As many know getting replacement transistors from Krell is non-existent. They're basically closed. I've attemted to contact them to no avail. I'm in need of the above transistors 484081 and 484002. Since these are no longer available I'm willing to change the complete channel out to get this up and running again. I would like some input as to what would be available that would do the job. Your input will be greatly appreciated.
John
John
I'll assume these part numbers are for output devices?
Electrotanya shows a (free) service manual download for Krell 200s/300s that shows 12 each MJ15024 and MJ15025 per channel.
These are old but pretty rugged devices from Motorola/OnSemi. Don't know if you can get newly manufactured ones anymore.
The service manual I saw contained no comments about criteria or specs for matching devices or selecting for a limited hFE range, etc.
But I do notice the emitter resistors are fairly large (1ohm) which can help make less than well-matched devices play together better.
Also, keep in mind these are TO-3 parts and many mfrs these days are ramping down (or have already quit) production of devices in the TO-3 package.
Good luck,
mlloyd1
PS Here is an old thread from 2003 that might have some info for you about replacements: https://www.diyaudio.com/community/...j15025-and-mj15024-pair-of-transistors.21490/
Electrotanya shows a (free) service manual download for Krell 200s/300s that shows 12 each MJ15024 and MJ15025 per channel.
These are old but pretty rugged devices from Motorola/OnSemi. Don't know if you can get newly manufactured ones anymore.
The service manual I saw contained no comments about criteria or specs for matching devices or selecting for a limited hFE range, etc.
But I do notice the emitter resistors are fairly large (1ohm) which can help make less than well-matched devices play together better.
Also, keep in mind these are TO-3 parts and many mfrs these days are ramping down (or have already quit) production of devices in the TO-3 package.
Good luck,
mlloyd1
PS Here is an old thread from 2003 that might have some info for you about replacements: https://www.diyaudio.com/community/...j15025-and-mj15024-pair-of-transistors.21490/
Actually, I believe they are special runs of 2SA1302 and 2SC3281 for Krell -- hence the 002 and 081 ending of the part numbers. Krell's version of MJ15022, MJ15023, MJ15024 and MJ15025 have part numbers of 484022, 484023, 484024 & 484025.
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I believe the circuits will work with either transistor set. In class a A or very high bias AB applications it’s hard to tell a difference between them. But the higher fT transistors are “better”. Even speed aside, gain is higher and uniformity an order of magnitude better. Use the 02/81 if you can get them, don’t sweat it if you can’t. Yeah, matching is beneficial but when you need 12 15024 that could prove interesting. MJ21193/4 are also an improvement in uniformity so they are an option.
Don’t be fooled by “MJ3281” on E-bay. RM’s are from the only run ever produced. They wanted a million piece order to do the special packaging.
Don’t be fooled by “MJ3281” on E-bay. RM’s are from the only run ever produced. They wanted a million piece order to do the special packaging.
Yesterday sucked. After checking all the semiconductors and passive components on the left channel I reassembled the board for testing. Prior to this I replaced all the electrolytic capacitors.
Well once it went past the soft start a small puff of smoke and then shut down. No words could have been said that I hadn't already used. Hmm, so I took it apart again but no smoking gun (literally). Then while testing a couple of components the answer raised it's ugly head. Everything had gone well changing out the capacitors so I was looking to see if one had blown, but I wasn't expecting find what I did. Since output board is attached to the heatsink the driver board sits on top of it with standoffs. Take a look at the top of the capacitors and you'll see the culprit. These are short to begin with, but not short enough. These are 11mm tall and I needed 8mm to have proper clearance.
So now I'm rechecking all the components and have ordered the shortest caps I can find (8mm). Sometimes it's the little things that really ruin your day.
Well once it went past the soft start a small puff of smoke and then shut down. No words could have been said that I hadn't already used. Hmm, so I took it apart again but no smoking gun (literally). Then while testing a couple of components the answer raised it's ugly head. Everything had gone well changing out the capacitors so I was looking to see if one had blown, but I wasn't expecting find what I did. Since output board is attached to the heatsink the driver board sits on top of it with standoffs. Take a look at the top of the capacitors and you'll see the culprit. These are short to begin with, but not short enough. These are 11mm tall and I needed 8mm to have proper clearance.
So now I'm rechecking all the components and have ordered the shortest caps I can find (8mm). Sometimes it's the little things that really ruin your day.
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Okay so I need a few suggestions. After replacing a few dead components, dent capacitors, and replacing all the output transistors with MJ15024 & Mj15025. I powered it up and fireworks. I'm becoming jinxed with this one. Any and all comments appreciated.
John
John
