So I acquired a Kenwood KR-7600. I tear it apart and look at the output devices to see whats in there. Low and behold one channel is BJTs and the other is using MOSFETS. I didn't know you could even do this. Everything else is the same. They just popped mosfets into it and had I not looked I would not have noticed.
One channel has 2SD425/2SB555 and the other has SK3359/SK3297. neither are OEM. I have a butt load of 2SD425/2SB555s so I believe I am going to swap the MOSFETS out for these so they at least match. Just thought this was quite odd. Even weirder is it seems to work just fine.
Jeff
One channel has 2SD425/2SB555 and the other has SK3359/SK3297. neither are OEM. I have a butt load of 2SD425/2SB555s so I believe I am going to swap the MOSFETS out for these so they at least match. Just thought this was quite odd. Even weirder is it seems to work just fine.
Jeff
I wonder if there are any other mods as far as bias to make that work. Likely will have different distortion figures for sure.
I just found a schematic for the KR-7600 from AudioKarma. Seems like it has complimentary BJT pairs.
I just found a schematic for the KR-7600 from AudioKarma. Seems like it has complimentary BJT pairs.
Why is this weird? One good amp is not going to sound different to another good amp.
I have 2SD425/2SB555. I have lots of them. I pulled them out of something. I forget what. And the SK3297 and 3359 are they MOSFETS?? I find both online. Some places say BJT some say MOSFET. Is there a (2)sk3359 that is a BJT and a sk3359 that is a MOSFET??
Measuring the supposed MOSFET pair may be the only way to know. Some people are known for stuffing just about anything in a package and selling it.
Used to happen with 6L6 variants too.
If you can measure bias on the output devices and they are the same between channels you could also call it good.
You can also use REW to measure an amp without having the usual test equipment.
Used to happen with 6L6 variants too.
If you can measure bias on the output devices and they are the same between channels you could also call it good.
You can also use REW to measure an amp without having the usual test equipment.
But this is not the original good amp but a clunky "repair" using absolutely different components.
To boot, two different channels inside the same amp, working side by side 😲
I would be surprised too.
This is not like, say, Hartke 3500 amplifiers which used MosFets for the first 4 or 5 years and then switched to Bipolars.
These amps were properly modded by designer and left factory with one or the other configuration.
And yes, those sound all the same.
Bias points should be very different unless they are lat fets. If that is the case they are better then bjt transistors.
Those are the 12A/100W baby brother to the D424/B554. RCA SK3297 is ”supposedly” Sanyo’s version of it (I forget the 2S# now, but I used a lot of them in the day - 2SD697 comes to mind but not sure now) and same as ECG280. I’m assuming RCA SK3359 is the PNP (ECG281). They are *not*2SK anything. If they were, one would be a 2SJ…..
The $64k question is whether to trust the RCA SK’s. Most of us don’t trust ECG/NTE any further than we can throw them.
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Well it works.
Im running a mismatched pair of speakers in the shop.
Maybe a mismatched amp would balance it out.
Blasting Duke Ellington, I truly dont care.
Sounds great.
Im running a mismatched pair of speakers in the shop.
Maybe a mismatched amp would balance it out.
Blasting Duke Ellington, I truly dont care.
Sounds great.
The Japanese JIS code should tell you what they are: https://www.eg.bucknell.edu/~dkelley/eceg350/lab/Reading_Transistor_Markings.pdf
2SD: NPN
2SB: PNP
2SK: N-channel FET (could be an N-channel JFET or an NMOS)
Why do you care anyway given that the amplifier works fine?
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