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Old 5th October 2007, 05:49 PM   #131
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Chetan Electronics also stocks authentic ones from original Toshiba bulk packs, though it seems to be out of stock presently. He also has TO-3 MJ21193/21194 and many other ON Semi power BJTs, but I haven't inspected them closely enough to tell if they're authentic. It's probably impossible to tell without a dissection.

Regarding the mismatched hFE, it's probably not a big issue for class-B/AB emitter-follower output stages. As long as the driver stage is capable of supplying the required base current, things will be ok, and the mismatch will be corrected by negative FB.

I now have 2 pairs of pulled 2sc5198/2sa1941 (lower spec, smaller-die versions of the 2sc5200/2sa1943) in TO3P packages, which are fairly nice replacements for legacy TO-3 transistors (2N3055/MJ2955 etc.). I'm trying to make up my mind on whether to experiment with them to build a small, high-end amp like the Leach or similar, or simply buy a used vintage Japanese discrete power amp from Chennai and upgrade the op-amps, semis and electrolytics. There are plenty of Sansuis and Onkyos floating around, and a few Nakamichi/Pass Stasis as well.

BTW, there's an inexpensive Chinese car power amp, 2 channels, which can probably do about 35W-40W/channel into 8 ohms that's available in S.P.Road. It's called the Bob BE-1202 or similar. I bought one, took it apart, and found that it's a discrete bipolar power amp, driven by an op-amp pre- and active-filter stage. A few simple upgrades (mainly power semis and caps) will allow it to give many years of excellent service. Not too bad for Rs.2200/- (~$55).
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Old 11th October 2007, 09:58 AM   #132
sant_ka is offline sant_ka  India
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Linuxguru,

Thanks for the info - it's very useful. I'll PM you on my Leach amp project.

Cheers,
Santhosh
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Old 29th November 2007, 09:41 PM   #133
OliverD is offline OliverD  Germany
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Default 2SC2705-Y and 2SA1145-Y

Hi,

I acquired some of those some years ago and bought lots more just a couple of days ago. The problem is, they don't look the same. I'm quite confident the ones I bought some years ago are originals. Now I want to find out whether Toshiba changed their package or whether I was sold counterfeits... Can you help?

First picture shows the transistors which I believe are genuine.
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Old 29th November 2007, 09:42 PM   #134
OliverD is offline OliverD  Germany
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Here's a cut tape of what I bought recently. Note the bent legs, different font, different ink color and marking layout with the strange dots...
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Old 29th November 2007, 09:44 PM   #135
OliverD is offline OliverD  Germany
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On the left the supposedly genuine part, on the right the suspect...
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Old 29th November 2007, 09:45 PM   #136
OliverD is offline OliverD  Germany
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Also the top looks quite different. On the tape, the protuberances from the mold are left or right, alternating. The supposedly genuine part has the protuberance in the middle.
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Old 30th November 2007, 12:32 AM   #137
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OliverD: Without electrical measurements, it's hard to be sure, but from appearance your taped 2sa1145s are also authentic. I've also seen taped 2sc2705s that look similar to your taped 2sa1145s, with splayed legs.
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Old 30th November 2007, 01:59 AM   #138
OliverD is offline OliverD  Germany
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Thank you.

I took some basic hfe measurements with a simple multimeter, and both the suspect and the genuine parts were ranging from 136 to 154. This is within the specs of the yellow rank, although on the lower side. What else could I measure with simple means?
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Old 30th November 2007, 02:48 AM   #139
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For a small-signal transistor, that's about the only easy measurement. Counterfeits often have suspiciously high hfe in the range of 300 and above - 130+ is OK, especially if it's clustered pretty tightly without large deviation. It seems genuine.
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Old 30th November 2007, 04:21 AM   #140
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Compare the capacitance of the devices.Larger die means more capacitance. So if the package has a smaller than usual die it will have a lower capacitance.
You will find more details on that in the original thread about fake power transistors on this forum.
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