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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Nov 2018, 9:27 pm   #1
John_BS
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Default Counterfeit transistors: a cautionary lesson

Some time ago I purchased four pairs of complementary output transistors for repairing Class B audio amplifiers: TO3P package SD718 / SB688.

I measured the low-current hfe of both the npn and pnp, and they were significantly higher than the figured quoted in the respective data-sheets, which made me suspicious, and I didn't use them.

During the course of this summer I managed to buy & restore a Tektronix 575 curve-tracer, and a recent amplifer project (all power transistors s/c in one channel!) led to a bit of further research on these transistors.

The 575 revealed two things:

  • the gain dropped rapidly above c. 0.5A collector current, and showed signs of "saturating" at quite a low collector current
  • they would exhibit secondary breakdown and destroy themselves if dynamically tested anywhere close to rated Vce
Whatever the chips are in these devices, they're not the ones marked on the package!

I've now splashed out on bulk-buying some power transistors from Radiospares, and these (as you'd expect) perform well /to spec. Anyone repairing an audio amplifier would probably only discover the fakes when the volume was turned up high for the first time.



John
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Old 18th Nov 2018, 6:56 am   #2
Diabolical Artificer
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Default Re: Counterfeit transistors: a cautionary lesson

Might have some of those John, but your sorted right? When I had to buy some OP Q's a while back I found quite a few on ebay but was wary, so I asked around on DIY audio to see who sells genuine Q's, it is a minefield.

Andy.
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Old 18th Nov 2018, 8:39 am   #3
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Default Re: Counterfeit transistors: a cautionary lesson

I tend to get my stock from CVC: https://www.chelmervalve.com

Haven’t had problem with anything from there. I did however buy some very rare 2n2219d transistors from eBay which are dual die matched pairs. They didn’t even test as transistors, being open circuit. Cracked one open with a dremel and there want even a die in it!

Just hand matched a couple of normal 2n2219’s then (from a bag of Philips ones I got a few years back) and it was fine.

I think a large part of the art of replacing transistors is finding something available and reliable and cheap that does the job even if it’s not exactly the same part.
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Old 18th Nov 2018, 9:05 am   #4
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Default Re: Counterfeit transistors: a cautionary lesson

Semiconductor prices too good to be true usually are when the goods comes out of China.
It was again confirmed by these ST 2N3055 I ordered from eBay for repairing a vintage Monacor power-supply.
As you can see the paint wasn't even dry when they packed the transistors.
I just can't understand how anyone can make a living out of selling at the prices they do?
The bare postage comes to more than what I paid for 10 transistors delivered.

/Torben
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Old 18th Nov 2018, 10:04 am   #5
John_BS
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Default Re: Counterfeit transistors: a cautionary lesson

Thanks, Andy, yes, over-sorted!



In fact if anyone needs a pair of 140V/10A TO3P output transistors, let me know!


The proliferation of fake devices originating mainly from China does make you wonder about the economics of manufacture; surely the packaging/encapsulation costs more than the actual die for transistors? So why bother with fakes?



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Old 18th Nov 2018, 10:18 am   #6
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Default Re: Counterfeit transistors: a cautionary lesson

I once bought half a dozen IRF640 power fets and they turned out to be terrible rubbish. The original pair in the (homebrew) transmitter could churn out about 20 watts of RF, but the new ones seemed to be incapable of delivering more than about 5w.
After ruining my nice layout investigating and modifying, I rebuilt using devices from a more reputable source and they worked fine.
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Old 18th Nov 2018, 10:29 am   #7
G4YVM David
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Default Re: Counterfeit transistors: a cautionary lesson

I also had trouble with fakes. I discovered that they weigh a lot less than genuine items (on the whole and regardless of type), so can be discerned on a scale.

I have to say that I cannot understand the economics of going to all the trouble of making a fake look so darned good and then not going one step further. They must roll off the same blooming line!
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Old 18th Nov 2018, 10:54 am   #8
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Default Re: Counterfeit transistors: a cautionary lesson

As part of a project, I needed then recently obsoleted 2SC3675 in reasonable quantity. NPN 900V, 100mA TO220 case. They used to be used in old colour televisions, and when flat screen took over, all the high voltage transistors kind of went the way of all dust. These were actually operating well within specification at 700V in this design.

