Hello all,
I picked up this unit dead. It's the Sonata version with 5 pairs of the obsolete K405/J115 OPT's. I found a pair of them were shorted, found a couple NOS on line, replaced them & all seemed well......at first. I was able to set the bias & play some music through it but the volume seemed a bit low. Anyhow, the next day I tried it again but after a few seconds my DBT went bright & I got a nasty hum through the speakers. I found I now have 60+vdc on the speakers outputs. I then did what I should've done first......pulled every opt & tested them instead of just finding the shorted pair & calling it good. I found two of the J115's tested with high voltage & another tested as a BJT.
I'll cut to the chase. I've learned through my searches that these opt's are hard to find......I paid $30 for the ones I found.......& that their replacements are also obsolete. I found an old thread here that suggested IRFP9140's would work but would need some modification on the PB's. I'm a novice, & this is a hobby........I've repaired some old receivers but am working with just a Fluke DMM & a component tester. My question is whether it would be better to replace all 10 pairs of OPT's in this with newer "replacements" & mods? I've learned that matching transistors is key, & I'm not sure that continuing to find/pay through the nose for the older units is the best long term fix.
I picked up this unit dead. It's the Sonata version with 5 pairs of the obsolete K405/J115 OPT's. I found a pair of them were shorted, found a couple NOS on line, replaced them & all seemed well......at first. I was able to set the bias & play some music through it but the volume seemed a bit low. Anyhow, the next day I tried it again but after a few seconds my DBT went bright & I got a nasty hum through the speakers. I found I now have 60+vdc on the speakers outputs. I then did what I should've done first......pulled every opt & tested them instead of just finding the shorted pair & calling it good. I found two of the J115's tested with high voltage & another tested as a BJT.
I'll cut to the chase. I've learned through my searches that these opt's are hard to find......I paid $30 for the ones I found.......& that their replacements are also obsolete. I found an old thread here that suggested IRFP9140's would work but would need some modification on the PB's. I'm a novice, & this is a hobby........I've repaired some old receivers but am working with just a Fluke DMM & a component tester. My question is whether it would be better to replace all 10 pairs of OPT's in this with newer "replacements" & mods? I've learned that matching transistors is key, & I'm not sure that continuing to find/pay through the nose for the older units is the best long term fix.
2SK1530/2SJ201 might work to replace K405/J115
IRFP9140 pin is different, biasing also will be different
Maybe you can use the chassis and power supply for diy amp
IRFP9140 pin is different, biasing also will be different
Maybe you can use the chassis and power supply for diy amp
Thanks for the reply. Those are also very hard to find as they're obsolete. I guess I'll just have to be patient & gather replacements as I find them. I don't have the knowledge or experience to build my own amp. This unit is in excellent condition cosmetically so I'd like to restore it.