcs. In my experience, chinese parts are usually ok. This time I'm not sure though.

I've tried the circuit with different JFETs. It worked fine for the most of them and I really should have left it at that. Maybe next time...

 

[JohnRoberts]

Thanks guys!

Ian, I've seen those - but I paid less than half the price of what Mouser charges for 100 pcs. In my experience, chinese parts are usually ok. This time I'm not sure though.

I've tried the circuit with different JFETs. It worked fine for the most of them and I really should have left it at that. Maybe next time...

Life is too short to use questionable parts. I value my labor much higher than component cost. 

China is notorious for selling counterfeit components.

If you got good parts good for you, if not that's life.

JR

 

[midwayfair]

They could easily be seconds -- intended for a certain part number but out of spec. Usually FETs are marked after they're sorted, though IIRC.