Bart Rydzynski
- Apr 14, 2016
- 39
- Joined
- Apr 14, 2016
- Messages
- 39
With R113 removed, the BASS channel is isolated except for the common 60 volt supply. Oscillation (squeal or motor-boating) requires uncontrolled in-phase feedback from output to input of an amplifier stage. Was the amp properly working when you bought it? Possible sources for feedback include wiring error, solder bridge, insufficient de-coupling of the power supply or creative rewiring of the amp..... the later possibly creating ground loops, inductive coupling or a high impedance path to the power supply filters. The fluctuating voltages indicate an unstable bias or voltage source.The transistors are DC coupled and they all interact. You may have a thermal problem with one of them. Have you used freeze spray on semiconductors before? You are getting close to needing a DC coupled, dual trace oscilloscope. Without knowing the history of the amp, I would first make sure there are no solder bridges. Next, check for wiring errors and make sure all the components are of proper value. Then check the 60 volt power supply to make sure there are no fluctuations.. Also, keep the GUITAR and MIC channel pots on zero.