Counterfeit transistors?

[Axtman]

Has anyone come across counterfeit transistors? What was your experience?

Personally, I have not had any counterfeits (fingers crossed and knocking on wood). I only buy from reputable distributors.

[g1]

The 'counterfeit' term can be a bit misleading with transistors, as they are often real transistors, just not the type they are labelled as. Such as a 5 amp part re-labelled as a 10 amp type.
Often they are an obsolete part number at a reasonable price.
I had an issue once where I saw a some oscillation only at full power into minimum load, the only thing I could think was causing it was the obsolete transistors I got off ebay. As the original type were not available from a regular supplier, I could never verify.
Sometimes the fakes will work in many applications that are not too demanding.

[The Dude]

......they are often real transistors, just not the type they are labelled as. Such as a 5 amp part re-labelled as a 10 amp type......

That's been my experience, also. The counterfeit parts simply can't handle their supposed rated specs. I've even cracked some apart to compare to real parts and the die and sometimes heat sinks are way smaller than original parts. I fail to understand why they do this. If you're going through the trouble to manufacture a part, why not build it correctly and robustly enough to handle specs. I wouldn't think it would cost substantially more.

[dmeek]

I ordered some LA4625 14-pin amplifier chips. I don't know what they were but they were completely non-functional. Probably not even amplifiers.
I had more luck with 2SJ115 / 2SK405 mosfets for a stereo amp. They looked good on the curve tracer and worked in the amp though the specified idle current was out of range of the trimmer.

[The Dude]

If there is an upside, at least most techs are aware of the fakes these days. I remember when they first started showing up on the market and the situation wasn't well known. You could spend a lot of wasted time trying to figure out why the parts you just installed shorted again. Did I miss something? Is there something else wrong causing the parts to explode? After chasing around looking for a problem that wasn't there, you'd realize it was only that your new parts were defective.

[Mick Bailey]

I had 10x 2N3055 that all shorted and when opened up there was a tiny wafer inside, about 1/5th the size of a genuine transistor. Really poor construction, too. Genuine parts worked perfectly in the same circuit.

Something I wasn't aware of at the time, and I got caught out with this, is some transistors can have different pinouts for the same type number (but there's an additional suffix letter) making the alternative types look like fakes when in circuit.

[John_H]

I'm waiting for delivery of some 2N2905A silicon transistors that I've been worried that they were real since I ordered them.

[nosaj]

I'm waiting for delivery of some 2N2905A silicon transistors that I've been worried that they were real since I ordered them.

I wouldn't worry if you ordered them from here
https://www.newark.com/multicomp-pro...5ad/dp/35C0695
nosaj

[Tassieviking]

Several years ago I got some J201 fets on Ebay, what i got were NPN transistors marked J201

[mozz]

Also some germanium fuzz face transistors, such as NKT275, AC128.

[loudthud]

They don't start out as fake transistors, they were made with the intent to be something else. Then, either because they didn't quite meet specifications or because there were just too many of them, they get marked as a more expensive or obsolete part and sold on ebay.

[Helmholtz]

I know of at least 2 cases where Fairchild labeled J201 ebay bought jfets were actually J202s. The labeling looked similar but not identical to originals.
In some circuits (e.g. source-follower) they may work but in 9V supplied gain stages they don't.

[Mark Black]

I got some 2SB/2SD types from MCM Electronics (affiliated with Newark) back in the early days of the fakes - maybe even before some of the reputable distributors had caught on. Those were for a big Crest 8001, and I got to watch quite a fireworks show when I pushed it hard into a dummy load! That was something like 22 power transistors plus a bunch of other components and time in the crapper, and was my intro to the existence of the fakes.

Cracking open old vs replacements revealed totally different innards.