Over the past several weeks I managed to acquire 3 Toshiba SC-335 power amps and 2 SY-335 preamps. I was only looking for one of each but circumstances led me to the others for such little cost I could not resist.
I took the advice and suggestions from this site to replace aging internal components and successfully achieved desired results with the first SC-335 power amp and duplicated the process for the other two. The second came out OK but although low enough, it's DC offset was unequal for both channels. Since it's well below what I understand to be too high (11.5mv & 24mv respectively) I shall be satisfied as it is.
The third was somewhat more troublesome.
After replacing the same devices and letting it idle for a time before taking any measurements, the heat sink was too hot to touch. Checking bias voltage at this time revealed well in excess of 1 volt.
After turning off & cool down I adjusted the pots and was ably to bring the idle current down substantially.
I encountered an anomaly whereby I could get the left channel bias down to 11.5mv (which is more or less what I was told it should be) but the right channel cannot be brought lower than about 24mv. That adjustment pot is at it's maximum travel and just a miniscule fraction of a turn more sends the voltage sky high.
I presume those pots have been known to degrade over time and as long as I can find a suitable replacement, I don't foresee a difficulty putting in new ones.
Would that be a worthwhile thing to do?
For the record, parts replacement included both pairs of differential transistors plus two others. Also all the electrolytics except the large filter caps.
I took the advice and suggestions from this site to replace aging internal components and successfully achieved desired results with the first SC-335 power amp and duplicated the process for the other two. The second came out OK but although low enough, it's DC offset was unequal for both channels. Since it's well below what I understand to be too high (11.5mv & 24mv respectively) I shall be satisfied as it is.
The third was somewhat more troublesome.
After replacing the same devices and letting it idle for a time before taking any measurements, the heat sink was too hot to touch. Checking bias voltage at this time revealed well in excess of 1 volt.
After turning off & cool down I adjusted the pots and was ably to bring the idle current down substantially.
I encountered an anomaly whereby I could get the left channel bias down to 11.5mv (which is more or less what I was told it should be) but the right channel cannot be brought lower than about 24mv. That adjustment pot is at it's maximum travel and just a miniscule fraction of a turn more sends the voltage sky high.
I presume those pots have been known to degrade over time and as long as I can find a suitable replacement, I don't foresee a difficulty putting in new ones.
Would that be a worthwhile thing to do?
For the record, parts replacement included both pairs of differential transistors plus two others. Also all the electrolytics except the large filter caps.
Yes, they do seem fairly important. There's a dedicated electronics parts store nearby I can visit to check for new ones.
EDIT: Checking that shop's website, I see that they stock these pots with a value of 330 ohms and what's on the board are 300 ohms.
Is this close enough?
EDIT: Checking that shop's website, I see that they stock these pots with a value of 330 ohms and what's on the board are 300 ohms.
Is this close enough?
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