Hello everyone!
I need a little help from the experts.
I am repairing a turntable with an amplifier 2 x 6W with germanium transistors, the model is a Philips 22GF560 from the 70s. There was a faulty left channel on the amplifier.
I checked that the AC187K was defective and replaced it with the same germanium transistor model.
I also replaced all the electrolytes on the PCB, cleaned all the potentiometers and adjusted the biasing of the output transistors according to the instructions. After the replacement, the voltages on the output transistors were appropriate and the amplifier played nicely on both channels.
The problem is the 100Hz hum (mains is 50Hz) that is heard on both channels. Hum is present even without a signal at the input.
When the volume knob is at 0 the hum is quite strong. By turning up the volume, the hum decreases, only to increase again when the volume is at its maximum.
I checked all the contacts and ground points on the amplifier and turntable, I could not solve the problem.
Can anyone help me how to solve this problem? I don't have an oscilloscope for any serious analysis, just a multimeter and a component tester.
Thanks for your attention and time.
I need a little help from the experts.
I am repairing a turntable with an amplifier 2 x 6W with germanium transistors, the model is a Philips 22GF560 from the 70s. There was a faulty left channel on the amplifier.
I checked that the AC187K was defective and replaced it with the same germanium transistor model.
I also replaced all the electrolytes on the PCB, cleaned all the potentiometers and adjusted the biasing of the output transistors according to the instructions. After the replacement, the voltages on the output transistors were appropriate and the amplifier played nicely on both channels.
The problem is the 100Hz hum (mains is 50Hz) that is heard on both channels. Hum is present even without a signal at the input.
When the volume knob is at 0 the hum is quite strong. By turning up the volume, the hum decreases, only to increase again when the volume is at its maximum.
I checked all the contacts and ground points on the amplifier and turntable, I could not solve the problem.
Can anyone help me how to solve this problem? I don't have an oscilloscope for any serious analysis, just a multimeter and a component tester.
Thanks for your attention and time.
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