2SB655 & 2SD675 transistor replacement?

Mat86

Mat86

Active Member
I need to replace the Hitachi 2SB655 and 2SD675 transistors on my amp, but not sure if there how to go about it.

I see there are 'NSC' 675s on ebay (NJ, not from China) and some worn 655s from a seller in Canada pulled from a donor unit. Would either of these be the way to go?

I've also been looking for forum-talk on modern substitutions, and noticed this 2011 thread where someone tried to replace them with OnSemi MJ21193 & MJ21194's (possibly with issues?), and in 2009 someone else suggested using MJ15024/25, with at least one guy happy with the results (but he bought fakes and they failed). In 2020 someone said it wasn't a perfect match, and then on another forum this year someone listed the same MJ15025s again as a possibility...

Is there a legit modern option I can order?
 
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This is a "TO-3" package (AKA TO-204), correct?

Here are some key parameters for the original 2SB655, if I got this transposed from the old datasheet correctly:
ft - 20MHz
Vcbo - 160V
Ic - 10A
Pmax - 100W

If you search DigiKey and/or Mouser, you will likely not find a replacement that meets all of these exactly, but there are devices that meet some and exceed others. If you prioritize matching the ft and meet or exceed the others, in this package, you have very few options. At that point, you can look at your schematic and decide what parameters matter most. You may need to compromise some on the ft in order to meet the others. There are some suppliers of NOS out there that may give you more options, likely at a higher cost.

I guess I should have said up front that buying these transistors from individuals or from the an auction site listing is a crapshoot. Legit and modern imply you're buying from an authorized distributor, which excludes most if not all auction site listings.
 
Jefft91 said:
This is a "TO-3" package (AKA TO-204), correct?

At that point, you can look at your schematic and decide what parameters matter most. You may need to compromise some on the ft in order to meet the others.

There are some suppliers of NOS out there that may give you more options, likely at a higher cost.

Legit and modern imply you're buying from an authorized distributor, which excludes most if not all auction site listings.
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- Yes, TO-3

- I may have to offload this to a technician then :confused: I'm in no position to look at the schematic and make such a call

- Is there a NOS supplier that carries the 655/675s?

- Right, if there's a modern part that would work from a place like Mouser then I'd vastly prefer that, but was checking ebay for the 655/675s since they're discontinued. FWIW the one seller with the 'NSC' brand 675 is based in the US with virtually no bad feedback (and thousands of positive)
 
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In a TO-3, an MJ15024G / MJ15025 pair ought to do it fine
MJ15023G onsemi | Mouser

you're looking at basically 10 bucks per transistor.

if you don't mind changing the package to a TO-3P, a 2SC5200 / 2SA1943 pair would work. The TO-3P don't work as well with sockets though. The rectangular pins don't plug into the round pin sockets terribly well.
2SC5200N(S1,E,S) Toshiba | Mouser

these are about $2.50 each
 
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Mat86,

Gadget73 makes a good recommendation. I can't comment on the ebay seller. If those are genuine parts, great, but there are reports of counterfeits that you can find in these forums. If the price is reasonable, maybe it's worth taking a chance? Otherwise, the replacements gadget73 suggests will plug in and work fine. Either way, let us know how it goes.
 
yeah sorry should have paid a little closer attention to that. I was looking at the datasheet and not paying attention to the fact that it wasn't the compliment, but the next-higher rated part number.

MJ15022G goes with MJ15023G, MJ15024G goes with MJ15025G. Either pair should work fine, the 22/23 are rated for 200 volts, the 24/25 are rated for 250. Originals are rated for 160 so either will sub, just depends what is available. The odd numbers will sub for the 2SB, the evens sub for the 2SD
 
Mat86 said:
Unfortunately the amp couldnt be repaired so dont know if those transistors would have worked out
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Thanks for taking the time to get back with me. Sorry to hear you weren't able to repair it. These are pretty rare and very good amps. I love mine to death.
 
tarior said:
Whaddya mean it couldn't be repaired? That's a pretty rare amp.
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power amp was fried and deemed not worth dumping more time & money into solving, I was hoping replacing the missing parts would have got it on the right track but that wasnt enough (and probably why someone parted out things in the first place)

was able to sell it as-is for the same I bought it as-is to someone who wanted to repair or part it, the cycle of life
 
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