Hi
I have replaced all the 4 original power transistors (2SC493) with 2SC1030. This transistors have the same collector emmiter voltage of 80V but a higher current rating of 6Amps. The 2SC493 is rated at 5Amps. After replacing the transistors, I tested the amp. There was aproblem. When I switched on the "loudness" and increased the volume more than half, the amp goes into "protect". Do I need to adjust the VR901 and VR902 on the protector circuit board. Can someone please advise on this.
Thanks
Carlos
I have replaced all the 4 original power transistors (2SC493) with 2SC1030. This transistors have the same collector emmiter voltage of 80V but a higher current rating of 6Amps. The 2SC493 is rated at 5Amps. After replacing the transistors, I tested the amp. There was aproblem. When I switched on the "loudness" and increased the volume more than half, the amp goes into "protect". Do I need to adjust the VR901 and VR902 on the protector circuit board. Can someone please advise on this.
Thanks
Carlos
That would seem to be this oldie.
By the symptoms, there's oscillation going on, possibly the power amp output is getting into the preamp (shared ground due to bad ground connection maybe?). Study the service docs to find out why that might be. Has the unit already been recapped? That's another fairly realistic possibility. This model is 45 years old after all! (At that time, quality in Japanese 'lytics wasn't exactly what it is today.) I would not normally expect the output transistors to affect small-signal response, but you never know. Note that a set this old may not yet follow today's recommended grounding practices; if there's any easy and promising way of improving things to be seen there, I'd consider a corresponding mod.
By the symptoms, there's oscillation going on, possibly the power amp output is getting into the preamp (shared ground due to bad ground connection maybe?). Study the service docs to find out why that might be. Has the unit already been recapped? That's another fairly realistic possibility. This model is 45 years old after all! (At that time, quality in Japanese 'lytics wasn't exactly what it is today.) I would not normally expect the output transistors to affect small-signal response, but you never know. Note that a set this old may not yet follow today's recommended grounding practices; if there's any easy and promising way of improving things to be seen there, I'd consider a corresponding mod.
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