Anyhow, I bought some from a company in London, soldered them in, attached to large heatsink, and turned on. Bang, smoke and sparks. It was impressive, with lots of collateral damage.

Put the remaining few on the curve tracer - they barely made 500V before breakdown. The company in question replaced them, and these seemed genuine and met Vceo spec.

No idea what the oriental fakers had relabelled as 2SC3675 , but it was not what it said on the package.

I laughed at MrBungle's post though! At least my fakes had silicon (of some description) in there.
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Old 18th Nov 2018, 1:25 pm   #9
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Default Re: Counterfeit transistors: a cautionary lesson

I have had issues with fake transistors. In one case the part which I ordered was a vintage high voltage N channel junction fet in a TO-5 case. I was sent some sort of re-labelled TO-5 silicon NPN transistor. Later I discovered the part number was incorrectly listed as a transistor in an equivalents manual. So the people who did it, looked in the manual for an equivalent, and re-labelled it. But that is not all, here is something that really impressed me:

I received some bright & shiny TO-5 transistors which looked far to shiny for the date codes.

I noticed some subtle bumps in the leads about 3 to 4mm from where they entered the package.

Under magnification I found that the wire leads on the device were once short (presumably pcb pulls) and they had welded longer wires on to each one and re tinned the leads to conceal it.

The leads at the interface-weld were cut at about 45 degrees and the welds were imperfect, some broke with force on bending the lead wire.

But the fact that somebody put in all that effort, for an inexpensive part really was something. I had no idea that the counterfeiters were going to such lengths, or perhaps should I say the environmentally conscious who are taking "recycling" to the next level.

I had also read that fakes parts have ended up in air bag controllers and in military supply chains and probably avionics systems.

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Old 18th Nov 2018, 2:36 pm   #10
Craig Sawyers
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Default Re: Counterfeit transistors: a cautionary lesson

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Originally Posted by Argus25 View Post
I had also read that fakes parts have ended up in air bag controllers and in military supply chains and probably avionics systems.
ESA are paranoid about this. They have a requirement that spacecraft parts are only procured through named agents which are each individually qualified and regularly visited by ESA. And every single part - whether active or passive - is accompanied by a test and qualification certificate. All this means that you have to renormalise the prices for parts by two to three orders of magnitude. The most eye popping one was Actel space grade FPGA's. 500 pin gullwing beasts that cost £30k each. And were subject to ITAR restrictions. Any we did not use had to be returned or destroyed. And stored under strict rules. The good news is that launching into space qualified as "destroyed"!
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Old 18th Nov 2018, 2:47 pm   #11
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Default Re: Counterfeit transistors: a cautionary lesson

This also happened when I worked for an MoD contractor. Some poor sod had to sit there with a curve tracer and some test rigs all day every day testing every damn transistor coming in. Supplier was Arrow mostly as well.

Turns out even the qualified parts had a slightly hooky supply chain.

Glad that wasn’t my job.
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Old 18th Nov 2018, 5:19 pm   #12
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Default Re: Counterfeit transistors: a cautionary lesson

Quite. Both mind numbing and very high responsibility. We were required to use ALTER, who are ESA's designated Common Parts Procurement Agents https://www.altertechnology-group.com/en/home/ .
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Old 18th Nov 2018, 6:24 pm   #13
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Default Re: Counterfeit transistors: a cautionary lesson

I once bought a lot of BC550 NPN transistors from ebay to repair a Quad 33 . Turned out to be PNP type ( hfe etc ok but pnp not npn ) now only buy from RS etc

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Old 18th Nov 2018, 7:28 pm   #14
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Default Re: Counterfeit transistors: a cautionary lesson

