Hi guys.
I know, the rule of thumb is to avoid Alitard when it comes to obsolete transistors ! But ! The picture on sellers site is showing NOS NEC 2SC3840/2SA1486. Well, you know the typical transistors from that period, plastic black/green TO-126 case with silverish painted markings on a
rough/mat surface. Something like this -->
But what I received is this -->
As you can see. Markings are made with a laser on a shiny surface. The NEC logo on 2SA1486 is missing ! Mind boggling situation. The back plate is a typical NEC transistor shape. You probably already know that Renesas took over NEC business back in 2010 and they continued to manufacture 2SC3840/2SA1486 for some time. You can even still buy them at Digikey but the minimum order is 345 pieces. Does anyone have a picture of these transistors made by Renesas btw ? I also did some hfe and Vceo (breakdown voltage) tests -->
2SA1486
Vceo - 730VDC
hfe - 60
hfe category - L
2SC3840
Vceo - 720VDC
hfe - 90
hfe category - K
So, according to NEC datasheets, these values are in the specified range. So guys, would you be so kind and share with me you opinions. Cheers.
I know, the rule of thumb is to avoid Alitard when it comes to obsolete transistors ! But ! The picture on sellers site is showing NOS NEC 2SC3840/2SA1486. Well, you know the typical transistors from that period, plastic black/green TO-126 case with silverish painted markings on a
rough/mat surface. Something like this -->
But what I received is this -->
As you can see. Markings are made with a laser on a shiny surface. The NEC logo on 2SA1486 is missing ! Mind boggling situation. The back plate is a typical NEC transistor shape. You probably already know that Renesas took over NEC business back in 2010 and they continued to manufacture 2SC3840/2SA1486 for some time. You can even still buy them at Digikey but the minimum order is 345 pieces. Does anyone have a picture of these transistors made by Renesas btw ? I also did some hfe and Vceo (breakdown voltage) tests -->
2SA1486
Vceo - 730VDC
hfe - 60
hfe category - L
2SC3840
Vceo - 720VDC
hfe - 90
hfe category - K
So, according to NEC datasheets, these values are in the specified range. So guys, would you be so kind and share with me you opinions. Cheers.
You probably got lucky. What they usually put in packages like that for fakes aren’t going to approach the 600 V rating. Just the fact that you actually measure 700 suggests they could real. Rig one up as a 300V 10 or 15 mA current source and if it doesn’t poof you’re probably good to go.
I was thinking about the same. Well, there is no other option but to put the suckers under real working conditions. Fortunately I have a test rig, 600W (+/-95VDC) amplifier adapted with quick connect / disconnect connectors for the pre-drivers, drivers and output transistors.
Btw, B+D Enterprises are selling 2SC3840/2SA1486-AZ and the picture is showing 2SA1486 with same markings (NEC logo is missing). Interesting, yesterday there were 20 pieces in stock and today none. A bit pricey btw. I will send them a message and ask them the source of these transistors. They are a reputable seller of obsolete parts and I hope they will be honest with me.
https://www.bdent.com/2sa1486-az-nec-switching-power-transistor.html
Cheers.
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$26? That’s gonna leave a mark. My standby parts for that position were the Fairchild 400 V pair (A1156 and C2752). Still in production, but of course out of stock.
Yea, $26 is a boner killer. Speaking of which, I have a bunch of ON Semi (Fairchild) KSA1156YS / KSC2752OSTU but the hfe difference between those two is huge, almost useless.
I wouldn’t call it “useless”— perhaps just “compromised”. The reason to use 400 or 600 volt parts is when your rail voltages go from the ridiculous to the sublime. At sane voltages there are more traditional choices for VAS’s, hfe enhancers, or predrivers. The match isn’t any worse than the MPSA44/A94, and they’re not going to cook the PCB or be in danger themselves dissipating 300 mW. At +/-150 to 175V a
little hFE mismatch is the least of your worries. Output triples and darlington VAS’s are more the rule rather than the exception there.
little hFE mismatch is the least of your worries. Output triples and darlington VAS’s are more the rule rather than the exception there.
