Hi,
I received this amp with both channels power transistors blown(2SA1104 & 2SC2579). I have replaced this transistors and all other blown components on the board. The amp works OK but the power transistors keep blowing.Sometimes they last for a few days, at times more than a week but eevantually they blow up. I have double checked all the components and they are OK. I suspect the quality of the power transistors. They are made in China and very much cheaper than the cost of normal power transistor. I am unable to get the original transistor here. I want to know. I have 2 pairs of different power transistors which are original but they have higher voltage and power rating(2SA1553 & 2SC4029). Can I substitute with this transistor? Please advise.
Thanks
Carlos
I received this amp with both channels power transistors blown(2SA1104 & 2SC2579). I have replaced this transistors and all other blown components on the board. The amp works OK but the power transistors keep blowing.Sometimes they last for a few days, at times more than a week but eevantually they blow up. I have double checked all the components and they are OK. I suspect the quality of the power transistors. They are made in China and very much cheaper than the cost of normal power transistor. I am unable to get the original transistor here. I want to know. I have 2 pairs of different power transistors which are original but they have higher voltage and power rating(2SA1553 & 2SC4029). Can I substitute with this transistor? Please advise.
Thanks
Carlos
Did you check the bias currents? How hard are you driving the amp, with what load? You can replace the outputs with higher rating ones, but be careful with speed (Ft), if the replacements are much faster, it can cause instability, or oscillation. (I just checked it, the replacements have 10Mhz Ft, while the originals 20)
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Thanks, since you have checked the replacement, do you think it would work OK
Carlos
Dear Friend,
I fitted in these transistor, hooked up a CD player and turned ON the amp. After about a minute or so, the relay suddenly turned off and then after a few seconds turned on again. This happened twice. I turned OFF the amp and adjusted VR1, the bias current trimmer. I turned it ON again and left it playing for almost 4 hrs. It works OK without any problem. Thanks dragonweed for your help.
Carlos
The symptoms you described suggest DC at the output. Did you measure the bias current at the emitter resistors, or just turned the pot randomly? If so it is not a good idea, you risk blowing the outputs without measuring it.
Does the amp have an offset adjustment trimmer? Unfortunately I couldn't find a schematic or service manual for that model, can you send a photo of the inside of the amp? Maybe I can identify the adjusting elements.
Does the amp have an offset adjustment trimmer? Unfortunately I couldn't find a schematic or service manual for that model, can you send a photo of the inside of the amp? Maybe I can identify the adjusting elements.
No, I did not measure the bias current at the emitter resistors. I just turned the pot randomly. The relay does not turn off anymore and dont you think that its OK and no DC leakage at the outputs. I have the service manual but I cannot upload because its says it exceeds the limit. Maybe I can send in to your mailbox if you provide your email address.
Thanks
Carlos
Hi
Bad news, the amp blew up again. I checked, all components are OK except the NPN power transistor on the channel B. I cannot upload the service manual here, its more than 6MB. Where can I uload this manual.
Thanks
Carlos
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