I was reading that these 2 power transistors Toshiba 2SB554 and 2SD424 are a similar replacement for the ones in a 1970s Marantz 510M amplifier, which are Motorola 461-2006 - 7539 and 462-2009 - 7626. Can anyone confirm that?
Yes.
Hope I'm not committing blasphemy by posting a link to another forum. There are a lot of people on there who like to rebuild the Marantz amplifiers.
https://audiokarma.org/forums/index.php?threads/marantz-510m-restore-detail-and-photos.144657/
Hope I'm not committing blasphemy by posting a link to another forum. There are a lot of people on there who like to rebuild the Marantz amplifiers.
https://audiokarma.org/forums/index.php?threads/marantz-510m-restore-detail-and-photos.144657/
Those Toshiba transistors were among the best available at the time. And they tended to be easier to get than MJ1502x in the days before the internet. It’s the other way around today, because 99% of D424’s sold are fake. The only remaining ones in existence are pulls from equipment.
I’m pretty certain 1502x (or even 1500x) were not available when the amp was first built. They came along in ‘80. Motorolas would have been something like a 2N3773 and similar PNP. Even the 6609 didn't even come along until the 80’s - they would have been using selected 2N6031’s.
I’m pretty certain 1502x (or even 1500x) were not available when the amp was first built. They came along in ‘80. Motorolas would have been something like a 2N3773 and similar PNP. Even the 6609 didn't even come along until the 80’s - they would have been using selected 2N6031’s.
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I had to rebuild a 510M about 20 years ago. It was the first time I had done that since Marantz had gone away. Originally Marantz used to provide a set of fully matched output devices. This was the correct way to get this done. I have heard of people installing new outputs with some luck. But the problem comes when someone tries to crank up the amp and the mismatched devices become unhappy and fail. I personally would not attempt to rebuild another without a good curve tracer, and a couple hundred devices to try and match.
Tell me about it...
My very first amplifier I owned is a Marantz 1200, and it started smoking one Friday evening back in about 2016, due to a speaker shorting. That began my journey rebuilding a Marantz amplifier. Part of the reason these amps are so popular is because each amp came with a schematic/service manual. There are several threads on Audio Karma related to modern transistors to use and the Marantz 1200 share the same/similar power amplifier board design with the Marantz model 250 and model 500. I also found that this design is very similar to the very well documented Leach Amplifier design:
https://leachlegacy.ece.gatech.edu/lowtim/
Todays semiconductor devices are well matched by lot number and you can buy a relatively good semiconductor testing device that will pretty accurately display the Hfe value. I had a Tektronix model 575 curve tracer, but sold it after I was finished rebuilding the model 1200. Big, bulky, lots of tubes, and had to do some calibration to measure the same characteristics the tester purchased on ePay in 2015 measured less expensively.
Mass flow meter/controllers and other devices now used to manufacture semiconductors weren't available in the early 1970s, so many semiconductor devices manufactured back then did not come off the manufacturing line with matching Hfe and other semiconductor characteristics.
My Marantz 1200 is still sounding great with my Polk Audio RTA-12s.
My very first amplifier I owned is a Marantz 1200, and it started smoking one Friday evening back in about 2016, due to a speaker shorting. That began my journey rebuilding a Marantz amplifier. Part of the reason these amps are so popular is because each amp came with a schematic/service manual. There are several threads on Audio Karma related to modern transistors to use and the Marantz 1200 share the same/similar power amplifier board design with the Marantz model 250 and model 500. I also found that this design is very similar to the very well documented Leach Amplifier design:
https://leachlegacy.ece.gatech.edu/lowtim/
Todays semiconductor devices are well matched by lot number and you can buy a relatively good semiconductor testing device that will pretty accurately display the Hfe value. I had a Tektronix model 575 curve tracer, but sold it after I was finished rebuilding the model 1200. Big, bulky, lots of tubes, and had to do some calibration to measure the same characteristics the tester purchased on ePay in 2015 measured less expensively.
Mass flow meter/controllers and other devices now used to manufacture semiconductors weren't available in the early 1970s, so many semiconductor devices manufactured back then did not come off the manufacturing line with matching Hfe and other semiconductor characteristics.
My Marantz 1200 is still sounding great with my Polk Audio RTA-12s.
The Jap devices (like the D424) were a lot better about matching than random off the shelf Motorola. By the time the MJ2119x (and MJL3281) came out, those problems were a thing of the past. It was Toshiba licensed technology.
Glad to hear of your luck with that rebuild. That is something I will likely not tackle again. You are correct that some of the newer devices are more stable, but I have still found noticeable discrepancies between manufacturers. I also learned the hard way that the 510m sections really need to be closely matched to avoid disaster. I actually soled off all of my Marantz amps years ago. But lately had a call from a customer that wanted to know if I wanted the 250m's back. They said the amps were humming. I asked "what song"...LOL