I'm doing some repair on an SX-2500 I picked up. It had been running ok with a couple of issues. One was with the auto-tuning, but fixed that. The other is a constant background hum. Following the thread here: http://www.audiokarma.org/forums/index.php?threads/sx2500-main-amp-unit-w23-004.412024/ My first fix was to recap the power supply, main amp, and protect boards, in that order. The hum got a little better, but did not go away. Next thing I did was re-flow all of the solder joints on the main amp board. Figured there could be a bad connection/bad ground somewhere. The hum is much less, but now I have a new issue - static/static bursts on both channels, though more so on the right channel. I thought maybe re-flowing the solder on one or more transistor connections may have been enough to push an old transistor over the edge. Decided to replace Q1 and 2 (2SC458) with KSC1845F, since 2SC458 is on the bad transistor list anyway. This did not cure the static issue. Now, I'm wondering what should be next? Q3 and 4 are 2SC627. Replacement from the above mentioned thread is KSC3503ES. However, I have KSC3503DSTU on hand. Looking at the spec sheets, these seem almost identical; however, KSC3503DSTU lists a maximum DC collector current as 0.6V, whereas KSC3503ES does not list this value. Can I use the KSC3503DSTU I have on hand, or do I need KSC3503ES in the repair thread I referenced? OR, is something else suspect?