# PF5102 - Fake or am I dumb?



## uranium_jones (Jun 4, 2021)

I just attempted to test one of a number of PF5102s that I ordered. Is there any way this makes sense? Because I thought it was supposed to be a JFET.


----------



## music6000 (Jun 4, 2021)

Houston, We have a problem.
Check first, you may have grabbed the wrong or misplaced Transistor.
If Not , it's a Fake!


----------



## uranium_jones (Jun 4, 2021)

thewintersoldier said:


> Where did you get them from. It's possible it's a fake.


It was a Chinese eBay seller so yeah, it's fake. I just ordered some from Smallbear to remedy the situation.


----------



## mnemonic (Jun 5, 2021)

I’ve got one of those mega328 testers and i think they have trouble with jfets, I tried testing some brand new SMD j201’s and it also thought they were BJT.

I bought them from a reputable seller and I’ve never heard of fake SMD j201’s as they are still in production and dirt cheap, so I used them anyway in a jfet preamp emulation pedal and they work great.


----------



## temol (Jun 5, 2021)

Cheap LCR meters often recognize JFET transistors as BJT. Use DMM and a battery.



			A closer look at the Fetzer Valve


----------



## fig (Jun 5, 2021)

mnemonic said:


> I’ve got one of those mega328 testers and i think they have trouble with jfets, I tried testing some brand new SMD j201’s and it also thought they were BJT.
> 
> I bought them from a reputable seller and I’ve never heard of fake SMD j201’s as they are still in production and dirt cheap, so I used them anyway in a jfet preamp emulation pedal and they work great.


They do misfire on JFETs . @finebyfine just went through the same thing. They bought a DCA75 and tested the same piece and it was good.

@quality_jones I'd read @temol 's suggestion before pitching them.


----------



## Kroars (Jun 5, 2021)

fig said:


> They do misfire on JFETs . @finebyfine just went through the same thing. They bought a DCA75 and tested the same piece and it was good.
> 
> I'd read @temol 's suggestion before pitching them.


Had the same issue.  The TC1 is a great little tester and I use it for all resistors & capacitors to make sure they’re good.  Although, I use my DCA 75 for everything else.


----------



## Feral Feline (Jun 5, 2021)

Don't throw stuff away!

Even if they are BJTs of unknown provenance, you could wire them up as clipping diodes ... or make little anthropomorphic sculptures, or paint them gaudy colours and tie them into a fly ... yes, I'm fishing for ideas here, but ... don't throw anything away, as soon as you do you'll find a use for whatever you just threw away — kinda like Murphy's law, only it's his cousin Murray (the garbage-man), yeah Murray's Law.


----------



## fig (Jun 5, 2021)

Feral Feline said:


> Don't throw stuff away!


It's okay...thousands of years from now...mankind humankind will drill to just below this strata and rebuild civilization from the landfills we are stockpiling today.....


----------



## temol (Jun 5, 2021)

I have many "fake" J201 transistors in TO-92 package. I'm not going to throw them away. Those are still JFETs, fully functional. Only parameters do not match J201 specs. I suppose those are J202 or other similar Jxxx transistors (judging by Vp and Idss). I can use them instead of 2N5457 or as a source followers (in buffers).

ps.
Unfrtunately I cannot say this about all fake components. I have tens of TL072 opamps from aliexpress. They have a sersious issue that makes them rather unusable in audio path - they introduce crossover distortion to the signal. I've read somewhere those chips are probably not TL072 but LM358 or other uncpecified.


----------



## finebyfine (Jun 5, 2021)

fig said:


> They do misfire on JFETs . @finebyfine just went through the same thing. They bought a DCA75 and tested the same piece and it was good.
> 
> @quality_jones I'd read @temol 's suggestion before pitching them.



Yep. Lots of ebay/ali jfets _are _fake but the atmega is notoriously bad at recognizing some JFETs for some reason. I had a few bags of what I thought were fake JFETs (they were from aliexpress and my atmega said were bjt pnp) ready to throw out before my dca75 came and just for shits and giggles tested some. J201s are extremely likely to be fake but other models are less so in my experience. If you're looking for them on the cheap a lot of the JFETs we use in pedal building are available SMD - which in my experience are more likely to be within spec from Aliexpress sellers - and it's a good excuse to dip your toe into the SMD world if you haven't before.

edit: another thing worth mentioning, and I try to say this a lot, is that AliExpress is a much better place to buy components from China than ebay. They're often some of the same sellers anyway. AliExpress puts reviews - both for sellers and for items - front and center, unlike ebay which basically has none. On AliExpress you're also technically putting money into escrow and the seller doesn't get that money until you've confirmed receipt, so buyer / seller disputes are more likely to end up in your favor.


----------



## mnemonic (Jun 5, 2021)

Kroars said:


> DCA 75


This looks cool, it’s going on my list.



finebyfine said:


> good excuse to dip your toe into the SMD world if you haven't before.


I’ve been considering lately, buying like 100 SMD j201’s and 5457’s off mouser, and some of those adapter boards, and doing my own, at least I’d be set for a while, and not have to pay £2 each. But is a normal soldering iron suitable for tacking on SMD’s?

ive got a good temperature controlled iron with a sharp tip.


----------



## finebyfine (Jun 5, 2021)

mnemonic said:


> I’ve been considering lately, buying like 100 SMD j201’s and 5457’s off mouser, and some of those adapter boards, and doing my own, at least I’d be set for a while, and not have to pay £2 each. But is a normal soldering iron suitable for tacking on SMD’s?



Should be but I might be imagining something else when you say a normal soldering iron. I'd buy a few and try it out either way. SMD soldering (sot-23 transistor packages, anyway) is much easier than I thought it'd be. I don't _like_ doing it but it's not a Herculean task. Just watch a few youtube videos and make sure you have good lighting.


----------



## Leftovernoise (Jun 5, 2021)

https://www.tubesandmore.com/products/transistor-jfet-n-ch-transistor-lo-freq-lo-noise-pf5102
		


I got mine from here for 2 builds. They are legit and work great.


----------



## uranium_jones (Jun 5, 2021)

So here's an update. This btw is for another Parentheses Fuzz board that still isn't working yet. I found like 4 remaining PF5102s from earlier, and I put them in the TC1. I also put in a J201 for kicks. Results are below. 

I'm open for getting more testing equipment or making some sort of test circuit eventually, but I don't really know what either will give me. All the questions I've asked my TC1 consist of (1) Hey, does this diode still work? (2) what's the hfe of this transistor and is it big enough? And now (3) is this JFET really a JFET? Because if I do get numbers from a JFET test, I won't know what it means. Heck, I still think that JFET means a FET that was made in Japan. (Looking forward to Korean KFETs whenever they hit the scene.)


----------



## PJS (Jun 5, 2021)

I did find once a bit of a tutorial on testing FETs using diode test mode in a multimeter.  Basically testing which legs will conduct/not conduct will give you a fair idea of the internal structure.  That will be able to confirm at least whether or not you have a FET.  You then need to measure voltages and currents to confirm which one you have.


----------