Well, actually I'm cloning Yamaha's T5N power amplifier but without that digital crap. After all these years I just want to get this done. For fun of course, not for commercial purposes. I don't want to go deep down into technical details since everything about Yamaha's EEEngine is explained in datasheets and on the net as well. So, it's a 2300W amp. The supply voltage is +/-160V. That's why I'm insisting on high voltage transistors, see datasheet. As you can see 2SA1924/2SC3425 are used in a cascode configuration and as pre-drivers. Since these transistors are way obsolete and unobtainium I decided to replace them with KSA1156YS/KSC2752OSTU. Btw, I have a bad OCD (perfection) 🙁 when it comes to matching transistors. I know it's hard to match PNP/NPN transistors but I wanted to find pairs with a reasonable close parameters. That's why I ditched KSA1156YS/KSC2752OSTU and now I'm trying with 2SC3840/2SA1486. Yamaha is also using them in their TXn series. The project has gone to the point of no return. Only a nuclear war with Russia can stop me. 😆 All components are in check except the transistors above. The PCB is almost done, some minor corrections needs to be done. Btw, the power supply is another story and I won't go into details here.
@wg-ski, you're an experienced member here and I appreciate all yours comments. Please look at the schematic and share with me your thoughts. Other members are welcomed as well. Regards.
@wg-ski, you're an experienced member here and I appreciate all yours comments. Please look at the schematic and share with me your thoughts. Other members are welcomed as well. Regards.
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You could probably sub either pair and not know the difference. The predrivers are in the main signal path, but it’s a triple EF. In a triple EF, the second stage beta and linearity are what is important. First stage current swing isn’t a lot, except when driving 2 ohms where the output stage beta falls to less than half. It’s expected and acceptable for distortion to increase at 2 ohms. In the EEEngine control circuit where the cascodes are the gain just isn’t that important.
I was using them as predrivers are VAS beta enhancers (First half of a darlington). in neither case was a screaming HFE needed, but a relatively low Cob and being heat sinkable were required. Supply voltage was a little more than what you’re playing with.
I was using them as predrivers are VAS beta enhancers (First half of a darlington). in neither case was a screaming HFE needed, but a relatively low Cob and being heat sinkable were required. Supply voltage was a little more than what you’re playing with.
Hi.
thank you for your reply. Here is the situation with KSA1156-Y/ KSC2752-O -->
Test voltage 5V
KSA1156-Y
Ib - 0.77mA
Ic - 102.5 mA
hfe - 133
Vbe - 705mV
KSC2752-O
Ib - 0.79mA
Ic - 31mA
hfe - 39
Vbe - 711mV
Looks nasty to me. What do you think about it ?
Cheers mate.
thank you for your reply. Here is the situation with KSA1156-Y/ KSC2752-O -->
Test voltage 5V
KSA1156-Y
Ib - 0.77mA
Ic - 102.5 mA
hfe - 133
Vbe - 705mV
KSC2752-O
Ib - 0.79mA
Ic - 31mA
hfe - 39
Vbe - 711mV
Looks nasty to me. What do you think about it ?
Cheers mate.
My NPNs were running in the 50’s with PNPs about 170. A little less spread, and 50-ish was plenty since my MPSA44’s were only running about 40. That’s what I was using till I noticed how HOT they were running, and the last thing I’d want is a cascade failure all the way from the VAS to the output.
Btw, here are the test results for 2SC3840/2SA1486 -->
Test voltage 5V
2SA1486-L
Ib - 0.790mA
Ic - 46mA
hfe - 58
Vbe - 683mV
2SC3840-K
Ib - 0.785mA
Ic - 65mA
hfe - 82
Vbe - 690mV
Well, looks like I'm sticking with these guys. That's probably the closest that I can get from Alitard. Probably they're genuine but I still have to test them under real working conditions. As you said, why would they make a fake TO126 700V transistor !
Btw, still no news from B+D Enterprises.
Test voltage 5V
2SA1486-L
Ib - 0.790mA
Ic - 46mA
hfe - 58
Vbe - 683mV
2SC3840-K
Ib - 0.785mA
Ic - 65mA
hfe - 82
Vbe - 690mV
Well, looks like I'm sticking with these guys. That's probably the closest that I can get from Alitard. Probably they're genuine but I still have to test them under real working conditions. As you said, why would they make a fake TO126 700V transistor !
Btw, still no news from B+D Enterprises.
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