Hello,good evening everyone, I have a question , hopefully someone can help. I recently bought 2sc2922 transistors (Sanken) but I am not sure whether they are genuine or fake.Sanken stop producing this transistor quite long ago. According to a web the easiest way to find fake trans is measure Cob ,so I measured capacitance btwn collector and emitter(using normal capacitor meter ). It shows 850 pf. According to 2sc2922' s spec , its typical value is 250 pf, but mine shows 850 pf. Is this means there are fake? Are there any way to identify a genuine 2sc2922 trans? Thank you at advance, your help highly appreciated.

 

Hello,good evening everyone, I have a question , hopefully someone can help. I recently bought 2sc2922 transistors (Sanken) but I am not sure whether they are genuine or fake.Sanken stop producing this transistor quite long ago. According to a web the easiest way to find fake trans is measure Cob ,so I measured capacitance btwn collector and emitter(using normal capacitor meter ). It shows 850 pf. According to 2sc2922' s spec , its typical value is 250 pf, but mine shows 850 pf. Is this means there are fake? Are there any way to identify a genuine 2sc2922 trans? Thank you at advance, your help highly appreciated.

Cob is not generally a parameter of great interest in most applications, and I'm not familiar with this device. If you are doing RF work then maybe it is important but trusting a meter might not be a good idea.

I think a great deal depends on our understanding of "fake":

1. It operates as a transistor but does not match some or all of the datasheet parameters.
2. It is a genuine part but rejected by someone for some reason.
3. It is a generic replacement part that meets some but not all of the original specifications
4. It was made by another company as a second source part

Some or all of the above could be true. Since most good designs do not depend on specific transistor parameters, I have to wonder what problem you imagine you will encounter. Certainly, it is tedious work to characterize a part, but if that is your only alternative then you have few choices. I guess I'd start with: "Is it a transistor"?

 

Welcome to AAC!

According to a web the easiest way to find fake trans is measure Cob ,so I measured capacitance btwn collector and emitter(using normal capacitor meter ).

You can't believe everything you find on the internet. That capacitance is measured under specific conditions:


Where you got them is a better indicator of whether they're genuine.

Are there any way to identify a genuine 2sc2922 trans?

Use a curve tracer to check parameters like beta and saturation voltage. If you don't have a curve tracer, you can build circuits to test, but that'll be more tedious.

Don't be tempted to check base-emitter breakdown voltage. That is likely to kill beta.

 

Thank you guys for your replies. The reason l looking for a genuine 2sc2922 is l am building naim nap 140 from scratch . I read on net that no matter how hard you try you cant get the naim sound in diy project. This what made me so obsses with this project. I am neither a scientist or wiseman but i believe that there r no such things as random or coinsidence in universe, everything happen based on physics laws n maths rules , even the results we get from throwing dice is based on physics n maths ,.......am I right???!!! . If we copy exactly what others do , we should get same result.... right? If I follow exactly the naim nap 140 schematic i shld get same sound ...right? I bought all available componenents (still in production) from element 14( a reputale company , so I ve no doubt abt these cmpnts) . But they dont have bc239c, ztx108 and 2sc2922 . I replaced ztx108 wit bc108 , which I bought fr El.14. I bought BC239B and2sc2922 from a local stores. The BC239b transistors have marked PH which means Philips semi,so i was very confident that thy r original. But when spray with perfume (which has alchohol) n rub it all the writings are gone. Is this means they are fakes? Since the profit margin is very little in small signal transistor , they dont bother to fake it .......aren't they? Should I use this doubtfull bc239b or replace with bc109 which I bought fr EL14. Both have same spec( low voltage , fast , low noise). They says the bc239c is very important to get THE NAIM SOUND. Should I go with rhe suspickus 2sc2922 or replace with njw0281 from EL14 ? If I replace these components , can I still get THE NAIM SOUND? Sorry for the long and late reply, I hope Naim Nap experts / amp experts out there help me , I so obsess wth this project. Thank you.

 

I wouldn‘t worry too much about it - from the circuit diagram and distortion plots it looks like a very ordinary quasi-comp class AB amplfier with fairly mediocre frequency response and distortion figures (about 0.05%). It looks the distortion improves with lower impedance loads which suggests a bit of crossover distortion. Use the NJW transistor - you will Probably get a real one, and you won‘t destroy the whole amplifier with a fake that fails.

 

According to 2sc2922' s spec , its typical value is 250 pf, but mine shows 850 pf.

Did your "normal capacitance meter" actually measure Cob with Vcb=10V and f=1MHz, as per the datasheet?

 

Just a note: CoB is the capacitance between the (C) collector and (B) base with the emitter (o) open, under specified bias conditions, as mentioned by @Alec_t