Determining if my 2N5457’s are FAKE

[awgearhart]

I bought a pack of 2N5457's using Amazon Prime (expecting they'd be legitimate transistors). I'm getting ready to build the SWAH from GuitarPCB and want to determine which of the ones I bought are fake (if any).

I've been reading a lot of articles about fake JFET's, using the MMBF5457 instead, all that Jazz.

Is there a way to determine if the transistor is fake just by measuring the bias voltage? I already did that and most of mine had resistance of ~135 Ohms. Some down around 100 Ohms, some close to 200 Ohms. Can I tell just by that if they are fake or not?

[bean]

I would put a simple test circuit on a breadboard to be sure. This should work. If you get relatively clean output they are most likely good to go.

[awgearhart]

So if there's any distortion in this circuit, it would mean the transistor is bad/fake?

[duck_arse]

it wouldn't hurt to post some pics of what you got, front and back, nice and clear, and we'll all pick holes in the markings - or not.

[awgearhart]

I had heard from a video of someone testing a 2N5457 that resistance values measured on the transistor itself between 100 and 200 ohms indicates a "good" transistor. Can I not just go off of this?

[idy]

SWAW uses the FET as a buffer. Anything working at your voltage like an FET will be fine. If your FETs test as FETs (and not reprinted BJTs or empty plastic beads) and they work in a basic circuit like the madbean booster schematic above, they will be fine fine fine in your circuit. If you needed a matched team for a phaser you would want fancier testing, maybe creating a graph for each one and choosing a closely matched set.

But we would all love to see pictures of them. Many of us live for pictures of suspicious transistors. WE NEED TO SEE PICTURES. Help us.

[awgearhart]

I don't have the transistors on me at the moment, but I'll post pictures of them when I get the chance.

[duck_arse]

But we would all love to see pictures of them. Many of us live for pictures of suspicious transistors. WE NEED TO SEE PICTURES. Help us.

someone had to say it.

[Eb7+9]

don't waste your time characterizing your devices by trying to bias them in a circuit that has NFB in it ...

do a search for measuring Vgs(off) and Idss using a 9volt battery and reasonably good DMM
(you can post the numbers here if you want ...)

if they fall within the datasheet Vgs(off)/Idss limits for 2n5457's chances increase that you didn't buy garbage

[awgearhart]

How do you measure Vgs(off)? I was trying to research but people had differing opinions, and the data sheet stated they used 15 V, not just 9 V. Does that make a difference? I don't have anything that can run 15 V exactly.

[Eb7+9]

to measure Vgs(off) : drain goes to +9v, gate to ground ... stick volt-meter between source and gnd to get a direct reading (... accuracy depends on impedance of meter)

to measure Idss : gate and source to gnd ... stick ammeter between drain and +9v to get direct reading (... jFET acts like a near-constant current source in this config)

---

the test voltage is just for reference, as long as you're not in the triode region ... with 2n5457's a 9volt test source guarantees you won't be

FYI, the big boys test at +15 and define Vgs(off) as the voltage corresponding to 1nA drain current ... the ATLAS transistor tester uses 5uA, not sure on its internally generated voltage ... the impedance of your dmm will determine this current, the lower being better

you can use a fresh 9v battery for testing provided you negligibly drain the battery throughout the totality of your testing
take your measurement and disconnect right away

if you have to test lots of devices use a regulated source

[awgearhart]

For those who wanted pictures, here they are! All of the transistors look identical. ARE THEY FAKE???

Going to test voltage/current spec values, then maybe create the circuit Madbean posted.

[awgearhart]

After measuring values for Vgs(off), I have the following:

Input voltage = 9 V
Minimum value = 0.121 V
Maximum value = 0.209 V

[awgearhart]

After measuring values for Idss, I have the following:

Input voltage = 9 V
Minimum current = 1.32 mA
Maximum current = 3.23 mA

The min/max currents corresponded with the min/max voltages. Do my measured values indicate if they are real 5457's?

I can post a spreadsheet of all 20 measured values if necessary...

[duck_arse]

For those who wanted pictures, here they are! All of the transistors look identical. ARE THEY FAKE???

Going to test voltage/current spec values, then maybe create the circuit Madbean posted.

can I ask a Q about the leads? do they seem "pressed out", or more like extruded? two Q's - if you bend a leg out, in the same plane as the flat, do you feel something of a small crak?

[awgearhart]

can I ask a Q about the leads? do they seem "pressed out", or more like extruded? two Q's - if you bend a leg out, in the same plane as the flat, do you feel something of a small crak?

I don't believe they seem "pressed out" or extruded... nor does bending a leg out flat with the bottom of the TO-92 case make a cracking sound.

Is it possible to tell just by my Vgs(off) and Idss readings?

[duck_arse]

tell, definitively, no. you'll be able to say yes, they match the datasheet numbers, or no, they don't match the specs listed.

[awgearhart]

Based on the data sheet (Vds = 15 V), it looks like the Vgs(off) should be a min of -0.5 V and max of -6.0 V.

Idss min should be 1 mA and max of 5 mA. But I'm only using 9 V, not 15 as shown in the data sheet.

I just want to know based on the values I measured (using a 9 V battery supply), can I use them in my circuits?

[awgearhart]

I created the circuit that Madbean illustrated, and all transistors produced a CLEAN guitar signal.

Based on that, and the values I was able to measure for Vgs(off) and Idss, are these transistors real, or can they at least act like a 2n5457??

[pinkjimiphoton]

on the swah, you can use pretty much any jfet on it. doesn't really matter, tho the pinout may be different. i've built a bunch of these... fun circuit, one of barry's best