jeromach
With sufficient thrust, ducks fly just fine
I did a full rebuild on a Sansui AU-20000 and encountered a lot of issues.
Fortunately, after ages of time, I managed to solve everything, but there's one thing that really gives me a headache.
Unfortunately this amp apparantly had been "treated" in a butchery, since a lot of things were a big mess. I saw it was worked on before I accepted the work on it, but boy, it was much much worse than I had seen at first glance.
Well, let's not waste too much time complaining, it's nearly ready and in the end it is the result that counts.
This one last big issue is the balance pot. The butcher replaced it for a non original part and it did not work as it should, so I have been testing some replacements, but none seem to be working okay.
A normal (100k) balance pot I took from a parts amp (probably an alps pot) made the sound come to the left when turning the knob to the left, to the right when turning the knob to the right, but no sound at all in the middle.
I then tried a regular (100k) pot, but now the sound is present when the knob is in the middle, but the left channel is a lot louder than the right channel.
My question therefore, does it need a special pot? And if so, would that still be obtainable somewhere?
Another issue, although a little less urgent; one of the heat sinks on which the power transistors are mounted gets a lot hotter than the other (almost too hot to touch). I adjusted the bias current according to the manual, so that is the same for both power stages.
I suspect that it might be caused by power transistors from different batches. The slaughter replaced the original transistors with MJ15022 and MJ15023. For the MJ15022 the batches are 9223 anhd 9607, for the 23 they are (BM)0213 and (BM)0331. Especially the first ones differ a long time in their producton period.
Any thoughts on that?
Here a pic of the culprit...
Fortunately, after ages of time, I managed to solve everything, but there's one thing that really gives me a headache.
Unfortunately this amp apparantly had been "treated" in a butchery, since a lot of things were a big mess. I saw it was worked on before I accepted the work on it, but boy, it was much much worse than I had seen at first glance.
Well, let's not waste too much time complaining, it's nearly ready and in the end it is the result that counts.
This one last big issue is the balance pot. The butcher replaced it for a non original part and it did not work as it should, so I have been testing some replacements, but none seem to be working okay.
A normal (100k) balance pot I took from a parts amp (probably an alps pot) made the sound come to the left when turning the knob to the left, to the right when turning the knob to the right, but no sound at all in the middle.
I then tried a regular (100k) pot, but now the sound is present when the knob is in the middle, but the left channel is a lot louder than the right channel.
My question therefore, does it need a special pot? And if so, would that still be obtainable somewhere?
Another issue, although a little less urgent; one of the heat sinks on which the power transistors are mounted gets a lot hotter than the other (almost too hot to touch). I adjusted the bias current according to the manual, so that is the same for both power stages.
I suspect that it might be caused by power transistors from different batches. The slaughter replaced the original transistors with MJ15022 and MJ15023. For the MJ15022 the batches are 9223 anhd 9607, for the 23 they are (BM)0213 and (BM)0331. Especially the first ones differ a long time in their producton period.
Any thoughts on that?
Here a pic of the culprit...