Even when buying from reputable distributors like ASWO you may be in for a surprise.
I needed a few 2N3773 to repair a motorcontroller-pcb and ordered from ASWO.
The new transistors lasted for about a week.
No other faults could be located and a fresh lot of 2N3773, again from ASWO, went in.
Another week passed and the pcb was back in for repairs.
I took the TO-3's apart and found rust covering much of the inside and a chip half the size it should be.
ASWO apoligized and supplied new parts.
Now several years following, the pcb works flawlessly.
I have yet to come across fake semiconductors from RS but their chinese produced ECC83/12AX7 is rubbish.
I had a 12AX7 filament break recently after a couple of hours of service.
The filament is usually the LAST thing to go bust in a valve imho.
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Old 18th Nov 2018, 7:31 pm   #15
MrBungle
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Default Re: Counterfeit transistors: a cautionary lesson

Not had any problems with the 12AU7’s I bought from them which were Chinese branded.

I remember my grandmother hitting her TV with a walking stick after her brand new valve went pop so this may have been a problem going back a while.
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Old 18th Nov 2018, 9:04 pm   #16
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Default Re: Counterfeit transistors: a cautionary lesson

I haven't come across fake transistors (yet) but a supplier sent me some IC's that were supposed to be new but were clearly 'pulls' from old PCBs!!!!
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Old 18th Nov 2018, 9:13 pm   #17
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Default Re: Counterfeit transistors: a cautionary lesson

The "MRF-" series of power transistors are widely faked; someone I know failed to build a 'classic' linear amp from one of the old Motorola design-notes, and only after much time wasted trying to get the thing to give more than a few Watts before chronic 'flattening' [output not increasing with increasing drive] occurred did he discover the transistors were more likely plastic-cased 2N3055s or something similarly unhappy above a few MHz.
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Old 18th Nov 2018, 9:17 pm   #18
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Default Re: Counterfeit transistors: a cautionary lesson

I think you can only get those as pulls out of old kit reliably now and that’s pretty hazardous.

One reason I have been building IRF510 based amplifiers. They aren’t hooky yet. I have considered buying myself a few hundred as a retirement hedge as if they pull them then it’s going to drive the prices up. Just like what happened with good BD139’s.
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Old 18th Nov 2018, 10:35 pm   #19
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Default Re: Counterfeit transistors: a cautionary lesson

I have the same problem here in the States.
One fairly good wholesaler told me the SK branded HOT's were OEM numbers, legitimate quality, that they had, so I ordered 2, with doubts.
Put one in and the set lasted 1 day before it failed.
I really read her the riot act, sent the other back, and told her they were "pure rubbish", Well I used different words, ok.
Ordered OEM Sony at 3 X the price, installed, no callback. That piece of junk xistor cost me 3 hours time for labor and I lost money on the job.
I never bought another SK product after that.
That being said, my friend at the wholesalers called me back to his bench when I made a parts run. He showed me a 'lytic that was marked 1000mfd, 50 V. It was open on the bench.
Inside was an obviously used/ salvaged 470 mfd at 35V PC mount 'lytic, that had leads extended with wire Off brand, Asian made part too. Counterfeit. People wonder why I check every part before I install it..........
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Old 19th Nov 2018, 2:48 am   #20
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Default Re: Counterfeit transistors: a cautionary lesson

Quote:
Originally Posted by FrankB View Post
I have the same problem here in the States.
One fairly good wholesaler told me the SK branded HOT's were OEM numbers, legitimate quality, that they had, so I ordered 2, with doubts.
Put one in and the set lasted 1 day before it failed.
I really read her the riot act, sent the other back, and told her they were "pure rubbish", Well I used different words, ok.
Ordered OEM Sony at 3 X the price, installed, no callback. That piece of junk xistor cost me 3 hours time for labor and I lost money on the job.
I never bought another SK product after that.
Sony is a special case, so this could go both ways. In case of HOT's and other special applications, they usually first designed the ideal circuit and then found a matching transistor. This 'finding' includes ordering binned/selected parts from the OEM, but they have been known to custom manufacture semiconductors or had them custom manufactured for them. In this case it was probably binned or selected from a standard type. So it isn't 100% sure that the SK one was a fake (though it could very well have been).
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