I bought a ML332 recently. During the recap, I noticed that the left side voltage gain board is much warmer then the right side's. I probed around and found that the bias of the left voltage gain board seems off, quite off. The picture attached explains. The +/-supply is +/-114v. The differences between the left board and right board are
1. Q12 collector, -45v vs -15v
2. U6 collector, 72v vs 55v.
The bias is very different. Because #2, the bias to the second stage through R110 & 110 are also off. Anyone has experience on that and what might be wrong? I am thinking to replace SSM2220 and 2N6730. They both are obsoleted, Mouser don't carry and I see some people are selling them on Ebay but with 2 weeks shipping time. Other than Ebay, any recommendation on where to buy obsoleted components.
Thanks,
cfy30
1. Q12 collector, -45v vs -15v
2. U6 collector, 72v vs 55v.
The bias is very different. Because #2, the bias to the second stage through R110 & 110 are also off. Anyone has experience on that and what might be wrong? I am thinking to replace SSM2220 and 2N6730. They both are obsoleted, Mouser don't carry and I see some people are selling them on Ebay but with 2 weeks shipping time. Other than Ebay, any recommendation on where to buy obsoleted components.
Thanks,
cfy30
Attachments
Thanks for responding.
Th amp had hum. I didn't check the voltages before recap. After recap, the hum is gone, but then I noticed that the left speaker has audible noise level and thus checked the biases.
Did the measurements at different nodes, detailed in the pdf attached. I only have the 336 schematics from this forum, and no 332 schematics. When tracing, I see 336 and 332 share the same circuit, but not identical. Is the info sufficient?
Th amp had hum. I didn't check the voltages before recap. After recap, the hum is gone, but then I noticed that the left speaker has audible noise level and thus checked the biases.
Did the measurements at different nodes, detailed in the pdf attached. I only have the 336 schematics from this forum, and no 332 schematics. When tracing, I see 336 and 332 share the same circuit, but not identical. Is the info sufficient?
The noisy transistors on the left side are 2N6730, MPS8099, 2N6718, 2N551 on the first differential stage or ? I was thinking to replace the transistors, including the Ux matched pairs also but most of them are obsoleted which Mouser do not carry. I see Ebay has some of them, from China. I wanted to nail down the bad ones, if possible, then replace.