stereofun
Super Member
This is the second time I've had this experience, so I just wanted to share. I recently did a major overhaul on a 999. In one side it had original output transistors (2sc898) and the other (2sd427) the gain between the 4 swung from 19-42 and the ft rating are 5mhz vs 7.5mhz
I decided that 4 new and matched onsemi mj21194g's were a better option. The semi's were all around the 60 mark for hfe and are rated at "minimum" 4mhz, which in some real life test I have dug out typically operates at 7-8 mhz.
After the rebuild the amp sounded very good, no question about it. I did however feel it lacked a little resolution - Then I recalled something interesting from an Eight rebuild some years ago. Here I also replaced the outputs with onsemis, but after a while also replaced the original drivers with onsemi mje15033/32's. The amp instantly sounded better, especially resolution at higher freqs.
Ok - so off to the bench. It's a pretty quick procedure...and nothing to loose.
The mica's are readily available for this package. There is nothing to it, other than cut the middle collector leg off and then determine which leg is the emitter/base, then simply insert and bend.
Here all four are done. Onsemi mje15033/32 - gain are 3 times the original and freq are on par at 30mhz
DO SET BIAS immediately after start up! - in this case the bias with the new drivers shot up to 85mA.
After some listening test I have settled on a bias of 50mA, amp runs only lukewarm but sounds noticeable better - more detail and more depth in the soundstage. Normally, I would never deviate from factory setting - but every tranny is replaced in this amp so all bets are off.
For gods sake keep the original output trannies if you have them, but if you dont - something we will see more often - consider going onsemi all the way, even if all the pre-drivers are fine. At the end I believe the amp sounds as good if not better than original and onsemis are very rugged and reliable.
I decided that 4 new and matched onsemi mj21194g's were a better option. The semi's were all around the 60 mark for hfe and are rated at "minimum" 4mhz, which in some real life test I have dug out typically operates at 7-8 mhz.
After the rebuild the amp sounded very good, no question about it. I did however feel it lacked a little resolution - Then I recalled something interesting from an Eight rebuild some years ago. Here I also replaced the outputs with onsemis, but after a while also replaced the original drivers with onsemi mje15033/32's. The amp instantly sounded better, especially resolution at higher freqs.
Ok - so off to the bench. It's a pretty quick procedure...and nothing to loose.
The mica's are readily available for this package. There is nothing to it, other than cut the middle collector leg off and then determine which leg is the emitter/base, then simply insert and bend.
Here all four are done. Onsemi mje15033/32 - gain are 3 times the original and freq are on par at 30mhz
DO SET BIAS immediately after start up! - in this case the bias with the new drivers shot up to 85mA.
After some listening test I have settled on a bias of 50mA, amp runs only lukewarm but sounds noticeable better - more detail and more depth in the soundstage. Normally, I would never deviate from factory setting - but every tranny is replaced in this amp so all bets are off.
For gods sake keep the original output trannies if you have them, but if you dont - something we will see more often - consider going onsemi all the way, even if all the pre-drivers are fine. At the end I believe the amp sounds as good if not better than original and onsemis are very rugged and reliable.
Attachments
Last edited:
