Where do you go for vintage parts like this?

[jerryk]

I am trying to find matched pair output transistors for an old Harman Kardon 870 amp.  They are 2SB755 AND 2SD845 transistors by Toshiba.  I did acquire a set off ebay but they sure look fake compared to the originals so I'm hesitant to go forward with them yet.

Jerry

[phil from seattle]

I believe you can replace those with 2SA1494 / 2SC3858 Sankens which appear to have (slightly better) availability. I'd do more research on that, though

[jerryk]

 I think they will work from what I see on the datasheet. My knowledge of amp design is minimal at best.  Most of the parts that I see are on ebay which raises the fake parts concern.  The 2SC3858 can be found at digikey but I would need a matched pair.  I did run across a supplier that list them as available pairs.  It's B+D Enterprises.  They say all parts are new and original.  Anyone ever deal with this company?

Any tips on how you found this out so fast.  The best cross reference site I have found so far is EI components but I have no idea how to search their site.  The transistors alone take up over 300 pages to go through one at time.  I only ask because I have a lot more parts to cross reference on this mid 1980's amp.

Thanks for your help - Jerry

[skyshaver]

Hi, transistor pair matching comes up a fair bit in synthesizer DIY, here's a link to an article by an authority in synth design talking about matching modern transistor pairs.

https://www.cgs.synth.net/modules/simple_transistor_matching.html

[alsetalokin4017]

https://www.utsource.net/itm/p/1552348.html
https://www.utsource.net/itm/p/1551846.html
You may be able to get a matched pair from them too.

I have made perhaps a dozen orders from UTSource and have not been "burned" yet. Shipping to my door in TX USA is in the 10-14 day range. I was even able to obtain some very obsolete original Motorola transistors for my old Interstate F43 "high voltage" function generator.

Your mileage may vary of course.

[nanofrog]

I did run across a supplier that list them as available pairs.  It's B+D Enterprises.  They say all parts are new and original.  Anyone ever deal with this company?

Yes.

They're a legitimate company IME, and I've not had issues with them.

[jerryk]

You guys are amazing as always.  I'm not sure why I'm so hell bent on fixing this amp. It's probably because it was my first unfinished project that caused me to buy an oscilloscope and then tear apart everything electronic that I had laying around.  I suppose I'm repaying a debt if I manage to fix it.  I was bummed when I saw that the hard to find output transistor was gone but I suspected some sort carnage from the speaker melt down that occurred.  There are more transistors to replace that I want to cross reference and the only guides that I have found out there are the NTE cross reference and the el-component.com site.  Not sure if there is any real all encompassing reference out there I'm missing.  Either way this have been a great help.

Thanks - Jerry

[drussell]

Hi, transistor pair matching comes up a fair bit in synthesizer DIY, here's a link to an article by an authority in synth design talking about matching modern transistor pairs.

He will be more concerned with them matching at a higher current than a multimeter will provide in that simple test.

[jerryk]

I did order/request some matched pairs of these transistors from Utsource.  I'm not sure what the results will be.  The transistors I'm trying to match are in the attached photos.  I know that R is the gain. The 3H and 3K I guess are date codes.  As for matching them when I get them I only know that the gain should all either be an R or O per the schematic.  Beyond that is there anything else I can check or do to insure pair matching other than match the date codes (if that is what 3K and 3H are) or whats been suggested above?

Jerry